Facies Analysis, Mineralogy, and Geochemistry of thePaleocene Ewekoro Formation, Dahomey B

Abstract

The extensive limestone (carbonate) deposits of the Paleocene Ewekoro Formation, were petrographically, mineralogically and geochemically investigated for depositional environmental interpretation. Thin section of selected samples were prepared for petrographical analysis. Mineralogical and geochemical analyses, using X-ray diffraction analysis (XRD), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP- OES), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were conducted on twenty limestone samples. Two microfacies including packstone and wackestone were identified on the basis component composition. The microfacies reflected fossils of organisms characteristic of low to moderate energy, shallow marine environments. Calcite dominates the mineral constituent of the limestone, with accessory minerals such as quartz, muscovite, and albite occurring is moderate amounts. The Post-Archean Australian Shale (PAAS) normalized REE+Y of the limestones displays relatively uniform patterns (enriched LREE, positive Ce anomaly, and High Y/Ho ratio) across the different lithologies. The enrichment of LREE and depletion of HREE as reflected by the (La/Yb)sn. (Dy/Yb)sn and (Nd/Yb)sn ratios suggest a non-seawater like characteristics, probably a brackish water environment. Elemental ratios of Eu/Eu*. La/Co, Th/Co, Th/Cr, and Cr/Th suggest terrigenous contributions derived probably from intermediate to felsic rocks. The geochemical proxies, including the V/(V+Ni), V/Ni, V/Mo, Th/U ratios, Ce anomaly, and Mn* indicate that the limestones were deposited in a shallow marine environment under a fluctuating oxidizing to reducing conditions.

Publication Info:

Author: Bankole, S.I. , Opatola, A.O., Onah, C.E., Ogunmodede, O.P.,

Volume: 60

Issue: March

Published By: Journal of Mining and Geology Vol. 60(1) 2024. pp. 57 - 71, 2024-03-01