Pub Date : 2024-08-23DOI: 10.1016/j.jafrearsci.2024.105401
The upper Cretaceous clastic facies of the Bahariya Formation host the main reservoir intervals in the north Western Desert (NWD) of Egypt. These clastics were deposited in a parallic depositional environment characterized by different scales of reservoir heterogeneities. However, the link between these heterogeneities and the depositional setting of the reservoir facies is still blurred. In this study, we investigate a highly-heterogeneous reservoir facies of Bahariya Formation in Yasser Field wells, NWD in order to construct a predictive framework for the distribution of the best reservoir rock types (RRTs) and flow zones. Seismic stratigraphy was integrated with core sedimentology to understand the depositional architecture of the reservoir facies. Moreover, conventional core analysis and wireline logs were interpreted to evaluate the scales of lithological and petrophysical heterogeneities in the different RRTs.
In the studied Yasser Field, the Bahariya Formation consists of tidal facies deposited in a wide range of tidally-influenced conditions. The seismic facies varies greatly with variation in the tidal regime. Best reservoir rock types RRTs are associated with tidal channels and amalgamated tidal bars (RRTI). RRTI rocks represent the main fluid flow conduits in the studied Bahariya reservoir. Lithological and petrophysical heterogeneities are more prominent in the tidal mud flat and mixed tidal flat facies which form RRTIII rocks. Linking seismic with sedimentary facies enabled us to predict the distribution of the best reservoir flow zones in the study region. The present results establish a framework for predicting the optimum reservoir quality facies based on integrating seismic, sedimentary and petrofacies. This framework could be applied in analogous tidally-influenced reservoir facies with high depositionally-controlled pore system heterogeneity.
{"title":"Linking petrophysical heterogeneity and reservoir rock-typing of the post-rift shallow marine siliciclastics to their depositional setting: The Upper Cretaceous Bahariya reservoirs, north Western Desert, Egypt","authors":"","doi":"10.1016/j.jafrearsci.2024.105401","DOIUrl":"10.1016/j.jafrearsci.2024.105401","url":null,"abstract":"<div><p>The upper Cretaceous clastic facies of the Bahariya Formation host the main reservoir intervals in the north Western Desert (NWD) of Egypt. These clastics were deposited in a parallic depositional environment characterized by different scales of reservoir heterogeneities. However, the link between these heterogeneities and the depositional setting of the reservoir facies is still blurred. In this study, we investigate a highly-heterogeneous reservoir facies of Bahariya Formation in Yasser Field wells, NWD in order to construct a predictive framework for the distribution of the best reservoir rock types (RRTs) and flow zones. Seismic stratigraphy was integrated with core sedimentology to understand the depositional architecture of the reservoir facies. Moreover, conventional core analysis and wireline logs were interpreted to evaluate the scales of lithological and petrophysical heterogeneities in the different RRTs.</p><p>In the studied Yasser Field, the Bahariya Formation consists of tidal facies deposited in a wide range of tidally-influenced conditions. The seismic facies varies greatly with variation in the tidal regime. Best reservoir rock types RRTs are associated with tidal channels and amalgamated tidal bars (RRTI). RRTI rocks represent the main fluid flow conduits in the studied Bahariya reservoir. Lithological and petrophysical heterogeneities are more prominent in the tidal mud flat and mixed tidal flat facies which form RRTIII rocks. Linking seismic with sedimentary facies enabled us to predict the distribution of the best reservoir flow zones in the study region. The present results establish a framework for predicting the optimum reservoir quality facies based on integrating seismic, sedimentary and petrofacies. This framework could be applied in analogous tidally-influenced reservoir facies with high depositionally-controlled pore system heterogeneity.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142076781","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 : 2024-08-22DOI: 10.1016/j.jafrearsci.2024.105387
Along northern-central Egypt, the oil accumulation and entrapment were mainly controlled by variable parameters including the stratigraphic architecture, sedimentary features, and tectonic evolutions. The present paper presents a new model for oil occurrences in the Abu Roash G Member (Cenomanian) along Gindi, Abu Gharadig and to a few extents the Beni Suef basins, in the northern-central part of the Western and Eastern Deserts of Egypt. The studied concessions include the Wadi El Rayan, East Bahariya and El Diyur (Gindi basin and Abu Gharadig basins, Western Desert) and the Ghariboun (Beni Suef Basin, Eastern Desert) fields. Twenty sedimentary facies were recorded from the studied subsurface sections of the Abu Roash G Member and grouped into three facies associations. A new depositional model is achieved where estuarine, open marine, deltaic distributaries, and tidal channel deposits are the main facies associations recorded in the studied Abu Roash “G". These deltaic and channel deposits occurred as an arch like form between open marine and estuarine deposits. These deltaic and tidal channel sandstone deposits act as a good reservoir to accumulate oil from nearby areas. As well, these areas were subjected to the well-known Syrian arch compressional deformation that affected northern Egypt during the Mesozoic, up to late Senonian time. A regional NE-SW oriented fold system took place, forming NE-SW oriented ridges in addition to the dextral strike-slip movement that took place along these ridges because of this compressional deformation.
To sum up, oil accumulation in the studied Abu Roash G Member was mainly controlled by facies distribution mainly of channel sandstone enhanced by the tectonic movements (Syrian Arc System) affecting the areas studied.
