Brief and intensive volcanic emissions from Ontong Java Nui heralded Oceanic Anoxic Event 1a

Abstract

The volcanic episode that formed Ontong Java Nui (OJN) in the western Pacific ~ 120 million-year-ago is thought to have triggered Oceanic Anoxic Event (OAE) 1a, yet the cause-effect relationship remains insufficiently understood. Here, we present a Pb-Os-C isotope dataset for tracking OJN volcanism across a sedimentary sequence containing OAE1a record in the central Pacific. Lead isotopic evidence strongly supports the deposition of OJN-sourced volcanic ash layers at this site after a paired seawater δ13Ccarb–187Os/188Os shift and before the onset of OAE1a. The δ13Ccarb–187Os/188Os shift is attributable to the signature of the initial submarine OJN eruption. The subsequent unradiogenic Pb isotope shifts could represent ash fallout from the brief, explosive subaerial/shallow-marine eruption phase accompanied by intensive volcanic degassing and emissions. The apparent time lag between explosive OJN volcanism and OAE1a is intriguing, which can be accounted for by the delayed increase in the productivity after gas emissions.