Geological Journal最新文献

Plutonic rocks typically have negligible matrix porosity and permeability. However, fractures and mineral alterations create storage space and flow pathways that turn plutonic rocks into fluid reservoirs. Despite significant hydrocarbon discoveries, naturally fractured reservoirs in plutonic rocks have been poorly studied. In most Colombian basins, the crystalline basement has undergone multiple deformational events and is thrust over the Cretaceous to Cenozoic source and reservoir rocks of the conventional petroleum system. This structural configuration is ideal for the migration of oil into a fractured basement. A multiscale fracture analysis, including field, petrographical and petrophysical techniques was conducted on the Permian and Jurassic plutonic basement of Upper Magdalena Basin in order to understand the controls on brittle deformation, the development of fracture networks and their potential to form hydrocarbon reservoirs. The results indicate that protolith textures and structures, including magmatic and mylonitic foliation, favours fracturing. Dykes exhibit higher fracture density (7–48 fractures/m), porosity (mean = 0.4%) and permeability (mean = 125,818.75 mD) than the host rock (2–25 fractures/m; 0.23%; 12,066.09 mD). Intersection zones from regional faults, are characterized by the highest fracture and lineament intensity. Our results suggest that dyke swarms and interacting damage zones can significantly enhance the reservoir quality of plutonic rocks by providing storage in fractures and fluid pathways to the host rock.

Quantitative calculation of single landslide risk has great significance for the prevention and treatment of landslides, through analysing the slope stability under different rainfall recurrence periods. In this study, the rainfall of the past 40 years in Xun'wu County of China is counted and the rainfall during the return periods of 10, 20 and 50 years are calculated to form three different rainfall conditions. Then, the stability of Cheng'nan landslide in Xun'wu County is calculated by the Geo-Studio 2007 software, and the probability of landslide occurrence is obtained by Monte Carlo theory under these three conditions. Next, the field investigation is employed to obtain the statistical results of the buildings and personnel in the affected area of Cheng'nan landslide. Finally, the risk of economic loss and casualty under the three conditions are calculated. It was demonstrated that: (1) Under the three conditions, the safety factor decreased gradually, the rate of decrease was slower in the first 3 days and faster in the middle period and there was still a downward trend after the end of the rain. (2) The probability of landslide occurrence during the rainfall return periods of 10, 20 and 50 years were 1.77%, 2.97% and 1.61%, respectively. Besides, the risk index of landslide was the highest under the condition of 20-years rainfall return period. (3) The economic loss risk and casualty risk in the rainfall return periods of 10, 20 and 50 years were 122,700-yuan and 4.11 people, 205,900-yuan and 6.89 people, as well as 11,600-yuan and 3.74 people, respectively.

The N-S oriented Zindapir anticline is an eastward verging mega-structure (~130 km along and ~40 km across the strike) in the eastern Sulaiman fold-and-thrust belt on the western margin of the Indian Plate in Pakistan. In this study, we carried out a lineament analysis of the anticline based on shuttle radar topographic mission (SRTM) images and digital elevation model (DEM) data to demonstrate the application of this technique for modelling of the fractured reservoirs. We used shaded relief images, variations in the vertical exaggeration, sun and azimuth angles to enhance the DEM data and structures in the area. Stereographic projections indicated that the anticline is an upright, asymmetrical, gentle, doubly plunging and east-vergent fold. The synthesized lineament map of the fractures indicates a total of 402 fractures across the Zindapir anticline. A total of 204 and 198 fractures were observed in the eastern and western limbs, respectively. Statistical analysis portrayed that the lineaments of the majority of fractures followed northwest-southeast (NW-SE) and west-northwest—east-southeast (WNW-ESE) trends. These are oblique or transverse to the fold axis and could be interpreted as shear and tensional fractures related to drag and compression along the western boundary of the Indian Plate. Our study provides an example of lineament analysis for structural characterization and modelling of fractured reservoirs in a collision-mountain setting.

Geochemical analysis was performed on the Cretaceous sequence of the Azhar-A-2 well in the West Beni Suef Basin (WBSB), Western Desert, Egypt, utilizing data on total organic carbon (TOC), kerogen composition, vitrinite reflectance (Ro%) and Rock-Eval pyrolysis. In addition, a 1D basin model was built to investigate the burial and temperature history of the study area. The most important Cretaceous source rocks are predominantly reported within the Albian Kharita Formation and Late Cenomanian-Santonian Abu Roash (AR) Formation. Based on visual kerogen tests and Rock-Eval pyrolysis, AR Formation (A, E, F, and G) are mixed oil- and gas-prone source rocks with kerogens ranging from type II to type III, where A/R ‘A and F’ Members show dominant oil-prone kerogen with the highest generative potential, while A/R ‘E and G’ Members are more gas-prone kerogen. Most samples of the lower Kh Formation were interpreted as gas-prone kerogen type III with low generative potential. On the other hand, the high amount of liptinite in the visual kerogen macerals is a strong indicator that the lower Petroleum Formation is an oil-prone rather than gas-prone source rock. The thermal maturity of the studied members increases consistently with depth, ranging from immature at the top of the AR Formation to the main/peak oil window at the base of the Lower Kharita Formation, which served as an active source rock for the hydrocarbons generated in the WBSB. The high value of the heat flow in the Beni Suef Basin (57 and 60 mW/m²) is a good indicator for the shallowing of the active source rock depth limit depth. From the study of the basin modeling, the main mature zone reached between 9811 and 11,090 ft in the middle of the Late Cretaceous (84.3–82.5 Ma) is through the L. Kharita Formation with three phases of hydrocarbon generation according to transformation ratio, where the second phase is the main stage in which TR is 5%–50%, showing the beginning of oil expulsion (Ro: 0.73%–0.78%, possibly 0.81%).

