First results from the deep drilling at Chew Bahir (S-Ethiopia)

Chew Bahir is one of the five sites drilled during 2013–14 in the framework of the Hominin Sites and Palaeolakes Drilling Project (HSPDP), in order to understand the climate and environmental history during the evolution of hominins in East Africa. The Chew Bahir record will concentrate on the younger part of that history and is further supported by collaborating projects, including the Cologne Collaborative Research Centre (CRC-806), the German and the British International Continental Drilling Project (ICDP). The site is located in the southern part of the Main Ethiopian Rift (MER) at about 500 m asl and lies close to the famous excavation of anatomically modern humans at Omo Kibish. Following a transect from west to east, 6 short cores (max. depth 11m) already delivered the basic understanding of sedimentation processes from the border to the centre of that former lake, mainly by using XRF scanning data. The age-models for these cores are based on 32 AMS radiocarbon dates, which roughly place the base of the centremost core at about 45ka BP. The K-record is one of the most promising proxies in all these cores allowing a climatic interpretation of wet and dry cycles (dry LGM, wet African Humid Period, dry Younger Dryas, wet early Holocene and dry Holocene since 5 ka BP) mostly triggered by solar radiation as well as changes in the position of the ITCZ and the Congo Air Boundary (CAB). In March 2014, a 41.5m deep core was taken from the centre of that basin. As with the short cores, the K counts measured by XRF scanning show fluctuations, which reflect climate change. 14C and OSL dating as well as palaeomagnetic measurements on this core are still in progress, but will be available by the time of the meeting. Preliminary stratigraphic indications suggest that this record may reach back to MIS5-–MIS6. In Nov-Dec 2014 the HSPDP deep drilling down to the target depth of 400m will take place and probably allows a palaeoenvironmental reconstruction back in time to nearly the origin of our ancestors