Geochemical characteristics and sedimentary environment of coal during Middle Jurassic in Yima Basin

In order to study the geochemical characteristics and sedimentary environment of the Middle Jurassic coal seam in the southwestern margin of the North China Plate, taking the coal of Yima Formation in Yima Basin as the research object to study the geochemical characteristics and sedimentary environment of Middle Jurassic coal seams in the southwest margin of the North China plate, based on the data from X-ray fluorescence spectrometer and plasma mass spectrometer. The results show that: The content of major element of SiO₂, P₂O₅ and K₂O are significantly higher, while the content of Al₂O₃ is lower compared with Chinese coals. Enrichment of Cs and deficit of Sb, Nb, Ta, Zr and Hf in trace elements. The rare earth elements are slightly enriched as a whole, with negative Eu anomalies and positive Ce anomalies, indicating that the coal seam was not affected by magma, hydrothermal and seawater, and the provenance is mainly terrigenous clastic. It shows that the coal forming environment in reductive environment, and the whole coal forming period is in semi-arid climate environment by the analysis of Th/U, V/ (V+Ni), Ce anomaly, Sr/Cu and climate index.