The Iullemeden Basin, also known as the Sokoto Basin spans Mali, western Niger, northwest Nigeria and northern Benin and began accumulating sediments in the Jurassic, followed by the Maastrichtian Rima Group, which records a brackish environment. Approximately one-tenth of the Chad Basin is situated in Nigeria. Albian Bima sandstone lie unconformably atop Precambrian basement rock, followed by the Turonian limestone and shale sequences of the Gongila Formation.