Geochemical Characteristics and Sedimentary Paleoenvironment of the Coal-Bearing Strata in the Xishanyao Formation: A Case Study of the Yihua Coal Mine in the Zhundong Coalfield, Xinjiang

The eastern Junggar Basin in Xinjiang harbors abundant coal resources within the Middle Jurassic Xishanyao Formation. However, the formation environment associated with these coal-bearing strata remains unclear. Geochemical characteristics serve as crucial geological indicators of the sedimentary period. Therefore, it is imperative to explore the geochemical attributes and sedimentary context of the coal-rich layers within the Middle Jurassic Xishanyao Formation in the Zhundong region to enhance the prospects of coal extraction and utilization. The elemental compositions, both major and trace, of the Xishanyao Formation were analyzed through X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). A comprehensive analysis was conducted on the sediment provenance, tectonic background, and depositional environment of the coal-bearing strata in the Xishanyao Formation. Moreover, through the utilization of a range of discrimination indices, including Sr/Cu, B/Ga, Sr/Ba, V/Cr, Ni/Co, and δCe, the paleo-depositional setting of the coal-containing layers was reconstructed. The findings suggest that the primary source rocks of the coal-bearing beds in the Xishanyao Formation consist of continental tholeiites, with the predominant material composition in the source region being felsic volcanic rocks originating from the upper crust. The tectonic backdrop of the source region is marked by a continental island arc environment. During the sedimentation period of the Xishanyao Formation, the depositional environment was characterized by a freshwater oxidizing setting. Additionally, it experienced a transition from arid-hot to humid-hot before returning to arid-hot conditions.