Paleoenvironmental context of the Pliocene A.L. 333 ” First Family” hominin locality, Hadar Formation, Ethiopia

10.1130/2008.2446(09) Detailed lateral study of strata associated with the A.L. (Afar Locality) 333 hominin locality provides paleoenvironmental information at geographic scales of hundreds of meters to kilometers as well as insights regarding alluvial deposition and pedogenesis in the middle Denen Dora Member of the Hadar Formation. A.L. 333 is dated at ca. 3.2 Ma and has produced over 260 surface and excavated specimens of Australopithecus afarensis. It represents an unusual source of high-resolution information about the paleoenvironmental context of this hominin. The in situ hominin fossils are associated with the final stages of filling of a paleochannel and were buried prior to the formation of overlying paleosols. Preserved bedding structures in the fine-grained hominin-producing strata provide evidence that the abandoned channel continued to aggrade prior to the onset of sustained pedogenesis. Pedogenic carbonates associated with the hominin level thus postdate the death and burial of the hominins, possibly by centuries to millennia. The reconstructed paleodrainage of the DD-2 sandstone (DD-2s) is oriented south to north and consists of a trunk channel, \~{}40 m wide and 3–5 m deep, connecting a tributary system south of A.L. 333 to a distributary system to the north, which likely ended on the deltaic plain associated with the basin's depocenter. The hominin concentration occurs in the upper part of the fill of the trunk channel. The burial of the hominin remains involved fine-grained deposition indicating low-energy, seasonal flood events, and there is no sedimentological evidence for a high-energy, catastrophic flood that could have caused the demise of the hominins.