Acta Geologica Sinica
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2.7 Ga Monzogranite on the Songnen Massif and Its Geological Implications
Acta Geologica Sinica - Tập 92 Số 3 - Trang 1265-1266 - 2018
Structural Characteristics of the Andaman Forearc Inferred from Interpretation of Multichannel Seismic Reflection Data Abstract The Andaman Forearc Basin (AFB) is asymmetric in configuration and filled with a ∼6 km‐thick pile of Neogene to Recent sediments (∼4 s in two‐way travel time: TWT) with distinct zonation. It shows gradual thinning up to ∼3 km (0.8 s in TWT) towards the eastern end with a seabed gradient of 1:30. Thick deformed sediments ∼2 s (TWT) of the Outerarc are associated with intense faulting and occasional folding caused by recent tectonics. Development of a series of faults within the upwarped sedimentary column of Oligocene top to Recent is observed with a rotated fault block. These features are manifestations of Recent igneous intrusion, and reveal the presence of a mild N–S compressional regime. Its effect on the AFB resulted in further uplift of sediments, which can now be seen as the Invisible Bank. Forward gravity modelling supporting our seismic interpretation reveals that it is associated with igneous intrusion from the Moho (∼9 km depth), and also suggests that continental crust underlies the AFB. Strong Bottom Simulating Reflector (BSR)‐like features in the Miocene sediments of Outerarc and Forearc basin at a depth of 0.6 s below the seabed suggest the inferred probable occurrence of gas hydrates in the AFB.
Acta Geologica Sinica - Tập 88 Số 4 - Trang 1145-1156 - 2014
Lower Triassic and Induan‐Olenekian Boundary in Chaohu, Anhui Province, South China Abstract: Since the West Pingdingshan Section in Chaohu was proposed as the candidate of the Global Stratotype Section and Point of the Induan‐Olenekian boundary in 2003, the Lower Triassic of Chaohu has been extensively studied. Based on the studies on the Lower Triassic of Chaohu, (1) a continuous conodont zonation is established, which has become an important reference for Lower Triassic stratigraphic correlation over the world; (2) the First Appearance Datum of conodont Neospathodus waageni was suggested and has been basically accepted as the primary marker to define the Induan‐Olenekian boundary; (3) a characteristic Lower Triassic excursion of carbon isotopes was brought to light and has been proven to be not only an excellent index for the stratigraphic correlation but also a unique indication for the perturbation of ecological environments in the aftermath of the end‐Permian mass extinction; (4) a magnetostratigraphic sequence is constituted with a certain biostratigraphic control in the low‐latitude region and it presents an important correlation to the Boreal sequence; (5) a cyclostratigraphic study provides an alternative method to constrain the age of the chronostratigraphic units; and (6) a scheme of the Olenekian subdivision is recently suggested to define the boundary between the Smithian and Spathian Substages. In addition, Chaohu is also the type locality of the Chaohuan Stage, the upper stage of the Lower Triassic in the China Chronostratigraphic System. Thus, the Lower Triassic of Chaohu is not only a classic sequence in South China, but also a key reference sequence to the investigation of the corresponding stratigraphy and geological events over the world. The recent achievements are viewed here for an overall understanding of the sequence. Then the current situation of the Induan‐Olenekian and Smithian‐Spathian boundaries is discussed to provide a reference for later works.
