Geological Journal最新文献

The Kutch Basin of western India exposes one of the most complete, fossiliferous marine Cenozoic sedimentary sequences of India. Precise depositional ages of these sequences are of great importance in the reconstruction of palaeoclimatic and palaeobiogeographic histories of the basin. Due to the poorly constrained foraminiferal biostratigraphic ages, we conducted high-resolution ⁸⁷Sr/⁸⁶Sr chronology of the various fossiliferous, stratigraphically continuous units of Oligocene–Miocene strata in Kutch Basin. Besides updating the previously determined ⁸⁷Sr/⁸⁶Sr chronology, we report new numerical depositional ages for Oligocene–Miocene formations and members, and correlated these ages to the existing biostratigraphic schemes. The new ⁸⁷Sr/⁸⁶Sr data indicates a depositional age range between 28.64 + 0.29/-1.11 and 23.51 + 1.53/-1.85 Ma (Rupelian-Chattian) for the Maniyara Fort Formation, between 23.07 + 0.94/1.39 and 18.09 + 0.24/-0.57 Ma (Chattian-Burdigalian) for the Khari Nadi Formation, and between 15.11 + 0.56/-2.87 and 12.29 + 1.22/-1.9 Ma (Langhian-Serravallian) for the Chhasra Formation. The sedimentation rate, determined through numerical ages derived from ⁸⁷Sr/⁸⁶Sr, indicates an increase in sedimentation for the Khari Nadi (0.23 ± 0.04 cm/kyr) and Chhasra (0.12 ± 0.04 cm/kyr) formations, likely related to uplift of the Himalaya-Tibetan plateau and intensification of the Indian Summer Monsoon. The bulk sediment element ratios (V/Ni, Ni/Co and V/Cr) indicate oxic to suboxic palaeo-redox conditions during deposition of the Oligocene–Miocene successions of the basin. Based on new and updated ⁸⁷Sr/⁸⁶Sr chronology, the depositional environments and sedimentation rates of the Kutch sequence are correlated with changes in sea-level, sedimentation rates in the Arabian Sea and Bay of Bengal, and the global climate changes across the Oligocene–Miocene boundary.

The tectonic deformation reaction to multi-plate convergence in the northern Guizhong Depression, as well as its geodynamic process, remain poorly understood. Two phases of intracontinental deformation are identified using field geological investigations, paleo-stress inversion and seismic reflection sections: (1) early NE–SW-directed compression during the Middle Triassic to Early Jurassic; (2) later NW–SE-directed compression during the Middle Jurassic to Early Cretaceous. The reconstruction of paleo-stress provides robust constraints on the spatiotemporal evolution of stress within the Guizhong Depression. The regional SW–NE-directed compression during the Middle Triassic to Early Jurassic was driven by the collision and convergence between the Indochina and South China blocks, resulting in the formation of NW–SE-directed compressional structures during the Indosinian Period. The later SE–NW-directed paleo-stress field was probably driven by the NW-directed subduction of the Paleo–Pacific Plate during the Middle Jurassic to Early Cretaceous.

The northeastern periphery of the Qaidam Basin is a crucial region for comprehending the northeastward growth of the Tibetan Plateau, as it documents Late Cenozoic crustal deformation that elucidates the plateau's growth process. In this study, we reconstruct three stages of crustal deformation in the northeastern periphery of the Qaidam Basin during the Late Cenozoic based on interpretation of growth strata from five seismic profiles, structural mapping of the typical superimposed folds and detailed detrital zircon analysis within the study area. (1) During the Early Miocene to Late Miocene period (23–8.6 Ma), there was NW–SE extensional deformation in the northeast margin of the Qaidam Basin, which exerted control over the deposition of the Youshashan Formation. (2) The NW–SE shortening occurred during the Late Miocene period (8.6–8.1 Ma), subsequent to the deposition of the Youshashan Formation and preceding the deposition of the Shizigou Formation, resulting in a parallel unconformity between these two geological units. (3) The intense shortening of the NE–SW direction occurred during the Late Miocene and Pliocene epochs (8.1–2.5 Ma). The timing of this deformation aligns with the sedimentary age of the Shizigou Formation, suggesting that the initial deformation age may represent the onset of NE extrusion from the Tibetan Plateau towards the northeast margin of the Qaidam Basin. The present study not only delineates a Late Cenozoic structural dome resulting from two-stage crustal shortening in the northeastern periphery of the Tibetan Plateau, but also provides a crucial evidence for reconstructing the Late Cenozoic intracontinental deformation process in this region.

