Distribution Of Rocks Research Articles

Prediction of Thin Pre-Salt Reservoir in PL Gas Field, Sichuan Basin

In this paper, the reservoir characteristics and favorable exploration zones of Jialingjiang Formation in Triassic Jialingjiang Formation in PL gas field, Sichuan Basin are studied in depth. By means of geophysical processing and prediction techniques such as seismic attribute analysis, inversion and structural interpretation, this paper focuses on the sedimentary facies, structure, fractures, reservoir thickness and physical properties of the porous reservoir in Jialingjiang Formation, in order to define the spatial distribution of the reservoir and the favorable exploration zones. The research results show that the development of Baiyun rock beach facies reservoir in Jiawumember is mainly concentrated in well area JT1-PS7-PY1, where the local deposition thickness increases and it is a favorable tidal beach facies zone. Based on multi-attribute analysis and phase-controlled p-wave velocity inversion, this paper predicts the lithology and gas distribution of carbonate and gypsum rocks in the Jiawu Member, revealing that the reservoir thickness of the Jiawu 1 submember is between 5 and 22 meters, and gradually thinning in the southeast direction. Based on paleogeomorphology analysis and fracture development characteristics, six favorable exploration areas with a total area of 48 square kilometers are selected, and three proposed well locations are proposed, which provide guidance for future exploration evaluation and deployment.

Effects of rock content and spatial distribution on the stability of soil rock mixture embankments

Soil-rock mixture embankments are essential for infrastructure stability, particularly in high-fill construction projects. This study evaluates the effects of rock content and spatial distribution of rock blocks on the bearing capacity, stability, and failure sliding surfaces of SRM embankments through static load model tests. An Equation for Sliding Surface of Block-Rock Content and Distribution was developed to calculate sliding surfaces based on rock content and distribution, and validated it through numerical simulation experiments. The results demonstrate that rock content significantly influences embankment stability. When rock content is below 60%, the shear outlet position of the sliding surface increases, and its curvature decreases as rock content rises, thereby enhancing the bearing capacity. Beyond 60% rock content, the internal structure densifies, markedly improving stability, although further increases yield diminishing returns. Additionally, the spatial distribution of rock blocks is crucial; concentrating rock blocks at the slope crest or toe enhances stability, while distributing them in the middle reduces it. These findings offer practical guidance for optimizing the design and construction of the soil-rock mixture embankments, emphasizing the importance of appropriate rock content and spatial distribution to achieve enhanced stability and safety.

Emplacement and landscape controls on ancient submarine volcanism: 3D seismic geomorphological analysis of Cretaceous volcanic activity in the Browse Basin, Australian North West Shelf

Ancient submarine volcanic systems preserved within sedimentary basins provide opportunities to investigate the time and spatial distributions of intrusive and extrusive rocks, though existing work has largely focused on the geometrical features of submarine volcanic products, with limited interrogation of their interactions with sedimentary processes. This study investigates a buried submarine volcanic system within the Browse Basin, Australian North West Shelf. Through the integration of three-dimensional seismic reflection survey with borehole data, our study reveals intricate geometric features of a submarine volcano and lava channels, and their relationship to an associated intrusive network of Early Cretaceous age that has been preserved beneath ∼3.5 km of sedimentary overburden. In planform, the volcano has a diameter >4.5 km with a preserved height reaching 650 m. Meandering lava flow channels extend ∼20 km southward of the volcanic edifice, forming lava lobes with pressure ridges at the flow termini. Abundant sheet intrusions, identified within underlying Jurassic and older strata, indicate a magma transport from the north. The localised accumulation of sills led to variations in paleo-seafloor topography, influencing the direction of lava flows and post-volcanic sedimentation patterns. Our findings have a broad range of implications encompassing submarine volcanism and their impacts on basin dynamics.

