Geological Society of America Fieldtrip No. 408

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Trip Leaders

Lee C. Nordt, Baylor University Steven G. Driese, Baylor University Jonathan Wiedenfeld, USDA-NRCS

Co-Sponsors

Sedimentary Geology Division of the Geological Society of America

Quaternary Geology and Geomorphology Division of the Geological Society of America

Pedology Division of the Soil Science Society of America

Society for Sedimentary Geology

October 3-4, 2008

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TRIP SUMMARY

EXAMINATION OF A VERTISOL CLIMOSEQUENCE ACROSS THE TEXAS

COAST PRAIRIE AND ITS IMPLICATIONS FOR INTERPRETING VERTIC

PALEOSOLS IN THE GEOLOGIC RECORD

Co-Sponsored by: Q

Field Trip #4 Cost: $360 Friday, October 3, Saturday October 4, 2008 Maximum: 21 Minimum: 15

LEADER: Lee Nordt Department of Geology One Bear Place #97354 Baylor University Waco, TX 76798 Ph: (254) 710-3362 / Fax: (254) 710-3639 lee_nordt@baylor.edu CO-LEADERS: Steven Driese Department of Geology One Bear Place #97354 Baylor University Waco, TX 76798 Ph: (254) 710-2361 / Fax: (254) 710-2673 steven_driese@baylor.edu Jonathan Wiedenfeld USDA-NRCS MLRA 150 Soil Survey Office 1402 Band Road Rosenberg, TX 77471 Ph: (281) 232-4668 DEPARTURE: Friday, October 3rd, 7:30 am from the check-out desk of the Holiday

Inn, 5549 Leopard Street, Corpus Christi, TX 78408 (1-800-361-289-5100). Please check out at 7:00 a.m., so we can depart promptly at 7:30 a.m.

Saturday, October 4th, 7:30 am from the check-out desk of the Hampton Inn, 7006, N. Navarro, Victoria, Texas, 77904 (1-361-573-9911). Please check out at 7:00 a.m., so we can depart promptly at 7:30 a.m.

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ITINERARY: On the morning of Friday, October 3rd, we will travel to the Welder Wildlife Refuge, San Patricio County to view a soil pit of the Victoria series. A box lunch will be provided. For the afternoon, we will travel to Victoria County to view a soil pit of the Laewest series. Lodging for participants will be in the city of Victoria at the Hampton Inn (see above). Dinner will be the responsibility of the participants.

On the morning of Saturday, October 4th, we will travel to Wharton

County to view a pit of the Lake Charles series. Box lunches will be provided. For the afternoon, we will travel to the Armand Bayou Nature Center in Harris County to view another pit of the Lake Charles series. We will return to the downtown Houston Convention Center by 7:00 PM (or earlier).

COST INCLUDES: Transportation, field trip handouts, boxed lunch, snacks, and water. SPECIALINSTRUCTIONS: Field boots and outdoor attire are recommended for entering and

viewing the soil pits. Rubber boots will be needed if inclement weather. Daytime temperatures range from 60 to 90 degrees F during October. Student drivers will provide transportation for participants from the Corpus Christi airport to the hotel. There will be a pre-meeting trip and mixer beginning at 8:00 pm. Breakfast will be available in the hotel lobby before departure on both Friday and Saturday mornings.

CANCELLATION: Must be made in writing and received by the Registration Coordinator, GSA Headquarters, PO Box 9140, Boulder CO 80301-9140, (303) 447-2020, by SEPTEMBER 19, to qualify for a refund. NO refunds for cancellation notices received after this date. Refunds will be processed as soon as possible after the meeting.

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PREFACELee C. Nordt and Steven G. Driese

Welcome to Texas and to the Texas Coast Prairie! We hope that you will find this an interesting and rewarding field trip. You may be wondering why two professors from the Department of Geology at Baylor University would be leading a field trip on soils for a Geological Society of America meeting? Nordt began his career as a pedologist and moved into the geological realm, whereas Driese, in contrast, began his career as a geologist and moved towards the pedological realm. We share a common interest in the geological record of soils and soil-forming processes. This field trip focuses on taxonomically-defined Vertisols according to the USDA-NRCS, which are characterized by macro- and micromophological characteristics formed in response to shrink-swell phenomena associated with seasonal precipitation cycles or seasonal soil-moisture deficit. Vertisols typically have at least 30% fine clays composed of highly expandable clays such as smectites, and seasonally have deep cracks. Interestingly, our experiences have shown that ancient Vertisols preserved as paleosols in the geologic (rock) record, which we term “paleoVertisols”, are actually extremely common ranging in age from the Precambrian through the Cenozoic. Most Paleozoic and Mesozoic-age redbed deposits in North America contain paleosols analogous to modern Vertisols. PaleoVertisols are over-represented in the rock record as compared with their present global distribution of 2-3%, which is a cause for concern because geologists are generally adherents to the principle of uniformitarianism (“the present is the key to the past”). Some possible hypotheses that might explain Vertisol over-representation in the geologic record include: (1) Strong preservational bias: Vertisols characteristically have a high fine-clay content, are cohesive, and the consolidated clay is erosionally resistant to both fluvial channel migration and to marine transgression. Vertisols characteristically form in low elevation/relief areas (floodplains and coastal mud margins are favored sites), and thus may have a higher preservation potential in the geological record. Also, less time is necessary for subaerial exposure and pedogenesis in order to form a paleosol because Vertisols are known to form very rapidly (within 10s to 100s of years). (2) Strong recognitional bias: Macroscale features of Vertisols, including pedogenic slickensides, gilgai, and angular blocky peds are diagnostic and are easy for geologists to identify in paleosols. The sepic-plasmic microfabrics of Vertisols are usually well-preserved in paleosols and visible in thin sections. The dominance of physical (shrink-swell) processes involved in the genesis of Vertisols implies that neither the presence of root traces, textural differentiation, carbonate redistribution nor color horizonation are necessary for their identification as paleosols. (3) Paleogeographic (latitudinal), paleoclimatic, and parent material factors: Vertisols can form over wide ranges of latitudes and under varying moisture regimes from parent materials that are base-rich to base-poor; the only strict climatic requirement is that a period of seasonal soil moisture deficit occurs. These hypotheses are best evaluated by comparative studies in which modern Vertisols are examined, from a geoscience perspective, with the expressed purpose of identifying an array of morphological and chemical features that have preservation potential in the geological record and which are climatically sensitive indicators. We have addressed these issues by climosequence studies of modern Vertisols from the Coast Prairie of Texas supported in the past by the US National Science Foundation. Our two-day field trip explores the climatic controls on Vertisols and how climate-dependent attributes are “translatable” to interpreting analogous paleosols in the geologic record.

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ACKNOWLEDGEMENTS We gratefully acknowledge the support of the National Science Foundation through grant EAR-9814607 awarded to Drs. Steven G. Driese, Lee C. Nordt, and Claudia I. Mora, and the generous in-kind contribution of soil characterization data provided by the USDA National Soil Survey Laboratory in Lincoln, Nebraska, which was coordinated by Dr. Warren C. Lynn. We especially thank Dr. Larry P. Wilding (Texas and A & M) for his help in formulating the climosequence concept for Vertisols in Texas, and for his assistance in describing and interpreting soil profiles. We also appreciate the field assistance and logistical support of a large contingent of Texas USDA-NRCS personnel, especially including Jon Wiedenfeld, Wesley Miller, and Conrad Nietsch, the support of Micheal Golden, (former State Soil Scientist of Texas), Michael Risinger (current State Soil Scientist of Texas) and the thesis research and field assistance of former University of Tennessee-Knoxville geology graduates Dana Miller, Amy Robinson, and Cindy Stiles, and former Baylor geology graduate Corey Crawford. We also acknowledge generous support for field trip logistical costs through the Baylor University Faculty Development Fund, and the helpful assistance of current Baylor Geology Ph.D. students Steve Ahr, Holly Meier, and Jason Mintz with field trip logistics and guidebook preparation.

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TABLE OF CONTENTS TRIP SUMMARY ........................................................................................................................... ii PREFACE ...................................................................................................................................... iv ACKNOWLEDGEMENTS ............................................................................................................ v TABLE OF CONTENTS ............................................................................................................... vi PART I: INTRODUCTION AND QUATERNARY ENVIRONMENTAL SETTING INTRODUCTION ........................................................................................................................... 1 OBJECTIVES OF FIELDTRIP ...................................................................................................... 2 CLIMATE ....................................................................................................................................... 5 VEGETATION ............................................................................................................................... 7 LAND USE ..................................................................................................................................... 8 QUATERNARY GEOLOGIC SETTING ...................................................................................... 9 PEDOLOGIC SETTING OF VERTISOLS .................................................................................. 12 SOIL FORMING FACTORS ON TEXAS COASTAL PLAIN ................................................... 14 SUMMARY OF INVESTIGATED SOILS .................................................................................. 16 PART II: ROAD LOG STOP 1: VICTORIA SERIES (VIC 409) ..................................................................................... 19 STOP 2: LAEWEST SERIES (LAW 469) ................................................................................... 33 STOP 3: LAKE CHARLES SERIES (LAC 481) ......................................................................... 47 STOP 4: LAKE CHARLES SERIES (LAC 201) ......................................................................... 61 PART III: INTERPRETING VERTIC PALEOSOLS IN THE GEOLOGIC RECORD INTERPRETING VERTIC PALEOSOLS IN THE GEOLOGIC RECORD ............................... 75 PRE-QUATERNARY PALEOSOLS ........................................................................................... 75 USING MODERN VERTISOLS TO INTERPRET PALEOZOIC PALEOSOLS ...................... 79 INTERPRETATIONS ................................................................................................................... 87 DISCUSSION ............................................................................................................................... 90 CONCLUSIONS ........................................................................................................................... 91 FUTURE RESEARCH ON PRE-QUATERNARY PALEOSOLS .............................................. 91 REFERENCES .............................................................................................................................. 93

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LIST OF FIGURES

Figure 1. Map showing locations of climosequence sampling sites visited during fieldtrip. ......................... 6 Figure 2. Average monthly precipitation and temperature climographs from study area ............................... 6 Figure 3. Natural regions in study area. .......................................................................................................... 8 Figure 4. Vegetation in study area .................................................................................................................. 9 Figure 5. Simplified geologic map of the study area ................................................................................... 10 Figure 6. Diagram showing bowl morphology and gilgai micro-relief characteristics of Vertisols ............. 12 Figure 7. NRCS soil mapping units and location of Victoria Pedon (VIC 409) on Rincon Bend USGS topographic map. VcA=Victoria clay, 0-1% slopes. .................................................................................... 20 Figure 8. San Patricio County General Soil Map and landscape position of Victoria soils .......................... 21 Figure 9. Victoria microlow and microhigh, San Patricio County, Texas. ................................................... 23 Figure 10. Photomicrographs of selected horizons from the Victoria pedon ............................................... 29 Figure 11. Depth plots of selected physical and chemical properties from the Victoria microlow and microhigh ..................................................................................................................................................... 31 Figure 12. NRCS soil mapping units and location of Laewest Pedon on Placedo USGS topographic map. The Laewest soil was previously part of the Lake Charles clay, 0-1% slopes (LaA). .................................. 34 Figure 13. Victoria County General Soil Map and landscape position of Laewest soil ............................... 35 Figure 14. View of Laewest soil. .................................................................................................................. 36 Figure 15. Photomicrographs of selected horizons from the Laewest pedon ............................................... 42 Figure 16. Depth plots of selected physical and chemical properties from the Laewest microlow and microhigh. .................................................................................................................................................... 44 Figure 17. NRCS soil mapping units and location of Lake Charles Pedon on Hungerford USGS topographic map. LcA=Lake Charles clay, 0-1% slopes. ................................................................................................. 48 Figure 18. Wharton County General Soil Map and landscape position of Lake Charles soils.. ................... 49 Figure 19. Panoramic view of Lake Charles ML and MH. .......................................................................... 50 Figure 20. Photomicrographs of selected horizons from the Lake Charles pedon ....................................... 56 Figure 21. Depth plots of selected physical and chemical properties from the Lake Charles microlow and microhigh. .................................................................................................................................................... 58 Figure 22. NRCS soil mapping units and location of Lake Charles Pedon on League City USGS topographic map. LcA=Lake Charles clay, 0-1% slopes. ............................................................................. 62 Figure 23. Harris County General Soil Map and landscape position of Lake Charles soils. ........................ 63

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Figure 24. Panoramic view of Lake Charles ML and MH. .......................................................................... 64 Figure 25. Depth plots of selected physical and chemical properties from the Lake Charles microlow and microhigh. .................................................................................................................................................... 72 Figure 26. Pennington Formation (325 Ma, Late Mississippian), Tennessee, USA) paleosol ..................... 76 Figure 27. Mack et al. (1993) classification for paleosols. ........................................................................... 77 Figure 28. Two examples of geochemical climate proxies derived from pre-Quaternary paleosols ............ 78 Figure 29. Estimates of Middle to Late Paleozoic atmospheric CO2 levels ................................................. 78 Figure 30. Climosequence sampling sites, designated by soil series ............................................................ 79 Figure 31. Fe chemistry of Texas climosequence for Vertisol microlows ................................................... 81 Figure 32. Fe chemistry of Texas climosequence for Vertisol microlows ................................................... 82 Figure 33. Carbonate (CaCO3) and S chemistry .......................................................................................... 83 Figure 34. Exchangeable-base chemistry. ................................................................................................... 84 Figure 35. Exchangeable-base chemistry ..................................................................................................... 85 Figure 36. Exchangeable-base chemistry ..................................................................................................... 85 Figure 37. Results of application of chemical index of alteration minus potash (CIA-K) for estimation of MAP (Sheldon et al. 2002) to actual measured MAP of Texas Vertisol climosequence ............................. 86 Figure 38. Application of Sheldon et al. (2002) CIA-K climofunction to Pennington Formation (Upper Mississippian) paleosol succession in eastern Kentucky .............................................................................. 87

LIST OF TABLES Table 1. Vegetation types in study area (after McMahan et al. 1984). ........................................................... 7 Table 2. Summary of Texas Vertisols examined for fieldtrip. ..................................................................... 17 Table 3. Field morphological description of the Victoria microlow, San Patricio County, Texas. ............. 24 Table 4. Field morphological description of the Victoria microhigh, San Patricio County, Texas. ............. 25 Table 5. Selected soil morphological features from the Victoria microlow. ................................................ 26 Table 6. Selected soil morphological features from the Victoria microhigh ................................................ 27 Table 7. Selected physical and chemical properties from the Victoria microlow and microhigh ............... 32 Table 8. Field morphological description of the Laewest microlow, Victoria County, Texas. .................... 37 Table 9. Field morphological description of the Laewest microhigh, Victoria County, Texas. ................... 38 Table 10. Selected soil morphological features from the Laewest microlow ............................................... 39

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Table 11. Selected soil morphological features from the Laewest microhigh. ............................................. 40 Table 12. Selected physical and chemical properties from the Laewest microlow and microhigh .............. 45 Table 13. Field morphological description of the Lake Charles microlow, Wharton County, Texas........... 51 Table 14. Field morphological description of the Lake Charles microhigh, Wharton County, Texas. ........ 52 Table 15. Selected soil morphological features from the Lake Charles microlow. ...................................... 53 Table 16. Selected soil morphological features from the Lake Charles microhigh. ..................................... 54 Table 17. Selected physical and chemical properties from the Lake Charles microlow and microhigh ..... 59 Table 18. Field morphological description of the Lake Charles microlow, Harris County, Texas. ............. 65 Table 19. Field morphological description of the Lake Charles microhigh, Harris County, Texas. ............ 66 Table 20. Selected soil morphological features from the Lake Charles microlow ....................................... 67 Table 21. Selected soil morphological features from the Lake Charles microhigh ...................................... 69 Table 22. Selected physical and chemical properties from the Lake Charles microlow and microhigh ...... 73 Table 23. Diagenetic alteration of paleoVertisols. ....................................................................................... 77 Table 24. Summary of Texas Vertisols examined for climosequence study. ............................................... 80 Table 25. Comparison between measured mean annual precipitation (MAP) and MAP estimated using chemical index of alteration minus potash (CIA-K) of Sheldon et al. (2002). ............................................. 87

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INTRODUCTION Vertisols (clay-rich soils with high shrink-swell potential) occur in many climatic settings and have distinctive pedogenic characteristics, including prominent bowl-like structures (gilgai), randomly oriented planar slickensides, and pedogenic carbonate and Fe-Mn oxide nodules (Lynn and Williams 1992; Coulombe et al. 1996a, 1996b; Soil Survey Staff 1998). Ancient Vertisol equivalents (i.e., paleoVertisols) have been widely identified in geologic successions, including Paleozoic rocks of the Appalachian basin in the eastern US, and effectively preserve morphologic, micromorphologic and geochemical characteristics formed within their paleopedogenic settings (Driese and Foreman 1992; Driese and Mora 1993; Caudill et al. 1996; Mora and Driese 1999; Driese et al. 1992; Driese et al. 2000; Driese et al. 2003; Stiles et al. 2001), even when buried to relatively great depths (to 10 km; Caudill et al. 1997; Mora et al. 1996; Mora et al. 1998). This preservation potential, combined with the dependence of some aspects of Vertisol chemical properties on climate, including the total Fe content of pedogenic Fe-Mn nodules and depth to calcic horizon (Stiles et al. 2001), total mass flux of elements on a total-soil basis (Stiles et al. 2003a), Ti/Zr contents vs. depth (Stiles et al. 2003b), and mass-balance on reagent-extractable soil chemistry using different particle size fractions (Nordt et al. 2004), collectively suggest that Vertisol geochemistry may be employed as a paleoclimate proxy. In order to fully utilize this paleoclimate proxy for interpreting the geologic (paleosol) record, one must first examine climate-dependent chemical trends in Quaternary (Pleistocene-Holocene) Vertisols formed in well-defined pedogenic settings. Much of the current interest in paleosols is driven by their potential to serve as climatic proxies in ancient environments. Because soils form at the atmosphere-lithosphere interface, they potentially provide the most direct geologic record of past climate. Paleoclimate information preserved in paleosols may ultimately prove superior to reconstructions inferred from rock type distributions and sedimentary facies or from the marine record, which are further removed from first-order paleoclimate proxies. Modern Vertisols are clay-rich soils characterized by macro- and micromorphology formed in response to shrink-swell phenomena associated with seasonal precipitation cycles. Many of these features preserve well in the ancient rock record, and vertic paleosols (hereafter "paleoVertisols") can be easily recognized in the field and petrographically. Climate is an important component in the formation of Vertisols because seasonal precipitation or soil-moisture deficits are necessary for the formation of shrink-swell properties (Coulombe et al. 1996a, b). Further, Vertisols develop and retain systematic pedogenic depth-functions typical of other soil orders, many of which correspond with climate (Stiles 2001; 2003b). Thus, (paleo)Vertisols should contain indicators of certain climatic variables, particularly temperature, wet/dry cyclicity and total rainfall. Many other aspects of the pedogenic environment are recorded in paleoVertisol morphology and geochemistry, including properties developed in coastal marine versus proximal alluvial environments, or in response to the impact of vascular plant evolution. Stable carbon isotopes of pedogenic carbonate and soil organic-matter constrain paleoatmospheric CO2 levels (Cerling 1991; Mora et al. 1996; Ekart et al. 1996, 1997) and the dominant ecosystem (i.e., C3 vs. C4 flora; Cerling, 1984; Amundson et al. 1988, 1996; Quade et al. 1989a; Kelly et al. 1991a; Nordt et al. 2002; Miller et al. ms). Most importantly, paleoVertisols are extremely common in the geological record, ranging in age from Proterozoic to Cenozoic (Button 1979; Retallack 1986; Gustavson 1991a,b) and formed at paleolatitudes ranging from equatorial-low latitude (Appalachian basin; refs. cited below) to 78o (Triassic of Antarctica; Retallack 1998). Virtually every Paleozoic redbed formation in the

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Appalachian Basin stratigraphic succession has common occurrences of paleoVertisols or vertic intergrades of other soil types (Driese and Foreman 1991, 1992; Driese et al. 1992, 1997; Driese and Mora 1993, 2001; Mora et al. 1991, 1996; Mora and Driese 1999; Joeckel 1995; Caudill et al. 1996, 1997). The wide spatial and temporal distribution of paleoVertisols reflects the potential for their formation under wide ranges of moisture regimes (from semi-arid to humid); the only strict climatic requirement is that the moisture is seasonally distributed. The widespread distribution also reflects the predominantly physical controls on Vertisol formation; these soils are not limited to specific environments or ecosystems (e.g., Spodosols or Histosols). Despite these detailed observations, geologists routinely interpret paleoVertisols simply as indicating the presence of seasonally wet-dry climates, without regard to other climatic variables such as paleoprecipitation (e.g., paleoVertisol references cited above). Retallack (1994) compiled a non-linear relationship for paleosols, including paleoVertisols, which predicts annual rainfall based upon the depth from the soil surface to pedogenic carbonate horizons. This relationship is based on measurements in Quaternary surface and buried soils representing a variety of soil orders and the relationship is not well constrained (Royer 1999). Our primary hypothesis is that paleoVertisols record more paleoclimatic information than has been reported in the geological literature. Our ability to discern this information has been hampered by a lack of comparative studies in which modern Vertisols are examined, from a geological perspective, and with the expressed purpose of identifying an array of climatically sensitive macro- and micromorphological, and chemical features, that have preservation potential in the geological record. Our initial characterization of a climosequence transect of modern Vertisols from the Coastal Prairie region of Texas, ranging from 600 to 1400 mm precipitation per year, has yielded several significant results pertinent to Vertisol development and soil-climate relationships.

OBJECTIVES OF FIELDTRIP The primary objective of this fieldtrip is to examine regional variations in field morphology, micromorphology, and soil chemistry across a Quaternary Vertisol climosequence, i.e., a transect of Vertisols in which major soil-forming factors, with the exception of climate (of which mean annual precipitation (MAP) is one component of climate), are held constant (Stiles 2001; Stiles et al. 2001, 2003a; Stiles et al. 2003b), and to test the applicability of derived climate proxy measures for interpreting the paleoclimate record from ancient (lithified) Vertisols preserved as paleosols. MAP is one of the most significant of the soil-forming factors that influence pedogenesis (Birkeland 1999), and we hypothesize that soil constituents are therefore leached to varying depths or mobile to varying degrees depending upon MAP and intensity of wetting and drying cycles (i.e., climosequence trends are manifested by MAP-dependent patterns in soil chemistry). A second objective is to show geoscientists how to use the standard soil wet-chemical characterization data that are readily available from the National Soils Database maintained by the Natural Resources Conservation Service (NRCS) of the US Department of Agriculture (USDA) to interpret chemical patterns in modern soils considered as analogs for paleosols. We also demonstrate how standard total soil analysis (X-ray fluorescence analyses of bulk soil expressed as wt% element or oxide) can be related to soil wet-chemical data, and, by extrapolation, related to geochemical patterns observed in paleosols. A third objective is to test whether or not the geochemical proxy for paleoprecipitation estimation proposed recently by Sheldon et al. (2002) has predictive capability for the Texas Vertisol

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climosequence, and by inference, for paleoclimate interpretations based upon the geochemistry of Paleozoic paleoVertisols from the Appalachian basin of the eastern US. Sheldon et al.’s (2002) proxy, defined as the “chemical index of alteration minus potash” (CIA-K), was developed using total soil (oxide or element) analyses from a suite of USDA Mollisols, Alfisols, and Ultisols, but did not specifically include Vertisols. Finally, we hope that our study illustrates how valuable linkages can be established when geologists work together with soil scientists, and with the NRCS in general. With this study we show that the strengthening of collaborations between the two research groups can yield valuable information for interpreting the climate records of both modern and ancient soils.

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QUATERNARY ENVIRONMENTAL CONTEXT OF THE TEXAS COAST PRAIRIE

CLIMATE The study area is within the western part of the Gulf Coastal Plain physiographic province (Fenneman 1938). Beginning in the study area, the Coastal Plain extends north to the Ouachita uplift in southern Oklahoma and westward to the Balcones escarpment in central Texas. The area selected for the field trip is mainly a flat, nearly featureless plain, though the coastal areas to the east are undulating and dune-like. Overall elevation of the study area varies from sea level to the east and up to 60 m inland. The flat landscape is traversed from northwest to southeast by low-gradient alluvial valleys of the Frio, San Antonio, Guadalupe, Lavaca, Colorado, Brazos, San Jacinto and Trinity Rivers (Figure 1). The general climate along the coast prairie of Texas is largely a function of proximity to the Gulf of Mexico and follows a slight gradient from subtropical humid in the east (near the Gulf) to subtropical subhumid in the southwest (inland) (Bomar 1995). Warm to hot and dry summers and mild winters are the norm. Temperature extremes are fairly well-modulated by southeasterly warm and moisture-laden winds from the Gulf of Mexico, though high humidity typically persists near the coast. In the wintertime, cold, high-pressure Canadian air masses from the north result in cool, cloudy and rainy weather across the region (Guckian et al. 1979; McEwen and Crout 1974; Miller 1982; Wheeler 1976). Annually across the study area average low temperatures range from approximately 15-21° C, while average high temperatures range from 27-29° C. The taxonomic soil temperature regime is hyperthermic, with mean annual temperatures (MAT) slightly greater than 22°C (see Figure 1). Between the cities of Beaumont and Corpus Christi, mean annual precipitation (MAP) ranges from approximately 1400 to 700 mm (Figure 1). Near the Houston area, near the Lake Charles soil pit at Armand Bayou (Stop #4), precipitation is highly variable, ranging from as low as 762 to as high as 1524 mm annually (Wheeler 1976). Annual rainfall across the study area is generally bimodal, with peaks occurring in Fall (September through October) due to tropical disturbances and occasional hurricanes in the Gulf, and as slow gentle rains and thundershowers in the Spring (April, May, and June) (Figure 2). Rainfall is more evenly distributed throughout the year near Houston, and heavy and light fogs are common because of the generally high humidity, which are due to the proximity to the Gulf of Mexico. Relative humidity can range from 60-75% year round and even reach 100% even during summer days (Guckian et al. 1979; Miller 1982; Wheeler 1976). As seen in Figure 1, the taxonomic soil moisture regime in the study area is udic to the east of the city of Victoria, where moisture deficit throughout the year is minimal. The udic soil moisture regime has no distinctive dry season, with no moisture deficit during growing season (<90 days). The ustic soil moisture region to the west experiences greater seasonality of rainfall and greater moisture deficit during the summer months, with wet/dry cycles and period moisture deficits (90-180 days).

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Figure 1. Map showing locations of climosequence sampling sites visited during fieldtrip.

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Figure 2. Average monthly precipitation (A) and temperature (B) climographs from counties in the study area. Data compiled from NRCS soils surveys for San Patricio, Victoria, Wharton, and Harris counties, Texas.

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VEGETATION Each of the Vertisol pedon localities visited during this field trip is located within the Gulf Coast Prairies and Marshes Natural Region as defined by the Texas Natural Resources Information System (TNRIS) (Figure 3). The Coastal Sand Plain, South Texas Brush Country, and Blackland Prairie Natural Regions flank the study area to the south, west, and northwest, respectively. Within these broadly defined natural regions exists a great degree of faunal and floral heterogeneity. For example, the Gulf Coast Prairie and Marshes Natural Region contains several vegetation communities including Mesquite-Blackbrush Brush, Mesquite-Granjeno Parks, Post Oak Woods/Forest, Post Oak Woods, Forest, and Grassland Mosaic, Bluestem Grassland, Mesquite-Live Oak-Bluewood Parks, and Marsh Barrier Islands (McMahan et al. 1984) (Figure 4). Distribution of these vegetation associations and commonly associated plants are presented in Table 1. Significantly there is an overall dominance of cropland species as areas have been converted to cropland during historic times. This has also resulted in the encroachment of several woody species (Kunze et al. 1963).

Table 1. Vegetation types in study area (after McMahan et al. 1984).

Association Distribution Common Associated Plants

Mesquite-Blackbrush Brush

shallow, gravelly or loamy soils in the South Texas Plains

lotebush, ceniza, guajillo, desert olive, allthrorn, whitebrush, bluewood, granjeno, guayacan, leatherstem, Texas pricklypear, tasajillo, kidneywood, yucca, desert yaupon, goatbush, purple three-awn, pink pappusgrass, hairy tridens, slim tridens, hairy grama, mat euphorbia, colenia, dogweed, knotweed leafflower, two-leaved senna

Mesquite-Granjeno Parks

sandy or loamy upland soils in the South Texas Plains

bluewood, lotebush, coyotillo, guayacan, Texas colubrine, tasajillo, Texas pricklypear, Pan American balsamscale, single-spike paspalum, hooded windmillgrass, tanglehead, Roemer three-awn, purple three-awn, tumble lovegrass, Lindheimer tephroasia, bullnettle, croton, slender evolvulvus, Texas lantana, silverleaf nightshade, firewheel

Post Oak Woods, Forest, and Grassland Mosaic

sandy soils of the Post Oak Savannah

blackjack oak, eastern redcedar, mesquite, black hickory, live oak, sandjack oak, cedar elm, hackberry, yaupon, poison oak, American beautyberry, hawthorn, supplejack, trumpet creeper, dewberry, coral-berry, little bluestem, silver bluestem, sand lovegrass, beacked panicum, three-awn, spranglegrass, tickclover

Bluestem Grassland Gulf Prairies and Marshes in grassland areas

bushy bluestem, slender bluestem, little bluestem, sliver bluestem, three-awn, buffalograss, Bermudagrass, brownseed paspalum, single-spike paspalum, smutgrass, sacahuista, windmillgrass, southern dewberry, live oak, mesquite, huisache, baccharis, Macartney rose

Mesquite-Live Oak-Bluewood Parks

South Texas Plains huisache, huisachillo, whitebrush, granjeno, lotebush, Berlandier wolfberry, blackbrush, desert yaupon, Texas pricklypear, woolybucket bumelia, tasajillo, agarito, Mexican persimmon, purple three-awn, pink pappusgrass, Halls panicum, slimlobe poppymallow, sensitive briar, two-leaved senna, mat euphorbia

Marsh/Barrier Island hydric lowlands landward of brackish marsh, Coastal Prairies and Marshes

water hyacinth, cattail, water-pennywort, pickerelweed, arrowhead, white waterlily, cabomba, coontail, duckweed

7

Figure 3. Natural Regions in study area. Data compiled from Texas Natural Resource Information System (TNRIS).

LAND USE Outside of urbanized areas the Texas Coast Plain region consists mainly of rangeland, cropland, and pasture. The pace of urbanization in San Patricio, Victoria, and Wharton Counties is minor when compared to that of the Houston area in Harris County. As of the 1976 soil survey of Harris County, approximately 40% of the county was classified as urban land, while the remainder was classified as pasture and range, cropland, woodland, federal land, and water areas (Wheeler 1976). The region has experienced tremendous growth since then and the amount of urban land is likely significantly higher. Across the remainder of the study area to the south, urbanized areas comprise <10% of the overall landscape (Guckian et al. 1979; Miller 1982). Farming and beef cattle production are dominant industries, and San Patricio County (location of Stop #1) relies economically on a viable fishing industry as well as water port facilities such as the intercoastal canal. Due to the excellent suitability of soils for field crop and grass production, agriculture has played an important part of the historical development of the Texas Coast Plain. Grain sorghum, cotton,

8

corn, flax, rice, and hay crops are among the highest yielding crops for the region. Beef cattle production is also an important local industry. The Houston metropolitan area is one of the leading centers for petrochemical manufacturing as well as agribusiness, various science-based industries, and is a leading producer of agricultural chemicals, fertilizers, and insecticides (Wheeler 1976). Regionally, commercial production oil and gas have historically been an extremely important industry since the early 1930s when the first oil and gas fields opened.

Figure 4. Vegetation in study area. Data compiled from Texas Parks and Wildlife Department and McMahan et al. 1984.

QUATERNARY GEOLOGIC SETTING The Texas Coastal Plain is a featureless, low lying 80-160 km- wide strip of terrain that dips gulfward at a gradient of about five feet per mile. It consists of a succession of progressively younger and southeasterly-dipping Paleocene through Quaternary terrigenous clastic rock and unconsolidated sediments that were deposited in the Gulf of Mexico basin as part of a fluvial-deltaic system (Figure 5). In the study area, these deposits are often are capped by eolian, littoral, and estuarine facies (Barnes 1975; Durbin et al. 1997). Fluvial responses to glacioeustatic sea level change, changing sediment supply, and accommodation space during the

9

Quaternary have greatly influenced the sediment architecture of the region. Episodes of sea level fall expose large continental shelf areas to subaerial weathering and soil formation. Fluvial systems respond by deeply incising their valleys to reach new base level equilibrium. Estuaries result during subsequent sea level rise, followed by gradual vertical and progradational sedimentation. The results of this long term repetitive sequence are Quaternary alluvial surfaces parallel to the modern coast. Within the study area three main Quaternary-age stratigraphic units of Pleistocene age are designated, from oldest to youngest, as the Willis, Lissie, and Beaumont Formations (Barnes 1982; Bradley 1985; Duessan 1924; Fisk 1938; Bernard 1950). The Pliocene to early Pleistocene Willis Formation consists of fluvial clay, silt, sand, and gravel deposits and is subdivided into two members based on the degree of weathering and age. The less weathered Willis member (Qwl) is strongly dissected into upland remnants surrounded by Middle Miocene deposits (Barnes 1982; 1992). The strongly weathered Willis member (Qwc) is preserved as a prominent outcrop scarps and contains abundant iron concentrations and ferric concretions (Barnes 1982; Barnes 1992).

