Gongola Basin Research Articles

Organic petrography, Rock\u2013Eval pyrolysis and biomarker geochemistry of Maastrichtian Gombe Formation, Gongola Basin, Nigeria

The Maastrichtian Gombe Formation is located within one of the inland basins of Nigeria (Gongola Basin). Surface and borehole samples of coal and interbedded shale of this formation were evaluated to determine the organic matter richness, quality, maturity, source and depositional environment through organic geochemical techniques such as total organic carbon (TOC) determination, Rock–Eval pyrolysis, chromatography and organic petrography. The genetic potential and average TOC value of the coals, shales and coaly shales are 38.03 wt%, 3.14 wt% and 12.1 wt%, respectively, indicating moderate-to-good source potential. HIs are less than 200 mgHC/gTOC for all the samples indicating Type III kerogen for most of the samples (gas prone) and plant contributions from terrestrial sources. The source rocks were characterized by high molecular weight n-alkanes which range from C10–C41 in the coals and C9–C41 in the shales. The n-alkanes distributions in the coals maximize at C29 indicating terrestrial sourced organic matter, while the shales maximize at C16 and C29 indicating mixed sources. Pr/Ph of the coals and shales ranges from (2.15–3.51) to (0.95–2.37), respectively, suggesting fluvio-deltaic deltaic and coastal swamp depositional environments. The predominance of pristane over phytane suggests humic origin of the organic matter. The sterane/hopane values (< 0.6) indicate incorporation of bacterial inputs commonly associated with terrigenous organic matter in the coals. The CPI is greater than unity, Tmax is generally < 435 °C and vitrinite reflectance less than 0.55 Ro for most of the samples and suggest the samples are of low maturity status to expel liquid hydrocarbon.

Depositional sub-environment of Gombe Sandstone in Kumo and its environs, part of Gongola Basin, Northern Benue Trough, Northeastern Nigeria

Evaluation of Gombe Formation in the area around Kumo part of Gongola arm was carried out with a view to determine its depositional sub environment in the area through detailed geologic mapping, litholog construction and petrographic as well as sieve analyses of the sandstone samples. Detailed geologic mapping in the study was carried out hence the production of the geologic map of the area. Other pertinent geologic information such as color, texture, sedimentary structures, thicknesses of different beds and their vertical and lateral changes were determined. Four samples each were collected and subjected to laboratory analyses (i.e sieve analysis and petrography). Three stream sections were identified and logged in the field and plotted using sed log computer program. The sections include Kandahar stream section where a sequence of sandstones, mudstone and ironstone of Gombe Formation along a stream channel with a total thickness of 5.2 m is recognized; the GRA stream section where strata of Gombe Formation with a thickness of 2.06 m comprising sandstone, mudstone and ferriginized sandstone caping were logged and the Jauro Bose stream section where strata with a total thickness of 2.0 m comprising of sandstones and ferriginized reddish brown sandstone and mudstone with ferriginized sandstone interbeds. The Gombe Formation in the study area is characterized by yellow to brown sandstones with interbedded mudstones, ferriginized sandstones and ironstones. Grain size analysis indicate that the sandstones of Gombe Formation in the study area is fine to very fine grained, moderately well sorted, strongly coarse skewed and leptokurtic to very leptokurtic. Petrographic results indicate that all the analyzed samples contain large percentages of quartz in excess of 65 – 71 % with greater than 10% matrix and are characterized by angular to subrounded grains of quartz, feldspar and rock fragment and fall within the domain of feldspathic wacke and lithic wacke in the QFL diagram for sandstone classification scheme. Field evidences like interbeds of mudstones within the sandstone beds, flaser beddings, parallel laminations and bioturbations suggest that the sandstones were deposited in a transitional environment influenced by tides. Additional evidence is observed from laboratory analyses results especially sieve analysis that indicate fine to very fine grained sands and moderately well sorting, coupled with the characteristic shapes and the level of maturity obtained from the petrographic results like the large percentage of quartz and the subangular to subrounded grains. Integrating the field evidences and the laboratory results, the depositional sub environment for the Gombe Formation in the study area is interpreted to be intertidal environment of tidal flat of an estuary.