Shear tests and meso-scale simulation of cold joint structures in rock-filled concrete: Considering the mutual contact effects between component materials

To realistically reflect the shear performance of the rock-filled concrete (RFC) between layers, this study relies on an RFC dam project in Guizhou Province. Test blocks, measuring 5 m × 4 m × 2 m with cold joints, were cast on site and subjected to shear tests. Additionally, a three-dimensional four-phase meso-model was developed, considering the mutual contact effects between component materials. The mechanical response and damage mechanism of the interlayer were analyzed using the cohesive zone model. The results confirm that the cohesive zone model effectively simulates interlayer cold joint structures. The damage modes of the RFC interlayer include cold joint debonding damage (Mode I) and plastic extrusion damage of self-compacting concrete (Mode II). As the exposed height of the rocks increases, the damage mode shifts from Mode I to Mode II, and higher normal stresses intensify Mode II damage. Meanwhile, the paths of crack extension depend on the distribution of shear-resistant rocks, with weak interfacial transition zones serving as “bridges’’ for crack propagation. The interlayer shear strength is positively correlated with the average exposed height of rocks and normal stresses, with the former having a more significant impact. Finally, the accuracy of the proposed shear strength prediction model for the RFC interlayer was validated by comparing it with results from other studies, providing useful references for meso-numerical modeling of RFC.

Hidden Archaean basement beneath the southwestern Yangtze Craton: Evidence from 2.8 Ga xenocrystic zircons in an early Cretaceous dolerite dyke

The distribution of Archaean basement rocks in the southwestern Yangtze Craton, China, is not well documented due to the scarcity of outcrops. In this study, we identified Meso–Neoarchaean zircons in a dolerite dyke that was emplaced in the Meso–Neoproterozoic Dongchuan Group in the southwestern Yangtze Craton. Ninety-seven analyses of zircons from the dolerite yielded two distinct U–Pb age groups. The younger group of zircons, characterised by euhedral crystals and relatively high Th/U ratios (0.15–2.03), has a weighted-mean age of 109.4 ± 3.0 Ma (n = 27), which is considered to be the emplacement age of the dolerite. The older group of zircons, with a weighted-mean age of 2831 ± 18 Ma (n = 33), crystallised during the Meso–Neoarchaean. These zircons might be xenocrysts captured during magma emplacement. Moreover, the zircons have εHf(t) values of −24.59 to −4.16 for the young population and −9.80 to −3.86 for the old population, indicating the dolerite was derived by melting of Archaean crustal igneous rocks. These results demonstrate the existence of Archaean rocks in the southwestern Yangtze Craton and provide new evidence for the spatial distribution of Archaean basement.

Analysis of the reservoir properties of rocks of the Lower Kura depression (Azerbaijan)

The article analyzes the features characterizing the Lower Kura depression (LKD). A number of hydrocarbon deposits have been discovered in this oil and gas region. The Kalmas underground gas storage facility, which has the largest volume in Azerbaijan, is also located in this area. In the LKD, all PS formations can be traced throughout the entire well section. The reservoir properties of the rocks were considered to study the features of the area. In order to study the reservoir properties in the well section, the field applies data obtained by using a complex of well logging (WL) methods (laterolog, spontaneous potential logging, induction logging, gamma logging, neutron logging, acoustic logging) and analyses of rock samples. The graphs were constructed to evaluate the relationship between petrophysical parameters (porosity, permeability, etc.) determined in the rocks involved in the well sections of the object of research. In the article, maps of porosity distribution, permeability and permeability of sandy siltstone rocks and fractions greater than 0.1 of the Productive Series of the South-Eastern Gobustan and Baku Archipelago, which are part of the Low Kura Depression, are plotted and analysed. Plots showing the porosity distribution of the Low Kura Depression by depth were also constructed and some results were obtained. Based on reservoir properties, the region is divided into 6 groups, and in each group intermediate values of the porosity and permeability coefficient are determined. In general, the porosity coefficient ranges within 5-25%, permeability – 1-250 mD. The reservoir properties of rocks vary over area from worse to better. The capacitance-filtration properties of rocks were studied. The rock samples analysed identified rocks with good and low reservoir characteristics. To study the variation in the determining factors, maps of the distribution of reservoir properties indicators (fractions greater than 0.1 mm; porosity and permeability in sand-siltstone-containing rocks) were compiled by area and their causes were determined by comparison with other oil and gas fields. It was found that with distance from the mouth of the Kura River (towards the right and left banks), the reservoir properties of the rocks deteriorate. This is due to an increase in the amount of clay in rocks. It is also clarified that the change in porosity coefficient does not depend on depth. The content of sand-siltstone composition in the rocks along the section is 20-50%.

