Carbon‐cycle perturbations and intensified continental chemical weathering linked to volcanism during the Jenkyns Event in the Ordos Basin

Abstract

The Jenkyns Event (~183 Ma) represents an exceptional warming period in the Jurassic, which is characterized by intense environmental and climate perturbation. The eruption of the Karoo‐Ferrar Large Igneous Province (K‐F LIP) triggered pronounced carbon isotope negative excursion (N‐CIE) in exogenic carbon reservoirs, global widespread organic carbon burial and extensive ocean anoxia. However, the synchronic coupling relationship between the carbon release, volcanic activity, and intense weathering induced by the K‐F LIP during this period remains poorly understood. In this study, detailed sedimentologic and geochemical studies were conducted on the terrestrial stratigraphy of the Lower Jurassic Fuxian Formation in the Ordos Basin. Three spore‐pollen assemblages have been identified, with the Cyathidites‐Deltoidospora‐Chasmatosporites assemblage suggesting a Pliensbachian age, the Classopollis‐Cycadopites‐Chasmatosporites assemblage indicating an early to middle Toarcian age, and the Cyathidites‐Cycadopites‐Psophosphaera assemblage indicating a late Toarcian age. The lower part of the Classopollis‐Cycadopites‐Chasmatosporites assemblage shows a negative CIE with a magnitude of 2.7‰, accompanied by organic carbon enrichment. Mercury concentrations and Hg/total organic carbon ratios also show peaks during the initial stage of the carbon isotope negative shift, implying a synchrony between volcanic activities and carbon perturbation. Furthermore, the Chemical Index of Alteration value has reached its maximum and the kaolinite content shows a sharp increase at the same position as the carbon isotope negative shift initiation, indicating a simultaneous enhancement of continental weathering during volcanic activity. The changing patterns of the continental weathering intensity encompassing the Jenkyns Event also indicate that continental weathering may have functioned as a significant approach to counteract the greenhouse effect caused by substantial volcanic CO2 emissions.