Palaeoenvironments of the Buia Homo site: High-resolution facies analysis and non-marine sequence stratigraphy in the Alat formation (Pleistocene Dandiero Basin, Danakil depression, Eritrea)

The Early to Middle Pleistocene Dandiero rift basin is located near the Buia village, 110 km south of Massawa (Eritrea), and is filled by about 1000 m of continental deposits bearing 1 My erectus-like human remains. The basin fill consists of six formations (from bottom up): Bukra sand and gravels (fluvial), Alat formation (fluvio-lacustrine), Wara sand and gravel (fluvial), Goreya formation (lacustrine), Aro sand (fluvio-deltaic) and Addai fanglomerate (alluvial fan). This paper is focused on the Homo-bearing deposits of the Alat formation. The Alat formation records several episodes of changing accommodation space, with repeated shifts from fluvial to lacustrine conditions. The first episode points to rapid lake formation followed by a progressive shallowing. The second episode records fluvial aggradation above a sequence boundary, followed by the development and progressive infill of a second lake. The third episode points to a rapid lake formation followed by deposition of deltaic and fluvial sediments. The last episode is characterised by fluvial deposition under low-accommodation conditions. The development of the lacustrine environments was probably controlled by tectonics, in accordance with its formation during regionally dry climatic conditions, although minor shifts toward wetter conditions cannot be excluded. Human remains occur in the upper Alat formation, where the transition from a deltaic to alluvial setting is characterised by high frequency, potentially millennial-scale, lake-level oscillations. The palaeoanthropological record in the Buia area seems to be correlated with water availability (lacustrine coastal plains and floodplains) in a relatively open and grassy environment (grassland- and savannah-dominated). The increase in fluvial discharge that occurred at the top of the Alat formation led to erosion and winnowing of the underlying fossil-bearing, fluvio-deltaic deposits. A large number of bones and artefacts were consequently accumulated at the base of channel fills, which represent a preferential horizon for fossil searching.