Journal of African Earth Sciences最新文献

The study aims to assess the effectiveness of using ASTER, Landsat 9, and airborne geophysical data to generate maps depicting hydrothermally altered regions and their correlation with radioactive-mineralized zones in Egypt's Um Had area. Various image processing methods were applied, including color composite images, band ratios, selective principal component analyses, and lineament extraction with enhancement procedures. The ASTER ratios identified the three types of hydrothermal alterations; phyllic, argillic, and propylitic, with other significant alteration zones related to mineralization. Airborne gamma-ray spectrometry contour maps displayed marked varied levels of total count (T.C), eU, eTh, and K, ranging from 1.2 to 21.2 Ur, 0.5 to 12.34 ppm, 1.45 to 28 ppm, and 0.13 to 3.65 %, respectively. The highest anomalies of these radioelements concentration have coincided with the alkali feldspar granite and along their intrusive contact zone with the Hammamat Group sedimentary rocks. Higher anomalies are well recorded in the center and eastern regions of Um Had's, according to the radioelements composite image. The lowest concentrations of these radioelements are associated with gneiss, ophiolitic mélange, metavolcanic, Hammamat Group sedimentary rocks, Taref Formation, and Wadi sediments. To mitigate local magnetic effects, the total aeromagnetic data was reduced to the north magnetic pole (RTP). Power spectrum analysis of the RTP data identified distinct magnetic wavelengths for regional-residual components. In order to identify near-surface magnetic lineaments, such as contacts, shear zones, faults, and dykes, advanced algorithms were applied to the RTP data data. The lineaments derived from ASTER and airborne magnetic data revealed dominant fault systems characterized by E–W, NE, NNW, NW and N–S trends, governing the structural framework of the study area. Depth levels of geological contacts and faults that represented pathways for altered and mineralized zones reached more than 1200 m (Euler deconvolution). These findings highlight the consistent results obtained when combining ASTER data with airborne survey data, allowing for the identification of hydrothermally altered zones and primary conductive zones.

The Dahomey Basin, located in southwestern Nigeria, is an energy-rich frontier basin with sedimentary successions consisting of both (onshore) terrestrial and (offshore) marine deposits. Since the discovery of several bitumen seeps, tar sands, and oil and gas shows offshore the basin and the successful production of the Aje Field, the basin has gained immense interest from academia and industry. Nevertheless, surface and subsurface research focusing on paleoclimatic conditions, primary productivity, anoxic conditions, paleowater depth, and hydrodynamic influence in the Dahomey Basin is less documented. To reconstruct paleoenvironmental conditions, subsurface data from the Araromi-Obu (A1) and Idiobiolayo (A15) cores were used. The average chemical index of alteration (CIA) values ranging from 63.01 to 94.88 reflect varying degrees of weathering intensity in the sediment source area of the Cretaceous Araromi Formation. These values show a transition from relatively low to considerably high degrees of weathering in the source region of the Araromi Formation. The analysis of CIA values and Ga/Rb, Sr/Cu, Sr/Ba, Ca/Al, and 100*Mg/Al ratios suggests that the Araromi Formation was deposited in a brackish to marine environment.

Furthermore, chemical alteration-sensitive geochemical indicators revealed prevailing warm, humid tropical climates during the late Cretaceous period, with likely minor arid intervals. In addition, the geochemical markers used (Ba/Al, U/Th, Ni/Co, authigenic uranium (Uau), P/Ti, and [(Fe₂O₃ + CaO + MgO)/(SiO₂ + Al₂O₃)] indicate poor paleoproductivity for the Araromi Formation deposited in an oxygen-rich marginal to shallow marine environment. The upper Cretaceous period was characterised by fluctuating hydrodynamic circulation, with a weak hydrodynamic regime in core A1 and transitioning to strong hydrodynamic conditions in core A15. The inferred paleowater depth corresponds to the salinity measurements, with the A1 core displaying elevated salinity, indicating a greater depth compared to the A15 core, which was deposited in a shallower environment and displays lower salinity.