Dynamic Responses and Damage of a Model Ship in Multi-Rock Grounding

Ship grounding onto multiple rocks is one of the scenarios where a ship may suffer severe hull damage, thus leading to some serious consequences, such as casualties, oil spill pollution, and property damage. Ship bottom raking is the most common and severe damage type in grounding caused by sharp rocks moving against the bottom plate. This paper investigates the dynamic responses of ship grounding onto multiple sharp rocks, which has rarely been studied in the literature. Nine ship grounding in-tank model tests were conducted to provide experimental data for ship grounding onto a single rock or multiple rocks. A simplified scaled ship model with replaceable bottom plating was designed and used in the model test. Some artificial cone rock models with a 1 mm tip radius and a 15° semi-apex angle were assumed. The damage modes of the bottom plating and motions during ship grounding onto multiple rocks were obtained and recorded in the model tests, as well as the longitudinal grounding resistances. The effects of the initial relative height of each rock and the size of rock distribution on the structural damage mode and dynamic response of a ship model in multi-rock ship grounding were investigated. In addition, the results obtained from single-rock and multi-rock ship grounding model tests are compared.

A Comprehensive Geophysical Exploration of Sedimentary Exhalative Deposits: An Example from the Huaniushan Lead–Zinc–Silver Polymetallic Deposit in Gansu, China

The Huaniushan lead–zinc–silver deposit is a hydrothermal sedimentary exhalative deposit (SEDEX), and the mining area has complex geological conditions, with the main tectonic structure being the Huaheitan–Shuangfengshan Fault (F3), which controls the distribution of strata and magmatic rocks. Since the discovery of the Huaniushan lead–zinc–silver deposit, diverse interpretations of its genesis and metallogeny have been proposed, making it challenging to establish a definitive geological explanation. Moreover, using a single geophysical exploration method relies on limited rock physical parameters, making it difficult to effectively characterize underground structures. The combined use of multiple geophysical methods can effectively integrate the geophysical characteristics of different rock physical parameters, reducing the multiplicity and uncertainty of the inverse interpretation of geophysical data. The comprehensive interpretation of three-dimensional inversion based on various geophysical data, the construction of geological–geophysical models on geological grounds, the establishment of hidden ore exploration and positioning, and the rapid evaluation of geophysical technological systems are the current research trends in mineral exploration. In light of this, in this study, we conducted research on the three-dimensional inversion interpretation of gravity and magnetoelectric exploration data of the Huaniushan sedimentary exhalative lead–zinc–silver polymetallic deposit and constructed a three-dimensional geological–geophysical model of the study area based on the obtained three-dimensional physical structure of the underground density, magnetization intensity, resistivity, and polarizability of the study area, in combination with related geological and drilling hole data. Finally, we comprehensively interpreted the favorable mineralization sites in the study area.