在埃及中北部地区,石油的积累和封存主要受地层结构、沉积特征和构造演化等可变参数的控制。本文提出了埃及西部和东部沙漠中北部金迪、阿布-加拉迪格以及贝尼苏埃夫盆地少数地区阿布-罗阿什 G 组(仙人掌纪)石油分布的新模型。所研究的特许矿区包括 Wadi El Rayan、East Bahariya 和 El Diyur(金迪盆地和阿布加拉迪格盆地,西部沙漠)以及 Ghariboun(贝尼苏伊夫盆地,东部沙漠)油田。在研究的阿布-罗阿什 G 组地下断面中记录了 20 个沉积面,并将其分为三个面系。在研究的阿布鲁阿什 "G "岩层中,河口沉积、开阔海相沉积、三角洲分布沉积和潮汐河道沉积是主要的沉积面组合。这些三角洲和河道沉积以拱形形式出现在开阔海域和河口沉积之间。这些三角洲和潮汐通道砂岩沉积是一个很好的储油层,可以积聚来自附近地区的石油。此外,这些地区在中生代一直到晚元古代都受到了著名的叙利亚拱形压缩变形的影响。总之,所研究的 Abu Roash G 组的石油储量主要受控于主要为槽沟砂岩的岩相分布,而影响所研究地区的构造运动(叙利亚拱系统)又增强了这种岩相分布。
{"title":"Facies controls and tectonic evolution on oil accumulation and entrapment in the Cenomanian Abu Roash G member, northern-central Egypt: Deltaic and channel sandstones as good reservoirs","authors":"","doi":"10.1016/j.jafrearsci.2024.105387","DOIUrl":"10.1016/j.jafrearsci.2024.105387","url":null,"abstract":"<div><p>Along northern-central Egypt, the oil accumulation and entrapment were mainly controlled by variable parameters including the stratigraphic architecture, sedimentary features, and tectonic evolutions. The present paper presents a new model for oil occurrences in the Abu Roash G Member (Cenomanian) along Gindi, Abu Gharadig and to a few extents the Beni Suef basins, in the northern-central part of the Western and Eastern Deserts of Egypt. The studied concessions include the Wadi El Rayan, East Bahariya and El Diyur (Gindi basin and Abu Gharadig basins, Western Desert) and the Ghariboun (Beni Suef Basin, Eastern Desert) fields. Twenty sedimentary facies were recorded from the studied subsurface sections of the Abu Roash G Member and grouped into three facies associations. A new depositional model is achieved where estuarine, open marine, deltaic distributaries, and tidal channel deposits are the main facies associations recorded in the studied Abu Roash “G\". These deltaic and channel deposits occurred as an arch like form between open marine and estuarine deposits. These deltaic and tidal channel sandstone deposits act as a good reservoir to accumulate oil from nearby areas. As well, these areas were subjected to the well-known Syrian arch compressional deformation that affected northern Egypt during the Mesozoic, up to late Senonian time. A regional NE-SW oriented fold system took place, forming NE-SW oriented ridges in addition to the dextral strike-slip movement that took place along these ridges because of this compressional deformation.</p><p>To sum up, oil accumulation in the studied Abu Roash G Member was mainly controlled by facies distribution mainly of channel sandstone enhanced by the tectonic movements (Syrian Arc System) affecting the areas studied.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142098877","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 : 2024-08-22DOI: 10.1016/j.jafrearsci.2024.105400
The study investigates the palynofacies, organic matter character, and hydrocarbon generation potential of this rock unit, based on surface and subsurface samples from the Ora Formation type-section in extreme northern Iraq and the Akkas-3 well in western Iraq, respectively. Dark, mostly oxidized, gelified platy amorphous organic matter (AOM) dominates the palynological components in the surface section, in addition to a few rounded spores and structured phytoclasts. In contrast, palynomorphs, including Ambitisporites avitus, Aneurospora spp., Vallatisporites verrucosus, Acinosporites spp., Verrucosisporites nitidus and the algae Botryococcus, are predominant in studied samples from the Akkas-3 well. Statistical cluster analysis identified three palynofacies types in the surface section based on stratigraphic variations in the particulate organic matter. These vary from high amorphous organic matter (AOM), moderate phytoclast, and low palynomorph abundances that represent proximal suboxic–anoxic shelfal environments to moderate to good AOM and low to moderate palynomorph abundances that represent distal suboxic–anoxic or distal dysoxic–anoxic shelfal environments. The organic petrographic study of the outcrop section also revealed the strong effect of oxidation, where dispersed terrigenous and amorphous organic materials in the form of granular and gelified forms dominate and reflect a terrestrial origin of these components. In the subsurface section, a mixed terrestrial and less marine or lacustrine origin characterized the studied organic matter, where land plant spores (sporinite), in addition to vitrinite and inertinite, are dominant with a few scattered liptinite macerals. The difference in thermal maturity between the outcrop and subsurface samples is likely due to the higher tectonic burial of the outcrop samples that form part of the Northern Thrust Zone of Iraq. Nevertheless, higher abundances of AOM (oil-prone kerogen type II) accumulated in the northern outcrop type section. This might imply that the Ora Formation has a higher potential for hydrocarbon production north of the Akkas field.
