Pub Date : 2024-09-26DOI: 10.1016/j.jafrearsci.2024.105436
This study investigates the structural style and tectonic evolution of Jurassic succession in southern Iraq, within the Zubair oil field, which are crucial for charging oil to the Cretaceous reservoirs, utilized 3-D seismic reflection data to explore its complex geological history. The field is located in the Mesopotamian plain on the northeast Arabian Plate in southern Iraq. Four folds recognized: Hammar, Shuaiba, Rafdyia, and Safwan, each shaped by specific geodynamic processes. Hammar, Shuaiba, and Safwan are characterized as salt-related folds, influenced by salt tectonics. Rafdyia is identified as a compression-related fold formed due to the convergence of the Arabian and Eurasian plates. Forty-seven faults were identified, with diversity patterns and spatial distributions suggesting a tectonic history marked by three distinct phases: extensional tectonics, extensional with concurrent salt activity, and plate convergence. These phases have created a series of graben structures that, along with the identified folds, highlight the role of three primary tectonic processes: basement tectonics, salt dynamics, and plate interactions in shaping the structural style of the Zubair oil field during the Jurassic time.
{"title":"Tectonic evolution and structural geology of the Jurassic succession in the Zubair oil field, southern Iraq","authors":"","doi":"10.1016/j.jafrearsci.2024.105436","DOIUrl":"10.1016/j.jafrearsci.2024.105436","url":null,"abstract":"<div><div>This study investigates the structural style and tectonic evolution of Jurassic succession in southern Iraq, within the Zubair oil field, which are crucial for charging oil to the Cretaceous reservoirs, utilized 3-D seismic reflection data to explore its complex geological history. The field is located in the Mesopotamian plain on the northeast Arabian Plate in southern Iraq. Four folds recognized: Hammar, Shuaiba, Rafdyia, and Safwan, each shaped by specific geodynamic processes. Hammar, Shuaiba, and Safwan are characterized as salt-related folds, influenced by salt tectonics. Rafdyia is identified as a compression-related fold formed due to the convergence of the Arabian and Eurasian plates. Forty-seven faults were identified, with diversity patterns and spatial distributions suggesting a tectonic history marked by three distinct phases: extensional tectonics, extensional with concurrent salt activity, and plate convergence. These phases have created a series of graben structures that, along with the identified folds, highlight the role of three primary tectonic processes: basement tectonics, salt dynamics, and plate interactions in shaping the structural style of the Zubair oil field during the Jurassic time.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142433492","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}
Pub Date : 2024-09-26DOI: 10.1016/j.jafrearsci.2024.105429
This study combines several provenance tools, analysis of published structural and geodynamic data, integrated with Low-Temperature Thermochronology (LTT) and time-Temperature Modelling (tTM) to reconstruct the evolution of source-to-sink systems feeding the Essaouira-Agadir Basin (EAB) during the Jurassic (Toarcian, Bathonian, and Kimmeridgian) and Lower Cretaceous (Hauterivian and Barremian).
LTT and tTM define timing and rate of subsidence and exhumation of the hinterland and allows modelling of the predicted age and lithology of eroding rock units from the most-likely source locations through time. Extrapolation of predicted surface geology allows recognition of the lithology of sedimentary overburden in the hinterland, much of which has been subsequently eroded and is not preserved in the modern surfical geological record.
Heavy mineral, petrography and detrital zircon data analysis was carried out on fluvial and shallow marine sandstones sampled from Jurassic and Cretaceous sections across in the EAB. The results document changing sediment source terrains through time. In the Early and Middle Jurassic, the heavy mineral and detrital zircon signature correlates with a Palaeozoic source, suggesting provenance was dominantly from erosion of Cambrian and Ordovician sandstone in the Central and Western Anti-Atlas. From the Late Jurassic to Early Cretaceous, the heavy mineral and zircon signatures have a strong affinity with Triassic sediments. This indicates a provenance switch to the exhuming West Moroccan Arch (MAM and Western Meseta), interpreted to have been largely covered by Triassic continental red beds at the time.
The results help in predicting sediment delivery offshore, into the deep-water basin, where sandstones are a target for hydrocarbon exploration. Defining timing of input, location and composition helps to de-risk exploration. All the intervals examined contained discrete fluvial systems entering in the EAB, suggesting multiple periods of clastic delivery. Results suggest the Middle Jurassic and Hauterivian and Barremian intervals offer the optimum time for delivery of coarse clastics to the shelf margin, and potentially into the deep basin. The source to sink maps developed in this study further characterize these systems, their provenance and timing.
