HIGH SPATIAL AND TEMPORAL RESOLUTION PALEOENVIRONMENTAL RECORDS FROM PALEOSOLS OF KENYA AND ETHIOPIA

In order to elucidate the response of hominin-bearing ecosystems to global climate, there is a need for increased resolution of regional paleoenvironmental data sets. Paleosols provide one of the most temporally and geographically resolved records of paleoenvironmental variability, the foundation for interpretations of changing fauna, including hominins. Many high temporal resolution time series of paleosol stable isotopes have been produced from hominin-bearing basins of East Africa, such as Olduvai, Baringo, and Turkana, most of which show a trend of increasing C₄ biomass from 4 Ma to present. The addition of new stable carbon isotope measurements and paleoprecipitation estimates from paleosols of the Plio-Pleistocene Nachukui Formation of the Turkana Basin, Kenya, makes this one of the most complete and highest resolution basin-scale records of paleoenvironmental change. A general trend of concurrently increasing C₄ biomass and aridity is marked by several periods of heightened aridity at 3.58-3.35, 2.52-2 and 1.81-1.58 Ma, during which not only the running mean, but variance of d¹³C and paleoaridity estimates increase. An increase in C₄ biomass during these periods not only increases the proportion of open habitats, but increases the ecological neg-entropy, a state function describing the heterogeneity of an ecosystem. New paleosol isotope data from the Busidima-Dikika region of the Afar basin in Ethiopia similarly show the classic trend of increasing d¹³C over the past 3.5 Ma. However, the focus of current research in this area is on documenting changes in ecological neg-entropy over time, a task that requires extensive collections of data. Current results support the variability selection hypothesis that early hominins evolved in changing mosaics of savannas, and reveal the local response of synchronic and diachronic habitat variability to climatic instability, suggesting that these factors drove the evolution of bovids and early hominins.