A PLIO-PLEISTOCENE DRILL CORE FROM THE BARINGO BASIN, CENTRAL KENYAN RIFT VALLEY

A 227 m drill core was collected from the Tugen Hills in the Baringo Basin as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP), an international collaboration aimed at collecting high-resolution records of paleoclimate and paleoenvironmental changes from East African Rift paleolake deposits. The ultimate goal of this research is to explore links between environmental change and early hominin evolutionary ecology. Single-crystal laser step-heating of K-feldspar phenocrysts from 34 different primary and reworked tuff units reveals that the uppermost part of the core is ~2.6 Ma and the deepest part is ~3.3 Ma, with further refinements of the core age progression are expected from correlation of tephra within the core to outcrop tuffs already dated nearby. The upper part of the core records a series of precessionally-driven lake cycles, documented by lacustrine diatomites and mudstones cycling with fluvial and alluvial coarse terrestrial sediments. Magnetic susceptibility, gamma density, color greyscale, and total inorganic/organic carbon content have been analyzed for this core and reveal variability in hydrologic patterns which correlate well with the lacustrine/terrestrial cycling observed in the upper portion of the core. In addition, time series analyses of the geophysical log and TOC/TIC data have been employed to identify cyclicities that may be related to specific external forcings, such as fluctuations in insolation or global climate events (e.g., onset of Northern Hemisphere glaciation). Data from the core have been correlated with outcrop sections developed in the Chemeron Formation that have yielded abundant vertebrate fossil assemblages, providing an opportunity to assess specific terrestrial community response to pervasive, short-term climatic change. Peak levels in TIC in this core are correlated with calcite nodules. Low TIC values in lacustrine intervals suggest circum-neutral pH lake conditions. TOC variability follows previously documented precessional scale variability in the upper part of core, suggesting it is a useful tool for tracking climate-driven lake fluctuations in intervals lacking diatomites. Overall, this core provides a unique opportunity to examine high-resolution terrestrial and lacustrine environmental proxies relevant to hominin evolution.