Geological Journal最新文献

Shale oil and gas resources are abundant in the Chang 7 shale of the Yanchang Formation in Ordos Basin. To determine the characteristics and influencing factors of hydrocarbon generation evolution of the Chang 7 shale, a series of thermal simulation experiments were conducted on low-maturity shale and kerogen samples. The results indicate that the maximum yield of shale oil are 294.5 and 304.3 mg/g TOC for kerogen sample at heating rates of 20 and 2°C/h, and the corresponding experimental temperatures are 360.2°C and 408.0°C, respectively. The utilization of lower heating rates is favourable for shale oil generation and it is recommended to employ a lower heating rate during in situ heating processes to maximize the economic benefits. The formation of crude oil cracking gas begins when simulating temperature exceeds 528.0°C (Easy R_o 2.6%) at a heating rate of 20°C/h and 480.0°C (Easy R_o 2.5%) at a heating rate of 2°C/h, as indicated by the carbon isotopic composition of gaseous hydrocarbons. The maximum oil production rate of the rock powder sample is 159.8 mg/g TOC, which is lower than that of the kerogen sample. It suggests that certain minerals in the Chang 7 shale may impede hydrocarbon generation. After the addition of pyrite, the highest yield of shale oil is 213.96 mg/g TOC, 33.9% higher than the yield of the original rock powder sample, reflecting the positive catalytic effect of pyrite on hydrocarbon generation of Chang 7 shale. Under geologic conditions, pyrite catalytic hydrocarbon generation may act primarily on the migration of organic matter by macromolecules, which considerably increases the probability of direct contact between pyrite and organic matter. Therefore, the organic-rich shale with high pyrite content in Chang 7 member is the preferred target for in situ conversion of shale oil and gas in the Ordos Basin.

A review of the S-velocity structure beneath South America, for the crust and upper mantle, is performed using a recent methodology based on Rayleigh wave analysis, and a new 3D S-velocity model (from 0 to 400 km depth) is achieved for this study area. The precise location and structure of the asthenosphere have been both determined from this new model, which have not been obtained in other previous studies, allowing to know how the different geological units that compose South America are delimited in terms of S-velocity and lithosphere thickness. For example, the highest S-velocities and the thickest lithosphere of the cratonic areas, are determined at the east of the Amazonian Craton and the São Francisco Craton. The lithosphere beneath the Guyana Shield is thinner than beneath the Central Brazil Shield, and the lithospheric root of the Amazonian Craton is determined deeper than the São Francisco Craton. The lithosphere at the east of the Central Brazil Shield is the thickest (~200-km thick). Another interesting feature depicted in terms of S-velocity and lithosphere thickness is the Transbrasiliano Lineament, which is determined in the crust and the upper mantle, confirming that it is not just a surface feature but a deep feature.

In this study, the effects of soil spatial variability on the behaviour of the embankment supported with a combined retaining structure (CRS) were investigated. The numerical model of the CRS embankment was established and validated with the field data. An application programming interface (API) was developed to deal with the data exchanging issue between the numerical model and the spatial variability characterization model. Based on the verified numerical model and the API, the probabilistic analysis with 500 Monte Carlo simulations was automatically computed. Three influencing factors of the retained soil (the mean of the friction angle, the variation of the friction angle and the vertical correlation length of the random field) are analysed by parametric analysis. The results show that the vertical correlation length of the random field is most important in the earth pressure calculation process, while the mean of the friction angle is the factor with least impact. On the whole, the spatial variability of soil properties has minimal impact on the distribution and magnitude of earth pressure behind the retaining structure.

The end of the Neoproterozoic global ice age has promoted the evolution of the Earth's surface system and initiated the ‘Great Explosion of Life’. Glaciation deposits provide valuable insights into the extreme climate conditions. In the southern margin of the North China Craton (NCC), an Ediacaran glacial deposit named ‘Luoquan Formation’ has been recently described in Luonan County, Shaanxi Province. It has significant characteristics of dark grey and black glacial deposits. Through extensive research in sedimentology, geochemistry and geochronology, the glacial sedimentary evolution sequence of the Luoquan Formation has been established. This research also help to define the age of the formation and reveal its provenance and sedimentary environment. The study reveals that four lithofacies associations were identified in the Luoquan Formation: diamictites, carbonates, dropstone-bearing rock and black shale. The Luoquan Formation has experienced three cycles of glacial advance–retreat. Sedimentological evidence suggests that the sedimentary environments of the Luoquan Formation evolved from subglacial (diamictite) to intertidal, then to intertidal lagoon, or from subglacial deposits to shoreface (inner shelf, subtidal), then to deep water basin and fine-grained turbidite and ice-rafting. The age of the Luoquan Formation is estimated to be 562–550 Ma constrained by indirect chronological and paleontological data, maybe representing an Upper Ediacaran glaciation that occurred later than the Gaskiers glaciation. The overall age profile of detrital zircons from the Luoquan Formation can be divided into six groups, ranging from 1.1 to 1.6, 1.85 to 1.95, ~2.1, ~2.3, ~2.5 and 2.65 to 2.9 Ga. These age groups are consistent with the Archean to Meso-Neoproterozoic magmatic–tectonic events in the southern margin of NCC, indicating they are ascribed to an origination directly from the southern margin of NCC. The Luoquan Formation exhibits the characteristics of isochronous and different sedimentary facies, with the glacial front moving from north to south. The discovery of Luoquan Formation in Lianshuigou section not only reflects the important significance of the restoration and reconstruction of the Ediacaran ice age, paleoenvironment and palaeogeography of the NCC but also provides significant evidence to support the further subdivision and correlation within the Ediacaran glacial deposits globally.

