AGE OF THE PRIMATE-BEARING DEPOSITS ON MABOKO ISLAND, KENYA

Renewed field work on the Miocene deposits of Maboko Island Benefit & McCrossin 1989 has produced a weath of new fossil material with important implications for vertebrate evolution in the early Neogene of East Africa. The deposits are of particular importance due to the abundance of primate fossils recovered from them. This report presents new geologic data concerning the stratigraphy and age of the fossiliferous deposits on Maboko. Maboko Island lies in the Winam Gulf of Lake Victoria (Figure 1). The geologic setting and history of research on the island have been reviewed by Andrewset al. 1981. Fossiliferous deposits were first reported from the island in 1930s and a Miocene age attributed to them on faunal grounds. Some controversy arose over the dating of the Maboko deposits, sparked by suggestion of an unconformity in the sequence and the presence of faunal elements of clearly Pleistocene age within the Miocene assemblage. The fluvial character of the Maboko deposits does include erosional surfaces, but there is no indication that they are of significant duration. Pleistocene fossils are found scattered about the island as a surface lag deposited during a late Pleistocene highstand of Lake Victoria. Subsequent studies on Maboko Island recovered additional fossil material, and suggested an age of 15-16 ma for the fauna, based on faunal considerations and isotopic dating of presumed correlative units exposed on the mainland (Andrewset al., 1981). This report presents the first numerical calibration of the age of the Miocene sequence on Maboko Island. © 1991 Academic Press Limited.