PALEOSOL CORE-LATIONS AND STABLE ISOTOPES IN THE EASTERN AFRICAN RIFT

Baringo Basin, Kenya is located within 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 the Baringo Basin through 222.6 meters of the Pliocene-Pleistocene Chemeron Formation dated from 3.29 Ma to 2.56 Ma. The mid-Pliocene Warming Period (mPWP), an important analogue for modern climate change, occurred from 3.26 to 2.95 Ma. Major Northern Hemisphere Glaciation (NHG) began shortly afterward at 2.7Ma. These units consist of alternating lacustrine and fluvial units, with paleosol units composing 57% of the core length. Pedogenic carbonates (δ¹³C_PC) from these paleosols are used to track environmental changes through changes in vegetation (C₃ vs. C₄ plants) and fractional woody cover (f_wc). Values of f_wc >0.8 indicate predominantly C₃ closed settings, while values <0.2 indicate predominantly C₄ open settings. These preliminary results indicate an overall decrease in woody cover in the Baringo Basin from 3.4 to 2.7 Ma. The Baringo Basin was a shrubland (f_wc= 0.4 to 0.8) from 3.26 to 3.22 Ma, a wooded grassland (f_wc= 0.1 to 0.4) from 3.22 to 2.84 Ma, and a dominantly C₄ grassland from 2.84 to 2.7 Ma. These transitions in the vegetation appear to correlate with the onset of the mPWP, mPWP intensification, and transition toward NHG respectively. A rapid spike in f_wc to shrubland vegetation from 2.7 to 2.6 Ma, before a return to wooded grassland from 2.6 to 2.58 Ma, may be related to the onset of Northern Hemispheric Glaciation. A steep dip in woody cover can be observed at 3.1 Ma that correlates to a known decline in CO₂. Previous applications of fractional woody cover in the East African Rift (Lake Turkana and Awash Valley) show similar transitions with marginally higher f_wc values. δ¹⁸O_PC values from BTB13 (-1‰ to -15‰) are more varied than values previously observed in the Baringo Basin (-4‰ to -8‰) and other East African Rift sites. Future research will focus on using clumped isotopes (Δ₄₇) to refine the effects of temperature on δ¹⁸O_PC fractionation in these pedogenic carbonates.