Extraction of lineaments and faults using gravity second horizontal derivative data obtained using Fourier transform

Linear anomalies are important in the interpretation of gravity data because they indicate some important structural features. Gravity anomalies obtained from horizontal derivatives generally reflect lineaments and faults or compositional changes which can describe structural trends of a region. This study involves the delineation of the Gongola basin structural trend based on the convolution between the Fourier kernel obtained from the second horizontal derivative (SHD) of the truncated horizontal plate model (THPM) and the gravity anomaly. The Fourier kernel for the second horizontal derivative was obtained through the application of Fourier transform over the expression of a Bouguer slab with exponential density contrast variation. The weighting density distribution is obtained through the determination of the mean depth perturbed by interfaces. The edges were identified by the closed maximum in the SHD gravity map. The results show that the region’s Bouguer gravity is characterized by elongated SE-NE negative gravity anomaly corresponding to a collapsed structure associated with a granitic intrusion beneath the region, limited by the fault systems. This was clearly evident on an isostatic residual gravity map. The horizontal gradients of the Bouguer gravity anomaly data from the basin defined the edges, lineaments and faults structures very clearly. Major and minor lineaments derived from the SHD map were transposed on the isostatic residual map. These features led to the production of the structural map of the study area. The NE-SE and E-W trending lineaments were interpreted as fault (strike-slip wrench) systems. The steep gradients evident in the gradient maps are reflection of sharp discontinuities or interfaces between basement blocks of contrasting properties, such as: fault, basement shear zones and intrusive contacts. The tectonic information brought about by the distribution of the lineaments was corroborated by the 2D gravity model of the basin. These models and fault map will complement the selection of the promising areas for detailed hydrocarbon mapping.

Lithostratigraphy and geochemical characterization of limestone deposits around Kushimaga Area in Yobe Of North-Eastern Nigeria

This study presents detailed petrographic and chemical compositional characteristic of limestone deposits for possible industrial uses and specifications. The study area falls within the Gongola basin, North-eastern Nigeria. Core limestone samples were collected from four boreholes at the depth of approximately 25 metres each in Kushimaga area around Gulani in Yobe state; north-eastern Nigeria. Lithological units were observed in the following sequence; topsoil and clay with an average thickness of 1.513m, limestone 5.553m, shale 7.853m respectively. Eleven limestone samples were selected from the boreholes for petrography and chemical analysis (Fluorescence Spectroscopy analysis). From the petrograhic studies the limestone samples are composed (visual estimate) of over 95% calcite, trace amounts of colourless already recrystallized fossil of planktonic forams and mollusc, weakly deformed greenish grains of glauconite about 0.2 to 0.3 mm in grain size, traces of opaque, isotropic, high relief iron oxide minerals with 0.03 to 0.5 mm grains sizes are present disseminated in the form of limonite. Traces of quartz and feldspar grains of silt size class were also noted in thin sections. With less than 10% grains the samples are classified as mudstone. The results of chemical analyses of limestone shows a range values of SiO 2 , 10.05wt% to 32.00wt% , CaO, 21.00wt% to 53.99wt%, MgO, 0.35wt% to 1.00wt%, Al 2 O 3 , 2.15wt% to 12.69wt%, Fe 2 O 3 , 1.28wt% to 4.90wt%, Na 2 O, 0.002wt% to 0.18wt%, K 2 O, 0.9wt% to 1.96wt%, TiO 2 , 0.21wt% to 1.00wt%, P 2 O 5 , 0.17wt% to 0.69wt%, MnO, 0.21wt% to 0.55wt%, loss on ignition, 21.98% to 36.87%, while the result of chemical classification of the limestone show a range of Ca/Mg, 23.33% to 125.68% and Mg/Ca, 0.00% to 0.04% of the Kushimaga limestone. However, the limestone beds of the research area were compared with other standard chemical industrial specifications. The study revealed that the limestone around Kushimaga area satisfies the chemical factors for Portland cement production but falls below the standard chemical specifications for other industrial uses; glass, sugar and Paint pigments and filler productions. Keywords: Argillaceous, bivariant, core, lithology, petrography and stratigraphy

