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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 将断裂后浅海硅质岩的岩石物理异质性和储层岩石类型与其沉积环境联系起来:埃及西部沙漠北部上白垩统巴哈里亚储层
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-23 DOI: 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.

巴哈利亚地层(Bahariya Formation)的上白垩统碎屑岩层是埃及西部沙漠北部(NWD)的主要储层。这些碎屑岩沉积在以不同规模的储层异质性为特征的准沉积环境中。然而,这些异质性与储层面沉积环境之间的联系仍然模糊不清。在本研究中,我们对西北地区亚西尔油田井中巴哈利亚地层的高度异质储层面进行了研究,以构建最佳储层岩石类型(RRT)和流动带分布的预测框架。地震地层学与岩心沉积学相结合,以了解储层面的沉积结构。此外,还对常规岩心分析和测井曲线进行了解释,以评估不同储层岩石类型(RRTs)中岩性和岩石物理异质性的规模。在所研究的 Yasser 油田中,Bahariya 地层由在各种潮汐影响条件下沉积的潮汐面组成。地震面随潮汐条件的变化而变化很大。最佳储层岩石类型RRT与潮汐通道和混合潮汐条带(RRTI)有关。RRTI岩石是所研究的巴哈利亚储层的主要流体流动通道。岩性和岩石物理异质性在形成 RRTIIII 岩石的潮泥滩和混合潮滩面层中更为突出。将地震与沉积面相联系起来,使我们能够预测研究区域最佳储层流动带的分布。本研究结果建立了一个基于地震、沉积和岩相综合预测最佳储层质量面的框架。该框架可应用于受潮汐影响、孔隙系统异质性高、受沉积控制的类似储层面。
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引用次数: 0
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 埃及中北部塞诺曼系 Abu Roash G 组分石油积累和蕴藏的地貌控制与构造演化:作为良好储层的三角洲砂岩和河槽砂岩
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-22 DOI: 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。
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引用次数: 0
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 通过对伊拉克北部和西部泥盆纪-早石炭世奥拉地层的古生物学有机岩石学调查,了解其烃源岩的沉积环境和热成熟度
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-22 DOI: 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.

本研究分别以伊拉克极北部奥拉地层类型剖面和伊拉克西部阿卡斯-3 井的地表和地下样本为基础,对该岩石单元的古生物学特征、有机质特征和碳氢化合物生成潜力进行了研究。地表剖面的古生物成分主要是深色、大部分被氧化、凝胶化的板状无定形有机质(AOM),此外还有一些圆形孢子和结构化的植化体。相比之下,Akkas-3 号井的研究样本中则以古绿藻为主,包括 Ambitisporites avitus、Aneurospora spp.、Vallatisporites verrucosus、Achinosporites spp.、Verrucosisporites nitidus 和藻类 Botryococcus。根据颗粒有机物的地层变化,统计聚类分析确定了表层剖面的三种古乐彩网类型。这些类型从代表近端亚缺氧-缺氧陆架环境的高无定形有机质(AOM)、中等植蚀作用和低古生物丰度,到代表远端亚缺氧-缺氧或远端缺氧-缺氧陆架环境的中等至良好 AOM 和低至中等古生物丰度不等。露头剖面的有机岩石学研究还显示了强烈的氧化作用,其中以颗粒状和凝胶状的分散陆生和无定形有机物质为主,反映了这些成分的陆地来源。在次表层断面,所研究的有机物具有陆地和较少海洋或湖泊混合来源的特征,其中陆地植物孢子(孢粉岩)以及玻璃岩和惰性岩占主导地位,还有一些零星的锂辉石大分子。露头样本和地下样本的热成熟度不同,可能是由于露头样本的构造埋藏较高,是伊拉克北部推覆带的一部分。然而,北部露头类型地段积累了较高丰度的 AOM(易生油的第二类角质)。这可能意味着奥拉地层在阿卡斯油田以北具有更高的碳氢化合物生产潜力。
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引用次数: 0
Geochemistry of the Late Cretaceous to Paleogene sedimentary deposits of the SW Anambra Basin (Nigeria): Implications for provenance, tectonic conditions, and hydrothermal influence 尼日利亚阿南布拉盆地西南部晚白垩世至古近纪沉积矿床的地球化学:对产地、构造条件和热液影响的启示
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-22 DOI: 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, TiO2 vs. 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.

