Northern Benue Trough Research Articles

Structural and Geochemical Characterization of Baryte Mineralization in Liji Area, Northern Benue Trough, Northeastern, Nigeria

Structural and Geochemical Characterization of Baryte Mineralization in Liji Area, Northern Benue Trough, Northeastern, Nigeria

Diagenesis and reservoir quality evolution of estuarine sandstones: Insights from the Cenomanian-Turonian Yolde Formation, northern Benue Trough, NE Nigeria

Estuarine sandstones often exhibit complex diagenetic pathways due to the interaction of fluvial and shallow marine processes, resulting in significant reservoir heterogeneities. The Yolde Formation is an important petroleum reservoir in the Northern Benue Trough, NE Nigeria. However, diagenetic and reservoir quality evolution of the formation are still poorly understood. This study utilizes thin-section petrography, XRD, SEM, and fluid inclusion microthermometry to analyse the composition, diagenesis, and reservoir quality of the sandstones. Results show that the sandstones are mainly arkose and subarkose in composition; they are generally well-sorted and vary in grain size from very fine-to coarse-grained. Three diagenetic stages are identified: early, middle, and late. The early stage includes feldspar dissolution, formation of kaolinite, development of clay coating, and mechanical compaction. The middle stage comprises the formation of authigenic chlorite and Fe-oxide cements. The late-stage diagenesis involves illitization of kaolinite, formation of dickite, albitization of K-feldspar, and precipitation of quartz overgrowths. The diagenetic evolution of the sandstones was strongly controlled by their compositional makeup. The feldspathic nature of the sandstones resulted in the formation of kaolinite, illite, and quartz overgrowths, through feldspar dissolution and silica supply. The inner and middle estuarine facies have inhibited the development of quartz overgrowths due to well-developed clay coatings, whereas the outer estuarine facies were well-cemented by quartz overgrowths due to lack of clay coatings. Illitic clay coatings were found to be effective in preventing quartz cementation. Fluid inclusion analysis reveals that the formation temperatures of the quartz overgrowths range from 98 °C to 135.5 °C, corresponding to burial depths ranging between 2.3 and 3.5 km. These findings would provide useful insights that would reduce the risks of exploration of the sandstones and also supplies potential input data for forward diagenetic modelling of their subsurface equivalents in similar depositional settings elsewhere.

Facies distribution, paleoenvironment and hydrocarbon potential of Kanawa Member of Pindiga Formation, Gongola Basin, Northern Benue Trough, Nigeria

The Gongola sub-basin is a frontier inland sedimentary basin consisting of Cretaceous to Tertiary sediments, believed to have been deposited in continental to coastal shallow marine complex. The Kanawa Member of Pindiga Formation is a sequence of limestone and shale. Sedimentology, facies analysis, biostratigraphy, thermal maturity assessment and kerogen typing were conducted on these strata to determine the facies, facies associations, facies successions, paleoenvironment, age, and hydrocarbon generation potential. The studied sequences are of Turonian–Santonian age, deposited due to a major transgression of the basal part of the Pindiga Formation. The shale-limestone series of the Kanawa Member is interpreted as lagoon-to-shallow marine deposits of a carbonate ramp depositional system. The sediments consist of mainly wackestone and packstone facies and shallow marine foraminiferal, suggesting that the Kanawa Member was deposited under low-energy condition. The presence of Ammobaculites subcretacea, Haplophragmoides bauchensis, Haplophragmoides pindigensis, Haplophragmoides excavata, Ammobaulites pindigensis, Ammobaculites bauchensis, Ammobaculites gombensis, Ammobaculites benuensis Ammoastuta nigeriana, Reophax guineana and Miliammina pindigensis foraminiferal assemblages, indicating Late Cretaceous age. Hydrocarbon potential is interpreted to be gas prone although, minor oil could be expected. These correspond to temperature range (TAI values) of 60 to 75 indicating thermally matured for both oil and gas generation.

Provenance and paleoenvironmental studies of Bima and Dukul Formations in the Yola Basin, Northern Benue Trough, Nigeria.

