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Genesis and Properties of Paleustalfs of North Central Texas: Morphological, Physical, and Chemical Properties¹

ABSTRACT

The Windthorst and Chaney soils are characterized physically by relatively sandy surfaces, well-developed argillic horizons that have a clay maximum in the upper Bt, and substrata that are dominated by sandstone. Chemically, they are characterized by a moderately acid to neutral reaction and an exchangeable cation suite dominated by Ca and Mg. A genetic relationship between these soils and the sandstone substrata is suggested by transect studies, morphological data, and particlesize data. However, particle-size data also strongly indicate a substantial influence by parent materials other than sandstone. Field relationships, namely a marked lateral change in soil texture and other properties near the limestone-sandstone contact, and evidence of downslope pedisediment transport of limestone residuum cast doubt on the importance of eolian additions as a primary pedogenic process responsible for observed textural differentiation. Though major eolian additions appear improbable, localized wind-reworking of surface horizons of these soils has likely been significant. Shale and siltstone interstratified with sandstone have contributed to the clay content of some pedons, but interbedded argillaceous sediments are not prerequisite for the formation of these soils. However, gradual sedimentary grading from sandstone to finer-textured strata during bedrock formation cannot be ruled out as possible clay sources for the argillic horizon. Microfabric analyses verify the concurrence between textural clay maxima and strongly developed argillic horizons. Between 9 and 15% of the cross-sectional area of upper Bt horizons is comprised of moderately to strongly oriented illuvial void and grain ferriargillans. Abundance and the illuviated character of argillans decrease with depth to Cr horizons which have granular fabrics with thin, embedded, and free-grain argillans inherited during sandstone formation.

¹ Contribution from the Soil and Crop Sciences Dep., Texas Agric. Exp. Stn., State Project no. H-6222. Presented before Div. S-5, Soil Sci. Soc. of Am., Ft. Collins, Colo., 7 Aug. 1979.

² Professor, Texas Agric. Exp. Stn. & Dep. of Agriculture, Tarleton State Univ., Stephenville; Professor, Texas Agric. Exp. Stn., College Station; Agronomist, USDA-SCS, Terrell, and Research Associate, Texas Agric. Exp. Stn., College Station. Mr. Moore was formerly a Soil Scientist, USDA-SCS, Stephenville.

Received for publication August 24, 1981. Accepted for publication January 5, 1983.