Lithological Characteristics, Petrographic and Ostracods Analyses of Carbonate Rocks in Parts of Sokoto Basin, Nigeria: Implications for Exploration Efforts and Petroleum Geology

Abstract

This study investigates sedimentological characteristics of carbonate rocks from borehole data, in some segment of the Iullemmeden Basin, northwestern Nigeria, with a focus on hydrocarbon exploration potential. This study involved the use of lithological description, petrographic and microfossil analyses on carbonates rocks in parts of Sokoto Basin. The borehole 2051, which penetrates a 32.0-meter sedimentary sequence, reveals four lithostratigraphic units which are shale, limestone, silty mudstone and claystone. The Gamba Formation comprises dark laminated shale, brownish claystone containing silt material with thickness of about 4 m. The Kalambaina Formation is characterized by light to milky whitish bioclast-rich limestone with a thickness of 11.5 meters. The Gamba Formation comprises 4 meters of brownish claystones with silt and dark laminated shales at the top in the study section. Detailed microfacies analysis identified mudstone, lithoclastic wackestone, lithoclastic packstone, bioclastic wackestone, and peloidal bioclastic packstone, indicative of varied depositional environments from low-energy to more dynamic shallow marine conditions. Ostracod data from the studied Paleocene interval revealed twelve species: Bairdia ilaroensis, Trachylebris teiskotensis, Cytherella sylvesterbradleyi, Cytherella sp., Paracosta cf. warensis, Buntonian beninensis, Cytherelloidea sp., Bairdia aegyptiaca, Paracosta kenfensis and Paracosta parakefensis. These species reflect a diverse marine ecosystem with varying depths and ecological niches, indicating a stable, productive marine environment with periodic freshwater influxes. The findings suggest potential hydrocarbon systems within the basin, with the Dange Formation's rich in dark shales acting as potential source rocks and the Kalambaina Formation's bioclast-rich limestones serving as promising reservoir rocks. In conclusion, the integration of lithological descriptions, microfacies classifications, and paleoecological data provides insight to the basin's depositional history and its implications for hydrocarbon exploration.