PALEOCLIMATE AND PALEOENVIRONMENTAL RECONSTRUCTION OF THE EARLY MIOCENE TINDERET SITES IN WESTERN KENYA AND THEIR IMPLICATIONS FOR HOMINOID EVOLUTION

Early Miocene Tinderet sites in western Kenya preserve some the earliest occurrences of large bodied hominoids like Proconsul. The sites are considered to be contemporaneous in age between 19 – 20 Ma. Koru, Karputay and Songhor sites are geographically close (~26 km apart) but preserve different catarrhine fossil assemblages, with some species found in all sites while others found in one site. To better assess early hominoid and stem catarrhine habitat preferences, a detailed paleoenvironmental and paleoclimatic reconstruction was done for three of the Tinderet sites: Koru 16 and Koru 21 and Karputay New. Paleosol development shows similar characteristics at each of these sites. The Karputay stratigraphic section is ~28m thick, comprising of a conglomerate at the base of the section followed by alternating deposits of weathered ash and poorly developed paleosols (Inceptisols), which are overlain by a thick lahar flow at the top of the section. The stratigraphic section at Koru 16 is ~8m thick and comprised of alternating deposits of weathered ash, weakly-developed paleosols, and a well-developed paleosol with vertic features at the base of the section. Koru 21 section is ~7m thick, and contains poorly developed paleosols between lithified carbonatite ash deposits. The sediments in all sites contain relatively unweathered volcanic material indicating the sites were frequently disturbed by eruptions from the nearby Tinderet volcanic complex. Shrink-swell features in the paleosols suggest that moisture was seasonally available. In the middle of the stratigraphic sequence in Koru 16, there are abundant large drab-haloed root traces and casts of fossil branches, roots, and tree stumps. The close proximity of multiple stump casts of varying diameters within the same stratigraphic layer suggest this interval may have been forested. Taken together, our results suggest that the Karputay and Koru fossil sites sampled frequently disturbed landscape within a seasonally dry climate, and that differences in the hominoid assemblages between the sites may be related to differences in the environment and vegetation structure.