CLIMATIC SIGNALS FROM LOESS-SOIL SEQUENCES IN THE CENTRAL GREAT-PLAINS, USA

Late Quaternary eolian deposits and buried soils in the central Great Plains are interpreted to reflect the fluctuation of climatic conditions under which they formed. The Loveland Loess was deposited approximately between 500 and 100 ka. Within the loess are four zones of pedogenic carbonate accumulation: after 416 +/- 35 ka; before 260 +/- 25 ka; around 193 +/- 22 ka; and before 92 +/- 7.0 ka. The pedogenic carbonate zones were probably formed under warm and dry conditions. The moderately weathered Barton sand at the Barton section and the equivalent Sandy Silt II at other sections, deposited between 92 +/- 7.0 and 69 +/- 6.4 ka, suggest windy, probably warm, and fluctuating moisture conditions. A reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very low rate of loess deposition. Overlying the reddish pedocomplex is the Sandy Silt I, probably a stratigraphic equivalent to the Roxana Silt dated at 40-30 ka in the Central Lowlands. The Gilman Canyon Formation (35-20 ka), a thick cumulic loessial and organic-matter-rich pedocomplex, developed under relatively moist and probably cool conditions. The Peoria Loess was deposited at a very rapid rate under dry and cold conditions. The Brady Soil (10.5-8.5 ka) was formed under relatively warm and moist conditions. The poorly weathered Bignell Loess was deposited during the warm and dry Altithermal Period (9-5 ka).