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Highlights: [•] Petrography and geochemistry data are applied in this research. [•] The Dulate arc is the primary source area. [•] REE mixing of provenance modelling method is used to determine the source rocks. [•] The sedimentary rocks deposit in a back-arc basin. [•] The back-arc basin formed by the southward subduction of the Zaysan–Erqis Ocean. [Copyright &y& Elsevier]

[Display omitted] • Intensive hydrothermal activity occurred during the deposition of the Lucaogou Formation. • The enrichment of both Sr and Li in the shales is consistent with a hydrothermal origin. • Hydrothermal activity supplied nutrients that enhanced paleoproductivity. Organic matter enrichment in black shales has frequently been linked with hydrothermal activity. However, it is poorly understood how hydrothermal activity affected paleo-environments and the enrichment of organic matter in ancient lacustrine sediments. The hydrothermal activity recorded in the Middle Permian Lucaogou Formation (LCGF) in the Jimusar Sag, Junggar Basin, Northwest China, provides an ideal sedimentary archive to explore this issue. The mineralogical composition, major and trace element, total organic carbon, and sulfur content of forty-three shale samples of the LCGF were investigated to better understand how hydrothermal activity influences organic matter enrichment in lacustrine shales. The terrigenous influx, redox conditions, paleoproductivity, hydrothermal effects, and organic matter enrichment mechanisms are discussed. The results show that the terrigenous influx is insufficient overall, and the lower section of the LCGF has less detrital materials than the upper section. The redox conditions of the bottom water of the lake in the Jimusar Sag during deposition of the LCGF were suboxic to anoxic, which, combined with relatively high paleoproductivity, is favorable for organic matter enrichment. Hydrothermal activity occurred more frequently during deposition of the lower section compared with the upper section of LCGF. Hydrothermal fluids provided sufficient nutrients to enhance organic matter production during deposition of the LCGF and resulted in organic matter enrichment. [ABSTRACT FROM AUTHOR]

Abstract: The Late Carboniferous palaeo-tectonic setting of the West Junggar region is comprised of arcs alternating with basins. Geochemical analysis of the sedimentary rocks associated with these arc-related basins was conducted to better constrain the provenance and tectonic setting. Major and trace element geochemistry data of Late Carboniferous mudstones and sandstones in the Hala-alat Mountains suggest that these sedimentary rocks and their source areas are characterized by the following four features: (1) sediments experienced a simple recycling process; (2) a low degree weathering conditions in the source areas; (3) compositional immature of the sedimentary rocks; (4) dominated by intermediate to felsic provenance, with a few intermediate to mafic sediments. Integrated with the palaeo-flow data and previous authors’ works, a fore-arc basin model is proposed for the tectonic setting of the sedimentary rocks. The Sawur arc is the primary provenance and supplies the major intermediate to felsic detrital fragments. The Bozchekul-Chingiz arc and Kexia oceanic island arc are the other two secondary sources. [Copyright &y& Elsevier]

• Productivity of marine plankton in Late Ordovician was largely reduced by the deposition of volcanic ashes in the ocean. • Weathering of volcanic ashes reduced the concentrations of atmospheric carbon dioxide. • The Late Ordovician glacial event was triggered by intense volcanic eruptions in a short time. Late Ordovician – Early Silurian bentonites and shales are widely distributed in the western Yangtze plate, South China. This study is to use these rocks to examine the mechanism of global cooling. We present total organic carbon content (TOC) and organic carbon isotope data. The TOC of the shales for the Qiliao (QL) and Shuanghe (SH) sections range from 0.21% to 5.88% with an average of 3.0%, and from 1.48% to 6.34% with an average of 2.91%, respectively. The organic carbon isotopic compositions of the shales from the QL and SH sections are 31.1‰–29.4‰ (average 30.3‰) and −30.8‰–29.1‰ (average 30.0‰), respectively. In combination with previous studies of the Katian to Hirnantian glaciation, two conclusions can be summarized: (1) shales in close proximity to volcanic ash (bentonite) layers exhibit obvious TOC reduction, which indicates that the deposition of volcanic ash inhibited the productivity of marine plankton; (2) the organic carbon isotope compositions of shales close to volcanic ash layers present positive excursions, reflecting the decline of the atmospheric carbon dioxide after the volcanic ruption. The main reason is probably that the intense volcanic eruptions created abundant volcanic ash for weathering. It is probably 840 × 1015 kg (1.9 × 1019 mol) carbon dioxide was consumed in the process of volcanic ash weathering, this would make the carbon dioxide content of the atmosphere drop to the threshold level, which triggered the global glacial event during the Early Hirnantian stage, and then the Earth entered into an ice age in the Late Ordovician. Therefore, this study provides a new point of view to understand the climate variation in the Earth's geological evolution history. [ABSTRACT FROM AUTHOR]

• Reviews on tectonics and paleoenvironment of the Junggar Basin are present. • An updated chronostratigraphic framework is provided for Permian Junggar Basin. • Dry climate and evaporative environment prevailed during deposition of source rocks. • Stable salinity stratification and limited dilution promoted organic matter burial. • Organic carbon burial in lakes may act as a significant carbon sink in Permian. The Junggar Basin in northwestern China is a typical "walled" sedimentary basin that has a prolonged basin evolution history from the Paleozoic to Cenozoic and is rich in petroleum resources. Permian strata reach thousands of meters in thickness and have been intensively studied for their record of regional tectonics and paleoenvironments. They have also been exploited for oil and gas for the past several decades. In this paper, we summarize perspectives on tectonic evolution, stratigraphic framework, sedimentary environments, and the paleoclimate of the Permian Junggar Basin and the adjacent Turpan Basin. Further, we discuss the mechanism and consequences of massive organic carbon burial. Based on a compilation of published radiometric dating datasets, an updated chronostratigraphic framework was proposed for the Junggar Basin. This framework constrains the ages of two main petroleum source intervals, the Fengcheng Formation and the Lucaogou and equivalent formations, as Early Permian and Middle Permian, respectively. Although a global warming and drying trend was present throughout the Permian Period, the regional climate over the Junggar Basin was drier in Early Permian and more humid in the Middle-Late Permian with short-term climatic fluctuations. During the deposition of the two petroleum source intervals, dry and temperate climate prevailed and evaporative lacustrine environment dominated. Organic matter enrichment was promoted by stable salinity stratification and limited dilution by inorganic sediments, leading to one of the richest lacustrine source rock deposits in the world. The average organic carbon burial rates were 11.2 gC/m2/yr for the Lucaogou Formation and 3.5 gC/m2/yr for the Fengcheng Formation, lower than the average organic carbon burial rate in modern lakes. However, considering the large areas of global tectonic lakes in the Permian Period, organic carbon burial in lacustrine environments could act as a significant carbon sink and impact the global carbon cycle and climate evolution. [ABSTRACT FROM AUTHOR]