The tectonic structures in the Niger Delta Basin are typical of an extensional rift system, but the added shale diapirism due to loading makes this basin unique. The main method of deformation is gravitational collapse of the basin, although the older faulting and deformation in the basin are related to the continental breakup and rifting of the African plate and South American plates. The overall basin is divided into a few different zones due to its tectonic structure. There is an extensional zone, which lies on the continental shelf, that is caused by the thickened crust. There is a transition zone, and then there is a contraction zone, which lies in the deep sea part of the basin.