{"title":"Mesozoic clastic provenance during post-rift evolution of the Essaouira Agadir Basin, Northern Morocco","authors":"","doi":"10.1016/j.jafrearsci.2024.105429","DOIUrl":"10.1016/j.jafrearsci.2024.105429","url":null,"abstract":"<div><div>This study combines several provenance tools, analysis of published structural and geodynamic data, integrated with Low-Temperature Thermochronology (LTT) and time-Temperature Modelling (tTM) to reconstruct the evolution of source-to-sink systems feeding the Essaouira-Agadir Basin (EAB) during the Jurassic (Toarcian, Bathonian, and Kimmeridgian) and Lower Cretaceous (Hauterivian and Barremian).</div><div>LTT and tTM define timing and rate of subsidence and exhumation of the hinterland and allows modelling of the predicted age and lithology of eroding rock units from the most-likely source locations through time. Extrapolation of predicted surface geology allows recognition of the lithology of sedimentary overburden in the hinterland, much of which has been subsequently eroded and is not preserved in the modern surfical geological record.</div><div>Heavy mineral, petrography and detrital zircon data analysis was carried out on fluvial and shallow marine sandstones sampled from Jurassic and Cretaceous sections across in the EAB. The results document changing sediment source terrains through time. In the Early and Middle Jurassic, the heavy mineral and detrital zircon signature correlates with a Palaeozoic source, suggesting provenance was dominantly from erosion of Cambrian and Ordovician sandstone in the Central and Western Anti-Atlas. From the Late Jurassic to Early Cretaceous, the heavy mineral and zircon signatures have a strong affinity with Triassic sediments. This indicates a provenance switch to the exhuming West Moroccan Arch (MAM and Western Meseta), interpreted to have been largely covered by Triassic continental red beds at the time.</div><div>The results help in predicting sediment delivery offshore, into the deep-water basin, where sandstones are a target for hydrocarbon exploration. Defining timing of input, location and composition helps to de-risk exploration. All the intervals examined contained discrete fluvial systems entering in the EAB, suggesting multiple periods of clastic delivery. Results suggest the Middle Jurassic and Hauterivian and Barremian intervals offer the optimum time for delivery of coarse clastics to the shelf margin, and potentially into the deep basin. The source to sink maps developed in this study further characterize these systems, their provenance and timing.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-25DOI: 10.1016/j.jafrearsci.2024.105428
This study is effected on the volcano-sedimentary terrain of Tabenken on the Oku massif. Here is a region predominantly underlain by a granitoid basement of Precambrian age (600 ma), overlain in most parts by alkali basalts, andesites, trachytes and rhyolites. Between the basement and volcanics is sandwiched a discontinuous sequence of sedimentary lithofacies composed of conglomerates, sandstones, claystones, siltstones and patches of coal raising the question of the palaeoenvironment. Petrographic analyses, major and trace element geochemistry and palynological analyses were conducted on samples of sediments. Palynological constituents found include amorphous organic matter, phytoclasts, opaque material and palynomorphs consisting of spores with no pollen grains. The presence of cuticles is environmental indicator for delta sediments while abundance of amorphous organic matter (AOM) suggests deposition in a reducing environment. Petrographic studies reveal two cycles of deposition; L1 and L2 separated by Cenozoic outpours. U/Th ratios for the analyzed samples range from 0.3, 0.06, 0.00 to 0.2 and fall within the range of sediments formed in oxidizing environments. This contrasts evidence from AOM hence suggests sediment input cut across climatic and environmental alterations over a long period of time. Sr/Ba ratios range from 0.08 to 0.25 with an average of 0.18 reflecting fresh water environment; while Rb/Sr ratios range from 0.2, 0.29, 0.33 and 0.45 being low and suggests sediments deposited under warm climatic conditions. Diagram of Roser and Korsch, 1986 reveals deposition in a passive margin while Al2O3/TiO2 and Th/Co ratios support sediment input of principally felsic origin with little input from mafic sources.
