OSTRACOD ASSEMBLAGE ANALYSIS FOR PALEOENVIRONMENTAL RECONSTRUCTION FROM THE PLEISTOCENE TO HOLOCENE TURKWEL CLIFF, WEST TURKANA, KENYA

The African Humid Period (AHP) (~14-5 ka) represents a time of lake transgressions and regressions of up to ~100 m in the Turkana Basin of northwest Kenya. Because of the impact of these lake level fluctuations on the surrounding ecosystems, they had a significant effect on the cultures and locations of human populations living around the lake margin. We investigated how paleoenvironmental changes during the AHP affected the ostracod taxonomy and assemblage associations as recorded in sediments of the Galana Boi Formation (14 ka to recent) from the Turkwel Cliff, West Turkana, Kenya. The goals of this study were two-fold: 1) to compare ostracod assemblages of the Turkwel Cliff to those derived from Kabua Gorge outcrops ~ 40 km to the north, and 2) to quantitatively differentiate morphologies of juvenile ostracods of the genus Limnocythere. Nine sediment samples were processed for ostracods, which included identifying genera, imaging valves, and quantifying morphological differences. Ostracods were not abundant in the Turkwel Cliff section (average n=135) but preservation was relatively good. The assemblages were dominated by the genera Limnocythere, Darwinula, and Hemicypris. The Turkwel Cliff and Kabua Gorge have been correlated using AMS radiocarbon dates and both outcrops have a depositional hiatus which corresponds to the Younger Dryas (~11.5 ka). Despite this agreement in lake level histories, the two localities contain different ostracod assemblages. This difference is hypothesized to be a function of paleoenvironments, as the Turkwel Cliff is proximal to the Turkwel River which is a source of sediment to the basin, while Kabua Gorge is more distil from significant fluvial inputs. Limnocythere shape analysis quantitatively distinguished morphological differences that may be a result of sexual dimorphism or interspecies variability. Recognizing the degree of morphological difference is a crucial first step towards the goal of identifying fossil ostracods to the species level and ultimately tying these species to paleolimnological conditions. This study increases the understanding of the spatial paleoenvironmental variability, and thus resource availability, that human populations would have encountered along the dynamic margin of Lake Turkana during the AHP.