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

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.

Brittle deformation in the Afikpo Basin (Southeast Nigeria): Evidence for a terminal Cretaceous extensional regime in the Lower Benue Trough, Nigeria

This paper deals with the regional and structural framework of the Cretaceous rocks in the Afikpo Basin located in the southeastern part of the Lower Benue Trough. Results from regional tectonics are presented together with those of the microtectonic analysis of microfaults in the Owutu-Afikpo-Adadama area in the basin. The Owutu-Afikpo-Adadama ridge at the north-central part of the basin marks the boundary between the Late Cenomanian-Turonian-Conianian sediments and the Campanian-Maastrichtian sandstones. This ridge trends N45oE on average and is faulted in three main directions, namely: (1) N-S normal faults; (2) NE-SW strike-slip faults; and (3) NW-SE strike-slip faults. The faulted rocks along these brittle discontinuities are mainly cataclastics with internal fracture cleavage and sigmoidal quartz mosaics that are reminiscent of extensional deformation. The cataclasites often bear slickenside striations. The NE-SW and NW-SE strike-slip faults are the results of the youngest brittle events on the Owutu-Afikpo-Adadama ridge. These faults were reactivated after deposition of the Campanian-Maastrichtain sediments (post-depositional faults) and, therefore, are post-Maastrichtain. Microfault analysis of these fault trends suggests an extensional regime that prevailed in the Lower Benue Trough. These results are of significance because this event is least poorly understood and less documented in contrast to the Cenomanian and Santonian events that affected the older Cretaceous strata in this region.

Paleo-environmental conditions,paleoclimatic significance and effects of weathering on clay deposits in the Lower Benue Trough,Nigeria.Mineralogical approach

Combined methods for mineralogical identifications were used to characterise the clay deposits within the Lower Benue Trough of Nigeria to interpret paleo-environmental conditions,the paleoclimatic significance of the trough,and effects of weathering on the minerals as factors that favour its deposition/accumulation within the trough which host other important industrial minerals like coal,barite,limestone etc.Bulk-sample random-powder XRD data and data for clay fractions deposited onto zero-background quartz plates were measured.The samples contained kaolinite,vermiculite,and traces of smectite,and the non-clay phases included quartz,microcline,and muscovite.All samples were unaffected after glycolation,confirming the absence of significant smectite.Muscovite was characterized by the nature of its 10Åbasal peak with a width of<0.10°2θ,which was very sharp.DTA/TGA results support the presence of kaolinite,and the characteristic kaolinite O-H,Al-OH,Si-OH and Si-O-Al FTIR bands also confirmed its presence.Vermicular and book-like morphologies were observed under the SEM,typical of kaolinitic clay from in situ alteration.High kaolinite abundance in these sediments is consistent with intense weathering of parent rocks rich in Al under wet/tropical paleo-climatic conditions with fresh and/or brackish water conditions in a continental setting.The variety of observed morphologies suggests that the deposits suffered more of chemical weathering.The clay deposits in Lower Benue Trough are quartz-rich,kaolinitic and derived from the chemical weathering of Al-rich source rocks.

Evaluation of hydrogeochemical characteristics of groundwater in parts of the lower Benue Trough,Nigeria

The aim of this work is to evaluate the hydrogeochemical characteristics of groundwater in parts of the lower Benue Through in Nigeria as well as to evaluate the variation in groundwater chemistry data and the suitability of the groundwater for drinking and other domestic purposes.This was based on chemical analyses of 44 water samples from existing wells and boreholes in the study area.From the statistical analysis(wide ranges,median and standard deviation),it is obvious that there are significant variations in the quality/composition of groundwater in the period of sampling.The calculated SAR,Na% and RSC values indicated that the water is of excellent to good quality and is suitable for irrigation.Na and HCO3 are dominant with respect to the chemical composition of the groundwater.On the basis of water chemistry,hydrochemical indices and factor analysis the dominant controls or processes affecting the distribution of geochemical variables in the study area have been shown to be water/rock interaction which is mainly controlled by carbonate and silicate dissolution as well as anthropogenic influence to a lesser extent.Additional processes include cation exchange reactions and reverse ion exchange to a minor extent.