Description of soft sediment deformational structure of the Campano-Maastrichtian Gombe formation of the Northern Benue Trough, N.E. Nigeria

Several soft sediment deformational structures were identified during fieldwork survey carried out on exposures of Gombe Formation in the Gongola sub–basin of the Northern Benue Trough at Gombe and environs. These soft sediment deformational structures includes: simple internal cusps, which occur wide spread across a single bed or intermittently across several beds, and slump structures that are represented by complex recumbent folds and concave upwards structures. These structures are proxy to syn-depositional energy operating within the depositional environment and this current research aims to evaluate their trigger mechanism. These deformational structures are commonly hosted in the mouth-bar deltaic sequences of the Gombe Formation. The deltaic setting is usually a locus for high sediment influx and accumulation. This may have generated high quantum of depositional energy which was probably responsible for the development of the syn-depositional soft sediment depositional structures in the Gombe Formation during Campano-Maastrichtian times. KEYWORDS: Gombe, Sandstone, Gongola Basin, soft sediment Benue trough.

Basement Depth and Sedimentary Velocity Structure in Gongola Basin

Basement depth in the Gongola basin is found to be much deeper than previously supposed. Gravity modelling of the upper Benue Trough, Nigeria revealed thick sedimentation with maximum values within the range 5.2 km-7.0 km. This is in contrast to the average value of 5.0 km suggested by earlier studies. Gravity modelling across the basin was carried out to determine the basement depth using the second vertical derivative as input anomaly profile. The seismic modelling process in this research involves the determination of the distribution of seismic velocity using the: depth-normalized velocity iteration technique, check shot and sonic log curves. The integrated depth algorithm (IDA) iterative process was adopted in the determination of the interval and depth normalized interval velocities to adequately address the depth conversion for the determination of the lithology of the basin. The localized nature of the interpreted velocity data were extrapolated away from and interpolated between acquisition location using the areal coverage provided by gravity and seismic data. The interpretation involves the integration of the seismic reflection profiles, well logs and potential field data to establish a model of the sedimentary thicknesses and seismic velocities throughout the basin. The Basement depth on the north east of the basin is 7.0 km, southeast is 5.2 km whilst the northwest and southwest ranges between 0.5 km and 1.0 km respectively. The basement depths obtained from the gravity model was compared with that obtained from reflection seismic observation from the study area and the relative error percent were 1.37% and 0.46% respectively. The Precambrian basement depth normalized interval velocities ranges between 6.2 km/s and 6.4 km/s respectively. The qualitative interpretation of the second vertical derivative shows that the rift architecture/geometry is controlled by high angle faults and extended graben structures that form the major depocenters that are predominant in the upper Benue rift system. The grabens, half grabens, faults and deep sedimentation interpreted from the seismic reflection data are hydrocarbon related structural features. Consequently, the potentially hydrocarbon (gas) rich Yolde/Bima (Cenomanian-Albian) stratigraphic formations at depth between 2.1 km and 2.7 km and the depth normalized interval velocity varies from 2.9 km/s to 3.3 km/s and it occurs within the southeast zone of the basin.

Radioactivity and hydrocarbon generation potential of sediments, Gongola Basin, Nigeria

Abstract Samples taken from Well Kolmani-1 in the Gongola Basin in the Upper Benue Trough of Nigeria were studied to estimate the radiogenic heat generated and to analyze the possible impact of radiogenic heat on hydrocarbon generation potential of the sediments. Thirty-eight samples taken from the different formations at intervals of 73.2 m including sand, shale, coaly shale, sandy shale, and shaly sand were analyzed for 40K, 238U, and 232Th using the well calibrated NaI (Tl) Gamma Ray detector System. The results showed that the activity concentrations of the radio-nuclides varied significantly within the sediments. The 40K concentrations were the highest. The radiogenic heat produced ranges widely from 228.44 pW/kg to 1 412.82 pW/kg. In Well Kolmani-1, sands and sandy shale are low heat production sediments, while the shale, coaly shale and silty sands are medium heat production sediments, the potential source rock (shale and coaly shale) medium in heat production (750 pW/kg to 1 500 pW/kg), can produce liquid and gaseous hydrocarbons. It is estimated that the radiogenic heat from the sediments contributed about 10.9% to 20.9% to the total surface heat flux in the basin. Therefore, the radiogenic heat generated by the sediments contributed significantly to the total surface heat flux, and should be taken into consideration in the simulation of basin thermal evolution.

