The Benue Trough originated from Early Cretaceous rifling of the central West African basement uplift. It forms a regional structure which is exposed from the northern frame of the Niger Delta and runs northeastwards for about lOOOkm to underneath Lake Chad, where it terminates. Regionally, the Benue Trough is part of an Early Cretaceous rift complex known as the West and Central African Rift System.
Tectonic phases and basin development on the Benue :o Trough are divisible into:
(1) An Early Cretaceous rift phase with fluviatile and lacustrine deposits;
(2) Late Early to Middle Cretaceous phase of rapid basin subsidence and initiation of marine transgression in all rift segments, characterised by submarine gravity flows with megaslumps and turbidites;
(3) Prolonged shelf and deep basin deposition especially in the southern part (Abakiliki Rift) under predominantly oxygen-deficient bottom conditions,
(4) Tectonism, involving deformation and a- magnetism and the formation of lead-zinc deposits from circulating hot brines,
(5) Late Cretaceous post-deformation subsidence with westward displacement of depocentres, especially in the Anambra Basin, where extensive coal forming swamps developed. Although several sub-basins or depocentres have been identified in the Benue Trough on geophysical (gravity) evidence, structurally and in terms of sediments three segments, the Lower, the Middle and the Upper Benue Trough, have been recognised.
