Search Results (5)

At the end of the Middle Permian Guadeloupe series, the Chinese region recorded the only internationally recognized large igneous provincial eruption event, known as the Emeishan LIP. The Yangtze region of South China records a series of short and almost synchronous geological events that accompanied the development of bio-geological events such as large-scale magmatic intrusion, plate rupture, magnetic pole anomalies, and ecological collapse. These events ultimately triggered the extinction of living organisms. However, the current study leaves several questions unanswered. What was the sequence of geological events? Are the global records of these events synchronized? What is the causal relationship between these events? This study discusses the sedimentary responses to various geological events using biofossils, fluid inclusion, carbon isotopic analysis, and astrochronological analysis. The results reflect the following: (i) Mantle plumes: Mantle plumes act as pathways for heated fluids to ascend from the Earth’s interior. The mantle plume reached the Moho surface in the mid-Wordian and affected the magnetic field at the Earth’s surface; (ii) Magnetic pole anomalies: The anomaly of the Earth’s magnetic poles appeared in the mid-Wordian stage, causing the originally stable plates to begin to split. The sea level changes dramatically, and the ancient landform pattern changes dramatically; (iii) Plate rupture: The rifting of plates accelerated the activity of deep hydrothermal fluids; the hydrothermal fluid gradually infiltrated the paleo-ocean after the J. altudaensis zone; (iv) Emeishan LIP: The volcano erupted at 260 Ma, and eventually led to the mass extinction. We aim to identify the initial triggers of various geological events by analyzing the sedimentary record. Full article

As the world’s largest accretionary orogen, the Central Asian Orogenic Belt (CAOB) underwent continuous juvenile crustal growth in the Phanerozoic. The northern margin of the North China Craton (NCC) and its adjacent area form the eastern segment of the CAOB, which is a key area for learning about the geological evolution of the Paleo-Asian Ocean (PAO). In the Permian, the west of the northern margin of the NCC was a post-collision extensional environment, while the east was in a subduction stage. As a connecting area, the Permian evolution of the PAO in the middle of the northern margin of the NCC has not been systematically studied. In order to fill the gap and understand the continuous temporal and spatial evolutionary process of the PAO, this paper focuses on the Permian granitic rocks in the Chifeng area. Zircon U-Pb dating and the geochemical analysis of whole-rock major and trace elements were conducted to build a granite chronological framework, and to discuss the genesis and tectonic background of the granitic rocks, along with tectono-magmatic evolutionary history in the Chifeng area. The respective LA-ICP-MS zircon U-Pb dating results from eight samples are 269 ± 1, 268 ± 3, 260 ± 4, 260 ± 1, 260 ± 1, 255 ± 2, 254 ± 2 and 256 ± 1 Ma, respectively. These results, combined with previous data, revealed that the Permian granitic rocks had undergone three events of magmatism: (1) monzogranitic-syenitic phase (294–284 Ma; Cisuralian); (2) monzogranitic phase (269–260 Ma; Guadalupian) and (3) late monzogranitic-syenitic phase (256–254 Ma; Lopingian). From the Early Permian (294–284 Ma) to the Middle Permian (269–260 Ma), granites with fine-medium-grained locally porphyritic texture and massive structure showed a high-potassium calc-alkaline series formed in a compressional setting, indicating a continuous collision between the Xing’an-Mongolian Orogenic Belt (XMOB) and the NCC. During the Late Permian-Early Triassic (256–248 Ma), granites with massive structure and medium-grained texture in the Chifeng area were magmatism dominated by A- and I-type granites of high-potassium calc-alkaline series, combined with the coeval basic rocks, which constituted a typical “bimodal” rock assemblage. This suggests that the Chifeng area was located in an extensional setting where the subducting slab broke off during the collision between the XMOB and NCC. These granitic plutons from the Permian are believed to have been generated by the subduction-collision of the Paleo-Asian oceanic crust beneath the NCC, according to emplacement time and occurrence location. Our findings provide strong evidence for Permian continuous temporal and spatial tectonic evolution and the characterization of the eventual closure of the PAO in Chifeng area at the northern margin of the NCC. Full article

