Journal of African Earth Sciences最新文献

{"title":"Erosion and shoreline retreat indicators in the Rabat-Salé littoral and their impact on coastal planning","authors":"El Miloudiya Naji ,&nbsp;M'hamed Aberkan ,&nbsp;Abderrahim Saadane ,&nbsp;M'hamed Nmiss","doi":"10.1016/j.jafrearsci.2025.105534","DOIUrl":"10.1016/j.jafrearsci.2025.105534","url":null,"abstract":"<div><div>In-depth field investigations have allowed us to assess the coastal sector of Rabat-Salé by describing various forms of erosion, the condition of historical monuments located by the ocean, and the ineffectiveness of hard solutions implemented against erosion. This emphasizes the primary anthropogenic causes of the degradation of the studied coastal environments, including former calcarenite quarries and old sewage drainage canals. The interaction of these anthropogenic factors with natural processes has led to a significant retreat of the coastal cliff, which is clearly visible on-site, posing a threat to certain constructions, notably historical monuments of great cultural value to the Kingdom. To quantify the retreat in the study area between 1993 and 2022, we utilized the Digital Shoreline Analysis System (DSAS), version 5 integrated into ArcGIS 10.4, which revealed relatively high rates with an average rate of 1.2 m per year. We also adopted another method by using threatened historical monuments to calculate average retreat rates of the shoreline using two old plans, one dating back to 1935 (1/1000 scale) for Fort Rottembourg and another from 1922 (1/2000 scale) containing two historical monuments: Borj Sirat and Borj Eddar. The calculations yielded average rates that align with those obtained through DSAS. Despite the risks associated with erosion in the study area, a regulatory framework for the protection and enhancement of the coastal environment (Law 81-12) has been in place since 2015, prohibiting any construction within 100 m of the shoreline. This distance can be extended in cases of significant threats, such as severe erosive activity. However, some projects are still located in high-risk erosion areas, where erosion may be further exacerbated by karstic phenomena affecting the substrate. The results of this study align well with the provisions of Law 81-12 (Article 12).</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105534"},"PeriodicalIF":2.2,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"c.2.02 Ga Ar40–Ar39 muscovite age from the Gulushabe fold structure, Motloutse Complex, near SW margin of Zimbabwe Craton: Imprint of Limpopo Complex or Magondi Belt tectonics?","authors":"H.M. Rajesh ,&nbsp;G.A. Belyanin ,&nbsp;T. Mokatse ,&nbsp;D.T. Mfa ,&nbsp;C. Vorster ,&nbsp;Y. Wan","doi":"10.1016/j.jafrearsci.2025.105535","DOIUrl":"10.1016/j.jafrearsci.2025.105535","url":null,"abstract":"<div><div>Meta-supracrustal rocks in medium-to high-grade terranes along Archean craton margins are, in the common case, more deformed than similar rocks within the craton. Multiple deformation episodes are possible and could be related to different stages of a single tectonic event or disparate ones. Geochronologic characterization of fabric forming minerals helps to place an individual deformational episode with respect to spatially associated tectonic events along the craton margin. This study focuses on the Shashe Group of metasedimentary rocks that define the large-scale Gulushabe fold structure in northeastern Motloutse Complex, Botswana, near its contact with the southwestern margin of the Zimbabwe Craton. Available detrital zircon geochronologic data indicate a depositional age of c.2.66–2.51 Ga for the protolith of these continental margin-type metasedimentary rocks. The upright NNE-trending Gulushabe fold structure is at variance with the regional northeasterly vergent folds from the northern–central Motloutse Complex and related to the Neoarchean (&lt;2.65 Ga) NE-directed thrusting of the medium-grade terrane over the craton margin. ⁴⁰Ar/³⁹Ar geochronology of muscovite in quartz mica schist from the NNE-trending refolded northwestern minor fold closure of the Gulushabe fold structure yielded a plateau (96% of ³⁹Ar) age of 2018 ± 11 Ma. The significance of the age is addressed in terms of Paleoproterozoic tectonics in the bounding terranes: Limpopo Complex to the south and Magondi Belt to the north. In the process, the Archean antiquity and extent of the Motloutse Complex, and the provenance of Shashe Group rocks are clarified. The results highlight the importance of delineating overprint events to better understand the tectonics along the contact of Archean craton and medium-to high-grade terranes.