{"title":"Application of petrography, geochemistry and palynology of the mid-Ordovician – Pennsylvanian sediments of Tabenken in the investigation of Palaeo-environmental alterations of the Oku massif, North West Cameroon","authors":"","doi":"10.1016/j.jafrearsci.2024.105428","DOIUrl":"10.1016/j.jafrearsci.2024.105428","url":null,"abstract":"<div><div>This study is effected on the volcano-sedimentary terrain of Tabenken on the Oku massif. Here is a region predominantly underlain by a granitoid basement of Precambrian age (600 ma), overlain in most parts by alkali basalts, andesites, trachytes and rhyolites. Between the basement and volcanics is sandwiched a discontinuous sequence of sedimentary lithofacies composed of conglomerates, sandstones, claystones, siltstones and patches of coal raising the question of the palaeoenvironment. Petrographic analyses, major and trace element geochemistry and palynological analyses were conducted on samples of sediments. Palynological constituents found include amorphous organic matter, phytoclasts, opaque material and palynomorphs consisting of spores with no pollen grains. The presence of cuticles is environmental indicator for delta sediments while abundance of amorphous organic matter (AOM) suggests deposition in a reducing environment. Petrographic studies reveal two cycles of deposition; L1 and L2 separated by Cenozoic outpours. U/Th ratios for the analyzed samples range from 0.3, 0.06, 0.00 to 0.2 and fall within the range of sediments formed in oxidizing environments. This contrasts evidence from AOM hence suggests sediment input cut across climatic and environmental alterations over a long period of time. Sr/Ba ratios range from 0.08 to 0.25 with an average of 0.18 reflecting fresh water environment; while Rb/Sr ratios range from 0.2, 0.29, 0.33 and 0.45 being low and suggests sediments deposited under warm climatic conditions. Diagram of Roser and Korsch, 1986 reveals deposition in a passive margin while Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> and Th/Co ratios support sediment input of principally felsic origin with little input from mafic sources.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420462","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}
Pub Date : 2024-09-24DOI: 10.1016/j.jafrearsci.2024.105435
The present study aims to evaluate the heavy metal pollution in the Farwa Lagoon, which is one of the most important coastal lagoons in NW Libya. The concentrations of six heavy metals (Fe, Zn, Pb, Ni, Cu, Cd) are measured in the surface sediment of the lagoon. Moreover, the contamination indices, including contamination factor, degree of contamination, pollution load index, geo-accumulation index, enrichment factor, risk factor, and potential ecological risk index, are applied. The results indicate that, Fe has the highest concentration, followed by Zn, Pb, Ni, Cu and Cd. The distribution patterns of metals reflect that the levels of Fe, Cu and Zn increase in the central part of the lagoon, whereas Cd and Pb increase in the central and western parts. In addition, the values of contamination factor reflect that the examined sites are moderately contaminated with Pb and Zn, whereas they are very highly contaminated with Cd. These findings lead to very high degree of contamination. Moreover, pollution load index reflects that the Farwa Lagoon is polluted. Finally, the study area is very highly ecological risk with Cd. The concentration of metals in the Farwa Lagoon is correlated with those from other regions in the Mediterranean region, such as Egypt, Algeria, Tunisia, Italy, France, and Turkey. The comparison reflects that the Farwa Lagoon has the highest concentrations of Cd and Zn.
{"title":"Heavy metals in the surface sediments of Farwa Lagoon, NW Libya: Assessment and correlation with other Mediterranean lagoons","authors":"","doi":"10.1016/j.jafrearsci.2024.105435","DOIUrl":"10.1016/j.jafrearsci.2024.105435","url":null,"abstract":"<div><div>The present study aims to evaluate the heavy metal pollution in the Farwa Lagoon, which is one of the most important coastal lagoons in NW Libya. The concentrations of six heavy metals (Fe, Zn, Pb, Ni, Cu, Cd) are measured in the surface sediment of the lagoon. Moreover, the contamination indices, including contamination factor, degree of contamination, pollution load index, geo-accumulation index, enrichment factor, risk factor, and potential ecological risk index, are applied. The results indicate that, Fe has the highest concentration, followed by Zn, Pb, Ni, Cu and Cd. The distribution patterns of metals reflect that the levels of Fe, Cu and Zn increase in the central part of the lagoon, whereas Cd and Pb increase in the central and western parts. In addition, the values of contamination factor reflect that the examined sites are moderately contaminated with Pb and Zn, whereas they are very highly contaminated with Cd. These findings lead to very high degree of contamination. Moreover, pollution load index reflects that the Farwa Lagoon is polluted. Finally, the study area is very highly ecological risk with Cd. The concentration of metals in the Farwa Lagoon is correlated with those from other regions in the Mediterranean region, such as Egypt, Algeria, Tunisia, Italy, France, and Turkey. The comparison reflects that the Farwa Lagoon has the highest concentrations of Cd and Zn.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142322391","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}
Pub Date : 2024-09-21DOI: 10.1016/j.jafrearsci.2024.105434
Uranium mineralisation is formed in a wide range of geological settings, including deep magmatic to surficial conditions, and ranges in age from Archean to recent. The success of exploration planning and the choice of efficient extraction methods in an environmentally sustainable manner depend clearly on the understanding of the uranium genesis model and the detailed knowledge of the mineralogy of the deposit.
Mauritania hosts eighty known uranium occurrences, mainly located in the oriental part of the Reguibat Shield. Some of these occurrences have been evaluated with the publication of estimated resources, and even exploratory mining works have been performed on some of them. However, the detailed genetic conditions prevailing for the genesis of most of these occurrences remain poorly studied. Exploration reports indicate that uranium mineralisation in the Reguibat Shield mainly occurs as high temperature deposits hosted by shear zones in granites (hydrothermal Na-metasomatic deposits) and low temperature deposits hosted by calcretes (Calcrete deposits), which form more than 70% of these occurrences.
