By the lakeshore: Multi-scalar geoarchaeology in the Turkana Basin at GaJj17, Koobi Fora (Kenya)

The Late Pleistocene archaeological record in the Turkana Basin is important for studying Homo sapiens evolution, but the record in this region is poorly documented, despite a long history of significant paleoanthropological discoveries. Ambiguity around ages and site formation processes are paramount problems. We investigated the chronometric, geological, archaeological, and paleoenvironmental context of GaJj17, a locality with an artifact-bearing deposit in the Koobi Fora region. Sedimentological facies analysis coupled with micromorphological evidence indicate the depositional environment at the site changed over time from a fluvial system to an aeolian one, forming the remnant lunate feature seen today. Caliche caps the site and likely mitigated erosion of the site during high lake stands; similar deposits (∼25 m²) are found within a 2 km radius and are archaeologically sterile. Optically stimulated luminescence dating indicates the deposit and associated artifacts and fossils were emplaced circa 52–43 thousand years ago. Small (average length ∼ 3.5 cm) flakes dominate the stone artifact assemblage and include unretouched triangular flakes on diverse raw materials indicating shared affinity with Middle and Late Pleistocene lithic toolkits elsewhere in eastern Africa. Hippopotamus, crocodiles, and fish are well-represented in the faunal assemblage, along with a small sample of terrestrial ungulate specimens. More taphonomic research to understand the accumulating agent(s) of the faunal assemblages is needed. These results contribute to our understanding of Late Pleistocene archaeological site formation processes in lacustrine contexts of the Omo-Turkana Basin.