PALEOENVIRONMENTAL RECONSTRUCTION OF LOCHERANGAN, A MIOCENE FOSSIL BEARING LOCALITY, TURKANA BASIN, KENYA

The Miocene is an important interval in the evolutionary history of primates in eastern Africa. Specifically, the Turkana Basin in northern Kenya contains a robust paleoecological record from the Oligocene to modern. Among Miocene sites in Turkana, Locherangan (~17.5 Ma) is unique as it preserves a significant lacustrine interval, bracketed below and above by fluvial sedimentation and soil development. While the primary exposure is spatially limited to a ~100 m² hill, prospecting in summer 2023 identified additional exposures of fossiliferous stratigraphic units, expanding the area of interest to 1 km². These fossiliferous units produced various reptiles, ungulate and mammalian fossils including hominoids. Paleosols are present throughout the section with an average thickness of 1.3 m. Paleosol stratigraphy varies in a manner that is consistent with changes in the depositional environment. The basal reddish-brown paleosols weathering fluvial and fluvial-lacustrine sediments are cumulative and overprint underlying paleosols. The pale olive and yellow paleosols in the middle of the section weather lake margin muds and are multistory in nature, clearly separated by under- and overlying fossiliferous shales. The uppermost reddish-brown paleosols return to a cumulative pattern but differ from basal paleosols with coarser textures and and clay accumulation (paleosol Bt horizons). Many paleosols also have evidence of vertic features, accumulation of pedogenic carbonate, and some evidence of poor drainage. Paleosol carbonates (n=4) have a mean δ¹³C of -10.41‰ VPDB, δ¹⁸O of -3.67‰ VPDB, and clumped isotope temperature T(Δ₄₇) of 32.5°C. We used two proxies that predict mean annual precipitation (MAP) using paleosol subsoil geochemistry: CALMAG (for Vertisols only) and a recently developed machine-learning model (RFMAP1.0). CALMAG results yield a mean of 1093±108 mm yr^-1, and RFMAP1.0 model results yield a mean of 1336±440 mm yr^-1, both indicating that Locherangan was characterized by a subhumid to humid environment. These additional data highlight the paleontological potential of Locherangan to provide insights from a dynamic Miocene lacustrine margin.