This paper focuses on the dominant uranium mineralisation systems (uraniferous calcretes and Na-metasomatite) of the oriental part of the Reguibat Shield and, to a lesser extent, other types of uranium deposits. Na-metasomatites are mainly originating from Neobirimian granite and basic rocks and occur through hydrothermal fluids, inducing regional metasomatism along NNW–SSE trending shear zones. While uraniferous calcretes in the area are found as subsurface layers covering a Proterozoic basement made of granitoid and associated gabbro-diorite massifs intersected by a network of mafic dykes. The uraniferous calcretes result from the weathering of the Neobirimian (Paleoproterozoic) granitic basement. Carbonate and uranium minerals (carnotite and tyuyamunite) crystallize as cementation materials within the granite arena. Two types of Neobirimian granites have been identified: the first one being an orientated coarse-grained porphyritic brown to pink granite, while the second one is a porphyritic grey medium-grained granite, whose mineralogy is mostly made up of plagioclase, K-feldspar, quartz, and chloritized biotite, while magnetite, apatite, titanite, zircon, uranothorite, and monazite are the accessory minerals.
{"title":"A review of the geological setting and economic potential of uranium occurrences in the proterozoic part of the Reguibat Shield of the west African Craton, in northern Mauritania","authors":"","doi":"10.1016/j.jafrearsci.2024.105434","DOIUrl":"10.1016/j.jafrearsci.2024.105434","url":null,"abstract":"<div><div>Uranium mineralisation is formed in a wide range of geological settings, including deep magmatic to surficial conditions, and ranges in age from Archean to recent. The success of exploration planning and the choice of efficient extraction methods in an environmentally sustainable manner depend clearly on the understanding of the uranium genesis model and the detailed knowledge of the mineralogy of the deposit.</div><div>Mauritania hosts eighty known uranium occurrences, mainly located in the oriental part of the Reguibat Shield. Some of these occurrences have been evaluated with the publication of estimated resources, and even exploratory mining works have been performed on some of them. However, the detailed genetic conditions prevailing for the genesis of most of these occurrences remain poorly studied. Exploration reports indicate that uranium mineralisation in the Reguibat Shield mainly occurs as high temperature deposits hosted by shear zones in granites (hydrothermal Na-metasomatic deposits) and low temperature deposits hosted by calcretes (Calcrete deposits), which form more than 70% of these occurrences.</div><div>This paper focuses on the dominant uranium mineralisation systems (uraniferous calcretes and Na-metasomatite) of the oriental part of the Reguibat Shield and, to a lesser extent, other types of uranium deposits. Na-metasomatites are mainly originating from Neobirimian granite and basic rocks and occur through hydrothermal fluids, inducing regional metasomatism along NNW–SSE trending shear zones. While uraniferous calcretes in the area are found as subsurface layers covering a Proterozoic basement made of granitoid and associated gabbro-diorite massifs intersected by a network of mafic dykes. The uraniferous calcretes result from the weathering of the Neobirimian (Paleoproterozoic) granitic basement. Carbonate and uranium minerals (carnotite and tyuyamunite) crystallize as cementation materials within the granite arena. Two types of Neobirimian granites have been identified: the first one being an orientated coarse-grained porphyritic brown to pink granite, while the second one is a porphyritic grey medium-grained granite, whose mineralogy is mostly made up of plagioclase, K-feldspar, quartz, and chloritized biotite, while magnetite, apatite, titanite, zircon, uranothorite, and monazite are the accessory minerals.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142312199","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}
Pub Date : 2024-09-20DOI: 10.1016/j.jafrearsci.2024.105433