Widespread coastal upwelling along the marginal Yangtze Platform (South China) during the early Cambrian: Implications for hyper-enrichment of organic matter

Early Cambrian Earth history witnessed significant changes in marine environments and biological evolution contemporaneous with extensive accumulation of organic-rich shale. However, major factors controlling hyper-enrichment of organic matter (OM) of lower Cambrian shale deposits remain controversial. Black shale of the lower Cambrian Niutitang Formation (NTT) of the marginal Yangtze Platform (South China) deposited during the Cambrian middle Age 2 are especially organic-rich, with total organic carbon (TOC) concentrations of as much as 13.0 wt%. Geochemical evidence suggests that cool, dry paleo-climatic conditions that prevailed on the Yangtze Platform during the Cambrian Fortunian-late Age 2, induced vigorous coastal upwelling. Paleo-productivity level assessments indicate that the magnitude of primary productivity contemporaneous with deposition of the NTT shale deposits exceeded that of modern upwelling systems (e.g., Peruvian Margin). The widespread occurrence of phosphate nodules within these deposits and decreased Co-EF × Mn-EF values of associated lower Cambrian black shale successions deposited along the margin of the Yangtze carbonate platform suggest extensive coastal upwelling. Widespread and strong coastal upwelling in tandem with elevated surface water primary productivity and anoxic (even euxinic) bottom water conditions are manifested by deposition of OM hyper-enriched black shale during Cambrian Fortunian to middle Age 2 time. However, weakened seasonal upwelling that appears to have prevailed during the late Cambrian Age 2 was accompanied by accumulation of NTT shale deposits of diminished TOC content. In summary, this study provides robust evidence of extensive coastal upwelling along the marginal Yangtze Platform during early Cambrian time that favored accumulation of OM hyper-enriched shale. These results help to elucidate the distribution of high-quality lower Cambrian natural gas source rocks in South China.

A novel method for evaluating shale gas preservation conditions in an area on a regional scale

The Youjiang Basin is the main area of the Middle Devonian shale gas resources in southern China, with complex geological conditions, diverse stratigraphic structures, low level of exploration and limited hydrocarbon geological data. In this study, a method is proposed for evaluating the regional shale gas preservation conditions, by which it is easy to obtain information (using available data from regional geological maps) and to process data (processed by computer software). This method was applied to the evaluation of the preservation conditions of the Middle Devonian shale gas in the Youjiang Basin. Information extracted from geologic maps includes exposed stratum, magmatic rock distribution, stratigraphic occurrence and surface fracture distribution. Evaluation criteria for three indexes (stratigraphy index, dip angle index and fracture index) were established to classify the preservation conditions into five types from good to bad. Based on the calculated values of comprehensive index (CI), the comprehensive evaluation each area: 11621.23 km2 for CI of 0.7–1.0, 37162.67 km2 for CI of 0.5–0.7, 57784.43 km2 for CI of 0.3–0.5, 69303.77 km2 for CI of 0.1–0.3, and 69303.77 km2 for CI of 0.0–0.1, accounting for 3.19%, 10.19%, 15.84%, 18.99% and 51.80% of the whole area, respectively. These results are highly consistent with the actual exploration discoveries, showing that in the northern and central parts of the Guizhong Basin, the southern part of the Xidamingshan Uplift, and the northern part of the Qiannan Basin, there are large areas with good shale gas preservation conditions.

Utilising the 3D mineral system approach to identify the source of alluvial gold deposits in Ibala Town, Southwest Nigeria: an In-depth geological and geophysical exploration

ABSTRACT The Ibala gold field, discovered by artisanal miners in 2018, is located east of Ibala town in Osun State, southwest Nigeria. As older mines are depleted and abandoned, miners are now investigating the source of the deposits, believed to be auriferous quartz veins. This study uses the mineral system approach to trace the origin of the alluvial gold in the Ibala area. The research is conducted in three phases: first, a detailed analysis of the region’s structural patterns and rock distribution is undertaken to understand the area’s tectonic history. Next, a 3D conceptual model is created using an integrated geological and geophysical modeeling techinque to identify exploration targets and map the mineral system components. Finally, on-site verification is performed to validate the findings. The study reveals that the gold originates from auriferous shear zones characterized by high conductivity and chargeability geophysical signatures. These zones were formed by auriferous fluids released during the metamorphic devolatilization of deep volcanic rocks. As the fluids migrated through shear zones, they interacted with host rocks, precipitating gold alongside pyrite. When weathered, the gold-bearing material is transported via drainage channels, which miners now exploit. By using a mineral system approach, this research pinpoints the primary gold sources, supporting more efficient resource management and sustainable mining practices in the region.

