Petrological and Geochemical Evaluation of the Paleocene-Eocene Lithofacies in Dahomey Embayment, Southwestern Nigeria

Abstract

The detail mapping and logging of the Ibese area within the Dahomey Basin has revealed the total thickness of the limestone to range between 12.0 m to 15.0 m. This study is based on qualitative lithologic, spectrochemical analyses via X-ray fluorescence and petrographic indices to understand the lithofacie, chemistry, viability of the sequences and depositional environment. This consists of milky to grey and nodular to massive fossiliferous limestone units while the sand content increases with depth. The composition of the major oxides in the thirty-seven (37) samples from six exploratory wells revealed that CaO (51% -56%), SiO 2 (2.6% -10.56%), Fe 2 O 3 (0.33% -0.94%), MgO (0.78% -1.02% and Al 2 O 3 (0.72% -0.98%) were the most abundant elements. The trend of the geochemical indices show increase in the percentage composition of CaO, and MgO down the sequences with high values which defined the depth of diagenetic re-distribution. The percentage composition of Al 2 O 3 , Fe 2 O 3 and K 2 O are significant indicating continental influence during diagenesis and diverse depositional episodes. The three different microfacies recognized based on depositional texture are shelly biomicrite, shelly biosparmicrite and alga biosparmicrite. The predominance of micrite as the cementing matrix revealed that the rock was deposited in a quiet shallow inner shelf environment occasioned by storm waves.

Geochemical characterisation of the Turonian-Maastrichtian bituminous sands in Dahomey Basin, Southwestern Nigeria

“…The Dahomey Basin was described by Whiteman (1982), as a massive wedge of Cretaceous to Recent sediments that lies unconformably on the basement. Its tectonic evolution allows the stratigraphic sequence to be divided into three sequences: (1) Precambrian to Triassic intra-cratonic rocks and Jurassic to lower Cretaceous, Continental to marginal marine rocks representing the pretransform stage; (2) Lower Cretaceous to late Albian rocks representing the syn-transform stage and (3) Cenomanian to Holocene rocks representing the post-transform stage (Boboye and Nzegwu, 2014;Boboye and Omotosho, 2017). Several works of literature documented the different aspects of the geology of the basin, some of which include Murat (1972), Adediran and Adegoke (1987), Omatsola and Adegoke (1981), Onuoha and Ofoegbu (1988), Nton et al (2006), Bolaji et al (2020) and Okoro et al (2021).…”