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Ancient deep-lacustrine fans serve as prolific hydrocarbon reservoirs and provide records of climatic and tectonic activity. The deep-lacustrine fans of the Lower Jurassic Sangonghe Formation in Turpan Basin have become the most important exploration targets as stratigraphic traps. An integrated analysis of field profile investigation, core examination, well logging and seismic reflection profile interpretation, and grain size distribution patterns has enabled the identification of a series of deep-lacustrine fans. The deep-lacustrine fans of the Lower Jurassic Sangonghe Formation, deposited in the Turpan Basin consist of sandy debris flow, bottom current reworking and turbidite lithofacies. The deep-lacustrine fans are depicted by the following geological and geophysical features: (1) abundant soft-sediment deformation structures, and dish structures, normal graded beddings and inverse graded bedding structures developed in the strata, (2) the grain size distribution on the C–M diagram is parallel to the C = M baseline and cumulative probability curves display a bi-segment pattern with the suspension components to be the dominant parts, (3) gamma-ray logging curve are inverse-cycle features and seismic reflection profiles are characterized of poor continuity, high amplitudes, scattered and lenticular shapes. The deep-lacustrine fans are favorable target reservoirs, and have become the most important exploration targets in the Turpan Basin. [ABSTRACT FROM AUTHOR]

This study focused on Middle Permian Lucaogou Formation saline lake source rocks, utilizing a combination of biomarkers and hydrocarbon generation thermal simulation to analyze their biological compositions, depositional environments, and hydrocarbon generation potential. The Pr/Ph ratio, Ph/nC18 ratio, and Pr/nC17 ratio indicate that the Lucaogou Formation was in a reducing environment during the deposition period, and the lower part of the Lucaogou Formation (P2l1) is more anoxic than the upper part of the Lucaogou Formation (P2l2). The maturity index 20S (%) and ββ (%) reflect that the maturity of organic matter in the P2l1 is slightly higher than that in the P2l2. The G/H index and the ETR index indicate that the stratification of the water column is better during the sedimentary period of Lucaogou Formation and the salinity of the P2l1 is higher than that of the P2l2. The biomarker parameters of nC21−/nC22+, CPI, S/H, and C22T/C21T reflect that the organic matter of the source rocks have a higher abundance of bacteria and algae than higher plants, and the contents of bacteria are more than that of algae. The (7- + 8-MMAs)/Cmax and (C28 + C29 − St)/St parameters indicate that cyanobacteria accounted for a certain proportion of bacteria, and the algae are mainly green algae. The co-evolution of the sedimentary environment and the biological composition reflects the control of the sedimentary paleoenvironment on biological composition. According to the relative content of cyanobacteria, green algae, and Rhodophyta, the source rocks of the upper and lower Lucaogou Formation correspond to the low-salinity type (LS-type) and the high-salinity type (HS-type), respectively. Compared with LS-type source rocks, HS-type source rocks have greater generation potential of oil and weaker gas generation potential. This study is valuable for the accurate assessment of source rocks and holds significant practical implications for the exploration of oil and gas resources. [ABSTRACT FROM AUTHOR]

The siliciclastic rocks in the Xishanyao (XSY) and Toutunhe (TTH) formations recorded the Middle Jurassic palaeogeographic evolution processes of the Bogda Mountains. To explore their provenance, the geochronological, geochemical, and petrological characteristics of the Middle Jurassic sandstones from the west Bogda area are analyzed in this study. The detrital grains of sandstones are generally poorly to moderately sorted and subangular to subrounded. Low to moderate CIA* (chemical index of alteration), PIA (plagioclase index of alteration), CIW (chemical index of weathering) and relatively high ICV (index of compositional variability) values indicate the overall low to moderate weathering intensity, low sediment recycling, and abundant first-cycle siliciclastics supply. The abundant acid volcanic lithic fragments and element contents/ratios of the sandstones indicate source areas dominated by felsic rocks. The detrital zircon U-Pb age spectrum of the lower XSY Formation is dominated by a single Carboniferous age group. Multiple Palaeozoic zircon U-Pb age groups exist in the middle-upper XSY Formation. The TTH Formation has a typical age of late Middle Jurassic. Combined with the sedimentological characteristics, it reveals that (1) the Eastern Bogda Mountains (EBM) were the only provenance for the lower XSY Formation; (2) both the Yemaquan arc and the EBM provided detritus for the middle XSY Formation; (3) the Yemaquan arc became a minor provenance for the TTH and upper XSY formations. Middle Jurassic palaeogeographic evolution in the EBM is inferred as follows: (1) during the deposition of the lower XSY Formation, the EBM suffered a rapid uplift and became an obvious positive relief; (2) the palaeorelief became high in the Yemaquan arc area and low in the EBM during the deposition of the middle XSY Formation; (3) the Yemaquan arc was considerably eroded, which caused the palaeotopography to decline sharply during the deposition of the upper XSY Formation; (4) the EBM uplifted again during the TTH Formation period, accompanied by volcanic activities at ~165Ma. [ABSTRACT FROM AUTHOR]