The Weishancheng area of Tongbai County, Henan Province, is an important Au-Ag polymetallic ore concentration area in China, characterized by a widespread distribution of plutons and frequent magmatic activities. To investigate the genetic relationship between magmatism and the mineralization of gold and silver polymetallic deposits in the area, this study focuses on the porphyritic monzogranite of the Liangwan pluton and the biotite granite of the Taoyuan pluton in detail. The zircon U-Pb age of the Liangwan pluton is 128.5 ± 0.7 Ma, placing its intrusion age in the Early Cretaceous. Similarly, the zircon U-Pb age of the Taoyuan pluton is 431.3 ± 2.7 Ma, indicating an intrusion age in the Early Silurian. Petrogeochemical analysis reveals that both the Liangwan and Taoyuan plutons exhibit high SiO₂, Na₂O and Al₂O₃ contents, along with low MgO, Fe₂O₃ and CaO contents, indicating a (high-K) calc-alkaline series, and have the properties of peraluminous I-type granite. The total rare earth elements (REE) concentrations are low, with noticeable fractionation between light and heavy REE, and a negative Eu anomaly. High-field-strength elements (such as Nb, Ta, P, Ti) are depleted, while the large-ion lithophile elements (such as Rb, K, Pb) are enriched. The ε_Hf(t) values of the Liangwan and Taoyuan plutons range from −16.1 to −18.8 and from 11.0 to 14.6, respectively. The mean values of Hf two-stage model ages (T_DM2) are 603 Ma and 2230 Ma, respectively. These results suggest that the Liangwan pluton may have formed through partial melting of ancient crustal materials in the Palaeoproterozoic, during extensional tectonic events following the subduction of Izanagi Plate. It appears closely linked to Au-Ag mineralization in the ore concentration area. The Taoyuan pluton likely originated from the depleted mantle and experienced some degree of crustal contamination. However, it is unrelated to regional mineralization.

This study takes the tight sandstone of the lower sub-member of the first member of the Eocene Shahejie Formation (Es₁^x) in the Suning area, Raoyang Sag, Bohai Bay Basin. Furthermore, it determines the rock type of the middle-deep tight sandstone through lithologic profiling, core observation and log data analysis. The genetic control factors of tight sandstone in the study area are analysed using conventional thin section, pore-casted thin section and scanning electron microscope, and the characteristics and genetic control factors of tight sandstone reservoirs are summarized. The research results show that the tight sandstones in this area are primarily feldspathic sandstone and feldspathic lithic sandstone, with high quartz contents, around 61.50%. The average porosity of the reservoir in the study area is 4.69%, and the average permeability is 2.92 mD, which are characteristics of low-porosity and low-permeability reservoirs. Through research, it has been found that the distribution of sedimentary facies and diagenesis in the study area control the development and distribution of ‘sweet spots’. Both compaction and cementation reduce the physical properties of the reservoir, while dissolution can increase porosity, thereby increasing the physical properties of the reservoir; dissolution resulted in an increase of approximately 3.57%–3.69% in the porosity of the tight reservoir in the study area, with an average porosity increase of 3.63%, and is the main controlling factor for the development of ‘sweet spots’ in the reservoir. The results provide an important basis for guiding the exploration and development of tight sandstone oil and gas in the lower sub-member of the first member of the Eocene Shahejie Formation (Es₁^x)in the Suning area.

The crystal-poor rhyolitic pumice is the product of extreme magma differentiation and is characterized by highly vesicular, honeycomb-like structure. However, little is known about the evolutionary history and the time of volatile saturation of the pumice-forming melt. A crystal-poor rhyolitic pumice (TVG7-1) has been collected from the Yoron Hole hydrothermal field in the middle Okinawa Trough, a young continental margin back-arc basin in the western Pacific. This study conducted a detailed analysis on the texture and in situ chemical composition of plagioclase, orthopyroxene and Fe-Ti oxides to reveal the evolution process, storage state and eruption triggers of eruptible silicic melt. Texture and zoning of specific minerals and mineral populations suggest a magmatic evolution history of open system. Additionally, the hollow reentrant texture, as well as results from plagioclase-liquid hygrometers, confirm a water-rich melt pocket. The exsolution of volatiles (H₂O, etc.), in this melt pocket, will contribute to local oxidation conditions, which may have been recorded by the concordant behaviour of FeO and An in plagioclase. Then, the overpressure caused by volatile exsolution would destabilize the magma chamber, which will eventually be broken by magma mixing/recharge, and lead to violent melt evacuation. Consequently, crystal size distribution (CSD) provides a new perspective on understanding the kinetic effect of magma mixing/recharge in the Okinawa Trough, especially on the mineral populations. Our study reveals the petrogenesis of crystal-poor rhyolite within the framework of the mush model, refines the magma evolution history and demonstrates that pumice magma reaches volatile saturation before the eruption.