Acta Geologica Sinica - Tập 85 Số 2 - Trang 399-407 - 2011
Phases of Environmental Evolution Indicated by Primary Chemical Elements and Paleontological Records in the Upper Pleistocene‐Holocene Series for the Salawusu River Valley, China Abstract: Studies of lithology, sedimentary facies and the distribution regularity of SiO2 and Al2 O3 contents and Al2 O3 /SiO2 ratio allow us to divide the Upper Pleistocene‐Holocene Series represented by the Milanggouwan section in China's Salawusu River valley into six segments: MGS1, MGS2, MGS3, MGS4, MGS5 and MGS6. The boundary ages for MGS1 (the Dishaogouwan and Dagouwan Formations), MGS2 (the upper Chengchuan Formation), MGS3 (the middle Chengchuan Formation), MGS4 (the lower Chengchuan Formation), MGS5 (most strata of the Salawusu Formation) and MGS6 (the bottom of the Salawusu Formation and the top of the Lishi Formation) correspond to those of MIS1, MIS2, MIS3, MIS4, MIS5 and MIS6, respectively, from deep sea sediments or continental glaciers. MGS5 can be subdivided into five subsegments (MGS5a, MGS5b, MGS5c, MGS5d and MGS5e) and the boundary ages of these subsegments correspond to those of MIS5a, MIS5b, MIS5c, MIS5d and MIS5e, respectively. Based on the paleoenvironment and paleoecology indicated by the primary chemical elements, fossil vertebrates, mollusks and pollen grains, we hypothesize that MGS1, MGS2, MGS3, MGS4, MGS5 and MGS6 and the subsegments of MGS5 match the corresponding stages for oxygen isotopes in the deep sea sediments and continental glaciers, and the substages of MIS5 in terms of climatic characters, further explaining the phenomena that determined the formation of the late Quaternary strata and the paleontology of the Salawusu River valley. These phenomena relate to fluctuations in the global climate (and particularly in the East Asian monsoon) during the glacial and interglacial periods.
Acta Geologica Sinica - Tập 81 Số 4 - Trang 555-565 - 2007
Prospects of Carboniferous Shale Gas Exploitation in the Eastern Qaidam Basin Abstract: Shale gas is a resource of emerging importance in the energy field. Many countries in the world have been making big financial investments in this area. Carboniferous shale in the eastern Qaidam Basin shows good exploration prospects, but limited research and exploration work for shale oil and gas resources has been undertaken. Geochemical analyses were performed on shale derived from the Upper Carboniferous Hurleg Formation in the eastern Qaidam Basin, Qinghai Province, and secondary electron imaging capability of a Field Emission scanning electron microscope (FE‐SEM) was used to characterize the microstructure of the shale. The reservoir and exploitation potential of the studied shale was assessed by comparison with research results obtained from the Barnett Formation shale in Fort Worth Basin, North America and the Basin shale of Sichuan province. The results indicate that the eastern Qaidam Basin Carboniferous shale is high‐quality source rock. There are four major microstructural types in the study area: matrix intergranular pores, dissolution pores, intergranular pores, and micro‐fractures. The size of the micropores varies from 6–633 nm, the majority of which is between 39–200 nm, with a relatively small number of micro‐scale pores ranging from 0.13–1 μm. The pore characteristics of the studied shales are similar to the North American and Sichuanese shales, indicating that they have good reservoir potential. No micropores are present in the organic matter, which is induced by its composition; instead we found an important lamellar structure in the organic matter. These micropores and microfractures are abundant, and are connected to natural visible cracks that form the network pore system, which controls the storage and migration of shale gas. This connectivity is favorable for shale gas exploitation, providing great scientific potential and practical value.
Acta Geologica Sinica - Tập 88 Số 2 - Trang 620-634 - 2014
Physical and Mechanical Characteristics of Shallow Surface Sediments in the Shenhu Area, South China Sea
Acta Geologica Sinica - Tập 93 Số S2 - Trang 53-56 - 2019
Liquid‐plastic Limit of Surface Sediments in North Slope of South China Sea
Acta Geologica Sinica - Tập 91 Số s1 - Trang 259-260 - 2017
Marine Geohazards: Review and Future Perspective Abstract With offshore resource exploration moving to the deep water, marine geohazards have been attracting attention from the academic and industry. Research achievements of marine geohazards were reviewed in this paper. We analyzed and discussed typical issues among marine geohazards, including coastal erosion, submarine slope failure, turbidity current and special hazards induced by gas hydrate dissociation, in terms of their definition, distribution, characteristics and case studies. Major international projects on marine geohazards headed by the United States, Europe, Japan and other international organizations are introduced as well. Three marine geohazard survey methods, including geophysical survey, geotechnical exploration and in‐situ observation, were summarized with a brief description of each approach, respectively. Especially, the history of marine geohazard researches in China is briefly reviewed, showing the disparity between China and developed countries in the study of marine geohazards narrows gradually. The potential research tendency in future was suggested.