Rock-Eval pyrolysis and organic petrographic analysis of the Maastrichtian coals and shales at Gombe, Gongola Basin, Northeastern Nigeria

The Gongola Basin forms one of the inland Cretaceous to tertiary sedimentary basins in Nigeria with relatively unknown petroleum system. In this study, the investigated source rock intervals of the Maastrichtian Gombe Formation are located at the Maiganga coal mine, near Gombe, Gongola Basin, Nigeria. The exposed part of the mine consists of about 35-m thick coarsening upward section with the basal part made up of coal and shale interbeds while the upper part consists of siltstone and sandstone and probably deposited in fluvio-deltaic environment. The coal and interbedded shale appear most prospective source rock facies in the formation and were evaluated with respect to their hydrocarbon source rock potential. The organic geochemical results showed high TOC for the coals (37.71–65.29 wt%) and moderate organic carbon concentration (1.19–4.81 wt%) for the shales. S2 values ranges from 57.96 to 103.21 mgHC/g rock and 0.51–6.22 mgHC/g rock for the coal and shales, respectively. The HI is less than 200 mgHC/gTOC in all the coal and shale samples suggesting Type III kerogen and predominant plant contributions from terrestrial sources. Consequently, gaseous hydrocarbon potential is exhibited in the source beds. The organic petrography shows vitrinite as dominant maceral followed by inertinites and liptinites with inorganic minerals like pyrite and kaolinite. The Tmax is less than 435 °C in all the samples indicating pre-oil window stage; this is corroborated by the Romax value ranging from 0.45 to 0.55 %. Plot of PI against Tmax indicates low level organic matter conversion while the vitrinite reflectance values suggest a sub-bituminous coal. The study suggests that the investigated coal and shale samples constitute good source rock and have potential for gas. The generally low HI in the coals and the associated shales indicate more allochthonous and hydrogen poor organic matters in the source beds. Maceral composition of the coals suggests wet swamp environment and predominance of arborescent vegetation type. At present level, the organic matters are immature to marginally mature deeper level equivalents might have generated gas.

Reservoir Potentials of the Cretaceous Gombe Sandstone, Gongola Basin, Upper Benue Trough, North Eastern Nigeria

The Campano - Maastrichtian Gombe Sandstone of the Gongola Basin of the Upper Benue Trough is composed of arenaceous lithology that is laterally extensive and has reached a thickness of over 300m. The petrophysical evaluation of the formation on the basis of bivariate plots, petrographic analysis and falling head permeability indicated average porosity values of 15%, 33% and 23% respectively. Average permeability values of 5.2D and 100md were also obtained from bivariate plots and falling permeameter analysis respectively. These values are comparable to the reservoir rocks of proven petroleum basin of the North Sea and Niger Delta. Therefore, the Gombe Sandstone can serve as a potential reservoir rock in the Gongola Basin.

Field Study of the Positive Flower Structures of the Gombe Inlier, Upper Benue Trough, Northeastern Nigeria

Abstract The Gombe inlier can be considered as a geological microcosm of the Gongola basin as it vividly displays general stratigraphic and structural styles within a relatively small, easily accessible area. The Cretaceous lithostratigraphic sequence of the Gombe inlier has been affected by sinistral strike-slip faults; the Gombe and Wuro Ladde-Wurin Dole faults with a Benue and Gongola trend respectively. Detailed study of these two faults shows that the Gombe fault is older and synsedimentary fault movement started in at least the mid-Santonian. Precambrian basement upthrust along the Gombe Fault is likely to have initiated during the first of the two compressive events that affected the upper Benue trough; the mid-Santonian N - S to N 174° E compression. The Wuro Ladde - Wurin Dole fault is relatively younger because (1) it sinistrally truncates the Liji hill anticlines that occur at the northern end of Gombe hill, resulting in a NEE - SWW trend, and (2) the orientation of transpressional structures along this fault suggest they developed during the end-Cretaceous N 140° E to N 150° E compression. Well-preserved transpressional structures along these faults provide the structural geologist a rare field examples to study their 3-dimensional (3D) geometry and kinematic evolution; and also as an analog for interpreting seismic reflection data that images complex strike-slip structures in the sub-surface.

