PALEO – ENVIRONMENT OF THE CAMPANIAN – MAASTRICHTIAN SEDIMENTS OF ANAMBRA BASIN, SOUTH EASTERN NIGERIA.

Abstract

The Anambra Basin evolved following the Santonian squeeze that affected all the basins in the West Central African Rift systems (WCARS) and changed the focus of sedimentation from the Benue Trough southward on what used to be the Anambra platform. Four significant outcrops occur within the Anambra Basin. The beds of each of the four outcrop sections were studied with a view to seeing possible correlation among them. The sections were identified as Enugu, Mamu and Ajali Formations. The Enugu Formation consists of shale as the dominant lithology, interbedded with thin layers of ferruginised sandstone and a heterolithic unit of shale, sandstone and siltstone. The palynomorphs recovered include; Buttinea andreevi, Zlivisporis blanensis, Laevigatosporites sp, Milfordia jardinea, Longapertites marginatus, Cingulatisporites ornatus, Polysphaeridium sp. suggesting a marine environment of deposition and Late Campanian to Early Maastrichtian. The Mamu Formation consists of sandstone, siltstone, shale, and coal; and abundance non-marine palynomorphs of Maastricthian in age. The shale is rich in Longapertites marginatus, Monocolpites marginatus, Reditiporites sp, Milfordia jardinei, Caudospora spp, Cingulatisporites ornatus. The cross-stratification associated with Ajali sandstones of the study area suggests deposition by migrating sand waves. The results from the statistical analysis show that, the sandstones range in grain size from medium to coarse-grained, poorly sorted sediments deposited in a river environment. The stratigraphic position of the outcrop section representing the Enugu Formation appear older than that of the Mamu Formation but palynomorphs occurrence suggests fair biostratigraphic correlation among the outcrops.