Acta Geologica Sinica - Tập 90 Số 4 - Trang 1455-1470 - 2016
Late Jurassic–Early Cretaceous Plutonism in the Northern Part of the Precambrian North China Craton: SHRIMP Zircon U–Pb Dating of Diorites and Granites from the Yunmengshan Geopark, Beijing Abstract: The Yunmengshan Geopark in northern Beijing is located within the Yanshan range. It contains the Yunmengshan batholith, which is dominated by two plutons: the Yunmengshan gneissic granite and the Shicheng gneissic diorite. Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U–Pb ages from 145 to 141 Ma, whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 Ma. Dikes that cut the Yunmengshan diorite record SHRIMP zircon U–Pb age of 162±2 and 156±4 Ma. The cumulative plots of zircons from the diorites show a peak age of 155 Ma, without inherited zircon cores, and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunmengshan granitic pluton, whose igneous zircons contain inherited zircon cores. The data presented here show that there were two pulses of magmatism: early diorites, followed c13 Ma later by true granites, which incorporated material from an older continental crust.
Acta Geologica Sinica - Tập 83 Số 2 - Trang 310-320 - 2009
Characteristics of Ore‐forming Fluid of the Gaoshan Gold‐Silver Deposit in the Longquan Area, Zhejiang Province and its Implications for the Ore Genesis Abstract The Gaoshan gold‐silver deposit, located between the Yuyao‐Lishui Fault and Jiangshan‐Shaoxing fault in Longquan Area, occurs in the Suichang‐Longquan gold‐silver polymetallic metallogenic belt. This study conducted an investigation for ore‐forming fluids using microthermometry, D‐O isotope and trace element. The results show that two types of fluid inclusions involved into the formation of the deposit are pure liquid phase and gas‐liquid phase aqueous inclusions. The homogenization temperature and salinity of major mineralization phase ranges from 156°C to 236°C (average 200°C) and 0.35% to 8.68% (NaCleqv) (average 3.68%), respectively, indicating that the ore‐forming fluid is characteristic of low temperature and low salinity. The ore‐forming pressure ranges between in 118.02 to 232.13′105 pa, and it is estabmiated that the ore‐forming depth ranges from 0.39 to 0.77 km, indicating it is a hypabyssal deposit in genesis. The low rare earth elements content in pyrites, widely developed fluorite in late ore‐forming stage and lack of chlorargyrite (AgCl), indicates that the ore‐forming fluid is rich in F rather than CI. The ratios of Y/Ho, Zr/Hf and Nb/Ta of between different samples have little difference, indicating that the later hydrothermal activities had no effects on the former hydrothermal fluid. The chondrite‐normalized REE patterns of pyrites from country rocks and ore veins are basically identical, with the characteristics of light REE enrichment and negative Eu anomalies, implying that the ore‐forming fluid was oxidative and derived partly from the country rocks. The δD and δ18O of fluid inclusions in quartz formed during the main metallogenic stage range from —105‰ to –69 ‰ and –6.01‰ to –3.81‰, respectively. The D‐O isotopie diagram shows that the metallogenic fluid is characterized by the mixing of formation water and meteoric water, without involvement of magmatic water. The geological and geochemical characteristics of the Gaoshan gold‐silver deposit are similar to those of continental volcanic hydrothermal deposit, and could be assigned to the continental volcanic hydrothermal gold‐silver deposit type.
Acta Geologica Sinica - Tập 90 Số 4 - Trang 1321-1340 - 2016
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