Figure 5. Simplified geologic map of the study area. Data compiled from Geologic Atlas of Texas, Bureau of Economic Geology.

10

The Lissie Formation consists of clay, silt, sand, and fine gravel, and exhibits significant pedogenic alteration that includes large carbonate concretions and iron and/or FeMn rhizoliths, concretions, and amorphous segregations. This laterally-continuous unit is level to gently rolling and is often marked with shallow depressions and pimple mounds (Barnes 1992). The Lissie Formation is cross-cut by numerous younger valley alluvial fills. The late Pleistocene-age Beaumont Formation, the youngest of these coastwise Quaternary formations, extends from the Texas-Louisiana border to southwest of Corpus Christi and exhibits meander ridge and swale topography (Figure 5) (Barnes 1982, 1992; DuBar et al. 1991; Blum and Price 1994). This unit is comprised of sandy clays and sands in multi-storied stacks of flood basin mud and splay sands (Blum et al. 1995). Developed on these are thick black A and E horizons, and well developed Bt and Bk horizons. This formation has been dated to more than 35,000 to 40,000 years B.P. by radiocarbon analysis (Birdseye and Aronow 1991), and to between approximately 70,000 to 115,000 years B.P. by TL dating techniques (Blum and Price 1994; Blum et al. 1995; Durbin et al. 1997). Spatial distribution of the Beaumont Formation reflects the distribution of fluvial channel, point bar, levee, backswamp, barrier island, coastal marsh, mudflat, and littoral facies. Three lithostratigraphic units are mapped for the Beaumont. The first unit includes stream channel, point bar, natural levee, backswamp, and coastal marsh and mud-flat deposits. The surface is almost featureless and characterized by relict river channels shown by meander patterns and pimple mounds on meanderbelt ridges, separated by areas of low, smooth, featureless backswamp deposits lacking pimple mounds (Barnes 1992). Floodbasin, backswamp, and abandoned channel-fill muds are of low permeability, high water holding capacity, high compressibility, high to very high shrink-swell potential, poor drainage, level to depressed relief, low shear strength, and high plasticity (Barnes 1982, 1992). The second Beaumont lithostratigraphic unit (Qbs) is mainly meanderbelt, levee, crevasse splay, and distributary sand facies that are dominantly clayey sand and silt of moderate permeability and drainage, low to moderate compressibility and shrink-swell potential, level relief with local mounds and ridges, and high shear strength (Barnes 1992). The final Beaumont unit includes interdistributary muds, abandoned channel fill muds, and fluvial overbank muds that are dominantly clay and mud of low permeability, high water holding capacity, high compressibility, high to very high shrink-swell potential, poor drainage, level to depressed relief, low shear strength, and high plasticity (Barnes 1982, 1992). Barrier island beach deposits (Qbb) are fine grained sand with high to very high permeability, low water holding capacity, low compressibility, low shrink-swell potential, good drainage, low ridge and depressed relief, high shear strength, and low plasticity (Barnes 1982, 1992). Post-Beaumont formations presumed Holocene in age were first differentiated by Bernard (1950) and include the informal Deweyville terraces and beds along major east Texas rivers. Along the Trinity, Brazos and Guadalupe rivers, as well as in outer coastal plain and deltas, up to three inset late Quaternary fluvial terraces are mapped stratigraphically between Recent floodplain deposits and the Beaumont surface (Blum et al. 1995). Large abandoned meander scars are the principal distinguishing geomorphic characteristic of these terraces. Deweyville deposits have been radiocarbon dated to between 13,000 and 30,000 years B.P. from a variety of unknown localities (see Morton et al. 1996), and from approximately 25,000 to 50,000 years B.P. with TL dating along the Nueces and Trinity rivers (Durbin et al. 1997; Morton et al. 1996). Recent radiocarbon dating of latest Pleistocene terraces along these same rivers inland of the coastal plain identifies a widespread period of deposition ending 15,000 to 20,000 years B.P. (Blum and Valastro 1994; Humphrey and Ferring 1994; Waters and Nordt 1995) that falls within the age range of the original concept of the Deweyville and may be correlative with youngest Deweyville deposits buried in the floodplains. Age discrepancies for late Quaternary alluvial deposits in the coastal plain are due to a combination of insufficient information about the locations of the radiocarbon-

11

dated samples and to the limitations of different dating techniques. Regardless of the discrepancy in the absolute chronology of Deweyville and other late Pleistocene terraces, terrace sequences are consistently mappable in most drainage basins between the floodplains and Beaumont Fm., including along the Rio Grande. Holocene valley fills, constituting floodplains and low terraces, can be traced inland along river valleys to obtain chronological estimates based on extensive radiocarbon dating. The two most common landforms are late Holocene terraces ranging in age from ~1000 to 5000 years B.P. and the modern floodplains dating to within the last 1000 years (Blum and Valastro 1994; Humphrey and Ferring 1994; Waters and Nordt 1995). Along the Rio Grande, a radiocarbon age obtained during the climosequence sampling phase identified a late Holocene terrace dating to ~1000 to 5000 years B.P.

PEDOLOGIC SETTING OF VERTISOLS At 1.5 Mha, statewide, Texas contains more Vertisols than any other state in the United States. Vertisols are widely distributed across the study area from Victoria to Houston and on the Beaumont Formation are representative of channel and floodbasin facies of Pleistocene deltaic environments. Vertisols are clay rich soils that exhibit significant changes in volume due to shrinking and swelling under changing soil moisture conditions (Coulombe et al. 1996). Undulating microtopographic and subsurface features referred to as gilgai microhighs (MH) and microlows (ML) are features unique to Vertisols (Figure 6). Shrink-swell is perhaps the most dominant property of Vertisols. Vertisols can form on a variety of parent materials of varying age and under different climates. Most have developed in recent (Quaternary) times, and are typically at low elevation and on footslope to depressional positions in the landscape. Vertisols typically support grassland and savannah, although mixed/ deciduous forest and scrub/shrub are also sometimes supported (Coulombe et al. 1996).

Figure 6. Diagram showing bowl morphology and gilgai micro-relief characteristics of Vertisols (modified from Lynn and Williams (1992).

Field Morphology and Physical Properties Vertisols are fine-textured soils and can contain up to 90% clay content. In order to classify as a Vertisol, the soil must have “a weighted average of 30% or more clay in the fine earth fraction either between the mineral soil surface and a depth of 18 cm or in an Ap horizon, whichever is

12

thicker, and 30% or more clay in the fine earth fraction of all horizons between a depth of 18 cm and either a depth of 40 cm, or a densic, lithic, or paralithic contact, duripan, or petrocalcic horizon if shallower.” (Soil Survey Staff 1998). If the soil clay content is not met but it exhibits high shrink/swell properties, as measured by the coefficient of linear extensibility (COLE), the soil can be considered as a vertic intergrade to other soil orders (Coulombe et al. 1996). In addition, the clay must exhibit significant shrink/swell properties which results in unique structure and features throughout the soil profile. Such properties include a layer of 25 cm or more thick, with an upper boundary within 100 cm of the mineral soil surface that has either slickensides close enough to intersect, or wedge shaped aggregates which have their long axes tilted 10 to 60 degrees from the horizontal. Soil cracks that open and close in response to drying and wetting are also a Vertisol requirement (Soil Survey Staff 1998). Another unique feature common to Vertisols also include gilgai, which are circular to linear mounds and depressions. Mukkara are another Vertisol feature and is a protrusion of soil material which penetrates from the subsoil through the upper layers, often contrasting in color and texture (Coulombe et al. 1996). Early pedogenic studies invoked a pedoturbation or self mixing model to explain the apparent lack of horizonation in Texas Vertisols (Kunze and Templin 1956; Templin et al. 1956, Nelson eta l. 1960, Kunze et al. 1963). Today, most investigators employ the soil mechanics model (Yaalon and Kalmar 1978; Knight 1980; Wilding and Tessier 1988) to explain the preservation of systematic pedogenic depth functions and the formation of slickensides, wedge shaped aggregates, and gilgai resulting from shear failure along stress zones. The characteristic common to all vertic soils is cracking of clays in the solum and shrinking and swelling of the soil matrix, driven by wet/dry cycles. The shrink/swell process is commonly ascribed to expansion and collapse of smectitic clays in the soil matrix, however, recent studies (Coulombe et al. 1996a, b) suggest it is driven by saturation and drying of very fine (<2μm) pores associated with the fine-clay fraction. Upon Vertisol wetting and expansion, excess volume creates shear stresses in the subsurface, followed by drying that creates contraction and the formation of surface cracks. The stresses are relieved by formation of a distinctive wedge-shaped ped structure (parallelipipeds), by failure along curved surfaces (pedogenic slickensides) and by a polygonal buckling of the land surface (gilgai). These features are inferred to begin to form very rapidly, perhaps even within tens to hundreds of years, however, no systematic study has been made (Wilding and Tessier 1988; Coulombe et al. 1996a, b). Earlier studies by Blodgett (1985, 1991, 1992) recognized three developmental phases of paleoVertisols, defined by macromorphology, which correlate loosely with climate. These phases reflect paleosols exhibiting weakly developed slickensides (interpreted to be paleoclimatically unconstrained) to paleosols bearing arcuate cross cutting slickensides and gilgai, to paleosols with maximum expression of vertic features. The latter, by analogy with present day soil/climate distributions, were deemed good candidates for formation under tropical and sub-tropical conditions with pronounced wet/dry cycles.

Chemical Properties Vertisols tend to be neutral to alkaline in reaction as most are derived from calcareous or base-rich parent materials. Dystric Vertisols with pH values of 4.5 or less do exist, resulting from acidification through the removal of carbonates and bases by leaching or chemical processes such as hydrolysis, acid sulfate weathering, and ferrolysis. For the most part, however, Vertisol pH worldwide ranges from 6.5 to 8.2 (Coulombe et al. 1996). Cation Exchange Capacity (CEC) of Vertisols ranges from 20 to 4 cmolckg-1 or higher, depending on mineral phases and soil organic

13

matter. Main exchangeable cations are Ca, Mg, K, and Na. Al, Mg, and H cations may increase and replace exchangeable Ca under acid conditions (Coulombe et al. 1996).

Mineralogical Properties Highly expandable smectites are a significant component of most Vertisols, though abundant kaolinite, illite, hallysite, hydroxyl-interlayered smectite clay minerals can also be present (Coulombe et al. 1996).

Taxonomic Classification Vertisols are one of 12 NRCS soil orders. There are 6 suborders, 23 great groups, and 155 subgroups within the Vertisol order (Soil Survey Staff 1998). Suborders are identified according to moisture and temperature regimes. Great groups reflect morphogenetic markers and processes, while subgroup categories represent intragrades to other soil orders. Currently, there are no diagnostic horizons associated with Vertisols. The main discriminator against other soil orders is the presence of slickensides (Coulombe et al. 1996).

Land Use and Management Vertisols are highly productive soils for crops; however, they represent unique land use challenges because of their extensive shrink/swell properties. Generally they are not suitable for waste and wastewater disposal and may contribute to potential contamination of surface and groundwater. Additionally they pose stability problems for buildings, roads, pipelines and utilities (Coulombe et al. 1996). Urban development is becoming increasingly widespread across Coastal Plain Vertisols. As a consequence, the high shrink-swell properties have buckled streets and sidewalks and cracked walls and foundations (Texas A&M Department of Soil and Crop Sciences 1986).

SOIL FORMING FACTORS ON TEXAS COASTAL PLAIN The Coastal Prairie region of Texas is an ideal location for examining a climosequence through modern Vertisols for a variety of reasons. It represents one of the largest continuous mapped belts of Vertisols in the U.S; nearly 4 million ha of Vertisols occur in ustic and udic moisture regimes on the Beaumont Formation along the coastal plain of Texas (Coulombe et al. 1996). Vertisols form in the broad, clayey, floodbasin facies between slightly elevated meander ridges. Furthermore, many of the soil-forming factors (parent material, time, landscape, and vegetation) can be held nearly constant.

Parent material The parent material for the Vertisols is the upper facies of the Beaumont Formation (Late Pleistocene), deposited as part of a large alluvial to deltaic system (Barton 1930; Metcalf 1940; Bernard and LeBlanc 1965; Dubar et al. 1991; Blum and Price 1994), and hence is comparable to the depositional setting for many of the Appalachian basin paleoVertisols in the eastern US (Cotter 1993; Caudill et al. 1996; Cotter and Driese 1998; Mora and Driese 1999). Vertisols in the upper Beaumont Formation form from the thick (4 to 6 m) floodbasin facies between slightly elevated and loamy meander ridges. The parent sediments of the Vertisols are relatively uniform

14

with respect to mineralogy (smectitic clays) and texture (fine and very fine clays) (Kunze et al. 1963). Time

The Beaumont Formation in the coastal plain of Texas has been dated to more than 35,000 to 40,000 years B.P. by radiocarbon analysis (Birdseye and Aronow 1991), and to between approximately 70,000 to 115,000 years B.P. by TL dating techniques (Blum and Price 1994; Durbin et al. 1997). Along the Trinity, Brazos and Guadalupe rivers, two late Quaternary terraces are mapped as part of the Deweyville Fm. between floodplains and the Beaumont surface (Blum et al. 1995). Deweyville deposits have been radiocarbon dated to between 13,000 and 30,000 years B.P. from a variety of unknown localities (see Morton et al. 1996), and from approximately 25,000 to 50,000 years B.P. with TL dating along the Nueces and Trinity rivers (Durbin et al. 1997; Morton et al. 1996). Recent radiocarbon dating of latest Pleistocene terraces along these same rivers inland of the coastal plain identifies a widespread period of deposition ending 15,000 to 20,000 years B.P. (Blum and Valastro 1994; Humphrey and Ferring 1994; Waters and Nordt 1995) that falls within the age range of the original concept of the Deweyville and may be correlative with youngest Deweyville deposits buried in the floodplains. Age discrepancies for late Quaternary alluvial deposits in the coastal plain are due to a combination of insufficient information about the locations of the radiocarbon-dated samples and to the limitations of different dating techniques. Regardless of the discrepancy in the absolute chronology of Deweyville and other late Pleistocene terraces, terrace sequences are consistently mappable in most drainage basins between the floodplains and Beaumont Fm., including along the Rio Grande. Holocene valley fills, constituting floodplains and low terraces, can be traced inland along river valleys to obtain chronological estimates based on extensive radiocarbon dating. The two most common landforms are late Holocene terraces ranging in age from ~1000 to 5000 years B.P. and the modern floodplains dating to within the last 1000 years ((Blum and Valastro 1994; Humphrey and Ferring 1994; Waters and Nordt 1995). Along the Rio Grande, a radiocarbon age obtained during the climosequence sampling phase identified a late Holocene terrace dating to ~1000 to 5000 years B.P. Because morphological and chemical maturity (steady-state) appear to be reached very rapidly Vertisols, particularly in wetter climates, difficulty in identifying Vertisols in the range 5000 to 15,000 years old does not unduly hamper this study.

Landscape The topography of the region is relatively flat and uniform, hence landscape is relatively constant. We purposely selected soils that were moderately drained to well drained and avoided poorly drained soils.

Vegetation and ecosystem Vegetation along the climosequence transect is relatively constant, being dominated in most places by C4 (warm-season) grasses, and subordinate C3 (trees and shrubs) vegetation. For soil orders such as Vertisols, which are dominated by physical (shrink-swell) processes (Dudal and Eswaran 1988; Wilding and Tessier 1988), the vegetation may play only a secondary role in soil development.

15

16

Climate The soil-forming factor of greatest interest in this fieldtrip – climate – is variable along the selected transect. A strong precipitation gradient exists across the region, from the city of Beaumont (northeast) to 200 km north of Brownsville (southwest), with latitude nearly constant (see Figure 1). Moisture regimes for the entire climosequence study included udic (143-167 cm/yr), udic-ustic (125-143 cm/yr), ustic (91-125 cm/yr), and aridic-ustic (60-91 cm/yr) (Soil Survey Staff 1998; Birkeland 1999). The League is the dominant soil series in the eastern, humid part of the climosequence, with the Lake Charles, Laewest, and Victoria series representing increasingly drier expressions.

SUMMARY OF INVESTIGATED SOILS The study area is within the NRCS Gulf Coast Prairie Major Land Resource Area (MLRA). The dominant vegetation across this MLRA is grasslands where climax species are big bluestem, seacoast bluestem, gulf cordgrass and marsh hay cordgrass. Streams and valleys contain typical hardwood vegetation such as water oak, post oak, cedar elm, sweet gum, American elm, hawthorn, sycamore, black gum and box elder. Wetland species contain white oak, willow oak, hackberry and sweet gum (Texas A&M Department of Soil and Crop Sciences 1986). Soils in this MLRA closely follow the Pleistocene sediments along terraces and alluvial bottomlands. On the Beaumont surface clayey Vertisols and Mollisols are typical on upland prairies with slopes of about 0.2 percent. Undisturbed areas exhibit gilgai microrelief (less than 1 foot) with large deep cracks during dry periods. These soils are used extensively for cultivations, improved pasture, and native pasture. Rice is the main crop, with additional cultivation of corn, cotton, and grain sorghum. Series data for each of the soil pits visited for this field trip (Victoria, Laewest, and 2 Lake Charles) are presented in Table 2.

T

able

2. S

umm

ary

of T

exas

Ver

tisol

s exa

min

ed fo

r fie

ldtr

ip.

Stop

#

Soil

Seri

es

Pedo

n N

o.

Tax

onom

ic

clas

sific

atio

nT

exas

C

ount

ySe

ries

Des

crip

tion

Lan

d us

e M

AP

(mm

) M

AT

-air

(o C

) M

oist

ure

regi

me

Stop

1

(VIC

409

) V

icto

ria

00P0

120

fine,

sm

ectit

ic,

hype

rther

mic

So

dic

Hap

lust

erts

San

Patri

cio

Ver

y de

ep, w

ell

drai

ned,

nea

rly le

vel

and

gent

ly sl

opin

g.

Ver

y sl

owly

pe

rmea

ble.

Slo

pes

from

0 to

3 p

erce

nt

Cro

p pr

oduc

tion

with

som

e liv

esto

ck g

razi

ng a

nd fo

rage

pr

oduc

tion.

Cro

ps a

re m

ainl

y gr

ain

sorg

hum

, cot

ton,

and

co

rn w

ith so

me

smal

l are

as in

veg

etab

les.

Nat

ive

gras

ses

are

little

blu

este

m, s

eaco

ast b

lues

tem

, fou

rflo

wer

tric

hlor

is,

vine

-mes

quite

, and

indi

angr

ass.

Impr

oved

pas

ture

is

mai

nly

coas

tal b

erm

udag

rass

or K

lein

gras

s. N

ativ

e w

oody

pl

ants

are

inva

ders

and

con

sist

mai

nly

of m

esqu

ite tr

ees,

spin

y ha

ckbe

rry,

hui

sach

e, b

razi

l, an

d lo

tebu

sh.

860

21.8

U

stic

Stop

2

(LA

W 4

69)

Laew

est

00P0

384

fine,

sm

ectit

ic,

hype

rther

mic

Ty

pic

Hap

lude

rts

Vic

toria

V

ery

deep

, m

oder

atel

y w

ell

drai

ned.

Ver

y sl

owly

pe

rmea

ble.

Slo

pes a

re

mai

nly

less

than

1

perc

ent,

but r

ange

fr

om 0

to 8

%.

Ran

gela

nd a

nd c

ropl

and.

Com

mon

cro

ps g

row

n ar

e gr

ain

sorg

hum

, cor

n, ri

ce, a

nd c

otto

n. T

urf g

rass

es a

re a

lso

grow

n. C

limax

rang

elan

d ve

geta

tion

cons

ists

of l

ittle

bl

uest

em, i

ndia

ngra

ss, e

aste

rn g

amag

rass

, sw

itchg

rass

, big

bl

uest

em, a

nd p

aspa

lum

s. Tr

ees i

nclu

de li

veoa

k, e

lm,

hack

berr

y, h

uisa

che,

and

mes

quite

alo

ng fe

nce

row

s, dr

aina

ge w

ays a

nd in

scat

tere

d m

otts

.

1000

21

.5

Udi

c

Stop

3

(LA

C 4

81)

Lake

C

harle

s 99

P049

1 fin

e,

smec

titic

, hy

perth

erm

ic

Typi

c H

aplu

derts

Wha

rton

Ver

y de

ep,

mod

erat

ely

wel

l dr

aine

d. V

ery

slow

ly

perm

eabl

e, le

vel t

o ge

ntly

slop

ing.

Sl

opes

mos

tly le

ss

than

1%

, but

can

ra

nge

up to

3%

Cul

tivat

ion

and

nativ

e pa

stur

e. C

rops

are

cor

n, c

otto

n, ri

ce,

and

grai

n so

rghu

m. N

ativ

e gr

asse

s inc

lude

littl

e bl

uest

em,

indi

angr

ass,

east

ern

gam

agra

ss, s

witc

hgra

ss, b

ig b

lues

tem

, an

d br

owns

eed

pasp

alum

. Mos

t are

as h

ave

scat

tere

d liv

e oa

k, w

ater

oak

, elm

, hac

kber

ry, a

nd h

uisa

che

trees

. Pin

e tre

es h

ave

encr

oach

ed in

som

e ar

eas.

1070

21

.3

Udi

c

Stop

4

(LA

C 2

01)

Lake

C

harle

s 99

P048

9 fin

e,

smec

titic

, hy

perth

erm

ic

Aqu

ic

Hap

lude

rts

Har

ris

Ver

y de

ep,

mod

erat

ely

wel

l dr

aine

d. V

ery

slow

ly

perm

eabl

e. L

evel

to

gent

ly sl

opin

g. S

lope

s m

ostly

less

than

1%

, bu

t can

rang

e up

to

3%

Cul

tivat

ion

and

nativ

e pa

stur

e. C

rops

are

cor

n, c

otto

n, ri

ce,

and

grai

n so

rghu

m. N

ativ

e gr

asse

s inc

lude

littl

e bl

uest

em,

indi

angr

ass,

east

ern

gam

agra

ss, s

witc

hgra

ss, b

ig b

lues

tem

, an

d br

owns

eed

pasp

alum

. Mos

t are

as h

ave

scat

tere

d liv

e oa

k, w

ater

oak

, elm

, hac

kber

ry, a

nd h

uisa

che

trees

. Pin

e tre

es h

ave

encr

oach

ed in

som

e ar

eas.

1320

20

.0

Udi

c

17

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18

STOP 1: VICTORIA SERIES (VIC 409) October 3, 2008

Welder Wildlife Refuge: Corpus Christi, Texas, San Patricio County

In San Patricio County, Victoria soils comprise approximately 53% of the Victoria-Raymondville-Orelia general soil map unit and consist of very deep, well drained, nearly level and gently sloping, clayey very slowly permeable soils that formed in calcareous clayey deltaic and marine sediments of the Beaumont Formation (Figure 7; Figure 8). Victoria soils occur widely on uplands, with slopes ranging from 0 to 3 percent and are moderately alkaline and contain a few concretions of calcium carbonate (Guckian and Garcia 1979). Within San Patricio County Victoria soils cover approximately 145,000 acres (32%). Mean annual air temperature is 21.8°C, and mean annual precipitation is 860 mm. Typically, most of the rainfall occurs during the months of April, May, June, September and October (see Figure 2). December, January, February and March are the driest months. Soil moisture regime at this location is ustic. The frost-free period for these soils ranges from 290 to 310 days. Taxonomically, these soils are classified as fine, smectitic, hyperthermic Sodic Haplusterts. The Victoria series is widely used for crop production with some areas used for livestock grazing and forage production. Some areas in crop production have supplemental irrigation where suitable water is available. Crops are mainly grain sorghum, cotton, and corn with some small areas in vegetables. Native grasses are mainly little bluestem, seacoast bluestem, fourflower trichloris, vine-mesquite, and indiangrass. Improved pasture is mainly coastal bermudagrass or Kleingrass. Native woody plants are invaders and consist mainly of mesquite trees, spiny hackberry, huisache, brazil, and lotebush. Wetness is a main limitation to the use of these soils for farming (Guckian and Garcia 1979).

Field Morphological Description

Field morphological data is provided below for both a microlow (ML) (Pedon ID: 99TX409003) and microhigh (MH) (Pedon ID: 99TX409003A) of the Victoria series (VIC 409), located in San Patricio County (Tables 3-6). The microlow exhibits an A-Bw-Bss-Bkss-Bkssy horizon sequence to a depth of 230 cm. The microhigh exhibits an A-Bw-Bss-Bkss-Bkssy-Bssy horizon sequence to a depth of 330 cm. This variability reflects differences in the pedogenic history between the microlow and microhigh. The ML and MH both contain moderate fine and medium subangular blocky peds in the A-Bw horizons. The Bss1 horizon of the ML contains prismatic peds grading to coarse prismatic ped structure within the Bkss1 and Bkss2 from 75-141 cm. Weak medium and coarse prismatic parting to moderate medium and coarse angular blocky and subangular blocky structure are present in the Bkssy1 and Bkssy2 horizons of the ML. In the MH, moderate fine and medium subangular blocky ped structure is found in the Bss1 and Bss2 horizons, from 36 to 73 cm. In the Bkss horizons, from 73 to 195 cm in the MH, ped structure grades from moderate medium prismatic and coarse prismatic to moderate medium angular blocky. The Bkssy horizons exhibit weak medium and coarse prismatic parting to moderate medium, weak medium, and coarse angular and subangular blocky structure. In the MH, the Bssy1 and Bssy2 horizons from 275 to 330 cm exhibit weak medium platy structure. The ML contains a gradual wavy boundary to coarse prismatic structural aggregates with firm, very hard consistence at a depth of 75 cm. This boundary is deeper in the MH, occurring at 144 cm. Black colors persist to greater depths in the ML (114 cm) than the MH (73 cm), followed by progressively lighter colors throughout the Bkss and Bkssy horizons.

19

Figure 7. NRCS soil mapping units and location of Victoria Pedon (VIC 409) on Rincon Bend USGS topographic map. VcA=Victoria clay, 0-1% slopes.

20

Figure 8. San Patricio County General Soil Map and landscape position of Victoria soils. Adapted from San Patricio County Soil Survey (Guckian and Garcia 1979).

21

The greatest abundance of FeMn concentrations in the ML occur in the Bkss2 and Bkss3 horizons at a depth range of 114 to 163 cm. These features consist of 5% fine distinct brown (10YR 4/3) concentrations with sharp boundaries on ped surfaces in light yellowish brown (2.5Y 6/3 matrix. These features reappear within the Bkssy horizons of the ML in somewhat lower abundance, between 178 and 230 cm. Within the MH, FeMn masses first appear in the Bss2 horizon from 54-73 cm, exhibiting sharp boundaries on the surfaces of slickensides. Peak abundance of FeMn concentrations are in the Bkss3 horizon at 144-195 cm and occur as 5 percent fine distinct brown masses on the surfaces of slickensides. In the Bkssy1 horizon these occur as fine prominent reddish yellow (7.5YR 6/8) concentrations with sharp boundaries in pore linings and along slickensides. In the Bkssy2 horizon they are in common abundance on slickenside surfaces. FeMn fine masses occur also within the Bkss3 and Bssy1 horizons to a depth of 300 cm. Slickenside development in the ML first appears in the Bss 1 horizon at 26-54 cm as common faint intersecting slickensides. From 54-178 cm, 30% prominent to distinct pedogenic slickensides are present through all Bss and Bkss horizons. Slickenside development decreases in the Bkssy horizons from 178-230 cm to 10% distinct. In the MH, slickenside development first appears as 30% prominent in the Bss1 horizon from 36-54 cm. Peak abundance of slickensides is in the Bss2 and Bkss1 as 75% prominent, from 54-119 cm. There is a decrease to 30% prominent in the Bkss2 and Bkss3, from 119 to 195 cm, and a further decrease in slickenside development the remainder of the profile, grading from 10% distinct in the Bkssy horizons to 10% faint in the Bssy horizons (275-300 cm). Hard carbonate nodules occur within both the ML and MH, although they first appear at greater depths within the ML, at 54 cm versus 36 cm in the MH. In the ML, few fine nodules are present throughout the Bss2-Bkssy2 horizons (54-230 cm), along with few to common, fine to medium to coarse masses. In the MH, common medium and coarse masses and few fine and medium masses occur throughout the Bkss2-Bkss3 horizons and Bkssy1 horizon. Few fine and medium nodules are present within the Bkssy2 horizon, from 214-231 cm. No nodules or masses are recorded below this depth in the MH. The depth to a strong matrix reaction with HCl was encountered abruptly and 75 cm in the ML, but only 54 cm in the MH. Common fine to medium roots and common fine tubular pores are present throughout the entire ML, and to a depth of 231 cm in the MH. Vertical crack infills with dark gray (10YR 2/1 to 10YR 4/1) clay are present in the ML from 75 to 210 cm. 1-10% fine to medium gypsum crystals are found throughout the ML from 141-230 cm, and in the MH from 144 to 330 cm.

22

Figure 9. Victoria microlow and microhigh, San Patricio County, Texas.

23

Table 3. Field morphological description of the Victoria microlow (Pedon ID: 99TX409001), San Patricio County, Texas. Data source: National Soil Information System, USDA-NRCS.

A--0 to 10 centimeters; black (10YR 2/1); moderate fine and medium subangular blocky structure; firm, hard when dry; many fine roots and common medium roots; many fine vesicular and common fine dendritic tubular pores; clear smooth boundary. Bw--10 to 26 centimeters; black (10YR 2/1); moderate medium subangular blocky structure; firm, hard when dry; common fine and medium roots; common fine and medium tubular pores; 10 percent faint pressure faces; clear smooth boundary. Bss1--26 to 54 centimeters; black (10YR 2/1); weak fine and medium prismatic parting to moderate medium angular blocky structure; firm, hard when dry; common fine roots; common fine tubular pores; 10 percent distinct pressure faces; very slight effervescence; gradual wavy boundary. common faint intersecting slickensides. Bss2--54 to 75 centimeters; 80 percent black (10YR 2/1) and 20 percent black (10YR 2/1); moderate medium prismatic parting to moderate medium angular blocky structure; firm, hard when dry; common fine roots; common fine tubular pores; 10 percent prominent slickensides (pedogenic) and 30 percent distinct slickensides (pedogenic); slight effervescence; gradual wavy boundary. few snail shell fragments; few fine nodules of calcium carbonate. Bkss1--75 to 114 centimeters; 70 percent very dark gray (10YR 3/1) and 30 percent black (10YR 2/1); weak medium and coarse prismatic parting to moderate medium angular blocky structure; firm, hard when dry; common fine roots; common fine tubular pores; 30 percent prominent slickensides (pedogenic); strong effervescence; gradual wavy boundary. few snail shell fragments; vertical cracks filled with black (10YR 2/1) clay; common fine nodules of calcium carbonate; common fine masses of calcium carbonate. Bkss2--114 to 141 centimeters; 60 percent light yellowish brown (2.5Y 6/3) and 40 percent dark gray (10YR 4/1); weak coarse prismatic parting to moderate medium subangular blocky structure; firm, very hard; common fine roots; common fine tubular pores; 30 percent prominent slickensides (pedogenic); strong effervescence; gradual wavy boundary. 5 percent fine distinct brown (10YR 4/3) iron-manganese concentrations with sharp boundaries on surfaces of peds in light yellowish brown (2.5Y 6/3) matrix; cracks filled with dark gray (10YR 4/1) clay; common fine and medium masses of calcium carbonate, few fine nodules of calcium carbonate. Bkss3--141 to 163 centimeters; 80 percent light brownish gray (2.5Y 6/2) and 20 percent dark gray (2.5Y 4/1); moderate medium subangular blocky structure; firm, very hard; common fine roots; common fine tubular pores; 30 percent distinct slickensides (pedogenic); 1 percent fine gypsum crystals; strong effervescence; gradual wavy boundary. 5 percent fine distinct brown (10YR 4/2) iron-manganese concentrations with sharp boundaries on surfaces in light brownish gray (2.5Y 6/2) matrix; cracks filled with dark gray (2.5Y 4/1) clay; consists of common medium and coarse masses of calcium carbonate, few fine nodules of calcium carbonate. Bkss4--163 to 178 centimeters; light brownish gray (2.5Y 6/2); moderate medium subangular blocky structure; firm, hard when dry; common fine roots; common fine tubular pores; 30 percent distinct slickensides (pedogenic); 3 percent fine gypsum crystals; strong effervescence; gradual wavy boundary. 5 percent vertical cracks filled with dark gray (10YR 4/1) clay; common medium and coarse masses of calcium carbonate. Bkssy1--178 to 210 centimeters; strong effervescence. see Bkssy1 of Victoria (high) description. Bkssy2--210 to 230 centimeters. see Bkssy2 horizon from Victoria (high) description.

24

25

Table 4. Field morphological description of the Victoria microhigh (Pedon ID: 99TX409001A), San Patricio County, Texas. Data source: National Soil Information System, USDA-NRCS.

