The Lake CHAd Deep DRILLing project (CHADRILL) - targeting ∼ 10 million years of environmental and climate change in Africa

Florence Sylvestre (1) , Mathieu Schuster (2) , Hendrik Vogel (3) , Moussa Abdheramane , Daniel Ariztegui (4) , Ulrich Salzmann (5) , Antje Schwalb (6) , Nicolas Waldmann (7)

1 AMU - Aix Marseille Université
2 IPGS - Institut de physique du globe de Strasbourg
3 UFZ - Helmholtz Zentrum für Umweltforschung = Helmholtz Centre for Environmental Research
4 Institut Forel and Department of Geology and Paleontology
5 Archäobotanik Afrikas
6 Technische Universität Braunschweig = Technical University of Braunschweig [Braunschweig]
7 Department of Marine Geosciences

At present, Lake Chad (∼ 13 • N, ∼ 14 • E) is a shallow freshwater lake located in the Sahel/Sahara region of central northern Africa. The lake is primarily fed by the Chari-Logone river system draining a ∼ 600 000 km 2 watershed in tropical Africa. Discharge is strongly controlled by the annual passage of the in-tertropical convergence zone (ITCZ) and monsoon circulation leading to a peak in rainfall during boreal summer. During recent decades, a large number of studies have been carried out in the Lake Chad Basin (LCB). They have mostly focused on a patchwork of exposed lake sediments and outcrops once inhabited by early hominids. A dataset generated from a 673 m long geotechnical borehole drilled in 1973, along with outcrop and seismic reflection studies, reveal several hundred metres of Miocene-Pleistocene lacustrine deposits. CHADRILL aims to recover a sedimentary core spanning the Miocene-Pleistocene sediment succession of Lake Chad through deep drilling. This record will provide significant insights into the modulation of orbitally forced changes in northern African hydroclimate under different climate boundary conditions such as high CO 2 and absence of Northern Hemisphere ice sheets. These investigations will also help unravel both the age and the origin of the lake and its current desert surrounding. The LCB is very rich in early hominid fossils (Australop-ithecus bahrelghazali; Sahelanthropus tchadensis) of Late Miocene age. Thus, retrieving a sediment core from this basin will provide the most continuous climatic and environmental record with which to compare hominid migrations across northern Africa and has major implications for understanding human evolution. Furthermore, due to its dramatic and episodically changing water levels and associated depositional modes, Lake Chad's sediments resemble maybe an analogue for lake systems that were once present on Mars. Consequently, the study of the subsurface biosphere contained in these sediments has the potential to shed light on microbial biodiversity present in this type of depositional environment. We propose to drill a total of ∼ 1800 m of poorly to semi-consolidated lacustrine, fluvial, and eolian sediments down to bedrock at a single onshore site close to the shoreline of present-day Lake Chad. We propose to locate Published by Copernicus Publications on behalf of the IODP and the ICDP. 72 F. Sylvestre et al.: The Lake CHAd Deep DRILLing Project (CHADRILL) our drilling operations onshore close to the site where the geotechnical Bol borehole (13 • 28 N, 14 • 44 E) was drilled in 1973. This is for two main reasons: (1) nowhere else in the Chad Basin do we have such detailed information about the lithologies to be drilled; and (2) the Bol site is close to the depocentre of the Chad Basin and therefore likely to provide the stratigraphically most continuous sequence.

Mots clés: remote; late miocene; pliocene; basin

Mots clés: sahara-desert

Domaines: Sciences de l'environnement; Milieux et Changements globaux

Florence Sylvestre, Mathieu Schuster, Hendrik Vogel, Moussa Abdheramane, Daniel Ariztegui, et al.. The Lake CHAd Deep DRILLing project (CHADRILL) - targeting ∼ 10 million years of environmental and climate change in Africa. Scientific Drilling, 2018, 24, pp.71 - 78. ⟨10.5194/sd-24-71-2018⟩. ⟨hal-02546047⟩