Sedimentological studies of some areas located within latitudes 11035’E & 12000’E, and longitudes 9014’N & 9025’N were undertaken to delineate the surface lithologies of the Yola sub-basin, in the Northern Benue Trough. Field observations of the surficial deposits at Mayolope, Taana, Kpasam and Bille revealed that they are Bima Formation while the ones in Abare are Dukul Formation. Paleoenvironmental studies based on the characteristics of lithofacies of these exposed sections and laboratory assessments of some selected samples showed that the Bima Formation was deposited in a continental setting while the Dukul Formation was deposited in a low-energy marine setting. Petrographic studies of framework components showed that the samples of the Bima Formation were predominated by quartz minerals, leading to their identifications as sandstones and classifications as quartzarenites while the samples of the Dukul Formation were limestones and were classified as bioclastic packstones. Heavy mineral compositions of the sandstones revealed their provenance; Zircon and Tourmaline with a combined amount of 60.1% suggested igneous and low-grade metamorphic rocks while rutile and staurolite with a total amount of 27.7% indicated contributions from high-grade metamorphic rocks.

Palynological Studies of Some Coaly Shales around Gamawa Kumo area, Gongola Basin, Northern Benue Trough, Nigeria

Thirty (30) outcrop samples from a section at Gamawa area, Gongola basin, Northern Benue trough were palynologically analyzed to determine age, and paleo-depositional conditions of the strata. Lithological the section is composed of silts, clays and sandstone intercalations at the base followed by coaly shales and bioturbated silty to fine-grained sandstones at the top. Samples were treated with Hydrochloric and Hydrofluoric acids to remove carbonates and silicates respectively and slides were prepared using standard techniques. A total of 1250 palynomorph specimens were recovered. A palynological age of Upper Maastrichtian was assigned to this interval best on the assemblage of Maastrichtian diagnostic marker species of Longapertites marginatus, Proxaperties operculatus, Spinizonocolpites Baculatus, Monocolpites marginatus especially by the abundance of Pollen Spinizonocolpites Baculatus. Based on the low palynomorph marine index and dominating presence of Palme group species, especially the Spinizonocolpites Species the study suggested a paleodepositional condition of a mangrove forest with evidence of tidal dominated estuarine conditions in mostly brackishwater and a temperate climate.

Compaction-induced porosity loss in the Cretaceous Bima Formation around Lakwaime and Dogon Dutsi, Yola Subbasin, Northern Benue Trough, NE Nigeria

The Bima Sandstone is an alluvial fan to braided river sedimentation that represents purely a siliciclastic depositional system. It is the oldest formation and the main reservoir unit in the entire Benue Trough. Porosity loss is an essential component of petroleum reservoirs that needs to be properly investigated for the purpose of hydrocarbon exploitation. Compaction and cementation processes are partly responsible for porosity loss in many known reservoirs around the world. Outcropping units of the formation around Lakwaime and Dogon Dutsi in Yola Sub-basin have been subjected to an integrated approach involving field observations, petrographic analysis and porosity measurements in order to understand the contribution of each of the processes. Modal composition of the samples shows that they are mostly lithic arkose to feldspathic litharenite, with quartz as the most common detrital mineral grain. Grain fracturing has been attributed to mechanical compaction, whereas grain contacts like sutured and concavo-convex are products of chemical compaction. The average values of compactional-porosity loss (COPL), cementational-porosity loss (CEPL), and compaction index (ICOMPACT) in the studied samples stand at 19.51%, 4.18% and 0.82 respectively. The study indicates that the role of compaction in porosity loss is greater than that of cementation as shown by the COPL-CEPL diagram and, as such considered to be generally responsible for the porosity loss in Bima Sandstone.

Chemostratigraphy of the Cretaceous Yolde Formation in Yola Sub-Basin, Northern Benue Trough, Ne Nigeria

This research aims to determine the chemostratigraphy of the Yolde Formation. The formation has been inadequately studied systematically in the light of chemostratigraphy. The existing works on the formation either lack representativeness in terms of the proxies used or are subjective during their division procedures. From the field studies, five (5) samples of sandstone and shale units of the Yolde Formation were collected. The samples were analyzed for both major and trace elements using an X-ray fluorescence machine. The following geochemical parameters were studied; Al2O3, Al2O3/Fe2O3, KO2/Al2O3, TiO2/Al2O3, CaO, Cr, Rb/Sc, and Zr. From the studies, six (6) chemozones were identified in the Yolde Formation. Transgressive and regressive depositional sequences were observed with a significant sequence boundary of maximum flooding surface which is a time-significant feature. The chemostratigraphic scheme could not only be comparable to the regional sequence stratigraphic scheme but also more objective and higher resolution. This research gives a systematic chemostratigraphic analysis of Yolde Formation, which testifies to the feasibility and potential of the usage of chemostratigraphy for stratigraphic development.

