PRELIMINARY TOC/TIC AND GEOPHYSICAL DATA FROM TWO HSPDP DRILL CORE SITES IN KENYA, WITH IMPLICATIONS FOR PLIOCENE HOMININ PALEOENVIRONMENTS

The Hominin Sites and Paleolakes Drilling Project (HSPDP) is an international collaboration whose goal is to collect drill cores from paleolake beds in an attempt to improve our understanding of the paleoclimatic and paleoenvironmental context of human origins in Africa during the Plio-Pleistocene. Using cores collected on the west side of Lake Turkana, and in the Tugen Hills/ Baringo Basin of Kenya we studied the total organic carbon (TOC) and inorganic carbon content (TIC) utilizing the Loss On Ignition method. These data, in combination with lithostratigraphic and geophysical log data, provide critical information about paleolake and lake margin environmental conditions over the cored intervals.

Cores were sampled every 64cm throughout both cores to a depth of 215m for the West Turkana site (covering the interval ~2.0-1.45Ma) and 227m for the Tugen Hills site (~3.45-2.5Ma). In the West Turkana (WTK) core we observe an overall upcore trend of decreasing TOC levels and variable TIC levels. This suggests a transition from a deeper lacustrine phase (TOC-rich, green-gray fossiliferous mudstones) to a regressive, shallow lacustrine interval (TOC poor, brown mudstone, siltstone and sandstone with CaCO₃ nodule bearing paleosols). High TIC throughout the lacustrine interval suggests moderately high pH conditions throughout the WTK record. In contrast, the Tugen Hills (BTB) core shows highly variable TOC values, with TOC concentrations in the upper part of the core inversely associated with magnetic susceptibility and subaerial/terrigenous deposits and positively correlated with lacustrine diatomites Peak levels in TIC in this core are correlated with calcite nodules and a lack of organic matter in that area of the core, with low values in lacustrine intervals, suggesting circum-neutral pH lake conditions. TOC variability follows previously documented precessional scale variability in the upper part of the BTB core, suggesting it is a useful tool for tracking climate-driven lake fluctuations in lacustrine intervals lacking distinctive diatomites.