Geochemical characterization of Cretaceous sandstones from the Southern Benue Trough,Nigeria     

Odigi M.I.  Amajor L.C. 《中国地球化学学报》2009,28(1):44-54

Geochemical studies of sandstones from the three lithostratigraphic successions in the southern Benue Trough of Nigeria were undertaken for a geochemical characterization of the sandstones, and to assess their strati-graphic and source evolution.Major and trace elements data were obtained from outcrop sandstone samples. The SIO2/Al2O2, Fe2O3/K2O ra-tios and CaO contents have been used to characterize the Cretaceous sandstones into Al-rich and high and low Fe2O3/K2O ratio sandstones. Results indicate that there are geochemical features that display stratigraphic trends across the succession from the Asu River Group, Eze-Aku Group to the proto-Niger Delta succession which may imply a discontinuous evolution from different source terrains of Precambrian and Mesozoic ages that supplied the sediments. The Asu River Group sandstones have lower SiO2, Al2O3, Fe2O3 and higher MgO; the Eze-Aku sand-stones have higher TiO2, CaO, alkalis and lower MgO while the proto-Niger Delta sandstones have higher SiO2, Al2O3, Fe2O3 and lower alkalis and CaO. These discontinuities signify the influence of tectonic impulses that af-fected the southern Benue Trough during the Cretaceous time. Changes in ratios of TiO2/Al2O3, Fe2O3, Cr and Zr suggest an increasingly mafic contribution to the depositional basin with time. The chemical index of alteration in-creases with time, possibly suggesting that a more intense weathering regime in the hinterland developed with time.  相似文献   

尼日利亚南部大陆边缘重力场特征及解释          下载免费PDF全文

尹君 《海洋学研究》2017,35(4):87-93

利用中国-尼日利亚国际合作航次获得的船载重力数据,分析了尼日利亚南部大陆边缘的自由空间重力异常和布格重力异常特征,并通过两条从陆架—陆坡—陆隆一直延伸到深海盆地的重力剖面拟合出地壳密度结构。研究结果表明,地壳厚度总体上从陆架、陆坡至深海平原呈现阶梯状减薄的趋势,东侧的减薄幅度大于西侧,东侧从24 km减小到10 km,西侧从21 km减小到14 km。  相似文献   

Rare-earth and trace elements and hydrogen and oxygen isotopic compositions of Cretaceous kaolinitic sediments from the Lower Benue Trough,Nigeria: provenance and paleoclimatic significance     

Anthony T.Bolarinwa  Sunday O.Idakwo  David L.Bish 《Acta Geochimica》2019,(3):350-363

This study evaluated the Cretaceous(Campanian–Maastrichtian) kaolinitic sediments of the Ajali/Mamu and Enugu/Nkporo Formations from the Lower Benue Trough of Nigeria. A combined method of inductively coupled plasma–mass spectrometry and isotope ratio mass spectrometry was used to investigate trace and rareearth element geochemistry and hydrogen and oxygen isotopic compositions. These data were then used to infer the sediments' provenance and paleoclimatic conditions during their deposition. The sediments contained low concentrations of most trace elements, with the exceptions of Zr(651–1352 ppm), Ba(56–157 ppm), V(38–90 ppm),and Sr(15.1–59.6 ppm). Average values of Co and Ni were1.5 and 0.7 ppm, respectively. Trace and rare earth element values were lower than corresponding values for upper continental crust and Post-Archean Australian Shale, with the exception of Zr. The samples showed only slight light rare-earth enrichment and nearly flat heavy rare-earth depletion patterns, with negative Eu and Tm anomalies,typical of felsic sources. Geochemical parameters such as La/Sc, Th/Sc, and Th/Co ratios support that the kaolinitic sediments were derived from a felsic rock source, likely deposited in an oxic environment.^(18 )O values ranged from+ 15.4 to + 21.2% for the investigated samples, consistent with a residual material derived from chemicalweathering of felsic rock and redeposited in a sedimentary basin(typical values of + 19 to + 21.2%). While in the basin, the sediments experienced extended interactions with meteoric water enriched in d D and d16 O. However,the variation in d D and d16 O values for the investigated samples is attributed to the high temperature of formation(54–91 °C). The d D and d^(18 )O values suggest that the sediments, although obtained from different localities within the Lower Benue Trough, formed under similar hot,tropical climatic conditions.  相似文献   