New insights into tectonostratigraphy and structural style of the Late Cretaceous sediments of Gongola Basin, Northern Benue Trough, NE Nigeria

Tectonostratigraphy of the Gongola Basin is still least understood. This study aims to present a new insight into tectonic evolution and structure of Gongola Basin based on field geology. The study revealed that sedimentation processes commenced in the depression created by tectonic subsidence as a result of Early Cretaceous tectonic events, which affected the basin and subsequently, reactivated the Santonian/Maastrichtian compression. The sediments were affected by Santonian and Maastrichtian compressions resulting in syn-sedimentary deformation and post-depositional faulting and folding. The imprints of dextral strike-slip faults and reverse faults on pre-Maastrichtian and Maastritchtian sediments formed as a result of reactivation of the pre-Santonian and Santonian faults. Active rifting phase followed by uplift and subaerial exposure as in Gombe inlier, and adjacent areas such as Teli Fault, Kaltungo, Burashika inliers followed by subsidence allowing for initial deposit of continental sediments and later, marine ingression which causes a change from continental to marine environments during Cenomanian. Eustatic adjustment in Late-Cenomanian to Early-Turonian led to first major transgression and short-regressive phase in middle Turonian-early Santonian. Mid-Santonian compression folded the sediments and was followed by subaerial erosion of parts of the folded sediments. Another eustatic adjustment in Late-Santonian-Campanian led to a short-lived transgression. A gradual retreat of the sea in the Maastrichtian resulted in progradation of Gombe Sandstone. Late Maastrichtian compression in end-Cretaceous tectonic event folded and tilted Gombe Sandstone, responsible for the angular unconformity that existed between Gombe Formation and overlying Paleocene sediments of Kerri-Kerri Formation, mostly restricted to NW of the basin.

Application of tetracyclic polyprenoid biomarkers in Yola Basin of the Northern Benue Trough, northeast Nigeria: Implications for source origin and paleoenvironment

Tetracyclic polyprenoids biomarkers (TPP) were investigated on the Cretaceous sediments of Yola Sub-basin based on gas chromatography-doublet mass spectrometry. This is with an objective to re-examine the organic source input and paleodepositional environment of the sediments. The study revealed that the Bima shales were deposited in the lacustrine environment under suboxic to relatively anoxic depositional condition while the analysed Yolde, Dukul, Jessu, Sekuliye and Numanha shale sediments were deposited within the marine environment under suboxic depositional condition. More so, the analysed Lamja coal and shale samples were deposited in a delta environment under oxic to suboxic depositional condition. The study therefore, suggest that the paleodepositional environments of the studied shale sediments within the Yola Sub-basin remain as continental (lacustrine), transitional (marine and delta) and could have the potential to generate appreciable quantity of oil and gas.

PALYNOFACIES STUDIES OF THE LATE CRETACEOUS (TURONIAN-MAASTRICHTIAN) STRATA FROM JAURO JATAU, GONGOLA SUB-BASIN, NORTHERN BENUE TROUGH, NIGERIA

Geographically located within Gombe, Bauchi, and Yobe states, the Gongola Sub-basin has drawn attention from several academics looking to increase Nigeria's oil reserves relative to the inland frontier basins. This paper's goal is to determine the thermal maturity of strata from drill samples of the Fika shales in Nigeria's Northern Benue Trough, Gongola Sub-basin. To predict the well section's maturity and kerogen type, this study uses optical and organic facies studies. Twenty-seven samples of ditch cuttings were prepared using the universally accepted acid palynological procedure. The dispersed mounted slides revealed a variety of pollen, spores, and palynomacerals upon microscopic inspection. The well section under study exhibits a range of thermal maturation from mature to late mature, indicating the possibility of producing oil and gas. This corresponds to a range of thermal alteration values of 4 – 6 and equivalent vitrinite reflectance (%Ro) values of 0.6% – 1.35%. The total recovered Sedimentary Organic Matter (SOM) in this study was classified into Palynomorphs, Amorphous Organic Matter (AOM) and Phytoclasts and plotted on a ternary graph. The Percentage frequencies of AOM, Phytoclast and Palynomorphs were compared with the zones of the Tyson Ternary diagram. Most of the distribution frequencies lie within zones II, IX, VI and Iva suggesting Kerogen types III (gas-prone) and II (oil-prone).

