USING PALEOSOLS TO RECONSTRUCT THE PALEOCLIMATE OF LATE PLEISTOCENE ARCHAEOLOGICAL SITES IN THE LAKE VICTORIA BASIN, KENYA

Lake Victoria, the largest lake in Africa by surface area, has varied in size through time due to climate change, chiefly changes in precipitation and hydrologic input. This study uses paleopedology to reconstruct the environment of this area during the Late Pleistocene, when modern humans dispersed across and out of Africa. Although this time is a critical interval in the behavioral evolution of Homo sapiens, data are sparse prior to the Last Glacial Maximum (LGM) from equatorial Africa. To better understand the role climate might have played in human evolution preceding the LGM, we studied sites located near Karungu, Kenya along the eastern margin of Lake Victoria. We measured, described, and sampled a series of three paleosols from Kisaaka, one of the major artifact- and fossil-bearing sites near Karungu. The oldest is a paleo-Vertisol, recognized by its pedogenic slickensides, wedge peds and gilgai topography that indicates precipitation seasonality. The basal paleo-Vertisol is overlain by two tuffaceous paleo-Inceptisols that are very weakly developed with few pedogenic structures except for root traces. Layers of tuff separate the two paleosols, and pedogenesis may have been interrupted by volcanic eruptions. Bulk and clay mineralogy were analyzed using X-ray Diffraction. Preliminary results indicate that smectite dominates all of the paleosols. Bulk geochemical analyses of major, minor, and trace elements, and the CALMAG and CIA-K proxies were used to estimate mean annual precipitation (MAP). MAP estimates of the Kisaaka paleosols range from 700-900 mm/yr, significantly less than modern MAP of ~1400 mm/yr. Both field observations of vertic features and MAP proxies suggest a paleoenvironment and paleoclimate significantly drier than today, consistent with the fossil fauna, which is dominated by alcelaphine antelopes and zebras indicative of semi-arid grasslands. Paleoenvironmental and paleoclimatic data obtained from Kisaaka paleosols, combined with paleontological evidence from Karungu, suggest a seasonally dry, open grassland environment for the Lake Victoria region during the Late Pleistocene that is vastly different from the closed bushland and forest habitats present today.