SOIL SUITABILITY CLASSIFICATION BY SMALL FARMERS     

M. A. Adewole Osunade 《The Professional geographer》1988,40(2):194-201

Procedures for soil suitability classification by small farmers of southwestern Nigeria are examined. Data were collected through interviews with 225 farmers at group and individual levels. The survey relied on the farmers'perception of some observable soil properties in the field. Soil properties included texture, color, organic matter, drainage condition of soil, and bulk density. The farmers determine soil types year round, irrespective of season, unlike the Hanunoo system. While soil types were identified by their texture and color characteristics, suitability classes were defined principally by texture. Eighteen soil types and four soil classes were identified for soil suitability classification projects designed for small farmers. The reliability and viability of the results of this study need to be verified through on-farm experiments.  相似文献   

Nitrates in shallow (regolith) aquifers around Sokoto Town, Nigeria     

K. O. Uma 《Environmental Geology》1993,21(1-2):70-76

Measurements from over 40 dug wells completed within the shallow lateritic aquifer around the city of Sokoto showed nitrate enrichment ranging between 20 and 100 mg/l and mostly above the limits recommended for domestic use. The values generally do not show any depth control but were less for forested and residential areas and more beneath agricultural farmlands. Evidence from earlier measurements suggests that the input of nitrates occurred only in the last ten years and could be easily linked to land use practices.  相似文献   

Application of remote-sensing data to groundwater exploration: A case study of the Cross River State, southeastern Nigeria   总被引：12，自引：2，他引：10  

A. E. Edet  C. S. Okereke  S. C. Teme  E. O. Esu 《Hydrogeology Journal》1998,6(3):394-404

 The Cross River State, Nigeria, is underlain by the Precambrian-age crystalline basement complex and by rocks of Cretaceous to Tertiary age. The exploration for groundwater in this area requires a systematic technique in order to obtain optimum results, but the non-availability of funds and facilities has made it extremely difficult to carry out site investigations prior to the drilling of water wells. Therefore, the failure rate is as high as 80%. In order to delineate areas that are expected to be suitable for future groundwater development, black and white radar imagery and aerial photographs were used to define some hydrological and hydrogeological features in parts of the study area. Lineament and drainage patterns were analysed using length density and frequency. Lineament-length density ranges from 0.04–1.52; lineament frequency is 0.11–5.09; drainage-length density is 0.17–0.94, and the drainage frequency is 0.16–1.53. These range of values reflect the differences in the probability of groundwater potentials. Results were then used to delineate areas of high, medium, and low groundwater potential. Study results also indicate that correlations exist between lineament and drainage patterns, lithology, water temperature, water conductivity, well yield, transmissivity, longitudinal conductance, and the occurrence of groundwater. Received, August 1994 · Revised, March 1996, June 1996 · Accepted, October 1996  相似文献   

A high-resolution Holocene ostracod record from the Sahel zone of Northeastern Nigeria     

Jonathan A. Holmes  Patrick A. Fothergill  F. Alayne Street-Perrott  R. Alan Perrott 《Journal of Paleolimnology》1998,20(4):369-380