{"title":"Depositional environments and thermal maturity of the hydrocarbon source rocks in the Devonian–Early carboniferous Ora Formation from palynological organic petrographic investigations in northern and western Iraq","authors":"","doi":"10.1016/j.jafrearsci.2024.105400","DOIUrl":"10.1016/j.jafrearsci.2024.105400","url":null,"abstract":"<div><p>The study investigates the palynofacies, organic matter character, and hydrocarbon generation potential of this rock unit, based on surface and subsurface samples from the Ora Formation type-section in extreme northern Iraq and the Akkas-3 well in western Iraq, respectively. Dark, mostly oxidized, gelified platy amorphous organic matter (AOM) dominates the palynological components in the surface section, in addition to a few rounded spores and structured phytoclasts. In contrast, palynomorphs, including <em>Ambitisporites avitus</em>, <em>Aneurospora</em> spp., <em>Vallatisporites verrucosus</em>, <em>Acinosporites</em> spp., <em>Verrucosisporites nitidus</em> and the algae <em>Botryococcus,</em> are predominant in studied samples from the Akkas-3 well. Statistical cluster analysis identified three palynofacies types in the surface section based on stratigraphic variations in the particulate organic matter. These vary from high amorphous organic matter (AOM), moderate phytoclast, and low palynomorph abundances that represent proximal suboxic–anoxic shelfal environments to moderate to good AOM and low to moderate palynomorph abundances that represent distal suboxic–anoxic or distal dysoxic–anoxic shelfal environments. The organic petrographic study of the outcrop section also revealed the strong effect of oxidation, where dispersed terrigenous and amorphous organic materials in the form of granular and gelified forms dominate and reflect a terrestrial origin of these components. In the subsurface section, a mixed terrestrial and less marine or lacustrine origin characterized the studied organic matter, where land plant spores (sporinite), in addition to vitrinite and inertinite, are dominant with a few scattered liptinite macerals. The difference in thermal maturity between the outcrop and subsurface samples is likely due to the higher tectonic burial of the outcrop samples that form part of the Northern Thrust Zone of Iraq. Nevertheless, higher abundances of AOM (oil-prone kerogen type II) accumulated in the northern outcrop type section. This might imply that the Ora Formation has a higher potential for hydrocarbon production north of the Akkas field.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142048279","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 : 2024-08-22DOI: 10.1016/j.jafrearsci.2024.105399
The Anambra Basin in southwestern Nigeria is part of the West and Central Africa Rift System (WCARS), with sedimentary successions comprising freshwater, deltaic, and marginal marine deposits. In the present study, we provide new mineralogical and geochemical data from mudrocks of the Campano-Maastrichtian Nkporo and Mamu formations and the Paleocene Imo Formation, intersected by the Owan-1 and Ubiaja wells. The analyses aim to identify source composition, sedimentary grain sorting, hydrothermal influence, and depositional environment, focusing on the understudied southwestern margin of the basin. Additionally, the data provide insights into the tectonic evolution of the Anambra Basin and its genetic link to the Benue Trough and other WCARS basins. The studied mudrocks contain detrital grains predominantly composed of quartz and clay minerals, with little feldspar. Major and trace element proxies used to evaluate sediment grain sorting reveal primarily fine-grained clastics, indicating long transport distances that correlate with the high clay mineral contents. The few coarse-grained deposits suggest periods of direct sediment input into the basin and less recycling. There is no evidence of hydrothermal influence in the basin. Therefore, a significant pelagic influence is proposed for the analysed sequence. This hypothesis is corroborated by the presence of gypsum, which is typically precipitated from seawater. Based on provenance-sensitive inorganic geochemical proxies (i.e., Cr/Th vs. Sc/Th, La/Th vs. Hf, Th/Co vs. La/Sc, Th/Sc vs. La/Sc, Th/U vs. Th/Sc, TiO2vs. Zr) and the identified detrital contributions to the Paleocene Imo Formation and Cretaceous Mamu and Nkporo formations, the studied siliciclastic rocks are interpreted to be derived primarily from proximal felsic plutonic rocks that were uplifted to the surface by tectonic processes. Distinction diagrams from discriminant functions show that the sediments of the Anambra Basin were deposited in a rift setting, which is consistent with the other WCARS basins.
