The composite Tertiary sequence of the Niger delta consists, in ascending order, of the Akata, Agbada, and Benin Formations. They compose an estimated 28,000 ft (8,535 m) of section at the approximate depocenter in the central part of the delta. The stratigraphic distribution of these rocks is poorly understood because of the lack of drilling information and outcrops. The Akata Formation represents the prodelta facies of a southward-prograding Tertiary delta. The Agbada Formation, which is an alternating sequence of sandstones and shales, represents deposits of delta-front, distributary-channel, and deltaic-plain environments. The Benin Formation consists of mainly medium to coarse-grained sandstones deposited in braided streams on sandy alluvial plains.