A--0 to 15 centimeters; very dark gray (10YR 3/1) clay; moderate fine and medium subangular blocky structure; firm, hard when dry; many fine roots and common medium roots; many fine dendritic tubular and common medium vesicular pores; 1 percent insect casts; slight effervescence; clear smooth boundary. few snail shell fragments. Bw--15 to 36 centimeters; dark gray (10YR 4/1) clay; moderate fine and medium subangular blocky structure; firm, hard when dry; common fine and medium roots; common fine dendritic tubular pores; 10 percent faint slickensides (pedogenic) and 10 percent faint pressure faces; 1 percent insect casts; slight effervescence; gradual smooth boundary.. few snail shell fragments. Bss1--36 to 54 centimeters; dark gray (2.5Y 4/1) clay; moderate fine and medium subangular blocky structure; very firm, very hard; common fine roots; common fine tubular pores; 30 percent prominent slickensides (pedogenic); 1 percent insect casts; slight effervescence; clear smooth boundary. few snail shell fragments; few nodules of calcium carbonate. Bss2--54 to 73 centimeters; dark gray (10YR 4/1) clay; moderate medium subangular blocky structure; very firm, very hard; common fine roots; common fine tubular pores; 75 percent prominent slickensides (pedogenic); strong effervescence; gradual wavy boundary. few snail shell fragments; less than 1 percent fine faint brown (10YR 4/3) iron-manganese masses with sharp boundaries on surfaces of slickensides; few nodules of calcium carbonate. Bkss1--73 to 119 centimeters; dark gray (10YR 4/1) clay; moderate medium prismatic parting to moderate medium angular blocky structure; extremely firm, extremely hard; common fine roots; common fine tubular pores; 75 percent prominent slickensides (pedogenic); strong effervescence; gradual smooth boundary. few nodules of calcium carbonate. Bkss2--119 to 144 centimeters; 80 percent dark gray (10YR 4/1) and 20 percent light yellowish brown (2.5Y 6/3) clay; moderate medium prismatic parting to moderate medium angular blocky structure; very firm, extremely hard; common fine roots; common fine tubular pores; 30 percent prominent slickensides (pedogenic); strong effervescence; gradual wavy boundary. common medium and coarse masses of calcium carbonate. Bkss3--144 to 195 centimeters; light brownish gray (2.5Y 6/2) clay; moderate medium and coarse prismatic parting to moderate medium angular blocky structure; firm, extremely hard; common fine roots; common fine tubular pores; 30 percent prominent slickensides (pedogenic); 3 percent fine gypsum crystals; strong effervescence; gradual wavy boundary. 5 percent fine distinct brown (10YR 4/3) iron-manganese masses on surfaces of slickensides; common medium and coarse masses of calcium carbonate. Bkssy1--195 to 214 centimeters; light gray (2.5Y 7/2) clay; weak medium and coarse prismatic parting to moderate medium and coarse angular blocky structure; very firm, very hard; common fine roots; common fine tubular pores; 10 percent distinct slickensides (pedogenic); 3 percent fine and medium gypsum crystals; strong effervescence; gradual wavy boundary. 1 percent fine prominent reddish yellow (7.5YR 6/8) iron concentrations with sharp boundaries in pore linings and along slickensides; few fine and medium masses of calcium carbonate. Bkssy2--214 to 231 centimeters; 70 percent light yellowish brown (2.5Y 6/3) and 30 percent brownish yellow (10YR 6/6) clay; weak coarse prismatic parting to weak medium and coarse subangular blocky structure; firm, hard when dry; common fine roots; common fine tubular pores; 10 percent distinct slickensides (pedogenic); 3 percent fine and medium gypsum crystals; strong effervescence; gradual wavy boundary. few fine and medium nodules of calcium carbonate; common fine very dark brown (7.5YR 2/2) masses of manganese on surfaces of slickensides. Bkssy3--231 to 275 centimeters; 70 percent light yellowish brown (2.5Y 6/3) and 30 percent brownish yellow (10YR 6/6) clay; weak coarse subangular blocky structure; firm, hard when dry; common fine roots; common fine tubular pores; 10 percent distinct slickensides (pedogenic); 3 percent fine very dark brown (7.5YR 2/2) manganese masses; 3 percent fine and medium gypsum crystals; strong effervescence; gradual smooth boundary. Bssy1--275 to 300 centimeters; 20 percent brownish yellow (10YR 6/8) and 80 percent light gray (2.5Y 7/2) clay; weak medium platy structure; firm, hard when dry; 10 percent faint slickensides (pedogenic); 3 percent fine manganese masses; 3 percent fine and medium gypsum crystals and 3 percent fine and medium gypsum masses; strong effervescence; gradual smooth boundary. Bssy2--300 to 330 centimeters; 60 percent brownish yellow (10YR 6/8) and 40 percent light gray (2.5Y 7/2) clay; weak medium platy structure; firm, hard when dry; 10 percent faint slickensides (pedogenic); 10 percent fine gypsum crystals and 3 percent fine and medium gypsum masses; strong effervescence.

Tab

le 5

. Sel

ecte

d so

il m

orph

olog

ical

feat

ures

from

the

Vic

tori

a m

icro

low

(Ped

on ID

: 99T

X40

9003

). sb

k =

suba

ngul

ar b

lock

y; a

bk =

ang

ular

blo

cky;

med

. = m

ediu

m

Hor

izon

D

epth

(cm

) B

ound

ary

Stru

ctur

e C

onsi

sten

ce

Col

orR

edox

feat

ures

Sl

icke

nsid

es

Car

bona

te

segr

egat

ions

R

eact

ion

Oth

er P

rope

rtie

s Fe

Mn

conc

entr

atio

n Fe

depl

etio

ns

A

0-10

cl

ear

smoo

th

mod

erat

e fin

e an

d m

ediu

m sb

k fir

m, h

ard

whe

n dr

y 10

YR

2/1

- -

- -

-

man

y fin

e ro

ots a

nd c

omm

on

med

. roo

ts; m

any

fine

vesi

cula

r an

d co

mm

on fi

ne d

endr

itic

tubu

lar p

ores

B

w

20-2

6 cl

ear

smoo

th

mod

erat

e m

ed. s

bk

firm

, har

d w

hen

dry

10Y

R 2

/1

- -

10 %

fain

t pr

essu

re fa

ces

- -

com

mon

fine

and

med

. roo

ts;

com

mon

fine

and

med

. tub

ular

po

res

Bss

1 26

-54

grad

ual

wav

y w

eak

fine

and

med

ium

pris

mat

ic

parti

ng to

mod

erat

e m

ed. a

bk

firm

, har

d w

hen

dry

10Y

R 2

/1

- -

10 %

dis

tinct

pr

essu

re fa

ces

-

very

sl

ight

co

mm

on fi

ne ro

ots;

com

mon

fin

e tu

bula

r por

es

Bss

2 54

-75

grad

ual

wav

y m

oder

ate

med

ium

pr

ism

atic

par

ting

to

mod

erat

e m

ed. a

bk

firm

, har

d w

hen

dry

10Y

R 2

/1

- -

10 %

pro

min

ent

30 %

dis

tinct

fe

w fi

ne n

odul

es

slig

ht

com

mon

fine

root

s; c

omm

on

fine

tubu

lar p

ores

; few

snai

l sh

ell f

ragm

ents

B

kss1

75

-114

gr

adua

l w

avy

wea

k m

ediu

m a

nd

coar

se p

rism

atic

pa

rting

to m

oder

ate

med

. abk

firm

, har

d w

hen

dry

70 %

10Y

R 3

/1

30 %

10Y

R 2

/1

- -

30%

pro

min

ent

com

mon

fine

no

dule

s co

mm

on fi

ne

mas

ses

stro

ng

com

mon

fine

root

s; c

omm

on

fine

tubu

lar p

ores

; few

snai

l sh

ell f

ragm

ents

; ver

tical

cra

ck

infil

ls w

ith 1

0YR

2/1

cla

y.

Bks

s2

114-

141

grad

ual

wav

y w

eak

coar

se

pris

mat

ic p

artin

g to

m

oder

ate

med

. sbk

firm

, ver

y ha

rd w

hen

dry

60 %

2.5

Y 6

/3

40 %

10Y

R 4

/1

5% fi

ne

dist

inct

10Y

R

4/3

-

30%

pro

min

ent

com

mon

fine

an

d m

ediu

m

mas

ses

few

fine

nod

ules

stro

ng

com

mon

fine

root

s; c

omm

on

fine

tubu

lar p

ores

; cra

ck in

fills

w

ith d

ark

gray

(10Y

R 4

/1) c

lay

Bks

s3

141-

163

grad

ual

wav

y m

oder

ate

med

. sbk

fir

m, v

ery

hard

whe

n dr

y

80 %

2.5

Y 6

/2

20 %

2.5

Y 4

/1

5% d

istin

ct

10Y

R 4

/2

-

30%

dis

tinct

co

mm

on

med

ium

and

co

arse

mas

ses

few

fine

nod

ules

stro

ng

com

mon

fine

root

s; c

omm

on

fine

tubu

lar p

ores

; cra

ck in

fills

w

ith d

ark

gray

(2.5

Y 4

/1) c

lay;

1%

fine

gyp

sum

cry

stal

s B

kss4

16

3-17

8 gr

adua

l w

avy

mod

erat

e m

ed. s

bk

firm

, har

d w

hen

dry

2.5Y

6/2

- -

30%

dis

tinct

co

mm

on

med

ium

and

co

arse

mas

ses

stro

ng

com

mon

fine

root

s; c

omm

on

fine

tubu

lar p

ores

; ver

tical

cra

ck

infil

ls w

ith d

ark

gray

(10Y

R

4/1)

cla

y; 3

% fi

ne g

ypsu

m

crys

tals

B

kssy

1 17

8-21

0 gr

adua

l w

avy

wea

k m

ed. a

nd

coar

se p

rism

atic

pa

rting

to m

oder

ate

med

. and

coa

rse

abk

very

firm

, ve

ry h

ard

whe

n dr

y

2.5Y

7/2

1%

fine

pr

omin

ent

7.5Y

R 6

/8

-

10%

dis

tinct

fe

w fi

ne a

nd

med

ium

mas

ses

stro

ng

com

mon

fine

root

s; c

omm

on

fine

tubu

lar p

ores

; 3%

fine

and

m

ed. g

ypsu

m c

ryst

als

Bks

sy2

210-

230

-

wea

k co

arse

pr

ism

atic

par

ting

to

wea

k m

ed. a

nd

coar

se sb

k

firm

, har

d w

hen

dry

70%

2.5

Y 6

/3

30%

10Y

R 6

/6

Com

mon

fine

7.

5YR

2/2

m

asse

s -

10%

dis

tinct

fe

w fi

ne a

nd

med

ium

nod

ules

st

rong

co

mm

on fi

ne ro

ots;

com

mon

fin

e tu

bula

r por

es; 3

% fi

ne a

nd

med

ium

gyp

sum

cry

stal

s

26

27

Tab

le 6

. Sel

ecte

d so

il m

orph

olog

ical

feat

ures

from

the

Vic

tori

a m

icro

high

(Ped

on ID

: 99T

X40

9003

A).

sbk

= su

bang

ular

blo

cky;

abk

= a

ngul

ar b

lock

y; m

ed. =

med

ium

H

oriz

on

Dep

th(c

m)

Bou

ndar

ySt

ruct

ure

Con

sist

ence

C

olor

Red

ox fe

atur

es

Slic

kens

ides

C

arbo

nate

se

greg

atio

ns

Rea

ctio

n O

ther

Pro

pert

ies

FeM

n co

ncen

trat

ion

Fe depl

A

0-

15

clea

r sm

ooth

m

oder

ate

fine

and

med

. sbk

fir

m, h

ard

whe

n dr

y 10

YR

3/1

- -

- -

slig

ht

man

y fin

e ro

ots a

nd c

omm

on m

ed.

root

s; m

any

fine

dend

ritic

tubu

lar a

nd

com

mon

med

. ves

icul

ar p

ores

; 1%

in

sect

cas

ts; f

ew sn

ail s

hell

frag

men

ts

Bw

15

-36

grad

ual

smoo

th

mod

erat

e fin

e an

d m

ed. s

bk

firm

, har

d w

hen

dry

10Y

R 4

/1

- -

10%

fain

t 10

%

pres

sure

fa

ces

-

slig

ht

com

mon

fine

and

med

. roo

ts; c

omm

on

fine

dend

ritic

tubu

lar p

ores

; 1%

inse

ct

cast

s; fe

w sn

ail s

hell

frag

men

ts

Bss

1 36

-54

clea

r sm

ooth

m

oder

ate

fine

and

med

. sbk

ve

ry fi

rm, v

ery

hard

whe

n dr

y 2.

5Y 4

/1

- -

30%

pr

omin

ent

few

nod

ules

sl

ight

co

mm

on fi

ne ro

ots;

com

mon

fine

tu

bula

r pre

s; 1

% in

sect

cas

ts; f

ew sn

ail

shel

l fra

gmen

ts

Bss

2 54

-73

grad

ual

wav

y m

oder

ate

med

. sbk

ve

ry fi

rm, v

ery

hard

whe

n dr

y 10

YR

4/1

<1

% fa

int

10Y

R 4

/3

mas

ses

- 75

%

prom

inen

t fe

w n

odul

es

stro

ng

com

mon

fine

root

s; c

omm

on fi

ne

tubu

lar p

ores

; few

snai

l she

ll fr

agm

ents

B

kss1

73

-119

gr

adua

l sm

ooth

m

oder

ate

med

. pr

ism

atic

par

ting

to

mod

erat

e m

ed. a

bk

extre

mel

y fir

m,

extre

mel

y ha

rd

whe

n dr

y

10Y

R 4

/1

- -

75%

pr

omin

ent

few

nod

ules

st

rong

co

mm

on fi

ne ro

ots;

com

mon

fine

tu

bula

r por

es

Bks

s2

119-

144

grad

ual

wav

y m

oder

ate

med

. pr

ism

atic

par

ting

to

mod

erat

e m

ed. a

bk

very

firm

, ex

trem

ely

hard

w

hen

dry

80%

10Y

R 4

/1

20%

2.5

Y 6

/3

- -

30%

pr

omin

ent

com

mon

med

ium

an

d co

arse

m

asse

s

stro

ng

com

mon

fine

root

s; c

omm

on fi

ne

tubu

lar p

ores

Bks

s3

144-

195

grad

ual

wav

y m

oder

ate

med

. and

co

arse

pris

mat

ic

parti

ng to

mod

erat

e m

ed. a

bk

firm

, ext

rem

ely

hard

whe

n dr

y 2.

5Y 6

/2

5% fi

ne

dist

inct

10Y

R

4/3

mas

ses

-

30%

pr

omin

ent

com

mon

med

ium

an

d co

arse

m

asse

s

stro

ng

com

mon

fine

root

s; c

omm

on fi

ne

tubu

lar p

ores

; 3%

fine

gyp

sum

cr

ysta

ls

Bks

sy1

195-

214

grad

ual

wav

y w

eak

med

. and

co

arse

pris

mat

ic

parti

ng to

mod

erat

e m

ed. a

nd c

oars

e ab

k

very

firm

, ver

y ha

rd w

hen

dry

2.5Y

7/2

1%

fine

pr

omin

ent

7.5Y

R 6

/8

-

10%

dis

tinct

fe

w fi

ne a

nd

med

ium

mas

ses

stro

ng

com

mon

fine

root

s; c

omm

on fi

ne

tubu

lar p

ores

; 3%

fine

and

med

. gy

psum

cry

stal

s

Bks

sy2

214-

231

grad

ual

wav

y w

eak

coar

se

pris

mat

ic p

artin

g to

w

eak

med

. and

co

arse

sbk

firm

, har

d w

hen

dry

70%

2.5

Y 6

/3

30%

10Y

R 6

/6

com

mon

fine

7.

5YR

2/2

m

asse

s -

10%

dis

tinct

fe

w fi

ne a

nd

med

ium

nod

ules

st

rong

co

mm

on fi

ne ro

ots;

com

mon

fine

tu

bula

r por

es; 3

% fi

ne a

nd m

ed.

gyps

um c

ryst

als

Bks

sy3

231-

275

grad

ual

smoo

th

wea

k co

arse

sbk

firm

, har

d w

hen

dry

70%

2.5

Y 6

/3

30%

10Y

R 6

/6

3% fi

ne 7

.5Y

R

2/2

mas

ses

-

10%

dis

tinct

-

stro

ng

com

mon

fine

root

s; c

omm

on fi

ne

tubu

lar p

ores

; 3%

fine

7.5

YR

2/2

Mn

mas

ses;

3%

fine

and

med

ium

gyp

sum

cr

ysta

ls

Bss

y1

275-

300

grad

ual

smoo

th

wea

k m

ed. p

laty

fir

m, h

ard

whe

n dr

y 20

% 1

0YR

6/8

80

% 2

.5Y

7/2

3%

fine

mas

ses

- 10

% fa

int

- st

rong

3%

fine

and

med

. gyp

sum

cry

stal

s and

3%

fine

and

med

. gyp

sum

mas

ses

Bss

y2

300-

330

- w

eak

med

. pla

ty

firm

, har

d w

hen

dry

60%

10Y

R 6

/8

40%

2.5

Y 7

/2

- -

10%

fain

t -

stro

ng

10%

fine

gyp

sum

cry

stal

s and

3%

fine

an

d m

ediu

m g

ypsu

m m

asse

s

Soil Micromorphological Description FeMn concretions with multiple concentric microbands or layers are abundant in the Victoria soil, with an average diameter of FeMn concretions from 1-2 mm (Figure 10A). Microbands are prominent because of layers of quartz silt and sand grains, which were engulfed during concretion precipitation. FeMn nodules (lacking multiple concentric microbands) are common in the Victoria soils. These generally exhibit smaller diameters than banded FeMn concretions, and contain quartz silt and sand grains. These nodules are also generally darker in color and more opaque than concretions. No FeMn pore linings (including simple coatings and hypocoatings) were observed in the Victoria soil. Interpedal pores and dendritic FeMn masses are rare in the Victoria soil. Hard carbonate (calcite) nodules are abundant to common in the Victoria soil, but the are generally of smaller diameter in the Victoria soil. Septarian shrinkage cracks with sparry calcite crystal linings are absent in the carbonate nodules of the Victoria soil (Figure 10C). Although some carbonate nodules are primarily microcrystalline calcite (micrite), many show evidence for recrystallization to microspar, which are bladed to prismatic to equigranular calcite crystals ranging from 5-25 �m in diameter (Figure 10D). Soft powdery masses of micrite are common in the Victoria soils. The calcite occurs as clusters of fine crystal fibers that coalesce and engulf soil matrix and quartz skeletal grains. Soft, powdery carbonate masses are more abundant in the MH than the ML. Within the Victoria soil, gypsum crystal masses occur both as a lining for soil fracture macropores and disseminated within the soil matrix (Figure 10E, F). Gypsum crystals are generally lozenge-shaped and rarely twinned, and range from 1-5 m in length. Although co-occurrence of both gypsum crystal masses and calcite nodules in the same soil sample are observed, carbonate typically is more abundant in the higher parts of soil profiles whereas gypsum is restricted to the lower portions of the same profiles. Sepic-plasmic (bright clay) matrix microfabrics are present but in low abundance in the Victoria soil. The most common fabric is masepic, characterized by oriented domains of clay minerals with bright interference colors that have one dominant orientation.

28

Figure 10. Photomicrographs of selected horizons from the Victoria pedon: All photomicrographs are taken in cross-polarized light. (A) MH, Bss2 horizon. (B) MH, Bkssy1 horizon. (C) MH, Bkssy1 horizon. (D) MH, Bkss1 horizon. (E) ML, Bssy1 horizon. (F) ML, Bkss4 horizon.

Selected Physical and Chemical Properties

Selected physical and chemical properties for the Victoria ML and MH are illustrated in Figure 11 and summarized in Table 7. Organic carbon content is greater in the ML than MH, likely due to more favorable soil moisture conditions in the ML. Organic carbon ceases to decline in both the ML and MH at about 200 cm, though is greater at greater depths in the ML. In the MH there is a spike in organic carbon at about 214 cm within the Bkssy2 horizon. The CaCO3 equivalent curve shows significant decalcification in the upper 150 cm of the ML, with a slight increase below that depth. CaCO3 equivalent is relatively constant in the upper 200 cm of the MH, with a slight increase below 300 cm.

29

30

Clay content is just over 50% in both the ML and MH. Fine clay is more abundant in the ML than the MH. Coefficient of linear extensibility (COLE) values are similar in the ML and MH and are relatively uniform with depth. The Feo/Fed ratio indicates that much more amorphous iron oxide (short order) occurs in the upper 200 cm of the profile in both the ML and MH, though more occurs in the MH and to greater depths. Percent Base Saturation (BS) is somewhat lower in the upper 54 cm of the ML, increasing to 100% throughout the remaining depth of the profile. BS is 100% throughout the MH. As indicated by pH trends, the ML has undergone more leaching than the MH. Cation Exchange Capacity (CEC) is slightly higher in the upper part of the ML than the MH and gradually decreases with depth. Exchangeable sodium percentage (ESP) in the ML increases sharply in the Bkss1 horizon of both the ML and MH. The CEC to clay ratio, used as an indicator of clay mineralogy, is similar in both the ML and MH and to similar depths. Montmorillonitic clays (CEC:clay values >.7) are in the uppermost part of the profile for both the ML and MH, with montmorillonitic to mixed (CEC:clay values from .5 to .7) below.

0 0 0 0 0 0

050

100

050

100

00.

250.

50

0.5

10

5010

00

510

050

100

050

100

01

20 50 100

150

200

250

300

350

01

2

Depth (cm)

025

50

050

100

00.

250.

50

0.5

10

510

050

100

050

100

01

20

2550

0 50 100

150

200

250

02

4Depth (cm)

MicrohighO

rgan

ic C

wt%

CaC

O3

Equi

v.W

t %

Cla

y C

onte

ntW

t %C

OLE

FeO

/Fe D

% B

SpH

CEC

cmol

ckg-

1ES

P%

Bd

g cm

-3

A Bw Bss

1

Bss

2

Bkss

1

Bkss

2

Bkss

3

Bkss

4

Bkss

y1

Bkss

y2

A Bw Bss1

Bss2

Bkss

1

Bkss

2

Bkss

3

Bkss

y1Bk

ssy2

Bkss

y3

Bssy

1

Bssy

2

Microlow

Fine

cla

y

Tot

al c

lay

Fine

cla

y

Tot

al c

lay

00.

51

CEC

7/C

lay

00.

51

Figu

re 1

1. D

epth

plo

ts o

f sel

ecte

d ph

ysic

al a

nd c

hem

ical

pro

pert

ies f

rom

the

Vic

tori

a m

icro

low

and

mic

rohi

gh (V

IC 4

09).

31

32

Tab

le 7

. Se

lect

ed p

hysi

cal a

nd c

hem

ical

pro

pert

ies f

rom

the

Vic

tori

a m

icro

low

and

mic

rohi

gh (V

IC 4

09).

Vic

tori

a Se

ries

(mic

rolo

w)

Dep

th (c

m)

Hor

izon

O

Cw

t%

TC

wt%

T

otal

Cla

yw

t%

Fine

C

lay

wt%

CO

LE

who

le

soil

CaC

O3

equi

v.

wt%

Fed

FeO

FeO

/Fe D

%B

S pH

CE

C7

NH

4 OA

C

cmol

c kg

-1

ESP

Bd

g cm

-3C

EC

7:cl

ay

0-

10

A

2.43

2.

43

49.2

37

.9

0.20

5 -

0.10

0.

06

0.60

98

6.

3 39

.8

1 1.

00

0.81

10

-26

Bw

1.

42

1.42

52

.8

39.6

0.

148

- 0.

10

0.05

0.

50

98

7.3

42.0

2

1.21

0.

80

26-5

4 B

ss1

1.05

1.

17

52.3

26

.5

0.14

3 1

0.10

0.

04

0.40

10

0 7.

5 36

.9

4 1.

28

0.71

54

-75

Bss

2 0.

82

1.18

51

.8

23.7

0.

157

3 0.

10

0.03

0.

30

100

7.8

35.4

11

1.

29

0.68

75

-114

B

kss1

0.

73

1.09

51

.6

25.3

0.

173

3 0.

10

0.04

0.

40

100

8.0

30.7

22

1.

23

0.59

11

4-14

1 B

kss2

0.

19

1.15

49

.9

27.5

0.

177

8 0.

10

0.04

0.

40

100

7.5

30.3

26

1.

19

0.61

14

1-16

3 B

kss3

0.

14

1.22

51

.1

24.2

0.

17

9 0.

10

0.04

0.

40

100

8.0

29.5

27

1.

21

0.58

16

3-17

8 B

kss4

0.

07

0.79

51

.1

14.6

0.

115

6 0.

10

0.04

0.

40

100

7.9

28.9

18

1.

42

0.57

17

8-21

0 B

kssy

1 0.

00

0.84

50

.5

26.7

0.

129

7 0.

20

0.04

0.

20

100

7.9

28.9

21

1.

43

0.57

21

0-23

0 B

kssy

2 0.

07

0.91

46

.1

18.0

-

7 0.

20

0.04

0.

20

100

7.9

26.9

20

-

0.58

V

icto

ria

Seri

es (m

icro

high

) 0-

15

A

1.78

2.

62

50.6

24

.1

0.15

3 7

0.10

0.

04

0.40

10

0 7.

5 36

.2

1 1.

22

0.72

15

-36

Bw

0.

78

1.98

52

.9

21.3

0.

153

10

0.10

0.

05

0.50

10

0 7.

6 35

.8

2 1.

26

0.68

36

-54

Bss

1 0.

56

1.88

53

.4

13.4

0.

147

11

0.10

0.

05

0.50

10

0 7.

7 34

.5

6 1.

26

0.65

54

-73

Bss

2 0.

47

1.79

54

.7

15.3

0.

150

11

0.10

0.

06

0.60

10

0 7.

9 35

.1

12

1.27

0.

64

73-1

19

Bks

s1

0.40

1.

60

56.6

15

.6

0.19

9 10

0.

10

0.06

0.

60

100

8.0

35.9

22

1.

15

0.63

11

9-14

4 B

kss2

0.

22

1.30

57

.1

21.0

0.

168

9 0.

10

0.04

0.

40

100

8.0

34.1

25

1.

23

0.60

14

4-19

5 B

kss3

0.

10

1.18

54

.9

27.6

0.

179

9 0.

10

0.05

0.

50

100

7.9

31.5

19

1.

22

0.57

19

5-21

4 B

kssy

1 0.

90

1.26

46

.9

15.6

0.

156

3 0.

20

0.05

0.

25

100

7.8

25.5

18

1.

27

0.54

21

4-23

1 B

kssy

2 0.

00

1.60

45

.6

19.2

0.

184

15

0.30

0.

04

0.13

10

0 7.

7 25

.7

18

1.17

0.

56

231-

275

Bks

sy3

0.03

1.

95

44.4

18

.2

0.17

0 16

0.

30

0.04

0.

13

100

7.9

26.4

22

1.

25

0.59

27

5-30

0 B

ssy1

0.

06

1.38

47

.2

20.5

-

11

0.30

0.

04

0.13

10

0 7.

8 28

.3

23

- 0.

60

300-

330

Bss

y2

0.10

2.

50

53.8

-

- 20

0.

50

0.05

0.

10

100

7.9

32.4

19

-

0.60

O

C%

= O

rgan

ic C

arbo

n

TC =

Tot

al C

arbo

n C

OLE

= C

oeff

icie

nt o

f lin

ear e

xten

sibi

lity

Fed =

dith

ioni

te e

xtra

ctab

le F

e Fe

o = o

xala

te e

xtra

ctab

le F

e

BS

= ba

se sa

tura

tion

CEC

= c

atio

n ex

chan

ge c

apac

ity

ESP

= ex

chan

geab

le so

dium

per

cent

age

Bd

= bu

lk d

ensi

ty

See

labo

rato

ry p

roce

dure

in S

oil S

urve

y S

taff,

199

6

STOP 2: LAEWEST SERIES (LAW 469) October 3, 2008

Victoria County, Texas

In Victoria County, Laewest soils, formerly grouped within the Lake Charles series, consist of nearly level to gently sloping, very deep, moderately well drained, very slowly permeable soils that formed in clayey sediments on broad coastal prairies (Figure 12, Figure 13, Figure 14). Laewest soils have slopes that are mainly less than 1 percent, but range up to 8%. Runoff is low on 0 to 1 percent slopes, medium on 1 to 3 percent slopes, high on 3 to 5 percent slopes, and very high on 5 to 8 percent slopes (Miller 1982). Parent material for the Laewest series is the Late Pleistocene Beaumont Formation, which consists of topographically flat, red calcareous alluvial-deltaic deposits 4 to 6 meters thick. Gilgai microhighs (<1° slope) and microlows characterize the landscape. Mean annual temperature in the study area is 21.5 °C and mean annual precipitation is 1000 mm per year. Soil moisture regime at this location is udic. Taxonomically, the Laewest soil is classified as a fine, smectitic, hyperthermic Typic Hapluderts. The Laewest soil is used mainly for rangeland and cropland. The most common crops grown are grain sorghum, corn, rice, and cotton. Turf grasses are also grown. Climax rangeland vegetation consists mainly of little bluestem, indiangrass, eastern gamagrass, switchgrass, big bluestem, and paspalums. Trees include liveoak, elm, hackberry, huisache, and mesquite along fence rows, drainage ways and in scattered motts (Miller 1982).

Field Morphological Description

Field morphological data is provided below for the Laewest ML (Pedon ID: 99TX469001) and MH (Pedon ID: 99TX469001A) (Table 8, Table 9, Table 10, Table 11). The ML exhibits an A-Bss-Bkss-B’ss horizon sequence to a depth of 265 cm. The MH exhibits an Ak-Bk-Bkss-Bss-B’ss horizon sequence to a depth of 265 cm. The ML contain moderate fine to medium subangular and angular blocky ped structure in the upper 74 cm, with the occurrence of fine to coarse wedge aggregates from the Bss3 through Bkss1 horizons, from 74 to 154 cm. From the Bkss2 horizon to the bottom of the profile at 265, structure is comprised of moderate medium and coarse angular blocky peds. Wedge-shaped peds are encountered in the MH beginning at 28 cm and continue through the Bkss3 horizon to a depth of 198 cm. Horizon boundaries in the ML are typically gradual, with firm, hard to very hard when dry consistence. In the MH, boundaries are generally gradual wavy, though clear wavy boundaries separate the Bkss 2, Bkss3, and Bss horizons and corresponds to the presence of wedge-shaped ped structures. Consistence in the MH ranges from firm to very firm when moist, and hard to very hard when dry. Dark yellowish brown colors with low values (2-3) and low chroma (1) in the ML persist to 154 cm (Bkss1 horizon). Soil colors become increasingly lighter with depth in the ML, with values increasing to 5-7, and chroma up to 8. In the B’ss2 horizon beginning at 222 cm, there is also a hue shift from yellowish brown to reddish brown. Yellowish brown colors in the MH are within the Ak horizon to 11 cm and become progressively lighter with depth. FeMn concentrations are found throughout the ML from 16 to 265 cm and consist of <1-1% fine spherical nodules in the upper 154 cm of the profile. Below this depth there are fine prominent strong brown (7.5YR 5/8) masses of oxidized Fe with sharp boundaries in the matrix and along ped faces and slickenside surfaces. Within the B’ss3 horizon at 245-265 cm, fine distinct Fe masses line pores.

33

Figure 12. NRCS soil mapping units and location of Laewest Pedon (LAW 469) on Placedo USGS topographic map. The Laewest soil was previously part of the Lake Charles clay, 0-1% slopes (LaA).

34

Figure 13. Victoria County General Soil Map and landscape position of Laewest soil (formerly grouped with Lake Charles soil). Adapted from Victoria County Soil Survey (Miller 1982).

35

Figure 14. View of Laewest soil.

Fe depletions in the ML are limited to the B’ss1 horizon from 176-222 cm and consist of 1% fine and medium distinct dark grayish brown (2.5Y 4/2) depletions with clear boundaries that line root pores and are on slickenside surfaces. In the MH, 1% fine (10YR 2/2) FeMn nodules are distributed throughout the Bk through Bkss3 horizons from 11 to 198 cm. Below 198 cm in the MH, FeMn concentrations include 1% fine prominent dendritic masses on slickenside surfaces, and fine distinct masses in matrix and pore linings. No Fe depletions are in the MH. Slickenside development is present in the ML from 16-265 cm, with greatest abundance in the Bss2-Bkss1 horizons, which ranges from 60-70% prominent and angled 40-50° from the horizontal. Lower horizons in the ML show a slight decrease in slickenside development from 45 to 25%, and 20-30° from the horizontal. Slickenside development is less pronounced in the MH, beginning in the Bkss1 horizon at 28 cm and extending to 265 cm. Peak development is reached in the Bkss2 horizon (55% prominent and 50-65°) from 119-172 cm. Development decreases below 172 cm from 40 to 25%, with angles from 20-30°. Carbonate nodules in the ML begin and are most abundant in the Bkss1 horizon from 118-154 cm, and decrease in lower horizons from <1-1% abundance. Cylindrical nodules are observed in the B’ss2 and B’ss3 horizons from 222 to 265 cm. In the MH, fine and medium nodules extend from the Ak horizon to the Bkss1 horizon at 119 cm depth. Beginning in the Bkss3 horizon there are 2% medium and coarse nodules, and <1% fine cylindrical nodules and masses in the Bss and B’ss3 horizons from 198-265 cm. The depth to a strong matrix reaction with HCl is encountered abruptly at 154 cm in the ML, but only 11 cm in the MH. Common very fine to coarse roots and fine tubular pores are present throughout the profiles of both the ML and MH. Vertical cracks 0.5 to 2.5 cm wide are in the Bss1 horizon from 16-43 cm, and 5-cm wide cracks infilled with 10YR 2/1 clay are found in the Bkss2 horizon at 154-176 cm. Plant phyotoliths are observed in the Bkss1 horizon from 118-154 cm. Less than 1% medium gypsum nests and <1% gypsum crystals are within the B’ss1 horizon, and the B’ss3 horizon contains very few very fine clean rounded quartz grains. In the MH, 1-3 cm crack infills with 10YR 4/1 clay occur in the Bk through Bkss1 horizons from 11-119 cm, with smaller 0.5 to 1 cm wide crack infills in the Bkss3 horizon from 172-198 cm.

