Records of organic carbon isotopic composition (δ~(13)C_(org)) and volcanism linked to changes in atmospheric pCO_2 and climate during the Late Paleozoic Icehouse

摘要

The Late Paleozoic Icehouse (LPI) provides a deep-time perspective for climate-glaciation-environment coevolution and offers potential insights into future climatic and environmental predictions. Most previous studies attributed climatic and environmental changes during the LPI to perturbations of atmospheric pCO(2), yet the driving mechanism for pCO(2) changes remains controversial. Although the environmental and climatic effects of volcanism have been recognized, its high-resolution geological records and links with changes in atmospheric pCO(2) and climate are rarely reported. We address this by investigating volcanic records (indicating by Hg/TOC ratio) and organic carbon isotope composition (delta C-13(org)) of paralic strata from the latest Gzhelian to Roadian stages in the North China Platform (NCP), China. Four delta C-13(org) negative excursions (latest Gzhelian, middle Artinskian, middle Kungurian and latest Kungurian stages) and two positive isotope plateaus (Asselian and Roadian stages) are identified. Each of the four negative isotope excursions coincides with peaks in Hg/TOC ratio and rising periods of atmospheric pCO(2). The co-occurrence of the negative isotope excursions and Hg/TOC peaks suggests volcanic origins for both the Hg and perturbations in the carbon cycle. The two positive isotope plateaus correspond to the glacial P1 and the climatic transition period to glacial P3 in Australia and to weak periods of volcanism. Our results provide clear insights into volcanism driving perturbations in environment, climate and the carbon cycle in deep time, and support the assertion that volcanism was sufficient to shift global climates from glacial to interglacial through greenhouse gas emissions during the LPI.