Acta Geologica Sinica ‐ English Edition最新文献

Twelve new dinosaur teeth have recently been recovered from three localities in the Upper Cretaceous Nenjiang Formation of the Songliao Basin. Although fragmentary, the material offers enough evidence to identify the following taxa: tyrannosaurids, dromaeosaurines, velociraptorines, hadrosauroids, and titanosaurs. In addition to the previously known dinosaurs from the basin, several new ones have been identified, extending the paleogeographic range of related taxa. The discovery of these new fossil remains provides valuable insights into dinosaur diversity and sheds light on the terrestrial ecosystem during the Late Cretaceous in the Songliao Basin.

Recent exploration has highlighted the critical role of strike-slip faults in shaping ultra-deep carbonate reservoirs in the Tarim Basin. This study integrates satellite imagery, UAV photogrammetry, outcrop surveys and microscopic analysis to investigate the architecture of these faults and their impact on reservoir petrophysical properties. The strike-slip faults exhibit cores consisting of calcite bands, fault breccias and fractures, while the damage zones are predominantly fractured. Thicker fault cores and fault zones are associated with more extensive reservoir development. Individual strike-slip fault zones are primarily characterized by two sets of fractures intersecting the fault at small angles. When two fault systems interact, the dominant pattern is two sets of fractures intersecting the main fault at small angles and one set at larger angles, facilitating the formation of large-scale reservoirs. We propose a model for the fault core, which primarily consists of a calcite band and fault breccias. These breccias are composed of original host rock, calcite cement and quartz, which exhibit poor physical properties, while fractures and vugs show favorable reservoir characteristics. This model offers valuable insights into the development of fault-controlled reservoirs, particularly in the Tarim Basin.

The Barud gneissic dome complex is situated along the ENE-trending dextral shear zone of the Qena–Safaga Line that serves as a significant tectonic boundary between the basement terrains of the Northern and Central Eastern Desert. These terrains exhibit distinct differences in crustal composition and deformation style. The Northern Eastern Desert and its extension into Sinai are predominantly composed of gneissic granites that are intruded by large batholiths of calc-alkaline and alkaline granites. Conversely, the Central and Southern Eastern Desert are commonly blanketed by a carapace of ophiolite-bearing volcano-sedimentary rocks of the Pan-African cover nappes. These northern terrains, just north of the Barud dome complex, the crust underwent significant NW–SE regional crustal extension across the Qena–Safaga Line, which sharply delineates the northern limit of the transpressional deformations linked to the Najd fault system in the Central and Southern Eastern Desert. Through comprehensive geological mapping and the integration of various geophysical, geochemical and geochronological data, this paper offers explanations for the contrasting geological features of the basement terrains on both sides of the Qena–Safaga Line and its analogous Fatira Shear Zone that plays a significant role in tectonic modeling of the Barud dome complex region. The Barud gneissic protolith experienced crustal shortening approximately 697 million years ago in the NW–SE direction, initiating dextral motion along the Fatira Shear Zone. Large batholiths of granodiorite/tonalite complex intruded the Barud gneissic dome protolith around 630 million years ago along the Qena–Safaga Line, at relatively shallow crustal depths, following the same orientation as the earlier shortening direction. Ongoing magmatic activity along the Qena–Safaga Line indicates intense magmatic underplating, resulting in significant intrusions of granodioritic melts into the early rifted crust of the Northern Eastern Desert and Sinai terrains. The crust of these northern terrains likely underwent isostatic compensation through uplifting and subsequent erosion. The disappearance of ophiolite-bearing belts and the presence of Paleo- to Mesoproterozoic continental-derived cobbles and ignimbrites in Sinai metasedimentary belts and Northern Eastern Desert molasse basins suggest that the northern terrains, located north of the Qena–Safaga Line, originated as a cohesive, thin continental crust that rifted off the eastern passive margin of the Sahara Metacraton during the early Neoproterozoic rifting of the Rodinia supercontinent.

Numerous intermediate to felsic igneous rocks are present in both subduction and collisional orogens. However, porphyry copper deposits (PCDs) are comparatively rare. The underlying factors that differentiate fertile magmas, which give rise to PCDs, from barren magmas in a specific geological setting are not well understood. In this study, three supervised machine learning algorithms: random forest (RF), logistic regression (LR) and support vector machine (SVM) were employed to classify metallogenic fertility in southeastern Tibet, Sanjiang orogenic belt, based on whole-rock trace element and Sr-Nd isotopic ratios. The performance of the RF model is better than LR and SVM models. Feature importance analysis of the models reveals that the concentration of Y, Eu, and Th, along with Sr-Nd isotope compositions are crucial variables in distinguishing fertile and barren samples. However, when the optimized models were applied to predict the datasets of Miocene Gangdese porphyry copper belt and Jurassic Gangdese arc representing collision and subduction settings respectively, a marked decline in metrics occurred in all three models, particularly on the subduction dataset. This substantial decrease indicates the compositional characteristics of intrusions across different tectonic settings could be diverse in a multidimensional space, highlighting the complex interplay of geological factors influencing PCD's formation.