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105535"},"PeriodicalIF":2.2,"publicationDate":"2025-01-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrogeochemical and hydrogeological baseline study following the mining of asbestos at the Havelock Mine, Bulembu, eSwatini","authors":"Christian Wolkersdorfer ,&nbsp;Kagiso S. More ,&nbsp;Elke Mugova ,&nbsp;Nokuthula Nchabeleng ,&nbsp;Anna Johanna Sotiralis","doi":"10.1016/j.jafrearsci.2024.105533","DOIUrl":"10.1016/j.jafrearsci.2024.105533","url":null,"abstract":"<div><div>This study examined the hydrogeological and hydrochemical conditions around Bulembu, eSwatini, two decades post-closure of the Havelock asbestos mine. On-site parameters and water samples underwent chemical and stable isotope analysis, supplemented by flow measurements and tracer tests with NaCl and uranine. Multivariate statistical analysis and PHREEQC modelling identified three water groups: i) low mineralised surface water (32 mg/L TDS), ii) mining-influenced water from the Havelock mine pool (212 mg/L TDS), and iii) tailings seepage water (411 mg/L TDS). All are earth alkaline, hydrogen carbonate-dominant, dominated by Mg and hydrogen carbonate ions. Surface water complies with WHO standards, except for elevated As in the mine pool and Cr in waste rock seepage. Chemical and tracer test results indicate a well-mixed, low-residence-time mine pool. Both the Tutusi river catchment and the upper Nkomazana catchment as well as water courses downstream of the abandoned mine exhibit pristine water quality. The authors propose inclusion of the area in a trans-boundary national park with the Barbeton Makhonjwa Mountains UNESCO World Heritage Site. They recommend amelioration of tailings, not remining, to safeguard the environment and local population from asbestos exposure.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105533"},"PeriodicalIF":2.2,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spatiotemporal variability of the Cenomanian macrobenthic fauna in Northeast Algeria: Species versus community level variations","authors":"Sihem Salmi-Laouar ,&nbsp;Samira Mendir ,&nbsp;Riadh Aouissi ,&nbsp;Gamal M.EL. Qot ,&nbsp;Rachel Kruft-Welton ,&nbsp;Mohamed S. Ahmed ,&nbsp;Ahmed A. Abdelhady","doi":"10.1016/j.jafrearsci.2024.105526","DOIUrl":"10.1016/j.jafrearsci.2024.105526","url":null,"abstract":"<div><div>Environmental changes can impact benthic fauna at multiple levels. To better understand these changes at both the species and community levels, the Cenomanian macrofossils from two regions in northeastern Algeria, Tébessa and Batna, were analyzed. The results revealed that while changes at the species level (morphology) and community level (ecology) followed similar patterns, they were not identical. Non-metric multidimensional scaling (NMDS) and permutational multivariate analysis of variance (PERMANOVA) tests of the morphological variations of 114 complete shells of the suspension-feeding trigonoid bivalve <em>Scabrotrigonia scabra</em> (Lamarck, 1819) showed significant differences (P &lt; 0.001) between the two regions. Two distinct echophenotypes were identified, with the first dominating in Tébessa and the second in Batna. The Batna echophenotype is characterized by smaller, flattened shells with numerous ribs, an adaptive strategy for stabilizing in soft substrates. Additionally, the smaller shells in Batna were linked to the oligotrophic conditions of the outer ramp setting, in contrast to the deeper outer ramp setting in Tébessa (mesotrophic). To further investigate environmental variations, the macrofaunal associations of the Cenomanian were examined. The NPMANOVA test indicated significant differences in faunal associations between the regions, with Batna exhibiting less diversity and a higher proportion of deposit-feeders, suggesting soft substrate conditions. In contrast, no significant differences were found among the faunal associations of the different Cenomanian substages, though ecological attributes showed minor, gradual changes. The early and middle Cenomanian fauna were dominated by epifaunal byssate taxa, while deposit-feeder taxa increased in the late Cenomanian, likely due to the global sea-level rise toward the end of the period. Overall, the paleogeographic setting (middle versus outer ramp) appears to have played a major role in shaping the ecological and morphological variations between Tébessa and Batna.