Enhanced lithological mapping in arid crystalline regions using explainable AI and multi-spectral remote sensing data

Lithological classification is essential for understanding the spatial distribution of rocks, especially in arid crystalline areas. Artificial intelligence (AI) recent advancements with multi-spectral satellite imagery have been utilized to enhance lithological mapping in these areas. Here we employed different AI models namely, Support Vector Machine (SVM), Random Forest Classification (RFC), Logistic Regression, XGBoost, and K-nearest neighbors (KNN) for lithological mapping. This was followed by the application of explainable AI (XAI) for lithological discrimination (LD) which is still not widely explored. Based on the highest accuracy and F1 score of the previously mentioned models, RFC model outperformed all of them, and hence, it was integrated with XAI, using the SHapley Additive exPlanations (SHAP) method.This approach successfully identified critical multi-spectral features for LD in arid crystalline zones when applied on the Landsat-8, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and SRTM-DEM datasets covering the Hammash and the Wadi Fatimah areas in Egypt and the Kingdom of Saudi Arabia, respectively. Field validation in the Hammash area confirmed the RFC model's efficacy, achieving a satisfactory 94% overall accuracy for 18 features. SHAP was able to identify the top ten features for proper LD over the Hammash area with 90.3% accuracy despite the complex nature of the ophiolitic mélange. For validation purposes, RCF was then utilized in the Wadi Fatimah region, using only the top 10 critical features rendered from the SHAP analysis. It performed well and had 93% accuracy. Notably, XAI/SHAP results indicated that elevation data, Landsat-8's Green Band (B3), and the two ASTER SWIR bands (B5 and B6) were essential and significant for identifying island arc rocks. Moreover, the SHAP model effectively delineated complex mélange matrices, primarily using ASTER SWIR band (B8). Our findings highlight the successful combination of RFC with XAI for LD and its potential utilization in similar arid crystalline environments worldwide.

The influence of major faults and fractures on the development of non-matrix porosity system in a pre-salt carbonate reservoir, Santos Basin – Brazil

Faults and fractures are central for characterizing the permeability distribution in carbonate reservoirs since they act as pathways for diagenetic fluids that often favor intense rock dissolution and permeability. Usually, high permeability zones and fractures are not easily recognized in seismic data due to limited resolution and they are often associated with higher concentrations of hydrocarbons or even significant fluid losses during drilling, thus creating a challenge for hydrocarbon exploration. In the Santos Basin, southeast Brazil, the pre-salt carbonate reservoirs from the Barra Velha Formation (BVE) are the main hydrocarbon producers in Brazilian Atlantic margin and well-known for being extremely heterogeneous, exhibiting complex dual-porosity systems. In this study, we built a conceptual model of these fracture zones and non-matrix porosity formation that helped narrowing the understanding of these complex systems. The characterization of faults and fractures was carried out using seismic, well-logs, and borehole image data to understand the influence of these structures in the porosity formation along the Barra Velha Formation. In the study area, three fault sets were defined (F1, F2, and F3) from seismic data. F1 represents to the larger faults, while the F3 fault set represents the smaller faults related to the reactivation of F1; both sets being oriented NE-SW. The F2 fault set is associated with the rift formation and is oriented to NNE-SSW. These three fault sets compartmentalized the studied area into different domains, each exhibiting distinct fracture sets. The natural open fractures were formed during the reactivation of rift faults and are oriented mainly NW, NNE-NNW, NE, and ENE and were identified across the entire study area, but with different intensity values. The fracture intensity closely relates to the distance from major faults where the wells with the highest fracture intensity occurs located 150–590 m from the larger F1 fault set. Scan-lines were conducted throughout the area to determine the fault width, and an average value of 1.2 km was established. Seven non-matrix porosity classes were characterized and classified into stratigraphically concordant and discordant non-matrix pore types at well scale through borehole image interpretation. The Barra Velha Formation exhibit higher occurrence of stratigraphically discordant non-matrix porosity related to fractured zones while stratigraphically concordant non-matrix porosity is mainly controlled by the paleotopography of the study area. Overall, non-matrix porosity formation tends to follow an orientation that suggests a preferential dissolution flow towards NE and ENE directions. Intervals with higher silica content shows a positive correlation with both fracture intensity and stratigraphically discordant non-matrix porosities. This work provides a conceptual model about the fractures and non-matrix porosity distribution in pre-salt carbonate rocks that can help address some of associated structural and stratigraphic uncertainties during field appraisal and development.

