Soils and landscape volution of eolian plains: the Southern High Plains of Texas and New Mexico

Sheets of eolian sediment cover many areas of the earth's urface, sand seas, dune fields, and loess sheets being the best known examples of such features. Less well known are deposits of sandy, eolian sediment forming extensive plains. An excellent example of such a region is the semi-arid Southern High Plains (northwest Texas and eastern New Mexico). The level landscape of the area was created by depositon of multiple, extensive (, ~ 80,000 km 2) sheets of eolian sediment (Biackwater Draw Formation) over the past 1.4+ Ma. This deposit grades from sandy (southwest) o silty and clayey (northeast) and is up to 27 m thick. Surface soils (at least 30,000 and possibly 120,000 years old) are well developed (5YR hues, agrillic horizons, 1-2 m thick with prismatic structure, Stage II-III calcic horizons) and are generally Paleus-tolls and Paleustalfs, with some Paleargids and Haplargids. Morphologic variation isdue mainly to textural variation of the eolian parent material, although locally thickness of the parent material nd wind erosion and cumulization are impor-tant factors, and locally slight variation in effective precipitation may be significant. The Blackwater Draw Formation contains as many as six well-developed buried soils, each formed in individual layers of eolian sediment, similar to or more strongly expressed (2.SYR hues, higher illuvial clay content) than the regional surface soils. The presence of the buried soils indicates that sedimentation was episodic and separated by long periods of relative landscape stability. Eolian pro-cesses also appear to have been important during the periods of stability and pedogenesis by providing clayey, calcareous dust hat was added to the soil, promoting formation of the argillic and calcic horizons. The sedimentologic and pedologi