Pb-Zn-Ba deposits in the Nigerian Benue Trough: A synthesis on deposits classification and genetic model

The Benue Trough stretching about 800–1000 km with a width ranging between 100 and 150 km, is a megarift structure whose origin was related to the opening of the south Atlantic during the early Cretaceous. This mega rift structure contains economically significant Pb-Zn-Ba-F deposits that form well-defined metallogenic belt about 600 km long in Nigeria. In the Southern Benue Trough (SBT), the Pb-Zn-Ba-F deposits are localized in four districts namely Abakaliki, Ishiagu, Wanikande and Gabu-Oshina and are hosted by carbonaceous shale; in the Central Benue Trough (CBT) the deposit is hosted in the silicified limestone and arkosic sandstone localized in Arufu, Akwana and Azara districts; while in the Northern Benue Trough (NBT) ores deposits occur in the arenaceous sediments of Yolo, Gombe and Gulani districts. Previously published sulfur (S) isotopic data of sulfides suggest that the ore-forming S was sourced from marine sulfates and the reduction of sulfate mainly by thermochemical sulfate reduction process in the CBT and NBT. Whereas in the SBT, bacterial sulfate reduction process is dominant. The compiled C-O isotopic compositions suggest that limestone and slightly metamorphosed sedimentary rocks supplied ore-forming materials to the hydrothermal systems through water/rock interaction. The available bulk Pb isotopic compositions for the ore minerals, the host sedimentary and crystalline rocks comprising the basement rocks as well as the basaltic rocks from the Trough suggest that the arkosic sandstone which is composed of detrital feldspars that was eroded from the Precambrian basement rocks could be the likely source of ore-forming metals. Our model proposed that the ore-forming fluids were sourced from the hot connate-brine that was expelled through compaction during the development of the deep sedimentary basins. Mesozoic magmatic events distributed throughout the basin likely provided the initial thermal flow and elevated the geothermal gradient. The hot brines could have leached the metals from the syn-rift continental formations. The tensional fractures serve as the conduit through which the metals migrated, leached abundant sulphate and precipitated their contents in the transcurrent fault system as sulfides, barite and associated polymetallic ores. The geological, mineralogical, and geochemical characteristics of the Nigerian Benue Trough Pb-Zn deposits are consistent with Mississippi Valley-type (MVT) Pb-Zn deposits in North Africa and the typical MVT ore deposits worldwide.

Maastrichtian – Paleocene environmental and climatic conditions in Koum Basin (northern benue trough, Cameroon) inferred using a multiproxy approach including sedimentology, mineralogy, and geochemistry

The Koum Basin is one of major intracontinental basins in northern Cameroon. It is part of the Upper Benue Trough and has genetic ties to the West and Central African Rift System. The main purpose of studying the Koum Basin sedimentary deposits was to re-examine the time of the deposition and constrain the palaeoenvironmental and paleoclimatic conditions during deposition. To accomplish this, we used a combination of sedimentologic, palynologic, mineralogic, and geochemical data. Claystone units interbedded with calcareous siltstones dominate sedimentary sequence, including few clay beds, fine to medium-grained sandstone, and rare marl layers. The palynomorph assemblage suggests a previously unknown Maastrichtian – Paleocene age in this basin. The sediments originated from intermediate igneous parent rocks with a relative contribution of felsic rocks. These rocks underwent low detritism (Si/Al: 2.51–4.43; K/Al: 0.11–0.36; Ti/Al: 0.05–0.10) and chemical weathering (CIA: 55–64; PIA: 56–68) in the source region. Consequently, deposits are immature (ICV values > 1) and weakly recycled (Si2O3/Al2O3 ratios ≤5). The organic matter analysis and the palynoflora assemblage, reveal Type III kerogen with significant contributions of Type II-III and type II kerogens, as well as a continental paleo-depositional environment with open rainforest to savannah vegetation. The clay minerals distribution suggests moderate illitization and chloritization processes and thus moderate burial diagenesis at temperatures ranging from 70 to 90 °C, also attested by immature to mature Tmax values (≤436 °C) marginally. The low CIA values and very low kaolinite contents, indicate dry climatic conditions. In addition, two major-element-based discrimination diagrams show that the parent rocks of clastic sediments formed primarily in a continental arc system, with a moderate contribution from the rift system and a low contribution from the oceanic island arc, implying compressional conditions, which is consistent with previous studies on the tectonic background of the region during the late Maastrichtian to Paleocene period.