The Molo-Sarychat multiphase pluton is situated along the fault systems of the ‘Main Structural Line of Tien Shan’ (known also as the ‘Nikolaev Line’). It comprises mafic to intermediate (monzodiorite, monzonite) and silicic (quartz monzonite, monzogranite and leucogranite-alaskite) rocks, followed by the late mafic (monzodiorite-porphyry to lamprophyre) dikes. Isotopic U-Pb zircon dating of quartz monzonite and monzogranite indicates their Early Permian age (ca. 293 to 286 Ma). The rocks appear to have been produced by remelting of a partially crystallized (mush) magma batch at deeper levels, which is evident by the presence of zircon antecrysts dated at some 306 to 320 Ma. These geochronological data are consistent with a post-collisional setting of the pluton that occurred after the cessation of subduction, which affected the Middle Tien Shan in the Late Palaeozoic. Geochemical signatures of the igneous rocks from the Molo-Sarychat pluton correspond to high-K calc-alkaline to shoshonitic series intrusions emplaced in a post-collisional setting. An initial shoshonitic magma was produced by a low-degree partial melting of the metasomatically enriched upper mantle, with amphibole fractionation in a deep (lower crustal) magma chamber. In this evolution, a generation, under the influence of mantle-supplied fluids and heat, granitic magmas in the crustal protolith can be suggested, with further mixing/mingling of the mantle-derived mafic (shoshonitic) magma and mantle-induced crustal granitic magma, followed by the magma fractionation and emplacement at shallower crustal levels. The skarn-porphyry Mo-Cu-W(-Au) mineralization associated with the Molo-Sarychat pluton complements the group of similar deposits associated with high-K calc-alkaline to shoshonitic series intrusions in the Middle Tien Shan and globally. The characteristic Mo-W-Cu-Au metal assemblage and the high endowment in W and particularly Mo can be related to the fertilization of subduction-modified subcontinental mantle in these metals, and its subsequent involvement in the magma generation in post-collisional setting. A certain role of crustal magma sources in the strong Mo endowment can be considered that would be consistent with some A-type granitoid affinity of the igneous rocks. The Early Permian age of these high-potassic intrusions supporting their post-collisional emplacement is remarkably similar to the age of hydrothermal alteration assemblages, previously reported for the super-large Kumtor Au deposit situated in a similar post-collisional setting nearby.

The Feidong Complex, located on the northeastern margin of the Yangtze Craton, exposes Precambrian basement rocks and is the subject of debate regarding its tectonic affinity. In this study, we conducted in situ U–Pb dating and Hf isotope analyses of zircons from basement rocks within the Feidong Complex. The results reveal crystallisation ages of ca. 2.45, 2.0 and 0.8 Ga for the granitic gneiss, amphibole biotite plagiogneiss and mylonitised monzonitic granite, respectively. The basement rocks with ages of ca. 2.45 and 2.0 Ga exhibit negative zircon ε_Hf(t) values (−10.48 to −0.13) and older two-stage model ages (T_DM2 = 2974 to 3296 Ma). We compared the zircon U–Pb ages and Hf isotopic characteristics of the basement rocks from the Feidong Complex with those of the southern margin of the North China Craton and the northern margin of the Yangtze Craton. Additionally, we also compared the metamorphic grades of rocks between the Feidong Complex and Susong Complex of the Dabie orogenic belt. We found that the Feidong Complex and the northern margin of Yangtze Craton share comparable zircon U–Pb ages and Hf isotopic characteristics. However, the metamorphic grades of the Feidong Complex were distinct from those of the Susong Complex. In particular, the basement rocks with an age of ca. 2.45 Ga formed within a subduction setting; those with an age of ca. 2.0 Ga formed during the subduction and collision associated with the assembly of the Columbia supercontinent; and those with an age of ca. 0.8 Ga experienced extensional processes before the breakup of the Rodinia supercontinent.

