Core stratigraphy constrains Bed IV archaeological record at HEB site, Olduvai Gorge, Tanzania
Abstract The Olduvai Gorge deposits contain a rich archaeological record documenting the evolution of hominin behavior over the last 2 million years. While archaeological assemblages in the lower sedimentary layers (Beds I-II) are well preserved in relatively secure chronostratigraphic contexts, the age of overlying beds is poorly constrained due to discontinuous exposures and lack of marker horizons, abundant erosional contacts and lack of unweathered, dateable material. As a result, Beds III-IV and the Masek Beds, have yet received little attention compared to the underlying beds. Recently, the Olduvai Gorge Coring Project (OGCP) acquired high resolution, stratigraphically continuous sedimentary cores of Palaeolake Olduvai through scientific drilling, in order to improve the geological and palaeoenvironmental contexts of the hominin record. While other studies reported in this volume have used palaeoenvironmental datasets from the cores to refine the Beds I-II records, this study combines outcrop and core stratigraphic methods to improve the chronology of Bed IV archaeological sites. Our recent excavation at HEB site demonstrates the importance of this approach to improve the stratigraphic positioning and relative age of Bed IV archaeological materials. Our results suggest that the HEB site is younger than previously thought because it was formed after depositional fill of an incised valley, which substantially removed much of lowermost Bed IV in the HEB area. The lithofacies at this site indicate lake expansion and development of Ngorongoro Highland sourced braided streams near the lakeshore at this time, which coincided with rich assemblages of artifacts, fossil fauna, and bones bearing butchery marks. This setting likely afforded a variety of resources to hominins including potable water, raw materials, refuge trees, and animal food, making HEB an important site for inferring the cultural and feeding behaviors of Homo erectus.