Liquefaction-induced lateral spread is a kind of ground deformation caused by soil liquefaction, which is a danger to houses, roads and other infrastructures. In order to systematically investigate the influence law of different parameters on lateral displacement, this paper establishes a numerical model of the seismic responses of gently sloping grounds through the open-source finite element software OpenSees and carries out a large number of calculations considering various working conditions. Based on the calculation results, eXtreme Gradient Boosting (XGBoost) and random forest (RF) regression are used to build the proxy models for lateral spread displacement prediction. The finite element model was verified by using the multiple VELACS No. 2 centrifuge experiments. Finally, the model was interpreted using SHapley Additive exPlanation (SHAP) method. The results of the model training showed that both models were able to achieve a good fit to the numerical calculation results, with the RF model having a smaller prediction error for the centrifuge experiments. The model interpretation results showed that the modified cumulative absolute velocity (CAV₅) was the most important input variable in the model, and the importance of ground slope (S), relative density (D_r) and thickness of liquefiable soil layer (H_L) was relatively high. In addition, the influence of each parameter on the lateral displacement is consistent with the actual situation, reflecting the rationality of the model prediction process. In addition, the results showed that there is a threshold for the modified cumulative absolute velocity (CAV₅) and Arias intensity (I_a) that leads to a significant increase in lateral displacement. The thresholds of CAV₅ and I_a are 1.3 g s and 1.0 m/s, respectively. These thresholds are in good agreement with the thresholds for triggering the overall initial liquefaction of the soil layer determined by related studies, which provides a reference for the evaluation of liquefaction-induced lateral displacement.

The central Inner Mongolia, located at the intersection of the northern margin of the North China Craton (NCC) and the Central Asian Orogenic Belt, is crucial for deciphering the Late Palaeozoic tectonic evolution associated with the subduction and closure of the Palaeo-Asian Ocean (PAO). Our study focused on petrology, detrital zircon LA–ICP–MS U–Pb geochronology and whole-rock geochemistry for the Late Carboniferous to Permian sandstones within the Shuanmazhuang, Dahongshan, Naobaogou, and Laowopu formations in Siziwang Banner, central Inner Mongolia. This comprehensive analysis shed light on the dynamic interplay between the NCC and the South Mongolia Block. Detrital zircon U–Pb ages in investigated samples mainly cluster between 250 and 2650 Ma, with significant peaks at 2.4–2.5 Ga, 1.8–2.0 Ga, 400–430 Ma, and 250–320 Ma, respectively. The geochemistry data are characterized by SiO₂ contents (56.29–77.95 wt. %), Na₂O / K₂O ratios (0.45–1.58) and SiO₂/Al₂O₃ ratios between 4.33 and 7.44. Moreover, they exhibit the slight enrichment in large ion lithophile elements (Rb and Ba) and the depletion in high field strength elements (Nb, Ta, Th, and U). These facts indicate that the sedimentary detritus predominantly originates from felsic sources, probably deriving from the Late Carboniferous–Permian continental island arc-related intermediate-acid igneous rocks, the Late Ordovician-Silurian magmatic rocks in the Bainaimiao arc and the basements of the NCC. Furthermore, our present results also suggest that during the Early–Middle Permian, accelerating oceanic crust subduction triggered significant magmatic events in Siziwang Banner, leading to rapid uplift and the erosion of arc magmatic rocks, as well as the abundant corresponding sediments. Subsequently, the gradual convergence and eventual collision between the NCC and the Southern Mongolian Block took place at the end of the Permian, representing final closure of the PAO.

