Volcanism driven Pliensbachian (Early Jurassic) terrestrial climate and environment perturbations

Abstract

Initial breakup of Pangaea and opening of the Central Atlantic Ocean during the Early Jurassic resulted in widespread volcanism and was accompanied by significant changes in atmospheric composition, climate and environment of the Earth's surface system. Although profound changes in global geochemical cycles, palaeoclimate, and palaeoenvironments during the early part of the Toarcian Stage have been extensively studied and attributed to the emplacement of the Karro-Ferrar Large Igneous Province (LIP), similar changes in other parts of the Early Jurassic are less well known, especially in terrestrial settings. We studied Pliensbachian aged terrestrial strata from the Dameigou section in the Qaidam Basin of the Qinghai-Tibet Plateau to elucidate climate and environmental changes and their potential driving mechanisms. Three significant climate and environment perturbations were recognized by high-resolution mineralogical and geochemical analyses, with each characterized by peaks in kaolinite composition that indicate relatively warm and humid climates. Each kaolinite peak is accompanied by proxy evidence that indicates anoxic redox conditions, high paleoproductivity, and strong continental weathering prevailed, and coincides with negative carbon isotope excursions and peaks in Hg/TOC ratios that record three episodes of concurrent volcanism. The three episodes of volcanism are correlated with global events and suggest volcanism as the driving mechanism for major global climate and environment perturbations during the Pliensbachian. Each interval of volcanism released massive quantities of greenhouse gases and Hg into the atmosphere, leading to negative carbon isotope excursions and mercury anomalies in sedimentary strata. Global climatic warming induced by volcanism resulted in an enhanced hydrological cycle and can be correlated with more humid climatic conditions, intensified continental weathering and organic matter burial, lake expansion, and eutrophication. Such changes have important negative feedback on the global carbon cycle by increasing consumption of CO 2 in lacustrine settings, which in the late Pliensbachian led to the restoration of similar climates and environments that occurred pre-volcanism in the study area. • High-resolution Pliensbachian terrestrial climate and environmental change record. • Volcanism identified from negative carbon isotope excursions and Hg/TOC peaks. • Kaolinite, C-values, V/Cr ratios, and P/Al ratio peaks associated with volcanism. • Three Pliensbachian volcanic events coincide with climate and environment changes. • Volcanism driving environmental and climate change in terrestrial setting.