尼日利亚西南部的阿南布拉盆地是中西部非洲裂谷系统(WCARS)的一部分,其沉积序列包括淡水沉积、三角洲沉积和边缘海洋沉积。在本研究中,我们提供了 Owan-1 和 Ubiaja 井穿过的坎帕诺-马斯特里赫特期 Nkporo 和 Mamu 地层以及古新世 Imo 地层泥岩的新矿物学和地球化学数据。这些分析旨在确定来源成分、沉积颗粒分选、热液影响和沉积环境,重点是研究不足的盆地西南边缘。此外,这些数据还有助于深入了解阿南布拉盆地的构造演化及其与贝努埃海槽和其他 WCARS 盆地的遗传联系。所研究的泥岩含有主要由石英和粘土矿物组成的碎屑颗粒,长石很少。用于评估沉积物颗粒分类的主要元素和痕量元素代用指标显示,沉积物主要是细粒砾岩,这表明沉积物的运移距离较长,与粘土矿物含量较高有关。为数不多的粗粒沉积物表明,沉积物直接进入盆地的时期较短,循环利用的时期较短。盆地内没有热液影响的证据。因此,我们认为所分析的沉积序列主要受浮游生物的影响。通常从海水中析出的石膏也证实了这一假设。根据对产地敏感的无机地球化学代用指标(即:Cr/Th vs. Sc/ThCr/Th与Sc/Th、La/Th与Hf、Th/Co与La/Sc、Th/Sc与La/Sc、Th/U与Th/Sc、TiO2与Zr)以及古新世伊莫地层和白垩纪马木地层和恩克波罗地层中已确定的碎屑成分,可解释为所研究的硅质碎屑岩主要来自于在构造过程中隆起到地表的近端长粒岩。根据判别函数绘制的判别图显示,阿南布拉盆地的沉积物是在裂谷环境中沉积的,这与其他 WCARS 盆地是一致的。
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引用次数: 0
Active deformation in the central section of the East African Rift from tectonic, volcanic, and hydrologic processes: Observations from satellite geodesy 从构造、火山和水文过程看东非大裂谷中段的活动变形:卫星大地测量观测
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-22 DOI: 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.

东非大裂谷系统(EARS)是一个活跃的大陆裂谷区,它承载着导致近期和当前地壳变形的各种过程。为了分析这些过程,我们利用哨兵-1干涉合成孔径雷达(InSAR),在2015年至2022年期间对视距线(LOS)变形进行高分辨率测量,以补充稀疏的全球导航卫星系统速度场。我们采用了一种广泛的勘测方法,以探测 EARS 中心区域内的新信号,并为未来重点研究构造、火山和/或水文变形以及跨越大地测量时间尺度的变化建立基线。通过这种区域方法,我们能够分辨出时间跨度从几周到几年不等的信号,其幅度大于 1 厘米/年。我们得到的形变场显示了与上述过程以及其他未知来源有关的各种信号。这包括内罗毕与地下水有关的高达 8.5 厘米/年的下沉,2021 年尼拉贡戈火山爆发期间高达 70 厘米的 LOS 位移,以及马尼亚拉盆地以 2.8 厘米/年的速度持续上升。我们更新了之前发布的对苏斯瓦火山和奥尔卡里亚地热场的 InSAR 测量结果。我们还显示,在肯尼亚裂谷约 200 公里的范围内,LOS 的变化幅度为 2 至 5 毫米/年,最大的差异率出现在图尔卡纳湖以南。总体而言,我们的研究结果凸显了仅依靠稀疏的全球导航卫星系统网络进行研究(如确定构造运动和裂谷开口的特征)的模糊性。这类研究很可能遗漏了许多重要信号,和/或包括被与目标过程无关的信号污染的站点。
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引用次数: 0
Analysis of very small-small theropod footprints data from Imilchil tracksite (Hig Central Atlas. Morocco). A concordance model for a global scale 分析来自伊米尔基尔足迹点(摩洛哥希格中央阿特拉斯)的超小型兽脚印数据。全球尺度的一致性模型
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-22 DOI: 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).

