PALEOCLIMATE AND PALEOENVIRONMENTAL FORCING ON EARLY HUMANS: LOI ANALYSIS OF THREE HSPDP DRILL CORE SITES IN KENYA AND ETHIOPIA

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 (northern Kenya-WTK), and from Tugen Hills/ Baringo Basin of central Kenya (BTB), and the northern Awash region of Ethiopia (NAO), we analyzed total organic carbon (TOC) and inorganic carbon (TIC) utilizing the Loss On Ignition (LOI) method. Multi- sensor core logging (MSCL), and lithostratigraphy provide a context for understanding the controls on our TOC/TIC records, and when combined, will ultimately better our understanding of the paleoenvironmental and paleoclimate history within each region.

Cores were sampled every 64cm to a depth of 215m for WTK (covering the interval ~2.0-1.4Ma), to 227m for the BTB site(~3.4-2.5Ma) and to 187m for NAO (~3.3-2.9Ma). In the WTK core we observe a large decrease in TOC from 139m to 0m correlating with a large increase in magnetic susceptibility (MS), indicative of an increasing supply of terrigenous sediments. High TIC throughout the lacustrine interval results from abundant shelly material deposited under above neutral pH conditions. Current data suggest a transition from a generally deeper lacustrine phase to a regressive shallow interval as the region became more arid. The BTB LOI record shows high and invariant MS and gamma density values observed in the lower portion of the core, indicative of a terrestrially dominated system before transitioning into a more variable system with higher MS values and lower overall gamma density. Variability with LOI in the top half of the core correlated with insolation and several diatomite intervals, suggesting an influence of astronomical forcing (Kingston et al, 2007). The NAO LOI data shows high invariable TOC with low TIC suggesting a persistent standing lake from 173MBS to 138MBS. While the top third of the core shows increased variability in variable TOC/TIC, indicating floodplains. Both BTB and NAO cores show increased variability in MSCL and LOI after ~3Ma, suggesting timing of these events may be related both to local factors and increased aridity in the region.