Chad Basin

The Chad Basin is the largest endorheic basin in Africa, centered approximately on Lake Chad. It has no outlet to the sea and contains large areas of semi-arid desert and savanna. The drainage basin is approximately coterminous with the sedimentary basin of the same name, but extends further to the northeast and east. The basin spans eight modern nations, including most of Chad and a large part of Niger, Algeria, Libya, Sudan, Nigeria, Cameroon, Central African Republic. A combination of dams, increased irrigation, climate change, and reduced rainfall are causing water shortages, contributing to terrorism and the growth of Boko Haram in the region. Lake Chad continues to shrink. The geological basin, which is smaller than the drainage basin, is a Phanerozoic sedimentary basin formed during the plate divergence that opened the South Atlantic Ocean. The basin lies between the West African Craton and Congo Craton, and formed about the same time as the Benue Trough. It covers an area of about . It merges into the Iullemmeden Basin to the west at the Damergou gap between the Aïr and Zinder massifs. The floor of the basin is made of Precambrian bedrock covered by more than of sedimentary deposits. The basin may have resulted from the intersection of an "Aïr-Chad Trough" running NW-SE and a "Tibesti-Cameroon Trough" running NE-SW. That is, the two deepest parts are an extension of the Benue Trough that runs northeast to the margin of the basin, and another extension running from below the present lake to below the Ténéré rift structure to the east of the Aïr massif. The southern part of the basin is underlain by another elongated depression. This runs in an ENE direction and extends from the Yola arm of the Benue trough. At times, parts of the basin were below the sea. In the northeastern part of the Benue Trough where it enters the Chad Basin there are marine sediments from the Late Cretaceous (100.5–66 Ma). These sediments seem to be considerably thicker towards the northeast.