Fejej Fj-1 tuff (South-Omo, Ethiopia): new tephrostratigraphical correlations based on geochemical compositions with the plio-pleistocene formations from the Omo-Turkana basin

Four isolated outcrops containing only volcanic glass shards were mentioned in the Fejej area (South-Omo, Ethiopia). Among them the FJ-1 tuff, was initially correlated with the basal H member of the Shungura formation. The new chemical composition obtained by X-ray fluorescence confirms the existence of a single volcanic event and an unique tuff truncated by erosion. The FJ-1 tuff could thus be correlated with the G-29 tuff in upper G member of the Shungura formation, itself correlated with the Borana Tuff intercalated in the Burgi Member of the Koobi Fora formation, or with the H-I tuff. In agreement with the magnetostratigraphy and the biostratigraphy, the FJ-1 tuff is dated between 1,95 Ma, age of the lower limit of the Olduvai subchron, and 1,90 +/- 0,03 Ma, the estimated age of the H tuff, located above the G-29 tuff in the Shungura Formation. The proposed tephrostratigraphical correlation demonstrates that the fluvial sediments and the archaeological level C I of the FJ-1 locality are contemporaneous with the base of Upper Burgi member of the Koobi Fora Formation and with the Upper G member or basal H member of the Shungura Formation.