The Qijiagou section on the southern margin of the Junggar Basin preserves thick and extensive Carboniferous carbonate rocks, and is the type section of the Upper Carboniferous in the Junggar Basin. Here, we studied the lithological assemblages and brachiopod fossils of the Upper Carboniferous Qijiagou Formation on the southern margin of the Junggar Basin. Outcrop observations indicate laterally variable thicknesses of this unit, comprising thick-bedded, fossiliferous, channelised, sandy, and calcareous limestone. Petrographic observations revealed four microfacies, indicating deposition of the formation in diverse depositional environments, including lagoonal to delta-dominated middle shelf settings. In addition, we identified 15 species of brachiopod fossils in 11 genera which belong to Spiriferida Waagen, Productida Sarycheva et Sokolskaya, and Strophomenida Öpik. Thus, based on the characteristics of the lithological assemblage and brachiopod fossils, we infer that the Qijiagou area had a relatively warm environment in the middle and late Late Carboniferous. This included a turbulent and shallow water body with two regressions which occurred in a carbonate platform sedimentary environment.
Abstract Ostracods are described for the first time from the red-coloured marine sandstones of Arisu section (Arisu red beds) of the Upper Ordovician Tierekeawati Formation in Kalpin area of northwestern Tarim Basin, Xinjiang Uygur Autonomous Region (Xinjiang), Northwest China. Twenty-two species belonging to thirteen genera are described and figured. The ostracod fauna suggests a probable Sandbian–Katian age for these beds. The palaeoecological assemblage of ostracod fauna implies the deposition in a nearshore-offshore environment during a regression when the Arisu red beds of the Tierekeawati Formation were laid down in the Tarim Basin. Many cosmopolitan and provincial genera were present in diversified ostracod fauna of the Arisu red beds, suggesting the possible biogeographic relationships among the Tarim, Tibet, and South China plates, as well as Europe and North America continents during the Late Ordovician. Ostracods experienced faunal exchanges between Laurentia and the Tarim Plate during the Late Ordovician Period.
According to fossil, sedimentation, microelement, featured mineral and clay mineral characteristics, an approach is conducted to the sedimentary environments including Late Carboniferous of northeastern margin, Early, Middle and Late Permian of northwestern and southern margins and eastern part of Junggar basin. It is suggested that the sedimentary environments of Fengcheng formation of Early Permain in northwestern margin, Lucaogou formation of Middle Permian in southern margin and Member-3 and Member-4 of Pingdiquan formation of Middle Permian in northeastern margin of Junggar basin could be bordtrland coastal lacustrine ones.
Vertebrate fossils are abundant in sandy mudstones of the Cretaceous Donggou Formation in the Sikeshu area, southern margin of the Junggar Basin, Xinjiang. Here, a few pycnodont remains from the Sikeshu area are described. Isolated elements are identified as a fragment of vomer and a fragment of prearticular referred to Xinjiangodus gyrodoides. These specimens are very small, corresponding to small pycnodont individuals. The larger specimens found in the Late Cretaceous in the United Kingdom, Spain, Morocco, and the United States were mostly from marine sediments, whereas the small specimens described here lived in continental paleoenvironments. The fossils are buried in situ, and their preservation methods involve carbonaceous pressing film and carbonate mineralization, of which carbonate mineralization is the main method. This research result fills the gap in Cretaceous Stenodon data in the Junggar Basin and provides important fossil data for the study of Cretaceous Stenodon in the Junggar Basin and even in Central Asia. This study provides a new perspective for understanding the paleoecology of inland lakes in western China at the end of the Cretaceous.
Gastropod fossils, mostly of small individuals, are abundant in the Palaeogene strata in the Sikeshu Depression on the southern margin of the Junggar Basin. The main groups are bithyniids and other prosobranchs. We studied the taxonomy and taphonomy of the gastropod assemblages of the Ziniquanzi Formation in the Sikeshu Depression. The gastropods inhabited muddy-bottom and shallow-water environments in a river floodplain and riverside setting. The results of this study are useful for recognising the Cretaceous–Palaeogene boundary, and demonstrate that the lake ecosystem had recovered from the end-Cretaceous mass extinction.
