EARLY MIOCENE CLIMATE AND LANDSCAPE CHANGE INFERRED FROM PALEOSOLS AT LOPEROT, WEST TURKANA, KENYA

The climate and ecological context of catarrhine evolution during the early Miocene (23-16 Ma) is essential to understanding how our primate ancestors interacted with the environment. To address this, we revisited Loperot, an early Miocene catarrhine fossil-bearing site dated to ~17 Ma in western Turkana, Kenya to expand the stratigraphic context and examine the paleosol geochemistry and profile morphology of the lower and upper beds of the previously described LpM4 section (Liutkus-Pierce et al., 2019). We added ~30 m of additional stratigraphic section above and below the previously described 27.8 m of section. Within the existing LpM4 sequence, paleosols from the lower half of the section have whole-rock TiO₂/Zr and TiO₂/Nb values that differ from those in the upper half, suggesting a change in provenance and parent material (e.g., varying contributions from volcaniclastic and/or basement rock terrain). Morphologically, paleosols in the lower half of the LpM4 section are silty and have subsoil B horizons with many pedogenic carbonate nodules (Bk horizons), whereas paleosols in the upper half of the LpM4 section are sandy and have subsoil B horizons with evidence of both pedogenic carbonate and clay films (Btk) along with evidence of poor drainage (Btkg). These trends in paleosol morphology up section may reflect changes in depositional environment, drainage and climate. Mean paleorainfall estimates using the RFMAP paleosol model for the lower Loperot beds are 500 mm/yr, whereas the upper Loperot beds are 680 mm/yr. Although these model estimates are within error of each other (±209 mm), the change in paleosol morphology between lower and upper units is conspicuous, suggesting that climate shifts changed water availability in the Loperot paleosol succession. Our rainfall reconstructions are consistent with previous work at Loperot that suggest catarrhines and other primates occupied semi-arid habitats during the early Miocene. Our current and future studies on the Loperot paleosols contribute to broader efforts to deconvolve the complex relative contributions of biology, climate, and tectonics to Neogene primate and mammal evolution in East Africa.