Tephrochronological analysis of the Plio-Pleistocene Chemeron Formation, Baringo Basin, Kenya: Refining stratigraphy and constraining chronology of vertebrate fossil sites

Tephrochronology provides a stratigraphic approach to correlating geologic and paleoenvironmental events using volcanic ash layers. Stratigraphic correlation, especially over local and regional scales, plays a vital role in tracing the evolutionary trajectory of our hominin relatives across space and time in eastern Africa. The goal of this study is to employ tephrochronology to distinguish tephra layers within the Chemeron Formation at the site of Sinibo, Kenya. The Chemeron Formation is a sequence of Plio-Pleistocene sediments spanning the 5.3 to 1.6 Ma interval in the eastern foothills of the Tugen Hills — a fault block in the Baringo Basin of the Kenyan Rift Valley. This formation is an ideal site for the application of tephrochronology, as it comprises multiple tuff units interbedded with fluvial and lacustrine deposits that yield mammalian fossils, including hominins. In this project tephra layers from the Sinibo section are differentiated by analysing the geochemistry of volcanic glass shards from the tephra and establishing potential isochronous volcanic events in the stratigraphic record. Tephra samples analysed in this study were collected in the field and analysed for major element geochemistry using an Electron Microprobe. Distinct tephras were reconfirmed, including the Lokochot and Tulu Bor tuffs that are found broadly across eastern Africa. Ultimately, the tephra sequence from the relatively continuous section at Sinibo will be used to constrain the chronostratigraphy of fossil sites in structurally disrupted sequences in the Chemeron Formation. This work builds upon previous analyses (Namwamba, 1993) and is integrated with existing stratigraphy.