The modern human fossils of the Kibish Formation

The Kibish Formation at the Lower Omo valley, with an aggregate thickness of 105m consists of lacustrine and deltaic deposits divided into four members (Brown and Fuller, 2008). It is a Middle Pleistocene to Holocene Formation, where two fossils of early Homo sapiens (Omo I and Omo II) were discovered in the lower sections of Member I. The Omo fossils were recently dated to 233 ± 22 kyr based on geochemical analyses that link the Kamoya’s Hominid Site (KHS) Tuff, which conclusively overlies Member I that contains Omo I, with a dated major explosive eruption of Shala volcano in the Main Ethiopian Rift (Vidal et al., 2022). Member I (~20m thick) is composed of sandstones, siltstones, and claystones, with minor tuffs, while member II (~32m thick) consists of a tuff at the base, overlain by uniformly bedded and laminated silty clays, thin sand stringers and fine sandstone. Member III (~30m thick) comprises sandstones with conglomerate lenses and one prominent 3-4m thick tuff at its base, the Aliyo tuff dated to ~104 ka. Member IV (~28m thick) forms laterally extensive deposits of sandstones and laminated silty clays forming the Kibish plain (Brown and Fuller, 2008).