DAHOMEY BASIN

This study examines the sedimentology, geochemical appraisal and palynofacies of the Maastrichtian–Paleocene Araromi Formation, situated in the eastern Dahomey Basin of southwestern Nigeria. The primary objectives is to evaluate the depositional environments, organic matter quality, and the hydrocarbon‐generation potential of the formation, thereby contributing to a broader understanding of the basin’s petroleum system.Integrated field observations and lithological analyses reveal an alternation of sandstones, shales, limestones, and siltstones, which collectively indicate a dynamic depositional system that evolved from fluvial to shallow marine settings. These facies transitions reflect varying energy conditions and sediment supply, suggesting periodic marine incursions during the late Maastrichtian to early Paleocene.Geochemical results show moderate to high Total Organic Carbon (TOC) values, accompanied by Hydrogen Index data consistent with a mixed assemblage of Type I and Type III kerogens. This mixture confirms the presence of both oil-prone and gas-prone organic matter, implying that the Araromi Formation possesses substantial potential for hydrocarbon generation under appropriate thermal maturity conditions.Palynofacies analyses further support these interpretations by revealing moderate palynological diversity. The presence of terrestrial pollen and spores, alongside abundant marine dinoflagellate cysts, confirms deposition during the late Maastrichtian to early Paleocene interval and indicates fluctuating terrestrial and marine influence. Amorphous organic matter dominates the offshore equivalents, suggesting deposition under reducing conditions that favored the preservation of hydrogen-rich organic material.Finally, the combined sedimentological, geochemical, and palynological evidence establishes the Araromi Formation as a significant source rock within the Dahomey Basin. The findings not only enhance understanding of the basin’s stratigraphic evolution and petroleum system but also highlight the formation’s relevance for future hydrocarbon exploration and development in southwestern Nigeria.

The petrographic and mineralogical analysis of siliciclastic and carbonate facies within the southeastern Dahomey Basin, Nigeria, was studied with the aim of interpreting their provenance, depositional environment, diagenetic evolution, and reservoir potential. Thirty three samples were collected and analyzed. Analysis involved X-ray diffraction (XRD) for mineralogical characterization and thin-section petrography for micro-structural and textural evaluation. Six representative samples were analyzed, comprising three siliciclastic units from depths of 1610– 1870 ft and three carbonate units from 730–930 ft across two wells within the study area. The siliciclastic samples are dominated by quartz, feldspar (orthoclase and albite), and muscovite, indicating derivation from granitic and gneissic sources of the Precambrian Basement Complex. Moderate textural maturity and the presence of albitized feldspars suggest limited reworking and shallow burial diagenesis. The carbonate samples, composed mainly of bioclastic and peloidal packstones to wackestones, reflect shallow-marine to outer shelf depositional settings, influenced by mixed carbonate–siliciclastic sedimentation during transgressive phases. Diagenetic features such as sparry calcite cementation, muscovite preservation, and feldspar albitization point to a multi-stage, low-thermal diagenetic history under closed-system conditions. High quartz content, low clay development, and early marine cementation collectively indicate moderate to good reservoir quality, with porosity largely preserved by mechanical rather than chemical processes. The results of petrography and mineralogy of Siliciclastics and Carbonate facies in Southeastern Dahomey Basin revealed that the units are potential for hydrocarbon-bearing reservoirs.