Geochemical Characteristics of Mudstones in the Permo-Carboniferous Strata of the Jiaozuo Coalfield and Their Paleoenvironmental Significance

Key words: 
• mudstones /
• main and trace elements /
• provenance analysis /
• paleoenvironment /
• Jiaozuo coalfield /

Abstract: Geochemical characteristics of mudstones contain a large amount of geological information, which are widely used in the analysis of provenance and sedimentary environments. The Permo-Carboniferous mudstones from the Jiaozuo Coalfield of Henan Province, northern China, were analyzed by means of X-ray fluorescence spectrometer and ICP-MS, and the major elements, trace elements, rare earth elements(REE) and minerals were determined. The provenance, source area weathering and paleoenvironmental characteristics are discussed. Argillaceous rocks were predominantly derived from post-Archean felsic igneous rocks based on the high values of Al₂O₃/TiO₂, low values of Cr/Zr,K₂O/Al₂O₃ and plots of Zr-TiO₂,Th/Co-La/Sc,Ni-Cr and (Gd/Yb)_N-Eu/Eu^*. The values of CIA were underestimated because of potassium metasomatism of the argillaceous source area reflected by Al₂O₃-CaO^*+Na₂O-K₂O diagrams and high clay mineral composition. Palaeo-weathering indices(CIW ratios) and Al₂O₃-CaO^*-Na₂O diagrams suggest that the source rocks were subjected to an extreme chemical weathering. Trace element composition characteristics (Sr/Ba, B/Ga) indicate that from the Benxi Formation to the early Taiyuan Formation, the sedimentary environment is marine facies, from the mid Taiyuan Formation to the early Shanxi Formation, the sedimentary environment is marine-continental transitional facies, from the mid Shanxi Formation to the Shangshihezi Formation, and the sedimentary environment is continental facies.