{"title":"Geochemistry of the Late Cretaceous to Paleogene sedimentary deposits of the SW Anambra Basin (Nigeria): Implications for provenance, tectonic conditions, and hydrothermal influence","authors":"","doi":"10.1016/j.jafrearsci.2024.105399","DOIUrl":"10.1016/j.jafrearsci.2024.105399","url":null,"abstract":"<div><p>The Anambra Basin in southwestern Nigeria is part of the West and Central Africa Rift System (WCARS), with sedimentary successions comprising freshwater, deltaic, and marginal marine deposits. In the present study, we provide new mineralogical and geochemical data from mudrocks of the Campano-Maastrichtian Nkporo and Mamu formations and the Paleocene Imo Formation, intersected by the Owan-1 and Ubiaja wells. The analyses aim to identify source composition, sedimentary grain sorting, hydrothermal influence, and depositional environment, focusing on the understudied southwestern margin of the basin. Additionally, the data provide insights into the tectonic evolution of the Anambra Basin and its genetic link to the Benue Trough and other WCARS basins. The studied mudrocks contain detrital grains predominantly composed of quartz and clay minerals, with little feldspar. Major and trace element proxies used to evaluate sediment grain sorting reveal primarily fine-grained clastics, indicating long transport distances that correlate with the high clay mineral contents. The few coarse-grained deposits suggest periods of direct sediment input into the basin and less recycling. There is no evidence of hydrothermal influence in the basin. Therefore, a significant pelagic influence is proposed for the analysed sequence. This hypothesis is corroborated by the presence of gypsum, which is typically precipitated from seawater. Based on provenance-sensitive inorganic geochemical proxies (i.e., Cr/Th <em>vs.</em> Sc/Th, La/Th <em>vs.</em> Hf, Th/Co <em>vs.</em> La/Sc, Th/Sc <em>vs.</em> La/Sc, Th/U <em>vs.</em> Th/Sc, TiO<sub>2</sub> <em>vs.</em> Zr) and the identified detrital contributions to the Paleocene Imo Formation and Cretaceous Mamu and Nkporo formations, the studied siliciclastic rocks are interpreted to be derived primarily from proximal felsic plutonic rocks that were uplifted to the surface by tectonic processes. Distinction diagrams from discriminant functions show that the sediments of the Anambra Basin were deposited in a rift setting, which is consistent with the other WCARS basins.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142088622","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 : 2024-08-22DOI: 10.1016/j.jafrearsci.2024.105390
The East African Rift System (EARS) is an active continental rift zone that hosts a diverse range of processes that result in recent and ongoing crustal deformation. To analyze these processes, we used Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) to complement the sparse GNSS velocity field with high resolution measurements of line-of-sight (LOS) deformation between 2015 and 2022. A broad survey approach was employed to detect new signals within the central section of the EARS, and to establish a baseline for future studies focused on tectonic, volcanic, and/or hydrologic deformation and change spanning geodetic time scales. With this regional approach, we were able to resolve signals varying over time-spans of a few weeks to several years that have magnitudes greater than ∼1 cm/yr. Our resulting deformation field shows a diverse range of signals related to the processes listed above as well as other unknown sources. This includes up to 8.5 cm/yr of groundwater-related subsidence in Nairobi, up to 70 cm of LOS displacement during the eruption of Nyiragongo in 2021, and steady uplift in the Manyara basin with a rate of 2.8 cm/yr. We update previously published InSAR measurements of Mount Suswa volcano, and the geothermal fields in Olkaria. We also show LOS change ranging between 2 and 5 mm/yr over a distances of approximately 200 km spanning the Kenya Rift with the greatest differential rates occurring south of Lake Turkana. More generally, our results highlight the ambiguity of relying solely on the sparse network of GNSS for studies such as those characterizing tectonic motion and rift opening. Such studies are likely missing many important signals and/or includes sites that are contaminated with signals unrelated to the target process.
{"title":"Active deformation in the central section of the East African Rift from tectonic, volcanic, and hydrologic processes: Observations from satellite geodesy","authors":"","doi":"10.1016/j.jafrearsci.2024.105390","DOIUrl":"10.1016/j.jafrearsci.2024.105390","url":null,"abstract":"<div><p>The East African Rift System (EARS) is an active continental rift zone that hosts a diverse range of processes that result in recent and ongoing crustal deformation. To analyze these processes, we used Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) to complement the sparse GNSS velocity field with high resolution measurements of line-of-sight (LOS) deformation between 2015 and 2022. A broad survey approach was employed to detect new signals within the central section of the EARS, and to establish a baseline for future studies focused on tectonic, volcanic, and/or hydrologic deformation and change spanning geodetic time scales. With this regional approach, we were able to resolve signals varying over time-spans of a few weeks to several years that have magnitudes greater than ∼1 cm/yr. Our resulting deformation field shows a diverse range of signals related to the processes listed above as well as other unknown sources. This includes up to 8.5 cm/yr of groundwater-related subsidence in Nairobi, up to 70 cm of LOS displacement during the eruption of Nyiragongo in 2021, and steady uplift in the Manyara basin with a rate of 2.8 cm/yr. We update previously published InSAR measurements of Mount Suswa volcano, and the geothermal fields in Olkaria. We also show LOS change ranging between 2 and 5 mm/yr over a distances of approximately 200 km spanning the Kenya Rift with the greatest differential rates occurring south of Lake Turkana. More generally, our results highlight the ambiguity of relying solely on the sparse network of GNSS for studies such as those characterizing tectonic motion and rift opening. Such studies are likely missing many important signals and/or includes sites that are contaminated with signals unrelated to the target process.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142048282","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 : 2024-08-22DOI: 10.1016/j.jafrearsci.2024.105389
In the ensemble of theropod footprints from the Imilchil macrosite, a group of small size separated from the rest is distinguished. We had detected this grouping in other sites studied by our team in La Rioja and in the work of drawing up scatter plots and frequency histograms of the measurements, on a global scale, of the length and width of the theropod footprints (these data are available on request from Farlow [[email protected]]). We analyze the particular grouping of small footprints, providing the study of the theropod footprint measurements of 14 new sites with dinosaur footprints in Imilchil and the graphical representation (frequency histograms and scatter plots) of the global data. The work has been done by projecting and comparing the length and width measurements of the Imilchil footprints and the global ones of what we call circumscribed geographical environments (TGC or Temporal Geographical Circumscriptions [cf. Mínguez Ceniceros et al., 2022]). The ichnotaxonomic study of the footprints referred to in this work can be found in Masrour et al., (2023). Finally we interpret the position of maxima and minima in the frequency diagrams, both of Imilchil, and of the other areas in which Farlow has found records (up to the year 2022).
