DETAILED STRATIGRAPHIC CORRELATIONS ACROSS THE PLEISTOCENE OLDUVAI BASIN, NORTHERN TANZANIA, AT THE OLDOWAN-ACHEULEAN TECHNOLOGICAL TRANSITION

Olduvai Bed II preserves a critically important Pleistocene paleoanthropological record, covering the disappearance of the Oldowan stone tool industry and its replacement by the Acheulean, the disappearance of Homo habilis and appearance of Homo erectus, and a transition from more humid to more arid conditions (with a shrinking lake and change in fauna). Bed II is lithologically complex with few widespread marker tuffs compared to underlying Bed I, making site-to-site correlations difficult. Detailed stratigraphic sections, with a focus on erosional surfaces, supplemented by the identification of key tuffs, help to identify land surfaces associated with key paleoanthropological sites currently and recently under excavation by the Olduvai Geochronology and Archaeology Project (OGAP) in Middle Bed II.

Tuff mineralogy and geochemistry (based on glass composition where available, and mineral assemblage and feldspar, hornblende, and augite compositional differences where altered) helps confirm the correlation of the Bird Print Tuff (BPT) and Tuff IID. These identifications have confirmed the stratigraphy proposed by Hay (1976) in most places, but also expand the range over which the BPT can be identified (to Loc. 88/ MNK) and suggest that Tuff IID at places in the Side Gorge (e.g. Loc. 91/ SHK Annexe) had been previously misidentified.

Closely-spaced stratigraphic sections within Lower and Middle Bed II between HWK-EE (a classic Oldowan site, sitting upon a disconformity overlying Tuff IIA) and Loc. 88/ MNK (MNK Skull site- also Oldowan, between Tuffs IIA and IIB; and MNK Main, an early Acheulean site sitting upon a disconformity overlying the BPT) help provide context for the transition between the Oldowan and Acheulean technologies, and provide a means to identify hominin-exploited landscapes within Middle Bed II.