The Upper Burgi Unconformity: A major hiatus in the fossiliferous Koobi Fora formation identified in area 116, east Turkana, Kenya

Abstract

The relatively continuous record of sedimentary deposits in the Koobi Fora Formation preserve fossilized hominins and archaeological assemblages that are crucial in our understanding of human origins. Despite this continuity, gaps in the stratigraphy represent essential components in establishing geologic context for paleoanthropological and archaeological finds. This study characterizes deposits directly associated with the Upper Burgi Unconformity (UBU) in Area 116 and connects these deposits with previous work done in the region to refine the geologic record of the basin. Area 116 presents the clearest documented occurrence of the UBU in the Koobi Fora Formation. The exposures provide information about the depositional environments preceding and following the low-relief hiatus in conjunction with a package of stratigraphically intermediate deposits that lend insight into the hiatus itself. While the origin of the UBU remains unknown, we discuss contemporary changes in climatic and tectonic context that may have contributed to a lack of deposition in the approximately 500,000 years between 2.0 and 2.5 Ma represented by the hiatus.