DETERMINING DEPOSITIONAL HETEROGENEITY THROUGH CLAY MINERALOGY AND PARTICLE SIZE ANALYSIS OF AN EARLY MIOCENE PALEO-FOREST PALEOSOL, HIWEGI FORMATION, RUSINGA ISLAND, KENYA

Understanding the selective pressures that helped drive early hominoid evolution requires an understanding of environmental dynamics and the habitats available to early Miocene primates. Fossil sites on Rusinga Island (Lake Victoria, Kenya) represent some of the best sites for understanding this relationship between environmental dynamics and hominoid evolution due to the quantity and quality of fossil specimens of early apes such as the catarrhines Proconsul and Dendropitchecus macenssi, preserved amongst evidence of the habitats in which they lived. While a significant amount of research has been focused on the paleontology of these primates, less work has been focused on the paleoenvironment, and the results of paleoenvironmental studies are contradictory. A recently discovered in situ fossil forest that stretches ~5km across 3 different fossil localities represents a unique opportunity to reconstruct the paleoenvironment in which early apes lived. This study examined clay mineralogy and grain size of paleosols at these three contemporaneous localities to determine if there were variations in paleoweathering and/or in depositional environment within and between sites in order to test for environmental variability across the landscape. X-ray diffraction (XRD) of oriented clay aggregates was performed to determine both temporal and spatial variations in clay mineralogy as a proxy for weathering. Clay mineral suites vary with paleosol depth, as expected for a soil profile, and are largely consistent spatially within and between localities. Particle size analyses conducted using a Mastersizer grain size analyzer were used as proxy for depositional energy. Grain size results indicate little variation with depth or between localities. These proxies suggest little variability in depositional energy or paleoweathering across the landscape. These results, coupled with our sedimentology and paleopedology data, suggest that during this particular interval of time the apes Dendropithecus and Proconsul most likely lived in a relatively uniformly forested environment.