2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 136-4
Presentation Time: 9:00 AM-6:30 PM


DEAN, Jonathan R.1, ASRAT, Asfawossen2, COHEN, Andrew S.3, FOERSTER, Verena4, JUST, Janna5, LAMB, Henry F.6, LENG, Melanie7, SCHĂ„BITZ, Frank5, TRAUTH, Martin H.4 and VIEHBERG, Finn5, (1)British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom, (2)Addis Ababa University, Addis Ababa, Ethiopia, (3)Department of Geosciences, University of Arizona, Tucson, AZ 85721, (4)Potsdam University, Potsdam, Germany, (5)University of Cologne, Cologne, Germany, (6)Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth, SY23 3DB, United Kingdom, (7)NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom, jond@bgs.ac.uk

There is currently a lack of long, continuous, Pleistocene records from east Africa, meaning it has been difficult to establish the relative influence of low- vs. high-latitude forcing on east African climate and climatic conditions at the time of anatomically modern human (AMH) origin and subsequent dispersal. We have been attempting to address these gaps in our knowledge by analysing sediments taken from Chew Bahir, an area of playa mudflats in southern Ethiopia close to the site of the oldest known AMH fossils.

In March 2014, Chew Bahir was cored to a depth of ~40 metres, and the resulting sediment sequence is estimated to cover the last ~115ka. Oxygen isotopes from bulk endogenic carbonates at Chew Bahir are interpreted mainly as a proxy for water balance, with more positive values indicating drier periods and more negative values wetter periods. There is a shift at ~60 ka from more variable and possibly wetter conditions, to more stable and potentially drier conditions in more recent times. This could be related to change from West African Monsoon-dominated climate to Indian Monsoon-dominated climate.

Additionally, in December 2014, the site was drilled to a depth of ~280 metres as part of the Hominin Sites and Paleolakes Drilling Project. The cores were opened and sampling started at LacCore in April 2014. An update on the progress of the analysis of this much longer sequence will be given and any preliminary isotope data presented.