Origin and depositional environment of oils and sediments in the Cretaceous Deep-Water Tano Basin, Ghana: Constraints from biomarkers

Abstract

Despite the significant discovery of hydrocarbon in the Cretaceous Deep-Water Tano Basin of Ghana, detailed molecular characteristics and paleo-depositional environment of the Basin are insufficiently documented in peer-reviewed works. Therefore, in our study, gas chromatography-mass spectrometric (GC-MS) and gas chromatographic (GC) analyses were used to characterize biomarkers obtained from organic matter (oils and rock extracts) to determine the organic matter source, the environment of deposition, and maturity. Sixteen (16) oil and ninety-eight (98) rock samples from seven wells were studied. The work has indicated that distributions of these biomarkers suggested that Cretaceous oils were derived from a mixed kerogen source (marine and terrestrial) deposited in anoxic to suboxic paleo depositional conditions. CPI, Ts/Tm and C29 ββ/(ββ + αα) sterane ratios plotted against C29 20S/(20S + 20R) sterane ratios indicates that the studied samples are relatively low to medium level maturity.