DEGREES OF CHANGE: RECONSTRUCTING PALEOTEMPERATURE AND PALEOSOL SOIL WATER IN BARINGO BASIN, KENYA

Baringo Basin, Kenya is located in the East African Rift and preserves the most continuous record of fossiliferous Neogene strata in equatorial eastern Africa. The BTB13 sediment core was drilled in Baringo Basin through Plio-Pleistocene strata (3.29 - 2.56 Ma) and records two major climate events: the mid-Pliocene Warming Period (mPWP; 3.25 - 2.95 Ma) which is an important analogue for modern climate change and the onset of global cooling leading to the Northern Hemisphere Glaciation (NHG; ~2.75 Ma). Paleosols (n = 78) compose 57% of the 222.6 m core that includes lacustrine, fluvial, alluvial, and tephra units. Stable C and O isotope ratios were measured from pedogenic carbonates (δ¹³C_PC , δ¹⁸O_PC) to track hydrologic and environmental changes (e.g., C₃ vs C₄ plants, fraction of woody cover, precipitation). δ¹³C_PC shows a transition from shrubland to wooded and C₄ grasslands in Baringo Basin as NHG intensified. Soil water δ¹⁸O (δ¹⁸O_sw) is a proxy for paleoprecipitation and changing seasonality due to shifts in the East African Monsoon– the region’s dominant precipitation regime. δ¹⁸O_PC depends on δ¹⁸O_sw , precipitation δ¹⁸O, and soil temperature, which are determined using carbonate clumped isotope thermometry (TΔ₄₇). TΔ₄₇, determined for eight paleosol carbonates, ranged from 15 - 29℃, indicating a gradual cooling trend (~8℃) as glaciation intensified, with warmer temperatures (~26℃) correlating with the mPWP. Reconstructed δ¹⁸O_sw values range from 2.9 to - 3.2‰ VSMOW and reveal hydrologic cycle fluctuations, but no long-term trend. C₄ vegetation and temperature changes broadly correlate with known increases in temperature and pCO₂ from global climate events, but additional Δ₄₇ analyses are needed to refine correlations. Additional ongoing work on paleosol bulk and clay mineralogy will provide insight into vegetational constraints and ultimately resource suitability for early hominins, as soil fertility is influenced by soil salinity and mineralogy. Paleosol bulk mineralogy, measured using X-ray diffraction, shows dominantly feldspathic and iron-oxide minerals, with poor quartz content due to basaltic parent materials. Feldspathic minerals are more abundant in the drier NHG, while iron-oxides are more abundant in the wetter mPWP. Cumulatively, these data indicate a positive correlation between soil fertility, iron-oxides, precipitation, and temperature.