SOIL CARBONATE CLUMPED ISOTOPE TEMPERATURES AND PALEOENVIRONMENTAL INTERPRETATIONS FROM THE MIOCENE OF THE TURKANA BASIN, EAST AFRICA

Miocene localities in the Turkana Basin are known for contributions to the primate fossil record, and for preservation of the ecosystems that directly preceded the rise of modern African megafauna. While terrestrial climate records from the Plio-Pleistocene in East Africa are well resolved, data from the Miocene are comparatively sparse. The early Miocene (23-16 Ma) in particular provides an opportunity for better understanding the connections between basin-scale paleoecology, continental rifting, and regional changes in hydroclimate. Carbon, oxygen, and clumped isotope measurements of soil carbonates, including CaCO₃ nodules and rhizoliths, enable interpretations of surface temperature, vegetation cover type, and water source and evaporative regime for soils that develop in arid settings. We present new measurements from Loperot (~17 Ma), located at the southwest corner of the modern Turkana Basin. These data extend a Middle and Late Miocene data set also from the Turkana Basin, for which the mean clumped isotope temperature is 35 ± 5 °C for soil carbonate nodules, rhizoliths, and other pedogenic carbonates and calculated soil water δ¹⁸O is 0.15 ± 1.7 ‰ VSMOW. All Miocene paleotemperatures appear to overlap with modern, near surface soil temperature measurements from 2019–2021. We also present soil carbonate clumped isotope measurements along with stratigraphic context from two other middle Miocene sites, Buluk and Locherangan — the data thus far are consistent with paleotemperatures similar to those in the modern Turkana Basin, suggesting that these conditions have persisted since the early Miocene, despite the ecosystem changes accompanying the expansion of C4 grassland dominated savannahs over the same time interval.