The present-day pressure pattern is the ultimate result of the evolution of paleo-pressure, so understanding the variation of stress throughout geological history is of great significance for oil and gas accumulation. In this study, the fission track method was used to reconstruct the cooling history of sandstone samples from the Yanchang Fm. in the central–eastern Ordos Basin and the cause of the low-pressure anomaly in the Yanchang Fm. was analyzed. The max. burial depth pressure was reconstructed and the pressure evolution of the formation in the Futan 1 well was simulated, using Petromod 1D. The fission track data and Petromod 1D simulation results indicate that the Yanchang Fm. reached its max. burial depth and experienced a high paleo-pressure of 30.92 MPa at around 100 Ma. Since the Late Cretaceous, the formation pressure evolution in the study area can be divided into two stages. From 100 to 20 Ma, the formation slowly uplifted, with the pressure gradually decreasing. Since the Miocene (about 20 Ma), the pressure rapidly decreased to the current pressure of approximately 6.92 MPa. Based on the above research results, the influence of pore rebound and temperature decrease on formation pressure was quantitatively calculated. The results show that during the first stage, the pressure reduction caused by pore rebound and cooling was 3.86 MPa and 3.49 MPa, respectively, with a decrease of about 12.48% and 11.28%. During the second stage, the pressure reduction caused by pore rebound and cooling was 6.32 MPa and 9.60 MPa, respectively, with a decrease of about 20.43% and 31.04%. The formation of low pressure in the Yanchang Fm. in the central and eastern basin is mainly controlled by pore rebound and temperature reduction, caused by erosion after stratigraphic uplift. The decrease in temperature plays a decisive role in determining the formation process of the low-pressure oil reservoir.

The SiO₂'–CaO/(CaO + K₂O) (S'CK) diagram is an empirically derived major element-based equivalent to the modal IUGS alkali feldspar–quartz–plagioclase classification scheme for granitoids. It employs the content of SiO₂ and CaO/(CaO + K₂O) ratio to approximate the IUGS classification diagram and a normative-based Q'–ANOR plot. Four trends have been superimposed onto the SiO₂'–CaO/(CaO + K₂O) diagram based on published datasets from the Peninsular Ranges (calcic: C), Tuolumne (calc–alkalic: CA), Sherman (alkali–calcic: AC), and Bjerkreim-Sokndal (alkalic: A) batholiths, which were employed to constrain the positions of the C–CA, CA–AC and AC–A suite boundaries on the SiO₂ versus (Na₂O + K₂O – CaO) (or modified alkali–lime index, MALI) granitic classification diagram. A merit of the SiO₂'–CaO/(CaO + K₂O) plot is identifying rock types comprising a suite and their relative abundances. The distinguished projections of five typical granitoid assemblages, which are summarized by Bonin et al. (2020), demonstrate the ability of SiO₂'–CaO/(CaO + K₂O) diagram to decipher their petrogenesis. The SiO₂' –CaO/(CaO + K₂O) plots for the plutonic suites of ‘known’ tectonic settings can reveal their evolution paths and the lithological statistics. Accordingly, it is suggested that the SiO₂'–CaO/(CaO + K₂O) plot can distinguish the tectonic environments of plutonic suits by comparing the plutonic suites or batholiths of ‘unknown’ tectonic context to the published datasets from granitoid suites formed within ‘known’ tectonic settings. The modified SiO₂'–CaO/(CaO + K₂O) diagram links the bulk chemical composition of granitoid suites to the likely source, magmatic evolution, and tectonic setting; thus, it may be a useful tectono-magmatic classification scheme for granitoid suites.

The water conductivity of karst collapsed column is affected by multiple factors such as the characteristics of its own column filling, structure and mining disturbance. As a structural water-conducting channel, fault usually plays a controlling role in hydrogeological structure. During the process of mine water hazard prevention and control, it was discovered that the lithology composition, compaction and cementation degree and water physical properties of karst collapsed column fillings were all non-conducting water, but due to the influence of combined development faults, some exploration drill holes showed concentrated water outflow. Based on this, the scientific hypothesis was proposed that fault cutting leads to water conduction in karst collapsed columns. The study comprehensively used methods like chronology, exploration data analysis, and hydrochemical testing to analyze the chronological relationship between faults and karst collapsed columns, their spatial relationship, outlet point distribution and water chemical properties, and the impact of faults on the water-conductivity of karst collapsed columns, which proved the effect of fault cutting on changing water conductivity of karst collapsed column. The research showed that later fault cutting through karst collapsed columns turned the originally non-conductive karst collapsed columns into water-conductive collapsed columns at the fault plane, creating a longitudinally connected water-conducting channel. A new model of fault cutting karst collapsed column to change the original water conductivity of karst collapsed column was proposed. The research results can provide a theoretical basis for the prediction of the water conductivity of the karst collapsed column. According to whether the karst collapsed column was cut by the fault, it was predicted theoretically, so as to determine the key areas of water conductivity detection and prevention and control, and has broad application prospects under the background of source control of mine water disaster.