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105526"},"PeriodicalIF":2.2,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ar/Ar geochronology of hydrothermal K-feldspar from the Mowana Cu Mine and implications for geotectonothermal evolution and Cu mineralisation in the Archean Matsitama Greenstone Belt, Zimbabwe Craton, northeastern Botswana","authors":"Thierry Bineli Betsi ,&nbsp;Tebogo Kelepile ,&nbsp;Kazuyasu Shindo ,&nbsp;Read Brown Mapeo ,&nbsp;Alfredo Camacho","doi":"10.1016/j.jafrearsci.2024.105521","DOIUrl":"10.1016/j.jafrearsci.2024.105521","url":null,"abstract":"<div><div>Unlike numerous Archean-Proterozoic greenstone belts worldwide, which are known to host orogenic and intrusion-related-type gold deposits, the Archean Matsitama Greenstone Belt (MGB) of NE Botswana hosts numerous base metal deposits/occurrences, including the Bushman Lineament (a regional brittle-ductile shear-hosted) Mowana Cu deposit. Economic copper mineralisation therein occurs as hypogene (chalcopyrite), supergene (chalcocite mainly), and oxidised (malachite, cuprite, tenorite, and chrysocolla) ores within quartz-K-feldspar-calcite veins. Due to the insufficiency of radiochronologic data, the geotectonic setting and evolution of the MGB are unclear, and the time of Cu introduction in the MGB remains contentious and unconstrained. In this study, hydrothermal K-feldspar spatially associated with Cu mineral phases in the ore veins was dated by ⁴⁰Ar/³⁹Ar to shed light on the window time of Cu mineralisation and understand the geological context of the MGB. K-feldspar from the hypogene ore-dominated and the oxidised ore-dominated areas yields similar integrated total fusion ⁴⁰Ar/³⁹Ar ages of <em>ca.</em> 550 Ma. Our new age is at odds with the Archean geological setting of the MGB and the <em>ca.</em> 2.2-1.9 Ga galena Pb-Pb age previously assigned to the Cu mineralisation within the MGB. This new age, however, reveals for the first time that the Pan-African thermal rejuvenation that was previously recognised in other portions of the Zimbabwe Craton also affected the MGB, therefore refining the spatial extent to which the Zimbabwe Craton underwent thermal rejuvenation. Our <em>ca</em>. 550 Ma age also highlights the possibility of a Neoproterozoic Cu mineralisation event at Mowana Copper Mine, in addition to the known Paleoproterozoic initial Cu introduction. This possible Neoproterozoic Cu mineralisation event at the Mowana Copper Mine is coincident with Cu events within the Kalahari Copper Belt as well as within the Central African and Zambian Copper belts, therefore highlighting the importance of the Pan-African Orogenesis in the Cu endowment of south-central Africa.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105521"},"PeriodicalIF":2.2,"publicationDate":"2024-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemistry and petrogenesis of mafic microgranular enclaves (MMEs) in the bougaffer granitoid, Saghro inlier, eastern anti-atlas belt, Morocco","authors":"Omar Outaaoui ,&nbsp;Ezzoura Errami ,&nbsp;Kadio Aka Donald Koua ,&nbsp;Abdellatif Jouhari ,&nbsp;Saber Salmi ,&nbsp;Abdelmalek ouadjou ,&nbsp;Nasser Ennih","doi":"10.1016/j.jafrearsci.2024.105528","DOIUrl":"10.1016/j.jafrearsci.2024.105528","url":null,"abstract":"<div><div>Mafic Microgranular Enclaves (MMEs) within granitoids are commonly interpreted as indicators of coexisting mafic magma that were derived from the mantle, which can offer valuable insights into the origins and evolution of primary mafic magmas. In this article, we investigate the petrography and bulk-rock major and trace elements geochemistry of quartz monzonite, the hosted MMEs, and the associated pink granite, from the Bougaffer pluton in the eastern Saghro Inlier. This study aims to clarify the petrogenetic processes that formed the MMEs and their granitoid host rocks. The MMEs are characterized by a microgranular texture and occur as ellipsoidal, angular and rounded shape, ranging in size from 2 to 80 cm, with sharp boundaries. They share the same mineral content as their host rocks though in distinct proportions, and are classified as monzonite