Lithostratigraphy and Inorganic Geochemical Studies of Cretaceous-Tertiary Lithofacies from Nigerian Three Inland Basin

Abstract

Studies from selected samples from Chad (Kanadi-1, Albarka-1 and Tuma-1), Sokoto (Dange-1) and Dahomey Basins (Seme-1), were subjected to detailed lithostratigraphic description and inorganic geochemical studies with the aim of determining the provenance, tectonic setting, depositional environment and geochemical characterization. This involves detailed lithologic description, Inductively Coupled Plasma Emission Spectrometry (ICP-ES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) through lithium metaborate fusion method. The lithologies of the study wells from Chad, Sokoto and Dahomey Basins comprise of mudstone, dark shale, brownish sandstone and light brownish shale; mudstone and dark brownish shale and clay, dark brownish shale, siltstone respectively. The geochemical result showed an abundance of SiO2 with an average of 75.05%, Al2O3 average of 12.51% (sandstone), values of 18.10% to 10.12% and 5.51% to 16.17% (shale). The abundance of Fe2O3 range from 2.12% to 8.56% while the other major elements have very low concentration. The high SiO2 content indicated a quartz rich adjoining source rock while low values of ratio K2O/Al2 O3 and Na2O/Al2O3, coupled with high average values (<70%) of Plagioclase Index of Alteration (PIA), Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) indicated intense weathering condition and humid climate at the source area. The sediments classification includes greywacke, arkose, litharenite and quartz arenite. A-K-F plot indicated transitional marine environment. Discrimination function plots revealed felsic igneous, quartzose sedimentary and intermediate igneous provenances. The plot of La-Th-Sc showed deposits of passive margin setting. Chondrite normalized REE plot showed an enrichment of light REE with strong negative Eu anomaly which is an indication of a felsic source. Conclusively, study areas consist of marine deposits with plutonic igneous rock as the main source rock couple with low grade metamorphic and quartzose recycled rocks deposited in transitional marine environment under intense weathering in a tropical, humid climatic condition.