Regional Perspectives of Quaternary Soils and Sediments On the Kansas High Plains.

The High Plains of southwestern Kansas are characterized by loess, dunes, and sand sheets reflecting a complex soil-geomorphic history of eolian and alluvial processes from the late Pleistocene to the present.  Field and laboratory investigations included a reconnaissance of 119 sites, and detailed characterization, clay mineralogy and micromorphology of 23 sites.  Radiocarbon ages and δ¹³ values of bulk soil samples were obtained from paleosols at selected sites.  Stratigraphic, soil, and geomorphic relationships combined with radiocarbon dating indicate at least three surfaces: (1) a late Pleistocene alluvial plain modified by eolian processes including Peoria loess deposition, (2) a nearly level to undulating Holocene alluvial surface, and (3) recent eolian-modified terraces of the Cimarron River.  The late Pleistocene alluvial plain has been subjected to erosional processes and deposition of Peoria loess. Soils that formed in late Pleistocene loess exhibited a sufficient clay increase for an argillic horizon, and > 1% oriented clay, mostly stress features rather than illuviated. Our data indicate that the climate gradually changed from a cooler, moist environment in the late Pleistocene to a warmer, drier period with increased eolian activity in the early to middle Holocene.  A stable period from about 10,000 – 11,000 yr BP resulted in the formation of the Brady paleosol that often contains a weakly to moderately-developed argillic horizon.  This was followed by dune reactivation and brief soil-forming periods in the middle Holocene.  With the return of a drier climate about 5600 yr BP, dune sand and sand sheets covered the area south of the Cimarron River. Sand dunes and sheets adjacent to the Cimarron River have minimal soil development, which indicates periodic reactivation by fluvial and eolian processes < 1500 yr BP.