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Li H.,Northwest University, China | Liu Y.-Q.,Northwest University, China | Li W.-H.,Northwest University, China | Yang R.,Northwest University, China | And 4 more authors.
Geological Bulletin of China | Year: 2013

Middle Permian Lucaogou Formation is characterized as lacustrine dark gray or gray carbonate rocks, interbeded with sandstone, thick balck mudstone and oil shale in Yangniuchang section, Urumchi, Xinjiang Province. The carbonate rocks were mainly composed of dark gray dolomicrite, then gray micrite. The dolomicrite comprised micro-crystalline dolomite, ankerite and calcite with mixture of clay-sized quartz and enrichment of organic matter. Three micromorphologies of dolomite were found under SEM, including microspheroids (9 μm in diameter), micro-rods (2 μm) and micron-sized (<5 μm) anhedral dolomite, and the micro-anhedral dolomite held the majority in dolomicrite. There were also found large amount of nanoparticles (70-150 nm in diameter) in the micrite with shape very similar to micrococcus. Compared with the micrite, dolomicrite has higher Sr value, Sr/Ca ratio, Mn value, and δ18O value, which indicate that the dolomicrite is formed in deeper anoxic water with higher salinity than micrite, and the dolomicrite lacks of replacement textures from micrite. The δ13CPDB of dolomicrite ranged from 9.2‰ to 15.6‰. The higher δ13C value may be the result of isotope fractionation led by methanogens. Such characteristics indicate that the dolomite precipitation had close relationship with the bacterial methanogenesis in methane-producing zone.

Yang Z.,Changan University | Yang Z.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | Chao H.,Changan University | Chao H.,Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits | And 2 more authors.
Earth Science Frontiers | Year: 2016

Qinling orogenic belt is a famous orogenic belt in central China, and it is also a typical intra-continental orogenic belt of continental tectonics. This type of orogenic belt did not undergo subduction of ocean crust to form such orogenic belt with main suture zone. It is not the collision orogenic belt that formed by the interaction between North China plate and Yangtz plate, and also not so-called composite orogenic belt. According to the composition, structural characteristics of different depth, cross-bridge structure, structural style in the transformation of basin and mountain, the structural characteristics of Shangxian-Danfeng tectonic zone and Mianxian-Lueyang tectonic zone as well as the distinct north-south direction structures in the central orogenic system (Qinling), the non-plate features of these characteristics are discussed. On the basis of above discussion, the thrust-Choula(or Choula) tectonic model for the formation of Qinling intra-continental orogenic belt is built. © 2016, Editorial Office of Earth Science Frontiers. All right reserved.

Yang Z.-Z.,No 203 Research Institute | Liu Y.-H.,Changan University | Zhao S.-L.,Shaanxi Institute of Geological Survey
Northwestern Geology | Year: 2013

According to the systematic investigation of the cross-sections in the boundary areas of Shaanxi, Henan and Hubei provinces, a new division of Nanhua-Cambrian is made on the previously measured sections in the area. It is suggested that the Liantuo formation of Nanhua era should exist in the district. The upper Cambrian should be restored as a formation name, and Shiwenzi formation should no longer represent both Wugongya formation in upper Cambrian and Shuihetian formation in lower Ordovician, due to the fact that the Shiwengzi formation in Zhashui area is merely magnesian carbonate deposits without fossils, located above the carbonaceous and silicious slate. According to the collected fossils and relics, the Cambrian can be clearly divided into lower, middle and upper (including Furongian) parts. The lithofacies palaeogeography features of each formation are systematically described, and provide significant foundation for regional strata division and provincial comparison.

Zheng N.,Chinese Academy of Geological Sciences | Li T.,Chinese Academy of Geological Sciences | You G.,Chinese Academy of Geological Sciences | Zhang S.,Shaanxi Institute of Geological Survey | And 2 more authors.
Acta Geologica Sinica | Year: 2012

Field investigation and laboratory research on flysch of the Liufengguan Group in Qinling indicate the following: (1) Sandstone of the Liufengguan Group is categorized as feldspathic lithic graywacke with a minor amount of lithic graywacke in the QFR triangular diagram. Grain size≤0.3 mm. Bedding plane structures such as groove casts and suspected flute casts can be found at the bottom of the sandstone. It is inferred that currents may have come from the southeast during deposition. Bedding structures such as ripple marks, graded bedding, parallel bedding, small-scale cross bedding, climbing bedding, suspected convolute bedding, microlamination and sliding structures have also been observed, which are of indicative significance. It is thought that the Liufengguan Group has the sedimentary characteristics of bedding, bedding plane structures and lithological assemblages of deep-sea low-density turbidity current deposits. The vertical succession of the Bouma sequence in the inner fan subfacies zone is generally incomplete: the assemblage of Ta and Tabc is commonly seen; the succession of the middle fan subfacies zone is relatively complete; and divisions Te and Tb are common in the outer fan subfacies zone. (2) The flysh of the Liufengguan Group is a sequence of deep-sea argillaceous-arenaceous submarine fan deposits, in which the authors recognize the inner, middle and outer fan subfacies and also nine types of lithofacies: normal graded sandstone (A1), medium- to thick-bedded, fine-grained sandstone (A2), medium- to thick-bedded and massive siltstone (A3), thin-bedded, fine-grained sandstone and mudstone (B1), irregular interbeds of thinbedded, fine-grained sandstone and siltstone (B2), thin-bedded, fine-grained sandstone (C1), very thin-bedded, fine-grained sandstone (D1), olistostromes (E1) and deep-sea mudstone (F). The inner fan consists of four microfacies: natural levee (A1), water channel (A2, A3) and olistostrome (E1); in the middle fan there also occur four microfacies, i.e., branch channel (B1), branch channel (B2), interdistributary bay (D1) and olistostrome. The outer fan is made up of the branch channel (C1) and sheet sand (D1) microfacies, which alternate vertically with sediments of deep-sea plain subfacies (F). There occur fining- and thinning-upward channel deposits in the outer-fan subfacies zone of the submarine fan of the Liufengguan Group observed in this study. The quartz content of the graywacke of the deposits is all higher than 40% and may reach as high as 60%. Therefore, on the basis of the aforementioned features, this flysh should be formed in a passive continental-margin tectonic environment.

Wang M.-Z.,Shaanxi Institute of Geological Survey | Dong F.-L.,No 2 Institute Of Geological Exploration | Liang Q.-F.,Shaanxi Institute of Geological Survey | Jin P.,Shaanxi Institute of Geological Survey | Zhang H.-F.,Shaanxi Institute of Geological Survey
Geology in China | Year: 2011

Geochemical exploration is an important means in geological prospecting, and whether geochemical anomalies can be effectively extracted or not decides the success or failure of this means. Based on a systematic summarization of previous studies, the authors propose an idea of fuzzy decision tree for extracting geochemical anomalies. Exemplified by the data obtained in 1:200000 stream sediment survey of southern Sanjiang region, this paper has validated the feasibility of the technology. Studies show that the composite anomalies of chemical elements coincide well with the known mine sites, and are much better than the anomalies based on element summation. The technique of fuzzy decision tree for extracting geochemical anomalies has not only theoretical value but also practical significance in ore-prospecting work of southern Sanjiang region.

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