Nature of the Campano-Maastrichtian Sub-Basins in the Gongola Basin, Nigeria

Geological mapping was carried out and outcrop sections were examined alongside palaeocurrent directions from the greater part of the Campano-Maastrichtian outcrops in the Gongola Basin in Nigeria. Palaeocurrent measurements were obtained from asymmetrical ripples, cross bedding and dune bedforms within the channel-filling sub-facies of the Arowa Formation, and the foresets of the tabular cross bedding displayed in the Duguri formation. A north-westerly to a northerly paleocurrent direction was determined for the Arowa formation, indicating that the open sea was located to north-north-west, while a unimodal palaeocurrent directions characterize the Duguri Formation. These currents transported sediment into the Dukku, Akko and Bashar sub-basins with an overall centripetal pattern. The main structural features of the western part of Gongola Basin from E-W, are the N-S, NE-SW and NW-SE trending faults. These series of faults controll the basin subsidence and deposition of the Campano-Maastrichtian succession in the Dukku, Akko and Bashar sub-basins.The lateral and vertical facies variation within the Campano-Maastrichtian succession are in consistence with the northerly retreat of the sea.

Lineament Extraction from SPOT 5 and NigeriaSat-X Imagery of the Upper Benue Trough, Nigeria

Abstract. The Upper Benue Trough is part of the Benue Trough of Nigeria and is comprised of three basins: the east–west trending Yola Basin (Yola Arm), the north–south trending Gongola Basin (Gongola Arm) and the northeast–southwest trending Lau Basin (Main Arm). This research is an ongoing research at understanding the structural framework of the Upper Benue Trough using several techniques including the use of Remote Sensing and GIS. Several digital image enhancement techniques such as general contrast stretching and edge enhancement were applied to the NigeriaSat-X and SPOT 5 image in ERDAS IMAGINE 9.2 after which structures were mapped out on-screen using ArcMap 10. The Digital Elevation Model (DEM) of the Trough was also used to enhance geomorphic features. The analysis carried out on the images revealed that lineaments are abundant in the Upper Benue Trough and they can be subdivided into four major trends, NE–SW, NW–SE, W–E and N–S in order of abundance and range in length from about 300 m to 26 km. Several faults were also mapped out within the Basin such as a sinistral fault around Bakoreji village in Bauchi, a dextral fault close to Kalmai town in Gombe and a dextral fault close to Wong in Taraba. It was discovered that some of the sites where minerals such as lead and zinc ores are being mined occur in the zones of high lineament density. This study shows the capability of the DEM, SPOT 5 and NigeriaSat-X images for lineament/structural interpretations.

Geochemistry of Kolmani-1 Well Sediments from the Upper Benue Trough, Gongola Basin, Northeastern Nigeria

