Vegetation in East Africa is generally thought to have shifted from forests to more open grasslands and savannas as global climate cooled and high-latitude ice sheets expanded during the Plio-Pleistocene. Such a shift would have greatly influenced landscape resources, and potentially hominin evolution as well. Existing records of African vegetation spanning these time-scales are generally derived from offshore marine records that record continental-scale changes, or paleosol carbonate records that record very local vegetation changes during the short time intervals of soil carbonate formation. Here we present a new record of basin-scale vegetation change from the late Pliocene (~3.3–2.6 Ma) derived from a drill core from the Chemeron Formation, located in the Baringo Basin/Tugen Hills region of the Kenya Rift Valley. Specifically, we present a new record of the relative abundance of C4 grasses and C3 vegetation based on the carbon isotopic composition of leaf wax biomarkers (δ13Cwax), which captures a signal of regional vegetation change. These data demonstrate that vegetation in the Baringo Basin varied greatly between C3 forests and C4 grasslands, and that vegetation exhibits both long-term (secular) trends and orbital-scale variations. The contribution of C3 plants was lower than estimates based on low-resolution carbon isotope data from paleosol carbonates and organic matter in the basin. C3 plants averaged ~53% of the vegetation during the late Pliocene, from ~3.3 to ~3.04 Ma, after which time δ13Cwax indicates more open vegetation and ~41% C3 plants. This transition may have been driven by changes in basin geomorphology, but also possibly occurred as part of larger-scale drying and expansion of C4 vegetation in East Africa. In addition to this secular change, we observe high amplitude variability in the δ13Cwax record including oscillations between ~80 and ~0% C3 plants. These vegetation changes are correlated with changes in precipitation inferred from δ2Hwax and lake level oscillations inferred from sedimentary facies, implying that high-amplitude, orbital-scale variations in precipitation drove significant changes in vegetation resources during the late Pliocene in the Baringo Basin. These variations have important implications for changes in terrestrial resources in light of the evolutionary innovations in the hominin fossil record related to changes in foraging strategies.
Bibliographical noteFunding Information:
We wish to thank Tristan Reinecke and Dheivanai Moorthy for sample preparation, Marcelo Alexandre, Rafael Tarozo, and Ewerton Santos for laboratory assistance, and the members of the Hominin Sites and Paleolakes Drilling Project (HSPDP) for useful discussions. Support for HSPDP has been provided by the National Science Foundation (NSF) grants EAR 1322017 , EAR 1338553 , BCS 1241790 , and the International Continental Drilling Program (ICDP). Research and drilling permits were provided by the Kenyan National Council for Science and Technology, the Kenyan Ministry of Mines, and the National Environmental Management Authority of Kenya, and facilitated by the National Museums of Kenya. We thank DOSECC Exploration Services for drilling supervision and Drilling and Prospecting International (DPI) for drilling services. Initial core processing and sampling were conducted at the US National Lacustrine Core Facility (LacCore) at the University of Minnesota. Data are freely available at the World Data Center-A for Paleoclimatology. We thank anonymous reviewers for helpful comments on an earlier version of this manuscript. This is publication 22 of the Hominin Sites and Paleolakes Drilling Project. Appendix A
© 2019 Elsevier B.V.
Copyright 2019 Elsevier B.V., All rights reserved.
- Carbon isotopes
- Human evolution
- Leaf waxes
- Organic geochemistry
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