The subduction of oceanic lithosphere during the Carboniferous Period contributed to the formation of widely distributed subduction-related volcanic rocks within the Junggar basin. These volcanic rock associations contain significant clues for understanding the subduction of the Keramaili oceanic lithosphere and the filling of the remnant oceanic basin. Here, we report regional gravity and magnetic data, petrology, geochemistry, and U–Pb dating for Carboniferous volcanic rocks from the North Junggar basin (NJB). Using samples from well Y-1, we distinguish upper and lower volcanic sequences on the basis of selected geochemical data. An isochronous stratigraphic framework of Carboniferous volcano-sedimentary sequences is then constructed and the petrogenesis of these volcanic rocks is discussed. Finally, we propose an explanation for the genesis of these diachronous Carboniferous volcano-sedimentary sequences. The results show that various volcanic rocks are distributed in different areas of the NJB, and mainly consist of calc-alkaline basalt–andesite–dacite assemblages and alkaline basalt–basaltic andesite–andesite assemblages. The geochemical data also demonstrate a binary nature of the Carboniferous volcanic rocks. In the eastern NJB, the lower and upper volcanic sequences are formed during the early and late Carboniferous, respectively. However, all of these volcano-related sequences in the western of the NJB are formed during the late Carboniferous. These volcano-sedimentary sequences exhibit a ‘ladder-style’ of temporospatial evolution from east to west. The geochemical results also indicate that the upper volcanic rocks include island arc components formed in an extensional setting, whereas the lower volcanic rocks were derived from deep crustal cycling metasomatism by various mantle components in a continental arc environment. Earlier closure of the Keramaili oceanic basin and slab roll-back of the Junggar oceanic lithosphere in eastern versus western Junggar basin led to the formation of these diachronous volcano-sedimentary sequences.

The physical and mechanical properties, microstructure degradation characteristics, and damage mechanism of natural gypsum rock under 15, 30, and 45 freeze–thaw cycles were studied by using a self-developed program-controlled freeze–thaw experimental device. The results show that compared with natural gypsum, with the increase in freeze–thaw cycles, the mass of the sample increases first and then decreases, Poisson's ratio increases, the density decreases, and the longitudinal wave velocity, the uniaxial compressive strength, and the elastic modulus decrease. Indexes decrease greatly in the early stage of freeze–thaw and slowdown in the later stage. With the increase in freeze–thaw cycles, the slope of the pre-peak stage of the stress–strain curve decreases, the compaction stage is significantly prolonged, and the brittleness of the post-peak failure process decreases. Failure cracks of the specimens after freeze–thaw cycles are mainly inclined shear failure and axial tensile cracks. The analysis shows that the freeze–thaw damage of gypsum rock is caused by the superposition and mutual promotion of water-rock softening and pore frost heave. The specific performance is the damage of crystal particles and the loose pore structure at the mesoscale. On this basis, the cracks gradually develop and expand, which is consistent with the macroscopic test results of the sample. The research results have reference significance for the construction scheme design and frost damage prevention of gypsum surrounding rock tunnels in cold regions.

Rare earth elements (REEs) and trace elements, due to their relative stability during sedimentary processes, are effective geochemical proxies for sediment provenance. In the Dongdaohaizi Depression of the eastern Junggar Basin, the provenance of the Middle Jurassic Sangonghe Formation remains contentious. In this study, representative sandstone samples were systematically collected from all three members of the Sangonghe Formation in both the Dongdaohaizi Depression and its western margin. Through comprehensive petrographic and geochemical analyses, we obtained the following results. The Sangonghe Formation is primarily composed of feldspathic lithic sandstones, lithic sandstones, and minor lithic–feldspathic sandstones. The heavy mineral assemblage includes zircon, garnet, chromite, and rutile, suggesting source rocks of intermediate to acidic igneous, metamorphic, and mafic lithologies. The total REE contents range from 101.84 to 192.68 μg/g, with an average of 161.80 μg/g. The ∑LREE/∑HREE ratios vary from 6.59 to 13.25 (average 10.96), and the average δEu values are close to 1. The δCe value ranges from 1.09 to 1.13 (average 1.11). Trace element discrimination diagrams, including La-Th-Sc, Th-Co-Zr/10, Th-Sc-Zr/10, and La/Y-Sc/Cr ternary plots, indicate that most samples fall within the continental island arc domain, with a few plotting in the passive continental margin field. Comparison with potential surrounding source regions reveals dual provenances: an eastern source from the Kalamaili Mountains and a western source from the Zhayier Mountains. During the Early Jurassic, these two orogenic belts acted as distinct sediment sources. The Zhayier Mountains provided stronger input, with fluvial and tidal processes transporting sediments into the basin, establishing the primary subsidence center in the west of the depression. By the Middle Jurassic, continued thrusting of surrounding fold belts caused a migration of the lake center and the main depocenter to the western edge of the Dongdaohaizi Depression, while the former depocenter gradually diminished. Furthermore, sustained erosion and denudation of the Mosowan Uplift during the Early–Middle Jurassic reduced its function as a structural barrier, thereby promoting increased mixing between eastern and western sediment sources. The study not only refines existing paleogeographic models of the Junggar Basin, but also demonstrates the utility of REE–trace geochemistry in deciphering complex provenance systems in tectonically active basins.

The evolution of the sedimentary environment in the Early Carboniferous Dawuba Formation of the Qiannan Depression significantly controlled the distribution of low-total organic carbon (TOC) sediments. In this study, the core samples were analyzed by thin section microscopy, field emission-scanning electron microscopy, pyrite morphology, X-ray diffraction, and geochemical analysis (TOC, sulfur, organic petrography, and major and trace elements). The formation is vertically divided into two members from bottom to top: Member 1 (average TOC = 1.15%) and Member 2 (average TOC = 0.88%). Depositional environment parameters indicate that Member 1 was in a suboxic-oxic transition environment, with weak detrital influx, and moderate paleoproductivity (more developed algae). Member 2 evolved into a stable oxic environment, with significantly enhanced detrital influx and reduced paleoproductivity. The correlations between multiple geochemical proxies (paleoredox, paleoproductivity, and terrestrial detrital influx) and TOC content indicate that high productivity in Member 1 was the main driver of organic matter accumulation, but the suboxic-oxic environment limited preservation efficiency (1.00% < TOC < 2.00%). Member 2, deposited during sea-level fall, experienced long-term oxic conditions and low productivity due to shallower water. Nevertheless, the partial reduction in the exposure time of organic matter within the oxic water column-driven by rapid detrital accumulation-represents a critical mechanism favoring organic-poor sediments (TOC < 1.00%). In conclusion, the development of low-TOC sediments in the Dawuba Formation reflects a transition from a relatively deep to shallow water column, where the synergistic effects of redox conditions, paleoproductivity, and terrigenous detrital influx controlled the distribution and enrichment of organic matter.