09:30 〜 09:45
[MIS06-02] Reaffirming the link between Early Cretaceous Ontong Java volcanic event and global environmental perturbations
キーワード：オントンジャワ海台、海洋無酸素事変1a、アプチアン
The volcanic eruption that formed Ontong Java Nui (OJN) is believed to have triggered substantial environmental disturbances during the Early Cretaceous, including global warming, decrease in the heavily calcified planktons, and Oceanic Anoxic Event (OAE) 1a. However, this general belief has been challenged recently due to apparent younger ages of OJN basalts that postdate Early Cretaceous environmental perturbations (Davidson et al., 2023). Yet, analysis of depositional ages from several drill sites, such as Deep Sea Drilling Program (DSDP) Sites 167 and 463, supports contemporaneous deposition of sediments that record environmental changes with OJN-derived volcanic ash layers (Matsumoto et al., 2024, 2025). Thus, the exact timing of OJN volcanism and its linkage with the sediments deposited during the Early Cretaceous environmental perturbations remain actively debated.
A more direct approach to resolve this problem is to determine the provenance of volcanic ash layers deposited in early Aptian. DSDP Site 167 on Magellan Rise close to OJN contains thick early Aptian (~120 Ma) tuffaceous sediments that are potentially derived from OJN volcanism. Therefore, this core is regarded as a valuable archive for constraining the timing of OJN eruptions and their environmental impact, but the lack of geochemical data for these tuffaceous sediments hindered correlating their provenance to OJN until now.
In this study, we conducted Pb isotopic analysis to trace the source of volcanic ash layers and assess their link to environmental perturbations. Our data confirm that these volcanic ash layers most likely originated from the OJN eruption. Specifically, stratigraphic variations in Pb isotopic compositions indicate a transition in OJN volcanism—from Kwaimbaita/Kroenke-like magma, which formed the lower part of OJN, to Singgalo-like magma, which formed the upper part. By integrating previously reported Os and C isotopic data, we suggest that this explosive volcanic phase was accompanied by extensive volatile emissions. Although this volcanic phase was brief, it likely contributed to succeeding long-term environmental disturbances, including global warming, ocean acidification, and OAE1a.
A more direct approach to resolve this problem is to determine the provenance of volcanic ash layers deposited in early Aptian. DSDP Site 167 on Magellan Rise close to OJN contains thick early Aptian (~120 Ma) tuffaceous sediments that are potentially derived from OJN volcanism. Therefore, this core is regarded as a valuable archive for constraining the timing of OJN eruptions and their environmental impact, but the lack of geochemical data for these tuffaceous sediments hindered correlating their provenance to OJN until now.
In this study, we conducted Pb isotopic analysis to trace the source of volcanic ash layers and assess their link to environmental perturbations. Our data confirm that these volcanic ash layers most likely originated from the OJN eruption. Specifically, stratigraphic variations in Pb isotopic compositions indicate a transition in OJN volcanism—from Kwaimbaita/Kroenke-like magma, which formed the lower part of OJN, to Singgalo-like magma, which formed the upper part. By integrating previously reported Os and C isotopic data, we suggest that this explosive volcanic phase was accompanied by extensive volatile emissions. Although this volcanic phase was brief, it likely contributed to succeeding long-term environmental disturbances, including global warming, ocean acidification, and OAE1a.