Sedimentology

This study integrates sedimentological and foraminifera analyses of five (5) ditch-cutting samples obtained at 60 ft intervals from depths 11,550 ft to 11,790 ft in the MF-3 Well, located within the Niger Delta Basin. The investigation aimed to study the sedimentology and foraminifera abundance patterns in the well and objectively interpret the lithologic characteristics, foraminifera diversity and abundance, age and depositional environments of the studied interval. Standard sedimentological and micropaleontological techniques were employed to process and examine the samples. Sedimentologic characteristics were determined based on textural parameters such as grain size, lithology, lithofacies, color, angularity, roundness and sorting . Each 20 g sample was soaked, washed, sieved, dried, and examined under a binocular stereo microscope for foraminifera identification and quantitative assessment. The sedimentological analysis revealed intercalating shalysand lithofacies, one (1) lithofacie unit . One (1) hydrocarbon play element (reservoir rock) was delinated in the well section. The associated minerals delineated in the well includes Iron oxide (heamatite), mica, quartz, feldspar, and tourmaline. The shaly sands are fine to medium-grained, moderately sorted, and quartz-rich, organic indicating marine incursions. The foraminifera analysis recovered the following species Hanzawaia strattonii, Ammonia beccarii, Haplophragmoides narivaensis, Cibicorbisinflata, Bolivina scalprata miocenica, Heterolepa pseudungeriana, Spirosigmoilina oligocaenica, Bathysiphon sp, Florilus costiferum (Nonion 4 sp), Trochammina sp, Epistominella vitrea, Valvulineria sp and Uvigerina subperegrina. A Middle to Late Miocene age and paralic to open shallow-marine (inner neritic) paleoenvironments of deposition was assigned to the studied well section

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.

This study examined the sedimentological and geochemical characteristics of problematic soils within the Lagos segment of the Dahomey Basin, Southwestern Nigeria, to understand their composition, depositional setting, and engineering implications. Eight borehole samples (BH1–BH8) were analyzed for particle size distribution, water content, density, and plasticity characteristics, while representative samples (L2 and L5) underwent X-ray diffraction (XRD) analysis. The particle size distribution results showed that the soils are predominantly fine- grained comprising of clayey or silty materials to fine grained sand with mean grain sizes between 3.30ϕ and 6.83ϕ. Sorting values between 3.54 and 4.86ϕ classified them as very poorly sorted sediments deposited under fluctuating, low-energy coastal conditions. Water content ranged from 23.8 % to 36.9 %, density from 1.77 to 1.88 g/cm³, and void ratios from
0.65 to 0.81, indicating moist, moderately compacted soils with high porosity. The liquid limit and plasticity index values, ranging from 37.7–58.2 % and 21.3–32.6 % respectively, revealed high plasticity and significant swelling potential. XRD results confirmed montmorillonite (41–42 %) as the dominant mineral, alongside quartz (33–39 %) and minor actinolite or albite. These properties collectively explain the soils’ poor strength, high compressibility, and moisture sensitivity. The study concludes that the Lagos coastal soils are expansive and structurally unstable, requiring stabilization, effective drainage, or deep foundations to support safe and durable engineering development within the Dahomey Basin