在伊米尔希尔大遗址的兽脚印群中,有一个体型较小的兽脚印群与其他兽脚印群截然不同。我们在拉里奥哈团队研究的其他遗址中,以及在绘制全球范围内兽脚印长度和宽度的散点图和频率直方图的工作中(这些数据可向 Farlow [[email protected]] 索取),都发现了这种分组现象。我们对小脚印的特殊分组进行了分析,提供了对伊米尔基尔 14 个新的恐龙脚印地点的兽脚印测量数据的研究,以及全球数据的图形表示(频率直方图和散点图)。这项工作是通过预测和比较伊米尔奇尔恐龙足迹的长度和宽度测量值以及我们称之为限定地理环境(TGC 或 Temporal Geographical Circumcriptions [参见 Mínguez Ceniceros 等人,2022 年])的全球足迹测量值来完成的。本研究中提到的脚印的图谱分类学研究可参见 Masrour 等人(2023 年)。最后,我们对伊米尔基尔以及 Farlow 发现记录的其他地区(截至 2022 年)的频率图中最大值和最小值的位置进行了解释。
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引用次数: 0
Structural architecture and metamorphism of the Mayombe Chain and Niari Basin (West Congo Belt) in Congo Brazzaville 刚果(布)马永贝链和尼亚里盆地(西刚果带)的结构构造和变质作用
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-20 DOI: 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.
通过对刚果(布)马永贝链和尼亚里盆地进行地质测绘,首次确定了西刚果带的构造结构和变质作用。由地壳尺度剪切带分隔的四个不同的构造-变质域现已被区分开来(尼阿里盆地(Niari Basin,NB)、东部马永贝链(Eastern Mayombe Chain,EMC)、中部马永贝链(Central Mayombe Chain,CMC)和西部马永贝链(Western Mayombe Chain,WMC))。其西部与 EMC 的分界线是贝洛山剪切带,该剪切带形成了西刚果造山带的末端推力系统。EMC 的构造风格以离散、大间距的低角度推力、逆断层和走向滑动断层为特征,从而形成了双重和/或正花构造。在这些高应变带之外,岩石被褶皱成平缓的同向和反向构造。西部的页岩中开始出现穿透性片岩。变质作用从东部的锚状条件向西部的低绿泥石面发展。CMC的典型特征是开放至封闭的直立至东北向褶皱、具有适度至陡峭西南倾角的S1片岩、开始出现区域性细圆劈理(S2)、频繁的反向推力和众多断层。变质条件仍为绿岩面。Loukenéné-Mandji推断带标志着CMC-WMC接触面,并与以生物玢岩为标志的变质阶跃相吻合。自生的古新生代片麻岩和片岩记录了 2110 至 1970 Ma 之间的晚埃伯尼期沉积、岩浆作用和变质作用,并与加蓬的埃伯尼期历史和巴西的 Transamazonian 造山运动进行了比较。在泛非事件期间,同源的比科西组从西面推覆在托尼安元火山碎屑岩和深成岩之上,然后这两个单元进一步褶皱和堆积。泛非大地构造的强度从水磨沟区东南部的开放式褶皱到闭合式褶皱,再到西北部以推覆构造为主的褶皱,古生代和新近古生代岩石在这里被转置为平行构造,并出现了明显的片理。伊利石和白云母的地质年代学记录了两个泛非事件,分别发生在 590-570 Ma(M1)和 520-500 Ma(M2),与巴西阿拉苏艾-里贝拉带的主要碰撞和晚期热事件有关。变质等级数从 M1 向西移动了 30 多公里到达 M2。姆皮奥卡组的云母和变质伊利石分别记录了 M1 和 M2,从而确定了 570 至 520 Ma 之间的沉积沉积,这意味着该组被解释为西刚果带的熔岩。
{"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}
引用次数: 0
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 阿拉伯-努比亚地盾中蛇绿岩超基性岩的碳化和硅化以及含金鳞片岩的形成:来自 Al-Barramiya 地区的案例研究
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-18 DOI: 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).

阿拉伯-努比亚地盾(ANS)西北角加巴尔-巴拉米耶地区的新近新生代晚期地幔断面含有不同程度的蛇纹岩化橄榄岩,这些橄榄岩沿剪切带和推覆面发生了强烈的蚀变,形成了含金的列表岩。它们可分为碳酸盐闪长岩、硅碳酸盐闪长岩和硅闪长岩(桦皮岩)。碳酸盐 listvenite 的特征是存在与寄主蛇绿岩类似的片理和变形构造,但在硅碳酸盐 listvenite 和硅质 listvenite 中却不存在此类构造,这表明它们出现在碳酸盐 listvenite 和蛇绿岩化之后。沿剪切带出现的列表岩以及蛇纹岩和铬尖晶石遗迹反映了它们是由沿推覆断层循环的热液对超基性岩进行变质作用而形成的。硅碳酸盐岩的特征是含有富长石,富含锌、铅、铜、银和金。稀土元素(REE)的含量在所研究的列表岩中有所不同。硅碳酸盐列表岩的稀土元素总量最低(∑₌0.98-2.56 ppm),而硅列表岩的稀土元素总量最高(∑₌15.70-21.42 ppm)。根据上述情况,碳酸盐橄岩最早是由原前弧橄榄岩板块蛇绿岩化过程中释放的含二氧化碳流体渗入形成的,其次是由蛇绿岩俯冲过程中释放的二氧化硅饱和及含二氧化碳流体活动形成的硅碳酸盐橄岩。由于蛇绿岩化橄榄岩的热液蚀变作用,富含Si和K的流体与Cr-闪锌矿发生元气反应,形成了硅碳酸盐鳞片岩中的富长石。在最后阶段,早期形成的二氧化硅-碳酸盐列表岩发生硅化作用而形成二氧化硅列表岩。巴拉米亚蛇绿岩地幔段的列表venit化导致了金、铅、锌、铜和银的富集。与碳酸盐闪长岩(119-191 ppb)和硅质闪长岩(156-233 ppb)相比,硅质-碳酸盐闪长岩含有更高浓度的金(899-2199 ppb)。
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引用次数: 0
Hydrochemical characterization and evaluation of irrigation water quality using indexing approaches, multivariate analysis, and GIS techniques in K'sob Valley, Algeria 利用索引方法、多元分析和地理信息系统技术对阿尔及利亚 K'sob 谷灌溉水质进行水化学特征描述和评估
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-15 DOI: 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