Multiple indicators (trace fossils, trace metals, and δ13Corg) are used to assess the depositional environments and controls on organic carbon accumulation in the Lower Carboniferous Nanmingshui Formation, Junggar Basin, NW China. The majority of trace fossils belong to the Nereites ichnofacies, representing low energy, oxygen‐poor, and relatively quiet bottom water environments. However, the shallow water trace fossil Planolites also appears in the strata, possibly reflecting variations in the bottom water oxygen contents of the turbidite succession. Redox proxies Th/U, V/Sc, and V/(V + Ni) reveal variable redox conditions; most of the samples are in the range from suboxic to anoxic depositional conditions. Ni and Cu show a positive correlation with TOC, but U and V have no correlation with TOC, also suggesting the redox conditions were mainly suboxic. The P/Al and Cu/Al ratios of all samples are higher than those of Post‐Archean Australian Shales (PAAS), and about two‐thirds of the samples' Ba/Al and Ni/Al ratios are close to or higher than PAAS, suggesting the Early Carboniferous Junggar Basin had relatively high palaeo‐productivity levels. δ13Corg values average − 23.75‰, reflecting a mixture of terrestrial organic and marine organic matter. The indexes of Ba/Al, Cu/Al, Ni/Al, and δ13Corg show good positive correlations with TOC, indicating the palaeo‐productivity played an important role for the organic matter accumulation. On the other hand, the TOC correlates inversely with redox proxies (Th/U, V/Sc, and V/(V + Ni)), suggesting the preservation conditions (anoxia) are not the control factor of organic matters accumulation. Using these multiple approaches, our results indicate that productivity was the primary factor controlling organic matter accumulation. [ABSTRACT FROM AUTHOR]

The Bogda Mountains, situated in the southern part of the Central Asian Orogenic Belt (CAOB), is an important intraplate orogenic belt for studying the Mesozoic tectonic evolution mechanism of the CAOB. The detailed palaeogeographic evolution process of the Bogda area during Early Jurassic times remains poorly understood. The sandstone petrography, sedimentary rock geochemistry, and detrital zircon U–Pb geochronology were integrated to research the provenance of the Lower Jurassic Badaowan and Sangonghe formations clastic rocks from the northern flank of the Bogda Mountains and further constrain the palaeogeographic evolution of Bogda Mountains. The petrological and geochemical data in this study indicate that the Lower Jurassic sediments were derived from a felsic source area. Compared with the Badaowan Formation, the source rocks for the Sangonghe Formation show more mafic characteristics. U–Pb age patterns of the Badaowan Formation have multiple age groups, and most of the zircon ages are concentrated in the Carboniferous and Late Permian–Early Triassic ages. The Late Permian–Early Triassic age group disappears in the U–Pb age spectrum of the Sangonghe Formation, and every peak age is 20–50 Ma younger than those of the Badaowan Formation. Combined with the compiled sedimentary facies and paleocurrent data, the felsic‐intermediate volcanic rocks and granitoid intrusions in the Harlik arc and the east of the Jueluotage belt were the predominant sources of the Badaowan Formation, and then the dominant source changed to the bimodal volcanic rocks in the Eastern Bogda Mountains during the Sangonghe Formation deposition period. Early Mesozoic palaeogeographic evolution of the Northern Tianshan belt is speculated: (1) the paleotopography of the Jueluotage belt had a differential uplift along its strike, transforming from high in the west during Triassic times to high in the east during early Early Jurassic times and (2) the Eastern Bogda Mountains initiated uplift during late Early Jurassic times. [ABSTRACT FROM AUTHOR]

The East China Sea Shelf Basin (ECSSB) is an important tectonic unit of the western Pacific active continental margin. It is divided further into a series of sags and basement ridges. The Xihu Sag on the east margin of the ECSSB is an important hydrocarbon exploration area and contains significant petroleum resources. The Huagang Formation is the major reservoir in Xihu Sag, and its provenance has been the focus of debate at all times. The major and trace elements (including rare earth elements) compositions were analyzed for the Oligocene Huagang Formation sandstone and mudstone samples in the Xihu Sag. The provenance and tectonic setting of these clastic rocks are discussed. The Chemical Index of Alteration value and A–CN–K diagrams suggest low to moderate weathering in the source areas of the Huagang Formation. The mudstones have lower index of compositional variation values (<1), indicating that the mudstone samples are compositionally mature, whereas the index of compositional variation values for the sandstone samples (0.59 to 1.87) indicate that the sandstones are compositionally immature and mature. The major and trace element composition and ratios of the clastic rock samples indicate that mudstones are mainly from Late Mesozoic igneous rocks in SE China, which is dominated by the acidic volcanic rock. The provenance of sandstones is from two different directions, the Central Uplift Group of ECSSB and the Taiwan–Sinzi Fold Belt with more mafic volcanic rock. Based on the geochemical analysis of the clastic rock samples, the tectonic setting of Xihu Sag was Japanese‐type continental margin during the Huagang Formation deposition time (Oligocene). [ABSTRACT FROM AUTHOR]