LOESS ACCUMULATION AND SOIL FORMATION IN CENTRAL KANSAS, UNITED-STATES, DURING THE PAST 400,000 YEARS

Based on interpolation of thermoluminescence dates and the mean accumulation rate of 0.034 mm yr(-1), four cycles of pedogenic CaCO3 accumulation are found within the Loveland Loess: 415-325ka, 325-250ka, 250-195ka and 195-95 ka. The four CaCO3 peaks correspond chronologically to marine oxygen isotope stages 11, 9, 7 and 5, respectively. The early Wisconsin (95-70 ka) was characterized by sand dune activity. The reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation (0.016 mm yr(-1)). The Gilman Canyon pedocomplex, enriched in organic matter and dated at 35-20 ka, was formed under a strong physical weathering regime and a relatively high rate of silt accumulation (0.15 mm yr(-1)), indicating a windy, relatively moist, probably cool environment. It developed when the Laurentide ice sheet was advancing and dust content in Greenland ice core was low. The Peoria Loess was accumulated at a rate of 0.3 mm yr(-1) in central Kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the Greenland ice core was the highest. Even the warm substage around 13 ka has some corresponding evidence in the central Great Plains. The well-developed Brady Soil, dated at 10.5-8.5 ka, indicates that the early Holocene was the optimal time for soil development since 20 ka. The poorly weathered Bignell Loess might have been deposited during the Altithermal Period from 8.5 to 6 ka.