GLOBAL PERTURBATIONS OF CARBON CYCLE DURING THE TRIASSIC-JURASSIC TRANSITION RECORDED IN THE MID-PANTHALASSA

To investigate environmental changes across the Triassic-Jurassic boundary (TJB), with a particular focus on possible relationships between perturbations of the carbon cycle in the mid-Panthalassa and CAMP volcanism, we established organic carbon isotope records in the Katsuyama section in the Inuyama area, Mino-Tanba belt, SW Japan. High-resolution record of Rhaetian to Hettangian δ¹³C_org values in the mid-Panthalassa contain three distinct negative carbon isotopic excursions (NCIEs) before and across the TJB: the Rhaetian NCIE1 and NCIE2 show a deviation of 5.0‰ from ca. -24.0‰ to ca. -29.0‰, whereas NCIE3 across the TJB shows a 3.5‰ deviation from ca. -23.5‰ to ca. -27.0‰. Our newly obtained NCIEs in the deep mid-Panthalassa can be correlated with the δ¹³C_org records in the shallow-marine Tethyan regions (i.e., precursor, initial, and main CIEs), suggesting that three NCIEs in the Tethys and mid-Panthalassa likely reflected the global perturbations of the carbon cycle. Three NCIEs before and across the TJB can be interpreted as the consequence of the multiple CAMP volcanic episodes; i.e., the release of thermogenic methane from organic-rich sediments by CAMP intrusive rocks for NCIE1 and large-scale volcanically derived carbon species for NCIE2 and NCIE3. In addition, progressive increase of atmospheric pCO₂ throughout three NCIEs was possibly attributed to accumulation of volcanically derived CO₂ from multiple CAMP eruptions, which resulted in the development of ocean acidification across the TJB. On the other hand, in view of the oxic conditions in the deep mid-Panthalassa during three NCIEs, the development of coeval oceanic anoxic-euxinic conditions was restricted solely to shallow-marine regions. Therefore, ocean acidification together with localized shallow-marine anoxia acted as environmental stresses on the biosphere, which eventually resulted in the severe biotic crisis at the end of the Triassic.