The Yu'erya gold deposit is a large-scale gold deposit in eastern Hebei. However, the ore genesis is controversial because the gold orebody is closely related to biotite granite in time and space. The hydrothermal processes of the Yu'erya gold deposit can be divided into early quartz (Q1)-pyrite stage, middle quartz (Q2)-sulphide stage and late quartz (Q3)-calcite stage. The Q1 is subdivided into Q1-1 and Q1-2 generations by SEM-CL images, and Q2 is subdivided into Q2-1 and Q2-2 generations. Three types of fluid inclusions (FIs), including aqueous-carbonic type (C-type), aqueous-rich type (W-type) and vapour-rich type (V-type), were observed in the Yu'erya gold deposit. The Q1-1 is dominated by C-type inclusions, and the other quartz is dominated by W-type inclusions. Laser Raman analysis shows that the initial ore-forming fluids mainly belong to the CO₂-H₂O-NaCl system and gradually transferred to the H₂O-NaCl system. The C-type inclusions of Q1-1 show the salinity of 3.1–10.1 (av. 6.9 ± 1.7) wt.% NaCl eqv., and the total homogenization temperature (T_h) of 305–391°C. The homogenization temperature decreases gradually from the early to the late stage, with insignificant change in salinity, indicating that fluid cooling is the main precipitation mechanism. Trapping pressures of C-type FIs are estimated at 206–284 MPa and 203–211 MPa for the early and middle stages, corresponding to the mineralization depths of 7.2–9.9 km and 7.1–7.4 km, respectively. The FIs in the early stage indicate that the initial ore-forming fluids are characterized by low salinity and CO₂ richness, which are different from those of the intrusion-related gold deposits, but consistent with the orogenic gold deposits.

The unclear understanding of the source rock characteristics for the Paleogene Dongying Formation in the Bozhong Sag leads to the lack of cognition in oil and gas exploration. This research systematically evaluated the discrepancy in geochemical characteristics of source rock intervals in the Dongying Formation based on detailed analysis using Rock-Eval pyrolysis, total organic carbon (TOC), vitrinite reflectance (R_o), maceral components, stable carbon isotopes and biomarker parameters. It discusses the organic matter sources, depositional environment, thermal maturity and hydrocarbon generation potential in the source rock intervals of the Dongying Formation. The organic matter abundance in the third member (E₃d₃) and lower sub-member of the second member (E₃d₂^L) of the Dongying Formation is higher, with an average TOC of 2.08% and 1.03%, respectively, indicating that these source rock intervals could have good and excellent quality. The source rocks of the Dongying Formation predominately contain exinite maceral group and type II₁ and II₂ kerogen. The thermal evolution is mainly in the low-mature and mature stages. The organic matter sources in the Dongying Formation are mainly dominated by mixed origin (the carbon isotope reversal of aromatics also provides a potential explanation). However, the values of 1,2,5−/1,3,6-trimethylnaphthalene, (1,2,5,6 + 1,2,3,5)-tetramethylnaphthalene/tetramethylnaphthalenes, methyldibenzofuran/methylphenanthrene (MDBF/MP) and dibenzofuran/phenanthrene (DBF/PHEN) parameters in the E₃d₃ and some samples in E₃d₂^L decipher relatively smaller values than other source rock intervals, proving the enhancement of the contribution of lower organisms. Moreover, the terrestrial input in the bottom-up deposition process of the Dongying Formation gradually increases. The depositional environment reveals the Dongying Formation source rocks mainly developed freshwater sulphur-poor lacustrine facies and shallow lake-fluvial delta facies in an open clay-rich sedimentary environment with poor water column stratification, belonging to the typical weak oxidation–reduction depositional conditions. The comprehensive geochemical evaluation concludes that the favourable supply of lower organisms and stable clay-rich depositional environment in the E₃d₃ interval of the Dongying Formation are potential explanations for the formation of lacustrine source rocks with high organic matter abundance, intermediate thermal evolution and excellent hydrocarbon generation potential, providing a good foundation for the exploration and development prospects of hydrocarbons.

More than 50 earthquakes occurred in the Luding region, including a 6.8-magnitude earthquake on September 5, 2022, which induced huge amounts of geological disasters. As the main triggered factors for the geological disasters, the vegetation, precipitation and temperature show regular changes on the time axis. Thus, this paper based on the spatial–temporal evolution of the precipitation, temperature and normalized difference vegetation index (NDVI), focuses on the susceptibility of the Luding area using the weighted information content method (ICM) and analytic hierarchy process (AHP) for the post-earthquake regional planning and reconstruction. In the Luding area, it was found that there were 18 debris flow gullies, and 470 geological disasters scattered in the debris flow gullies. The NDVI of the study area has been declining in recent years, with only about 12% of the NDVI increasing from 2015 to 2020. From 2011 to 2015, the annual cumulative precipitation has been dropping overall, while the July average temperature has increasing quadratic functions after decreasing trend. Furthermore, the studied area's geological hazards susceptibility was classified into five categories, with extremely low susceptibility accounting for 5.82%, low susceptibility accounting for 13.61%, moderate susceptibility accounting for 38.54%, high susceptibility accounting for 39.96% and extremely high susceptibility accounting for 2.08%. The geological disasters in moderate, high and extremely high susceptibility accounted for approximately 95.08%, and the covered area of geological disasters in moderate, high and extremely high susceptibility accounted for 88.06%. Through the receiver operating characteristic (ROC) curve of the model verification found the AUC = 0.743. The geological hazards susceptibility study results show that the approach is useful for the analysis and prevention of geological disasters.

