RECONSTRUCTION OF EARLY PLIOCENE HYDROCLIMATE FROM CHEMERON FORMATION PALEOSOLS IN THE BARINGO BASIN, KENYA

The Early Pliocene was the last interval of sustained global warmth and CO₂ levels comparable to 21^st century conditions. The Chemeron Formation in the Baringo Basin, central Kenya, preserves lacustrine and alluvial strata from the Late Miocene through early Pleistocene. In this study, we analyzed paleosols from an early Pliocene interval of the Chemeron Formation to characterize paleo-hydroclimatic conditions. Bulk samples of the uppermost B horizon from six paleosols were ground in a Shatterbox. The resulting powders were oven-dried for 2 hr at 105-110°C. Fused beads were generated with a 9:1 flux to sample ratio using anhydrous lithium borate flux and roasted in a Katanax 300 electric fluxing furnace at 1050°C. The concentration of 11 major and minor elemental oxides was measured on the fused beads using a 1-kW WD-XRF spectrometer. Loss-on-ignition was measured on aliquots of paleosol samples using a NEY 525 muffle furnace for 1.75 hr at 950°C. Overall, the paleosols have high Fe₂O₃ and TiO₂ concentrations and are depleted in mobile base oxides (CaO, MgO, Na₂O, K₂O). Calculated weathering index values were generally high for all samples (CALMAG: 84-89; CIA: 82-87). Consequently, estimates of mean annual precipitation (MAP) from the CALMAG proxy range from 1480-1580 mm. Likewise, rainfall estimates from the RF-MAP_1.0 model were sub-humid (ca. 1300-1800). These MAP estimates are roughly double modern values in the Central Kenyan Rift Province. Our ongoing work will include analysis of other horizons in these paleosol profiles to calculate mass-balance between parent materials and weathered horizons.