Jornal de Geologia e Geofísica
Acesso livre

Abstrato

Sedimentology, Depositional Architecture and Paleogeography of Turonian to Early Maastrichtian Successions, Western Flank of Abakaliki Anticlinorium

William John, Ezike OR, Onuigbo EN

This work was carried out to delineate surface geologic boundary between the southern Benue Trough and the Anambra Basin, determine the depositional environments and paleogeography of the encountered formations across the basins. Three formations were mapped with their boundaries delineated and they include: the Eze-Aku Sandstone Facies and the Awgu Shale (including the Agbani Sandstone Member) of the southern Benue Trough and the Nkporo Formation (including the Owelli Sandstone Member) of the Anambra Basin. The environments of depositions were interpreted through integration of lithology, textures, sedimentary structures and boundary contacts between one bed and another. Three lithofacies units were interpreted within the Eze-Aku Sandstone Facies. They are: the basal unit consists of dark grey fissile shale which grades upsection into siltstone and capped by trough cross-bedded and bioturbated pebbly sandstone. The Eze-Aku Formation is interpreted to be deposited in a lower delta plain (bay fill) facies associations which includes the interdistributary bay and the crevasse splay–natural levee environments. The Awgu Formation is interpreted to be deposited in a subaqueous delta plain facies association with the lower Awgu Shale being deposited in prodelta environment while the overlying Agbani Sandstone was deposited in delta mouth bar environment. The uppermost part of the Agbani Sandstone is interpreted to be deposited in a fluvial point bar facies association exhibiting lower channel floor, mid bar and upper bar environments.The Nkporo Formation is characterized by a tidally influenced estuarine deposits facies association with the lower Owelli Sandstone being deposited in environments ranging from tidal channels to intertidal flat. Overlying this unit is the Nkporo Shale which is interpreted to be deposited in environments ranging from offshore through lower–middle shoreface to intertidal flats. Paleocurrent analysis of the three formations indicates that the sediments of the Eze-Aku Formation were sourced possibly from the Oban Massif in the ESE direction of the current, the Awgu and Nkporo Formations paleocurrents plots showed a NNE direction showing that its provenance could possibly be from the older sediments of the Abakaliki Anticlinorium.