Environmental sustainability is essential to the country's financial position and economic growth. Geopolitical situations and green activities significantly contribute to enhancing sustainable development goals. The purpose of this study is to evaluate the impact of green finance, investment in renewable energy sources and geopolitical risk on the environmental sustainability of the Middle East and North America (MENA) region over the period 2000–2021. When using a cross-sectional dependence autoregressive distributed lag model (CS-ARDL), it is discovered that a rise in geopolitical risk will decrease environmental performance in the form of carbon dioxide emission. At the same time, the other factors (green finance and investment in renewable energy) have a positive relationship with sustainability. This observation can be ascribed to the association between increased geopolitical risk and the inclination of crude oil consumers, who are most affected by such risk, to contemplate renewable energy as an alternative to conventional energy sources. This finding could also be attributed to the fact that clean energy is becoming more affordable. In addition, the augmented mean group model findings provide more evidence that a negative linkage is found between geopolitical risk and environmental sustainability. The findings have repercussions for regulators as well as investors who are active in the renewable energy markets.

In the Dom Feliciano Belt, Brazil, the Pinheiro Machado Complex (PMC) includes diorites, tonalites, granodiorites, syenogranites and granites, whose evolution is related to several magmatic pulses and complex petrogenetic processes. Two magmatic stages were identified (early and late), resulting in different rock subgroups. The geochemical data showed that the early magmatism was chemically affected by partial melting. Geochemical modelling results suggest that fractional crystallization processes with assimilation of around 40% from the crustal basement and the decoupling of assimilated magma are crucial for the PMC rocks' genesis. Geochemical data also show that during the early magmatism, the subsequent process of early diorite anatexis developed by heating and continuous activity of the underlying magma chamber possibly occurred at a melting rate of 5%–10%. The hybrid rocks have contributions from the mixing process related to early terms, showing geochemical correlations in the major element curves, for the early diorite and syenogranitic melt members, at 60%–50% and 50%–40%, respectively. Slab failure tectonic context is related to the multi-intrusive events dynamics recorded in the studied rocks. Recharge and melting events of the recently formed crust due to the constant heating of new pulses of deep slab melting would explain the magmatic interactions observed in the Complex. The results demonstrate that the studied rocks crystallized in an open system, including mixing processes to form hybrid rocks, physical disaggregation and assimilation of early intrusions, truncation, dragging and erosion of early mushes by younger pulses.

Fluid diapirs are widespread in the northern South China Sea (SCS), are significant indicators of the existence and distribution of hydrocarbons and natural gas hydrates and are of great petroleum geological significance. Based on high-precision 3D seismic and drilling data, this paper analyses the tectonic features and genetic mechanism of a fluid diapir zone in the northern SCS and a development model of fluid diapirs is proposed herein. Studies have revealed that the northern SCS large-scale fluid diapir zone is located within a concealed structural transition zone, which is consistent with the spatial distribution location and direction of a concealed structural transition zone and that the formation of a fluid diapir zone is strongly influenced by the structural transition zone. Fluid diapirs are large continuously spreading bright reflection zones in shallow surface layers and are downwards converging high-variance ribbons in middle and shallow layers, all of which are spreading in a NW–NNW orientation on the plane. The profile shows a conical or mushroom-shaped shape that converges from shallow to deep, with a height of approximately 7 km and is characterized by a compound gas chimney fuzzy zone. The main body of the concealed structural transition zone is a slope structure and is flanked by large-scale NW–NNW-oriented fault systems. Minor en echelon spreading NW–NNW-oriented faults and fractures are developed within the structural transition zone and are soft linkages that match well with the distribution direction and location of the fluid diapirs. On the profile, the overall display is a composite flower-like structure dispersed from deep to shallow, which belongs to a large strike-slip fault zone with a tectonic transformation effect. A comprehensive analysis suggests that the formation and development of the structural transition zone are mainly controlled by pre-existing structures in the basement and that minor faults, fractures and slope zones within the structural transition zone serve as dominant pathways for the migration of deep overpressure fluids and gas hydrates. Consequently, the concealed structural transition zone provides favourable conditions for fluid diapirs to develop. Moreover, the stratigraphic overpressure systems mainly caused by gas generation provided the main driving force for the formation of fluid diapirs. Obviously, the development location, distribution direction, formation and evolution of the northern SCS fluid diapirs are jointly controlled by internal minor faults and fractures of the Eocene-Miocene structural transition zone and the overpressure of the rifting period after the Pliocene. The main development period of the northern SCS large-scale fluid diapirs was the second phase of the Dongsha Movement. During the exploration of gas hydrates and hydrocarbons in the Pearl River Mouth Basin, it is essential to consider the mutually restricting relationships between fluid diapir structures and gas hy