T207 Investigating Earth’s Past, Present, and Future with Continental Scientific Drilling

Tuesday, 24 September 2024
1:30 PM - 5:30 PM
212A

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

Paper number: T207-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

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 (δ13CPC , δ18OPC) to track hydrologic and environmental changes (e.g., C3 vs C4 plants, fraction of woody cover, precipitation). δ13CPC shows a transition from shrubland to wooded and C4 grasslands in Baringo Basin as NHG intensified. Soil water δ18O (δ18Osw) is a proxy for paleoprecipitation and changing seasonality due to shifts in the East African Monsoon– the region’s dominant precipitation regime. δ18OPC depends on δ18Osw , 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 δ18Osw 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.

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403195

© Copyright 2024 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.