{"title":"Analysis of very small-small theropod footprints data from Imilchil tracksite (Hig Central Atlas. Morocco). A concordance model for a global scale","authors":"","doi":"10.1016/j.jafrearsci.2024.105389","DOIUrl":"10.1016/j.jafrearsci.2024.105389","url":null,"abstract":"<div><p>In the ensemble of theropod footprints from the Imilchil macrosite, a group of small size separated from the rest is distinguished. We had detected this grouping in other sites studied by our team in La Rioja and in the work of drawing up scatter plots and frequency histograms of the measurements, on a global scale, of the length and width of the theropod footprints (these data are available on request from Farlow [<span><span><span>[email protected]</span></span><svg><path></path></svg></span>]). We analyze the particular grouping of small footprints, providing the study of the theropod footprint measurements of 14 new sites with dinosaur footprints in Imilchil and the graphical representation (frequency histograms and scatter plots) of the global data. The work has been done by projecting and comparing the length and width measurements of the Imilchil footprints and the global ones of what we call circumscribed geographical environments (TGC or Temporal Geographical Circumscriptions [cf. Mínguez Ceniceros et al., 2022]). The ichnotaxonomic study of the footprints referred to in this work can be found in Masrour et al., (2023). Finally we interpret the position of maxima and minima in the frequency diagrams, both of Imilchil, and of the other areas in which Farlow has found records (up to the year 2022).</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S1464343X2400222X/pdfft?md5=ed43afa4cc9c53490e24a906fb4f8bf8&pid=1-s2.0-S1464343X2400222X-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142084109","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 : 2024-08-20DOI: 10.1016/j.jafrearsci.2024.105369
Geological mapping of the Mayombe Chain and Niari Basin of Congo Brazzaville allows for the first time defining the structural architecture and metamorphism of the West Congo Belt. Four different tectono-metamorphic domains, separated by crustal-scale shear zones, are now distinguished (Niari Basin (NB), Eastern (EMC), Central (CMC) and Western (WMC) Mayombe Chain).
The NB is marked by only weak regional deformation under middle to upper diagenetic conditions. It is delimited in the west from the EMC by the Mount Belo Shear Zone forming the terminal thrust system of the West Congo orogen.
The tectonic style in the EMC is characterized by discrete, widely-spaced low-angle thrusts, reverse faults and strike-slip faults resulting in the formation of duplex and/or positive flower structures. Off these high-strain zones, the rocks are folded into gentle syn- and anticlines. Penetrative schistosity starts in shales in the western part. The metamorphism increases from eastern anchizonal conditions to lower greenschist facies in the west. The EMC is juxtaposed along the Moukondo thrust/back-thrust system with the CMC.
The CMC is typified by open to closed upright to NE-verging folds, S1 schistosity with moderate to steep SW dips, onset of regional crenulation cleavage (S2), frequent reverse thrusts and numerous faults. Metamorphic conditions remain in the greenschist facies. The Loukenéné-Mandji Thrust marks the CMC-WMC contact and coincides with a jump in metamorphic grade marked by biotite-in.
The WMC consists of Palaeoproterozoic basement stacked with Neoproterozoic rocks. Autochthonous Palaeoproterozoic gneiss and schist record Late Eburnean sedimentation, magmatism and metamorphism between 2110 and 1970 Ma, which are compared with the Eburnean history in Gabon and the Transamazonian orogeny in Brazil. The allochthonous Bikossi Group was thrust during the Pan-African event from the west over Tonian metavolcaniclastic and plutonic rocks before further folding and stacking of both units. The intensity of Pan-African deformation increases from open to closed folds with spaced cleavage in the southeast of the WMC to thrust-dominated tectonics in the northwest, where the Palaeo- and Neoproterozoic rocks are transposed into parallelism with the pronounced schistosity.
Geochronology of illite and muscovite documents two Pan-African events at 590-570 Ma (M1) and at 520-500 Ma (M2) that are related to the main collisional and late thermal events in the Araçuai-Ribeira Belt in Brazil. Metamorphic isogrades shifted from M1 to M2 for more than 30 km to the west. Detrital mica and metamorphic illite of the Mpioka Group record M1 and M2, respectively constraining sedimentary deposition between 570 and 520 Ma, which implies the interpretation of the group as molasse of the West Congo Belt.