Linking diagenesis and reservoir quality to depositional facies in marginal to shallow marine sequence: An example from the Campano-Maastrichtian Gombe Sandstone, Northern Benue Trough, NE Nigeria

Fluvio-deltaic strata host significant volumes of hydrocarbons in different basins across the world, and are characterized by depositional heterogeneities and varying diagenetic overprints, owing to complex interactions of different depositional processes in diverse sub-environments. An understanding of the heterogeneities at different scales is critical to the prediction of reservoir quality distribution and architecture in these strata. The Campanian-Maastrichtian Gombe Sandstone is one of the targeted reservoirs in recent hydrocarbon exploration in the Northern Benue Trough, NE Nigeria. However, to date, the diagenetic and reservoir quality evolutions of the sandstone are not well understood. In this study, a multi-technique approach (consisting of thin-section petrography, scanning electron microscopy, and X-ray diffraction analyses) was employed to link depositional facies and diagenesis to reservoir quality. Results of the study indicate that the sandstones are principally arkosic and subarkosic in composition, and were deposited in lower delta front/prodelta, upper delta front/mouth bar, distributary channel, and interdistributary tidal bar/channel depositional environments. The sandstones experienced both shallow burial and some relatively of deep burial diagenesis. Kaolinite is the most abundant eogenetic cement in the sandstones, and was particularly found to be more abundant in the interdistributary tidal bar/channel and lower delta front/prodelta depositional environments due to their significant amounts of reactive detrital feldspars and muscovite precursors, respectively. The interdistributary tidal bar/channel and the distributary channel depositional facies were highly susceptible to siderite cementation, owing to their proximity to organic-rich mudstone lithofacies. Mechanical compaction was more intense in the lower delta front/prodelta than in the interdistributary tidal bar/channel sandstones, due to the presence of high clay matrix content in the former, which enhanced ductility and close packing. The interdistributary tidal bar/channel sandstones form the best reservoir quality because of the very low amounts of detrital pore-filling matrix (average 1%; n = 24) and less compaction compared to the lower delta front/prodelta, upper delta front/mouth bar and distributary channel sandstones. Grain-coating smectitic clays were best developed in the lower delta front/prodelta, upper delta front/mouth bar and distributary channel, whereas they are poorly developed in the interdistributary tidal bar/channel sandstones. The overall low volumes of deep burial, mesogenetic cements in the sandstones (e.g., illite, dickite, and quartz overgrowths) suggest that the Gombe Sandstone spent short residence time in mesogenetic realm before being uplifted. The results of this study would provide useful input data and understanding that can be utilized for forward diagenetic modelling and burial history construction for the subsurface Gombe Sandstone reservoir in the Northern Benue Trough and similar sedimentary formations elsewhere.

Assessment of Reservoir Quality of the Cretaceous Yolde Sandstone: A Case Study of Doma Stream, Gongola Basin, Northern Benue Trough, Northeast Nigeria.

Sedimentology, petrography and petrophysical studies were applied to the Cretaceous Yolde Formation sediments along the Doma stream, to evaluate its reservoir quality. The Yolde Formation along the Doma Stream is composed of lithologies that are laterally extensive and have reached a thickness of about 80m. They are lithologically made of sandstones with dark grey mudstones, laminated shales and grey to pale yellow limestones. The Sandstones are structurally characterized by planar, tabular and trough cross-beds, convolute beds, and hummocky cross-stratifications with reactivation surfaces. Some of the sediments are bioturbated. The petrophysical evaluation indicated porosity values ranging from 6% to 26%, and permeability values between 12.7mD and 108mD. These values are comparable to the reservoir rocks of proven petroleum basins of the North Sea and Niger Delta. Therefore, the Yolde Sandstones of the study area can have great potential to serve as good reservoir rock in the Gongola Basin.