灌溉在满足日益增长的粮食生产需求和促进经济发展方面发挥着至关重要的作用。为了满足粮食供应和经济发展的需求,必须强调评估干旱地区水质的重要性。本研究旨在评估和预测姆西拉地区(阿尔及利亚东北部)K'sob 谷地的水质是否适合农业使用。为此,综合使用了灌溉水质量指数(IWQIs)、地理信息系统(GIS)分析和多元统计方法。在四个季节从 10 个地表水地点采集的 40 份样本中测量了多个理化参数,如温度 (T°)、氢离子浓度 (pH)、电导率 (EC)、溶解性固体总量 (TDS)、浊度 (Turb)、化学需氧量 (COD)、Ca2+、Mg2+、Na+、K+、HCO3-、Cl-、SO42-、NO3-、NO2-、NH4+、PO4- 和 SiO22+。主要阳离子和阴离子的浓度如下:Na+>Ca2+>K+>Mg2+和SO42->HCO3->Cl->NO3-表示Na-Cl-K或Na-SO4混合水层。各参数(T、pH、浊度、盐度、化学需氧量、NH4+、Cl-、SO4- 和 NO2-)均有显著的季节性变化(p <0.05)。此外,不同站点之间的参数也存在明显的空间差异(p < 0.05):TDS、EC、Ca2+、Na+、HCO3-、SO4-、NO3- 和 PO43-(p < 0.05)。灌溉水质量指数(IWQI)、钠吸附率(SAR)、钠百分比(Na%)、凯利指数(KI)和渗透指数(PI)的数值分别在 28.1 和 56.8、5.65 和 12.45、75 和 87、2.61 和 6.54 以及 83 和 97 之间变化,并记录到显著的季节效应。根据 Wilcox 图,70% 的样本不适合灌溉,30% 的样本有问题。IWQI 图显示,50% 的样本属于非常不适合灌溉的类别,而 20% 和 30% 的样本分别属于较差和不适合灌溉的类别。K'SobValley 水的主成分分析(PCA)和分层聚类分析(HCA)显示,根据元素组成和季节变化,水可分为三个不同的类别。本研究获得的结果对地表水管理很有价值。此外,所开发的方法可作为一种有用的工具,用于确定干旱和半干旱环境中与地表水有关的关键水文地质化学成分。
{"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>&gt;Ca<sup>2+</sup>&gt; K<sup>+</sup> &gt; Mg<sup>2+</sup>, and SO<sub>4</sub><sup>2−</sup> &gt; HCO<sub>3</sub><sup>−</sup> &gt; Cl<sup>−</sup> &gt; 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 &lt; 0.05). Additionally, a significant spatial variation (p &lt; 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 &lt; 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}
引用次数: 0
The application of diamondoids indices for oils from Block 4 of the Muglad Basin in the middle of Africa 非洲中部穆格莱德盆地 4 号区块石油的金刚石指数应用
IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-08-15 DOI: 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.

对苏丹穆加尔德盆地 4 号区块的一系列原油样本进行了菱形类丰度和分布研究,以探讨各种菱形类参数对石油来源、热成熟度和生物降解信息的有效性。4 号区块的所有原油均由阿布-加布拉地层下部的湖泊源整体生成,并可进一步分为两个原油组:尼姆-阿兹拉克隆起区的油组以及 K-3 井和 B-1 井的油组。它们都是石油窗口内的成熟油,尼姆-阿兹拉克隆起带的四种原油略有生物降解。K-3 井和 B-1 井石油中的类钻烃浓度,尤其是二烷烃浓度高于尼姆-阿兹拉克隆起带的石油。类钻 石的浓度主要受石油来源的控制,而热成熟度和生物降解的影响可能有限。作为热成熟度指标的异构化比率在成熟阶段并不适用,但 DMDI-2、4,8/3,4-DMD 和 1-EA/3-EA 可以明显区分两类原油。K-3 和 B-1 井的石油浓度比明显低于楝树-阿兹拉克隆起区的石油浓度比,这些浓度比包括新提出的参数,如 MAs/DMAs、DMAs/TMAs、D/MDs、MDs/DMDs 等,是石油窗口内有机层和石油组划分的有效指标。
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Journal of African Earth Sciences
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