Structure of the Paleozoic basement in the Senegalo-Mauritanian basin (West Africa)

The interpretation of 2D seismic surveys from the Senegalo-Mauritanian basement and the reappraisal of rock-samples from oil exploration drillings provide new insights into the structure of the Appalachian-Mauritanian belts and the overlying Carboniferous and Permian basins. Two different units have been evidenced below the Mesozoic sedimentary cover : a lower unit (Unit 1 : basement) and an upper unit (Unit 2 : Late Palaeozoic basins). Unit 1 shows two distinct tectonic areas : the northern area with two different belts evidenced on both sides of the Senegalese block and the southern area exhibiting various tilted blocks making part of the Palaeozoic (Ordovician to Devonian) Bové basin. In the northern area the Western Thrust Belt is thrust over the Senegalese block while to the east, the so-called Mauritanian belt is thrusted over the West African craton. In the Mauritanian belt area, the youngest deformed sediments belonging to the outcropping Bove basin are Famennian in age. The Mauritanian inner belt underwent two tectono-metamorphic events (circa 330 and 270 Ma). Unit 2 which is unconformably capping both the Western Thrust Belt and the southern tilted blocks of the Paleozoic Bové basin (Casamance basin) is locally affected by eastward and westward-verging thrusts. Unit 2 is dated to the Early Permian by palynomorphs, and could have formed between the early (340–320 Ma) and late (270 Ma) Variscan tectonic events. The subsurface Late Palaeozoic basins from Senegal and Mauritania are interpreted as intra Variscan belt basins, similar to those suspected by seismic investigations off shore Guinea and Mauritania.