36

Table 8. Field morphological description of the Laewest microlow (Pedon ID: 99TX469001), Victoria County, Texas. Data source: National Soil Information System, USDA-NRCS. A--0 to 16 centimeters; black (10YR 2/1) clay, black (10YR 2/1), dry; moderate fine and medium subangular blocky structure; firm, hard when dry; common very fine and fine roots and common coarse roots; common fine vesicular pores; 10 percent faint pressure faces; 1 percent insect casts; clear smooth boundary. Bss1--16 to 43 centimeters; black (10YR 2/1) clay, black (10YR 2/1), dry; moderate medium subangular blocky structure; firm, very hard; common very fine and fine roots; few fine tubular pores; 30 percent distinct pressure faces; gradual smooth boundary. Lab sample # 00P02640. 20 percent distinct slickensides tilted at 20 to 40 degrees from the horizontal; less than 1 percent fine spherical black (7.5YR 2/1) iron-manganese nodules; less than 1 percent fine iron manganese masses; common cracks 0.5 to 2.5 centimeters wide. Bss2--43 to 74 centimeters; black (10YR 2/1) clay, black (10YR 2/1), dry; moderate medium subangular blocky structure; firm, very hard; common very fine and fine roots; common very fine tubular pores; gradual smooth boundary. Lab sample # 00P02641. 60 percent prominent slickensides tilted at 50 degrees from the horizontal; less than 1 percent fine black (7.5YR 2/1) iron-manganese nodules; less than 1 percent fine iron manganese masses. Bss3--74 to 118 centimeters; black (10YR 2/1) clay, very dark gray (10YR 3/1), dry; moderate medium angular blocky, and moderate fine and medium wedge structure; firm, very hard; common very fine and fine roots; gradual wavy boundary. Lab sample # 00P02642. 70 percent prominent slickensides tilted at 50 degrees from the horizontal; 1 percent fine snail shell fragments; less than 1 percent fine iron-manganese nodules. Bkss1--118 to 154 centimeters; very dark gray (10YR 3/1) clay, very dark gray (10YR 3/1), dry; moderate medium and coarse wedge parting to strong medium and coarse angular blocky structure; firm, very hard; common very fine roots; clear wavy boundary. Lab sample # 00P02643. 60 percent prominent slickensides are tilted at 40 to 50 degrees from the horizontal; 5 percent fine spherical carbonate nodules with few having a hollow center; 1 percent medium plant phytoliths; less than 1 percent fine iron-manganese masses. Bkss2--154 to 176 centimeters; 70 percent dark gray (10YR 4/1) and 30 percent yellowish brown (10YR 5/8) clay; moderate medium and coarse angular blocky structure; firm, very hard; 1 percent fine carbonate nodules; strong effervescence; gradual wavy boundary. Lab sample # 00P02644. common very fine roots on surfaces of slickensides; 45 percent distinct slickensides tilted at 40 degrees from the horizontal with dark gray (10YR 4/1) organic coats on slickenside surfaces; less than 1 percent fine prominent strong brown (7.5YR 5/8) masses of oxidized iron with sharp boundaries in matrix; 1 percent fine carbonate nodules; 2 percent medium and coarse carbonate masses with few having fine nodules in the center; common cracks 5 centimeters wide filed with black (10YR 2/1) clay. B'ss1--176 to 222 centimeters; 80 percent brownish yellow (10YR 6/6) and light yellowish brown (10YR 6/4) clay; moderate medium and coarse angular blocky structure; firm, hard when dry; strong effervescence; gradual wavy boundary. Lab sample # 00P02645. common v.fine roots on surfaces of slickensides; 40% distinct slickensides tilted at 20 to 30 degrees from the horizontal with dark gray (10YR 4/1) organic coats on slickenside surfaces; 1% fine & medium distinct dark grayish brown (2.5Y 4/2) iron depletions with clear boundaries lining root pores & on slickenside surfaces; 1% fine distinct strong brown (7.5YR 5/8) masses of oxidized iron with sharp boundaries in matrix; 1% fine distinct very dark brown (7.5YR 2/2) iron-manganese masses along ped faces with sharp boundaries; 1% v.fine iron-manganese masses on slickenside surfaces; less than 1% fine carb. nodule; less than 1% fine & med. carb. masses; less than 1% med. gypsum nests; less than 1% med. gypsum crystals B'ss2--222 to 245 centimeters; 80 percent brownish yellow (10YR 6/6) and 20 percent light gray (2.5Y 7/1) clay; moderate medium and coarse angular blocky structure; firm, hard when dry; common very fine roots; common very fine tubular pores; strong effervescence; gradual wavy boundary. Lab sample # 00P02646. 30% distinct slickensides tilted at 20 to 30 degrees from the horizontal; 1% fine prominent dendritic very dark brown (7.5YR 2/2) iron-manganese masses on slickenside surfaces with sharp boundaries; 1% fine prominent reddish yellow (5YR 6/8) masses of oxidized iron in matrix with clear boundaries; light gray (2.5Y 7/1) matrix is mostly along slickenside surfaces and as a depletion on root pores; less than 1 percent fine cylindrical carbonate nodules; very few very fine clean rounded quartz grains throughout. B'ss3--245 to 265 centimeters; 70 percent yellow (10YR 7/6) clay, 25 percent light gray (2.5Y 7/1), dry; moderate coarse angular blocky structure; firm, hard when dry; strong effervescence. Lab sample # 00P02647. 25 percent distinct slickensides tilted at 20 to 30 degrees from the horizontal; 1 percent fine prominent yellowish red (5YR 4/6) masses of oxidized iron lining pores with sharp boundaries; 1 percent fine distinct strong brown (7.5YR 5/6) masses of oxidized iron lining pores with clear boundaries; 2 percent fine prominent dendritic black (7.5YR 2.5/1) iron-manganese masses on slickenside surfaces with sharp boundaries; less than 1 percent fine cylindrical carbonate masses; lighter gray (2.5Y 7/1) matrix is mostly along slickenside surfaces.

37

38

Table 9. Field morphological description of the Laewest microhigh (Pedon ID: 99TX469001A), Victoria County, Texas. Data source: National Soil Information System, USDA-NRCS. Ak--0 to 11 centimeters; dark gray (10YR 4/1) clay, dark gray (10YR 4/1), dry; moderate medium subangular blocky, and moderate fine and medium angular blocky structure; very firm, very hard; common very fine and fine roots and medium roots; common fine interstitial pores; very pale brown (10YR 8/3) carbonate nodules and 5 percent fine and medium white (10YR 8/1); gradual wavy boundary. Bk--11 to 28 centimeters; dark grayish brown (2.5Y 4/2) clay, grayish brown (2.5Y 5/2), dry; moderate medium angular blocky structure; very firm, very hard; common very fine and fine roots; common fine tubular pores; 8 percent fine and medium carbonate nodules; strong effervescence; gradual wavy boundary. common cracks 1 centimeter to 3 centimeters in width filled with dark gray (10YR 4/1) clay; 1 percent fine spherical very dark brown (10YR 2/2) nodules of iron-manganese; about 4 percent of the horizon is brown (10YR 5/3) clay. Bkss1--28 to 119 centimeters; dark grayish brown (2.5Y 4/2) clay, grayish brown (2.5Y 5/2), dry; moderate medium wedge, and moderate coarse wedge parting to moderate coarse platy structure; very firm, very hard; very few very fine roots between peds; common fine tubular pores; 1 percent fine very dark brown (10YR 2/2) iron-manganese nodules; 15 percent fine and medium carbonate nodules; violent effervescence; gradual wavy boundary. 45 percent distinct gray (2.5Y 5/1) slickensides tilted at 50 to 65 degrees from the horizontal; common cracks 1 centimeter to 3 centimeters in width filled with dark gray (10YR 4/1) clay. Bkss2--119 to 172 centimeters; light olive brown (2.5Y 5/3) clay, light yellowish brown (2.5Y 6/3), dry; moderate medium wedge, and coarse structure; very firm, very hard; very few very fine roots between peds; few very fine tubular pores; 1 percent fine very dark brown (10YR 2/2) iron-manganese nodules; violent effervescence; clear wavy boundary. 55 percent prominent grayish brown (2.5Y 5/2) and dark gray (10YR 4/1) slickensides tilted at 40 to 65 degrees from the horizontal. Bkss3--172 to 198 centimeters; yellowish brown (10YR 5/4) clay; moderate medium and coarse wedge structure; very firm, very hard; very few very fine roots; few very fine tubular pores; 1 percent fine very dark brown (10YR 2/2) iron-manganese nodules; 3 percent worm casts and 2 percent medium and coarse carbonate nodules; violent effervescence; clear wavy boundary. 40 percent distinct grayish brown (2.5Y 5/2) slickensides tilted at 55 degrees from the horizontal; common cracks .5 to 1.5 centimeters wide filled with dark gray (10YR 4/1) clay. Bss--198 to 205 centimeters; 80 percent brownish yellow (10YR 6/6) and 20 percent light gray (2.5Y 7/1) clay; moderate medium and coarse angular blocky structure; firm, hard when dry; common very fine roots; common very fine tubular pores; strong effervescence; gradual wavy boundary. 30 percent distinct slickensides tilted at 20 to 30 degrees from the horizontal; 1 percent fine prominent dendritic very dark brown (7.5YR 2/2) iron-manganese masses on slickenside surfaces with sharp boundaries; 1 percent fine prominent reddish yellow (5YR 6/8) masses of oxidized iron in matrix with sharp boundaries; 2 percent fine distinct reddish yellow (7.5YR 6/8) masses of oxidized iron in matrix with clear boundaries; light gray (2.5Y 7/1) matrix is mostly along slickenside surfaces and as a depletion on root pores; less than 1 percent fine cylindrical carbonate nodules; very few very fine clean rounded quartz grains throughout. B'ss3--205 to 265 centimeters; 70 percent yellow (10YR 7/6) and 25 percent light gray (2.5Y 7/1) clay; moderate coarse angular blocky structure; firm, hard when dry; strong effervescence. 25 percent distinct slickensides tilted at 20 to 30 degrees from the horizontal; 1 percent fine prominent yellowish red (5YR 4/6) masses of oxidized iron lining pores with sharp boundaries; 1 percent fine distinct strong brown (7.5YR 5/6) masses of oxidized iron lining pores with clear boundaries; 2 percent fine prominent dendritic black (7.5YR 2.5/1) iron-manganese masses on slickenside surfaces with sharp boundaries; less than 1 percent fine cylindrical carbonate masses; light gray (2.5Y 7/1) matrix is mostly along slickenside surfaces.

Tab

le 1

0. S

elec

ted

soil

mor

phol

ogic

al fe

atur

es fr

om th

e L

aew

est m

icro

low

(Ped

on ID

: 99T

X46

9001

). sb

k =

suba

ngul

ar b

lock

y; a

bk =

ang

ular

blo

cky;

med

. = m

ediu

m

Hor

izon

D

epth

(cm

) B

ound

ary

Stru

ctur

e C

onsi

sten

ce

Col

orR

edox

feat

ures

Sl

icke

nsid

es

Car

bona

te

segr

egat

ions

R

eact

ion

Oth

er P

rope

rtie

s Fe

Mn

conc

entr

atio

n Fe

dep

letio

ns

A

0-16

cl

ear

smoo

th

mod

erat

e fin

e an

d m

ed. s

bk

firm

; har

d w

hen

dry

10Y

R 2

/1

- -

- -

-

com

mon

ver

y fin

e an

d fin

e ro

ots;

com

mon

coa

rse

root

s;

com

mon

fine

ves

icul

ar

pore

s; 1

% in

sect

cas

ts

Bss

1 16

-43

grad

ual

smoo

th

mod

erat

e m

ed.

sbk

firm

; ver

y ha

rd

10Y

R 2

/1

<1%

fine

sphe

rical

7.5

YR

2/1

Fe

Mn

nodu

les;

<1%

fine

FeM

n m

asse

s -

20%

dis

tinct

(2

0-40

°)

- -

com

mon

ver

y fin

e an

d fin

e ro

ots;

few

fine

tubu

lar

pore

s; c

omm

on c

rack

s 0.5

to

2.5

cm

wid

e B

ss2

43-7

4 gr

adua

l sm

ooth

m

oder

ate

med

. sb

k fir

m; v

ery

hard

10

YR

2/1

<1

% fi

ne sp

heric

al 7

.5Y

R 2

/1

FeM

n no

dule

s; <

1% fi

ne F

eMn

mas

ses

- 60

% p

rom

inen

t (5

0°)

- -

com

mon

ver

y fin

e an

d fin

e ro

ots;

com

mon

ver

y fin

e tu

bula

r por

es

Bss

3 74

-118

gr

adua

l w

avy

mod

erat

e m

ed.

abk

and

mod

erat

e fin

e an

d m

ed.

wed

ge

firm

; ver

y ha

rd

10Y

R 2

/1

10Y

R 3

/1

<1%

fine

FeM

n no

dule

s

-

70%

pro

min

ent

(50°

) -

com

mon

ver

y fin

e an

d fin

e ro

ots;

1%

fine

snai

l she

ll fr

agm

ents

Bks

s1

118-

154

clea

r wav

y m

oder

ate

med

. an

d co

arse

w

edge

par

ting

to st

rong

med

. an

d co

arse

abk

firm

; ver

y ha

rd

1YR

3/1

<1

% fi

ne F

eMn

nodu

les

-

60%

pro

min

ent

(40-

50°)

5%

fine

sphe

rical

no

dule

s with

few

ha

ving

a h

ollo

w

cent

er

-

com

mon

ver

y fin

e ro

ots1

%

med

. pla

nt p

hyto

liths

Bks

s2

154-

176

grad

ual

wav

y m

oder

ate

med

. an

d co

arse

abk

fir

m; v

ery

hard

70

%

10Y

R 4

/1

30%

10

YR

5/8

<1%

fine

pro

min

ent s

trong

bro

wn

(7.5

YR

5/8

) mas

ses o

f oxi

dize

d Fe

w

ith sh

arp

boun

darie

s -

45%

(40°

) with

da

rk g

ray

(10Y

R

4/1)

org

anic

co

ats o

n su

rfac

es

1% fi

ne n

odul

es

stro

ng

com

mon

ver

y fin

e ro

ots o

n su

rface

s of s

licke

nsid

es;

com

mon

cra

cks 5

cm

wid

e fil

led

with

10Y

R 2

/1 c

lay

B’s

s1

176-

222

grad

ual

wav

y m

oder

ate

med

. an

d co

arse

abk

fir

m; h

ard

whe

n dr

y 80

%

10Y

R 6

/6

20%

10

YR

6/4

1% fi

ne d

istin

ct 7

.5Y

R 5

/8 m

asse

s ox

idiz

ed F

e w

/sha

rp b

ound

arie

s in

mat

rix; 1

% fi

ne d

istin

ct 7

.5Y

R 2

/2

FeM

n m

asse

s alo

ng p

ed fa

ces w

ith

shar

p bo

unda

ries;

1%

ver

y fin

e Fe

Mn

mas

ses o

n sl

icke

nsid

e su

rfac

es

1% fi

ne a

nd m

ed.

dist

inct

dar

k gr

ayis

h br

own

(2.5

Y 4

/2) F

e de

plet

ions

with

cle

ar

boun

darie

s lin

ing

root

po

res a

nd o

n sl

icke

nsid

e su

rfac

es

40%

dis

tinct

(2

0-30

°) w

ith

dark

gra

y (1

0YR

4/

1) o

rgan

ic

coat

s on

surf

aces

<1%

fine

nod

ules

; <1

% fi

ne a

nd m

ed.

mas

ses

stro

ng

com

mon

ver

y fin

e ro

ots o

n su

rface

s of s

licke

nsid

es;

<1%

med

. gyp

sum

nes

ts;

<1%

med

. gyp

sum

cry

stal

s

B’s

s2

222-

245

grad

ual

wav

y m

oder

ate

med

. an

d co

arse

abk

fir

m; h

ard

whe

n dr

y 80

%

10Y

R 6

/6

20%

2.5

Y

7/1

1% fi

ne p

rom

inen

t den

driti

c 7.

5YR

2/

2 Fe

Mn

mas

ses o

n sl

icke

nsid

e su

rfac

es w

ith sh

arp

boun

darie

s; 1

%

fine

prom

inen

t 5Y

R 6

/8 m

asse

s of

oxid

ized

Fe

in m

atrix

with

cle

ar

boun

darie

s

-

30%

dis

tinct

(2

0-30

°)

<1%

fine

cy

lindr

ical

nod

ules

st

rong

co

mm

on v

ery

fine

root

s;

com

mon

ver

y fin

e tu

bula

r po

res;

ver

y fe

w v

ery

fine

clea

n ro

unde

d qt

z gr

ains

B’s

s3

245-

265

- m

oder

ate

coar

se a

bk

firm

; har

d w

hen

dry

70%

10

YR

7/6

25

% 2

.5Y

7/

1

1% fi

ne p

rom

inen

t 5Y

R 4

/6 m

asse

s of

oxi

dize

d Fe

lini

ng p

roes

with

sh

arp

boun

darie

s; 1

% fi

ne d

istin

ct

7.5Y

R 5

/6 m

asse

s of o

xidi

zed

Fe

linin

g po

res w

ith c

lear

bou

ndar

ies;

2%

fine

pro

min

ent 7

.5 Y

R 2

.5/1

Fe

Mn

mas

ses o

n sl

icke

nsid

e su

rfac

es w

ith sh

arp

boun

darie

s

-

25%

dis

tinct

(2

0-30

°)

<1%

fine

cy

lindr

ical

mas

ses

stro

ng

-

39

40

Tab

le 1

1. S

elec

ted

soil

mor

phol

ogic

al fe

atur

es fr

om th

e L

aew

est m

icro

high

(Ped

on ID

: 99T

X46

9001

A).

sbk

= su

bang

ular

blo

cky;

abk

= a

ngul

ar b

lock

y; m

ed. =

med

ium

H

oriz

on

Dep

th(c

m)

Bou

ndar

y St

ruct

ure

Con

sist

ence

C

olor

R

edox

feat

ures

Sl

icke

nsid

es

Car

bona

te se

gr.

Rea

ctio

n O

ther

Pro

pert

ies

FeM

n co

ncen

trat

ion

Fede

plet

ions

A

k 0-

11

grad

ual

wav

y m

oder

ate

med

. sbk

an

d m

oder

ate

fine

and

med

. abk

very

firm

; ve

ry h

ard

10Y

R 4

/1

- -

- 10

YR

8/3

nod

ules

an

d 5%

fine

10Y

R

8/1

-

com

mon

ver

y fin

e an

d fin

e ro

ots a

nd

med

. roo

ts; c

omm

on fi

ne in

ters

titia

l po

res

Bk

11-2

8 gr

adua

l w

avy

mod

erat

e m

ed. a

bk

very

firm

; ve

ry h

ard

2.5Y

4/2

2.

5Y 5

/2

1% fi

ne sp

heric

al 1

0YR

2/

2 Fe

Mn

nodu

les

- -

8% fi

ne a

nd m

ed.

nodu

les

Stro

ng

com

mon

ver

y fin

e an

d fin

e ro

ots;

co

mm

on fi

ne tu

bula

r por

es; c

omm

on

crac

ks 1

-3 c

m in

fille

d w

ith 1

0YR

4/1

cl

ay

Bks

s1

28-1

19

grad

ual

wav

y m

oder

ate

med

. w

edge

and

m

oder

ate

coar

se

wed

ge p

artin

g to

m

oder

ate

coar

se

plat

y

very

firm

; ve

ry h

ard

2.5Y

4/2

2.

5Y 5

/2

1% fi

ne 1

0YR

2/2

FeM

n no

dule

s

-

45%

dis

tinct

2.5

Y

5/1

(50-

65°)

15

% fi

ne a

nd m

ed.

nodu

les

viol

ent

very

few

fine

root

s; c

omm

on fi

ne

tubu

lar p

ores

; com

mon

cra

cks 1

-3

cm in

fille

d w

ith 1

0YR

4/1

cla

y

Bks

s2

119-

172

clea

r wav

y m

oder

ate

med

. w

edge

and

coa

rse

very

firm

; ve

ry h

ard

2.5Y

5/3

2.

5Y 6

/3

1% fi

ne 1

0YR

2/2

FeM

n no

dule

s -

55%

pro

min

ent

2.5Y

5/2

and

10

YR

4/1

(40-

65°)

-

viol

ent

very

few

ver

y fin

e ro

ots;

few

ver

y fin

e tu

bula

r por

es

Bks

s3

172-

198

clea

r wav

y m

oder

ate

med

. and

co

arse

wed

ge

very

firm

; ve

ry h

ard

10Y

R 5

/4

1% fi

ne 1

0YR

2/2

FeM

n no

dule

s -

40%

dis

tinct

2.5

Y

5/2

(55°

) 2%

med

ium

and

co

arse

nod

ules

vi

olen

t ve

ry fe

w v

ery

fine

root

s; fe

w v

ery

fine

tubu

lar p

ores

; 3%

wor

m c

asts

; co

mm

on c

rack

s 0.5

to 1

.5 c

m w

ide

fille

d w

ith 1

0YR

4/1

cla

y B

ss

198-

205

grad

ual

wav

y m

oder

ate

med

. and

co

arse

abk

fir

m; h

ard

80%

10Y

R 6

/6

20%

2.5

Y 7

/1

1% fi

ne p

rom

inen

t de

ndrit

ic 7

.5Y

R 2

/2 F

eMn

mas

ses o

n sl

icke

nsid

e su

rfac

es w

/sha

rp

boun

darie

s; 2

% fi

ne

dist

inct

7.5

YR

6/8

mas

ses

of o

xidi

zed

Fe in

mat

rix

w/c

lear

bou

ndar

ies

-

30%

dis

tinct

(20-

30°)

<1

% fi

ne

cylin

dric

al n

odul

es

stro

ng

com

mon

ver

y fin

e ro

ots;

com

mon

ve

ry fi

ne tu

bula

r por

es; v

ery

few

ve

ry fi

ne c

lean

roun

ded

qtz

grai

ns

B’s

s3

205-

265

-

mod

erat

e co

arse

ab

k fir

m; h

ard

70%

10Y

R 7

/6

25%

2.5

Y 7

/1

1% fi

ne p

rom

inen

t 5Y

R

4/6

mas

ses o

f oxi

dize

d Fe

lin

ing

pore

s with

shar

p bo

unda

ries;

1%

fine

di

stin

ct 7

.5Y

R 5

/6 m

asse

s of

oxi

dize

d Fe

lini

ng

pore

s with

cle

ar

boun

darie

s; 2

% fi

ne

prom

inen

t 7.5

YR

2.5

/1

FeM

n m

asse

s on

slic

kens

ide

surf

aces

w

/sha

rp b

ound

arie

s

-

25%

dis

tinct

(20-

30°)

<1

% fi

ne

cylin

dric

al m

asse

s St

rong

-

Soil Micromorphological Description FeMn concretions with multiple concentric microbands or layers are common in the Laewest soil, with an average diameter of FeMn concretions from 1-2 mm (Figure 15A, B). Some FeMn concretions contain core areas that are massive, and therefore resemble the FeMn nodules described below (Figure 15B). FeMn nodules (lacking multiple concentric microbands) are internally massive and homogenous in thin section, and are abundant in the Laewest soil. These nodules exhibit smaller diameters than banded FeMn concretions, and contain quartz silt and sand grains, which were engulfed during nodule precipitation. FeMn nodules exhibit both diffuse and sharp boundaries with the enclosing soil matrix, and are generally darker in color and more opaque than concretions. No FeMn pore linings (including simple coatings and hypocoatings) were observed in the A horizons of the Laewest ML or MH. Pore linings consist mainly of simple coatings, but also include hypocoatings that impregnate the soil matrix adjacent to the pore wall. FeMn pore linings of interpedal pores and dendritic FeMn masses are abundant to common in the yellowish red soil material characterizing the deeper B’ss horizons. Hard carbonate (calcite) nodules are abundant to common though the morphology and size of the hard carbonate masses vary significantly. Septarian shrinkage cracks with sparry calcite crystal linings are present in carbonate nodules. Rare is evidence for additions of carbonate as layers added to the margins of the nodules (Figure 15C). Although some carbonate nodules are primarily microcrystalline calcite (micrite), many show evidence for recrystallization to microspar, which are bladed to prismatic to equigranular calcite crystals ranging from 5-25 �m in diameter (Figure 15D). Soft powdery masses of micrite are not common in the Laewest soil, and as with the Victoria soil, are more abundant in the MH than the ML. No gypsum crystal masses were observed. Sepic-plasmic (bright clay) matrix microfabrics are abundant (Figure 15E). The most common fabric is masepic, characterized by oriented domains of clay minerals with bright interference colors that have one dominant orientation. Bimasepic and lattisepic fabrics are also locally developed in the Laewest soils, in which there are two preferred directions of clay orientation, thereby imparting a lattice- or trellis-like pattern. Sepic-plasmic fabrics are also developed around the periphery of larger skeletal grains (quartz sand or silt), FeMn concretions or nodules, or hard carbonate nodules (Figure 15E). Microslickensides on ped faces can be recognized by occurrences of a single bright band or layer of parallel-oriented clay minerals (Figure 15F).

41

Figure 15. Photomicrographs of selected horizons from the Laewest pedon: All photomicrographs are taken in cross-polarized light. (A) ML, Bss3 horizon. Fe-Mn nodule that exhibits diffuse boundary and lack of concentric banding. (B) MH, Bkss3 horizon. Fe-Mn concretion that shows faint concentric banding. (C) MH, Bkss2 horizon. Micritic, hard carbonate nodule showing growth band increments (arrow) added to exterior of nodule. (D) ML, Bkss2 horizon. Hard carbonate nodule showing evidence for pervasive recrystallization to microspar and preservation of sparry calcite lining septarian shrinkage cracks. (E) MH, Bkss2 horizon. Stress cutans and sepic-plasmic fabric formed in soil matrix adjacent to edge (arrow) of recrystrallized and Fe-stained hard carbonate nodule. (F) MH, Bkss2 horizon. Sepic plasmic fabric developed in soil matrix and microslickensides (arrow) formed at interpedal boundaries

42

Selected Physical and Chemical Properties

Selected physical and chemical properties for the Laewest ML and MH are summarized in Table 11 and illustrated in Figure 16. Organic carbon content is greater in the ML than MH, likely due to more favorable soil moisture conditions in the ML. Organic carbon ceases to decline in the ML at about 250 cm, and about 175 cm in the MH. In the MH there is a spike in organic carbon at about 205 cm within the Bss horizon. The CaCO3 equivalent curve shows significant decalcification in the upper 150 cm of the ML, with an increase to 14% in the Bkss2 horizon. CaCO3 equivalent is relatively constant in the upper 250 cm of the MH, ranging between 13 and 20%. Total clay in the ML ranges from 49 to 60%, and 51 to 67% in the MH. Fine clay is much more abundant in the ML, ranging from 15 to 41%, while the MH fine clay ranges from 8.9 to 19.7%. Coefficient of linear extensibility (COLE) values are higher in the ML than the MH; both are relatively uniform with depth. The Feo/Fed ratio indicates that much more amorphous iron oxide (short order) occurs in the upper 200 cm of the profile in both the ML and MH, though more occurs in the ML. Base saturation % (BS) is somewhat lower in the upper 118 cm of the ML, increasing to 100% from the Bkss1 through the B’ss3 horizons. BS is 100% throughout the MH. As indicated by pH trends, the ML has undergone more leaching than the MH. Cation Exchange Capacity (CEC) is slightly higher in the upper part of the ML than the MH and gradually decreases with depth, though remains relatively constant throughout the MH. Exchangeable sodium percentage (ESP) is low in the upper profile of both the ML and MH, increasing to 11% in the Bkss1 horizon (188 cm) in the ML, and to the Bkss3 horizon (172 cm) in the MH.

The CEC to clay ratio, used as an indicator of clay mineralogy, reveals montmorillonitic clays (>.7) in the ML to a depth of 176 cm, and 205 cm in the MH. Below these depths, clay mineralogy is montmorillonitic to mixed (0.5 to 0.7).

43

00.

51

050

100

050

100

00.

51

050

100

05

100

5010

00

12

0 50 100

150

200

250

300

01

2

Depth (cm)

050

100

050

100

00.

250.

5 00.

51

05

100

5010

00

5010

00

12

025

500 50 100

150

200

250

300

01

2Depth (cm)

MicrohighO

rgan

ic C

wt%

CaC

O3

Equi

v.W

t %

Cla

y C

onte

ntW

t %C

OLE

FeO

/FeD

% B

SpH

CEC

cmol

ckg-

1ES

P%

Bd

g cm

-3

A

Bss1

Bss2

Bks

s1

Bks

s2

B’s

s1

B’ss

2

B’s

s3

Ak Bk B

kss1

Bks

s2

Bss

Bks

s3

B’ss

3

Microlow

Fine

cla

y

Tota

l cla

y

Bss3

Fine

cla

y

Tota

l cla

y

00.

51

00.

51

0 0 0 0 0 0 0

050

100

CEC

7/C

lay

Fi

gure

16.

Dep

th p

lots

of s

elec

ted

phys

ical

and

che

mic

al p

rope

rtie

s fro

m th

e La

ewes

t mic

rolo

w a

nd m

icro

high

(LA

W 4

69).

44

45

Tab

le 1

2. S

elec

ted

phys

ical

and

che

mic

al p

rope

rtie

s fro

m th

e L

aew

est m

icro

low

and

mic

rohi

gh (L

AW

469

).

Lae

wes

t Ser

ies (

mic

rolo

w)

Dep

th (c

m)

Hor

izon

O

Cw

t%

TC

wt%

T

otal

Cla

yw

t%

Fine

C

lay

wt%

CO

LE

who

le

soil

CaC

O3

equi

v.

wt%

Fed

FeO

FeO

/Fe D

%B

S pH

CE

C7

NH

4 OA

C

cmol

c kg

-1

ESP

Bd

g cm

-3C

EC

7:cl

ay

0-

16

A

1.89

1.

89

50.7

41

.8

0.13

6 -

0.3

0.15

0.

50

93

5.7

46.2

2

1.29

0.

91

16-4

3 B

ss1

1.26

1.

26

49.8

36

.2

0.14

5 -

0.3

0.11

0.

36

96

5.8

46.3

3

1.21

0.

93

43-7

4 B

ss2

1.22

1.

22

53.2

33

.1

0.15

6 -

0.2

0.09

0.

45

96

6.2

49.3

6

1.28

0.

93

74-1

18

Bss

3 1.

15

1.15

56

.3

32.0

0.

162

- 0.

2 0.

08

0.40

10

0 7.

0 50

.8

8 1.

29

0.90

11

8-15

4 B

kss1

0.

50

0.98

55

.1

16.3

0.

153

4 0.

2 0.

06

0.30

10

0 7.

8 45

.8

11

1.23

0.

83

154-

176

Bks

s2

0.19

1.

87

60.0

15

.0

0.17

1 14

0.

5 0.

06

0.12

10

0 7.

9 44

.6

13

1.19

0.

74

176-

222

B'ss

1 0.

05

1.97

59

.1

19.4

0.

167

16

0.6

0.06

0.

10

100

7.9

39.3

13

1.

21

0.66

22

2-24

5 B

'ss2

0.00

1.

78

48.8

19

.4

0.15

3 15

0.

4 0.

05

0.13

10

0 7.

9 31

.7

12

1.42

0.

65

245-

265

B'ss

3 0.

34

1.90

53

.6

18.7

0.

133

13

0.5

0.05

0.

10

100

7.9

36.4

13

1.

43

0.68

Lae

wes

t Ser

ies (

mic

rohi

gh)

0-11

A

k 1.

39

2.95

51

.6

11.8

0.

138

13

0.3

0.08

0.

27

100

7.7

44.8

1

1.34

0.

87

11-2

8 B

k 0.

34

2.26

52

.2

10.2

0.

130

16

0.3

0.09

0.

30

100

7.8

45.2

1

1.25

0.

87

28-1

19

Bks

s1

0.59

2.

39

52.4

10

.2

0.13

8 15

0.

3 0.

09

0.30

10

0 7.

8 44

.9

2 1.

34

0.86

11

9-17

2 B

kss2

0.

00

1.68

54

.3

8.90

0.

152

14

0.3

0.08

0.

27

100

7.9

45.5

5

1.30

0.

84

172-

198

Bks

s3

0.08

1.

88

58.6

12

.3

0.17

3 15

0.

4 0.

08

0.20

10

0 8.

0 45

.2

11

1.24

0.

77

198-

205

Bss

0.

23

2.27

67

.9

19.1

0.

227

17

0.7

0.08

0.

11

100

7.9

47.2

14

1.

16

0.70

20

5-26

5 B

'ss3

0.00

2.

37

67.3

19

.7

0.18

4 20

0.

6 0.

08

0.13

10

0 8.

0 45

.4

13

1.21

0.

