GEOCHEMICAL CHARACTERIZATION OF PLIO-PLEISTOCENE PALEOSOLS IN THE BTB-13 CORE BARINGO, KENYA

Pliocene to early Pleistocene hominin fossil sites in eastern Africa typically lack quantitative paleoclimate reconstructions. Developing new quantitative estimates of paleoprecipitation using paleosols will facilitate a better understanding of paleoenvironments, paleoclimates, and their connections to faunal change in this critical time and place. This study focuses on paleoclimate reconstruction and paleosol analysis using records from the Baringo-Tugen Hills-Barsemoi drill core (BTB-13), located within the Baringo Basin of the Central Kenyan Rift spanning 3.29-2.56 Ma. Our ongoing research includes X-ray fluorescence and loss-on-ignition analysis of 97 paleosol samples from across the BTB-13 core. Samples were oven dried at 105-110°C for a minimum of 2 hours and then ground to a fine powder using a mortar and pestle. The powders were then fused into glass beads using a 9:1 flux to sample ratio in a Katanax 300 furnace operated at 1050 °C. Sample splits of oven-dry powders were placed in a Ney 525 muffle furnace at 950°C for 105 minutes to measure loss of ignition (LOI). Initial LOI analyses range from 5.4-14.3%, consistent with clay-rich, calcic paleosols. A total of 69 out of 97 fused beads were analyzed for major and minor elemental oxides on a 1kW Malvern PANalytical Zetium X-ray fluorescence spectrometer and paired with LOI measurements. The results were used to plot elemental trends, weathering indices, and mean annual precipitation (MAP) over time to indicate important intervals of change. For the weathering indices CIA and MIA were calculated and to estimate past rainfall RF-MAP and PPM_1.0 proxies were used. Elevated Fe and Al concentrations in the 3.09-2.97 Ma interval potentially reflect more intense weathering under higher rainfall. Overall, weathering index values and estimated MAP decrease from the Pliocene through early Pleistocene in the core, corroborating published paleovegetation trends. Future work includes completing XRF and LOI analysis through the bottom of the core to more fully sample the Mid-Piacenzian Warm Period.