Tunnel waste constitutes a prevalent by-product of highway construction in high-altitude mountainous and hilly regions. Sulphide minerals exhibit a unique distribution pattern within the alpine hills. Consequently, tunnel excavation can disrupt the stability of these sulphide minerals, rendering the tunnel waste susceptible to generating secondary environmental hazards during stockpiling. This research delves into the migration and transformation dynamics of potential environmental pollutants in tunnel waste through geoenvironmental simulation techniques. Controlled variables were employed to simulate various conditions, including surface illumination, internal anaerobiosis, water content and aerobic environments. The study's findings indicate that the presence of pyrite in the waste stream primarily drives the secondary contamination of the tunnel waste. Pyrite within the slag tends to react and form sulphuric acid in the stockpile environment, thus creating an acidic milieu that exacerbates the release of existing contaminants. The emergence of an anaerobic environment and a photocatalytic system composed of Fe/Ti substances in the waste stream serves to further accelerate pollutant release. This study thoroughly investigates the primary causes of environmental pollution during the stockpiling of tunnel slag and assesses the potential environmental impact scenarios. The outcomes of this research offer substantial theoretical and empirical support for the management of slag generated during the tunnel construction process.

Based on pressure test data, well logging data and geological conditions, the distribution and cause of overpressure in the western Qaidam Basin are analysed. The contribution of different overpressure causes is quantified, and the main controlling factors of overpressure at different evolution stages are further divided. This is useful for analysing the pressure state in different geological historical periods and indicating the direction of oil and gas migration. The research results show that the formation pressure coefficient in the western part of the Qaidam Basin is mainly in the range of 0.5–2.1, and the pressure coefficient generally decreases from the depression to the edge. According to the stress variation characteristics and logging response of overpressure, two models of acoustic travel time-vertical effective stress and electrical resistivity-vertical effective stress are established to identify and quantify the cause of overpressure for loading and unloading. Through the analysis of logging curves, acoustic velocity-density cross-plot and geological conditions, the causes of overpressure in western Qaidam Basin was clarified. The overpressure calculation results of different origins show that the main controlling factors of overpressure in the Kunbei fault stage are disequilibrium compaction and tectonic extrusion, with contribution rates of 38% and 52%, respectively. The overpressure in Mangya depression is caused by disequilibrium compaction, tectonic extrusion and hydrocarbon generation, with overpressure ratios of 30%, 32% and 38% respectively. The overpressure of the Dafengshan uplift can contribute up to 53% of the disequilibrium compaction, and the contributions of tectonic extrusion and hydrocarbon generation are 28% and 19%, respectively. Finally, the evolution of residual pressure in the upper segment of the Xiaganchaigou Formation ($��{E_3}^2�$) in western Qaidam Basin can be divided into four evolution stages: undercompaction stage (42.8–40.5 MPa), normal compaction stage (40.5–12.0 MPa), hydrocarbon generation pressurization stage (12.0–2.8 Ma) and pressure release stage (2.8 Ma-present).

A flare-up of granitoids occurred at 465–445 Ma in the South Altyn Tagh, synchronously with the exhumation of subducted continental crust. Nevertheless, it remains enigmatic whether a petrogenetic connection exists between them. Here, we report a 454–451 Ma monzogranite pluton, which is characterized by abundant inherited zircons, located in the northern margin of the South Altyn Tagh high-pressure (HP)—ultrahigh-pressure (UHP) metamorphic terrane. U–Pb ages and Hf–O isotopic compositions of inherited and synmagmatic zircons are investigated to trace the source rocks and petrogenesis of this pluton. The inherited zircons (zircons that predate the magmatism) exhibit a wide range of ages from 2618 to 484 Ma, displaying three major peaks at 1800–1100 Ma, 1000–800 Ma and 500 Ma. By comparing these inheritance age patterns with zircon spectra of main (meta-)sedimentary sequences and the widespread Early Neoproterozoic granites (presently as granitic gneisses) in South Altyn Tagh, along with zircon εHf(t) and whole-rock Nd isotopic composition, we argue that the main source rocks of the studied monzogranite are Early Neoproterozoic granitic gneisses and Late Mesoproterozoic paragneisses from the South Altyn Tagh HP–UHP metamorphic terrane. The ca. 500 Ma inherited zircons have a metamorphic origin, which is simultaneous with the peak metamorphic ages of HP–UHP metamorphic rocks in the Altyn Tagh Complex. These observations indicate that the source rocks of the monzogranite pluton are the subducted continental crust, which underwent metamorphism at ca. 500 Ma and followed by partial melting at 454–451 Ma. In addition, synmagmatic zircons exhibit variable δ¹⁸O and εHf(t) values ranging from 5.4 to 11.7‰ and from −19 to +10.3, respectively, indicating a minor contribution of mantle-derived melts in the formation of the monzogranite. Given the studied pluton and contemporaneous extensive granitoids (465–445 Ma), characterized by similar geochemistry and source rocks, are synchronous with the final exhumation of subducted South Altyn Tagh continental crust, we propose that the reworking of exhumed continental crust at middle to lower crustal depths is their main petrogenesis.