Electrical Resistivity Imaging (ERI) of basin fills in some parts of Eastern Dahomey

Abstract

Stratigraphic and geophysical analyses of an outcrop at Onikintibi were done with the aim of
understanding basin architecture and predicting depositional history. The palynological studies defined
the age of the units, and clarified the lithology of the basal component. Three principal lithology types
found are conglomeratic sands, compacted ferruginised sandstone, and the weathered basement; these
units have resistivity values of >1000 m, >1019 m and <400 m. The basal layer is derived from porphyritic
granite protolith. In addition, coarsening-upward stacking pattern of the reddish-brown conglomerate
suggests prevalence of continental conditions. High thickness of the Ise units at the western edge
suggests greater accommodation space and subsidence during basin development; consequently, the
layer tapers to the east in response to waning current. The occurrence of Monoporites annulatus,
Laevigatosporites and Acrostichum aureum imply the outcrop is post Paleocene. Longapertites sp. is an
extant plant taxa with known ecological preferences assigned to Nypa (a mangrove plant), thus vegetation
comparable to Nypa mangrove may have occurred in the region. The lithologic units over the weathered
basement are rocks of the Abeokuta group in Eastern Dahomey Basin.