and monzodiorite with high-K calc-alkaline to shoshonitic composition. The MMEs show lower SiO₂ contents and higher TiO₂, CaO, MgO, Fe₂O₃t, and Al₂O₃ contents compared to their host granitoids. The MMEs and their host granitoid display several similarities, including the same mineralogy and similar total-rock compositions, suggesting a genetic relationship. The MMEs are most likely cumulates formed during the initial phase of the same magmatic system that produced the Bougaffer quartz monzonite. A two stages model is proposed, involving rapid solidification within the cogenetic host granitoid magma at the chamber boundaries, leading to the formation of crystal accumulations at the bottom of the magma chamber as cumulates. These cumulates were later fragmented and disturbed due to subsequent magma recharge and the convection induced within the magma chamber.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105528"},"PeriodicalIF":2.2,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Kogi west geophysical mineralisation appraisal using Analytical Hierarchy Process (AHP)","authors":"Fahad Abubakar ,&nbsp;Ismail Ahmad Abir ,&nbsp;Abdulrasheed Adamu Hassan","doi":"10.1016/j.jafrearsci.2024.105532","DOIUrl":"10.1016/j.jafrearsci.2024.105532","url":null,"abstract":"&lt;div&gt;&lt;div&gt;In a recent report by the Nigerian Geological Survey Agency, new minerals, including gold, lepidolite, and tantalite, were discovered in the western part of Kogi State. If found in sufficient quantities, these commercially valuable minerals have the potential to drive technological advancement, create jobs, and promote economic growth, which are crucial for the sustainable development of Nigeria. This study aims to delineate these occurrences, extensions, and other potential mineralisation zones using integrated high-resolution airborne magnetic and gamma-ray spectrometry geophysical datasets aided by the Analytical Hierarchy Process (AHP) and weighted overlay analysis (WOA). The AHP and WOA algorithms were employed based on expert opinions and the accuracy of each signal enhancement technique to delineate the mineralisation potential of the study area (using the IMOs as control). Centre for Exploration Targeting (CET) grid analysis, analytic signal (Asig), and Euler deconvolution were used to enhance the magnetic datasets, while radiometric ratios and ternary images were utilised for the radiometric datasets. The Asig categorises the magnetic amplitude into low (&lt;0.023 nT/m), intermediate (0.023–0.105 nT/m), and high (&gt;0.105 nT/m). It reveals magneto-structures and intrusive zones, which are potential targets for mineralisation. WNW-ESE and NE-SW are the dominant fault trends, with the IMOs being more consistent with NE-SW faults. The estimated depth of potential mineralisation zones ranges from 20.87 to 87.34 m. The ternary image and radiometric ratio maps (K/Th and Th/K) indicate that the mineralisation zones have undergone advanced weathering, resulting in potassium leaching and thorium enrichment. Asig, lineament density, and the Th/K ratio map were integrated to assess the mineralisation potential. Employing the ArcGIS weighted overlay tool and AHP evaluation, the mineralisation potential of Kogi West was classified as high, intermediate, or low. 90% of the IMOs fall within the high class, while 10% are in the intermediate category. The high-potential zones should be prioritised for further exploration and exploitation. The high correspondence indicates the effectiveness of the integrated geophysical approach in identifying regions with favourable geological conditions for mineralisation. However, while the study provides a promising framework for targeting potential mineral deposits, future exploration activities should consider the following implications to improve the reliability and applicability of the results: validation with ground-truthing, incorporating other geophysical methods (such as electrical, gravity, and electromagnetic surveys), and acknowledgement of eventualities that high potential mineralisation zones not been economically viable, may be due to poor mineral grade or volume. These endeavours and acknowledgements will refine the current understanding of the high-potential mineralisation zones and expand t","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105532"},"PeriodicalIF":2.2,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171380","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrogenesis