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 Junggar Basin basement comprises microcontinental blocks amalgamated through successive paleo-oceanic accretion events. Stratigraphic and provenance studies within the basin are crucial for reconstructing its evolution and understanding the closure of paleo-oceanic systems. This study presents an integrated petrographic and geochemical analysis of the Lower Jurassic Badaowan Formation sandstones in the Dongdaohaizi Depression, located in the eastern Junggar Basin. The results reveal a progressive decrease in lithic fragment content and an increase in quartz content from older to younger strata within the Badaowan Formation, indicating an increase in compositional maturity. Provenance analysis indicates that the sandstones are predominantly derived from tuffaceous rocks, granites, basalts, and minor metamorphic rocks. Heavy mineral assemblages, including zircon, chromian spinel, tourmaline, and garnet, suggest parent rocks consisting primarily of intermediate to acidic igneous rocks, mafic igneous rocks, and metamorphic rocks. Integrated petrographic and geochemical data from the surrounding areas of the Dongdaohaizi Depression confirm that the Badaowan Formation sandstones are primarily sourced from the eastern Kelameili Mountain. The continued uplift and migration of the Kelameili Mountain during the Early Jurassic played a dominant role in shaping the sedimentary provenance. LA-ICP-MS analyses reveal that the rare earth element (REE) concentrations in the Lower Jurassic sandstones are slightly lower than the average REE content of the upper continental crust. The sandstones exhibit weak differentiation between light and heavy REEs, reflecting a depositional environment characterized by anoxic reducing conditions. Geochemical results indicate a tectonic setting dominated by a passive continental margin and continental island arc in the source area. Synthesizing these findings with related studies, we propose that the Kelameili Ocean, as part of the Paleo-Asian Ocean, underwent a complex evolution involving multiple oceanic basins and microcontinental subduction–collision systems. From the Middle Ordovician to Late Silurian, the Kelameili region evolved as a passive continental margin. With the onset of subduction during the Middle Devonian to Early Carboniferous, the eastern Junggar Basin transitioned into a continental island arc system. This tectonic transition was likely driven by episodic or bidirectional subduction of the Kelameili Ocean.