Research on Genesis of Pyrite near the Permian-Triassic Boundary in Meishan, Zhejiang, China

Abstract

Abstract The content and crystal forms of pyrite and sulfur isotope composition of pyrite sulfur as well as its vertical distribution near the Permian-Triassic (P/T) boundary in the Meishan section, Changxing county, Zhejiang province, China were studied using geological, petrological, mineralogical and geochemical methods (techniques). The result showed that the genesis of abundant pyrites in bed 24e2 at the uppermost part of the Changxing Formation in the Meishan section may be related to volcanic activity. In bed 24e2 of the Meishan section, pyrite has its highest content of 1.84% and the sulfur isotope composition has the highest δ 34 S value at +2.2‰ which is very similar to that of the average value of volcanic gas. There are some volcanic products such as β-quartz, siliceous cylinders and siliceous spherules which coexisted with pyrites in beds 24e2 and 24f. It can be concluded that a large quantity of volcanic ash fell into the South China Sea and was incorporated into marine sediments during the formation of limestone at the uppermost part of the Changxing Formation. The volcanic eruption with massive amounts of H 2 S and SO 2 gas at the end of the Permian period resulted in the enrichment of H 2 S in the South China Sea areas. The reaction of H 2 S with reactive iron minerals formed the mass of abundant pyrites.