This study uses Landsat Thematic Mapper (TM), Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM), and aeromagnetic data to examine possible reactivation of the Ediacaran, NE-trending Ad Damm Fault Zone (AFZ) and the Fatima Fault Zone (FFZ) in the western Arabian Shield. Reactivation is by latest Paleogene to Neogene and Quaternary structures of the Red Sea. The AFZ is the tectonic boundary between the Tonian Jeddah terrane in the northwest and the Asir terrane to the southeast of the Arabian Shield. The AFZ and FFZ coincide with possible onshore continuation of a transform fault that separates the sea floor spreading segment of the Red Sea in the south from its transitional segment to the north. It has been suggested that the AFZ is a candidate for the formation of a future onshore transform fault that would result in an eastward jump of the Red Sea sea floor spreading center onto the Arabian Shield. The future spreading center will follow the latest Neogene to Quaternary volcanic rocks (Harrat) that are exposed on the eastern side of the Red Sea. The Landsat TM image and the SRTM DEM show that the AFZ dissects the Red Sea topographic escarpment, and both the AFZ and FFZ control paleo-drainage system (wadis). The aeromagnetic data show that there is a ∼100 km wide zone between the AFZ and FFZ dominated by NE-trending short wavelength magnetic anomalies, possibly related to regional tectonic fabric. Additionally, the aeromagnetic data show that both fault zones dissect NW-trending short wavelength magnetic anomalies, interpreted as latest Paleogene to earliest Neogene dike swarms associated with the opening of the Red Sea. This dissection also includes possible Red Sea related narrow marginal grabens and horsts that were formed onshore and offshore parallel to the Red Sea shoreline. Red Sea-related structure might have reactivated the AFZ and FFZ.

Mauritania, with its ancient (Archean to Paleoproterozoic) and desertic terrains and gentle relief, has been under-explored in terms of impact structures. To date, two confirmed impact craters, namely Tenoumer and Aouelloul, and four circular structures for which an impact origin has been suggested, are known in Mauritania. This work aims at a systematic exploration of circular structures in Mauritania and provide a comprehensive database to support their exploration and elucidate their origin. This approach includes multi-scale search on Google Earth images, and a preliminary assessment of their origin using available geological, geophysical, and geochemical data as well as Digital Elevation Models. A total of 50 new circular structures were detected during our survey, adding to four candidates previously identified. They are distributed throughout the territory with an important fraction of them being located in the Taoudeni basin. The diameters of these structures vary from 60 m to 7.5 km with a right-skewed distribution. A preliminary assessment of the possible origins of these circular structures is proposed and the most promising candidates for potential meteoritic impact sites are listed for future investigations.

The South Rifian Ridges are located in northern Morocco, to the south of the Gibraltar Arc, and constitute a portion of the south Rifian corridor in the Rif belt front. These active fault-related folds, separated by the Volubilis piggy back basin, were structured since the Late Miocene due to the reactivation of Triassic graben fault systems in the context of the Eurasia-Africa convergence.

For the first time, a combination of morphotectonic and gravity analysis coupled with field Kinematic data have been used to characterize the main structures responsible for the Late Miocene to recent evolution of the area.

The morphotectonic analysis based on the dynamics of drainage network analysis allowed the isobase lineament mapping to depict a general view of the tectonic framework of the South Rifian Ridges. The interpretation of gravity data, including maps derived from the Bouguer and residual anomalies, allowed subsurface geometric features characterization and revealed buried salt diapirs to establish a new structural map. Evidenced structures confirm previously interpreted ones and support the presence of new masked faults, with the presence of compressional and extensive deformations. The main inferred structures are the NW-SE oriented buried Prerif Nappe fronts. Rooted faults related to the main ridges show reverse displacement and are expressed by high-angle reverse faults, while the NW oriented normal faults within Volubilis basin, in the field, are probably related to an active subsidence. This event is related to the current NW-SE continental collision, within a context of transition from thin to thick skinned tectonics. Our results shed light on the Miocene to Quaternary tectonics that have taken part in the closure of the South Rifain marine gateway.

