Aspect Of Sedimentological Evaluation Of Exposures Of Eastern Dahomey Basin, At Ijeshaijebu, Southwestern Nigeria

ABSTRACT

The study area, Ijesha-Ijebu falls within the Nigeria sector of the Eastern Dahomey Basin. It lies within the contact zone between the south-western basement rocks and the Eastern Dahomey Basin. The principal objective of this project work is to deduce the depositional environment and identify the formations in the study area. The field and laboratory investigation were carried out during this project work. Nineteen (19) rock samples collected were described for its: grain texture, color, and orientation of grains and identification of the mineralogical composition were carried out. Measurement of strike and dips of cross-beddings, measurement of each bed along the profile, taking of photographs of important sedimentary structures such as burrows, dissolution, and unconformity and logging of the exposure were done on the field. The laboratory investigation involves grain size analysis and petrographic analysis. The lithofacies recognized are: Clay Unit, Sandstone Unit, and Conglomerate Unit. On the basis of the integrated studies of the grain texture and palaeocurrent direction, it was concluded that the exposure does not have a defined sequence. The result of the studies also suggests that the exposure possesses a fining upward sequence and a fining downward sequence. The result of the grain size distribution shows that the sediments ranges from Unimodal to Trimodal, poorly sorted to moderately sorted. The textural group ranges from gravelly sand to sandy gravel. The result of the petrographic analysis indicates that the sandstone have high quartz content; the size of the grains ranges from angular to subangular. This suggests that the sediments were deposited from a short distance and the environment of deposition is mainly Continental (Fluvial).