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The North Qilian orogenic belt is the key in the exploration of the formation and assembly of Asia. The Early–Middle Devonian Xueshan Formation, which is deposited in the north area of North Qilian Orogenic Belt, is the most important for revealing the evolution basin–mountain transition of the North Qilian Belt. In order to reveal the tectonic evolution of the central orogenic belt in China and Paleozoic global plate reconstruction, it is necessary to perform provenance analysis of the Xueshan Formation. Eighteen samples were collected from Yumen and Yongchang profiles in the west of North Qilian Belt (WN), and 16 samples were obtained from Gulang and Jingtai profiles in the east of North Qilian Belt (EN). The compositions of clastic conglomerates and the sandstones suggested that felsic volcanic was the main source of the WN Xueshan Formation deposits and that the sedimentary and metamorphic rocks were the main source of the EN sediments. According to major geochemistry indexes, such as Al2O3/SiO2 ratio ranging from 0.08 to 0.37 and the chemical index of alteration less than 80, the source rocks were moderately weathered and of moderately matured. The samples from the EN were relatively enriched in Cr, Ni, Sc, and V elements and depleted in Hf element. However, those from the WN were enriched in Hf without the enrichment of Cr, Ni, Sc, or V. The samples from WN showed a strong negative Eu anomaly, but the samples from EN showed a weak negative Eu anomaly or a positive Eu anomaly. All the above geochemical characteristics suggested the prominent input of felsic clasts with granitic rocks into the WN. Meanwhile, the discrimination diagrams of trace elements implied that WN rocks were derived from continental island arc and that the EN rocks were derived from orogenic belt and the passive continental margin. The North China Plate subducted southwards and formed subduction‐related arc magmatism along the southern margin of the North Qilian Terrane during the Early–Middle Devonian. In conclusion, the WN is a fore‐arc basin, but EN is a foreland basin. [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]

Using analyses of the lithology, sequences, paleoenvironment, and tectonic setting, the depositional system of the Carboniferous Huanglong Formation in the eastern Sichuan Basin was identified. The lithological characteristics of the Lower Member, Middle Member, and Upper Member were analyzed and classified. Before the use of carbon, oxygen, and strontium isotopes in the analysis, all of the geochemical data were tested for validity. On the basis of the Z values obtained from carbon and oxygen isotopes, the paleoenvironments of the three members were elucidated. Lower Member was dominantly an enclosed marine environment with intense evaporation and little freshwater input into the sea. Middle Member developed in a semi-enclosed to normal marine environment with many rivers. Upper Member was formed in a normal marine environment. The east Sichuan Basin was enclosed by paleouplifts before the deposition of the Huanglong Formation, forming a relatively enclosed depositional setting. Paleogullies developed in the Silurian strata that underlie the Carboniferous rocks; these paleogullies can be identified. On the basis of a comprehensive analysis, we propose that the Huanglong Formation developed in a platform system. Four microfacies were identified: supratidal flat, dolostone flat, grain shoal, and shelf microfacies. The high-permeability and high-porosity characteristics of the grain shoal microfacies are favorable for hydrocarbon accumulation, while the supratidal flat and shelf microfacies developed very few high-quality reservoirs. The paleogullies, in which increased amounts of grain shoal microfacies developed, controlled the distribution of high-quality reservoirs. [ABSTRACT FROM AUTHOR]