NEW NEOGENE FLUVIO-LACUSTRINE FAUNAL ARCHIVES FROM THE DANAKIL DEPRESSION, EAST AFRICA: IMPLICATIONS FOR HUMAN ORIGINS, PALEOCLIMATE AND CONTINENTAL RIFTING

We report initial findings from field survey and laboratory studies on stratified sediments from the Miocene-Pliocene age “Red Series” collected near the town of Ayumen in the presently arid Danakil Depression, Afar region of the East African Rift. Within the study area, paleolake sediments are exposed along the southern flank of the Danakil horst. Vertebrate and invertebrate fossils recovered include crocodiles, fish and aquatic reptiles, gastropods and ostracodes. The assemblage present suggests a fluviolacustrine paleoenvironment, and we infer that a shallow, fresh-brackish lake was connected to local drainages. This interpretation is consistent with the sedimentological features of these beds, and is comparable to other lake systems documented in the East African Rift system, particularly within the Omo and Hadar regions of Ethiopia. A suite of Ar-Ar dates on associated interstratified basalts provide the first chronology for this presently undocumented paleolake, and enable precise correlations to other fossil contexts within the East African Rift. An abundance of fossil wood preserved in the described section reflects mesic conditions during the Early Pliocene. Deposition of the Danakil Formation was closely linked to late Neogene continental rifting and volcanism in the Afar Triangle Triple-Point Junction, as well as with the separation of the Danakil Microplate from the rest of Africa. The Ar dates indicate that the sequence coincides with the pivotal and problematic interval of hominin origins and dramatic global climate change in the Miocene. This sequence is among the oldest documented continental strata in the Afar Triangle.