Shale reservoir has strong heterogeneity in mineral composition and oil content even at a short distance in the same interval. To better understand the accumulation mechanism of shale oil and hydrocarbon migration tendency in the interval, and explore the main influencing factors of distribution. This paper employed various methods, including thin-section observation, TOC (total organic matter (OM)) analysis, rock pyrolysis, Soxhlet extraction, group component separation, and GC–MS (gas chromatography mass spectrometry) analysis of saturated hydrocarbons. The shale oil samples were collected from an exploratory well in the Songliao Basin, and the distribution and enrichment characteristics of shale oil interlayers were analysed. The results show that the first member of Qingshankou Formation (K₂qn¹) could be divided into six small layers. From Q1 to Q6, the lithofacies could be divided into three types: high-frequency laminar shale, massive shale, and bioclastic shale. The lacustrine matrix shale of K₂qn¹ in Songliao Basin has medium TOC, and high oil contents, OM conversion rate. The TOC ranges from 1.5 to 4.2 wt%, S₁ varies between 1.4 and 4 mg/g, S₂ falls within the range of 4 to 10.6 mg/g, Tmax ranges from 351 to 497°C, and the OSI varies between 57 and 115.34 mg HC/g rock. The lower part of the K₂qn¹, Q1–Q4, characterized by high-frequency laminar shale, contained residual shale oil, while the upper part of the K₂qn¹, Q5 and Q6, characterized by bioclastic shale and massive mudstone, and are dominated by in-situ type shale oil. The crude oil in K₂qn¹ is homologous, and primarily undergoes micro-migration. The Q5–Q6 section has the highest light oil content, while other regions with notable light components are located in the middle of Q1, the upper sections of Q2, Q3, and Q4.Q1–Q4 are primarily composed of residual shale oil, whereas Q5–Q6 is primarily composed of in-situ shale oil, and the primary micro-migration direction of shale oil occurs laterally within Q1–Q4. The lateral migration of each section mainly occurs at the upper part of Q3 and Q4, the lower part of Q1 and Q2, the bottom of Q5, and the interface between Q6 and the second member of Qingshankou formation (K₂qn²). The block mudstone retains in-situ shale oil, especially light hydrocarbons. Within the high-frequency laminar shale, there is strong horizontal connectivity, and lateral hydrocarbon expulsion serves as the primary mechanism for micro-migration in Q1–Q4. This paper can provide reference values for K₂qn¹ Formation shale oil and the migration and differential reservoir formation of medium and high-maturity matrix shale oil.

The Chagai belt to the north of the Afghan block and the east of the Iranian block in the western part of Pakistan is known for occurrence of Oligocene to Miocene calc-alkaline magmatic belt. The present study discusses the characteristics of episodic magmatic activities that contributed to mineralization for the Reko Diq porphyry complex in the western part of the Chagai belt. U–Pb dating of zircons from volcanic rocks of the Reko Diq porphyry complex yielded ages of 25.8 ± 1.8 and 12.29 ± 0.44 Ma for two phases of magmatic crystallization. Geochemical analyses of whole-rock rhyolite and dacite indicate that the rock units are peraluminous calc-alkaline, derived from Andean-type subduction. The magma was formed due to partial melting of the thickened mafic lower crust in a continental arc setting in relation to the subduction of the Neotethys along the Makran subduction zone. The abundance of zircons, Hf, REE, U/Pb and Th indicates high degrees of magmatic evolution. Moreover, the Sr and Nd isotopic data indicate the fractional contribution of depleted N-MORB mantle to the Reko Diq magmas through bulk mixing with magmas derived from the lower continental crust. Short-lived magmatic systems repeated magma injection, and various episodes of hydrothermal fluid flow have led to the formation of porphyry mineralization. Emplacement of the Reko Diq porphyry complex and related Cu–Au mineralization is associated with a series of tectonic–magmatic events at different episodes of the Oligocene–Miocene times.