and geodynamic model for (Ta, Nb)-fertilized Nuweibi albite granite, Egyptian Nubian Shield: Juvenile crust-mantle mixing and metasomatic enhancement","authors":"Mohamed Th S. Heikal ,&nbsp;Mokhles K. Azer ,&nbsp;Mohamed S. Kamar ,&nbsp;Mohamed O. Ibrahim ,&nbsp;Mohamed Abd El Monsef","doi":"10.1016/j.jafrearsci.2024.105530","DOIUrl":"10.1016/j.jafrearsci.2024.105530","url":null,"abstract":"<div><div>Nuweibi Albite Granite (NAG, 1.3 km² as total area) is considered one of the well-known highly evolved, rare metals-bearing pluton in the Egyptian Nubian Shield. The Nuweibi area constitutes ophiolite assemblage (metagabbros, serpentinites and related talc-carbonates), tuffaceous metasediments with their associated hornfelse, granodiorite-tonalite and post-tectonic albite granite, the latter is cross cutting by aplite and basaltic dykes. The present work focuses on the geochemical characteristic of NAG, using new data of whole-rock geochemistry and mineral chemistry to address-out approach on its origin, geodynamic evolution and genetic relation with the Ta-Nb mineralization. The main (Ta, Nb)-bearing minerals include; tantalite, columbite, wodginite and calciomicrolite. The geochemical analyses revealed that, the studied NAG has peraluminous, within-plate, post-collisional, A-type characters. It exhibits an enrichment of Na₂O (up to 6.56 wt%) reflecting the alkaline affinity (σ up to 6.19), closing to alkaline trend of an extensional regime. The REEs tetrad effect is well pronounced with negative Eu anomaly, which is most remarkable toward the closing of magma at the late magmatic stage of fractionation. The analytical criteria support the evolution of NAG through highly evolved magmatic fractionation (in major) and later metasomatic replacement (in minor). The abundance of rare metals such as (Ta, Nb), suggests the strong influence of fluorine and aqueous fluid system in the residual melt. With respect to the magmatic origin of NAG through advanced degree of fractionation, a complex set of geological processes including crust-mantle mixing, partial melting and fluid flux-volatiles interaction (i.e. metasomatism) have been involved during the geodynamic evolution.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105530"},"PeriodicalIF":2.2,"publicationDate":"2024-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geochemical evaluation of calcareous coal horizons, Gebel Crystal, Western Desert, Egypt: Paleoenvironmental implications","authors":"Asmaa F. El-Moghazy,&nbsp;Nader A.A. Edress","doi":"10.1016/j.jafrearsci.2024.105529","DOIUrl":"10.1016/j.jafrearsci.2024.105529","url":null,"abstract":"<div><div>Crystal Mountain (also called Gebel Crystal) is a famous karst feature in the Western Desert of Egypt. It is a huge, unroofed cave composed of chalky limestone that constitutes the host rock of the Upper Cretaceous Khoman Formation. The cave filling consists of alternating irregular strata composed of calcareous coal horizons with complex sinkholes, detrital material, calcite crystals, and red sandstones. These coal horizons have attracted the attention of many scientists to explain the depositional environment, coal types, and ash minerals. However, there are no recent studies about the detailed paleoenvironmental conditions of these coal horizons. Accordingly, different calcareous coal horizons from the Gebel Crystal were examined to determine the paleoenvironment of the deposits. Coal samples were subjected to mineralogy and organic geochemistry to determine the nature, origin and density of the vegetation cover paleoenvironment. In addition, analyses of major and trace elements of the studied coal samples were performed to determine the different paleoenvironmental conditions of the deposits, such as paleoclimate, paleosalinity, organic matter origin, and paleo-redox conditions. The results reveal that the calcareous coal is a very low-grade coal (average ash content 40.96 wt%) with a low-rank lignite type (soft brown coal), which belongs to the ortho-lignite and/or lignite A and B facies. Type III kerogen was observed to be the main precursor of the humic peat, lignite, and sub-bituminous coal, and organic matter maturation suggests immature diagenesis stage. The immature diagenesis stage is consistent with the concept that excludes a hydrothermal