Scientific deep drilling in the Chew Bahir basin: advantages and pitfalls of two overlapping sediment cores

Abstract. Chew Bahir, a lake that is dry for most of the year, located in a tectonic basin in the southern Ethiopian Rift, was the target of several scientific drilling expeditions between 2009 and 2014. The aim of these expeditions was to explore the basin and its lake sediments as an archive of past changes in the environmental conditions during the evolution of our species, Homo sapiens. In more than 25 publications, the scientific findings derived from the analysis of the sediments were presented and discussed in detail. In the present paper, we provide the background information on the project's origins, planning and implementation – that is, information that has not yet been presented in scientific papers, or only very briefly, but which could be important for those working on similar projects in the future. Herein, we particularly focus on the advantages and disadvantages of obtaining twin cores at a short distance, aiming at a continuous high-quality composite core, a strategy that had to be defended during the planning stage of the project due to the higher costs involved but which is considered to be the best practice for scientific drilling in modern sedimentary basins.