The coal-forming environment during mass extinction in the latest permian: Evidence from geochemistry of rare Earth elements

Abstract

The C1 coal of Latest Permian during mass extinction in eastern Yunnan was studied to reveal the terrestrial paleoenvironment and influence of geological events on coal-formation during mass extinction. An analysis of Rare Earth Elements (REEs) was conducted on the C1 coal from the Yantang Mine of Xuanwei, eastern Yunnan Province, which was deposited during the latest Permian. A total of 24 samples from coals, partings, roofs and floors from the C1 coal were taken from the fresh face in the underground mine. The results of the REEs analysis indicated that the total REE content (∑REE) in the C1 coal varies from 23.99 μg/g to 267.94 μg/g, averaged 122.69 μg/g. The C1 coal is enriched in light REE (LREE) relative to heavy REE (HREE), signifying the fractionation between LREE and HREE. Most samples of the coal seam C1 are depleted in Eu in various degrees and slightly depleted in Ce, especially two partings in sub-seams B1 and B3 which show the significant negative Eu anomalies. The geochemical characteristics of REE reveal that the C1 coal was deposited in a weak oxidation environment; the sedimentary environment was turbulent during the middle-later stage of coal-forming process; the C1 coal was affected by the basalt clastic materials from the Khangdian Oldland and acidic synsedimentary volcanic ash in the coal-forming period. The geochemical characteristics of Tonsteins in C1 coal are similar to those of marine Permian-Triassic boundary (PTB) volcanic ash layers in South China, which are both derived from the felsic volcanism caused by the closure of the Paleo-Tethys at the southwestern margin of the South China. Furthermore, the C1 coal was also affected by the eruption of Siberian large igneous province (SLIP) in the early stage.

The Coal-Forming Environment at the End of the Late Permian and Its Control on Trace Elements: A Case Study of the C3 Coal Seam of the Xuanwei Formation in Eastern Yunnan, China

“…The samples were preprocessed by low-temperature airproof acid digestion. The procedure has been described in detail by Wang et al (2023). The prepared samples were then analyzed using inductively coupled-plasma mass spectrometry) (Finnigan MAT, Thermo Fisher Scientific, Waltham, MA, USA), with a relative analysis error of ± 5%, according to the Chinese Standard GB/T 14506.30-2010.…”

“…This is a large area of ancient crystalline rocks reduced to a low relief by lengthy erosion through the Late Paleozoic, which was significantly affected by Emeishan mantle plume activity (He et al, 2006;Wang et al, 2022;Shao et al, 2023). Controlled by a transgression from the east throughout the Late Permian and Early Triassic, the depositional environments in eastern Yunnan and western Guizhou during the Late Permian vary from marine, transitional to terrestrial facies from east to west (Figure 1b) ( Wang et al, 2012;Wang et al, 2023;Shao et al, 2023). The continental Late Permian-Early Triassic strata in southwest China are subdivided into the Xuanwei and Kayitou Formations in ascending order (Figure 1c) (Shen et al, 2011;Shao et al, 2013;Zhang et al, 2016).…”