Volcanism-induced late Boda warming in the Late Ordovician: Evidence from the Upper Yangtze Platform, South China

Abstract

Late Boda warming was the last warm episode in the Late Ordovician, and little is known about its cause. Volcanism was a hypothetical candidate that triggered this warming event owing to its potential to enhance the atmospheric CO2 level. Here, we conducted a high-resolution petrographic and geochemical study on the bentonite beds-bearing intervals from the Upper Ordovician Wufeng Formation in South China. This investigation enables us to find the detailed process of paleoenvironmental repercussions induced by volcanism from both short-term and long-term perspectives. The short-term effect was revealed by a 25-cm-long drill core bracketing three cycles of volcanic activity. Three nearly identical cycles have been identified, and each cycle is comprised of a bentonite bed, a siliceous clay-rich mudstone interval, a radiolarian bed, and a siliceous mudstone interval with intercalations of thin pyrite layer. During the eruption stage, a series of environmental and biogeochemical disruptions were brought to the local system, including ocean fertilization, the elevation of paleoproductivity, the onset of euxinia/intensified ocean anoxia, a warmer climate, and enhanced weathering. With the waning of volcanic activities, the volcanic impacts weakened, and a relatively stable water-column chemistry, microbial populations, diversity, and community structure were established until the onset of the subsequent volcanic event that broke equilibrium. The long-term effect was illustrated by the correlation between the distribution of bentonite beds and coeval global sea-level fluctuations. Our results show that intense and frequent volcanic activities in South China, probably contributed by coeval volcanic activities from other regions worldwide, exerted a cumulative heating effect on the global system, contributing to late Boda warming.