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- ItemPalynostratigraphy of Late Cretaceous subsurface sediment of southern Bornu Basin, Nigeria: implications for depositional environments and palaeoclimatic predictions.(Elsevier, 2024-02-02) Adepehin, Ekundayo JosephSedimentary records are helpful in tracking ancient environments and climates. By analysing Late Cretaceous subsurface sediment from the Gaibu-1 Well in the southern Bornu Basin, Nigeria, predominantly arenaceous lithologies were identified, and five stratigraphic sub-divisions were recognised: Bima, Yolde, Gongila, Fika (Upper, Middle, and Lower members), and Gombe Formations. Palynozonation facilitated the identification of four assemblage zones (A1 – A4): A (1) Triorites africaensis, A (2) Cretacaeiporites scabratus/Odontochitina costata, A (3) Droseridites senonicus, and A (4) Syncolporites/Milfordia spp. These findings suggest that the subsurface Cenomanian – Maastrichtian (younger) successions were deposited in the inner continental shelf (4600–3420 m), middle continental shelf (3420-2300 m), and distal middle continental shelf (2300-1500 m) settings. This Late Cretaceous succession is characterised by monocolpate pollens resembling modern Cenomanian palms, Nypa vegetation in wet lowland habitats, and conifer vegetation in relatively dry hinterlands during the Turonian-Maastrichtian, all under a tropical to subtropical climate systems. The data advocate that the Late Cretaceous era was characterised by prevalent tropical to subtropical climates featuring warm and humid conditions. This aligns seamlessly with the recognised Cretaceous Palmae Province of Africa–Southern America. This research demonstrates the reliability of integrated sedimentological and palynozonation datasets for refining the current understanding of ancient depositional environments and climate.
- ItemPore modification mechanisms in a deeply buried non-marine sandstone: the Early Cretaceous Upper Sarir Sandstone Formation, Sirte Basin, Libya.(Elsevier, 2021-04-28) Adepehin, Ekundayo JosephCritical understanding of the reservoir pore-system is crucial for effective fluid-flow. Core-sedimentological description (40 core plugs), petrography (thin section and scanning electron microscopy with energy dispersive spectrometry), x-ray diffractometry, and high-resolution imaging were integrated to characterize pore-modification processes in a deeply buried (ca. 12470–12558 Ft.) non-marine sandstone. The reservoir is dominantly subrounded to subangular, well-sorted to moderately well-sorted, and medium-to fine-grained quartz arenite and lithearenite. Framework ranges from matrix-supported to matrix-devoided types. With a mean point-counted composition of Q95F0L5, quartz is the dominant mineral in all samples. Core-derived porosity and permeability range from 0.88 to 16.89% (Average 9.99%) and ~0.00–431.06 mD (Average 66.42 mD), respectively. Intergranular (ɸI), micro (ɸμ), fracture (CF), and dissolution (Diss) porosities constitute an estimated 60%, 35%, 3%, and 2% of the total porosity. The pore-spaces are randomly distributed and largely disconnected from one another. Connected pores are linked by necking, tubular, and lamellar pore throats. Pore-destructive diagenetic processes occurred mainly in the early-intermediate diagenetic phase, and to lesser extent in the late diagenetic phase. Pore-enhancement processes were of sparse occurrences. Mechanical compaction, quartz overgrowth development, kaolinitization, sideritization, and calcite cementation are the main pore-occluding processes identified. Quartz overgrowth increased with depth and it shows an inverse relationship with poro-perm. The formation of quartz overgrowth haloes in the Upper Sarir Sandstone Formation were most likely formed from non-insitu silica mobilized into the pore system during post-rift cooling. This study confirms the need for careful heterogeneity modelling even in non-marine deposited reservoir sandstone, notwithstanding their known clean nature in contrast to mud-rich marine reservoirs.
