Characteristics of Buried Alluvial Paleosols Dating to the Pleistocene-Holocene Transition in Semi-Arid Western Kansas.

        A systematic study of late Quaternary landscape evolution in stream valleys of the semi-arid High Plains of western Kansas documented widespread, deeply buried paleosols that formed in terrace fills of large streams (> 5th order), in alluvial fans, and in draws. Radiocarbon ages indicate that most large streams were characterized by slow aggradation accompanied by cumulic soil development from ca. 11,500 to 10,000 ¹⁴C yr B.P. In the valleys of some large streams, these processes continued into the early Holocene. The soil-stratigraphic record in the draws of western Kansas indicates slow aggradation punctuated by episodes of landscape stability and pedogenesis beginning as early as ca. 13,300 ¹⁴C yr B.P. and spanning the Pleistocene-Holocene boundary. The development record of alluvial fans in western Kansas is similar to the record in the draws; slow aggradation was punctuated by multiple episodes of soil development between ca. 13,000 and 9,000 ¹⁴C yr B.P.

        Based on the paleosol record and a large suite of radiocarbon ages, alluvial settings in the valleys of high-order streams in the study area were relatively stable during the Pleistocene-Holocene transition. No evidence exists for high-magnitude floods that would have rapidly deposited large volumes of fine-grained sediment on floodplains during this period. Instead, small quantities of alluvium were gradually deposited, allowing soil development to keep pace with alluviation. The result was "upbuilding" or cumulization of soils, a process that also occurred in draws and on alluvial fans during this period.

        In the valleys of a few streams, cumulization during the Pleistocene-Holocene transition resulted in the development of a single thick, organic-rich soil. In most steam valleys, however, pedocomplexes consisting of two or more soils with overthickened horizons formed between ca. 11,500 and 9,000 ¹⁴C yr B.P. These pedocomplexes are products of fluctuating rates of alluviation. Cumulization periodically slowed or completely ceased, resulting in the formation of discernable stable surfaces within the pedocomplexes.