A 2.6-MILLION-YEAR RECORD OF STONE TOOLS FOUND PRIMARILY IN FLUVISOLS AT GONA, AFAR DEPRESSION, ETHIOPIA

The Gona Paleoanthropological Research Project area in the Afar region of Ethiopia contains one of the most complete records of archaeological sites anywhere in the world, from the earliest Oldowan dated to 2.6 Ma, extending through the Later Stone Age dated to ca. 12-7 ka. This makes Gona an ideal place to examine long-term trends in hominin-environment interaction. We revisited archaeological sites at Gona and characterized the paleopedology and found evidence of paleo-Fluvisols and -Vertisols. Greater than 80% of sites spanning from the Oldowan to the Later Stone Age are found in paleosols resembling modern day weakly-developed fluvial soils, with A-C and A-Bk-C profiles. Paleosol morphology shows presence of bedding, incipient soil structure development and overprinting after burial. Stratigraphy and lithofacies show that these paleo-Fluvisols were proximal to either the ancestral Awash River or a distal fan channel. Burial rates were likely rapid due to proximal flooding, which is consistent with the lack of subsoil development in many of these paleosols. This style of sedimentation and weathering resembles a narrow (5-10 m width) strip of land in a modern-day channel shelf and bar setting, separating the river from the adjacent gallery forest. The frequent association of artifacts with these weakly-developed paleosols indicates a long history of hominin reliance on proximal stream water and gallery forest resources. Most paleosol studies at Gona and elsewhere in eastern Africa use paleo-Vertisols or other more well-developed calcareous paleosols to reconstruct paleoenvironment. Our work suggests that there is a potential spatial and temporal decoupling between those well-studied paleosols and the more weakly-developed ones where archaeology is commonly found.