- ItemImpacts of Land-Use Change, Associated Land-Use Area and Runoff on Watershed Sediment Yield: implications from the Kaduna watershed(MDPI, 2022-01-22) Adepehin, Ekundayo JosephAn uncontrolled sediment influx from the watershed upstream is a known threat to dam stability, while the pattern and amount of sediment yield are influenced by the predominant upstream land-use and land cover (LULC) types, precipitation amount, and intensity. Hence, the need to monitor sediment yield accumulation and its controlling factors in dam operation becomes crucial. In this paper, the Soil andWater Assessment Tool (SWAT) was used to assess the roles of landuse change, land cover area, and runoff on watershed’s sediment yield based on change detection analysis between 1975 and 2013 in the Kaduna Watershed (Nigeria), Western Africa. The SWAT standard procedures for the simulation of hydrological characteristics and sediment yields prediction were adopted. The datasets were calibrated for a period of 46 years and validated using 2015–2017 measured flow data, and suspended sediments concentration (SSC) acquired between March and October 2018. The model function was statistically determined using the Nash-Sutcliffe (NS), the coefficient of determination (r2) and the percentage of observed data (p-factor). The evaluation results of the SWAT model yielded NS, r2 and p-factor of 0.71, 0.80, and 0.86, respectively. These data suggest that the model performed satisfactorily for streamflow and sediment yield predictions. Findings suggest that the extinction of evergreen forests and a significant change in land-use from range grasses and forest to agriculture generic and residential types between 1975 and 2013, which resulted in surface runoff, sediment yield, and flow alteration. Evapotranspiration increased by 22.40% between 1975 and 2013. These changes have negatively impacted the watershed runoff by 56.00% and model sediment yield by 68.00% at the end of 2013. Thus, these variations can influence various human activities in the watershed, such as food security, livestock, energy production and water supply. It is hypothesized from the presented data that land use types exact a more dominant control on runoff and sediment yield than land cover area, although climatic influence may not be ruled out.
- ItemProvenance, palaeoclimate and palaeoenvironments of a non-marine Lower Cretaceous facies: Petrographic evidence from the Wealden Succession(Elsevier, 2021-01-15) Adepehin, Ekundayo JosephPetrographic datasets from sedimentary rocks are very useful for reconstructing their palaeoenvironmental settings especially when field and fossil datasets are unobtainable or inadequate. This study presents the first detailed and comprehensive petrographic study of the four formations constituting the non–marine Lower Cretaceous of the Weald Sub-basin of south-east England and employed petrographic descriptions to reconstruct their palaeoenvironmental settings. >120 samples were subjected to petrographic (QEMSCAN®, SEM, and thin section) analyses, which revealed that the framework composition of sediments is largely quartz-dominated (quartz arenites and subarkose) and has minor amounts of feldspar and lithics. The nature of the quartz arenites suggests that the Wealden successions were likely sourced from a stable interior craton/passive platform within a continental block and possibly from recycled flat-lying platforms such as low-lying granitic and gneissic bedrocks. The nature, maturity and the compositions of the sandstones suggest palaeoclimatic conditions were probably mildly hot and moist at the massifs and these perhaps favoured intense chemical weathering. The significant quantity of micas suggests that the Wealden sediments largely experienced very insignificant degrees of turbulence and agitation en-route depositional sites, thus yielding unwinnowed sediments. The presence of micaceous minerals, poor winnowing effect, and the general absence of diagenetic glauconite validate non-marine depositional environments. The palaeoenvironmental changes that occurred in the Lower Cretaceous in the Weald Sub-basin reflect (at least in part) palaeogeographic changes in NW Europe.
- ItemForaminiferal patterns and palaeoenvironmental inferences from DEL-1 well, offshore Niger Delta(Elsevier, 2021-10-23) Adepehin, Ekundayo JosephThe Miocene Epoch (23.3–5.3 Ma) represents a remarkable time in the Earth's geological history with significant palaeoclimatic and palaeoenvironmental relevance. In this study, microfossils recovered from the DEL-1 (4600–9460 ft) well in the western Detachment Fold Zone, offshore Niger Delta in the Gulf of Guinea were used to construe the age, palaeoenvironment, and palaeoecology of the penetrated successions. Standard foraminiferal analyses were carried out on one hundred and forty-eight (148) ditch cuttings retrieved from the studied interval following standard laboratory and identification procedures. Globigerinatella spp./Catapsydrax dissimilis Concurrent-range Zone (M3/N6), Fohsella birnageae Lowest Occurrence Subzone (M4b/N7), and Orbulina suturalis Lowest Occurrence Zone (M6/N9) of early to middle Miocene were identified. An overall progradational coastal and shelfal facies dominated by argillaceous and arenaceous sediment in the early and middle Miocene is construed, whereas interpreted palaeoenvironment of deposition indicates fluctuation between coastal deltaic, inner, middle, and outer neritic system with some fluvio-marine incursions between 4600 and 9460 ft intervals. The identified early Miocene succession is characterised by significantly high ecological parameters (diversity, evenness, richness), low salinity, and relatively high occurrence of foraminifera faunas compared to the middle Miocene. The relationships between the foraminiferal faunas and environmental factors suggest the local ecologic niche exhibits environmental heterogeneity that might have influenced even distribution of different microhabitat faunal preferences. Whereas the contributing influence of arenaceous sediment on the general dearth of microfossils in the upper section of the well cannot be neglected, the foraminiferal signatures reflect the ubiquitous middle Miocene carbonate crash event, and thus confirm its occurrence in the Gulf of Guinea.