Major and Rare Earth Element Characteristics of Late Paleozoic Coal in the Southeastern Qinshui Basin: Implications for Depositional Environments and Provenance
Chunlan Yu, Nana Mu, Wenhui Huang, Wenguo Xu, Xiaokuan Feng
Abstract
O (0.04%) (on a whole-coal basis). Through correlation analysis and cluster analysis, the occurrence states of major elements in the Shanxi and Taiyuan Formations are different. The average rare earth elements and yttrium (REY) value in the study area is 88.68 μg/g (on a whole-coal basis). The mean light REY (LREY)-to-heavy REY (HREY) ratio is 26.33. The mean values of δEu, δCe, Y, and Gd are 0.60, 0.99, 1.07, and 1.02, respectively. The Shanxi Formation is dominated by the L-type REY enrichment, while the Taiyuan Formation is dominated by the M-H-type REY enrichment. The fractionation degree of REY in the Taiyuan Formation is lower than that in the Shanxi Formation. Rare earth elements in Shanxi coal mainly occur in clay minerals, and some rare earth elements are adsorbed and enriched by vitrinite. Rare earth elements in Taiyuan coal mainly occur in clay minerals and pyrite, and some rare earth elements occur in inertinite. A warm, humid, low-salinity, oxidizing, and acidic environment was favorable for REY enrichment. The coal-forming environment was weakly oxidizing and reducing, and the paleosalinity of the water was relatively high during late Paleozoic coal deposition in the southeastern Qinshui Basin. The paleotemperature of the Shanxi Formation is higher than that of the Taiyuan Formation. The provenance is mainly from an upper crustal felsic source region, the source rocks are mainly post-Archean sedimentary and calcareous mudstones mixed with some granite and alkaline basalt from the Yinshan Upland, and the tectonic setting of the source area mainly includes island arcs and active continental margins.