The Chew Bahir Drilling Project - Deconvolving climatic versus tectonic forcing in the source-to-sink sediment system of extensional provinces: New insights from the Chew Bahir Basin, South Ethiopia

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The complex kinematic evolution of continental rifts and the conspiring effects of climate and tectonics on the surface-process system requires a holistic approach in deciphering paleoenvironmental changes reflected in drill cores. Such an approach must entail the reconstruction of the tectono-geomorphic characteristics of the sediment source-routing-sink system, because erosion and sediment transport are mainly a function of topography, climate, and lithology. Here, we propose such a study of the Chew Bahir catchment in southern Ethiopia, aimed at linking the tectonogeomorphic evolution of the basin with the sediment-routing system, and ultimately the depositional record of the Chew Bahir drilling site, to be obtained under the auspices of the International Continental Drilling Program (ICDP). The recovered drill core is expected to corresponding to an interval spanning at least the ultimate 800-1,200 kyr, targeted to provide data on environmental change to better assess hominin evolution and migration. By integrating our catchment-wide study with the drilling record we aim at deconvolving climatic and tectonic forcing impacting sediment routing and deposition in the Chew Bahir basin. Our results will improve the understanding of three important aspects of the sedimentary records of extensional systems and their relationship with major hominin migration corridors. These include: 1) the forcing mechanisms impacting landscape development; 2) sediment production and deposition; and 3) the paleo-environmental significance of sedimentary deposits in a crucial sector of the East African Rift. In order to achieve these goals, we will follow a four-tiered approach: I) determine the spatiotemporal variations in sediment sources and routing by provenance analysis and dating of fluvial terraces; II) quantify modern and past erosion rates using cosmogenic nuclides and sediment volumes estimated from seismic reflection profiles; III) establish the timing of fluvial captures and drainage reversals in the catchment; and IV) link the tectono-geomorphic evolution with the sedimentary record of the ICDP drillhole. We will use sedimentological techniques in provenance analysis and constrain the age of terrace deposits using cosmogenic nuclides and 14C, to cover a broad age spectrum. Our geomorphic analysis will be aided by 12-m digital elevation models obtained from TanDEM-X data. Together, the tectono-geomorphic analysis, the provenance study, and new geochronology of sedimentary deposits will provide an unprecedented data set that will be ultimately linked to the depositional record of the drillhole in the basin center, thus contributing to our understanding of the link between environmental change and hominin evolution in light of active tectonics and repeated climate change.