The Permian-Triassic boundary event: a geochemical study of three Chinese sections

Trace elements were determined in two well-documented Chinese Permian-Triassic (P/Tr) boundary sections (Meishan and Shangsi) and in a new section (Liangfenya). Iridium concentrations range from 3 to 87 pg/g, at or below levels in common sedimentary rocks. The results contrast with previous reports of high Ir concentration in the Meishan and Shangsi sections and offer no support to suggestions of a major meteoroid impact at the end of the Permian. A notable feature in each of these widely separated P/Tr sections (500–1500 km) is the existence of 2–5 light-colored clay layers at and near the boundary. These clay layers are strongly enriched in Cs, Zr, Hf, Ta, and Th and depleted in Cr, Co, and Ir, indicating that they are altered ash, apparently from the same massive silicic volcanic eruptions. We estimate the magnitude of these eruptions to be a few thousand km³ of magma, a volume comparable to the great Toba eruption.