EARLY MIOCENE VEGETATION RECONSTRUCTION USING BULK ORGANIC MATTER AND PEDOGENIC CARBONATE ISOTOPE ANALYSIS FROM MORUOROT, WEST TURKANA, KENYA

The Early Miocene is a critical interval for understanding environments associated with early apes and their floral communities. This study focuses on reconstructing vegetation using stable carbon isotopes (ẟ¹³C) of bulk organic carbon and pedogenic carbonate from paleosols preserved in the Lothidok Formation at the Moruorot site complex in West Turkana, Kenya. Prior analyses of bulk organic and herbivore tooth enamel ẟ¹³C were consistent with exclusively C₃ plants being present in the Lothidok Formation; however, a larger number and variety of paleosol samples have recently been collected and can potentially offer more insight into paleovegetation at Moruorot. Paleosol samples were powdered and homogenized with a mortar and pestle, decarbonated, and analyzed on an EA-IRMS to measure bulk organic carbon ẟ¹³C values. Samples from four paleosols were analyzed in triplicate and span the Moruorot, Kalodirr, and Naserte Members of the Lothidok Formation. Initial bulk organic ẟ¹³C results have an average of –27 ‰ and standard deviation of ~0.2 ‰ per paleosol. Analytical precision of the analyses was within 0.07 ‰ based on repeat analysis of an acetanilide standard (-30.6 ‰). Our isotope analyses suggest that the vegetation at Moruorot was exclusively C₃, and there is no evidence for C₄ plants in the bulk organic pilot samples, in agreement with prior multi-proxy studies. However, pedogenic carbonates were recently recovered from at least one paleosol, which will provide an independent substrate to test for C₄ plant presence in West Turkana during the Early Miocene. These carbonates will be critically evaluated using thin sections prior to microdrilling to produce powders for ẟ¹³C analysis. Additional bulk organic ẟ¹³C analysis will include a total of 32 paleosol samples analyzed in triplicate. Overall, our pilot data suggests that there were exclusively C₃ plants at the Moruorot site complex during the Early Miocene. We will further test the bulk organic matter and pedogenic carbonates using additional samples and independent proxies to obtain a more certain range of ẟ¹³C values and clearer interpretation of paleovegetation at the site.