<div><div>The Ain Dibba and Ain Kissa phosphorites, located north of Tebessa town, NE Algeria, belong to the Upper Cretaceous-Paleocene-Eocene Afro-Arabian phosphatic province that extends from Morrocco to the Middle East. These two phosphorite showings, which were partly exploited at the beginning of the 20th century, were deposited during the Late Paleocene (Thanetian) times on the northern basin of the Kasserine Paleo-Island. Although they are not yet economically very important, the present petrological and geochemical study contribute highly to the knowledge of their critical trace and REE contents as well as the understanding of their paleo-depositional environment. Petrographic and XRD data show that these phosphorites are mainly composed of pellets, coprolites, bioclasts and rare glauconite, gypsum, quartz grains and zeolites. These constituents are cemented by calcareous, siliceous or rarely clayey matrix. The pellets and coprolites are composed mainly of cryptocrystalline carbonate fluor-apatite (CFA). The XRF and ICP-MS chemical analyses of these phosphorites, show they are not as rich as those from Kef Essenoun and Bled El Hadba southern basin, neither in P<sub>2</sub>O<sub>5</sub> nor in REE contents. P<sub>2</sub>O<sub>5</sub> concentrations range from 14.16 to 26.57 wt% (average = 20.24 ± 4.33 wt%, n = 15), with only one sample having 31.89 wt% P<sub>2</sub>O<sub>5</sub>, whereas ΣREE contents range from 171 to 344 ppm (average = 252 ± 69 ppm, n = 9) and, therefore, considered as moderately REE-enriched phosphorites. Ce anomaly values display a decrease from the lower to the upper phosphorite sub-layers (from −0.57 down to −0.72), suggesting an increase from relatively sub-oxic to more oxic conditions. The Eu anomalies range from 0.89 to 1.35 for Ain Dibba and from 0.93 to 1.35 for Ain Kissa phosphorites. The highest Ce/Ce∗ and lowest Eu/Eu∗ anomalies are recorded in the lower layers, often enriched in both REE and glauconite contents, whereas the lowest Ce/Ce∗ and highest Eu/Eu∗ anomalies, reflecting more oxic conditions, are characteristics of the glauconite-free and REE-poor upper layers. The gradual timewise transition from relatively sub-oxic to oxic conditions (from the lower to the upper layers) is also recorded in the redox-sensitive (Cr, Ni, V, U) trace element data. This implies that during early diagenesis, the sedimentary environment became slightly reduced, which enabled intensive uptake of both REE and some trace element (e.g., Cr, V, Ni, U) mainly from pore-water through substitution and adsorption mechanisms onto apatite and glauconite minerals. This is noticed especially in the lower phosphorite layers of both Ain Dibba and Ain Kissa deposits. In a larger scale, the Ain Dibba and Ain Kissa phosphorites show lower REE contents, lower Ce and Eu anomalies, and lower redox-sensitive trace element contents than those of the southern (Kef Essenoun and Bled El Hadba) and eastern (Tunisian) basins of the Kasserine paleo-Is
Ain Dibba 和 Ain Kissa 磷矿位于阿尔及利亚东北部泰贝萨镇以北，属于上白垩世-古新世-始新世非洲-阿拉伯磷矿带，该磷矿带从摩洛哥延伸到中东。这两个磷酸盐矿床沉积于晚古新世（塔尼蒂）时期的卡塞林古岛北部盆地，在 20 世纪初被部分开采。虽然它们在经济上还不是很重要，但目前的岩石学和地球化学研究对了解它们的关键痕量和 REE 含量以及了解它们的古沉积环境有很大帮助。岩石学和 X 射线衍射数据显示，这些磷酸盐岩主要由球粒、共生岩、生物碎屑岩以及稀有的青云石、石膏、石英颗粒和沸石组成。这些成分由石灰质、硅质或极少数粘土质基质胶结而成。颗粒和桡长石主要由隐晶碳酸盐氟磷灰石（CFA）组成。对这些磷酸盐岩进行的 XRF 和 ICP-MS 化学分析表明，无论是 P2O5 还是 REE 含量，它们都不如 Kef Essenoun 和 Bled El Hadba 南部盆地的磷酸盐岩丰富。P2O5 含量从 14.16 到 26.57 wt%（平均 = 20.24 ± 4.33 wt%，n = 15）不等，只有一个样本的 P2O5 含量为 31.89 wt%，而 ΣREE 含量从 171 到 344 ppm（平均 = 252 ± 69 ppm，n = 9）不等，因此被认为是中度富含 REE 的磷酸盐岩。Ce异常值从磷酸盐岩下层向上层递减（从-0.57下降到-0.72），表明磷酸盐岩从相对亚缺氧状态上升到较缺氧状态。艾因迪巴磷酸盐岩的 Eu 异常值从 0.89 到 1.35 不等，艾因基萨磷酸盐岩的 Eu 异常值从 0.93 到 1.35 不等。Ce/Ce∗最高、Eu/Eu∗最低的异常记录在下层，通常富含 REE 和白榴石，而 Ce/Ce∗最低、Eu/Eu∗最高的异常反映了更多的氧化条件，是不含白榴石和 REE 贫乏的上层的特征。氧化还原敏感性（铬、镍、钒、铀）微量元素数据也记录了从相对亚氧化到氧化条件（从下层到上层）的逐步时间过渡。这意味着，在早期成岩过程中，沉积环境变得略微酸化，这使得REE和一些微量元素（如铬、钒、镍、铀）主要通过磷灰石和青金石矿物的置换和吸附机制从孔隙水中大量吸收。这种情况在艾因迪巴和艾因基萨矿床的磷酸盐岩下层尤为明显。在更大范围内，与卡塞林古岛南部盆地（Kef Essenoun 和 Bled El Hadba）和东部盆地（突尼斯）的磷酸盐岩相比，Ain Dibba 和 Ain Kissa 磷酸盐岩显示出较低的 REE 含量、较低的 Ce 和 Eu 异常，以及较低的氧化还原敏感微量元素含量。这些地球化学特征表明，在北非和中东地区的古新世-始新世磷酸盐形成过程中，北部盆地的磷酸盐岩是通过上升流沉积在更为开阔、较浅、含氧和搅拌环境中的。
{"title":"The Ain Dibba and Ain Kissa phosphorites, Tebessa (NE Algeria): REE depletion versus shallow, open depositional environment during the Paleocene-Eocene phosphogenesis in North Africa","authors":"","doi":"10.1016/j.jafrearsci.2024.105433","DOIUrl":"10.1016/j.jafrearsci.2024.105433","url":null,"abstract":"<div><div>The Ain Dibba and Ain Kissa phosphorites, located north of Tebessa town, NE Algeria, belong to the Upper Cretaceous-Paleocene-Eocene Afro-Arabian phosphatic province that extends from Morrocco to the Middle East. These two phosphorite showings, which were partly exploited at the beginning of the 20th century, were deposited during the Late Paleocene (Thanetian) times on the northern basin of the Kasserine Paleo-Island. Although they are not yet economically very important, the present petrological and