The Upper Cretaceous successions of Wadi Umm-Khayshar, southern Galala Plateau, North Eastern Desert, Egypt, are composed of highly diversified faunas and subdivided from base to top into the Galala (Middle–Late Cenomanian), Maghra El Hadida (Latest Cenomanian–Late Turonian), Matulla (Coniacian–Santonian), and Sudr (Campanian–Maastrichtian) formations. Five ammonite biozones are recorded in the studied section: Neolobites vibrayeanus, Vascoceras cauvini (late Cenomanian), Vascoceras proprium, Choffaticeras segne, and Coilopoceras requienianum (Turonian) zones. The paleoenvironments of the Upper Cretaceous succession are interpreted based on detailed study and microfacies analysis that reflect a deposition in a homoclinal ramp platform ranging from intertidal to deep subtidal. The paleoecology of the Cenomanian–Turonian succession in the studied section is explained based on a detailed study of macrofaunal associations and sedimentary facies. Quantitative analysis (Q-mode cluster analysis, using the Raup–Crick Paired group method) of 1029 macrobenthic specimens, including 45 species of mollusks and echinoids yielded five macrofaunal associations (A–E) that are described and interpreted as remnants of communities. The nektonic elements are represented by 235 cephalopod specimens of 20 species; heatmap cluster analyses show the distribution of these specimens during the Upper Cenomanian–Turonian stages. Environmental parameters (substrate consistency, rate of sedimentation, water energy, surface-water productivity, and oxygen availability) controlled the distribution of the studied macrofauna. The five associations are divided into two major groups: low-stress associations (A, B, C, and D), and a high-stress association (E). The low stress associations are recorded from two different habitats: (1) a high-energy, firm substrate habitat, dominated by epifaunal bivalves, large epifaunal gastropods and a regular echinoid; (2) a low-energy, soft substrate habitat dominated by infaunal bivalves and echinoids. The high stress association is dominated by only two species and recorded from a high-energy shoal environment during a regression phase. A detailed study of macrobenthos and cephalopods provides a good paleoecological understanding of Cenomanian–Turonian succession in the Wadi Umm–Khayshar section.

Large basins are currently the global focus for geothermal development, with their hydrothermal system being controlled by a variety of factors, such as basement relief and fracture development. Donglihu is located at the north of the Cangxian uplift in the North China Basin, the concentrated geothermal resource development zone in North China. This study systematically collects temperature logging data and long-term dynamic monitoring of water level and water quality as well as group well tracer test data carried out in this area in recent years, on the basis of which the hydrothermal controlling role of the deep hidden faults is systematically analyzed. The results show that the Cangdong fault communicates with different geothermal reservoirs in the shallow part and plays a specific role in the water-heat channel of the local area. As a result, the high-value area of the geothermal temperature gradient in the sedimentary layer of the Donglihu area is distributed around the Cangdong fault. The geothermal reservoir temperature of the Minghuazhen Formation within the influence of the fault is also significantly higher than the regional average, the hydraulic head of different geothermal reservoirs showing a consistent and synergistic trend. However, the water quality has been stable for many years without any apparent changes. This understanding has a particular significance for further deepening understanding of the geothermal genesis mechanism in sedimentary basins and guiding future geothermal exploration and development in the Donglihu area.

Controlled by fluctuating paleoclimates and sedimentary environments, the organic and inorganic features of the Lucaogou Formation exhibit strong heterogeneity in the vertical profile, challenging conventional geological interpretation. To elucidate the possible influence of heterogeneity on resource evaluation, a high-resolution sampling approach was applied to an 86.2 cm long core from the Lucaogou Formation of the Jimsar sag in the Junggar Basin. 86 sets of samples were micro-drilled from the core and subjected to comparative Rock-Eval pyrolysis. Following the classical guidelines, the organic abundance, kerogen type, and maturity of source rocks were exhaustively analyzed. Experimental results revealed that organic richness and composition vary significantly under different sedimentary backgrounds, which in turn leads to differential hydrocarbon generation. The combination of hydrocarbon generation, transport, and expulsion results in peculiar patterns for hydrocarbon accumulation in the Lucaogou Formation. Laminated shales in the Lucaogou Formation serve as both hydrocarbon source rocks and reservoirs, with laminae being migration pathways. Organic-rich dolomites in the Lucaogou Formation have a considerable hydrocarbon-generating capacity and present the characteristics of self-generation and self-storage. However, massive mudstones act purely as hydrocarbon source rocks.