Journal of African Earth Sciences最新文献

Numerical stratigraphic forward modelling is useful to understand and reconstruct the relative sea-level and sediment supply history responsible for particular strata. This analysis uses BARSIM, a simple 2D forward stratigraphic process-response model that simulates wave and storm processes, applied with an inverse modelling optimisation method to better understand the history of Pleistocene strata in the Achakkar basin of the Tangier region, Morocco. Observations of grain size and bed thickness in four outcrop vertical sections are matched with BARSIM model output to estimate the lowest-error best-fit relative sea level and sediment supply histories that may have controlled deposition of the observed strata assuming deposition over a 10 ky period, consistent with available dating from outcrop sections. The best-fit relative sea level history drops from 4.88 to −2.82 m with two lower-amplitude highstands in between, most likely representing interglacial eustatic and tectonic event. The best-fit sediment supply is variable through time and different for each vertical section, with greatest variation from 11.7 to 2.11 m²y^-1 over the 10 ky interval in the north-east vertical section. The spatial and temporal variation of sediment supply in the four vertical sections represents typically dynamic depositional conditions in shallow marine nearshore areas. On the other hand, it can indicate high stratigraphic incompleteness caused by periods of non-deposition or erosion with temporal variations in sediment supply. The optimum way for the simple model to reproduce short intervals of high sedimentation rate separated by longer periods of hiatus and deposition followed by erosion results in a discontinuous stratigraphic record.

The present study aims to investigate the relationship between tectonic activity, climate changes and Quaternary travertine deposition around Kurkur Oasis in the southern Western Desert of Egypt. Our findings, based on field observations and structural investigations, revealed that extensional tectonics played a significant role in the formation and the distribution of travertine deposits in the study area. Three main travertine morphotypes are documented: fissure ridge, spring mound, and terrace mound along with four lithotypes: crystalline crust, fine-grained lithoclast, paper-thin raft, and reed. The spatial distribution of these travertine occurrences indicates that travertines located closest to the springs exhibit crystalline crust and paper-thin raft lithotypes. While, the reed and the fine-grained lithoclastic types are situated farther from the water sources. Terraces mounds are related to pluvial episodes, which led to travertine deposition in the suitable tectonically created depressions. A two-stage hypothesis for travertine deposition are proposed herein, involving tectonic fissuring and the circulation of carbonated water. These results may enhance our understanding of travertine formation and have broader implications for geological research in similar tectonic environments.

Landslides are a significant global risk due to their impact on nature, society, and the economy. The Al Hoceima-Ajdir region is highly susceptible to geohazards such as earthquakes and ground instabilities caused by local tectonic movements and specific climatic and geomorphological conditions. This study aims to assess landslide susceptibility in Al Hoceima-Ajdir using a digital mapping approach that integrates the geostatistical Frequency Ratio tool, geomatic tools, and field observations. The frequency ratio method, a widely used technique in geospatial analysis, evaluates the relative frequency of landslides based on the spatial distribution of conditioning factors such as slope, lithology and land use – land cover. This method calculates the ratio of the frequency of landslides within specific classes of these factors to their respective frequencies in the entire study area. This research introduces a novel susceptibility map highlighting major threats to several natural and touristic sites crucial to the region's socio-economic activities. The susceptibility map was developed by analyzing 40 historical landslides along various predisposing factors, including topographic, geo-hydrological, and anthropogenic parameters. The results identify areas prone to landslides and classify their susceptibility into five levels ranging from very high to very low, with each level indicating a different degree of risk and requiring a specific set of preventive measures. The reliability of this map was evaluated using the Receiver Operating Characteristics (ROC) method, demonstrating a high accuracy of 89%, further validated by field visits. This high-precision susceptibility map is significant for pre- and post-risk management, enhancing prevention and mitigation strategies. It also protects society, the economy, and the environment by providing a reliable regional planning and hazard management tool. The findings of this study offer a significant advancement in the methodology for landslide susceptibility assessment and present a model that can be adapted to other regions facing similar geohazards. The research underscores the importance of integrating geostatistical tools with field data to produce accurate and actionable susceptibility maps, benefitting the global scientific community by improving hazard prediction and management strategies.

Trace element signatures are tracked to unravel the genetic history of ore deposits in several mineral systems. This is particularly true for pyrite, a ubiquitous component of many ore-forming systems, including orogenic gold deposits. Here, we critically compare the efficacy of utilizing Uniform Manifold Approximation and Projection (UMAP) versus Principal Component Analysis (PCA) as dimensionality reduction tools applied to a 31 element dataset collected using Laser Ablation Inductively Coupled Mass Spectrometry of pyrite grains from the Kibali gold district (Democratic Republic of Congo). Because of the non-linearity inherent to mineral chemistry and because of its superior preservation of local (distances within clusters) and global (separation between clusters) data relationships, the UMAP approach outperforms dimensionality reduction by PCA. We further present a workflow in which UMAP dimensionality reduction is followed by k-means clustering to guide the classification of pyrite generations in the Kibali case study. Validating this approach with trace elements and UMAP + k-means on a seed-by-seed petrography basis shows that the workflow significantly enhances the original pyrite classification, previously based on texture. This study thus emphasizes the utility of employing advanced statistical analysis methods to capture the intricate nature of pyrite formation. These findings will shape best practices for handling large multi-element datasets in pyrite mineral chemistry studies and are extrapolatable to other mineral systems in which trace element signatures are used to infer the conditions of ore deposit genesis.