geochemical study contribute highly to the knowledge of their critical trace and REE contents as well as the understanding of their paleo-depositional environment. Petrographic and XRD data show that these phosphorites are mainly composed of pellets, coprolites, bioclasts and rare glauconite, gypsum, quartz grains and zeolites. These constituents are cemented by calcareous, siliceous or rarely clayey matrix. The pellets and coprolites are composed mainly of cryptocrystalline carbonate fluor-apatite (CFA). The XRF and ICP-MS chemical analyses of these phosphorites, show they are not as rich as those from Kef Essenoun and Bled El Hadba southern basin, neither in P<sub>2</sub>O<sub>5</sub> nor in REE contents. P<sub>2</sub>O<sub>5</sub> concentrations range from 14.16 to 26.57 wt% (average = 20.24 ± 4.33 wt%, n = 15), with only one sample having 31.89 wt% P<sub>2</sub>O<sub>5</sub>, whereas ΣREE contents range from 171 to 344 ppm (average = 252 ± 69 ppm, n = 9) and, therefore, considered as moderately REE-enriched phosphorites. Ce anomaly values display a decrease from the lower to the upper phosphorite sub-layers (from −0.57 down to −0.72), suggesting an increase from relatively sub-oxic to more oxic conditions. The Eu anomalies range from 0.89 to 1.35 for Ain Dibba and from 0.93 to 1.35 for Ain Kissa phosphorites. The highest Ce/Ce∗ and lowest Eu/Eu∗ anomalies are recorded in the lower layers, often enriched in both REE and glauconite contents, whereas the lowest Ce/Ce∗ and highest Eu/Eu∗ anomalies, reflecting more oxic conditions, are characteristics of the glauconite-free and REE-poor upper layers. The gradual timewise transition from relatively sub-oxic to oxic conditions (from the lower to the upper layers) is also recorded in the redox-sensitive (Cr, Ni, V, U) trace element data. This implies that during early diagenesis, the sedimentary environment became slightly reduced, which enabled intensive uptake of both REE and some trace element (e.g., Cr, V, Ni, U) mainly from pore-water through substitution and adsorption mechanisms onto apatite and glauconite minerals. This is noticed especially in the lower phosphorite layers of both Ain Dibba and Ain Kissa deposits. In a larger scale, the Ain Dibba and Ain Kissa phosphorites show lower REE contents, lower Ce and Eu anomalies, and lower redox-sensitive trace element contents than those of the southern (Kef Essenoun and Bled El Hadba) and eastern (Tunisian) basins of the Kasserine paleo-Is","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142322394","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}
Pub Date : 2024-09-19DOI: 10.1016/j.jafrearsci.2024.105432
The East African Rift Valley (EARV) is characterized by diverse geology, including crystalline, volcanic, and metamorphic rocks, shaped by tectonic activity leading to complex faulting and fractured zones. These fractured zones in hard rock serve as crucial groundwater reservoirs, often explored using electric resistivity methods. Countries surrounding the EARV, such as Burundi, Djibouti, the DR Congo, Eritrea, Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Tanzania, Uganda, and Zambia, share similar geological features linked to the rift system. Groundwater investigation in these regions, particularly using geo-electric resistivity methods, is essential for understanding subsurface geology, potential aquifers, and structural features, additionally, water quality, and dominant water sources of these countries are reviewed to categorize twelve countries based on the availability of the groundwater investigations and country status. The review results highlight some countries rely on weathered and fractured basement aquifers concentrated in specific areas, while others utilize aquifers associated with various geological settings and surface water as alternative sources due to the limited yield from basement complex aquifers. Therefore, 12 countries were classified broadly into three types, and a resistivity distribution map was created to visually show the present status of research and development works of the existence of gaps and limitations, which is generally in line with this comprehensive review. The outcomes of this study are useful for future research and sustainable development by informing the resistivity distribution trend and water resource usage in each country, as a result, expecting to contribute to the effective utilization of groundwater resources in the challenging crystalline basement and volcanic rock environments of the region.