Wear load analysis of conical cutter crushing rock based on SPH to SPH interaction method

Wear is the main failure type for conical cutters. The main load causing its wear is difficult to measure in the test, and the existing simulation models cannot simulate the wear load. Thus, the three-dimensional dynamic model for conical cutter crushing rock is established based on the SPH-SPH interaction method to analyze the relationship between the cutting performance factors and cutter wear. The factors are taken into account such as the stress distribution of rock, kinetic energy and internal energy and displacement of rock, cutting load of cutter, stress of cutter. Then, it is studied that the effect of cutting angle on the cutting performance parameters such as specific energy consumption, rock avalanching, cutting load, load fluctuation, cutter tip stress and cutter side stress. Finally, the cutting angle selection reference of the cutter is given under different consideration factors.

ANALYSIS OF GRANITE ROCK WEATHERING IN THE PARMONANGAN AREA USING LANDSAT 8 SATELLITE IMAGERY

A research has been conducted to analyze the weathering of granite rocks in the Parmonangan area using Lansat 8 satellite imagery which aims to determine the distribution of rocks, weathering processes, and types of rock forming elements in Parmonangan District, North Tapanuli Regency. The method used is using shp geologic map data and Lansat-8 image data processed using Arcgis Map 10.6.1 to determine the distribution of rocks and land cover. XRF is used to identify compounds and rock-forming elements. The results obtained by the rock distribution of the parmonangan area are in the form of the Kluet Formation, Sibolga Complex and Toba Tuff. Land cover in the parmonagan area has differences from 2016 to 2024. Open land in 2024 has increased and the cloud cover obtained has also increased. The rock elements found are Al2O3 (25.31), SiO2 (24.97), K2O (1.56), TiO2 (0.81), Mn2O (30.66), Fe2O3 (4.66), ZrO2, (0.21), Sb2O3 (0.16), and BaO (0.17).

Impact of Tethyan domain evolution on the formation of petroleum systems in the Sichuan super basin, SW China

Based on the “unidirectional break-up and convergence” geodynamic model, this study investigates the impact of the evolution of the Tethyan domain on the formation of petroleum systems in the Sichuan super basin and explores the enrichment pattern of natural gas. The results show that, firstly, the Sichuan Basin and its surrounding areas have experienced two unidirectional rifting-aggregation cycles triggered by the Proto-Tethys Ocean and the Paleo-Tethys Ocean during the Neoproterozoic to Triassic. During Jurassic–Cenozoic, the Sichuan Basin is incorporated in the circum-Tibetan plateau basin-mountain coupled tectonic domain system. The episodic tectonic movements within the plate control the sedimentary infill styles. Second, the evolution of the Tethyan domain, paleoclimatic environment and major geological events controlled the formation and distribution of high-quality source rocks within the basin. The rift valley and intracratonic rift, passive continental margin slope, and intracratonic sags are favorable areas for the development of source rocks. Third, the evolution of the Tethyan domain, supercontinent cycles, global sea level changes, and tectono-climatic events controlled the distribution of carbonate platform and reservoir-caprock combinations. The cratonic platform margins and sub-platform internal high terrains are key areas for finding carbonate high-energy facies belts. Syndepositional paleo-uplifts and surrounding slopes, regional unconformities, and later faults zone are areas where large-scale carbonate reservoirs are distributed. The regional evaporite or shale caprock are beneficial for the large-scale preservation of oil and gas in the basin. Fourth, the spatio-temporal matching relationship of reservoir forming factors influenced by the early tectonic-sedimentary evolution pattern and the degree of later tectonic modification is the key to oil and gas enrichment. Future oil and gas exploration should focus on potential gas systems during the Sinian rift period, Cambrian pre-salt gas systems in the eastern and southern Sichuan, as well as whole oil and gas systems of Permian and Triassic.

