Tephrostratigraphy of the Chemeron Formation Baringo Basin, Kenya

The Baringo Basin, in the northern Rift Valley of Kenya, has long been a focus of interest for various academic disciplines. Its deposits, ranging in age from the Miocene to the Pleistocene, with mammalian fossil localities have not only provided an opportunity for intensive study but have also raised hopes for the area as a possible source for hominid or hominoid fossils in the range 5-12 Ma. This interest has been encouraged by finding primate fossils among the numerous mammalian fossil bones collected thus far. In the Baringo Basin chronological control for the stratigraphy of the Chemeron Formation has been scanty. Only a few dates are available, and these essentially bracket the whole formation. Since the formation is considered to be broadly coeval with the Koobi Fora, Nachukui, and Shungura Formations of the Omo Group in northern Kenya and southern Ethiopia, the focus of this study is to use tephra to correlate the Chemeron Formation with formations of the Omo Group as a basis for establishing both stratigraphic and chronologic control. The study makes it possible to compare tephrostratigraphic correlations with those made on paleontological, archeological and anthropological bases, and enable a more detailed paleogeographic and paleoenvironmental analysis. About 15 tephra layers have been identified within the Chemeron Formation, three of which correlate with tuffs within the Turkana Basin and one of which correlates with a tuff from Kanapoi. The remaining tuffs allow for correlation between isolated outcrops in the Baringo Basin itself. This is very useful because exposures in the Baringo Basin are small and widely scattered. From the correlations established in this study it appears that the Chemeron Formation ranges in age from somewhat less than 1.6 Ma to approximately older than 4 Ma.