67

OC

% =

Org

anic

Car

bon

TC

= T

otal

Car

bon

CO

LE =

Coe

ffic

ient

of l

inea

r ext

ensi

bilit

y Fe

d = d

ithio

nite

ext

ract

able

Fe

Feo =

oxa

late

ext

ract

able

Fe

BS

= ba

se sa

tura

tion

CEC

= c

atio

n ex

chan

ge c

apac

ity

ESP

= ex

chan

geab

le so

dium

per

cent

age

Bd

= bu

lk d

ensi

ty

See

labo

rato

ry p

roce

dure

in S

oil S

urve

y S

taff,

199

6

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46

STOP 3: LAKE CHARLES SERIES (LAC 481) October 4, 2008

Wharton County, Texas

In Wharton County, Lake Charles soils comprise approximately 80% of the Lake Charles Association and consist of very deep, somewhat poorly drained, very slowly permeable, level to gently sloping, and black to dark gray clayey soils on a featureless plain (uplands) where slopes are mostly less than 1%, but can range to 3% (Figure 17, Figure 18, Figure 19). Lake Charles soils are slightly acidic to mildly alkaline in the surface layer of black clay, underlain by mildly alkaline clay (McEwen and Crout 1974). Within Wharton County County this series covers approximately 158,000 acres (23%). This soil is within the NRCS Land Capability Classes IIe-1 and IIw-2, meaning that they generally have high available water capacity, are usually moist and located adjacent to major drainages. Gilgai microhighs and microlows characterize the landscape. Mean annual temperature in the study area is 21.3 °C and mean annual precipitation is 1070 mm per year. Soil moisture regime at this location is udic. Taxonomically, the Lake Charles soil is classified as a fine, smectitic, hyperthermic Typic Hapluderts. Lake Charles soils are well suited to row crops such as corn, cotton, rice, and grain sorghum. Native grasses include little bluestem, indiangrass, eastern gamagrass, switchgrass, big bluestem, and brownseed paspalum. Most areas have scattered live oak, water oak, elm, hackberry, and huisache trees. Pine trees have encroached in some areas. (McEwen and Crout 1974).

Field Morphological Description

Field morphological data is provided below for the Lake Charles ML (Pedon ID: 99TX481001) and MH (Pedon ID: 99TX481001A) (Table 13, Table 14, Table 15, Table 16). The ML has an A-Bss-Bssk-2Bssk profile to a depth of 250 cm and the MH an Ak-Bkss-2Bkss profile down to a depth of 300 cm. The width between the ML and MH in the excavated pit was about 2 m, with surface gilgai relief of less than 10 cm. The MH has fewer wedge-shaped aggregates than the ML. The ML contains an abrupt smooth boundary to coarse structural aggregates with extremely firm consistence at a depth of 176 cm. This boundary is more diffuse in the MH possibly because of a less well defined weathering front. Black colors persist to a depth of 83 cm in the A and upper Bss horizons of the ML, followed by progressively lighter colors through the lower Bss horizons. A transition to reddish brown colors then occurs in the Bkss horizons beginning at 176 cm. In contrast, the darkest colors in the MH are very dark gray, which turn reddish yellow at nearly the same depth as the ML at 181 cm. These color distributions indicate more favorable plant-soil moisture relations in the ML. The greatest abundance of iron manganese concentrations occur in the uppermost horizons of the ML and in the lower solum of the MH. This observation could result from our inability to detect and properly describe the abundance of iron manganese segregations in the field. However, iron manganese concentrations in the upper part of the ML may also reflect a more poorly drained environment with those in the MH being relict or from physical translocation from the ML by lateral thrusting. Iron depletions along macrovoids at depths in both the ML and MH indicate that by-pass flow is an important pedogenic process, particularly along slickenside surfaces and root channels that are relatively stable. Slickenside development is similar between the ML and MH with the first appearance beginning by a 15-to 28-cm depth and the greatest abundance within a 78- to 83- cm depth. Slickenside angle and abundance begin to decrease below a depth of 175-180 cm, thus defining the zone of maximum shrink-swell activity. However, slickenside angle and thickness of the zone containing the most slickensides, is greater in the ML, perhaps because the ML experiences greater extremes in wet/dry cycles.

47

Figure 17. NRCS soil mapping units and location of Lake Charles Pedon (LAC 481) on Hungerford USGS topographic map. LcA=Lake Charles clay, 0-1% slopes.

48

Figure 18. Wharton County General Soil Map and landscape position of Lake Charles soils. Adapted from Wharton County Soil Survey (McEwen and Crout 1974).

49

Hard carbonate nodules occur throughout both profiles, but are more prevalent in the upper part of the MH. The MH appears to have received additional carbonate from lateral thrusting from the ML as indicated by 20-30% nodules occurring between a depth of 15 and 78 cm. Excluding thrust zones, the zone of maximum accumulation in both the MH and ML occurs at the contact where shrink-swell activity diminishes, or in a range of 157-165 cm. Iron stains are common on carbonate nodules in the ML probably reflecting ferrous iron mobilization and reprecipitation as ferric oxyhydroxides in the more poorly drained subennvironment. Given a better drained environment in the MH, the presence of iron stains on carbonate nodules between a depth of 33 and 78 cm may indicate physical thrusting of materials from the ML where the iron stained carbonate formed. The depth to a strong matrix reaction with HCl was encountered abruptly at 165 cm in the ML, but only at 33 cm in the MH. Above these depths carbonate nodules are floating in a noncalcareous matrix. Crayfish krotovina are common in the ML with crack infills and lateral intrusions more common in the MH. In the MH, crack infills occur to a depth of 104 cm with lateral intrusions occurring throughout the profile. This suggests that both processes of cracking/infilling and lateral thrusting contributed to formation of the upper 1 m of soil in the MH. Crayfish krotovina in the ML attest to greater moisture content throughout the year.

Figure 19. Panoramic view of Lake Charles (LAC 481) ML and MH.

50

Table 13. Field morphological description of the Lake Charles microlow (Pedon ID: 99TX481001), Wharton County, Texas. Data source: National Soil Information System, USDA-NRCS. A1--0 to 12 centimeters; black (2.5Y 2/1) clay; moderate fine and medium subangular blocky structure; firm, hard when dry, very sticky, very plastic; common fine roots; common fine tubular pores; less than 1 percent very fine and fine rounded nodules of iron-manganese; less than 1 percent fine rounded nodules of calcium carbonate coated with brownish yellow (10YR 6/8); clear smooth boundary. A2--12 to 28 centimeters; black (2.5Y 2/1) clay; moderate fine and medium subangular blocky structure; firm, hard when dry, very sticky, very plastic; common fine roots; common fine tubular pores; 1 percent distinct pressure faces; clear smooth boundary. Bss1--28 to 59 centimeters; black (2.5Y 2/1) clay; moderate medium and coarse subangular blocky structure; firm, very hard; common fine roots; many fine tubular pores; common distinct intersecting slickensides that are tilted 60 to 70 degrees to the horizontal; few fine rounded nodules of calcium carbonate coated with brownish yellow (10YR 6/8) iron; clear smooth boundary. Bss2--59 to 83 centimeters; black (2.5Y 2/1) clay; moderate medium and coarse subangular blocky structure; very firm, very hard; common fine roots; common fine and medium tubular pores; common distinct intersecting slickensides that are tilted 60 to 70 degrees to the horizontal; less than 1 percent fine rounded nodules of calcium coated with brownish yellow (10YR 6/8) iron; less than 1 percent very fine and fine rounded nodules of iron-manganese; gradual wavy boundary. Bss3--83 to 123 centimeters; very dark gray (2.5Y 3/1) clay; moderate medium wedge parting to moderate fine and medium angular blocky structure; very firm, very hard; common fine and medium tubular pores; common fine roots along surfaces of slickensides; many prominent intersecting slickensides that are tilted 50 to 60 degrees to the horizontal; gradual wavy boundary. Bss4--123 to 147 centimeters; dark gray (2.5Y 4/1) clay; moderate medium wedge parting to moderate fine and medium angular blocky structure; very firm, very hard; very slight effervescence; common fine roots along surfaces of slickensides; many prominent intersecting slickensides that are tilted 40 to 50 degrees to the horizontal; few crawfish krotovinas 3 to 4 cm in diameter filled with a mixture of grayish brown (2.5YR 5/2), dark gray (2.5Y 4/1), and yellowish red (5YR 5/6) clay; less than 1 percent fine faint light olive brown (2.5Y 5/3) iron concentrations with diffuse boundaries along surfaces of slickensides; clear smooth boundary. Bkss1--147 to 165 centimeters; dark gray (2.5Y 4/1) clay; moderate medium and coarse wedge parting to moderate fine and medium angular blocky structure; very firm, very hard; very slight effervescence; common fine roots on surfaces of slickensides; many prominent intersecting slickensides that are tilted 30 to 40 degrees to the horizontal; few crawfish krotovinas 3 to 4 cm wide and filled with a mixture of grayish brown (2.5Y 5/2), dark gray (2.5Y 4/1), and yellowish red (5YR 5/6) clay; few fine rounded uncoated nodules of calcium carbonate; clear smooth boundary. Bkss2--165 to 176 centimeters; grayish brown (2.5Y 5/2) clay; weak medium and coarse wedge parting to moderate medium and coarse angular blocky structure; very firm, very hard, very sticky, very plastic; strong effervescence; common very fine and fine roots along surfaces of slickensides; common distinct intersecting slickensides that are tilted 30 to 40 degrees to the horizontal; few crawfish krotovinas 3 to 4 cm in diameter and filled with a mixture of grayish brown (2.5Y 5/2), dark gray (2.5Y 4/1), and yellowish red (5YR 5/6) clay; 5 percent fine and medium rounded nodules of calcium carbonate and 1 percent of the nodules are coated with brownish yellow (10YR 6/8) iron; abrupt smooth boundary. Bkss3--176 to 200 centimeters; reddish brown (5YR 5/4); weak medium and coarse subangular blocky structure; extremely firm, extremely hard, slightly sticky, slightly plastic; very few very fine and fine roots; strong effervescence; few crawfish krotovinas 3 to 4 cm in diameter and filled with a mixture of grayish brown (2.5Y 5/2), dark gray (2.5Y 4/1), yellowish red (5YR 5/6) clay, and few fine rounded masses and nodules of calcium carbonate; common distinct intersecting slickensides that are tilted 15 to 25 degrees to the horizontal; 7 percent fine and medium grayish green (5G 5/2) iron depletions with sharp boundaries on surfaces of slickensides; 1 percent fine and medium rounded nodules of calcium carbonate in matrix; gradual wavy boundary. Bkss4--200 to 250 centimeters; yellowish red (5YR 5/6) clay; moderate medium and coarse wedge parting to moderate medium and coarse subangular blocky structure; extremely firm, extremely hard, slightly sticky, slightly plastic; very few very fine roots; strong effervescence; common prominent intersecting slickensides that are tilted 10 to 20 degrees to the horizontal; 5 percent fine and medium grayish green (5G 5/2) and 2 percent fine gray (2.5Y 5/1) iron depletions with sharp boundaries on surfaces of slickensides; 1 percent fine and medium rounded nodules of calcium carbonate.

51

52

Table 14. Field morphological description of the Lake Charles microhigh (Pedon ID: 99TX481001A), Wharton County, Texas. Data source: National Soil Information System, USDA-NRCS. Ak1--0 to 15 centimeters; very dark gray (10YR 3/1) clay; weak medium subangular blocky parting to moderate fine and medium granular structure; friable; many fine roots; common fine and medium interstitial pores; few fine masses of grayish brown (2.5Y 5/2) clay throughout; 3 percent subrounded nodules of calcium carbonates 2 to 4 mm in size; matrix is noncalcareous; clear smooth boundary. Ak2--15 to 33 centimeters; very dark gray (2.5Y 3/1) clay; moderate fine and medium angular blocky structure; friable; common fine roots; few fine interstitial and tubular pores; 30 percent distinct pressure faces; slight effervescence; few fine distinct intersecting slickensides; 20 percent light yellowish brown (2.5Y 6/3) masses and nodules of calcium carbonate along surfaces of slickensides; clear smooth boundary. Bkss1--33 to 78 centimeters; dark gray (2.5Y 4/1) clay; strong fine and medium angular blocky structure; friable; common fine roots; few fine tubular pores; strong effervescence; common distinct intersecting slickensides that are tilted 40 to 50 degrees to the horizontal; 30 percent fine and medium rounded nodules of calcium carbonate and 1 percent nodules of calcium carbonate and 1 percent nodules of calcium carbonate coated with brownish yellow (10YR 6/8) iron; abrupt wavy boundary. Bkss2--78 to 104 centimeters; weak red (7.5R 4/4) clay; moderate fine and medium angular blocky structure; firm; common fine roots; few very fine tubular pores; strong effervescence; many distinct intersecting slickensides that are tilted 30 to 45 degrees to the horizontal; 5 percent of matrix are cracks filled with very dark gray (2.5Y 3/1) clay 1cm to 3cm wide; 5 percent subrounded nodules of calcium carbonate 2 to 4 mm in size; 10 percent masses of olive brown (2.5Y 4/3) clay 1 to 3 cm in size mixed within the weak red (7.5YR 4/4) matrix material; 5 percent of the horizon is a reddish yellow (7.5YR 6/6) strongly effervescent clay intrusion 4 to 8 cm wide that arcs from the upper part of the Bkss3 horizon and extends to the lower part of the Bkss1 horizon; abrupt wavy boundary. Bkss3--104 to 157 centimeters; dark grayish brown (2.5Y 4/2) clay; strong medium and coarse angular blocky structure; firm; common fine roots; few very fine tubular pores; strong effervescence; common distinct intersecting slickensides that are tilted 30 to 50 degrees to the horizontal; 5 percent fine and medium subrounded nodules of calcium carbonate; 5 percent of the horizon is a strong brown (7.5YR 5/6) strongly effervescent clay intrusion 4 to 8 cm wide that arcs from the upper part of the Bkss4 horizon and extends to the lower part of the Bkss2 horizon; abrupt wavy boundary. Bkss4--157 to 181 centimeters; light olive brown (2.5Y 5/4) clay; strong medium and coarse angular blocky structure; firm; common fine roots; few very fine pores; strong effervescence; common distinct coarsely grooved intersecting slickensides tilted 30 to 60 degrees to the horizontal; 10 percent fine and medium nodules of calcium carbonate concentrated near contact with Bss1 horizon; 10 percent of the horizon is a strong brown (7.5YR 4/6) strongly effervescent clay intrusion 4 to 10 cm wide that arcs from the Bss1 horizon and extends to the lower part of the Bkss3 horizon; 4 percent fine rounded black (10YR 2/1) iron-manganese nodules and masses; clear wavy boundary. Bss1--181 to 260 centimeters; yellowish red (5YR 5/6) clay; strong medium, and very coarse angular blocky structure; firm; common fine roots; strong effervescence; common distinct intersecting slickensides that are tilted 20 to 60 degrees to the horizontal; 2 percent fine and medium prominent light brownish gray (2.5Y 6/2) iron depletions on surfaces of slickensides; 10 percent fine rounded black (10YR 2/1) iron-manganese nodules and masses; 2 percent fine nodules of calcium carbonate; 10 percent of the horizon is reddish yellow (7.5YR 7/6) clay mixed with the yellowish red (5YR 5/6) matrix material; abrupt wavy boundary. Bss2--260 to 300 centimeters; yellowish red (5YR 5/6) clay; strong very coarse angular blocky structure; very firm; very few very fine roots; strong effervescence; common prominent intersecting slickensides that are tilted 20 to 40 degrees to the horizontal; 8 percent fine and medium light brownish gray(2.5Y 6/2) iron depletions on surfaces of slickensides; 1 percent fine masses of black (10YR 2/1) dendritic masses of iron-manganese on surfaces of slickensides; less than 1 percent fine nodules of calcium carbonate.

Tab

le 1

5. S

elec

ted

soil

mor

phol

ogic

al fe

atur

es fr

om th

e L

ake

Cha

rles

mic

rolo

w (P

edon

ID: 9

9TX

4810

01).

sbk

= su

bang

ular

blo

cky;

abk

= a

ngul

ar b

lock

y; m

ed. =

med

ium

H

oriz

on

Dep

th(c

m)

Bou

ndar

ySt

ruct

ure

Con

sist

ence

C

olor

Red

ox fe

atur

es

Slic

kens

ides

C

arbo

nate

se

greg

atio

ns

Rea

ctio

n O

ther

Pro

pert

ies

FeM

n co

ncen

trat

ion

Fe d

eple

tions

A1

0-12

cl

ear

smoo

th

mod

erat

e fin

e sb

k fir

m

2.5Y

2/1

1%

fine

, har

d -

- 1%

fine

, ha

rd

none

m

any

fine

root

s; 1

0YR

6/8

Fe

stai

ns o

n ca

rbon

ate

nodu

les

A

2 12

-28

clea

r sm

ooth

m

oder

ate

med

. sbk

fir

m

2.5Y

2/1

-

- -

- no

ne

com

mon

fine

root

s

Bss

1 28

-59

clea

r sm

ooth

m

oder

ate

med

. sbk

ve

ry fi

rm

2.5Y

2/1

-

- co

mm

on

dist

inct

(60-

70°)

<1%

fine

, ha

rd

none

co

mm

on fi

ne ro

ots;

10Y

R 6

/8

Fe st

ains

on

carb

onat

e no

dule

s

Bss

2 59

-83

grad

ual

smoo

th

mod

erat

e m

ed. s

bk

very

firm

2.

5Y 2

/1

<1%

, fin

e,

hard

, on

slic

kens

ides

-

com

mon

di

stin

ct (6

0-70

°)

<1%

fine

, ha

rd

none

co

mm

on fi

ne ro

ots;

10Y

R 6

/8

Fe st

ains

on

carb

onat

e no

dule

s

Bss

3 83

-123

gr

adua

l w

avy

mod

erat

e m

ed.

wed

ge

very

firm

2.

5Y 3

/1

- -

man

y pr

omin

ent

(50-

60°)

-

none

co

mm

on fi

ne ro

ots o

n sl

icks

Bss

4 12

3-14

7 cl

ear

smoo

th

mod

erat

e m

ed.

wed

ge

very

firm

2.

5Y 4

/1

- -

man

y pr

omin

ent

(40-

50°)

-

none

co

mm

on fi

ne ro

ots o

n sl

icke

nsid

es.;

few

med

. kr

otov

ina

(2.5

Y 4

/1, 5

YR

5/6

) B

kss1

14

7-16

5 cl

ear

smoo

th

mod

erat

e m

ed.

wed

ge

very

firm

2.

5Y 4

/1

- -

man

y pr

omin

ent

(30-

40°)

1% fi

ne,

hard

no

ne

com

mon

fine

root

s on

slic

kens

ides

; few

med

. kro

tovi

na

(2.5

Y 4

/1, 5

YR

5/6

) 2B

kss2

16

5-17

6 ab

rupt

sm

ooth

m

oder

ate

med

. w

edge

very

firm

2.

5Y 5

/2

- -

com

mon

di

stin

ct (3

0-40

°)

5% m

ed.,

hard

st

rong

co

mm

on fi

ne ro

ots o

n sl

icke

nsid

es; f

ew m

ed. k

roto

vina

(2

.5Y

4/1

, 5Y

R 5

/6);

few

(10Y

R

6/8)

Fe

stai

ns o

n ca

rbon

ate

nodu

les

2Bks

s3

176-

200

grad

ual

smoo

th

wea

k co

arse

sbk

extre

mel

y fir

m

5YR

5/4

-

com

mon

fine

5G

5/2

on

slic

kens

ides

com

mon

di

stin

ct (1

5-25

°)

3% m

ed.,

soft/

hard

st

rong

co

mm

on fi

ne ro

ots o

n sl

icke

nsid

es; f

ew m

ed. k

roto

vina

(2

.5Y

4/1

, 5Y

R 5

/6)

2Bks

s4

200-

250

- m

oder

ate

coar

se sb

k ex

trem

ely

firm

5Y

R 5

/6

- co

mm

on fi

ne

5G 5

/2 o

n sl

icke

nsid

es

com

mon

pr

omin

ent

(10-

20°)

1%, m

ed.,

soft/

hard

st

rong

fe

w fi

ne ro

ots

53

54

Tab

le 1

6. S

elec

ted

soil

mor

phol

ogic

al fe

atur

es fr

om th

e L

ake

Cha

rles

mic

rohi

gh (P

edon

ID: 9

9TX

4810

01A

). sb

k =

suba

ngul

ar b

lock

y; a

bk =

ang

ular

blo

cky;

med

. = m

ediu

m

Hor

izon

D

epth

(cm

) B

ound

ary

Stru

ctur

e C

onsi

sten

ce

Col

orR

edox

feat

ures

Sl

icke

nsid

es

Car

bona

te

segr

egat

ions

R

eact

ion

Oth

er P

rope

rtie

s Fe

Mn

conc

entr

atio

n Fe

dep

letio

ns

Ak1

0-

15

clea

r sm

ooth

w

eak

med

. sbk

fr

iabl

e 2.

5Y 3

/1

- -

- 3%

, fin

e,

hard

no

ne

man

y fin

e ro

ots;

few

2.

5Y 5

/2 in

trusi

ons

Ak2

15

-33

clea

r sm

ooth

m

oder

ate

med

. abk

fr

iabl

e 2.

5Y 3

/1

- -

few

dis

tinct

20

%

fine/

med

., ha

rd

slig

ht

com

mon

fine

root

s

Bks

s1

33-7

8 ab

rupt

w

avy

mod

erat

e m

ed. a

bk

firm

2.

5Y 4

/1

- -

com

mon

dis

tinct

(4

0-50

°)

30%

, fin

e/m

ed.

hard

stro

ng

com

mon

fine

root

s;

10Y

R 6

/8 F

e st

ains

on

carb

onat

e no

dule

s (in

trusi

ons)

B

kss2

78

-104

ab

rupt

w

avy

mod

erat

e m

ed. a

bk

firm

7.

5Y 4

/4

- -

man

y di

stin

ct

(40-

50°)

5%

, fin

e,

hard

st

rong

co

mm

on fi

ne ro

ots;

5%

2.

5Y 3

/1 c

rack

infil

ls

(1-3

cm

wid

e); 1

5%

intru

sion

s, 4-

8 cm

wid

e (2

.5Y

4/3

, 7.5

YR

4/6

) B

kss3

10

4-15

7 ab

rupt

w

avy

stro

ng

med

. abk

fir

m

2.5Y

4/2

-

- co

mm

on d

istin

ct

(40-

50°)

5%

fin

e/m

ed.,

hard

stro

ng

com

mon

fine

root

s; 5

%

intru

sion

s, 4-

8 cm

wid

e (7

.5Y

R 4

/6)

Bks

s4

157-

181

clea

r w

avy

stro

ng

med

. abk

fir

m

2.5Y

5/4

4%

, fin

e,

hard

com

mon

dis

tinct

(4

0-60

°)

10%

fin

e/m

ed.

hard

stro

ng

com

mon

fine

root

s;

10%

intru

sion

s, 4-

10 c

m

wid

e (7

.5Y

R 4

/6)

2Bks

s5

181-

260

abru

pt

wav

y st

rong

co

arse

ab

k

firm

5Y

R 5

/6

10%

, fin

e,

hard

/sof

t fe

w fi

ne

(2.5

Y 6

/2)

on

slic

kens

ides

com

mon

dis

tinct

(3

0-60

°)

2%, f

ine,

ha

rd

stro

ng

com

mon

fine

root

s;

10%

intru

sion

s, 4-

8 cm

w

ide

(7.5

YR

7/6

), 5Y

R

5/6)

2B

kss6

26

0-30

0

-

mod

erat

e co

arse

ab

k

very

firm

5Y

R 5

/6

1%, f

ine,

ha

rd/s

oft

soft;

de

ndrit

es o

n sl

icke

nsid

es

com

mon

fine

(2

.5Y

6/2

) on

sl

icke

nsid

es

com

mon

pr

omin

ent (

20-

40°)

1%, m

ed.,

hard

st

rong

fe

w fi

ne ro

ots

2C

400-

435

- -

- -

- -

- -

- -

Soil Micromorphological Description The ML and MH of the Lake Charles soil have a porphyoskelic related distribution throughout. They also exhibit a dominance of sepic fabric in the upper part, reflecting shear stress that gradually shifts to asepic fabric below 160 cm. More specifically, the fabric in the upper profile of both the ML and MH is vo-ma-in sepic (Figure 20A-C) with randomly distributed coarse fragments illustrating skelsepic fabric (Figure 20A, D, F). Asepic material is dominant at depth because of an abundance of micaceous silt and coarse clay (Figure 20E, G, H). Consistent with previous interpretations, the MH, although still dominated by sepic fabric in the upper part, reveals irregularities with depth from asepic material being thrust laterally and upward from the ML (Figure 20C). Sepic fabric is supported in the field by slickensides and wedge-shaped aggregates, and in the laboratory by high COLE and a dominance of smectite. Voids in both the ML and MH are dominated by vughs and planes, the latter being more abundant in the upper shrink-swell zone. Except for the Bss4 horizon where planar voids are most dominant micromorphically, the ML was a relatively uniform depth distribution of voids. The void abundance in the MH is similar to the ML and decreases sharply below a depth of 150 cm, as planar voids (Figure 20B,C) decrease in abundance in the asepic zone (Figure 20E,G, H). Crack infills are also more common in the upper sepic zone and contain numerous quartz grains in a less dense matrix (Figure 20B). Carbonate segregations observed micromorphologically reveal a depth trend similar to that observed in the field and with CaCO3 equivalence. The maximum expression of hard carbonate nodules in the ML is at 147-165 cm, and excluding thrust zones, the zone of maximum carbonate accumulation in the MH is more diffuse and occurs between 104 and 181 cm. The zones of maximum m carbonate accumulation terminate at the sepci/asepic boundary in both the ML and MH. The hard nodules are typically micritic with abrupt boundaries, iron stains, occluded quartz, and skelsepic fabric indication g that formation occurred in the upper sepic zone and that nodule growth has since terminated (Figure 20A, D). Many hard carbonate nodules in the sepic zone are multi-aggregated with internal septarian voids (Figure 20D). This suggests that the hard carbonate nodules have experienced numerous growth cycles within the shrink-swell zone above the sepic/asepic contact. Soft carbonate masses reach a maximum slightly below the depth of hard carbonate nodule accumulation in the asepic zone of both the ML and MH. However, in the MH the carbonate nodule and soft mass distribution is much more irregular, consistent with field observations and characterization data. Soft carbonate segregations have gradual boundaries, typically do not occlude quartz, do not have iron stains, lack skelsepic fabric, and occur in micaceous-rich material (Figure 20E, H). These features suggest that the soft carbonate masses formed at depth in the asepic zone where they are still forming. This higher abundance of soft masses in the upper profile of the MH coincides with asepic material being thrust upward from the ML, transporting the soft masses along the way. FeMn concretions in the ML show similar depth trends regardless if they have abrupt concretionary boundaries or diffuse soft mass boundaries. However, hard FeMn concretions with abrupt boundaries show a slight peak abundance in the ML and MH at the same depth as the hard carbonate nodule zone at the sepic/asepic contact. In the sepic zone, some hard concretions have concentric rings that may have formed seasonally. They also occlude quartz and generate skelsepic fabric and abrupt boundaries (Figure 20A, F). The soft iron masses have diffuse and irregular boundaries that reflect contemporaneous features from redox cycles consistent with high Feo/Fed ratios. As with hard carbonate nodules the hard FeMn concretions with abrupt boundaries and skelsepic fabric are apparently no longer growing. Ferrans are difficult to see micromorphologically in the upper profiles probably because of unstable ped surfaces from shrink-swell activity and perhaps because of dark pigmentating from

55

organic matter. However, the abundance, when observable, is somewhat greater in the ML, probably attesting to more poorly drained conditions. In both the ML and MH there is an abrupt increase in ferrans along water conducting voids, such as root channels and slickenside surfaces, in the asepic zone below a depth of 150 cm. Ped surfaces in this lower zone are more stable than in the sepic zone, and labile organic substances are sufficient for microbial consumption and anaerobiosis to occur. This is consistent with the presence of iron depletion zones in the same horizons described in the field. Argillans are visible in the lowermost asepic zone of both the ML and MH (Figure 20H), but not in the upper sepic zone where shrink-swell activity is greatest. This indicates that clay translocation has indeed occurred in this soil, but is only preserved at depth in the asepic zone where void surfaces are more stable. Point counts indicate the argillan abundances are less than 1%.

Figure 20. Photomicrographs of selected horizons from the Lake Charles (LAC 481) pedon: All photomicrographs are taken in cross-polarized light. (A) MH, Bkss3, 104-157 cm; (B) ML, Bss2, 59-85 cm; (C) ML, Bkss1, 147-155 cm; (D) ML,Bss4, 123-147 cm; (E) ML, Bkss3, 176-200 cm; (F) ML, Bss1, 28-59 cm; (G) ML, Bkss4, 200-250 cm; (H) Bkss4, 200-250 cm. All thin sections represent vertically oriented slabs. Q = quartz;, SE = sepic; AS = asepic; MS = masepic; SK = skelsepic; FM = iron manganese concretion; K= carbonate nodule; CI = crack infill; V= void; PV = planar void; A = argillan; F = ferran.

Selected Physical and Chemical Properties

Selected physical and chemical properties for the Laewest ML and MH are illustrated in Figure 21 and summarized in Table 17. Clay content is slightly over 60% and uniform with depth in both the ML and MH of the Lake Charles soil. Overall, fine clay is slightly more abundant in the upper profiles and coarse clay in the middle to lower profiles. However, sand content abruptly decrease and silt content increase at a depth of 165 cm in the ML, with a similar but more diffuse depth trend in the MH. These trends point to the presence of a lithologic discontinuity. COLE values in the ML are relatively high throughout and uniformly decrease with depth. A similar trend is observed in the MH except that the depth distribution is not as uniform, reflecting lateral thrust zones emanating from deep in the profile of the ML. Organic carbon content is greater in the ML than MH, undoubtedly because of more favorable soil moisture conditions in

56

57

the ML. The depth at which organic carbon ceases to decline is at 175 cm in the ML and at only 75 cm in the MH. The microtopography thus has profound effects on differences in carbon storage and distributions between the ML and MH. As indicated by carbonate content and pH trends, the ML has experienced more leaching and to a greater depth than the MH. Relatively low matrix pH in the upper part of the MH attests to physical thrusting of carbonate nodules into this zone after carbonate leaching. The CaCO3 equivalent curve in the ML shows nearly compete decalcification in the upper profile, and then an increase at depth coinciding with the maximum abundance of carbonate nodules as observed in the field. However, below the carbonate maxima, the CaCO3 equivalent decrease very little, whereas the nodule content diminishes sharply. This indicates that most of the detrital parent material carbonate from the upper profile was reorganized into pedogenic nodules and not translocated to greater depth in a disseminated form. Some calcium and bicarbonate ions from detrital carbonate dissolution may have wicked up from the ML to MH from evaporative pumping, forming soft carbonate masses in the Ak and Bkss horizons. Both the CaCO3 equivalent and nodule content show erratic depth functions in the MH, again refelcting physical thrusiting into the MH and confounded with possible in situ pedogenic carbonate translocations. However, below a 1-m depth where the thrust zones terminate in the MH, the carbonate bulge occurs at abound the same depth in both profiles suggesting that the carbonate zone formed prior to the formation intense shrink-swell processes. The Feo/Fed ratio indicates that much more amorphous iron oxide (short order) occurs in the upper profile that in the lower profile in both the ML and MH, and that more occurs in the ML to greater depths. This is consistent with excessive water recharge into the ML during rainfall events, inducing short-term anaerobic conditions. It is likely that at least some of the Feo in the MH formed from lateral capillary flow emanating from the ML. The more stable form of pedogenic iron, Fed (crystalline), persists at depth below the textural break where shrink-swell activity is less.

050

100

050

100

00.

51

00.

51

050

100

00.

510

0.2

0.4

05

100

5010

00

5010

00

12

0 50 100

150

200

250

300

350

02

4

Depth (cm)

050

100

050

100

00.

250.

500.

20.

46

78

90

5010

00

5010

00

12

025

500 50 100

150

200

250

300

02

4Depth (cm)

MicrohighO

rgan

ic C

wt%

CaC

O3

Equi

v.W

t %

Cla

y C

onte

ntW

t %C

OLE

FeO

/FeD

% B

SpH

CEC

cmol

ckg-

1ES

P%

Bd

g cm

-3

A1

Bss

1

Bss

2

Bkss

1Bk

ss2

Bks

s3

Ak1

Bkss

1

Bkss

2

Bks

s3

Bss

1

Microlow

Fine

cla

y

Tota

l cla

y

Bss

3

Fine

cla

y

Tota

l cla

y

A2

Bss4

Bkss

4

Ak2

Bks

s4

Bss

2

CEC

7/C

lay

Figu

re 2

1. D

epth

plo

ts o

f sel

ecte

d ph

ysic

al a

nd c

hem

ical

pro

pert

ies f

rom

the

Lake

Cha

rles

mic

rolo

w a

nd m

icro

high

(LA

C 4

81).

58

59

Tab

le 1

7. S

elec

ted

phys

ical

and

che

mic

al p

rope

rtie

s fro

m th

e L

ake

Cha

rles

mic

rolo

w a

nd m

icro

high

(LA

C 4

81).

Lak

e C

harl

es S

erie

s (m

icro

low

)

Dep

th (c

m)

Hor

izon

O

Cw

t%

TC

wt%

T

otal

Cla

yw

t%

Fine

C

lay

wt%

CO

LE

who

le

soil

CaC

O3

equi

v.

wt%

Fed

FeO

FeO

/Fe D

%B

S pH

CE

C7

NH

4 OA

C

cmol

c kg

-1

ESP

Bd

g cm

-3C

EC

7:cl

ay

0-12

A

1 3.

07

3.07

62

.4

43.8

0.

174

-0.

8 0.

30

0.38

10

0 7.

0 55

1

1.13

0.

