Molluscan biostratigraphy of the Koobi Fora hominid-bearing deposits

Abstract

Since the discovery¹ of late Cenozoic hominid-bearing deposits in the Koobi Fora area, north Kenya, a variety of studies^2–9 have been undertaken to provide a chronostratigraphical and palaeoenvironmental context for the important palaeoanthropological and early archaeological discoveries^1,10. Unfortunately, although the exposures are areally extensive (>1,000 km²), they are broken up into subareas (Fig. 2); these local sections are often difficult to correlate with one another due to intervening bush cover and faulting. Here I summarize a molluscan biostratigraphical analysis which demonstrates serious stratigraphical miscorrelations between certain local sections, including some previously indicated by vertebrate evidence. These miscorrelations require substantial revisions to current stratigraphical interpretation of the Koobi Fora deposits. In particular, both the Suregei and Tulu Bor tuff horizons actually represent different levels. Although the Tulu Bor is considered to overlie the Suregei, some exposures currently attributed to the Tulu Bor are actually older than some units previously mapped as the Suregei. Fortunately, the stratigraphical miscorrelations reported here do not significantly affect the relative placement of the mollusc faunas reported in a previous evolutionary analysis¹⁵; superpositional relationships in the areas from which these faunas were collected (mainly collecting areas 102, 103, 110, 123, 202 and 203) are unaffected by the miscorrelations reported here.