The ostracod record from Kajemarum Oasis in the Sahel zone of Northeastern Nigeria covers the last c. 4000 cal. years of a 5500 cal. year lake-sediment sequence. The first appearance of ostracods, around 4000 cal. yr BP, reflects the switch from a very dilute lake during the mid-Holocene, to slightly oligosaline conditions that favoured the occurrence and preservation of ostracods. Between 3800 and 3100 cal. yr BP, the lake remained permanent and fresh or slightly oligosaline, with a Ca-Mg-HCO3 composition. A rise in salinity c. 3100 cal. yr BP, accompanied by a change to more variable conditions on a seasonal to interannual timescale, led to the influx of more-euryhaline taxa. Oligosaline conditions continued between 3100 and 1500 cal. yr BP. Around 1500 cal. yr BP, there was a sharp rise in salinity, probably accompanied by a shift to Na-CO3-type water, with marked seasonal and interannual variability. Salinity decreased after 900 cal. yr BP, although short-term variations were marked between 900 cal. yr BP and the top of the sequence, 95 cal. yr BP. Changes in the species assemblages and ostracod abundance were a response to climate-driven variations in the seasonal and interannual stability of the lake, together with changes in its salinity and solute composition, but there is no simple relationship between ostracod faunas and salinity. Within Kajemarum, there is no evidence of ostracod assemblages typical of deep, fresh water, nor of hypersaline Na-Cl waters. The sediments associated with the freshest waters at Kajemarum did not favour ostracod preservation, and the driest climatic conditions were associated with oligosaline to mesosaline water of Na-CO3-type. The species-poor assemblages reflect the short-term instability of the lake, coupled with the limited opportunities for the colonisation of this isolated basin.  相似文献   

Single zircon evaporation ages: Evidence for the Mesoproterozoic crust in the southeastern Nigerian basement complex     

Ekere E.Ukwang  Barth N.Ekwueme  Alfred Krner 《中国地球化学学报》2012,31(1):48-54

The Ukwortung area of the Obudu Plateau exposes high-grade metamorphic rocks of upper amphibolite to granulite facies. Zircon grains from three locations of Southwest Obudu Plateau were dated by the Pb-Pb dating method. This single zircon radiometric dating method confirms the occurrence of Mesoproterozoic crust in the southeastern Nigeria basement complex. The pyroxene gneiss (granulite facies) sample from Biereberi near Ukpe yielded a mean age of 2061.4±0.4 Ma, suggesting the presence of Paleoproterozoic crust. The combined 207Pb/206Pb ratios from the garnet-biotite gneiss in the area gave a mean age of 1794.4±0.4 Ma. This further confirms the pres-ence of Paleoproterozoic crustal components within the Obudu Plateau. The Mesoproterozoic (1548.8±0.5 Ma) and Neoproterozoic (619.8±0.9 Ma) ages were obtained from two populations of zircon grains from the leucogranite in Okordem, Southwest Obudu. These "signatures" collaborate the occurrence of Mesoproterozoic ages in the Afar region and Cameroon basements along with the southeastern Nigerian basement complex, constituting the major portion of the West Central African mobile belt. The zircon age of 1794.4±0.4 Ma may probably be the maximum depositional age of the meta-sediment (garnet-biotite gneiss) and the age of 1548.8±0.5 Ma may be interpreted as the time of emplacement of the granitoid. The Neoproterozoic age (619.8±0.9 Ma) probably records the metamorphic event that was prevalent during the Pan-African period and thus affected the area.  相似文献   

Oil ‘futures’: Shell’s Scenarios and the social constitution of the global oil market   总被引：1，自引：0，他引：1  

Anna Zalik 《Geoforum》2010,41(4):553-564

This article explores the relationship between the oil industry’s representation of operating conditions in key sites of extraction and the constitution of oil futures markets. An analysis of Shell Oil’s recent Scenarios publications, the ‘Trilemma Scenarios to 2025’ and subsequent ‘Scramble and Blueprints Scenarios to 2050’, provides insight into both the (global) social construction of oil prices and the oil industry’s reaction to social resistance in its operating environment - whether in the form of movements for resource sovereignty or climate change activism. Examining the implications of these two Scenario publications for key sites of Shell investment, the Nigerian Niger Delta and the Canadian Tar Sands, the article demonstrates that understanding the discursive implications of ‘peak oil’ for the petroleum industry requires contextualizing discussions of ‘scarcity’ within business agents role in shaping oil futures markets, and private industry’s interest in the ongoing development of unconventional fossil fuel sources. While the role of deregulated futures trading receives little attention in the Shell Scenarios, speculative trading - and thus perception concerning supply among business agents - is central to shaping global oil prices and thus the social conditions of the oil market.  相似文献   

Species Composition and Gear Characteristics of the Macrobrachium Fishery of the Cross     

Francis M. Nwosu 《青岛海洋大学学报(英文版)》2010,(1):71-75

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