Depositional environment and diagenesis of Late Cretaceous-Early Paleogene carbonates on the Benin flank, southwestern Nigeria

Abstract

Carbonates of Late Cretaceous-Early Paleogene occur on the Benin Flank, southwestern Nigeria. Depositional environment and diagenetic history of the carbonates have not been extensively described. Outcrop sections and cores on Benin Flank were logged, sampled and analyzed in order to determine the depositional environment and diagenetic history of the carbonate rocks, through field-based studies, petrographic studies (employing both optical and scanning electron microscopy, SEM) and mineralogical studies using XRD (X-ray powder diffraction) analytical technique. Based on field studies, core description and petrographic investigations, two lithofacies have been identified, namely: wackestone (associated with mottled dolomite) and bioclastic wackestone-packstone. The Late Cretaceous-Early Paleogene limestone on the Benin Flank is interpreted to have been formed in low-energy environment along the shelf. Mineralogical composition of the analyzed limestone samples indicate that calcite was the original carbonate mineral in the limestone. The observed diagenetic fabrics of the analyzed carbonate samples suggest that the Late Cretaceous-Early Paleogene carbonates on the Benin Flank have been subjected to some post-depositional alterations, namely micritization, development of microspar, compaction, dissolution, dolomitization and calcite-filled microfractures.