88

12-2

8 A

2 2.

17

2.17

62

.5

38.7

0.

168

- 0.

9 0.

31

0.34

10

0 6.

9 56

.9

1 1.

13

0.91

28

-59

Bss

1 1.

81

1.81

58

.1

38.5

0.

156

- 0.

7 0.

23

0.36

10

0 7.

0 54

.4

2 1.

27

0.94

59

-83

Bss

2 1.

73

1.73

60

.5

39.6

0.

153

- 0.

7 0.

18

0.26

10

0 7.

1 56

.4

3 1.

28

0.93

83

-123

B

ss3

1.31

1.

31

62.2

31

.2

0.15

2 -

0.6

0.17

0.

28

100

7.5

57.8

5

1.29

0.

93

123-

147

Bss

4 0.

54

0.90

64

.3

21.2

0.

150

3 0.

8 0.

15

0.19

10

0 7.

7 53

.4

6 1.

30

0.83

14

7-16

5 B

kss1

0.

30

0.78

63

.0

19.3

0.

134

4 0.

9 0.

16

0.18

10

0 7.

8 49

.9

7 1.

35

0.79

16

5-17

6 B

kss2

0.

03

2.55

61

.3

30.2

0.

118

21

1.1

0.07

0.

06

100

8.0

35.5

7

1.43

0.

58

176-

200

Bks

s3

0.00

2.

29

62.2

30

.1

0.11

0 19

1.

1 0.

08

0.07

10

0 8.

0 33

.1

8 1.

47

0.53

20

0-25

0 B

kss4

0.

07

2.47

61

.5

30.9

0.

096

20

1.2

0.07

0.

06

100

8.0

31.3

9

1.52

0.

51

Lak

e C

harl

es S

erie

s (m

icro

high

) 0-

15

Ak1

2.

34

2.46

65

.5

48.1

0.

109

1 0.

9 0.

28

0.31

10

0 7.

2 56

.7

1 1.

51

0.87

15

-33

Ak2

1.

24

1.24

67

.1

35.1

0.

174

- 0.

9 0.

17

0.19

10

0 7.

3 57

.3

2 1.

18

0.85

33

-78

Bks

s1

0.79

0.

91

65.6

21

.6

0.16

5 1

0.8

0.15

0.

19

100

7.6

55.9

2

1.21

0.

85

78-1

04

Bks

s2

0.00

2.

88

58.5

24

.3

0.16

6 24

0.

9 0.

08

0.09

10

0 8.

0 37

.3

5 1.

09

0.64

10

4-15

7 B

kss3

0.

15

0.87

62

.3

18.9

0.

128

6 1.

0 0.

14

0.14

10

0 8.

0 48

.7

5 1.

38

0.78

15

7-18

1 B

kss4

0.

10

1.54

61

.2

20.7

0.

161

12

0.9

0.10

0.

11

100

7.9

45.1

6

1.23

0.

74

181-

260

Bss

1 0.

08

2.72

60

.2

31.4

0.

128

22

1.1

0.05

0.

05

100

8.0

32.5

7

1.40

0.

54

260-

300

Bss

2 0.

00

2.70

55

.8

27.6

0.

096

22

1.2

0.05

0.

04

100

8.0

28.2

8

1.54

0.

51

O

C%

= O

rgan

ic C

arbo

n

TC =

Tot

al C

arbo

n C

OLE

= C

oeff

icie

nt o

f lin

ear e

xten

sibi

lity

Fed =

dith

ioni

te e

xtra

ctab

le F

e Fe

o = o

xala

te e

xtra

ctab

le F

e

BS

= ba

se sa

tura

tion

CEC

= c

atio

n ex

chan

ge c

apac

ity

ESP

= ex

chan

geab

le so

dium

per

cent

age

Bd

= bu

lk d

ensi

ty

See

labo

rato

ry p

roce

dure

in S

oil S

urve

y S

taff,

199

6

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60

STOP 4: LAKE CHARLES SERIES (LAC 201) October 4, 2008

Armand Bayou, Harris County, Texas

In Harris County, Lake Charles soils comprise approximately 31% of the Lake Charles-Bernard association and consist of very deep, moderately well drained, very slowly permeable, level to gently sloping soils on a featureless plain where slopes are mostly less than 1%, but can range to 3% (Wheeler 1976). In undisturbed places, gilgai microhighs and microlows characterize the landscape. Lake Charles soils are in slightly lower positions on the landscape than the Bernard soils (Figure 22, Figure 23, Figure 24). In non-urbanized areas Lake Charles soils cover approximately 89,000 acres (7.9%) within Harris County. Mean annual temperature in the study area is 20.0 °C and mean annual precipitation is 1320 mm per year. Soil moisture regime at this location is udic. Taxonomically, the Lake Charles soil is classified as a fine, smectitic, hyperthermic Aquic Hapludert. Lake Charles soils are used mainly in cultivation and native pasture. Crops are corn, cotton, rice, and grain sorghum. Native grasses include little bluestem, indiangrass, eastern gamagrass, switchgrass, big bluestem, and brownseed paspalum. Most areas have scattered live oak, water oak, elm, hackberry, and huisache trees. Pine trees have encroached in some areas.

Field Morphological Description

Field morphological data is provided below for the Lake Charles ML (Pedon ID: 99TX201001) and MH (Pedon ID: 99TX4201001A) (Table 18, Table 19, Table 20, Table 21). The ML has an A-Bw-Bss-Bkss-B’ss profile to 300 cm and the MH an Ak-Bkssg-Bkss-Bss profile down to a depth of 270 cm. Both the ML and MH are dominated by angular blocky ped structure. There is higher structure variability in the ML, which exhibits weak fine and medium subangular blocky structure in the A horizon, as well as weak to moderate medium to coarse prismatic structure within the Bw through Bss2 horizons. The B’ss1 horizon of the ML also exhibits weak medium and coarse prismatic structure. Finally, the B’ss2 through B’ss4 horizons in the ML exhibit fine and medium platy structure parting to moderate fine angular blocky ped structure. Within the MH, the weak coarse angular blocky structure in the Ak horizon parts to moderate fine and moderate medium to weak coarse angular blocky structure throughout the remainder of the profile. Horizon boundaries within the ML are typically abrupt to gradual and smooth to wavy. Clear wavy horizon boundaries are the most common in the MH. Also present are a clear smooth Ak-Bkssg1 boundary, and an abrupt wavy Bkssg3-Bkssg4 boundary. Consistence is firm in the ML to a depth of 88 cm and transitions into very firm from 88 to 300 cm. In the MH, consistence is firm through the Bss1 horizon to a depth of 235 cm, and very firm in the Bss2 horizon from 235-270 cm. FeMn concretions in the upper 151 cm of the ML (A through Bss4 horizons) range from 1 to 3% fine and medium nodules. Fine prominent to distinct Fe concentrations of 1 to 3% with clear to sharp boundaries along root pore linings occur within the upper 65 cm (A through Bss1 horizons), increasing to 10 and 15% in the Bss2 through Bss4 horizons (88-151 cm). The Bkss1 horizon (151-171 cm) contains 3% fine spherical strong brown FeMn concentrations, with less than 1% fine prominent strong brown Fe concentrations with diffuse boundaries along the surfaces of slickensides and as a halo around FeMn nodules. Within the Bkss2 through B’ss1 horizons (177-242 cm), 1 to 5% fine and medium prominent light yellowish brown Fe concentrations are present. Common fine FeMn nodules are also observed at the top of the B’ss2 horizon (242 cm). Within the MH 1 to 2% fine prominent Fe concentrations with clear boundaries on ped surfaces and root pore linings are present, along with a few rounded black FeMn nodules 2-4 mm in

61

Figure 22. NRCS soil mapping units and location of Lake Charles Pedon (LAC 201) on League City USGS topographic map. LcA=Lake Charles clay, 0-1% slopes.

62

Figure 23. Harris County General Soil Map and landscape position of Lake Charles soils. Adapted from Harris County Soil Survey (Wheeler 1976).

63

diameter within the Bkssg2 horizon. Fe concentrations with diffuse boundaries on slickensides reach their highest abundance in the Bkssg4 and Bkssg4 horizons (67-148 cm), at 15 to 35%, respectively. Also within this zone are rounded, black FeMn nodules from 2 to 8 mm in diameter. In the Bkssg6 through Bss1 horizons (148-235 cm) 3 to 5% spherical black and fine distinct Fe concentrations are present, occurring on slickensides, Fe depletions, and on ped boundaries. Rounded FeMn nodules 1-2 mm occur throughout the Bkss through Bss2 horizons (177-270 cm). Fe depletions in the ML are present beginning at 16 cm depth within the Bw, Bss2, Bss4, and Bkss1 through B’ss4 horizons and are manifested as 1 to 3% faint gray to greenish depletion zones along the boundaries and surfaces of peds, on slickensides, and along root pore linings. In the MH, Fe depletions occur lower in the profile, beginning at 49 cm in the Bkssg3 through Bkssg5 horizons. Within this zone they occur as 5 to 10% dark gray depletions with diffuse to clear boundaries on slickensides. Fe depletions are also present within the Bkss horizon (177-202 cm) and Bss2 horizon (235-270 cm), occurring as 2 to 5% gray and light greenish gray depletions with clear boundaries on throughout and on slickensides. Faint slickensides first occur in the Bw horizon (16-44 cm), increasing to common and distinct in the Bss1 through Bkss1 horizons (44-177 cm). Within this zone, slickensides are tilted at 30-50° from the horizontal. Slickensides are common but faint throughout the Bkss2 through B’ss2 horizons (177-261 cm) and are tilted from 15 to 20° from the horizontal. In the B’ss3 and B’ss4 horizons (261-300 cm), are 10-15% red fractured conchoidal blocks; faint slickenside development occurs through these two horizons in the ML. In the MH, faint slickenside development first appears as 1% faint in the Ak horizon. From the Bkssg1 through the Bss2 horizons (10-270 cm), slickenside development ranges from few to many and from distinct to prominent. Tilt angles range from 15 to 40°. Carbonate nodules in the ML occur within the Bkss1 through B’ss2 horizons (151-261 cm), ranging from few to common fine and medium. The depth to a strong matrix reaction with HCl was encountered abruptly at 242 cm within the B’ss2 through B’ss4 horizons. Carbonate segregations in the MH occur as few fine nodules (2-10 mm) coated with olive yellow Fe, uncoated nodules, and masses of calcareous red clay mixed with nodules. The depth to a strong matrix reaction with HCl was encountered in the MH abruptly within the Bkss through Bsss horizons (177-270 cm). Common very fine and fine roots and common fine and very fine tubular pores occur throughout the entire profile of the ML. Within the MH common fine and very fine roots occur throughout the profile, though fine tubular pores are generally fewer and are not found in the lowermost horizons. In the ML, active krotovinas 1-5 cm wide are within the A horizon, and are infilled in the Bw, and Bss3 through B’ss2 horizons (88-261 cm) with grayish brown and very dark gray material. No krotovinas are recorded in the MH.

Figure 24. Panoramic view of Lake Charles (LAC 201) ML and MH.

64

Table 18. Field morphological description of the Lake Charles microlow (Pedon ID: 99TX201001), Harris County, Texas. Data source: National Soil Information System, USDA-NRCS.

A--0 to 16 centimeters; very dark gray (10YR 3/1) clay; weak fine and medium subangular blocky structure; firm, very sticky, very plastic; many very fine and fine roots; common very fine and fine interstitial pores; 1 percent fine iron-manganese nodules; few fine pores filled with coarse material; few active unfilled krotovinas 1 to 5 cm wide; 3 percent fine distinct brown (7.5YR 4/4) iron concentrations with sharp boundaries along root pores linings; clear smooth boundary. Bw--16 to 44 centimeters; black (2.5Y 2/1) clay; weak medium prismatic parting to moderate medium and coarse angular blocky structure; firm, very sticky, very plastic; common very fine and fine roots; common fine tubular pores; 1 percent faint slickensides (pedogenic) and 1 percent distinct pressure faces; 1 percent fine and medium iron-manganese nodules; 1 percent fine prominent strong brown (7.5YR 5/6) iron concentrations with clear boundaries along root pore linings; 1 percent fine faint gray (2.5YR 5/1) iron depletions with clear boundaries on surfaces of peds; gradual smooth boundary. Bss1--44 to 65 centimeters; dark gray (2.5Y 4/1) clay; moderate medium prismatic parting to moderate medium angular blocky structure; firm, very sticky, very plastic; common very fine and fine roots; common fine tubular pores; 1 percent medium iron-manganese nodules; common distinct intersecting slickensides that tilt 30 to 45 degrees from the horizontal; 3 percent fine prominent yellowish red (5YR 5/6) iron concentrations with sharp boundaries along root pore linings; gradual wavy boundary. Bss2--65 to 88 centimeters; dark gray (2.5Y 4/1) clay; weak coarse prismatic parting to moderate medium angular blocky structure; firm, very sticky, very plastic; common very fine and fine roots; common very fine and fine tubular pores; 1 percent medium iron-manganese nodules; common distinct intersecting slickensides that tilt 35 to 55 degrees from the horizontal; 10 percent fine faint light yellowish brown (2.5Y 6/3) iron concentrations with diffuse boundaries on surfaces of slickensides and peds; 3 percent fine faint gray (2.5Y 5/1) iron depletions with clear boundaries on surfaces of slickensides and peds; gradual wavy boundary. Bss3--88 to 117 centimeters; gray (2.5Y 5/1) clay; moderate medium angular blocky structure; very firm, very sticky, very plastic; common fine roots; very fine and fine tubular pores; 1 percent fine and medium iron-manganese nodules; few crawfish krotovina 1 to 5 cm wide filled with grayish brown (2.5Y 5/2) and very dark gray (2.5Y 3/1) material; few active unfilled krotovinas; common distinct intersecting slickensides that tilt 40 to 55 degrees from the horizontal; 15 percent fine faint light yellowish brown (2.5Y 6/3) and 3 percent fine and medium distinct light yellowish brown (2.5 Y 6/4) iron concentrations with diffuse boundaries on surfaces and interiors of peds; clear wavy boundary. Bss4--117 to 151 centimeters; light brownish gray (2.5Y 6/2) clay; moderate medium angular blocky structure; very firm, very sticky, very plastic; common fine roots; very fine and fine tubular pores; 1 percent fine and medium iron-manganese nodules; few crawfish krotovinas 1 to 5 cm wide filled with grayish brown (2.5Y 5/2) and very dark gray (2.5Y 3/1) material; common distinct intersecting slickensides that tilt 30 to 40 degrees from the horizontal; 15 percent fine and medium faint light yellowish brown (2.5Y 6/4) iron concentrations with diffuse boundaries on surfaces of slickensides and on interiors of peds; 1 percent fine distinct greenish gray (5BF 6/1) iron depletions with diffuse boundaries on surfaces of slickensides and on interiors of peds; few fine and medium iron-manganese nodules; clear wavy boundary. Bkss1--151 to 177 centimeters; light yellowish brown (2.5Y 6/3) clay; weak medium and coarse subangular blocky structure; very firm, very sticky, very plastic; common fine roots; very fine and fine tubular pores; 3 percent fine spherical strong brown (7.5YR 5/6) iron-manganese concretions; few crawfish krotovinas 1 to 5 cm wide filled with yellowish red (5YR 5/6) and very dark gray (2.5YR 3/1) material; common distinct intersecting slickensides that tilt 30 degrees from the horizontal; 5 cm wide arcing yellowish red (5YR 5/6) clay intrusion from the Bkss2 horizon; 3% fine faint gray (2.5Y 5/1) iron depletions with clear boundaries on surfaces of slickensides; less than 1 percent fine prominent strong brown (7.5YR 5/6) iron concentrations with diffuse boundaries along surfaces of slickensides and as a halo around manganese nodules; 1% fine faint greenish gray (5BG 6/1) iron depletions with sharp boundaries along root pore linings; few fine nodules of calcium carbonate; gradual smooth boundary. Bkss2--177 to 212 centimeters; reddish brown (5YR 5/4) clay; weak coarse subangular blocky structure; very firm, very sticky, very plastic; very few very fine and fine roots; very fine and fine tubular pores; few crawfish krotovinas filled with dark gray (10YR 4/1) and reddish brown material; common faint intersecting slickensides that tilt 20 degrees from the horizontal; 7 percent fine prominent gray (2.5Y 6/1) iron depletions with clear boundaries on surfaces of slickensides; 1 percent fine prominent greenish gray (5BG 6/1) iron depletions along root pore linings; 1 percent fine prominent light yellowish brown (10YR 6/4) iron concentrations with diffuse boundaries between peds; common fine nodules of calcium carbonate; gradual wavy boundary. B'ss1--212 to 242 centimeters; red (2.5YR 5/6) clay; weak medium and coarse prismatic structure; very firm, very sticky, very plastic; very few very fine and fine roots; few very fine and fine tubular pores; few crawfish krotovinas 0.5 to 1.5 cm wide filled with dark gray (2.5Y 4/1) and red (2.5YR 4/8) material; common faint intersecting slickensides that tilt 20 degrees from the horizontal; 5 percent fine and medium prominent yellow (2.5Y 7/6) iron concentrations with diffuse boundaries on surfaces of peds; 3 percent fine prominent greenish gray (5BG 6/1) iron depletions with clear boundaries on root pore linings; few fine and medium nodules of calcium carbonate; clear smooth boundary. B'ss2--242 to 261 centimeters; red (2.5YR 5/6) clay; moderate fine and medium platy parting to moderate fine angular blocky structure; very firm, very sticky, very plastic; very fine and fine roots; very fine and fine tubular pores; strong effervescence; few crawfish krotovinas 1 to 2 cm wide filled with gray (2.5Y 6/1), red (2.5YR 5/6) clay and few fine very pale brown (10YR 8/2) nodules of calcium carbonate; common faint intersecting slickensides that tilt 15 to 20 degrees from the horizontal; common fine and medium prominent light greenish gray (10Y 7/1) iron depletions with clear boundaries on root pore linings; common fine nodules of iron-manganese at top of horizon. B'ss3--261 to 279 centimeters; red (2.5YR 4/6) clay; moderate fine and medium platy parting to moderate fine angular blocky structure; very firm, very sticky, very plastic; very few very fine and fine roots; few very fine and fine tubular pores; strong effervescence; 10 percent of horizon are red (2.5YR 4/8) fractured conchoidal blocks; common faint intersecting slickensides that tilt 15 to 20 degrees from the horizontal; 10 percent fine and medium prominent light greenish gray (10Y 7/1) iron depletions with clear boundaries along root pore linings. B'ss4--279 to 300 centimeters; red (2.5YR 5/6) clay; moderate fine and medium platy parting to moderate fine angular blocky structure; very firm, very sticky, very plastic; very fine and fine roots; very fine and fine tubular pores; 10 percent faint slickensides (pedogenic); strong effervescence; 15 percent of horizon are red (2.5YR 4/8) fractured conchoidal blocks; 10 percent lenses 1 to 2 cm thick of light yellowish brown (10YR 6/4) silt loam; common fine and medium prominent light greenish gray (10Y 7/1) iron depletions with clear boundaries along root pore linings.

65

66

Table 19. Field morphological description of the Lake Charles microhigh (Pedon ID: 99TX201001A), Harris County, Texas. Data source: National Soil Information System, USDA-NRCS.

Ak--0 to 10 centimeters; dark gray (2.5Y 4/1) clay; weak coarse angular blocky parting to moderate medium granular structure; firm, very sticky, very plastic; many fine roots; common fine interstitial pores; 1 percent faint slickensides (pedogenic); 2 percent fine prominent strong brown (7.5YR 4/6) iron concentrations along root pore lining; few fine uncoated nodules of calcium carbonate; matrix is noncalcareous; clear smooth boundary. Bkssg1--10 to 27 centimeters; grayish brown (2.5Y 5/2) clay; moderate medium angular blocky structure; firm, very sticky, very plastic; common fine roots; few fine interstitial pores; 30 percent faint slickensides (pedogenic); few rounded 2 to 4 mm black (10YR 2/1) nodules of iron- manganese; 2 percent fine prominent yellowish red (5YR 5/8) iron concentrations with clear boundaries on surfaces of peds and on root pore linings; few 2 to 10 mm weakly indurated nodules of calcium carbonate coated with olive yellow (2.5Y 6/6) iron; few masses of calcareous red (2.5YR 5/8) clay 5mm to 1cm in size mixed with calcium carbonate nodules; matrix is noncalcareous; clear wavy boundary. Bkssg2--27 to 49 centimeters; grayish brown (2.5Y 5/2) clay; moderate fine and medium angular blocky structure; firm, very sticky, very plastic; common fine roots; few fine tubular pores; common distinct weakly grooved intersecting slickensides that are tilted 20 to 40 degrees from the horizontal; 1 percent fine prominent strong brown (7.5YR 5/6) iron concentrations with clear boundaries on roots pore linings; few rounded 2 to 4 mm black (10YR 2/1) nodules of iron-manganese; common weakly indurated nodules of calcium carbonate coated with olive yellow2.5Y 6/6) iron; few masses of calcareous red (2.5YR 5/8) clay 5mm to 1cm in size mixed with calcium carbonate nodules; matrix is noncalcareous; clear wavy boundary. Bkssg3--49 to 67 centimeters; grayish brown (2.5Y 5/2) clay; moderate fine and medium angular blocky structure; firm, very sticky, very plastic; common fine roots; few fine tubular pores; slight effervescence; many weakly grooved distinct intersecting slickensides that are tilted at 30 to 40 degrees from the horizontal; 5 percent fine distinct dark grayish brown (2.5YR 4/2) iron depletions on surfaces of slickensides; few rounded 2 to 10 mm black (10YR 2/1) nodules of iron-manganese; common weakly indurated nodules of calcium carbonate coated with olive yellow (2.5Y 6/6) iron; common masses of calcareous red (2.5YR 5/8) clay 5mm to 2cm in size mixed with calcium carbonate nodules; abrupt wavy boundary. Bkssg4--67 to 105 centimeters; grayish brown (2.5Y 5/2) clay; moderate medium and coarse angular blocky structure; firm, very sticky, very plastic; common fine roots; few fine tubular pores; strong effervescence; many weakly grooved distinct intersecting slickensides that are tilted at 15 to 30 degrees from the horizontal; 15 percent medium faint olive brown (2.5Y 4/4) iron concentrations with diffuse boundaries on surfaces of slickensides; 10 percent medium faint dark gray (2.5Y 4/1) iron depletions with diffuse boundaries on surfaces of slickensides; common uncoated rounded nodules of calcium carbonate 2 to 5mm in size; few rounded nodules of black (10YR 2/1) of iron-manganese 4 to 8 mm in size; clear wavy boundary. Bkssg5--105 to 148 centimeters; gray (2.5Y 5/1) clay; moderate medium and coarse angular blocky structure; firm, very sticky, very plastic; common fine roots between peds; few very fine tubular pores; slight effervescence; many prominent coarsely grooved intersecting slickensides; 35 percent fine and medium distinct light yellowish brown (2.5YR 6/4) iron concentrations with diffuse boundaries on surfaces of slickensides; 10 percent fine prominent dark gray (2.5Y 4/1) iron depletions with clear boundaries on surfaces of slickensides; common rounded black (10YR 2/1) nodules of iron-manganese 2 to 8mm in size; common rounded uncoated nodules of calcium carbonate 2 to 15mm in size; clear wavy boundary. Bkssg6--148 to 177 centimeters; gray (5Y 6/1) clay; moderate medium and coarse angular blocky structure; firm, very sticky, very plastic; common fine roots; few fine tubular pores; 3 percent spherical black (10YR 2/1) iron-manganese concretions; slight effervescence; common distinct finely grooved intersecting slickensides that are tilted at 30 to 35 degrees to the horizontal; 40 percent coarse prominent light yellowish brown (2.5Y 6/3) iron concentrations with diffuse boundaries on surfaces of slickensides; common rounded black (10YR 2/1) iron-manganese concretions; few rounded uncoated strongly indurated nodules of calcium carbonate 2 to 3 mm in size; clear wavy boundary. Bkss--177 to 202 centimeters; yellowish red (5YR 5/6) clay; weak coarse angular blocky structure; firm, very sticky, very plastic; common fine roots between peds; strong effervescence; common distinct finely grooved intersecting slickensides that are tilted 35 to 50 degrees to the horizontal; 5 percent fine distinct pale brown (10YR 6/3) iron concentrations with diffuse boundaries; 2 percent fine prominent gray (5Y 5/1) iron depletions with clear boundaries throughout; few fine dendritic black (10YR 2/1) iron-manganese concentrations in gray (5Y 5/1) iron depletions; common rounded nodules of black (10YR 2/1) iron-manganese 1 to 2 mm in size; few rounded uncoated strongly indurated nodules of calcium carbonate 2 to 3 mm in size; clear wavy boundary. Bss1--202 to 235 centimeters; yellowish red (5YR 4/6) clay; weak coarse angular blocky structure; firm, very sticky, very plastic; common very fine and fine roots; strong effervescence; few distinct finely grooved intersecting slickensides that are tilted at 20 to 40 degrees to the horizontal; 5 percent medium prominent light yellowish brown (2.5Y 6/3) iron concentrations with clear boundaries on surfaces of peds; common rounded nodules of black (10YR 2/1) iron-manganese 1 to 2mm in size; few medium masses of iron manganese on surfaces of slickensides; few masses of calcium carbonate 3 to 5mm in size; clear wavy boundary. Bss2--235 to 270 centimeters; red (2.5YR 4/6) clay; strong coarse angular blocky parting to moderate medium angular blocky structure; very firm, very sticky, very plastic; common very fine and fine roots; strong effervescence; common prominent coarsely grooved intersecting slickensides that are tilted 35 to 45 degrees to the horizontal; 5 percent fine and medium prominent light greenish gray (10Y 7/1) iron depletions with clear boundaries on surfaces of slickensides; 1 percent fine prominent light yellowish brown (2.5Y 6/3) iron depletions on surfaces of slickensides; common rounded black nodules of (10YR 2/1) iron-manganese 1 to 2mm in size; common fine masses of black (10YR 2/1) iron-manganese on surfaces of slickensides.

Tab

le 2

0. S

elec

ted

soil

mor

phol

ogic

al fe

atur

es fr

om th

e L

ake

Cha

rles

mic

rolo

w (P

edon

ID: 9

9TX

2010

01).

sbk

= su

bang

ular

blo

cky;

abk

= a

ngul

ar b

lock

y; m

ed. =

med

ium

H

oriz

on

Dep

th(c

m)

Bou

ndar

ySt

ruct

ure

Con

sist

ence

C

olor

Red

ox fe

atur

es

Slic

kens

ides

C

arbo

nate

se

greg

atio

ns

Rea

ctio

n O

ther

Pro

pert

ies

FeM

n co

ncen

trat

ion

Fe d

eple

tions

A

0-

16

clea

r sm

ooth

w

eak

fine

and

med

. sbk

fir

m

10Y

R

3/1

1% fi

ne F

eMn

nodu

les;

3%

fine

di

stin

ct F

e co

ncen

tratio

ns w

ith

shar

p bo

unda

ries a

long

root

por

e lin

ings

-

- -

-

man

y ve

ry fi

ne a

nd fi

ne

root

s; c

omm

on v

ery

fine

and

fine

inte

rstit

ial p

ores

; fe

w a

ctiv

e un

fille

d kr

otov

inas

1-5

cm

wid

e B

w

16-4

4 gr

adua

l sm

ooth

w

eak

med

. pr

ism

atic

pa

rting

to

mod

erat

e m

ed. a

nd

coar

se a

bk

firm

2.

5Y

2/1

1% fi

ne a

nd m

ed. F

eMn

nodu

les;

1%

fine

pro

min

ent F

e co

ncen

tratio

ns w

ith c

lear

bo

unda

ries a

long

root

por

e lin

ings

1% fi

ne fa

int g

ray

(2.5

YR

5/1

) de

plet

ions

with

cle

ar

boun

darie

s on

ped

surf

aces

1% fa

int

slic

kens

ides

an

d 1%

di

stin

ct

pres

sure

fa

ces

- -

com

mon

ver

y fin

e an

d fin

e ro

ots;

com

mon

fine

tu

bula

r por

es

Bss

1 44

-65

grad

ual

wav

y m

oder

ate

med

. pr

ism

atic

pa

rting

to

mod

erat

e m

ed. a

bk

firm

2.

5Y

4/1

1% m

ediu

m F

eMn

nodu

les;

3%

fin

e pr

omin

ent y

ello

wis

h re

d 5Y

R

5/6

conc

entra

tions

with

shar

p bo

unda

ries a

long

root

por

e lin

ings

-

com

mon

di

stin

ct (3

0-45

°)

- -

com

mon

ver

y fin

e an

d fin

e ro

ots;

com

mon

fine

tu

bula

r por

es

Bss

2 65

-88

grad

ual

wav

y w

eak

coar

se

pris

mat

ic

parti

ng to

m

oder

ate

med

. abk

firm

2.

5Y

4/1

1% m

ed. F

eMn

nodu

les;

10%

fine

fa

int l

ight

yel

low

ish

brow

n (2

.5Y

6/

3) F

e co

ncen

tratio

ns w

ith d

iffus

e bo

unda

ries o

n sl

icke

nsid

es a

nd

peds

3% fi

ne fa

int g

ray

(2.5

Y 5

/1) F

e de

plet

ions

with

cle

ar

boun

darie

s on

slic

kens

ide

and

ped

surf

aces

com

mon

di

stin

ct (3

5-55

°)

- -

com

mon

ver

y fin

e an

d fin

e ro

ots;

com

mon

ver

y fin

e an

d fin

e tu

bula

r po

res

Bss

3 88

-117

cl

ear w

avy

mod

erat

e m

ediu

m a

bk

very

firm

2.

5Y

5/1

1% fi

ne a

nd m

ed. F

eMn

nodu

les;

15

% fi

ne fa

int l

ight

yel

low

ish

brow

n (2

.5Y

6/3

) and

3%

fine

and

m

ed. d

istin

ct li

ght y

ello

wis

h br

own

(2.5

Y 6

/4) F

e co

ncen

tratio

ns w

ith d

iffus

e bo

unda

ries o

n su

rfac

es a

nd

inte

riors

of p

eds

-

com

mon

di

stin

ct (4

0-55

°)

- -

com

mon

fine

root

s; v

ery

fine

and

fine

tubu

lar

pore

s; fe

w c

raw

fish

krot

ovin

a 1

to 5

-cm

wid

e fil

led

with

gra

yish

bro

wn

and

very

dar

k gr

ay

mat

eria

l

Bss

4 11

7-15

1 cl

ear w

avy

mod

erat

e m

ed. a

bk

very

firm

2.

5Y

6/2

1% fi

ne a

nd m

ediu

m F

eMn

nodu

les;

15%

fine

and

med

ium

Fe

conc

entra

tions

with

diff

use

boun

darie

s on

surf

aces

of

slic

kens

ides

and

ped

inte

riors

; few

fin

e an

d m

ed. F

eMn

nodu

les

1% d

istin

ct g

reen

ish

gray

Fe

depl

etio

ns

with

diff

use

boun

darie

s on

surf

aces

of

slic

kens

ides

and

ped

in

terio

rs

com

mon

di

stin

ct (3

0-40

°)

- -

com

mon

fine

root

s; v

ery

fine

and

fine

tubu

lar

pore

s; k

roto

vina

s 1-5

cm

w

ide

fille

d w

ith g

rayi

sh

brow

n an

d ve

ry d

ark

gray

m

ater

ial

Bks

s1

151-

177

grad

ual

smoo

th

wea

k m

ed.

and

coar

se

sbk

very

firm

2.

5Y

6/3

3% fi

ne sp

heric

al st

rong

bro

wn

FeM

n co

ncen

tratio

ns; <

1% fi

ne

prom

inen

t stro

ng b

row

n Fe

co

ncen

tratio

ns w

ith d

iffus

e

3% fi

ne fa

int g

ray

Fe

depl

etio

ns w

ith c

lear

bo

unda

ries o

n su

rfac

es o

f

com

mon

di

stin

ct (3

0°)

few

fine

no

dule

s of

CaC

O3

-

com

mon

fine

root

s; v

ery

fine

and

fine

tubu

lar

pore

s; fe

w c

raw

fish

krot

ovin

as 1

to 5

cm

wid

e

67

Hor

izon

D

epth

(cm

) B

ound

ary

Stru

ctur

e C

onsi

sten

ce

Col

or

Red

ox fe

atur

es

Slic

kens

ides

C

arbo

nate

se

greg

atio

ns

Rea

ctio

n O

ther

Pro

pert

ies

FeM

n co

ncen

trat

ion

Fe d

eple

tions

bo

unda

ries a

long

surf

aces

of

slic

kens

ides

and

as a

hal

o ar

ound

M

n no

dule

s;

slic

kens

ides

; 1%

fine

fa

int g

reen

ish

gray

de

plet

ions

with

shar

p bo

unda

ries a

long

ro

ot p

ore

linin

gs

fille

d w

ith y

ello

wis

h re

d an

d ve

ry d

ark

gray

m

ater

ial;

5 cm

wid

e ar

cing

yel

low

ish

red

clay

in

trusi

on fr

om b

kss2

ho

rizon

s B

kss2

17

7-21

2 gr

adua

l w

avy

wea

k co

arse

sb

k ve

ry fi

rm

5YR

5/

4 1%

fine

pro

min

ent l

ight

yel

low

ish

brow

n co

ncen

tratio

ns w

ith d

iffus

e bo

unda

ries b

etw

een

peds

7% fi

ne p

rom

inen

t gr

ay F

e de

plet

ions

w

ith c

lear

bo

unda

ries o

n su

rfac

es o

f sl

icke

nsid

es; 1

% fi

ne

prom

inen

t gre

enis

h gr

ay F

e de

plet

ions

al

ong

root

por

e lin

ings

com

mon

fa

int (

20°)

co

mm

on fi

ne

nodu

les o

f ca

co3

-

very

few

ver

y fin

e an

d fin

e ro

ots;

ver

y fin

e an

d fin

e tu

bula

r pre

s; fe

w

craw

fish

krot

ovin

as fi

lled

with

dar

k gr

ay a

nd

redd

ish

brow

n m

ater

ial

B’s

s1

212-

242

clea

r sm

ooth

w

eak

med

. an

d co

arse

pr

ism

atic

very

firm

2.

