USING A MULTI-PROXY APPROACH TO REFINING PALEOENVIRONMENTAL AND PALEOCLIMATIC RECONSTRUCTIONS OF THE HOLOCENE AT LAKE TURKANA, KENYA

The Turkana Basin preserves 4 Ma of sedimentary record that shows oscillations from freshwater lacustrine environments to throughflowing fluvial ones due to the combine effects of climate and tectonics. In addition to the hominin-rich Plio-Pleistocene record, there is an equally robust Holocene one, spanning a highstand event from 11,000-5,000 yr BP. At this time Lake Turkana reached a maximum level ~80 m higher than today and periodically overflowed into the Nile drainage basin through a spillway in the northwest. Extensive Holocene-aged lacustrine deposits of the Galana Boi Formation remain around the shores of modern Lake Turkana. The primary focus of this study was on this record preserved at Kabua Gorge, near Kalakol, Kenya. From outcrops, this study a) compiled seven sections to generate a composite lithostratigraphic section for the Galana Boi for West Turkana. This section compliments work from Koobi Fora to the east and the Kibish region to the north. b) Sequence stratigraphic principles were applied to assist in reconstructing changes in Holocene lake levels at Kabua Gorge. c) Within lacustrine intervals, individual lamination thicknesses were measured from outcrops to look for patterns with the potential to increase the understanding of annual to decadal controls on deposition. d) New AMS radiocarbon dates on charcoal and bulk ostracod samples were added to this sequence to refine the age model and to document how sedimentation rates fluctuated with time. e) Finally, regularly sampled bulk sediments from the lacustrine phases were picked for ostracods to study both assemblage diversity and total abundance. Ostracods have been shown to be a sensitive to changing hydrological conditions so by coupling with the other proxies, it is possible to trace the paleoecological impacts of regressive and transgressive events. Recent work has resulted in Holocene lake level reconstructions based off of shoreline elevations. However, this method is limited as there is still a great deal of uncertainty surrounding regressive events within the broader highstand. This study at Kabua Gorge provides another means of determining paleohydrologic conditions and through them, assists in refining paleoclimate and paleoenvironmental reconstructions.