Environmental perturbations during the latest Permian: Evidence from organic carbon and mercury isotopes of a coal-bearing section in Yunnan Province, southwestern China

摘要

The end-Permian mass extinction (EPME) is sudden, but prior to which, the ecological resilience has diminished. The Late Permian is an important geologic period for coal formation associated with extensive volcanic activities in South China and adjacent regions. Here we present a systematic analysis of organic carbon and mercury isotopes as well as elemental geochemistry and mineralogy of a coal-bearing section from the Lianying Coalfield in Yunnan Province, South China. The data show that organic carbon δ~(13)C values are negatively shifted by -25.22‰ to -25.99‰ in pyroclastic tonstein partings, which are near-synchronous with the negative Eu anomaly (0.48-0.52), significant Hg enrichment (130-352 ppb) and near-zero Δ~(199)Hg (-0.08-0.07‰). These C and Hg isotope anomalies and associated geochemical signatures, which are manifested by characteristic Al_2O_3/ TiO_2, Zr/TiO_2, and Nb/Yb ratios, are likely caused by subduction or collision-related volcanism. Our study provides evidence for the occurrences of volcanism before the advent of EPME, which played a significant role in stressing the environment and consequently diminishing the ecological resilience in the latest Permian.