solution for the formation of calcite in the coal samples. The dominance of inertinite (49.2%) and liptinite (32.4%) over huminite (18.3%) as macerals indicates that the desiccation phase took place in the mire prior to final preservation. Paleoenvironmental indices such as tissue preservation index (TPI), gelification index (GI), vegetation index (VI), ground water index (GWI) and facies diagrams suggest the dominance of marsh vegetation in the limno-telmatic, rheotrophic mire system. Piedmont alluvial plain and back-barrier with freshwater supply are inferred as the depositional sites for the studied calcareous coal formation. The mineralogical composition of the coal horizons consists of carbonate (calcite and manganocalcite), quartz, and evaporite (halite and anhydrite) minerals. The results of the paleoenvironmental indicators (e.g., Sr/Ba, Rb/K₂O, Sr/Cu, V/(V + Ni), V/Cr, Ni/Co, V/Ni, Co/Ni, sulfur, and C-value) reveal that freshwater conditions were dominant during the deposition of the coal horizons. The prevailing paleoclimate was an arid climate, which was responsible for the formation of the evaporite minerals. The organic matter originated from terrestrial sources of plant material, and the coal horizons were deposited under suboxic redox conditions.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105529"},"PeriodicalIF":2.2,"publicationDate":"2024-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Confirmation and significance of high quality and oil prone source rocks in the southeast African offshore","authors":"Zhaoming Wang,&nbsp;Zhixin Wen,&nbsp;Chengpeng Song,&nbsp;Ruiyin Chen,&nbsp;Zhengjun He,&nbsp;Xiaobing Liu,&nbsp;Tianyu Ji,&nbsp;Yanyan Chen","doi":"10.1016/j.jafrearsci.2024.105531","DOIUrl":"10.1016/j.jafrearsci.2024.105531","url":null,"abstract":"<div><div>The offshore region of East Africa has undergone extensive geological evolution since the Permian period, characterized by two stages of rifting phases followed by a subsequent stage of passive margin development. The stratigraphic record in this area is comprehensive, indicating the formation of multiple series of source rocks. Recent discoveries have identified over 200 trillion cubic feet of natural gas in the Ruvuma Basin, in addition to a modest quantity of light crude oil found onshore in Mozambique. However, the precise origins of hydrocarbons in this region remain unclear. In this study, the paleo-position restoration technique for oil and gas fields was utilized to reconstruct the paleo-positions of key wells and reservoirs during critical periods of source rock development. Three significant Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) wells drilled in the offshore region of East Africa were selected for source rock assessment. The geochemical data obtained from these wells were systematically analyzed, resulting in the creation of continuous geochemical profiles that elucidate the characteristics of the thick, high-quality, oil-prone marine source rocks formed in the southern offshore region of East Africa during the Upper Jurassic to Lower Cretaceous periods. These source rocks exhibit high total organic carbon (TOC) and hydrogen index (HI) values, indicating a robust capacity for hydrocarbon generation. They are widely distributed and predominantly consist of oil-prone Type II1-II2 kerogen. The sequence of source rocks with elevated TOC exceeds 115 m in thickness. Carbon isotope data from methane and ethane in natural gas samples suggest that the hydrocarbons in the onshore and southern offshore areas of East Africa are derived from these Upper Jurassic to Lower Cretaceous marine source rocks, thereby indirectly indicating significant exploration potential for these source rocks. Based on seismic sections, a hydrocarbon accumulation model has been developed for the southern offshore region of East Africa. This model comprises multiple series of source rocks that provide sufficient hydrocarbon supply, effective source-reservoir-seal assemblages, and near-source hydrocarbon migration and accumulation. The findings of this study enhance confidence in hydrocarbon exploration within the study area and further delineate potential areas and directions for future exploration efforts.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105531"},"PeriodicalIF":2.2,"publicationDate":"2024-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}