{"title":"Structural architecture and metamorphism of the Mayombe Chain and Niari Basin (West Congo Belt) in Congo Brazzaville","authors":"","doi":"10.1016/j.jafrearsci.2024.105369","DOIUrl":"10.1016/j.jafrearsci.2024.105369","url":null,"abstract":"<div><div>Geological mapping of the Mayombe Chain and Niari Basin of Congo Brazzaville allows for the first time defining the structural architecture and metamorphism of the West Congo Belt. Four different tectono-metamorphic domains, separated by crustal-scale shear zones, are now distinguished (Niari Basin (NB), Eastern (EMC), Central (CMC) and Western (WMC) Mayombe Chain).</div><div>The NB is marked by only weak regional deformation under middle to upper diagenetic conditions. It is delimited in the west from the EMC by the Mount Belo Shear Zone forming the terminal thrust system of the West Congo orogen.</div><div>The tectonic style in the EMC is characterized by discrete, widely-spaced low-angle thrusts, reverse faults and strike-slip faults resulting in the formation of duplex and/or positive flower structures. Off these high-strain zones, the rocks are folded into gentle syn- and anticlines. Penetrative schistosity starts in shales in the western part. The metamorphism increases from eastern anchizonal conditions to lower greenschist facies in the west. The EMC is juxtaposed along the Moukondo thrust/back-thrust system with the CMC.</div><div>The CMC is typified by open to closed upright to NE-verging folds, S<sub>1</sub> schistosity with moderate to steep SW dips, onset of regional crenulation cleavage (S<sub>2</sub>), frequent reverse thrusts and numerous faults. Metamorphic conditions remain in the greenschist facies. The Loukenéné-Mandji Thrust marks the CMC-WMC contact and coincides with a jump in metamorphic grade marked by biotite-in.</div><div>The WMC consists of Palaeoproterozoic basement stacked with Neoproterozoic rocks. Autochthonous Palaeoproterozoic gneiss and schist record Late Eburnean sedimentation, magmatism and metamorphism between 2110 and 1970 Ma, which are compared with the Eburnean history in Gabon and the Transamazonian orogeny in Brazil. The allochthonous Bikossi Group was thrust during the Pan-African event from the west over Tonian metavolcaniclastic and plutonic rocks before further folding and stacking of both units. The intensity of Pan-African deformation increases from open to closed folds with spaced cleavage in the southeast of the WMC to thrust-dominated tectonics in the northwest, where the Palaeo- and Neoproterozoic rocks are transposed into parallelism with the pronounced schistosity.</div><div>Geochronology of illite and muscovite documents two Pan-African events at 590-570 Ma (M1) and at 520-500 Ma (M2) that are related to the main collisional and late thermal events in the Araçuai-Ribeira Belt in Brazil. Metamorphic isogrades shifted from M1 to M2 for more than 30 km to the west. Detrital mica and metamorphic illite of the Mpioka Group record M1 and M2, respectively constraining sedimentary deposition between 570 and 520 Ma, which implies the interpretation of the group as molasse of the West Congo Belt.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142318670","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 : 2024-08-18DOI: 10.1016/j.jafrearsci.2024.105388
Late Neoproterozoic mantle section in the Gabal Al-Barramiya area, the northwestern corner of the Arabian-Nubian Shield (ANS), contains variably serpentinized peridotites that are highly altered along shear zones and thrust planes to form gold-bearing listvenites. They can be categorized into carbonate listvenite, silica-carbonate listvenite and silica listvenite (birbirite). Carbonate listvenite is characterized by the presence of schistosity and deformation fabrics similar to the host serpentinites, but such fabrics are absent in the silica-carbonate and silica listvenites, suggesting that they postdate carbonate listvenite and serpentinization. The presence of listvenites along shears zones and the presence of relics of serpentine and Cr-spinel reflects their formation through metasomatism of ultramafic rocks by hydrothermal fluids circulating along the thrust faults. Silica-carbonate listvenite is characterized by the presence of fuchsite and is enriched in Zn, Pb, Cu, Ag, and Au. Rare earth element (REE) contents differ between the studied listvenites. Silica -carbonate listvenite has the lowest total REE (∑₌0.98–2.56 ppm), whereas the silica listvenite contains the highest total of REE (∑ ₌ 15.70–21.42 ppm). Based on the above, carbonate listvenite is the earliest to form by the infiltration of CO2–bearing fluids released during serpentinization of the original fore-arc peridotite slab, followed by formation of silica-carbonate listvenite due to the activities of SiO2–saturation and CO2-bearing fluids released during ophiolite obduction. Fuchsite in silica-carbonate listvenite formed as a result of metasomatic reactions of Si- and K-rich fluids with Cr-spinel due to hydrothermal alteration of serpentinized peridotite. Silica listvenite formed at the final stage by the silicification of the early formed silica-carbonate listvenite. Listvenitization of the mantle section of the Al-Barramiya ophiolite led to concentration of Au, Pb, Zn, Cu and Ag. The silica-carbonate listvenite contains higher concentration of gold (899–2199 ppb) than the carbonate listvenite (119–191 ppb) and silica listvenite (156–233 ppb).
