Paleoclimate and Paleoenvironments of Early to Middle Miocene strata in West Turkana, Kenya: proxy records of forests, woodlands, and hydroclimate change

The Lothidok Range west of Lake Turkana, Kenya contains a rich paleontological record, including multiple well-preserved Miocene fossil ape taxa. Our work, as part of the West Turkana Miocene Project, seeks to integrate new paleontological surveys with modern tools in geologic mapping, stratigraphic analysis, geochronology, and proxy-based climatic and environmental reconstructions. The Early Miocene Moruorot and Kalodirr localities are well known for fossils of the ape taxa Afropithecus, Turkanapithecus, and Simiolus. Our work at Moruorot demonstrates that these ape taxa were coeval and are preserved in humid alluvial fan complexes. Paleovegetation proxies based on stable carbon isotope ratios in paleosol organic matter (δ13Com = -28 to -31 ‰) and pedogenic carbonates (δ13Cpc = -9 to -12 ‰) are consistent with C3 plants thriving in a forested ecosystem. This interpretation is bolstered by the presence of calcified branches and fruits in lahar deposits. We also use a paleosol bulk geochemical proxy for mean annual precipitation (MAP), which yields values of 1700-1900 mm, which requires intense seasonality of rainfall for pedogenic carbonate stability. In contrast to the Early Miocene paleoenvironments, nearby Middle Miocene deposits at Esha that contain at least one newly discovered fossil ape taxon preserve floodplain paleosols that suggest seasonal woodland conditions (δ13Com = -19 to - 27‰, δ13Cpc = -6.5 to -12 ‰) with a minor fraction of C4 plants in a C3-dominated biome. The paleosol bulk geochemical proxy yields MAP estimates of 500-1000 mm, notably drier than the Early Miocene paleosols. This multi-proxy investigation demonstrates that the West Turkana region experienced drying from the Early to Middle Miocene, and that both time intervals were much wetter than modern conditions. Our ongoing work is focused on refining the stratigraphy and geochronology at both known and newly discovered Early and Middle Miocene sites, and placing systematically collected fossils within a well resolved geological and paleoenvironmental framework across the southern Lothidok Range.