5YR

5/

6 5%

fine

and

med

. pro

min

ent

yello

w F

e co

ncen

tratio

ns w

ith

diff

use

boun

darie

s on

ped

surf

aces

3% fi

ne p

rom

inen

t gr

eeni

sh g

ray

depl

etio

ns w

ith c

lear

bo

unda

ries o

n ro

ot

pore

lini

ngs

com

mon

fa

int (

20°)

fe

w fi

ne a

nd

med

ium

no

dule

s of

caco

3 -

very

few

ver

y fin

e an

d fin

e ro

ots;

few

ver

y fin

e an

d fin

e tu

bula

r por

es;

few

cra

wfis

h kr

otov

inas

.5

to 1

.5 c

m w

ide

fille

d w

ith d

ark

gray

and

red

mat

eria

l B

’ss2

24

2-26

1

-

mod

erat

e fin

e an

d m

ed.

plat

y pa

rting

to

mod

erat

e fin

e ab

k

very

firm

2.

5YR

5/

6 co

mm

on fi

ne n

odul

es o

f FeM

n at

to

p of

hor

izon

co

mm

on fi

ne a

nd

med

ium

pro

min

ent

light

gre

enis

h gr

ay

depl

etio

ns w

ith c

lear

bo

unda

ries o

n ro

ot

pore

lini

ngs

com

mon

fa

int (

15-

20°)

few

fine

pal

e br

own

nodu

les

of c

aco3

stro

ng

very

fine

and

fine

root

s;

very

fine

and

fine

tubu

lar

pore

s; fe

w c

raw

fish

krot

ovin

as 1

to 2

cm

wid

e fil

led

with

gra

y an

d re

d cl

ay

B’s

s3

261-

279

-

mod

erat

e fin

e an

d m

ed.

plat

y pa

rting

to

mod

erat

e fin

e ab

k

very

firm

2.

5YR

4/

6

-

10%

fine

and

med

. pr

omin

ent l

ight

gr

eeni

sh g

ray

Fe

depl

etio

ns w

ith c

lear

bo

unda

ries a

long

ro

ot p

ore

linin

gs

10%

red

frac

ture

d co

ncho

idal

bl

ocks

; co

mm

on

fain

t sl

icke

nsid

es

(15-

20°)

-

stro

ng

very

few

ver

y fin

e an

d fin

e ro

ots;

few

ver

y fin

e an

d fin

e tu

bula

r por

es

B’s

s4

279-

300

-

mod

erat

e fin

e an

d m

ed.

plat

y pa

rting

to

mod

erat

e fin

e ab

k

very

firm

2.

5YR

5/

6

-

com

mon

fine

and

m

ed. p

rom

inen

t lig

ht

gree

nish

gra

y Fe

de

plet

ions

with

cle

ar

boun

darie

s alo

ng

root

por

e lin

ings

15%

red

frac

ture

d co

ncho

idal

bl

ocks

; 10%

fa

int

slic

kens

ides

-

stro

ng

very

fine

and

fine

root

s;

very

fine

and

fine

tubu

lar

pore

s; 1

0% le

nses

1-2

cm

th

ick

of li

ght y

ello

wis

h br

own

silt

loam

68

Tab

le 2

1. S

elec

ted

soil

mor

phol

ogic

al fe

atur

es fr

om th

e L

ake

Cha

rles

mic

rohi

gh (P

edon

ID: 9

9TX

2010

01A

). sb

k =

suba

ngul

ar b

lock

y; a

bk =

ang

ular

blo

cky;

med

. = m

ediu

m

Hor

izon

D

epth

(cm

) B

ound

ary

Stru

ctur

e C

onsi

sten

ce

Col

orR

edox

feat

ures

Sl

icke

nsid

es

Car

bona

te se

greg

atio

nsR

eact

ion

Oth

er P

rope

rtie

s Fe

Mn

conc

entr

atio

n Fe

dep

letio

ns

Ak

0-10

cl

ear

smoo

th

wea

k co

arse

ab

k pa

rting

to

mod

erat

e m

ed.

gran

ular

firm

2.

5Y 4

/1

2% fi

ne p

rom

inen

t st

rong

bro

wn

Fe

conc

entra

tions

alo

ng ro

ot

pore

lini

ngs

-

1% fa

int

few

fine

unc

oate

d C

aCO

3 no

dule

s -

man

y fin

e ro

ots;

co

mm

on fi

ne

inte

rstit

ial p

ores

Bks

sg1

10-2

7 cl

ear w

avy

mod

erat

e m

ed.

abk

firm

2.

5Y 5

/2

2% fi

ne p

rom

inen

t ye

llow

ish

red

Fe

conc

entra

tions

with

cle

ar

boun

darie

s on

ped

surf

aces

and

root

por

e lin

ings

-

30%

fain

t fe

w 2

-10

mm

wea

kly

indu

rate

d C

aCO

3 no

dule

s co

ated

with

oliv

e ye

llow

Fe;

fe

w m

asse

s of c

alca

reou

s re

d cl

ay 5

-10

mm

mix

ed

with

CaC

O3

nodu

les

-

com

mon

fine

ro

ots;

few

fine

in

ters

titia

l por

es

Bks

sg2

27-4

9 cl

ear w

avy

mod

erat

e fin

e an

d m

ed. a

bk

firm

2.

5Y 5

/2

1% fi

ne p

rom

inen

t st

rong

bro

wn

Fe

conc

entra

tions

with

cle

ar

boun

darie

s on

root

por

e lin

ings

; few

roun

ded

2-4

mm

bla

ck F

eMn

nodu

les

-

com

mon

di

stin

ct (2

0-40

°)

com

mon

wea

kly

indu

rate

d C

aCO

3 no

dule

s coa

ted

with

ol

ive

yello

w F

e; fe

w m

asse

s of

cal

care

ous r

ed c

lay

5-10

mm

mix

ed w

ith C

aCO

3 no

dule

s

-

com

mon

fine

ro

ots;

few

fine

tu

bula

r por

es

Bks

sg3

49-6

7 ab

rupt

w

avy

mod

erat

e fin

e an

d m

ed. a

bk

firm

2.

5Y 5

/2

-

5% fi

ne d

istin

ct

dark

gra

yish

br

own

Fe

depl

etio

ns o

n sl

icke

nsid

es

wea

kly

groo

ved

(30-

40°)

com

mon

wea

kly

indu

rate

d C

aC03

nod

ules

coa

ted

with

ol

ive

yello

w F

e; c

omm

on

mas

ses o

f cal

care

ous r

ed

clay

5-2

0mm

mix

ed w

ith

CaC

O3

nodu

les

slig

ht

com

mon

fine

ro

ots;

few

fine

tu

bula

r por

es

Bks

sg4

67-1

05

clea

r wav

y m

oder

ate

med

. an

d co

arse

abk

fir

m

2.5Y

5/2

15

% m

ed. f

aint

oliv

e br

own

Fe c

once

ntra

tions

w

ith d

iffus

e bo

unda

ries

on sl

icke

nsid

es; f

ew

roun

ded

blac

k Fe

Mn

nodu

les 4

-8 m

m

10%

med

. fai

nt

dark

gra

y Fe

de

plet

ions

with

di

ffus

e bo

unda

ries o

n sl

icke

nsid

es

man

y w

eakl

y gr

oove

d (1

5-30

°)

com

mon

unc

oate

d ro

unde

d C

aCO

3 no

dule

s 2-5

mm

; st

rong

co

mm

on fi

ne

root

s; fe

w fi

ne

tubu

lar p

ores

Bks

sg5

105-

148

clea

r wav

y m

oder

ate

med

. an

d co

arse

abk

fir

m

2.5Y

5/1

35

% fi

ne a

nd m

ed.

dist

inct

ligh

t yel

low

ish

brow

n Fe

con

cent

ratio

ns

with

diff

use

boun

darie

s on

slic

kens

ides

; com

mon

ro

unde

d bl

ack

FeM

n no

dule

s 2-8

mm

10%

fine

pr

omin

ent d

ark

gray

Fe

depl

etio

ns w

ith

clea

r bo

unda

ries o

n sl

icke

nsid

es

man

y pr

omin

ent

coar

sely

gr

oove

d

com

mon

roun

ded

unco

ated

C

aCO

3 no

dule

s 2-1

5 m

m

slig

ht

com

mon

fine

root

s be

twee

n pe

ds; f

ew

very

fine

tubu

lar

pore

s

Bks

sg6

148-

177

clea

r wav

y m

oder

ate

med

. an

d co

arse

abk

fir

m

5Y 6

/1

3% sp

heric

al b

lack

Fe

Mn

conc

entra

tions

; 40

% c

oars

e pr

omin

ent

light

yel

low

ish

brow

n Fe

co

ncen

tratio

ns w

ith

diff

use

boun

darie

s on

slic

kens

ides

; com

mon

-

com

mon

di

stin

ct

finel

y gr

oove

d (3

0-35

°)

few

roun

ded

unco

ated

st

rong

ly in

dura

ted

CaC

O3

nodu

les 2

-3m

m

slig

ht

com

mon

fine

ro

ots;

few

fine

tu

bula

r por

es

69

70

Hor

izon

D

epth

(cm

) B

ound

ary

Stru

ctur

e C

onsi

sten

ce

Col

or

Red

ox fe

atur

es

Slic

kens

ides

C

arbo

nate

segr

egat

ions

R

eact

ion

Oth

er P

rope

rtie

s Fe

Mn

conc

entr

atio

n Fe

dep

letio

ns

roun

ded

blac

k Fe

Mn

conc

retio

ns

Bks

s 17

7-20

2 cl

ear w

avy

wea

k co

arse

ab

k fir

m

5YR

5/6

5%

fine

dis

tinct

pal

e br

own

Fe c

once

ntra

tions

w

ith d

iffus

e bo

unda

ries;

fe

w fi

ne d

endr

itic

blac

k Fe

Mn

conc

entra

tions

in

gray

Fe

depl

etio

ns;

com

mon

roun

ded

nodu

les o

f bla

ck F

eMn

nodu

les 1

-2 m

m

2% fi

ne

prom

inen

t gra

y Fe

dep

letio

ns

with

cle

ar

boun

darie

s th

roug

hout

com

mon

di

stin

ct

finel

y gr

oove

d (3

5-50

°)

few

roun

ded

unco

ated

st

rong

ly in

dura

ted

nodu

les

of C

aCO

3 2-

3 m

m

stro

ng

com

mon

fine

root

s be

twee

n pe

ds

Bss

1 20

2-23

5 cl

ear w

avy

wea

k co

arse

ab

k fir

m

5YR

4/6

5%

med

. pro

min

ent l

ight

ye

llow

ish

brow

n Fe

co

ncen

tratio

ns w

ith c

lear

bo

unda

ries o

n pe

ds;

com

mon

roun

ded

nodu

les o

f bla

ck F

eMn

1-2

mm

; few

med

. m

asse

s of F

eMn

on

slic

kens

ides

-

few

dis

tinct

fin

ely

groo

ved

(20-

40°)

few

mas

ses o

f CaC

O3

3-5m

m

stro

ng

com

mon

ver

y fin

e an

d fin

e ro

ots

Bss

2 23

5-27

0

-

stro

ng c

oars

e ab

k pa

rting

to

mod

erat

e m

ed.

abk

very

firm

2.

5YR

4/6

co

mm

on ro

unde

d bl

ack

FeM

n no

dule

s 1-2

mm

on

slic

kens

ides

5% fi

ne a

nd

med

. pro

min

ent

light

gre

enis

h gr

ay F

e de

plet

ions

with

cl

ear

boun

darie

s on

slic

kens

ides

; 1%

fine

pr

omin

ent l

ight

ye

llow

ish

brow

n Fe

de

posi

tions

on

slic

kens

ides

com

mon

pr

omin

ent

coar

sely

gr

oove

d (3

5-45

°)

-

stro

ng

com

mon

ver

y fin

e an

d fin

e ro

ots

Selected Physical and Chemical Properties

Selected physical and chemical properties for the Lake Charles (201) ML and MH are illustrated in Figure 25 and summarized in Table 22. Organic carbon content is slightly higher in the A horizon of the MH than the ML, but is in greater amounts to greater depths within the ML. Organic carbon ceases to decline in the ML at about 177 cm in the Bkss1 horizon, and at about 148 in the MH BKssg5 horizon. The CaCO3 equivalent curve shows nearly complete decalcification in the upper 150 cm of the ML, with a significant increase below that depth, beginning in the Bkss1 horizon. Similarly, greater decalcification occurs in the MH to 177 cm depth, with a significant increase in CaCO3 below this depth beginning in the Bkss horizon. Total clay (wt%) in the ML increases from 36.2% in the A horizon to its maximum expression of 61.6% in the Bkss2 horizon (177-212 cm). The fine clay fraction in the ML ranges between 22.8 and 35.7% through the entire profile, with slightly elevated values throughout the Bss1 through Bss4 (44-151 cm). In the MH, total clay content is less variable with depth than the ML, but is consistently in greater abundance throughout the profile, ranging from 43.5 to 58.0%. The fine clay fraction in the MH ranges from 20.5 to 31.8%. Coefficient of linear extensibility (COLE) values in the upper 65 cm of the ML range from 0.093 to 0.114, then abruptly increase to 0.132 in the Bss2 horizon and maintain a relatively uniform value throughout the remainder of the profile. In the MH, COLE values are relatively uniform with depth throughout the entire profile and range from 0.112 to 0.133. The Feo/Fed ratio indicates that much more amorphous iron oxide (short order) occurs in the upper 100 cm of both the ML and MH, with higher values consistently recorded for the MH. Below 100 cm, values are similar in both the ML and MH, and decrease steadily with depth. Percent Base Saturation (BS) is lower in the upper 44 cm of the ML, increasing to 100% throughout the remaining depth of the profile. BS is 100% throughout the MH. As indicated by pH trends, the ML has undergone more leaching than the MH (lower pH) within the upper 175 cm. Cation Exchange Capacity (CEC) values are similar with depth in both the ML and MH. Exchangeable sodium percentage (ESP) is greater in the ML than the MH and to greater depths, reaching nearly 15% at 280 cm in the ML. The CEC to clay ratio, used as an indicator of clay mineralogy, is similar in both the ML and MH and to similar depths. Both the ML and MH are dominated by montmorillonitic clays (CEC:clay values >.7) in the upper 150 cm of the profile, with montmorillonitic to mixed (CEC:clay values from .5 to .7) below that depth.

71

050

100

050

100

00.

51

00.

51

050

100

050

100

00.

510

0.2

0.4

05

100

5010

00

5010

00

12

0 50 100

150

200

250

300

02

4

Depth (cm)0

5010

00

0.25

0.5 0

0.2

0.4

05

100

5010

00

5010

00

12

025

500 50 100

150

200

250

300

350

02

4Depth (cm)

MicrohighO

rgan

ic C

wt%

CaC

O3

Equi

v.W

t %

Cla

y C

onte

ntW

t %C

OLE

FeO

/FeD

% B

SpH

CEC

cmol

ckg-

1ES

P%

Bd

g cm

-3

A Bw

Bss

1

Bks

s1

Bks

s2

B’s

s1

B’s

s2B

’ss3

Ak

Bks

sg1

Bks

sg3

Bkss

Microlow

Fine

cla

y

Tota

l cla

y

Bss

3

Fine

cla

y

Tota

l cla

y

Bss

2

Bss

4

B’s

s4

Bks

sg2

Bks

sg4

Bks

sg5

Bks

sg6

Bss

1

Bss

2

CEC

7/C

lay

Figu

re 2

5. D

epth

plo

ts o

f sel

ecte

d ph

ysic

al a

nd c

hem

ical

pro

pert

ies f

rom

the

Lake

Cha

rles

mic

rolo

w a

nd m

icro

high

(LA

C 2

01).

72

73

Tab

le 2

2. S

elec

ted

phys

ical

and

che

mic

al p

rope

rtie

s fro

m th

e L

ake

Cha

rles

mic

rolo

w a

nd m

icro

high

(LA

C 2

01).

Lak

e C

harl

es (L

AC

201

) mic

rolo

w

Dep

th (c

m)

Hor

izon

O

Cw

t%

TC

wt%

T

otal

Cla

yw

t%

Fine

C

lay

wt%

CO

LE

who

le

soil

CaC

O3

equi

v.

wt%

Fed

FeO

FeO

/Fe D

%B

S pH

CE

C7

NH

4 OA

C

cmol

c kg

-1

ESP

Bd

g cm

-3C

EC

7:cl

ay

0-16

A

2.

32

2.32

36

.2

26.3

0.

114

- 0.

7 0.

25

0.36

91

5.

9 29

.3

2 1.

15

0.81

16

-44

Bw

1.

50

1.50

35

.8

25.4

0.

098

- 0.

8 0.

18

0.23

97

5.

4 28

.2

4 1.

48

0.79

44

-65

Bss

1 1.

01

1.01

37

.3

28.9

0.

093

- 0.

9 0.

14

0.16

10

0 5.

7 28

.5

5 1.

51

0.76

65

-88

Bss

2 0.

65

0.65

46

.3

35.7

0.

132

- 1.

0 0.

07

0.36

10

0 6.

3 35

.0

6 1.

40

0.76

88

-117

B

ss3

0.47

0.

47

52.5

33

.8

0.13

1 -

0.9

0.07

0.

08

100

6.9

39.3

8

1.39

0.

75

117-

151

Bss

4 0.

29

0.29

49

.7

29.8

0.

12

- 0.

8 0.

08

0.10

10

0 7.

4 36

.7

8 1.

45

0.74

15

1-17

7 B

kss1

0.

11

0.23

46

.5

25.3

0.

117

1 1.

0 0.

08

0.08

10

0 7.

9 31

.2

10

1.46

0.

67

177-

212

Bks

s2

0.04

1.

00

61.6

28

.2

0.10

9 8

1.3

0.07

0.

05

100

8.0

33.6

11

1.

49

0.55

21

2-24

2 B

'ss1

0.07

1.

27

58.6

27

.6

0.11

7 10

1.

3 0.

08

0.06

10

0 8.

1 29

.5

12

1.45

0.

50

242-

261

B'ss

2 0.

00

2.29

48

.9

22.3

0.

112

19

1.0

0.05

0.

05

100

8.2

26.0

13

1.

49

0.53

26

1-27

9 B

'ss3

0.04

1.

96

47.8

22

.8

0.11

1 16

1.

2 0.

04

0.03

10

0 8.

2 26

.0

14

1.45

0.

54

279-

300

B'ss

4 0.

00

2.25

54

.5

24

0.09

6 19

1.

4 0.

04

0.03

10

0 8.

1 36

.6

10

1.51

0.

67

Lak

e C

harl

es (L

AC

201

) mic

rohi

gh

0-

10

Ak

2.60

2.

6 43

.5

31.8

0.

126

- 0.

9 0.

18

0.20

10

0 6.

7 36

.5

1 1.

12

0.84

10

-27

Bks

sg1

0.63

0.

75

49.9

26

.1

0.13

3 1

1.1

0.13

0.

12

100

7.4

36.0

1

1.35

0.

72

27-4

9 B

kssg

2 0.

26

0.74

47

.9

21.9

0.

120

4 1.

0 0.

08

0.08

10

0 7.

8 34

.0

2 1.

41

0.71

49

-67

Bks

sg3

0.38

1.

22

45.1

20

.4

0.12

4 7

0.8

0.06

0.

08

100

7.9

31.8

4

1.46

0.

71

67-1

05

Bks

sg4

0.06

0.

66

46.8

21

.6

0.11

5 5

0.8

0.10

0.

13

100

7.8

33.4

5

1.46

0.

71

105-

148

Bks

sg5

0.10

0.

46

44.8

23

.5

0.11

5 3

1.4

0.11

0.

08

100

7.9

32.3

4

1.49

0.

72

148-

177

Bks

sg6

0.03

0.

15

46.3

25

.3

0.12

6 1

0.8

0.10

0.

13

100

7.8

28.8

8

1.42

0.

62

177-

202

Bks

s 0.

01

2.29

52

.9

25.6

0.

108

19

1.1

0.06

0.

05

100

8.1

30.0

11

1.

49

0.57

20

2-23

5 B

ss1

0.00

2.

76

56.4

26

.4

0.11

2 23

1.

2 0.

04

0.03

10

0 8.

1 30

.4

12

1.46

0.

54

235-

270

Bss

2 0.

00

2.12

58

.0

28.9

0.

119

18

1.2

0.05

0.

04

100

8.1

32.6

12

1.

45

0.56

O

C%

= O

rgan

ic C

arbo

n

TC =

Tot

al C

arbo

n C

OLE

= C

oeff

icie

nt o

f lin

ear e

xten

sibi

lity

Fed =

dith

ioni

te e

xtra

ctab

le F

e Fe

o = o

xala

te e

xtra

ctab

le F

e

BS

= ba

se sa

tura

tion

CEC

= c

atio

n ex

chan

ge c

apac

ity

ESP

= ex

chan

geab

le so

dium

per

cent

age

Bd

= bu

lk d

ensi

ty

See

labo

rato

ry p

roce

dure

in S

oil S

urve

y S

taff,

199

6

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74

INTERPRETING VERTIC PALEOSOLS IN THE GEOLOGIC RECORD

PRE-QUATERNARY PALEOSOLS

Paleopedology is the study of the genesis, properties, climate, and landscape records of fossil soils, or paleosols. Pre-Quaternary paleosols are buried, “fossilized” soil horizons, which are older than 2 Ma; they are also commonly lithified, i.e., converted from soil into rock by the geological processes of burial diagenesis (Retallack 1991). Unlike the more rigid definition used by soil scientists, who consider a soil to be a body of geologic material that supports plant life, geoscientists interpret pre-Quaternary paleosols as any former subaerially exposed surfaces or layers of earth material that have been affected by physical, chemical, and biological weathering processes, but evidence for the presence of plants is not considered a prerequisite for identification of a fossil soil (Retallack 2001). This broader geological definition allows for greater flexibility in examining parts of earth history during which terrestrial plants were not present. Impetus for the study of pre-Quaternary paleosols largely originated with Dr. Gregory Retallack at the University of Oregon, who has published a widely used textbook on paleopedology (Retallack 2001). In a 1985 Geological Society of America Penrose Conference on paleosols (organized by Dr. Retallack) geoscientists, for the first time, began to think about soils of the past set in the backdrop of “deep” geologic time. Recognition and interpretation of pre-Quaternary paleosols requires the use of multidisciplinary approaches that involve integration of field morphological, microscopic, and geochemical data, as well as an appreciation for evolutionary changes in terrestrial biota and flora that have occurred over time (Mora and Driese 1999). Field morphological features such as plant root traces (in post-Silurian paleosols), soil horizons, and soil structures (especially peds or natural soil aggregates), are very diagnostic for pre-Quaternary paleosol identification (Figure 26A) (Retallack 1988). Micromorphological (thin section) features are commonly well preserved in paleosols and include root and soil animal traces, peds, and concentrations (or evidence for removal) of soil constituents such as clays, carbonates, Fe-Mn oxides, etc. (Figure 26B) (Driese and Foreman 1992; Mora and Driese 1999). Geochemical patterns related to weathering and element translocation, including molecular ratios of oxides or elements (Figure 26C) (Retallack 2001), concentration ratios (molecular ratios normalized to an assumed immobile element such as Ti; Driese and Foreman 1992), and mass-balance (residual enrichment, volume change during weathering, and mass transport, normalized to an immobile element such as Ti or Zr; Driese et al., 2000), provide supporting evidence for interpretations of paleosols. Stable isotopes, especially �13C values of paleosol organic matter and pedogenic carbonate, are useful in identifying terrestrial sources of organic matter and ecosystem types (Cerling 1991); most plant communities during the Paleozoic and Mesozoic eras were C-3 (Calvin cycle), with �13C values of soil organic matter averaging –26‰ PDB and pedogenic carbonate values ranging from –5 to –12‰ PDB (Mora et al. 1996; Mora and Driese 1999). The �18O values of pedogenic carbonate, if not diagenetically altered, can be used as proxies for meteoric water compositions and paleotemperatures (Cerling, 1984), but most values measured for Paleozoic pedogenic carbonates have been apparently reset during burial diagenesis (Mora and Driese 1999).

75

Figure 26. Pennington Formation (325 Ma, Late Mississippian), Tennessee, USA) paleosol. Used by Caudill et al. (1996) to estimate mean annual paleoprecipitation (MAP) of 648 + 141 mm/yr based on depth to pedogenic carbonate horizon relationship (Retallack, 2001). (A) Field photograph: A (surface), Bss (slickensided B) and Bkss (slickensided B with pedogenic carbonate) refer to paleosol horizons. Note angular blocky ped structure in outcrop. (Scale card is 15 cm long.) (B) Thin-section photomicrograph of paleosol which exhibits sepic-plasmic (oriented bright clay) microfabric related to seasonal cycles of wetting and drying and associated clay shrinking and swelling, as well as dark-colored Fe-Mn oxide nodule used by Stiles et al. (2001) to estimate MAP of 989 mm based on wt% Fe content. (Cross-polarized light.) (C) Molecular ratios for paleosol, including calcification (CaO + MgO/Al2O3), clay accumulation (Al2O3/SiO2), Fe accumulation (Fe2O3/Al2O3), and salinization (Na2O/K2O). Note carbonate and Fe accumulation in deeper portion of paleosol, but relatively uniform clay content and salinization.

Problems in recognition of, and interpreting paleoclimates from pre-Quaternary paleosols, include extensive burial diagenetic alteration (Retallack 1991). Commonly cited diagenetic alteration processes include physical compaction and consequent modifications of original soil thickness and morphology, oxidation of soil organic matter, burial gleization (Fe loss, largely through microbial reduction), color modifications (intensification) related to dehydration and recrystallization of hydrous mineral phases (such as FeOOH), recrystallization of soil smectites to illites (or even to metamorphic mineral assemblages; Table 23), and exchange of oxygen isotopes between burial fluids and pedogenic carbonates and clays (Mora and Driese 1999). Mack et al. (1993) proposed an alternative paleosol classification because of burial diagenetic alteration and associated lack of preservation of features necessary to rigorously apply USDA Soil Taxonomy (Figure 27). Evolutionary changes in terrestrial plant and animal communities over time also create difficulties in paleosol interpretations because of attendant changes in morphological features such as root traces, which are: 1) not present in Ordovician paleosols; 2) rhizomatous and fine in Silurian paleosols; and 3) larger, deeper, and more “modern” in Devonian and post-Devonian paleosols (Driese and Mora 2001).

76

Table 23. Diagenetic alteration of paleoVertisols. High clay-content paleosols with extensive shrink-swell features such as slickensides are compared with a modern soil analog (Houston Black series), as a function of increasing burial depth, temperature and time (Driese et al., 2000; Rye and Holland, 2000).

Name, Geologic Age Burial Depth (km) Burial Temperature (oC) Clay Mineral

Assemblage wt% K2O Houston Black

(modern) surface 22o Mean Annual Temp. Na-smectite 1.29 wt%

Pennington (325 Ma) 2-3 km 60-90 oC illite (+ kaolinite + chlorite) 4.61 wt%

Hekpoort (2.25 Ga) 12-15 km 350 oC sericite – muscovite – chlorite 9.50 wt%

Figure 27. Mack et al. (1993) classification for paleosols.

Current research on pre-Quaternary paleosols no longer concerns simple identification of paleosols in the geologic record, but instead focuses on the use of paleosols as proxies for reconstructions of paleoclimate, paleolandscape evolution, and paleoatmospheric chemistry. Paleoclimate reconstructions primarily emphasize making estimates of mean annual precipitation (MAP) by using a variety of proxy measures, including: 1) depth to pedogenic carbonate (Bk) horizon (Figure 26A) (Caudill et al. 1996); 2) Fe content of pedogenic Fe-Mn nodules and concretions (Figure 26B; Figure 28A) (Stiles et al. 2001); 3) chemical indices of weathering based on bulk geochemistry (Figure 26C; Figure 28B) (e.g., Chemical Index of Alteration minus Potash or CIA-K, Sheldon et al., 2002); and 4) total element mass-flux and mass-balance calculations (Stiles et al., 2003a, b). Paleolandscape reconstructions in which topography or hydrology are important variables (interpretation of paleocatenas) are commonly conducted at both local as well as at more regional scales. Reconstructions of Phanerozoic pCO2 employ the CO2-carbonate paleobarometer of Cerling (1991) to interpret Paleozoic (Mora et al., 1996; Mora and Driese, 1999) and Mesozoic paleoatmospheres. This technique utilizes the �13C values measured from pedogenic carbonates, measurements of �13C values of paleosol organic matter (or an estimate of based on marine proxy records), and assumptions of soil productivity to estimate paleoatmospheric pCO2, and these results are in good agreement with pCO2 estimates based on long-term mass-balance carbon models (Figure 29). Studies of oxygen levels of Precambrian atmospheres focus on measuring Fe contents and Fe losses during weathering of Precambrian paleosols, which has been further expanded to include other redox-sensitive elements, as well as the ratio of oxygen demand to demand for CO2 during weathering (Rye and Holland, 2000). Other research directions include systematic studies of root diameter, depth, and density in paleosols using root traces, and relating these changes to development of soil morphology (Driese and Mora, 2001), widespread deposition of black shales, and carbon sequestration.

77

Figure 28. Two examples of geochemical climate proxies derived from pre-Quaternary paleosols. (A) Estimates of paleoprecipitation (MAP) for mid-Mississippian (Maccrady), Late Mississippian (Pennington) and Early Permian (Dunkard) Appalachian basin paleoVertisols based on measured Fe content of paleosol Fe-Mn bodules and using regression equation of Stiles et al. (2001) for total Fe content of Fe-Mn nodules in modern soil analogs in Texas, USA. Note that estimated MAP ranges from 850-1310 mm/yr). (From Stiles et al., 2001, used with permission). (B) Mean annual precipitation (MAP) for six Appalachian basin paleoVertisols estimated using measured bulk chemistry and regression equation of Sheldon et al. (2002) that relates MAP to Chemical Index of Alteration minus Potash (note: CIA-K = molar ratio of Al2O3/(Al2O3+Na2O+CaO) x 100, and the linear regression obtained is P = 14.265(CIA-K)-37.632, r2 = 0.73, where P = MAP in mm/yr), which shows an increase of 400-500 mm MAP during latest Mississippian time in southeastern Kentucky, USA.

Figure 29. Estimates of Middle to Late Paleozoic atmospheric CO2 levels. Values are expressed as times present atmospheric level and are derived from Appalachian basin paleosols (closed symbols are data from Mora et al., 1996; other sources (patterned symbols) of pedogenic carbonate-based estimates are referenced in Driese and Mora, 2001), calculated using the soil carbonate carbon isotope paleobarometer of Cerling (1991). Other proxy-based estimates include stomatal density (open symbols) and carbon mass-balance model (line) (see discussion in Driese and Mora (2001).

78

USING MODERN VERTISOLS TO INTERPRET PALEOZOIC PALEOSOLS As mentioned in the introduction to this field guide, the primary objective of this fieldtrip is to highlight regional variations in field morphology, micromorphology, and soil chemistry across a Quaternary Vertisol climosequence and to test the applicability of derived climate proxy measures for interpreting the paleoclimate record from ancient (lithified) Vertisols preserved as paleosols in the Appalachian Basin, USA. This study involved the four soil pits examined for this field trip, as well as 8 others that were previously sampled within the climosequence. Thus, the analytical results are inclusive of all soil pits for the climosequence study. Figure 30 illustrates the locations of soil pits examined for this study. Table 24 presents summary data for each of the 12 examined soil pits.

Figure 30. Climosequence sampling sites, designated by soil series: 1 = League; 2 = Lake Charles; 3 = Laewest; 4 = Victoria. MAP = mean annual precipitation.

79

Table 24. Summary of Texas Vertisols examined for climosequence study.