Late Carboniferous (Pennsylvanian) ostracods are described from East Junggar in Xinjiang Uygur Autonomous Region (referred here as Xinjiang) of northwestern China. Twenty-one species belonging to 11 genera are recognized. Among them, two are new, Acratia xinjiangensis sp. nov. and Healdianella shiqianensis sp. nov. These species can be referred to the Ostracod Assemblage‐3 (OA-3) of the Shiqiantan Formation, and together with zircon U-P dating suggest a probable Moscovian–Kasimovian (middle–late Pennsylvanian) age for the unit. The OA-3 found in the limestones of the Shiqiantan Formation inhabited in open oceanic island arc context that is ecologically equivalent to the Eifelian Mega-Assemblage, and incorporated smooth-podocopid associations. The Shiqiantan Formation OA-3 thus implies a foreshore to offshore environmental transition within a post-collision rift basin.Zhengjiang Luo [luozj@petrochina.com.cn],Rui Wang [Wangrui@petrochina.com.cn],Aliya Amuti [alya@petrochina.com.cn] andYong Deng [dengyong@petrochina.com.cn], PetroChina Xinjiang Oilfield Company Research Institute of Experiment and Detection and Joint Laboratory of Stratigraphy and Palaeontology, Xinjiang Oilfield Company, Nanjing Institute of Geology and Palaeontology, CAS, Karamay, Xinjiang 834000, PR ChinaYucong Sun [18635935938@163.com], Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China; University of Chinese Academy of Sciences (UCAS), Beijing 100049, PR China;Wenkun Qie [wkqie@nigpas.ac.cn] andJunjun Song [jjsong@nigpas.ac.cn] State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing 210008, PR China; University of Chinese Academy of Sciences (UCAS), Beijing 100049, PR China.
Xiaopinggou, the northeast area of the Dabancheng, outcrop a set of pillow lava assemblage which has exposed this area completely. In this paper, we have taken this place as an example and explained the geological meaning of the U-Pb age of the single zircon grain which was based on magmatic crystallization and statistical theory. It provided an important clue for the geotectonic setting and geological age of the evolution of the Bogda structural belt. Rocks like Pillow basalt, dacite, and pyroclastic are found in the Xiaopinggou region of the Dabancheng pillow lava assemblage. The weighted average age of 21 single zircon grains in dacite using LA-ICP-MS U-Pb dating data was 326.0±2.8Ma. Only the primary zircon crystallization ages in the magma chamber were represented by these ages. The Pillow lava assemblage in Xiaopingou was not diagenetically older than the early stage of the Late Carboniferous (the end-stage of the Bashkirian), according to the four single-grain zircon ages of the most recent crystallization, which yields a concordant age of 315.4±1.3Ma. This age is consistent with the geological age determined by the fossils in the Liushugou formation.
Several oil and gas fields have been found in which oil and gas were mainly derived from the Jurassic coaly source rocks in the Junggar Basin, northwest China. Pyrolysis experiments were performed on two coals (J23C1 and FM1C2) and one type III kerogen of mudstone (Di9S1) from Jurassic strata in the basin at two heating rates of 20 and 2 °C/h in confined systems (gold capsules). Hydrogen indices and H/C atomic ratios of the three samples J23C1, FM1C2, and Di9S1 are 83, 197, and 226 mg/g TOC, and 0.70, 0.86, and 1.01, respectively. The measured maximum oil yields for the three samples are 59.37, 175.75, and 80.75 mg/g TOC, respectively, inconsistent with hydrogen indices and H/C atomic ratios. However, the measured maximum gas yields (∑C1–5) for the three samples are 90.69, 157.24, and 198.15 mg/g TOC, respectively, consistent with hydrogen indices and H/C atomic ratios. This result is interpreted by kerogen Di9S1 containing mainly crossed alkane moieties with both terminals attached to aromatic rings while coals J23C1 and FM1C2 contain mainly alkane moieties with only one terminal attached to an aromatic ring based on kerogen 13C NMR spectra and the oil yield relative to gas yield and compositions of liquid components produced in confined pyrolysis. The crossed alkane moieties were hardly released as liquid alkanes but likely further cracked into gaseous components during pyrolysis. Jurassic strata contain some effective oil source rocks which produced enough amount of oil required for oil expulsion and formation of commercial oil reservoirs in oil generative window (Ro 0.6–1.35%). The amounts of gaseous hydrocarbons generated from the Jurassic coaly source rocks are generally low in oil generative window due to low transformation ratios. Elevated maturity (Ro > 1.35%) is a critical controlling factor to the Jurassic coaly source rocks generating sufficient gaseous hydrocarbons and forming commercial gas reservoirs.
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