Detección de roca intrusiva alterada mediante tomografía de resistividad eléctrica: El caso del área de San Luis, zona central de Panamá

This work investigates the potentiality of the 2D electrical resistivity tomography method to delineate an altered intrusive rock domain. The detection and characterization of such altered domains are crucial to understanding local hydrogeological conditions. Here, the target is the San Luis area, located in the northern part of the Estibaná River watershed, within the Los Santos Province in the central region of the Isthmus of Panama. First, a detailed geological survey was carried out to better constrain the tectonic structures. Then, two geological sections were developed based on two 2D electrical resistivity tomographies. A geoelectrical simulation process was conducted in both sections to set theoretical models whose model responses (synthetic field data set) would be consistent with the observations. After appropriate selection of the inversion parameters by using the Boundless Electrical Resistivity Tomography (BERT) code, the observations were processed, resulting in low calculation errors (2 < 0.51). Based on the superficial geological information and the results of the geophysical modelling, two profiles were established, depicting the lateral and in-depth distribution of rocks and sediments. The limit of the Ocú-Parita fault zone was identified as well. The results of the 2D inversion of the synthetic data, obtained with the established theoretical models, are consistent with the 2D inversion of the observations. Electrical resistivity tomography studies can be useful in establishing groundwater management models, particularly in areas that experience severe water scarcity during the dry season.

Prototypical basin reconstruction and evolutionary models for the Precambrian of the Qinshui Basin, North China craton

The thick Precambrian strata in the Qinshui Basin (QB) have high potential for hydrocarbon exploration. Tectonic evolution restoration and prototype basin reconstruction are key to hydrocarbon exploration and evaluation for Precambrian strata. We studied the 2D/3D seismic data and Precambrian field outcrops of the QB to elucidate its geological attributes, major regional unconformities, tectonostratigraphic framework, tectonic evolution and prototype basin. The Precambrian strata of the QB are the sedimentary products of the continuous transgression from south to north and are more appropriately attributed to the Xiong'er Aulacogen in the Changchengian and Jixian periods. We identified six regional unconformities: the Archean or Palaeoproterozoic/Xiong'er Group, the Xiong'er Group/Chy, Chc/Chl, Chl/Jxl, the Jxl/Cambrian System, and the Ordovician/Carboniferous. Seven tectonostratigraphic units can be delineated: the Archean–Palaeoproterozoic, Xiong'er Group, Yunmengshan–Cuizhuang, Luoyukou, Jixian, Cambrian–Ordovician, and Carboniferous–Triassic tectonostratigraphic units. The tectonic evolution was divided into seven stages: the formation and evolution of the basement (∼1800 Ma), the synrift stage in the Xiong'er period (1800–1720 Ma), the postrift stage in the Yunmengshan–Luoyukou period (1720–1600 Ma), the passive continental margin basin stage in the Jixian period (1600–1400 Ma), the marine craton stage during the Cambrian–Ordovician (542–440 Ma), the marine–continental transitional–continental craton stage during the Carboniferous–Triassic (316–200 Ma), and the intense deformation stage (200–0 Ma). Three stages of prototype basin models of the Precambrian in the QB have been reconstructed: (1) In the synrift basin model, numerous normal faults have developed, and the section shows a symmetrical composite graben. The topography in the south is low, that in the north is high, and the northeast and northwest areas are palaeo-uplifted. A set of volcanic rocks with coarse-grained clasts was deposited. (2) In the postrift basin model, the fault activity weakened, and the depositional range became larger than that of the synrift stage, and a set of marine clastic–carbonate rocks was deposited showing a gradual coarsening–upwards trend. (3) In the passive continental margin basin model, the fault became almost inactive, the topography was low in the southeast and high in the northwest, and the depositional area was more widespread, resulting in a set of marine carbonates. These results contribute to a better understanding of the break-up process of the Columbia supercontinent and the Precambrian evolution of the North China Craton (NCC) and can be used to predict the distributions of source rocks and hydrocarbons.