SSS Number (abbreviation)

Texas County

Soil Series LatitudeNorth

LongitudeWest

Elev. (m) above SL

MAP (cm)

MAT-air (oC)

Moistureregime

Age(ka)

S00TX-245-1 (LEG 245A)

Jefferson League 30o02'22.0" 94o11'35.2" 7.0 144 20.5 udic <35-40

S00TX-245-2 (LEG 245B)

Jefferson League 29o52'38.5" 94o19'11.5" 5.2 144 20.5 udic <35-40

S00TX-71-1 (LEG 71)

Chambers League 29o48'9.0" 94o33'22.0" 7.9 134 20.5 udic-ustic <35-40

S99TX-201-1 (LAC 201)

Harris Lake Charles

29o35'40.0" 95o43'14.0" 4.0 132 20.0 udic-ustic <35-40

S99TX-157-1 (LAC 157)

Fort Bend Lake Charles

29o24'2.0" 95o43'36.0" 20.1 117 21.0 ustic <35-40

S99TX-481-1 (LAC 481)

Wharton Lake Charles

29o25'38.0" 96o04'35.0" 33.6 107 21.3 ustic <35-40

S99TX-239-1 (LAW239)

Jackson Laewest 28o52'48.2" 96o24'10.0" 11.0 104 21.5 ustic <35-40

S99TX-469-1 (LAW 469)

Victoria Laewest 28o43'6.8" 96o45'30.0" 100 21.5 ustic <35-40

S99TX-391-1 (LAW 391)

Refugio Laewest 28o28'24.8" 97o01'58.2" 19.5 84 21.6 aridic-ustic

<35-40

S99TX-409-3 (VIC 409)

San Patricio

Victoria 28o06'45" 97o20'59.1" 86 21.8 aridic-ustic

<35-40

S01TX-355-1 (VIC 355A

Nueces Victoria 27o48'22" 97o43'31.0" 25.9 86 21.8 aridic-ustic

<35-40

S01TX-355-2 (VIC 355B)

Nueces Victoria 27o33'49" 97o33'10.5" 8.3 86 22.3 aridic-ustic

<35-40

Methods During the previous sampling of these sites, large pits (2 m wide, 3-5 m long, 2 to 3.5 m deep) were excavated and transected the undulatory microtopographic and subsurface gilgai microhighs (MH) and microlows (ML). Bulk soil samples for XRF total soil geochemical analyses were collected at 10 cm depth intervals from both MH and ML pedons, to the maximum excavated depths (2.0-4.3 m) at each location, in attempts to extract samples of both sola (A and B horizons) as well as unweathered or least-weathered parent materials (C or R horizons). Parallel suites of bulk samples, collected by NRCS, Baylor, and Texas A&M University researchers by soil horizon, were sent to the USDA National Soil Survey Laboratory in Lincoln, NE for standard soil characterization. Soil profiles were described and soil horizons defined using standard pedological techniques (Soil Survey Staff 1998). After manual removal of macroscale (> 2 mm) organic matter and oven drying at 60o C, pressed pellets were prepared from bulk, powdered soil samples and analyzed for selected major, minor, and trace elements using a Philips wavelength-dispersive X-ray Fluorescence (XRF) Analyzer at the University of Tennessee (methodology defined in Singer and Janitzky 1986). The XRF analytical protocol employed appropriate clay soil standards and reports major elements in oxide weight percent and trace elements in ppm. Particle size, and other wet-chemical soil characterization data (e.g., pH, ammonium acetate-extractable cations, dithionite citrate-extractable cations, acid oxalate-extractable cations, CaCO3 equivalent, total S, etc.), were determined at the USDA National Soil Survey Laboratory in

80

Lincoln, Nebraska; the laboratory methods for these analyses are described in Soil Survey Staff (1996). Wet- chemical and geochemical data were preferentially utilized from ML pedons because of the higher correlations of whole-soil geochemical data derived from ML pedons with MAP, in contrast with the poorer correlations of the whole-soil geochemical data derived from MH pedons (cf. Stiles 2001; Stiles et al. 2001; Stiles et al. 2003b).

Fe Soil Chemistry Higher-MAP soils (League and Lake Charles series) show a consistent pattern of dithionite citrate-extractable Fe (Fedith) with depth, ranging from 0.5 to 1.0 wt% Fedith in the upper profile and maintaining these values to 150 cm depth, but increasing to 1.25-2.0 wt% at greater depths (Figure 31A). The League soils may have slightly elevated Fedith concentrations relative to the Lake Charles soils. The soils constituting the lower MAP portion of the climosequence (Laewest and Victoria series) display a depth pattern for Fedith that is similar to that of the higher MAP soils, but the total concentrations of Fedith are much lower and range from 0.1-0.4 wt%, with higher concentrations (0.4-0.8 wt%) measured in the deeper soil in two Laewest profiles (LAW 239 and 469) (Figure 31B).

Figure 31. Fe chemistry of Texas climosequence for Vertisol microlows. A) wt% dithionite citrate-extractable Fe (Fedith) vs. depth for Vertisol pedons from higher-MAP portion of climosequence. B) wt% Fedith vs. depth for Vertisol pedons from lower-MAP portion of climosequence. C) wt% acid oxalate-extractable Fe (Feoxal) vs. depth for Vertisol pedons from higher-MAP portion of climosequence. D) wt% Feoxal vs. vs. depth for Vertisol pedons from lower-MAP portion of climosequence.

81

Higher MAP soils also show a consistent pattern of acid oxalate-extractable Fe (Feoxal) with depth, ranging from 0.2 to 0.4 wt% Feoxal in the upper profile and maintaining these values to 50 cm depth, but decreasing to 0.05-0.15 wt% at greater depths (Figure 31C). The soils constituting the lower MAP portion of the climosequence display a depth pattern for Feoxal similar to that of the wetter soils, but the total concentrations of Feoxal are much lower and range from 0.05 to 0.17 wt% in the upper profile, with lower concentrations (0-0.05 wt%) measured in the deeper soil (Figure 31D). One of the Victoria profiles (VIC 355B) contained essentially no Feoxal. A crossplot of Fedith vs. Feoxal suggests a positive covariation between the two types of Fe measurements, and that upper sola (A and B horizons) are characterized by generally lower Feoxal concentrations (< 0.1 wt%), even for very high Fedith concentrations of up to 2 wt% (Figure 32A). Total Fe content (measured as Fe2O3 by XRF) of the Lake Charles profiles located in closest proximity to the Brazos River Valley drainage system show the highest total Fe contents (LAC 481 and 157), which range from 4.5 to 5.5 wt% (Figure 32B). The lowest total Fe concentrations of 2.5-3.5 wt% occur in the higher-MAP League (LEG 245A) and Lake Charles (LAC 201) profiles, but also in a lower-MAP Laewest (LAW 469) profile (Figure 32B). Many, but not all, of the profiles exhibit patterns of increasing total Fe with increasing soil depth. Overall the depth patterns for total Fe appear less pronounced than for Fedith and Feoxal. A crossplot of total Fe vs. Fedith indicates a positive covariation between these two types of Fe measurements, and that baseline values of total Fe of 2-4 wt% typify soil samples with low Fedith (Figure 32C). A crossplot of total Fe vs. Feoxal indicates no apparent systematic covariation between these two types of Fe measurements (Figure 32D).

Figure 32. Fe chemistry of Texas climosequence for Vertisol microlows. A) Crossplot of wt% Fedith vs. wt% Feoxal for all pedons showing two different trends for upper and lower sola. B) wt% Total Fe (measured as Fe2O3 by XRF) vs. depth for selected pedons. C) Crossplot of wt% total Fe (measured as Fe2O3 by XRF) vs. wt% Fedith for all pedons showing positive covariation. D) Crossplot of wt% total Fe

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(measured as Fe2O3 by XRF) vs. wt% Feoxal for all pedons showing lack of covariation. Climate-sensitive chemical proxies of MAP include dithionite citrate-extractable Fe (Fedith) and acid oxalate-extractable Fe (Feoxal), which are higher in higher-MAP soils, but total Fe, by itself, is not a unequivocal proxy for estimating MAP in Vertisols. Carbonate and Sulfate Soil Chemistry Higher-MAP soils (League, Lake Charles series) show no measurable calcium carbonate equivalent (CaCO3equiv) to depth of 150 cm, and high concentrations of CaCO3equiv, ranging widely from 2.5 to 20 wt%, at greater depths (Figure 33A). Two of the League profiles (LEG 245B, 071) have no measurable CaCO3equiv to a depth of 250 cm, and overall lower concentrations than the other profiles. The Laewest profiles appear to represent a transition between the higher-MAP and the other lower-MAP soils (Victoria series), especially LAW 239, which displays a depth behavior for wt% CaCO3equiv that resembles the patterns of the higher-MAP soils (Figure 33B). Each of the Laewest soils has little measurable CaCO3equiv within 50 cm of the soil surface, and increasing CaCO3equiv with increasing depth. However, in contrast with the higher-MAP soils, the Victoria soils do have CaCO3equiv measurable to the soil surface, with progressive increases in the concentrations of CaCO3equiv at the soil surface with decreasing MAP (Figure 33B). Although not

Figure 33. Carbonate (CaCO3) and S chemistry. Abbreviations for pedons are defined in Table 1. A) wt% CaCO3 equivalent (CaCO3equiv) vs. depth from higher-MAP ML pedons (abbreviations for pedons are defined in the text). B) wt% CaCO3equiv vs. depth from lower-MAP ML pedons. C) Crossplot of wt% CaO (measured using XRF) vs. wt% CaCO3equiv showing general positive covariation. D) wt% S vs. depth for all ML pedons containing measurable S. The depth-distribution of CaCO3equiv effectively differentiates between higher-MAP League and Lake Charles soils and lower-MAP Laewest and Victoria soils. The higher-MAP soils are mainly leached of carbonate to an effective depth of 100-150 cm, and free carbonate is present in the soils at progressively shallower depths, and in higher concentrations, with decreasing MAP. The presence of gypsum differentiates low-MAP Victoria soils from higher-MAP soils.

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shown here, bivariate plots of wt% CaO (measured using XRF) versus soil depth appear very similar to the plots of CaCO3eqiv versus depth presented previously. A crossplot of wt% CaO vs. wt% CaCO3equiv shows the expected positive covariation, and suggests that the baseline values of CaO for bulk soil matrix lacking free CaCO3 range between 1.0 and 1.5 wt% (Figure 33C). Soils representing the higher-MAP (League, Lake Charles, Laewest) portions of the climosequence contain little or no measurable S (Figure 33D). The S content of these soils ranges between 0.01 and 0.04 wt%, with a suggestion of slightly elevated values at the soil surface. The lowest-MAP (Victoria) soils, in contrast, have S contents that range from 0.05 to 0.1 wt% at the surface, to concentrations as high as 0.2-1.1 wt% in deeper portions of the profiles (Figure 33D). The major inflection in S concentration occurs at a soil depth of about 100 cm. Chemistry of Other Exchangeable Base Cations Consistent patterns in the concentrations of ammonium acetate-extractable Na (Naacet), apparent across the climosequence, are characterized by increasing Naacet with decreasing MAP. All soils have concentrations of 0.5-1.5 meq/100 g Naacet at the soil surface, with progressively greater concentrations to a characteristic depth that is deeper in the higher-MAP soils and that shallows progressively in the lower-MAP soils. The lower-MAP Victoria soils stand out as having the highest measured concentrations of 10-15 meq/100 g Naacet, whereas the intermediate-MAP Laewest soils exhibit a pattern that is intermediate between the higher-MAP League and Lake Charles soils and the lower-MAP soils (Figure 34A). One Laewest pedon (LAW 239) is an exception and has anomalously low Naacet concentrations similar to those measured in the higher-MAP soils. Total Na (measured as Na2O by XRF) ranges from below detection limit to as high as 1.5 wt% (Figure 34B). There is a general positive covariation between total Na and Naacet, with lower-MAP soils having higher concentrations of both measures of Na. The data suggest that there may have been problems with the XRF instrument when samples from the LAC 157 pedon were analyzed, because these are the only samples with recorded Na2O concentrations below detection limit.

Figure 34. Exchangeable-base chemistry. A) Ammonium acetate-extractable Na (meq/100 g; Naacet) vs. depth for all ML pedons. B) Crossplot of wt% total Na (measured as Na2O by XRF) vs. Naacet (meq/100 g) for all ML pedons showing positive covariation. Concentrations of ammonium acetate-extractable K (Kacet) show a pattern across the climosequence characterized by increasing Kacet with decreasing MAP, although it is not as strongly expressed as the pattern for Naacet (Figure 35A). Lower-MAP soils (Laewest, Victoria) have higher concentrations of 0.5-2.5 meq/100 g Kacet at the soil surface, with progressively

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decreasing concentrations to a characteristic depth between 50 and 100 cm. The higher-MAP League and Lake Charles soils stand out as having the lowest measured concentrations of 0.25-0.5 meq/100 g Kacet (Figure 35B). Total K (measured as K2O by XRF) ranges from 0.75 to 2.5 wt% (Figure 35B). There is a general positive covariation between total K and Kacet, with lower MAP soils having higher concentrations of both measures of K.

Figure 35. Exchangeable-base chemistry. A) Ammonium acetate-extractable K (meq/100 g; Kacet) vs. depth for all ML pedons. B) Crossplot of wt% total K (measured as K2O by XRF) vs. Kacet (meq/100 g) for all ML pedons showing positive covariation. The concentrations of ammonium acetate-extractable Mg (Mgacet) show a pattern across the climosequence that follows neither the pattern for Naacet nor that for Kacet with decreasing MAP, i.e., four Lake Charles pedons (LAC 201, 157, 481) and one Laewest pedon (LAW 239) all have higher concentrations of 9-12.5 meq/100 g Mgacet at the soil surface, with progressively increasing concentrations to as high as 15-20 meq/100 g Mgacet at a characteristic depth between 100 and 200 cm (Figure 36A). Both the higher-MAP League and lower-MAP Laewest (except for pedon 239) and Victoria soils stand out as having much lower measured concentrations of 2.5-7 meq/100 g Mgacet, with both the driest and wettest pedons showing essentially no variation with depth (Figure 36A). Total Mg (measured as MgO by XRF) ranges from 0.7 to 4 wt% (Figure 36B). There is a general positive covariation between total Mg and Mgacet, although neither relate directly with MAP, as was discussed previously.

Figure 36. Exchangeable-base chemistry. A) Ammonium acetate-extractable Mg (meq/100 g; Mgacet) vs. depth for all ML pedons. (B) Crossplot of wt% total Mg (measured as MgO by XRF) vs. Mgacet (meq/100

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g) for all ML pedons showing positive covariation. The abundances and depth-distributions of Naacet, Kacet, and Mgacet effectively separate higher-MAP League and Lake Charles soils, intermediate-MAP Laewest soils, and lower-MAP Victoria soils. Reactive Na and K are generally present in higher concentrations and closer to the soil surfaces in the lower-MAP soils, and generally decrease with increasing MAP be cause of removal by leaching under higher-MAP conditions, but Mgacet is one exception to this pattern.

Chemical Index of Alteration Minus Potash (CIA-K) Results of application of the chemical index of alteration minus potash (CIA-K) geochemical proxy for climate, developed recently by Sheldon et al. (2002), to the Texas Vertisol climosequence are summarized in Table 25 and Figure 371. There is good general agreement between measured MAP and MAP predicted by CIA-K (r2 = 0.82) for Texas Vertisol climosequence samples analyzed from ML pedons, although there is an apparent offset of about 100-150 mm between the measured MAP and the MAP predicted using CIA-K (Figure 37A). Furthermore, the plot of measured MAP versus MAP predicted using CIA-K is curvilinear, rather than a straight line (Figure 37A). The results for samples analyzed from MH pedons are generally poor and show considerable scatter (Figure 37B).

Figure 37. Results of application of chemical index of alteration minus potash (CIA-K) for estimation of MAP (Sheldon et al. 2002) to actual measured MAP of Texas Vertisol climosequence. A) CIA-K for all ML pedons show strong positive linear (or curvilinear) correlation between predicted MAP and measured MAP. B) CIA-K for all MH pedons, showing lack of strong linear correlation between predicted MAP and measured MAP. Results of application of the CIA-K geochemical proxy for climate to the Upper Mississippian Pennington Formation paleoVertisols at Pound Gap, Kentucky, are summarized in Figure 38. The CIA-K values for the lower, reddish-gray, calcareous paleoVertisols (134 to 210 m beneath the base of the Pennsylvanian) range from 54.5 to 63.3, which yielded MAP estimates ranging from 740 to 866 mm. The CIA-K values for the upper, low-chroma, non-calcareous, redoximorphic paleoVertisols (30 to 40 m beneath the base of the Pennsylvanian) range from 80 to 93, which produced MAP estimates ranging from 1100 to 1291 mm. The depth-to-calcic-horizon paleo-precipitation proxy of Retallack (1994) and as modified for Vertisols in Stiles et al. (2001) could

1 CIA-K = molar ratio of Al2O3/(Al2O3+Na2O+CaO) x 100, and the linear regression obtained is P = 14.265(CIA-K)-37.632, r2 = 0.73, where P = MAP in mm/yr

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not be applied to these paleosols as an independent cross-check of the estimated MAP values because the paleosols are all erosionally truncated.

Figure 38. Application of Sheldon et al. (2002) CIA-K climofunction to Pennington Formation (Upper Mississippian) paleosol succession in eastern Kentucky. Note the change from drier to wetter conditions over time, approaching the Mississippian-Pennsylvanian boundary.

Table 25. Comparison between measured mean annual precipitation (MAP) and MAP estimated using chemical index of alteration minus potash (CIA-K) of Sheldon et al. (2002).

Pedon Microlow CIA-K Microlow MAP Microhigh CIA-K Microhigh MAP MAP measured LEG 245A 78.5 1081 85.4 1180 1437 LAC 201 84.8 1172 58.5 797 1321 LAC 157 81.7 1127 94.1 1304 1170 LAC 481 81.0 1117 78.0 1075 1124 LAW 239 74.9 1031 16.6 199 1066 LAW 469 73.7 1014 30.5 397 1000 LAW 391 61.4 839 28.5 369 924 VIC 409 49.4 667 35.2 464 844

INTERPRETATIONS

Soil Chemistry Climate-sensitive chemical proxies of MAP include dithionite citrate-extractable Fe (Fedith), acid oxalate-extractable Fe (Feoxal), CaCO3 equivalent (CaCO3equiv), total S, and ammonium acetate-extractable Na, K, and Mg (Naacet, Kacet, and Mgacet, respectively). Fedith very effectively defines a separation between higher-Fedith and higher-MAP, and lower-Fedith and lower-MAP soils; the depth-variation pattern in which Fedith is lower nearer the soil surfaces and higher at depth reflects the tendency for Fe removal to occur in the upper sola (combined A and B horizons), whereas Fe concentration occurs in lower sola (Figure 31A, B). This is also supported by mass-balance and total-mass-flux calculations for total Fe as well as for Fedith (Stiles 2001; Stiles et al. 2003b; Nordt et al. 2004). Feoxal also effectively defines a separation between higher-Feoxal and higher-MAP, and lower-Feoxal and lower-MAP soils; the depth-variation pattern in which Feoxal is higher nearer the soil surfaces and lower at depth reflects the tendency for “reactive” or poorly ordered Fe concentration to occur in the upper sola, whereas reactive Fe is “fixed” in lower sola (Figure 31C, D). This is also supported by mass-balance and total-mass-flux calculations for Feoxal (Nordt et al.

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2004). The variable distributions of Fedith and Feoxal in upper vs. lower sola in the Texas Vertisols (Figure 32A) possibly reflect two different pedogenic “domains”, as defined by Stiles et al. (2003b) using Ti/Zr depth distributions. Alternatively, Nordt et al. (2004) found a discontinuity in the Lake Charles soils separating two different parent materials that was identifiable with % sand and Zr, but not with % silt or Ti, and cited pedogenesis as the likely mechanism for “blurring” the discontinuity. One cannot discount that the depth patterns for Fedith and Feoxal may also record climate-induced variability in saturation vs. reduction periods and saturation-reduction temporal and spatial “dislinkage” due to the lower hydraulic conductivities of the clay soil matrices (Jacob et al. 1997). Variability in Fe chemistry due to seasonal floodwater events and water-table perching (e.g., Wright 1999; Wright et al. 2000) seems less likely because of site selection aimed at ensuring uniform drainage class across the climosequence, and lack of proximity to modern active fluvial systems. Indeed, all of the soil sites occur in about the same type of landscape position. In pedology Fedith is commonly termed "free” pedogenic iron; Fedith resides primarily in minerals that are the products of pedogenic processes, and the dithionate reduces all Fe3+ to Fe2+ during processing. Fedith is therefore not the same as total Fe, because there is always some well-crystallized hematite and goethite that is resistant to dissolution in Fe-bearing minerals inherited from the parent material (Schwertmann 1988; Schwertmann and Taylor 1989). Nevertheless, Fedith does covary positively with total Fe (measured as Fe2O3 by XRF), and this implies that, all else being equal, higher-MAP soils are likely to have higher total Fe content (Figure 32C). However, one cannot discount the variability in total Fe that is related to differences in parent material or source area; e.g., we noted previously that the soils formed in the Brazos River drainage basin (which has headwaters sourced in Permo-Triassic redbeds; LAC 157 and 481 pedons) are not the highest-MAP soils, yet they have the highest total Fe (Figure 32B), therefore total Fe, by itself, is not a unequivocal proxy for estimating MAP in Vertisols and paleoVertisols. But total Fe content of Fe-Mn nodules is clearly a MAP proxy (Stiles et al. 2001). The total Fe vs. Fedith crossplot further suggests that the Texas Vertisols minimally contain 2-4 wt% Fe2O3 that is in mineral forms that are not extractable using dithionite-citrate (Figure 32C). These mineral phases likely include crystalline hematite and other Fe-bearing minerals (mainly biotite; Nordt et al. 2004), which were inherited from the fluviodeltaic parent materials in the Beaumont Formation. Fe data from a U.S. Virgin Islands Vertisol (Hogensborg series) formed on basalt with a higher initial Fe content show a Fedith to Fe2O3 relationship similar to that of the Texas Vertisols but offset to higher initial Fedith and Fe2O3 concentrations (Driese, 2004). The relationship between Fe2O3 and Feoxal is not very apparent (Figure 32D), and this lack of covariation for many of the profiles likely reflects the fact that the Feoxal iron pool consists of more reactive Fe that is associated with noncrystalline, amorphous, or short-range ordered Fe oxyhydroxides such as ferrihydrite (Schwertmann 1988; Schwertmann and Taylor 1989). These, in turn are likely a manifestation are local (pedon-scale) variations in soil hydrology.

Carbonate and Sulfate Soil Chemistry All Vertisols in the climosequence, even the higher-MAP League and Lake Charles soils, contain carbonate (calcite) in varying amounts, but only the lower-MAP Victoria soils contain calcium sulfate (gypsum) (Figure 33). The depth distribution of CaCO3equiv effectively differentiates between higher-MAP League and Lake Charles soils and lower-MAP Laewest and Victoria soils (Figure 33A, B). The higher-MAP soils are essentially leached of carbonate to an effective depth of 100 to 150 cm, and free carbonate is present in the soils at progressively shallower depths, and in higher concentrations, with decreasing MAP. Stiles et al. (2001) previously noted a linear relationship between MAP and depth to pedogenic carbonate-enriched horizons (DCH) for Texas Vertisol climosequence ML pedons: MAP = 303.82 + 6.53 DCH (r2 = 0.96, P < 0.005). The

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robust nature of this relationship contrasts with the poorer (but still statistically significant) general fit of DCH and MAP of Retallack (1994), which was based on a compilation of data from Inceptisols, Aridisols, Mollisols, and Alfisols. It also contrasts with the very poor fit of DCH and MAP obtained by Royer (1999) that was based on an even larger USDA soils database that probably included too wide a spectrum of soil textures and ages to ensure statistical significance (Retallack 2000). DCH should be an effective MAP proxy in paleoVertisols, assuming that one can verify that there has been minimal erosional truncation and burial compaction (cf. Caudill et al. 1996, 1997). The abundance and depth distribution of S (assuming that it all resides within gypsum) also effectively distinguishes between higher-MAP League, Lake Charles, and Laewest soils, which contain little or no measurable S, and lower-MAP Victoria soils, which contain abundant S (Figure 33D). S is effectively moved deeper into soil profiles than is CaCO3 because of the higher solubility of gypsum relative to calcite (Doner and Lynn 1989).

Other Exchangeable Base Cations The abundances and depth distributions of Naacet, Kacet, and Mgacet effectively separate higher-MAP League and Lake Charles soils, intermediate-MAP Laewest soils, and lower-MAP Victoria soils (Figure 34, Figure 35, Figure 36). Reactive Na and K are generally present in higher concentrations and closer to the soil surfaces in the lower-MAP soils, and generally decrease with increasing MAP because of removal by leaching under higher-MAP conditions (Figure 34A, Figure 35A). Mgacet is one exception to this pattern because all three Lake Charles pedons (LAC 201, 157, and 481) and one Laewest pedon (LAW 239) have Mgacet concentrations that are substantially higher than the other higher-MAP and lower-MAP soils, which overlap substantially in their Mgacet concentrations (Figure 36A). The cause for this relationship between Mgacet and MAP is unclear, but it might relate to proximity to the Brazos River drainage basin and subtle differences in parent material or source area, such as were previously discussed in the context of variations in total Fe analyses (Figure 32B). Because of the positive covariation between Naacet, Kacet, and Mgacet and total Na, K, and Mg (measured as Na2O, K2O, and MgO, respectively, by XRF; Figure 34B, Figure 35B, Figure 36A), formulation of the geochemical MAP proxy CIA-K, as proposed by Sheldon et al. (2002), appears appropriate for testing on the Texas Vertisol climosequence. The excellent fit (r2 = 0.82) for estimated MAP vs. measured MAP for the ML pedons (Figure 37A), as compared with the poor fit of these same two parameters for MH pedons (Figure 37B), is consistent with results presented by Stiles (2001) and Stiles et al. (2003b) for mass-balance and total-mass-flux calculations for the Texas Vertisol climosequence. The apparent offset of 100-150 mm/yr between the measured MAP and the MAP predicted using CIA-K suggests that the CIA-K paleoprecipitation proxy underestimates, by 20-30%, the actual measured MAP (Figure 37A). Although our Kacet and wt% K2O data for the climosequence suggest that wt% K2O should be included in the CIA climofunction (see Figure 35A, B), Sheldon et al. (2002) excluded K2O from the climofunction because illitization of smectites, which is a common diagenetic alteration of paleosols that causes them to behave chemically as K “sponges”, negates its use for MAP estimation of paleosols. Mora and Driese (1999), Driese et al. (2000), and Driese et al. (2003) recently documented elevated K2O in paleoVertisols in Upper Mississippian paleoVertisols in Tennessee, verifying that elevated concentrations of K2O are prevalent in Paleozoic paleoVertisols. Therefore, it is appropriate to exclude K2O from MAP climofunctions applied to paleoVertisols.

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To further test the robustness of the CIA-K climofunction equation we used bulk XRF chemistry of Upper Mississippian Pennington Formation paleosols exposed at Pound Gap, Kentucky (Greb 1998; Greb and Caudill 1998), which predicted a MAP pattern characterized by wetter conditions over time (about 500 mm/yr!), in agreement with qualitative predictions made by the paleoclimate model of Cecil (1990) of increasing wetness approaching the Mississippian-Pennsylvanian boundary in the Appalachian basin (Figure 37). The change from lower (740-866 mm) to higher (1100-1280 mm) MAP, over a time interval estimated to be no more than 1-2 million years (Harland et al. 1989), is also consistent with the morphological changes in the paleoVertisols; the lower paleosols are reddish-gray and generally higher chroma, and have carbonate concentrations, whereas the upper paleosols are lower chroma, lack carbonate concentrations, and are strongly leached of Fe. These morphologic differences collectively suggest that the lower paleosols (with lower MAP estimates) were formed in a drier climate and were less leached and more freely drained, whereas the upper paleosols (with higher MAP estimates) were wetter, less leached, and more poorly drained (Jacob et al. 1997; Retallack 2001; Vepraskas 1994, 2001).

DISCUSSION A valid question that ought to be posed related to this study is, namely, how can a geoscientist relate climatically dependent variations in wet soil chemistry for interpreting paleoclimates of paleosols preserved in the geologic record? After all, these solution-based analytical procedures for soils cannot be appropriately applied to lithified paleosols. Indeed, much of the controversy regarding direct application of USDA Soil Taxonomy (Soil Survey Staff 1998) to paleosol nomenclature arises largely because the physical and chemical characterization data necessary for soil taxonomy are not measurable from lithified paleosols (Retallack 2001). Bulk (or total) soil chemistry, to our knowledge, is the only chemical analysis that is directly interchangeable between soils and paleosols. However, diagenesis is a potential mechanism for blurring, or even erasing, primary pedogenic patterns of bulk chemistry (Retallack 1991; Retallack 2001). Fortunately, in comparative studies of modern and ancient (Mississippian) Vertisols, Driese et al. (2000) and Driese et al. (2003) found that with the exception of K2O many pedochemical patterns are retained in diagenetically modified paleosols, and they postulated that it is possible that paleoVertisols behave as nearly closed geochemical systems during diagenesis because of their high clay content and low permeabilities, and thus it is reasonable to use bulk geochemistry of paleoVertisols for interpreting pedogenic processes and paleoclimate. Alkali, alkaline earth, and redox-sensitive elements are appropriate choices for tracking variations in soil moisture and hydrology related to variable MAP conditions, because of their sensitivity to leaching and removal (Na, K, Ca, Mg) by soil water, or increased mobility and redistribution due to changes in redox conditions (Fe). An additional question concerns effects of climate changes operating during pedogenesis; the probable ages (35,000 to 40,000 yr B.P.) of the soils constituting the climosequence age span the last Pleistocene (Wisconsinan) glacial maximum and thus formed during a time of changing climate. So are we certain that the wet chemistry and bulk geochemistry of the Vertisols record only the current climate conditions, and are not a composite overprinting of both past and current climate? We cannot answer this question with certainty, although stable-isotope measurements from soil organic matter and soil carbonates from this same Vertisol climosequence indicate that: (1) carbon isotope values of both soil organic matter and carbonates track the inferred climate and ecosystem changes from late Pleistocene (cooler, wetter) to mid-Holocene (warmer, drier) to current late Holocene conditions rather faithfully, in a deeper to shallower vertical transect within each pedon, and (2) oxygen isotope values of soil

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carbonates are all reset to values representing equilibrium exchange with modern soil water (Miller 2000). Thus there is evidence for both preservation (�13C) and resetting (�18O) of late Pleistocene to Holocene climate signals, depending upon the chemical proxy examined. Because of the robustness of the geochemical proxy for climate (CIA-K) proposed by Sheldon et al. (2002) and developed from a wide variety of soil types and ages, we hypothesize that it is reasonable to compare, as we have done here, patterns of variations in solution-based chemistry in modern Vertisols to those whole-rock geochemical patterns measured in paleoVertisols and to assume that they reflect principally the later (or last) climate conditions during pedogenesis. Indeed, the wet chemistry and bulk chemistry approaches appear to provide approximately the same information on climate, thus verifying the effectiveness of the bulk chemistry approaches for studying and interpreting lithified paleosols, and modern soils can serve as a valuable guide for determining which suites of MAP-sensitive elements should be examined in paleosols for interpreting paleoclimate and especially paleo-MAP.

CONCLUSIONS The results of this study indicate that there are regional variations in soil chemistry in microlow pedons of a Vertisol climosequence sampled across the Texas Coast Prairie. Variations in soil chemistry related to varying MAP are readily apparent (Figures 31-37; Table 25). Non-uniform distributions of Fe, carbonate, S, and exchangeable base cations provide chemical discrimination across the climosequence in response to changes in intensity of wetting and drying cycles and chemical leaching. Higher-MAP Vertisols are characterized by higher Fedith, Feoxal, and total Fe, lower CaCO3equiv, none or minimal total S, and lower concentrations of Naacet and Kacet. The lower-MAP Vertisols have lower Fedith, Feoxal, and total Fe, higher CaCO3equiv, significant total S, and higher concentrations of Naacet and Kacet, as compared with the higher-MAP Vertisols. The total element (geological) analogs to these wet-chemical (pedological) measures provide geologists with whole-soil (or whole-rock, for paleosols) approximations; as an example, the chemical index of alteration minus potash (CIA-K) of Sheldon et al. (2002) provides significant prediction of measured MAP for the Texas Vertisol ML pedons with r2 = 0.82. The CIA-K climofunction also predicts a decrease in MAP of about 500 mm for an Upper Mississippian succession of paleoVertisols in the Pennington Formation at Pound Gap, Kentucky, which is consistent with previously published paleoclimate models that predicted an increase in MAP from the Mississippian into the Pennsylvanian in the Appalachian basin region of the eastern US based on coal thicknesses and paleosol distributions (e.g., Cecil 1990). Finally, previous geochemical studies have suggested that Vertisols are unusual in terms of their high degree of retention of primary (pedogenic) chemical characteristics, in spite of burial diagenetic alteration (Driese et al. 2000; Driese et al. 2003), thus there are many opportunities available to use the geochemistry of paleoVertisols to estimate MAP of paleoenvironments. This demonstrates the strength of an integrated approach to interpreting paleosols using modern soil analogs, and how combining the expertises of both geologists and soil scientists towards a common goal can yield insights useful for both fields. The National Soils Database maintained by the USDA-Natural Resources Conservation Service (NRCS) offers a wealth of soil characterization currently underutilized, but potentially very useful to geologists.

FUTURE RESEARCH ON PRE-QUATERNARY PALEOSOLS Study of pre-Quaternary paleosols appears to be heading in many future directions. One important research area involves studies of soil chronosequences (a suite of related soils in which

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all soil-forming factors are held constant except for the time duration of pedogenesis) in order to interpret the time significance of paleosols in the geologic record (Stiles et al., 2003a, b). Because paleosols represent unconformities within otherwise conformable stratigraphic successions, the ability to resolve time in paleosols is extremely important in terms of interpreting earth history. U-Pb age-dating of pedogenic carbonates offers a promise of improved chronology of pre-Quaternary paleosols, whose ages place them beyond the limits of C-14 or other dating methods commonly used for Quaternary paleosols. Applications of paleosol research to interpretations of sequence stratigraphy will help to connect time and sea level-base level relationships between marine and terrestrial stratigraphic sections. Careful documentation of continental traces of invertebrate animals (paleoichnological studies), especially those relating soil animals and their relationship to soil forming-processes in the past, is yet another area that is currently developing.

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