The Baringo-Tugen-Barsemoi 2013 drillcore (BTB13), acquired as part of the Hominin Sites and Paleolakes Drilling Project, recovered 228 m of fluviolacustrine sedimentary rocks and tuffs spanning a ~3.29–2.56 Ma interval of the highly fossiliferous and hominin-bearing Chemeron Formation, Tugen Hills, Kenya. Here we present a Bayesian stratigraphic age model for the core employing chronostratigraphic control points derived from 40Ar/39Ar dating of tuffs from core and outcrop, 40Ar/39Ar age calibration of related outcrop diatomaceous units, and core magnetostratigraphy. The age model reveals three main intervals with distinct sediment accumulation rates: an early rapid phase from 3.2 to 2.9 Ma; a relatively slow phase from 2.9 to 2.7 Ma; and the highest rate of accumulation from 2.7 to 2.6 Ma. The intervals of rapid accumulation correspond to periods of high Earth orbital eccentricity, whereas the slow accumulation interval corresponds to low eccentricity at 2.9–2.7 Ma, suggesting that astronomically mediated climate processes may be responsible for the observed changes in sediment accumulation rate. Lacustrine transgression-regression events, as delineated using sequence stratigraphy, dominantly operate on precession scale, particularly within the high eccentricity periods. A set of erosively based fluvial conglomerates correspond to the 2.9–2.7 Ma interval, which could be related to either the depositional response to low eccentricity or to the development of unconformities due to local tectonic activity. Age calibration of core magnetic susceptibility and gamma density logs indicates a close temporal correspondence between a shift from high- to low-frequency signal variability at ~3 Ma, approximately coincident the end of the mid-Piacenzian Warm Period, and the beginning of the cooling of world climate leading to the initiation of Northern Hemispheric glaciation c. 2.7 Ma. BTB13 and the Baringo Basin records may thus provide evidence of a connection between high-latitude glaciation and equatorial terrestrial climate toward the end of the Pliocene.
Bibliographical noteFunding Information:
We wish to acknowledge our gratitude to our late colleague, Dr. Andrew Hill, whose career-long dedication to the geology and paleontology of the Baringo Basin fired our own interest in this fascinating and complex area. We are grateful for discussions and ongoing contributions by our colleagues of the Baringo-Tugen Hills-Barsemoi (BTB), Baringo Paleontology Research Project (BPRP), and Hominin Sites and Paleolakes Drilling Project (HSPDP) research groups. This project was supported by the International Continental Drilling Program (ICDP) and the National Science Foundation [grants EAR 1123942 , BCS 1241790 , EAR 1338553 , and EAR 1322017 ]. 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, Drilling and Prospecting International (DPI) for drilling services and the US National Lacustrine Core Facility for core handling, processing and storage facilities. This is publication #21 of the Hominin Sites and Paleolakes Drilling Project.
© 2019 Elsevier B.V.
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- Chemeron Formation