The Middle Permian Maokou Formation in the Sichuan Basin has huge resources and is an important target for natural gas exploration. In recent years, significant exploration breakthroughs have been made in the dolomite field of member Mao-2 in central Sichuan, and the gas production of several wells has exceeded 1 × 10⁶ m³/d, indicating promising prospects for exploration. However, the origin of the dolomite reservoir in member Mao-2 remains ambiguous, which restricts the accurate prediction of favorable reservoirs. This study focuses on drilling in the Hechuan area as its research object, by using a detailed description of the cores from member Mao-2 of seven wells; samples were selected for tests of the degree of dolomite cation ordering, stable carbon and oxygen isotopic compositions, strontium isotopic composition, rare earth elements, LA-ICP-MS element mapping and U-Pb dating. It is clarified that: (1) The crystalline dolomite of member Mao-2 in the Hechuan area is the main reservoir rock, and the heterogeneous vugs and fractures are the main reservoir space. The dolomite in member Mao-2 has been characterized by a low degree of cation ordering value (avg. 0.59), with values of δ¹³C (avg. 3.87‰), δ¹⁸O (avg. −7.15‰) and ⁸⁷Sr/⁸⁶Sr (avg. 0.707474) having similar geochemical characteristics to Middle Permian seawater; the REEs normalized distribution patterns have similar characteristics to limestone; and the U-Pb age (261.0~262.0 Ma) corresponds to the age in the Capitanian stage of the Permian Guadalupian Series. (2) Petrological studies show that member Mao-2 has vertical karstification zonation characteristics; syngenetic karstification controls the formation of a large-scale fracture-cave system in the phreatic zone; the dolomitization of sediment in the fracture-cave system occurred during the penecontemporaneous period with locally restricted seawater. (3) The main controlling factors of the reservoir were syngenetic karstification, early dolomitization and hydrothermal dissolution related to Emei taphrogenesis. The research results are of great significance for dolomite reservoir prediction; the highlands of paleogeomorphology with syndepositional faults are favorable areas for dolomite reservoirs. Full article

Characterizing geological heritage sites (geosites) available in Russia remains an urgent task. The present study focuses on two geosites from the vicinity of Kazan—a large city on the Volga River. They are attributed to the standardized geoheritage types and scored by means of several criteria. It is found out that the Pechischi geosite represents nine geoheritage types, from which the stratigraphical type (stratotype section of the Upper Kazanian regional unit of the Guadalupian) and the geohistorical type (history of the Permian System studies) are the most important. This geosite reaches 675 out of 750 maximum possible scores, and it is ranked globally. The Cheremushki geosite represents six geoheritage types, from which the stratigraphical type (reference section of the Urzhumian regional unit of the Guadalupian) and the paleontological type (locality of diverse fossils, including tetrapods) are the most important. This geosite reaches a score of 250 and is ranked nationally. The undertaken study allows for recommending several actions for the effective conservation and exploitation of these geosites. The innovative interpretation is that the presence of geosites at the urban periphery makes its general (not only geological) heritage value comparable to that of the city’s center. Full article

An occurrence of vein U-Mo mineralization is located in the Majerská valley near Čučma, about 7 km to the NNE of the district town of Rožňava (Eastern Slovakia). Mineralization is hosted in the acidic metapyroclastics of the Silurian Bystrý Potok Fm. (Gemeric Unit), and originated in the following stages: (I.) quartz I, fluorapatite I; (II.) quartz II, fluorapatite II, zircon, rutile chlorite, tourmaline; (III.) uraninite, molybdenite, U-Ti oxides; (IV.) pyrite I, ullmannite, gersdorffite, cobaltite; (Va.) galena, bismuth, tetradymite, joséite A and B, Bi₃(TeS)₂ mineral phase, (BiPb)(TeS) mineral phase, ikunolite; (Vb.) minerals of the kobellite–tintinaite series, cosalite; (VI.) pyrite II; (VII.) titanite, chlorite; and (VIII.) supergene mineral phases. The chemical in-situ electron-microprobe U-Pb dating of uraninite from a studied vein yielded an average age of around 265 Ma, corresponding to the Guadalupian Epoch of Permian; the obtained data corresponds with the age of Gemeric S-type granites. The age correlation of uraninite with the Gemeric S-type granites and the spatial connection of the studied mineralization with the Čučma granite allows us to assume that it is a Hercynian, granite-related (perigranitic) mineralization. Full article