Aims: To assess the source rock characteristics and the depositional environment through Geochemical studies of sediment samples from the Upper Benue Trough. Place and Duration of Study: Department of Geology, Obafemi Awolowo University, Nigeria and The Activation Laboratory Ltd, Ontario, Canada between February 2011 and March 2012. Methodology: Eighteen samples made up of sand, shale, coaly shale, shaly sand and sandy shale, occurring between the depths of 18.3 m and 2725 m were analysed for thirty-four elements, comprising eight major, twelve trace, and fourteen rare earth elements (REE) using the Inductively Coupled PlasmaMass Spectrometry technique. Results: The results show that the sediments are compositionally rich in Al2O3 and Fe2O3. The low TiO2 values of compared to those of Post-Archean Australian average shale (PAAS) suggest that they were derived from more evolved felsic source rock. The relatively low average Rb/Sr and high Th/U ratios indicate that moderate to more intense weathering occurred in the source rock area. The absolute rare earth elements (REE) concentrations were in the order of coaly shale > shale > sandy shale > shaly sand > sand. Original Research Article British Journal of Applied Science & Technology, 4(20): 2931-2945, 2014 2932 Conclusion: The Al2O3/TiO2, Eu/Eu*, Th/Sc, La/Sc, Th/Co, La/Co, and Th/Cr ratios indicate that the sediments were probably derived from felsic source rocks. In addition, the high LREE/HREE ratios and the negative Eu anomaly also support felsic source rocks for the sediments whilst the very low V/Cr ratios indicate that these sediments were deposited under anoxic environment, consistent with the series of horst and graben structural framework model of the Benue Trough.

Late Cretaceous palynostratigraphy in the Gongola Basin (Upper Benue Trough, Nigeria)

Palynostratigraphic study that utilizes mainly spores and pollen was done on the Cretaceous sequences of the well Nasara-1 of the Gongola Basin of the Upper Benue Trough, Nigeria. The recovered spores and pollen in the well made the identification of five palynological zones possible: Droseridites senonicus (Coniacian–Santonian), Cretacaeiporites scabratus (Turonian), Triorites africaensis (Upper Cenomanian), Afropollis jardinus (Lower–Middle Cenomanian) and Elateroplicites africaensis– Elaterosporites klaszii– Elaterosporites protensus (Upper Albian). These zones are similar and correlatable to other Cretaceous palynologic zones in the West Africa and northern South American basins.

Evolution of Gongola Basin Upper Benue Trough Northeastern Nigeria

Evolution of Gongola Basin Upper Benue Trough Northeastern Nigeria

PETROLEUM PROSPECTIVITY OF CRETACEOUS FORMATIONS IN THE GONGOLA BASIN, UPPER BENUE TROUGH, NIGERIA: AN ORGANIC GEOCHEMICAL PERSPECTIVE ON A MIGRATED OIL CONTROVERSY

Organic geochemical studies of Cretaceous formations in the Gongola Basin, northern Nigeria, show TOC values that are generally higher than the minimum (0.5 wt %) required for hydrocarbon generation. Data from Rock‐Eval pyrolysis and biomarker studies indicate the presence of both terrestrial and marine derived Types II and III organic matter, which is immature in the Gombe Formation and of marginal maturity in the Yolde Formation. Immature Type III to IV OM is present in the Pindiga Formation; and Type III OM, with a maturity that corresponds to the conventional onset (or perhaps peak) of oil generation occurs in the Bima Formation. However, Bima Formation samples from the 4710 – 4770 ft (1435.6 – 1453.9 m) depth interval within well Nasara‐1 indicate Type I OM of perhaps lacustrine origin (H31R/H30 ratio generally ≤0.25).Although the Nasara‐1 well was reported to be dry, geochemical parameters (high TOCs, S1, S2 and Hls, low Tmax compared to adjacent samples, a bimodal S2 peak on the Rock‐Eval pyrogram, a dominance of fluorinite macerals), together with generally low H3IR/H30 biomarker ratios within the 4710–4770 ft (1435.6–1453.9 m) interval, suggest the presence of migrated oil, perhaps sourced by lacustrine shales in the Albian Bima Formation located at as‐yet unpenetrated depths.The presence of the migrated oil in the Bima Formation and its possible lacustrine origin suggest that the petroleum system in the Gongola Basin is similar to that of the Termit, Doba and Doseo Basins of the Chad Republic, where economic oil reserves have been encountered.