{"title":"Groundwater resources investigation using geophysical method in crystalline basement and volcanic rock regions of countries belonging to the East African Rift Valley: A review","authors":"","doi":"10.1016/j.jafrearsci.2024.105432","DOIUrl":"10.1016/j.jafrearsci.2024.105432","url":null,"abstract":"<div><div>The East African Rift Valley (EARV) is characterized by diverse geology, including crystalline, volcanic, and metamorphic rocks, shaped by tectonic activity leading to complex faulting and fractured zones. These fractured zones in hard rock serve as crucial groundwater reservoirs, often explored using electric resistivity methods. Countries surrounding the EARV, such as Burundi, Djibouti, the DR Congo, Eritrea, Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Tanzania, Uganda, and Zambia, share similar geological features linked to the rift system. Groundwater investigation in these regions, particularly using geo-electric resistivity methods, is essential for understanding subsurface geology, potential aquifers, and structural features, additionally, water quality, and dominant water sources of these countries are reviewed to categorize twelve countries based on the availability of the groundwater investigations and country status. The review results highlight some countries rely on weathered and fractured basement aquifers concentrated in specific areas, while others utilize aquifers associated with various geological settings and surface water as alternative sources due to the limited yield from basement complex aquifers. Therefore, 12 countries were classified broadly into three types, and a resistivity distribution map was created to visually show the present status of research and development works of the existence of gaps and limitations, which is generally in line with this comprehensive review. The outcomes of this study are useful for future research and sustainable development by informing the resistivity distribution trend and water resource usage in each country, as a result, expecting to contribute to the effective utilization of groundwater resources in the challenging crystalline basement and volcanic rock environments of the region.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357222","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}
Pub Date : 2024-09-19DOI: 10.1016/j.jafrearsci.2024.105431
Urban flood risk mapping has become crucial for effective mitigation and urban planning. This study assesses and maps flood risk in the city of Zaio, Morocco, using machine learning and Multi-Criteria Decision Analysis (MCDA) techniques to overcome data scarcity challenges. We employed the Random Forest (RF) model with nine flood conditioning factors for flood hazard and the Analytical Hierarchy Process (AHP) for vulnerability assessment. To enhance RF model performance, we compared three hyperparameter tuning techniques: Bayesian Optimization (RF-BO), Genetic Algorithm (RF-GA), and Grid Search (RF-GS). RF-BO demonstrated superior accuracy in flood hazard modelling. Flood vulnerability was assessed using AHP, incorporating social and physical factors. The final flood risk map was produced by combining the RF-BO hazard model with the AHP vulnerability assessment. Results indicate that flood hazard in Zaio is significantly affected by factors such as topography and distance to rivers. Moreover, areas with high population density closer to rivers, especially in the south-western residential area, were found to be more exposed to flood risk. The findings highlight the utility of ML models, MCDA, and hyperparameter optimization in urban flood risk mapping, enabling the identification of high-risk urban areas that should be prioritized for flood protection efforts. This approach proves especially valuable in ungauged regions with limited hydrological data.
