Abstract

A reinterpretation of the depositional environments of the Anambra Basin succession in the light of modern sedimentological models has necessitated a revision of the late Cretaceous paleogeography of southeastern Nigeria. The phases of transgressions and regressions in the Campanian in the Campanian to Paleocene within the Anambra Basin are reviewed, based on these new interpretation. Thus, it has been shown, for example, that the Mamu Formation and the overlying Ajali Sandstone are both part of a continued controlled Maastrichtian transgression, which started in the late Campanian, superimposed on a regional geoidal eustatic sea level rise, which lasted until the Paleocene. This contrasts with the interpretation favouring a regressive phase of a short-lived Maastrichtian transregression, as has been previously thought by some workers. Tectonic movements within the basin have been shown to have been active during the late Cretaceous sedimentary cycles, as demonstrated by variations in the thickness patterns across the basin. Lateral facies variations both within and across formation boundaries, from north to south, as well as the occurrences of a large-scale slumps and other types of syn-sedimentary deformation structures attributed to tectonic activity further attest to the active nature of the basin during the period of sedimentation. The pattern of subsidence is also thought to have been influenced by earth tremors and periods of “quiescene”, particularly in the northern Ankpa sub-basin.

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