Source-rock potential and paleoenvironment of the Coniacian Numanha Formation, northeastern Nigeria: An integrated palynofacies and geochemical approach

A study of source-rock characterization and paleoenvironmental interpretation has been carried out on a relatively thick Coniacian sedimentary succession from the Numanha Formation in the Guyuk area of the Yola arm in the Northern Benue Trough, northeastern Nigeria. The aim is to provide organic facies data for the assessment of its hydrocarbon generating potential owing to the high prospects of its lateral equivalent Fika Shale in the Gongola arm of the Northern Benue Trough. The investigation of 98 samples from three outcrop sections [09° 50′ N, 11° 51′ E; 09° 54′ N, 11° 50′ E; 09° 54′ N, 11° 49′ E] which includes palynofacies analysis, spore/pollen coloration, and geochemical analyses enabled an evaluation of organic matter richness and quality. Measured TOC ranges between 0.01 and 7.4% which reflects poor to good organic richness, while visual kerogen characterization shows thermally mature Type II-III kerogen indicative of oil and gas prone materials. Recovered palynomorphs comprised both marine (dinoflagellate cysts, microforaminiferal test linings) and terrestrial (spores, pollen, freshwater alga Pediastrum) taxa. These palynomorphs vary in proportion at different horizons of the sections indicating shoreline fluctuations. Except for the Kurnyi section, amorphous organic matter occurs in minor percentages, indicating low preservation potential during deposition. All data indicate that the Numanha Formation was deposited in a highly proximal to mud-dominated oxic shelf environment.

Palynofacies and sea level changes in the Upper Cretaceous of the Yola Basin, Northern Benue Trough, Northeastern Nigeria

Upper Cretaceous sediments (Numanha and Lamja Formations) in the Yola basin of Northern Benue Trough have been investigated in order to characterize the particulate organic matter (POM) in the samples. The aim is to understand the rapid facies changes in both vertical and lateral direction of the formations and the relative abundance of the different organic components within the sections. The investigation involved 62 samples from four outcrop sections. The analysis involved series of laboratory procedure ranging from sample preparation, chemical treatment with HCl and HF, sieving, slide cover and completion then the counting of 300 particles per sample. The samples yielded sufficient organic residues for detailed palynofacies analysis. The organic constituents observed in the studied samples have been classified into phytoclast, palynomorp and amorphous organic matter groups. The phytoclast group predominates in almost all the sections followed by the palynomorp group with little amount of amorphous organic matter (AOM). The palynofacies parameters used for the study are the continental/ marine and opaque/translucent ratios which led to the construction of the sea-level variation pattern for the formations using Tilia 2.0.2 program.

Role of diagenetic alterations on porosity evolution in the cretaceous (Albian-Aptian) Bima Sandstone, a case study from the Northern Benue Trough, NE Nigeria

The Cretaceous Bima Sandstone is a potential hydrocarbon reservoir that is currently being explored in the Northern Benue Trough, NE Nigeria. The sedimentological characteristics and tectonic evolution of the formation have been extensively studied by previous researchers. However, the impact of diagenetic alterations on porosity evolution of the sandstone is poorly understood. This study employed a multi-technique approach, including thin-section petrography, SEM, XRD, and cathodoluminescence analyses to investigate the role of framework composition, primary depositional characteristics, and diagenetic alterations on porosity evolution of the sandstones. The results of the study indicate that the Bima Sandstone has a present-day intergranular porosity ranging from 0 to 25.9%, averaging 5.8%. Diagenetic alterations, including mechanical and chemical compaction and quartz cementation, have significantly modified the porosity of the sandstones more than the primary depositional features (grain size and sorting). Porosity reduction was mainly due to mechanical compaction (av. 32.1%) than cementation (av. 7.4%). Quartz overgrowths (up to 15%) are the most abundant cement in the sandstones, formed primarily due to lack of grain-coating clays. The main eogenetic alterations related to shallow burial include dissolution and kaolinitization of feldspars and, to some extent, mechanical infiltration of smectitic clays, which formed largely discontinuous clay coatings and pore-filling clays. Mesogenetic alterations related to deep-burial include the formation of quartz overgrowths, transformation of kaolinite and smectite into illite, and pervasive albitization of both plagioclase and K-feldspar, which is exclusively associated with the deepest, Lower Bima Sandstone Member, and has significantly reduced the secondary porosity in the sandstones. Telogenetic alterations related to uplift, mainly include dissolution and kaolinitization of unstable feldspars, which has significantly increased the present-day, secondary porosity of the sandstones to up to 15%. Pore-filling clays (chlorite, illite, and kaolinite) have had a small impact on the intergranular porosity of the sandstones, mainly because of their low volume. The study provides insights into how diagenesis can significantly affect the reservoir porosity of the sandstones and could also assist in reducing the risk of exploration of the fluvial reservoir in the basin and elsewhere.