Determining pore size distribution in rocks using shear‐thinning fluids: Utilisation of the method in geomorphology

AbstractThe pore space characteristics of geological materials are closely related to their mechanical, transport and hydraulic properties. In geomorphology, pore size distribution (PSD) is an important characteristic in rock weathering, evaporation and other studies. In an effort to find novel methods to determine the PSD, perhaps to bypass the disadvantages of the current techniques, there has been a growing interest in the use of non‐Newtonian fluids. In this contribution, we are particularly interested in the method recently introduced by Abou Najm and Atallah (the ANA method), which exploits the way in which the flow of different shear‐thinning fluids distributes differently in the pore space to compute the functional PSD estimation. We performed a set of saturated flow experiments with aqueous xanthan gum solutions of different concentrations, using as simple as possible laboratory settings, and we implemented a modified version of the previously introduced numerical model to obtain the PSDs of four sandstone and one tuff samples. The results are compared with conventional mercury intrusion porosimetry, showing a good agreement regarding the dominant pore size and a notable similarity in the distributions. Several limitations were identified as well, such as the lack of information on relatively small pores (<5–10 μm for the samples studied) and the potential issues in obtaining a more detailed distribution. We conclude that the ANA method is promising for geomorphological evaporation and rock durability studies, particularly for coarser materials such as sandstone, but it also encounters challenges for certain applications, especially for fine‐grained rocks. It must be acknowledged that the ANA method has been tested on a limited range of materials and further investigation is required to fully explore its capabilities and limitations.

Compositional diversity of late Mesozoic granites rooting from the subducted crust in the Qinling–Dabie orogenic belt

Continental subduction has been identified in many orogens, such as the Alps, the Himalayas, and the Dabie; however, better understanding of the mechanism and outcome of different subduction processes remains desirable. The Qinling–Dabie orogen in Central China shows an asymmetric distribution of Triassic ultrahigh-pressure metamorphic rocks and syn- and post-tectonic granitoid plutons, thereby providing an excellent means by which to probe the diverse processes of continental subduction. Many late Mesozoic granitoid plutons that formed in post-orogenic or even anorogenic settings are widely distributed in both the Qinling and Dabie tectonic units and can be useful for studying the composition of materials beneath the crust because of their conspicuous compositional diversity. In the present study, we report zircon ages and NdHf isotopic compositions for the Shangcheng and Heyu granite plutons, which represent late Mesozoic plutons in Dabie and Qinling. When compared with those of the Shangcheng pluton, the wide range of Nd isotopic values and the slightly depleted Hf isotopic compositions of the Heyu pluton indicate that there may be juvenile crust beneath the Qinling tectonic unit that is not present beneath the southern margin of North China. The currently undetectable juvenile material in this region may be an important candidate source of the late Mesozoic magmatism and metal mineralization in the southern margin of North China. The compositional diversity of these granites, as indicated by the NdHf isotopic compositions, is attributed to the nature of the deep crust within the orogenic belt, and the magmatic origins of this region are discussed in the present study.