{"title":"Carbonatization and silicification of ophiolitic ultramafic rocks and formation of gold-bearing listvenites in the Arabian-Nubian shield: A case study from the Al-Barramiya district","authors":"","doi":"10.1016/j.jafrearsci.2024.105388","DOIUrl":"10.1016/j.jafrearsci.2024.105388","url":null,"abstract":"<div><p>Late Neoproterozoic mantle section in the Gabal Al-Barramiya area, the northwestern corner of the Arabian-Nubian Shield (ANS), contains variably serpentinized peridotites that are highly altered along shear zones and thrust planes to form gold-bearing listvenites. They can be categorized into carbonate listvenite, silica-carbonate listvenite and silica listvenite (birbirite). Carbonate listvenite is characterized by the presence of schistosity and deformation fabrics similar to the host serpentinites, but such fabrics are absent in the silica-carbonate and silica listvenites, suggesting that they postdate carbonate listvenite and serpentinization. The presence of listvenites along shears zones and the presence of relics of serpentine and Cr-spinel reflects their formation through metasomatism of ultramafic rocks by hydrothermal fluids circulating along the thrust faults. Silica-carbonate listvenite is characterized by the presence of fuchsite and is enriched in Zn, Pb, Cu, Ag, and Au. Rare earth element (REE) contents differ between the studied listvenites. Silica -carbonate listvenite has the lowest total REE (∑₌0.98–2.56 ppm), whereas the silica listvenite contains the highest total of REE (∑ ₌ 15.70–21.42 ppm). Based on the above, carbonate listvenite is the earliest to form by the infiltration of CO<sub>2</sub>–bearing fluids released during serpentinization of the original fore-arc peridotite slab, followed by formation of silica-carbonate listvenite due to the activities of SiO<sub>2</sub>–saturation and CO<sub>2</sub>-bearing fluids released during ophiolite obduction. Fuchsite in silica-carbonate listvenite formed as a result of metasomatic reactions of Si- and K-rich fluids with Cr-spinel due to hydrothermal alteration of serpentinized peridotite. Silica listvenite formed at the final stage by the silicification of the early formed silica-carbonate listvenite. Listvenitization of the mantle section of the Al-Barramiya ophiolite led to concentration of Au, Pb, Zn, Cu and Ag. The silica-carbonate listvenite contains higher concentration of gold (899–2199 ppb) than the carbonate listvenite (119–191 ppb) and silica listvenite (156–233 ppb).</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142045043","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 : 2024-08-15DOI: 10.1016/j.jafrearsci.2024.105385
Irrigation plays a vital role in addressing increasing need for food production and promoting economic advancement. To meet the demands for food supply and economic progress, it is essential to underscore the significance of assessing water quality in dry regions. The current study was carried out to evaluate and predict the suitability of water quality for agricultural use in the K'sob valley in the M'sila region (Northeast Algeria). A combination of irrigation water quality indices (IWQIs), Geographic Information System (GIS) analysis and multivariate statistical methods were used for this purpose. Several physicochemical parameters, such as temperature (T°), hydrogen ion concentration (pH), electrical conductivity (EC), total dissolved solids (TDS), turbidity (Turb), chemical oxygen demand (COD), Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3−, NO2−, NH4+, PO4− and SiO22+ were all measured from 40 samples collected at ten surface water locations during four seasons. The concentrations of the main cation and anion were shown as follows: Na+>Ca2+> K+ > Mg2+, and SO42− > HCO3− > Cl− > NO3− indicating mixed Na-Cl-K or Na-SO4 water facies. Significant seasonal variation for each parameter (T, pH, Turbidity, Salinity, COD, NH4+, Cl−, SO4−, and NO2−) was reported (p < 0.05). Additionally, a significant spatial variation (p < 0.05) was observed among different stations for the parameters: TDS, EC, Ca2+, Na+, HCO3−, SO4−, NO3−, and PO43− (p < 0.05). The irrigation water quality index (IWQI), sodium adsorption ratio (SAR), sodium percentage (Na%), Kelly index (KI), and permeability index (PI) had values varying between 28.1 and 56.8, 5.65 and 12.45, 75 and 87, 2.61 and 6.54 and 83, and 97, respectively, and a significant seasonal effect was recorded. According to the Wilcox diagram, 70% of samples were unsuitable for irrigation, while 30% of samples were questionable. The IWQI map revealed that 50% of the samples fell within the very poor category for irrigation, while 20% and 30% of the samples were inside the poor and unsuitable categories, respectively. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) of K'SobValley water revealed three different categories of water based on elemental composition and seasonal variations. The results obtained in this study can be valuable for surface water management. Furthermore, the developed methodology can serve as a useful tool for id