Analysis of high-resolution airborne-magnetic data for hydrocarbon generation and preservation potential evaluation of Yola sub-basins, northern Benue Trough, northeastern Nigeria

High-resolution airborne-magnetic data acquired over the Yola extension of the northern Benue Trough, northeastern Nigeria, were analyzed to delineate rock distribution, define basement geometry, determine sedimentary thicknesses, and highlight structural framework among others for the hydrocarbon prospect evaluation of sub-basins in the extension. Filtered and refined magnetic intensity data were subjected to Analytic Signal, Horizontal and Vertical Tilt Derivatives and Euler deconvolution depth weighting analyses to enhance various geological features requisite for petroleum prospect evaluation. Sedimentary rock units flanked the northeast and south widely occur in the central part with volcanic rock intrusions delineated within the sedimentary terrain. Extracted lineaments (less than 5 km and up to 45 km) were observed to dominantly follow the established Benue Trough and Yola sub-basin evolutionary trend along the NE–SW and ESE–WNW directions, respectively. Three prominent sub-basins with sedimentary thicknesses in excess of 3 km and width of more than 60 km, separated by basement highs of mostly volcanic intrusions origin, were identified. The occurrence of relatively thick and extensive sub-basins which are underlain by structurally active basement rocks suggests relatively high geothermal gradient for generation of hydrocarbon from organic matter rich source rocks while the generated oil and gas are preserved within intra-sedimentary structural traps created when the basement fractures were reactivated.

Preliminary source rock evaluation, paleo-depositional environment and hydrocarbon generation potential of the cretaceous organic-rich outcrops of Mayo-Figuil River, Babouri-Figuil Basin, Northern Benue Trough (Yola arm) Cameroon: Insights from bulk geochemistry

Babouri-Figuil sedimentary basin is considered the most northerly and one of the most attractive intracontinental Cretaceous basins in North Cameroon, which contains organic-rich deposits presumed to be oil shale levels. The fieldwork carried out as part of this study enabled to delineate six lithological units mainly consisting of black shales, marls, orange clay, black to grey clays and limestones. Twenty-two samples from the studied section were subjected to bulk organic (Rock Eval pyrolysis) and inorganic (biophiles XRF-trace element) geochemistry to investigate their hydrocarbon generation potential. Field data and organic geochemical analysis of organic matter reveal that three of the six lithological units are potential hydrocarbon source rocks; these are units 1 (1.50 ≤ TOC ≤3.98%), 2 (0.47 ≤ TOC ≤1.17%) and 4 (TOC = 24.74%) consisting mainly of black to grey clays and black shales. These source rocks are discontinuously distributed throughout the studied section with a cumulative stratigraphic thickness of 275 cm. The organic matter contained in unit 1 is mainly Type II/III (182 ≤ HI ≤ 382 mg HC/g TOC) with a significant contribution in Type II kerogen. It is mature (443 °C ≤ Tmax ≤448 °C) at the base (MF-1, -2, -3 and -4) and immature (Tmax = 416 °C < 435 °C) at the top (MF-5). Unit 2 contains early-mature type III organic matter (98 ≤ HI ≤ 155 mg HC/g TOC; 438–439 °C). Organic matter in unit 4 is also early-mature and has generated mainly oil (Type I or IIS). The combination of proxies of biophile trace elements (cross plots Ni/Co vs. V/Ni and V vs. Ni) indicates that this organic matter is of mixed source, both marine and terrestrial origin, deposited under oxic-dysoxic conditions. Thus, subject to further geochemical analyses and given the pessimistic predictions from outcrop samples, these units are conventional effective source rocks in place of the early reported immature oil shale levels.

Depositional setting of the late cenomanian to early turonian sediments of Yola sub-basin, northern Benue trough, Nigeria: From lithofacies and palynofacies

No Abstract.