Terrestrial Sedimentation in a Pleistocene Rift-Shoulder Setting: Implications for Early Homo Habitat at Oldupai Gorge, Tanzania

Rift basins are excellent repositories for continental sedimentation over geological time scales, yet bed-scale studies that constrain local environmental change are uncommon. In this study, we visit a renowned setting, the archaeologically significant Oldupai Gorge on the western margin of the East African Rift System in Northern Tanzania, to investigate drivers of paleoenvironmental change revealed through detailed sedimentological investigation. We focus on an understudied section at Elang’ata Oljurusi (Geolocality-75), which contains a record of laterally continuous tuffaceous layers embedded in sedimentary sequences that span 2.0–1.14 Ma (Beds I and II). Exquisite geological exposures are leveraged to deduce the environment in which early hominins resided in this underexplored part of the basin.

We use detailed sedimentological analysis, including measured stratigraphic sections, paleocurrent measurements, and tuff samples from five archaeological trenches that expose the oldest sedimentary systems of the region (i.e., Beds I and II). Results from the 30-m-thick section reveal an interplay of dominantly lacustrine to lacustrine margin facies (claystones and mudstones) in Bed I, alternating with thin, very-fine to fine-grained tuffs and tuffaceous sandstones. Bed II comprises a range of fluvial sandstones and conglomerates that were deposited by eastward-flowing rivers, as well as floodplain claystones and occasional lacustrine mudstones, and tuffs. The results are consistent with an interpretation that sedimentation took place in conjunction with significant faulting, which corresponded with the Oldupai paleolake shifting to the east and shrinking. Hominin occupations of fluvial flood plains reflect this changing paleo-landscape.