The Rotifera Fauna Of Gongola River Basin, Northeast Nigeria

This study was undertaken to characterize the taxa composition, distribution pattern and the abundance of rotifers in surface waterbodies in the Gongola basin of Nigeria, West Africa. It was based on the analysis of net zooplankton samples collected from the River Gongola, its flow-through reservoirs, borrow-pit ponds and pools, over the two seasons of one annual cycle. The Rotifera fauna comprised thirty Monogononta species dominated by members of families Brachionidae (43 %) and Lecanidae (23 %). The fauna showed high similarity with those of most other Nigerian inland waterbodies and all the species are either cosmopolitan or cosmotropical in zoogeographical distribution. About one half of the recorded species occurred common to both the lotic and lentic waterbodies while about 40% and 10% were restricted to lotic water and lenthic waters respectively. The most widely distributed and abundant species were Keratella tropica and Brachionus calyciflorus while the two species restricted to lentic waterbodies were Asplanchna priodonta and Mytilina ventralis. A number of species showed a definitive pattern of distribution along the horizontal course of the River Gongola. These included Keratella tropica, K. lenzi, Filinia opoliensis and Lecane curvicornis which increased downstream as opposed to Lecane bulla and Platyias quadricornis which decreased downstream. Species richness and diversity indices generally increased downstream while species evenness index decreased downstream. Some species varied with the size of lentic waterbodies while others showed potential to serve as indicators of water habitat type. The fauna was qualitatively richer but quantitatively poorer during the rainy season than in the dry season due to the associated effects of rainfall, stream discharge and physico-chemical water quality. Keywords: Rotifera zooplankton, community structure, distributional pattern, Gongola basin, West Africa IFE Journal of Science Vol. 9 (1) 2007 pp. 1-16

Geological mapping using fractal technique

In this work the use of fractal scaling exponents for geological mapping was first investigated using theoretical models, and results from the analysis showed that the scaling exponents mapped isolated bodies but did not properly resolve bodies close to each other. However application on real data (the Mamfe basin, the Gongola basin and the Younger granite province in Nigeria) showed good correlation with the geological maps of the areas. The results also indicated that basement rocks can generally be represented by scaling exponents with values ranging between -3.0 and -2.0. Keywords : Fractal, dimension, susceptibility, spectra, scaling exponent Nigerian Journal of Physics Vol. 18 (2) 2006: pp. 277-286

Microfacies analysis, depositional environments and diagenetic history of the limestone facies of the Pindiga Formation, Gongola Basin, Nigeria

Microfacies analysis, depositional environments and diagenetic history of the limestone facies of the Pindiga Formation, Gongola Basin, Nigeria

NASARA‐I WELL, GONGOLA BASIN (UPPER BENUE TROUGH, NIGERIA): SOURCE‐ROCK EVALUATION

Well Nasara‐I, one of three exploration wells recently drilled in the Gongola Basin in the Upper Benue Trough (onshore Nigeria), was tested and found to be dry. The well penetrated an entirely Cretaceous succession comprising the Pindiga, Yolde and? Bima Formations, and standard organic geochemical analyses were carried out to assess the source‐rock potential of selected samples. Total organic carbon (TOC) contents were found generally to be very low, with no values exceeding 1.0wt%, and about one‐half of them ranging between 0.50 and 0.87wt%. Hydrogen indices (Hls) correlated against Tmax indicate some gas‐generative potential.However, in the depth interval between 4,710ft and 4,770ft, TOC values of between 52.1 and 55.2 wt% were recorded; these are characteristic of coals. This is the first report of a coal within the Pindiga, Yolde or Bima Formations. Hls were between 564 and 589 mgHC/gTOC and Tmax was 423–428°C. Although hydrogen indices can be misleading in assessing the oil‐generative potential of a coal, values as high as those recorded in Nasara‐I permit oil‐generative capabilities to be inferred.Total ion chromatograms of the saturated hydrocarbon fractions of the coaly samples show some ramping of unresolved complex mixtures attributable to biodegradation. Further biomarker data indicate a dominance of low molecular weight n‐alkanes (C15–C25), pristane/phytane ratios of 0.8 to 1.3, and very high contents of C28 regular steranes. These attributes, together with the very high Hls, indicate that some oils generated from a probably deeper‐seated or laterally‐located (and yet to be identified) lacustrine source rock must have migrated and been adsorbed into the coaly facies, which were later intermittently subjected to anoxic to suboxic biodegradation processes.