The Dodoma region located in Central Tanzania is a semi-arid area characterised by scarce surface water resources. Because of climate change and dependence on groundwater resources in the Dodoma urban area, there is currently an increased demand for water due to low groundwater recharge and high groundwater withdrawals due to the growing population. There is therefore a need to explore potential deep aquifer systems around the Dodoma urban area to meet the increasing water demand. This study uses lithological logs, pumping tests, and electromagnetic survey data to delineate the subsurface lithologies to locate potential deep aquifer system in the area. Results show that the shallow aquifer system is unconfined in some areas with resistivity values ranging from 11 to 28 Ωm and semi-confined in other areas with resistivity values ranging from 19 to 27 Ωm. The unconfined aquifer extends up to 60 m, while the semi-confined aquifer extends between 50–55 m and 65–120 m. The study found a potential deep aquifer system at a depth of between 200 and 290 m, with resistivity values ranging from 11 to 20 Ωm. Currently, this deep aquifer system has not been exploited as most boreholes in the area are only up to 150 m deep. The main lithology in the study area is weathered and fractured granite, with different degrees of weathering and fracturing, indicating a hard-rock aquifer system. This study adds valuable knowledge on the location of potential deep aquifer systems in the area for proper groundwater utilisation and management.

The Tadaout-Tizi n’Rsas (TTR) polymetallic (Pb, Cu, Zn) vein field, located at the southeastern of the Moroccan eastern Anti-Atlas, is hosted in sedimentary sandstone formations of the Ktaoua Group of the upper Ordovician. These deposits are reported to be late Variscan to Post-variscan in age, and are related to the emplacement of late Permian doleritic magma event outcropping in the Tafilalet region. Structural and paragenetic studies of the TTR mineralization deposit were conducted in order to establish a general model of the mineralization. A two-stage model of the formation of the mineralized veins of the TTR vein field is proposed herein. The first episode is attributed to the late Variscan phase. It is a trantensive regime characterized by the presence of lenticular structures related to the normal dextral movement of the major faults. This episode is coeval with the emplacement and brecciation of the polymetallic mineralization of the TTR vein field (galena, chalcopyrite, sphalerite, and pyrite). The second episode is associated with normal faults, during the extensional phase corresponding to the tectonic relaxation of shortening (Upper Permian) and more probably during the Atlantic rifting. It is characterized by the formation of a banded texture of mineralization.

In this study, we investigated the nature and characteristics of petroleum fluids in a super-global basin situated in the central north of Libya. With over 100 discovered fields (comprising oil and gas), this study aimed to understand the basin's petroleum accumulation mechanism (PAM), thereby shedding light on the factors contributing to significant petroleum discoveries in North Africa (Libya). The primary objective of this study was to provide a detailed regional refined oil family distribution and new insights into the total petroleum system (TPS) of the basin. This analysis was based on the integration of regional geology and organic geochemistry. Additionally, we utilized the physical properties of petroleum, such as API and sulphur content (%S), to obtain a better understanding of the regional physical nature of petroleum types and properties. Organic geochemical data for the basin fields were compiled, focusing on key biological marker and carbon isotope (‰ δ¹³C) data for saturated and aromatic compounds. These data were used to understand the origin, depositional source, and thermal maturity of the generated, migrated, and accumulated petroleum fluids. The study established specific types of organofacies and their relationships with petroleum phase characteristics, including type and quality, categorized into known groups (e.g., B, C, and D/E). Hierarchical cluster analysis (HCA) and map-based presentation approaches were used to determine the spatial types and distributions of oil and gas families in the basin. This was achieved by selecting the input parameters from various datasets and defining the significant parameters to characterize the distribution patterns. The findings indicate that the bulk fluid of the Sirt Basin primarily resembled Brent oil, which was characterized by a very low sulphur content (less than 1.4%). The API gravity ranged from 30 to 65, reflecting a diverse range of oil types within the basin. The crude oils in the basin were primarily derived from marine organofacies, predominantly from type B. This inference is supported by related biomarkers such as regular steranes and isoprenoids. Furthermore, the analysis of carbon isotopes provided a similar indication, with values ranging from −32 to −27 for ‰ δ¹³C for saturates and −31.2 to −25.4 ‰ δ¹³C for aromatic compounds. The thermal maturity biomarker ratio (Ts/Ts + Tm) of the Sirt Basin crude oils varied from 0.35 to 0.92, suggesting different levels of thermal maturity, typically ranging from the mid to late mature stages. This observation is consistent with the indication based on the 22S/22S + 22R ratio. The basin exhibited four dominant oil families and eight subfamilies with the same geochemical characteristics (HCA-based analysis), including early and later generations, relatively sulphurized oils, and condensate families.