Organic geochemical evaluation of the oil/gas-generative potential of organic matter in Cretaceous strata from the Lower Benue Trough,Nigeria

An analytical procedure involving Rock-Eval pyrolysis of whole-rocks was adopted on fresh outcrop samples covering the three lithostratigraphic units in the Afikpo Basin of the Lower Benue Trough. Three petroleum systems are present in the Cretaceous delta frame: the Asu-River Group, the Eze-Aku Group and proto-Niger Delta sequences. The Afikpo Basin has been correlated to three petroleum systems in the Lower Congo Basin, Niger Delta and the Anambra Basin. The organic geochemistry of the shales, carbonaceous mudstones and coal beds show relatively moderate to high total organic carbon contents. The best potential hydrocarbon source rocks are the Eze-Aku Group and proto-Niger Delta shales, carbonaceous mudstones and coal beds where maturation was attained. The high total organic contents, thermal maturity and terrigenous characters of the Asu-River Group, Eze-Aku Group and proto-Niger Delta sediments, suggest the presence of a large amount of natural gas with a small quantity of oil accumulation. Variations in source rock facies were observed from one lithostratigraphic unit to another, and initial HI values as a function of TOC were proposed for each lithostratigraphic unit. The results also show that TOC, HI, OI, S2 and Tmax vary from older to younger rocks. The Tmax values discriminate the rocks into immature and mature source rocks. Source rocks with high Tmax suggest high geothermal gradient/or recycled organic matter. Also high Tmax and S2 yield indicate late and post maturity. Recycled organic matter is characterized by low Tmax. The principal source rocks for gas in the Afikpo Basin are the Eze-Aku Group and proto-Niger Delta beds deltaic systems, consisting mainly of III to IV kerogens with a subordinate amount of type II organic matter. Based on the obtained results, it is concluded that the Cretaceous shales, carbonaceous mudstones and coals in the Afikpo Basin of the Lower Benue Trough are capable of generating and expelling hydrocarbons in the case of sufficient maturity.

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

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/Al2O3, Fe2O3/K2O ratios 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 sandstones 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 increases with time, possibly suggesting that a more intense weathering regime in the hinterland developed with time.

Heavy metal concentrations in soils and plants in the vicinity of Arufu lead-zinc mine, Middle Benue Trough, Nigeria

This study focused on the influence of base metal mining on heavy metal levels in soils and plants in the vicinity of Arufu lead-zinc mine, Nigeria. Soil samples (0-15 cm depth) and plant samples were collected from cul-tivated farmlands in and around the mine, the unmineralized site and a nearby forest (the control site). The samples were analyzed for heavy metals (Fe, Zn, Mn, Cu, Pb, Cr and Cd) by Atomic Absorption Spectrophotometry (AAS). The physical properties of soils (pH and LOI) were also measured. Results showed that soils from cultivated farm-lands have neutral pH values (6.5-7.5), and low organic matter contents (<10%). Levels of Zn, Pb and Cd in culti-vated soils were higher than the concentrations obtained from the control site. These heavy metals are most probably sourced from mining and agricultural activities in the study area. Heavy metal concentrations measured in plant parts decreased in the order of rice leaves>cassava tubers>peelings. In the same plant species, metal levels decreased in the order of Zn>Fe>Mn>Cu>Pb>Cr>Cd. Most heavy metals were found in plant parts at average concentrations normally observed in plants grown in uncontaminated soil, however, elevated concentrations of Pb and Cd were found in a few cassava samples close to the mine dump. A stepwise linear regression analysis identified soil metal contents, pH and LOI as some of the factors influencing soil-plant metal uptake.

Petrology, physicochemical and thermal analyses of selected cretaceous coals from the Benue Trough Basin in Nigeria

Abundant coal resources that were previously neglected due to a crude oil boom need revitalisation and integration into the national electricity mix to address the energy demands of the Nigerian population.Selected coal samples from the Benue Trough sedimentary basin in Nigeria were examined by various techniques,including proximate and ultimate analyses,organic petrography,Fourier transform infrared ray spectroscopy,and thermogravimetric analysis.Based on vitrinite reflectance,the Lafia-Obi(OLB),Garin Maiganga(GMG),Imiegba(IMG),and Okaba(OKB)coals are classified as subbituminous,while the Lamja1(LMJ1),Lamja2(LMJ2)and Chikila(CHK)coals are high volatile B bituminous.The Enugu(ENG)coal is on the boundary between subbituminous and high volatile C bituminous.Organic petrographic results indicate vitrinite and fusinite contents steadily increase from the Lower Benue Trough coals to the Upper Benue Trough coals,while semifusinite and total mineral contents follow a reverse pattern.Thermal decomposition occurred in three stages,i.e.,drying,devolatilization,and coke formation above 700°C;and the coal reactivity follows the following order,ENG>IMG>IGH>CHK>LMJ>OKB>GMG>LFB.The higher temperatures(above 900°C)are required to decompose the coals for efficient energy recovery.The LMJ1,LMJ2,OLB,CHK,GMG,and OKB coals can be exploited for electricity power generation.However,the Imeagha and Enugu coals are best suitable for both cement and power generation.