{"title":"Flood risk decomposed: Optimized machine learning hazard mapping and multi-criteria vulnerability analysis in the city of Zaio, Morocco","authors":"","doi":"10.1016/j.jafrearsci.2024.105431","DOIUrl":"10.1016/j.jafrearsci.2024.105431","url":null,"abstract":"<div><div>Urban flood risk mapping has become crucial for effective mitigation and urban planning. This study assesses and maps flood risk in the city of Zaio, Morocco, using machine learning and Multi-Criteria Decision Analysis (MCDA) techniques to overcome data scarcity challenges. We employed the Random Forest (RF) model with nine flood conditioning factors for flood hazard and the Analytical Hierarchy Process (AHP) for vulnerability assessment. To enhance RF model performance, we compared three hyperparameter tuning techniques: Bayesian Optimization (RF-BO), Genetic Algorithm (RF-GA), and Grid Search (RF-GS). RF-BO demonstrated superior accuracy in flood hazard modelling. Flood vulnerability was assessed using AHP, incorporating social and physical factors. The final flood risk map was produced by combining the RF-BO hazard model with the AHP vulnerability assessment. Results indicate that flood hazard in Zaio is significantly affected by factors such as topography and distance to rivers. Moreover, areas with high population density closer to rivers, especially in the south-western residential area, were found to be more exposed to flood risk. The findings highlight the utility of ML models, MCDA, and hyperparameter optimization in urban flood risk mapping, enabling the identification of high-risk urban areas that should be prioritized for flood protection efforts. This approach proves especially valuable in ungauged regions with limited hydrological data.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357243","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}
Pub Date : 2024-09-11DOI: 10.1016/j.jafrearsci.2024.105423
The East African Rift System (EARS) is a prime example of continental rifting, characterized by its iconic topographic features, which are significantly shaped by the interplay of tectonic and climatic forces. This review synthesizes past decades of morphotectonic studies (recent studies) on the plateau landscapes of the EARS, focusing particularly on their interiors and margins, and highlights their crucial role in advancing our understanding of landscape evolution. The paper revisits the legacy of geologic research in the EARS and delves into recent morphotectonic studies that quantify the rates and patterns of plateau incision, exhumation, and uplift through advanced thermochronological and topographic analyses. Additionally, the review identifies key unresolved questions, such as the origins of the plateau topography–whether from volcanic activity or mantle plume influence and explores how these plateaus maintained high elevations during the humid Oligocene Epoch without significant incision. The recent work described in this paper alongside legacy perspectives, continues to refine our geological understanding of the EARS, with broader implications for studies worldwide.
{"title":"Review of morphotectonic studies in the East African Rift System: Insights from legacy research to modern advances","authors":"","doi":"10.1016/j.jafrearsci.2024.105423","DOIUrl":"10.1016/j.jafrearsci.2024.105423","url":null,"abstract":"<div><div>The East African Rift System (EARS) is a prime example of continental rifting, characterized by its iconic topographic features, which are significantly shaped by the interplay of tectonic and climatic forces. This review synthesizes past decades of morphotectonic studies (recent studies) on the plateau landscapes of the EARS, focusing particularly on their interiors and margins, and highlights their crucial role in advancing our understanding of landscape evolution. The paper revisits the legacy of geologic research in the EARS and delves into recent morphotectonic studies that quantify the rates and patterns of plateau incision, exhumation, and uplift through advanced thermochronological and topographic analyses. Additionally, the review identifies key unresolved questions, such as the origins of the plateau topography–whether from volcanic activity or mantle plume influence and explores how these plateaus maintained high elevations during the humid Oligocene Epoch without significant incision. The recent work described in this paper alongside legacy perspectives, continues to refine our geological understanding of the EARS, with broader implications for studies worldwide.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142327032","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}
Pub Date : 2024-09-07DOI: 10.1016/j.jafrearsci.2024.105415
An exceptional hypertrophic batoid rostrum of exceptional size (TL = 146 cm) and four fragmentary rostral teeth collected from the marine Maastrichtian of the Dakhla Formation, Egypt. Both the macroscopic aspects (with the presence of a "wood-like" layer that covers the central part of the rostrum and the presence of skin denticles at the bases of the ventral face) and microscopic characters (presence of tessellated cartilage in the central part of the rostrum and of laminated cartilage in the peripheral areas of it) demonstrate that the rostrum belongs to a large specimen of the genus Onchopristis Stromer, 1917. The absence of complete rostral teeth prevents the establishment of a new species. Nonetheless, the described finds demonstrate, for the first time, that the genus Onchopristis persisted in the euryhaline areas of North Africa until the end of the Cretaceous.
{"title":"The first described Onchopristis Stromer, 1917, (Elasmobranchii: †Onchopristidae) from the marine Maastrichtian of Dakhla Formation, Western Desert, Egypt","authors":"","doi":"10.1016/j.jafrearsci.2024.105415","DOIUrl":"10.1016/j.jafrearsci.2024.105415","url":null,"abstract":"<div><p>An exceptional hypertrophic batoid rostrum of exceptional size (TL = 146 cm) and four fragmentary rostral teeth collected from the marine Maastrichtian of the Dakhla Formation, Egypt. Both the macroscopic aspects (with the presence of a \"wood-like\" layer that covers the central part of the rostrum and the presence of skin denticles at the bases of the ventral face) and microscopic characters (presence of tessellated cartilage in the central part of the rostrum and of laminated cartilage in the peripheral areas of it) demonstrate that the rostrum belongs to a large specimen of the genus <em>Onchopristis</em> Stromer, 1917. The absence of complete rostral teeth prevents the establishment of a new species. Nonetheless, the described finds demonstrate, for the first time, that the genus <em>Onchopristis</em> persisted in the euryhaline areas of North Africa until the end of the Cretaceous.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142241756","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}
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