The Eocene epoch experienced significant fluctuations in climate, ranging from intense greenhouse warming to icehouse cooling, which profoundly impacted the global depositional systems. The middle – upper Eocene deposits in Garet Gehannam, Fayum area, Egypt, present an exciting opportunity to explore paleoenvironmental dynamics using a multiproxy dataset of calcareous nannofossils, benthic foraminifera, ostracods, and molluscan assemblages. Calcareous nannofossil biostratigraphy constrained the studied sequence to the NP17 and NP-19-20 zones. Furthermore, three 3^rd-order depositional sequences, BAR.SQ.1, BAR.SQ.2, and PR.SQ.3 were identified. The BAR.SQ.1 sequence encompasses the Gehannam Formation, with a transgressive systems tract (TST) and a highstand systems tract (HST). The BAR.SQ.2 sequence corresponds to the lower Birket Qarun Formation and exhibits a TST/HST pattern. The PR.SQ.3 sequence, however, consists solely of a TST spanning the upper Birket Qarun and Qasr El Sagha formations. The main trend of our multiproxy-based sea level curve shows an overall stepped Tethyan sea level regression within the 2^nd-order cycle. This regression is characterized by a transition from outer neritic to inner settings, interrupted by two minor 3^rd-order transgressive pulses. This sea level trend was likely driven by global eustatic changes and regional tectonic uplift related to the final collisional phase between Africa/Arabia and Eurasia, which led to the closure of the Neotethys Ocean. Multiproxy faunal analysis reveals a pronounced upsection shift from low-oxic and mesotrophic conditions to well-ventilated, oligotrophic settings tracking long-term sea level fall. The lowering of the sea level may have expanded aerobic ventilation windows on the continental shelf while potentially reducing nutrient influx. Our multiproxy sequence stratigraphic and paleoenvironmental analysis provides insights into the complex interplay of tectonic, eustatic, and climatic influences on the region during the middle – late Eocene episode along the southern Tethyan margin.

The low quality of the seismic resolution of the studied Cambrian Pre-Cenomanian formations, which rest directly on the basement in the October Field in the Gulf of Suez, requires study, and the structure pattern controlling these formations is uncertain. The poor quality of the seismic data resolution in the Gulf of Suez is due to the presence of thick sequences of evaporites represented by the South Gharib and Zeit formations. Therefore, the current study used seismic reflection data integrated with well-log data to define the structural-stratigraphic setting of the pre-Cretaceous Nubian reservoir sequence. The study aims at locating and delineating zones having excellent reservoir potential within the Nubian sequence horizons (Nubian Transition, main Nubian, Nubian marker-1, and Nubia marker-2, referred to as NT, MN, M1 and M2, respectively) through the integration of the 3D static modelling and the petrophysical parameters deduced from the well-log data processing. A detailed petrophysical analysis, based on the wireline logs of some wells, was performed to determine the lithological units using two types of cross plots (Neutron-Density and M-N plots), and the different petrophysical parameters that characterize the various Nubian horizons were also computed. 3D modelling was used to visualise the lateral and vertical changes of the reservoir characteristics. The seismic mapping reveals that the Nubian structure is controlled by an NW-SE trending (Clysmic trend) of an NE-plunging asymmetrical anticlinal feature unconformably resting on a basement horst. The main structure is affected by two major normal faults, which trend NW, andis cut by two smaller sub-parallel faults that disturb the core of the structure, which is unaffected by the easterly oriented faults of the Aqaba trend. The petrophysical analyses indicate that the Nubian sandstones have intervals of good reservoir quality, with a total net-pay thickness of about 500 m, net sand ratios (60–90 %), effective porosity (10–25 %), and hydrocarbon saturation (85%), which may encourage further drilling, especially in the southeast portion. The result of this study can be extended to the other Nubia sandstones resting on the basement complex in the Gulf of Suez.