A Comparative Study of Element Cycling in the Soil-Plant System: A Case Study of Shaly and Calcareous Soils, Southern Benue Trough, Nigeria

This study focused on the cycling of major and trace elements in the soil-plant system in parts of Southern Benue Trough, Nigeria. Surface soil samples and cassava crop samples were collected from cultivated farmlands underlined by shaly and calcareous soils and were analysed using standard techniques. The results show that shaly soils are relatively acidic (pH, 4.8 - 6.6) with high level of organic matter content (OM, 3.2% - 8.7%) compared to calcareous soils (pH, 5.6 - 7.2;OM 1.6% - 7.0%). The soils are enriched in elemental composition relative to the world average abundances in soil. The maximum levels of K, Al, and Zn were obtained from shaly soils. The computed accumulation factors are generally <1. Elemental levels decreased in the plant parts in the order tuber > leaf > stem. Significant correlation was obtained between elemental associations of calcareous surface soils compared to that of shaly soils. R-mode factor analysis revealed the controls of soil geochemistry to include lithology, anthropogenic and environmental factors. A stepwise linear regression analysis identified soil elemental component, pH and organic matter as some of the factors influencing soil-plant metal uptake.

Background Geochemistry of Soil in Part of Girei District, Upper Benue Trough, N. E. Nigeria

Soil geochemical study aimed at determining the background levels of trace and major elements in soils of a relatively small part (MAUTECH Campus) of Girei District has been carried out. The results show that the contents of trace and major elements in the area are generally low and vary by factors ranging from about 3 times (As, V), about 4 times (Ni, W), about 6 times (Cd, Rb, Be), about 10 times (Cr, Ba, Br), about 7 times (Se), about 18 times (Mo), about 30 times (Co) and about 45 times (Pb). The low contents reflect the granites and migmatite gneisses bordering the study area and suggest that the soil was derived from these granites with little contribution from the mafic gneisses. Correlations amongst elements are significant at the probability level of 0.01. Among the major elements;Mg has a strong positive relationship with Ca (0.88), and Al (0.74) while Fe is also strongly related to Al (0.69). Several trace elements have very strong positive relationship with one another: Ba-As (0.91), Be-As (0.93), Be-Ba (0.91), Cs-Ba (0.91), As-Cs (0.85), Cr-Ba (0.85), Cr-Be (0.85), Cs-Be (0.88), As-Ce (0.94) and Cs-Cr (0.86). Mn and Mo are poorly related with most of the trace elements. Among the rare earth elements, Eu is strongly related to Dy (0.98), Gd (0.99) and Lu (0.96) just as Dy is strongly related to Er (0.99), Eu (0.98), Gd (0.98) and Lu (0.98). These strong positive correlations among elements suggest that chemical and physical factors control elements associations in parent materials and soil forming processes. Consequently, the data may serve as a reference standard in the assessment and monitoring of possible future environmental issues related to trace and/or major element contamination.

Impact of Past Mining Activities on Water Resources Around Active and Abandoned Mines and Quarries in Ebonyi State,South-Eastern Nigeria-A Mini Review

This paper presents a review on previous activities of mining on water resources around active and abandoned mines/quarries across Ebonyi State,South-Eastern,Nigeria.As high demand for water increases due to population growth and rapid development across the state,it is of upmost importance to periodically review water quality and also monitor water resources.However,less information is available on evaluation of impact on mining activities on water resources.For the purpose of this research,related articles were downloaded from Google,published article on effect of mining on water resources was download and thoroughly studied to evaluate effect of mining on water resources of the study area.Findings revealed that past mining activities has lead to chains of complex chemical reactions that has altered the quality of water resources.