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 that 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. Pedogenic carbonate nodules and rhizoliths were identified by thin section, powdered by drilling, then analyzed on an Isoprime Multiflow-IRMS to measure the inorganic carbon ẟ¹³C values. Most samples were analyzed in triplicate and span the Moruorot, Kalodirr, and Naserte Members of the Lothidok Formation. Bulk organic ẟ¹³C results have an average of -28.8‰ and standard deviation of 1.4‰ per paleosol. Analytical precision of the analyses was within 0.1‰ 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 samples, in agreement with prior multi-proxy studies. Pedogenic carbonates recently recovered from two paleosol profiles in the upper Moruorot Member provided an independent substrate to test for C₄ plant presence in West Tukana during the Early Miocene. Carbonate ẟ¹³C results have an average of -10.8‰ and standard deviation of 0.6‰ per sample, indicative of no C₄ biomass at the site. Overall, data suggests that there were exclusively C₃ plants in a forest biome at the Moruorot site complex during the Early Miocene.