Reconstruction of the Pleistocene Environment and Climate of the Olorgesailie Basin

Abstract

The Smithsonian’s Human Origins Program team recovered drill core from the Olorgesailie paleolake in the East African Rift that is likely to contain records of environmental change relevant to hominin evolution. Archeological sites in the Olorgesailie basin show significant innovations in tool use technologies during the mid-late Pleistocene. Core from the Olorgesailie/Koora region has been subject to initial analyses, including XRF scanning. This study focuses on a 10 meter laminated sequence of this core that spans between 100 and 133 meters below the surface. This sequence was not deposited continuously and is interrupted by multiple unconformities as well as sections of tephra and gravels. Characterization of the laminations and banding throughout the 10 meters of core, including characterization of fine (~1mm) laminations in a 1 meter section, and understanding their link to the regional environment, will aid in reconstructing the history of sediment deposition at this location in response to sub-millennial timescale environmental change. XRF profiles of elemental concentrations across the laminated core section reveal quasi-cyclic variability in multiple environmental variables that represent various aspects of the lake catchment system and at several frequencies. For example, high Si:K and Ca content are interpreted to represent increased diatom productivity and autochthonous carbonate precipitation in the lake, respectively, and vice versa. Microfacies analyses of thin sections and sediment slabs provide a qualitative assessment of dark and light laminae and aid in assessing the relationship between elemental content, minerals, and lacustrine processes. Spectral wavelet analyses were conducted on data from the finely laminated Olorgesailie sediment core and on both the modern and Last Glacial Maximum sedimentary deposits from Lake Challa (Wolff 2011), which is located 240 km from the Olorgesailie paleolake and serves as a modern analogue for comparison. Through this comparative analysis, we interpret the paleoenvironmental results from the Olorgesailie sequence in the context of the Pleistocene epoch.