{"title":"Hydrochemical characterization and evaluation of irrigation water quality using indexing approaches, multivariate analysis, and GIS techniques in K'sob Valley, Algeria","authors":"","doi":"10.1016/j.jafrearsci.2024.105385","DOIUrl":"10.1016/j.jafrearsci.2024.105385","url":null,"abstract":"<div><p>Irrigation plays a vital role in addressing increasing need for food production and promoting economic advancement. To meet the demands for food supply and economic progress, it is essential to underscore the significance of assessing water quality in dry regions. The current study was carried out to evaluate and predict the suitability of water quality for agricultural use in the K'sob valley in the M'sila region (Northeast Algeria). A combination of irrigation water quality indices (IWQIs), Geographic Information System (GIS) analysis and multivariate statistical methods were used for this purpose. Several physicochemical parameters, such as temperature (T°), hydrogen ion concentration (pH), electrical conductivity (EC), total dissolved solids (TDS), turbidity (Turb), chemical oxygen demand (COD), Ca<sup>2+</sup>, Mg<sup>2+</sup>, Na<sup>+</sup>, K<sup>+</sup>, HCO<sub>3</sub><sup>−</sup>, Cl<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, NO<sub>3</sub><sup>−</sup>, NO<sub>2</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup>, PO<sub>4</sub><sup>−</sup> and SiO<sub>2</sub><sup>2+</sup> were all measured from 40 samples collected at ten surface water locations during four seasons. The concentrations of the main cation and anion were shown as follows: Na<sup>+</sup>>Ca<sup>2+</sup>> K<sup>+</sup> > Mg<sup>2+</sup>, and SO<sub>4</sub><sup>2−</sup> > HCO<sub>3</sub><sup>−</sup> > Cl<sup>−</sup> > NO<sub>3</sub><sup>−</sup> indicating mixed Na-Cl-K or Na-SO<sub>4</sub> water facies. Significant seasonal variation for each parameter (T, pH, Turbidity, Salinity, COD, NH<sub>4</sub><sup>+</sup>, Cl<sup>−</sup>, SO<sub>4</sub><sup>−</sup>, and NO<sub>2</sub><sup>−</sup>) was reported (p < 0.05). Additionally, a significant spatial variation (p < 0.05) was observed among different stations for the parameters: TDS, EC, Ca<sup>2+</sup>, Na<sup>+</sup>, HCO<sub>3</sub><sup>−</sup>, SO<sub>4</sub><sup>−</sup>, NO<sub>3</sub><sup>−</sup>, and PO<sub>4</sub><sup>3−</sup> (p < 0.05). The irrigation water quality index (IWQI), sodium adsorption ratio (SAR), sodium percentage (Na%), Kelly index (KI), and permeability index (PI) had values varying between 28.1 and 56.8, 5.65 and 12.45, 75 and 87, 2.61 and 6.54 and 83, and 97, respectively, and a significant seasonal effect was recorded. According to the Wilcox diagram, 70% of samples were unsuitable for irrigation, while 30% of samples were questionable. The IWQI map revealed that 50% of the samples fell within the very poor category for irrigation, while 20% and 30% of the samples were inside the poor and unsuitable categories, respectively. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) of K'SobValley water revealed three different categories of water based on elemental composition and seasonal variations. The results obtained in this study can be valuable for surface water management. Furthermore, the developed methodology can serve as a useful tool for id","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142049248","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 : 2024-08-15DOI: 10.1016/j.jafrearsci.2024.105384
The abundances and distribution diamondoids were studied with a series of crude oil samples from Block 4 of the Mugald Basin in Sudan, to investigate the validity of various diamondoid parameters on the oil source, thermal maturity and biodegradation information. All crude oils of Block 4 were generated by lacustrine source in lower part of the Abu Gabra Formation as a whole, and can be further divided into two crude oil groups: oil group of the Neem-Azraq Uplift and oil group of K-3 well and B-1 well. They are all mature oils within oil window and four crude oils from the Neem-Azraq Uplift were slightly biodegraded. The concentrations of diamondoids in oils of K-3 well and B-1 well, especially the concentration of diamantanes, are higher than those of oils from the Neem-Azraq Uplift. The concentrations of diamondoids are mainly controlled by source of oil, while the influence of thermal maturity and biodegradation may be limited. The isomerization ratios as indicators of thermal maturity are inapplicable at the mature stage, but DMDI-2, 4,8/3,4-DMD and 1-EA/3-EA can clearly distinguish the two groups of crude oils. The concentration ratios of oils from K-3 and B-1 wells are significantly lower than these of oils from Neem-Azraq Uplift, and these concentration ratios including newly proposed parameters such as MAs/DMAs, DMAs/TMAs, D/MDs, MDs/DMDs and so on, are effective indicators on organofacies and oil group division within oil window.
{"title":"The application of diamondoids indices for oils from Block 4 of the Muglad Basin in the middle of Africa","authors":"","doi":"10.1016/j.jafrearsci.2024.105384","DOIUrl":"10.1016/j.jafrearsci.2024.105384","url":null,"abstract":"<div><p>The abundances and distribution diamondoids were studied with a series of crude oil samples from Block 4 of the Mugald Basin in Sudan, to investigate the validity of various diamondoid parameters on the oil source, thermal maturity and biodegradation information. All crude oils of Block 4 were generated by lacustrine source in lower part of the Abu Gabra Formation as a whole, and can be further divided into two crude oil groups: oil group of the Neem-Azraq Uplift and oil group of K-3 well and B-1 well. They are all mature oils within oil window and four crude oils from the Neem-Azraq Uplift were slightly biodegraded. The concentrations of diamondoids in oils of K-3 well and B-1 well, especially the concentration of diamantanes, are higher than those of oils from the Neem-Azraq Uplift. The concentrations of diamondoids are mainly controlled by source of oil, while the influence of thermal maturity and biodegradation may be limited. The isomerization ratios as indicators of thermal maturity are inapplicable at the mature stage, but DMDI-2, 4,8/3,4-DMD and 1-EA/3-EA can clearly distinguish the two groups of crude oils. The concentration ratios of oils from K-3 and B-1 wells are significantly lower than these of oils from Neem-Azraq Uplift, and these concentration ratios including newly proposed parameters such as MAs/DMAs, DMAs/TMAs, D/MDs, MDs/DMDs and so on, are effective indicators on organofacies and oil group division within oil window.</p></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142084108","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}