The metallogeny of gold in northeastern Mozambique is still debated, with the main point of contention being the timing of mineralization with respect to regional tectonism, metamorphism, and magmatism. In this study, we applied Re–Os sulfide geochronology to constrain the age of gold mineralization in the Nanlia and Makorongo prospects hosted by the Xixano Complex, in the southern part of the Mozambique Belt. In addition, chemical analyses of host rocks and sulfides complement the discussion on the genesis of mineralization. Single-mineral Re–Os model ages of pyrite and pyrrhotite in quartz veins constrain the occurrence of gold mineralization in the Nanlia and Makorongo prospects between ca. 580 and ca. 560 Ma. This mineralization age interval postdated the timing of peak metamorphism of the host rocks established at ca. 631–607 Ma and is contemporaneous with the metamorphism of basement rocks between ca. 607 and ca. 564 Ma, during the thrusting of tectonic nappes in the last stage of the Pan-African orogeny. In addition, the strike of the veins in the Nanlia and Makorongo prospects is parallel to the local orientation of the thrust fault that separated the overlying rocks from the basement rocks and the dominant S1 foliation of the host rocks. These geochronological and structural data indicate a close relationship between auriferous veins in the study area and the Pan-African thrust fault associated with the emplacement of the tectonic nappes. We propose a metamorphic model for the gold mineralization in the Nanlia and Makorongo prospects, in which the mineralizing fluids were sourced mainly from dehydration of basement rocks, as a result of prograde metamorphism triggered by the juxtaposition of the Neoproterozoic tectonic nappes, including the Xixano Complex, during the last stage of the Pan-African orogeny. The mineralizing fluids ascended through the Pan-African thrust faults and structures to the overlying rocks, where the gold was deposited along the S1 foliation.

Climate change, a global concern, has significant implications for rainfall and temperature patterns. A critical knowledge gap exists in understanding these implications for the Ramis catchment of the Upper Wabi-Shebelle Basin. This research projects future rainfall and temperature patterns in the Ramis catchment of the Upper Wabe-Shebelle basin. The projection utilized a multimodel comprising eight distinct general circulation models from coupled model intercomparison phase six (CMIP6) data simulation. These models were selected based on their performance, considering two shared socioeconomic pathways (SSP2-4.5 and SSP5-8.5). The Quantile Mapping (QM) bias correction technique, implemented in R, was used to enhance the reliability of extracted data. The Mann‒Kendall (MK) trend test method was employed to analyze temperature and precipitation trends for two future periods, 2030–2060 and 2061–2090, annually and seasonally. The results suggest a decrease in rainfall during the spring and Winter seasons for 2030 to 2060 and 2061 to 2090 respectively, potentially leading to water scarcity that could impact crop growth and water supply. A decreasing trend in annual rainfall was observed from 2030 to 2060 under SSP2-4.5 and SSP5-8.5 scenarios. The study also uncovered significant and consistent warming trends in maximum and minimum temperatures across the Ramis catchment under both the SSP2-4.5 and SSP5-8.5 scenarios. Rainfall Anomaly Index (RAI) analysis predicts a minor increase in rainfall in the Ramis catchment from 2030 to 2090 under both scenarios, with a notable RAI decrease expected in 2043–2071, indicating potential drought conditions. These findings offer critical insights for regional climate change impact assessments across the Ramis catchment.

Drilling fluid loss is one of the key challenges in the drilling operations of oil and gas wells, which has a direct effect on the formation damage and production operations. Hence, it is very important to study mud loss and investigate the factors affecting its locations. In this study, the fluid distribution model and its influencing factors in the Oligo-Miocene Asmari reservoir have been studied. For this purpose, the drilling data, mud loss maps, mud weight, and the condition of mud loss in one field have been analyzed. Additionally, this study aims to provide a more precise understanding of mud loss within the reservoir, as well as examining its correlation with drilling issues. The drilling history of the wells and maps of the mud weight required for drilling the Asmari Formation in different parts of the field were used.The drilling challenges encountered in the examined wells were systematically analyzed, and distribution maps highlighting the prevalence of these issues across various sectors were generated. Also, the density of wells with drilling problems was determined in different parts of the field, and areas with high risk were introduced. The results of this study show that the highest amount of loss, a volume of 120 bbl/h, has been occurred in the main anticline areas of the field (the southeast and northwest areas of the structure), where the highest mud weight of about 130 lb/ft³ was used. Most of the wells with drilling problems are located in this area of the field. Wells situated farther away from this region were drilled with notably reduced risk levels compared to those in closer proximity.

The application of rock physics modeling has been a breakthrough in oil and gas industry and has greatly managed exploration and interpretation risk. In the Rio del Rey Basin, the rock physics method was used to ascertain the reservoir's characteristics and relate them to the elastic characteristics. Using conventional techniques to connect to the elastic properties and assess various rock physics diagnostics, the estimated petrophysical parameters were water saturations, porosity, and shale volume. By connecting the saturated bulk modulus to its porosity, the bulk modulus of the porous frame, the bulk modulus of the mineral matrix, and the bulk modulus of the pore filling fluids, the Gassmann fluid replacement modeling was used to simulate various fluid scenarios. Finally, an evaluation was conducted on rock physics boundaries and cement models. The reservoirs are rated as extremely good based on the results. The rock physics model generated showed the friable sand model is a suitable model for the said basin and the rock physics bounds that were evaluated indicated that the sediments are deposited below the critical porosity and less compacted thereby depicting a soft sand model. Conventional petrophysical study would not be able to reveal the clustering of the gas sands from the brine sand and the shale zone in connection to the geologic trend as demonstrated by the rock physics template. The anticipated model will be useful to extrapolate the study to other sedimentary basins in Cameroon and estimate porosity from the impedance acquired from seismic data throughout the basin.