Determining the style and provenance of magmatic activity during the Early Aptian Oceanic Anoxic Event (OAE 1a)

Large igneous province (LIP) volcanism has been proposed as a key trigger of several major climate and environmental perturbations during the Phanerozoic Aeon. Large-scale carbon emissions associated with one or both magmatic degassing from Greater Ontong-Java Plateau (G-OJP) intrusion organic-rich sediments by High Arctic LIP (HALIP) sills have widely suggested Early Aptian Oceanic Anoxic Event (OAE 1a: ~120 Ma). However, respective roles two LIPs sources in causing this crisis remain debated. Here, six records OAE 1a Pacific, Tethyan, Arctic, South Atlantic realms are investigated, combining mercury (Hg) concentrations osmium- (Os-) isotope ratios proxies activity. Together previously published datasets, results indicate globally consistent Os-isotope evidence for activity 1a, but geographically variable stratigraphic Hg trends. Clear enrichments that match activity, suggest Hg-cycle perturbation onset documented at Pacific site extremely proximal to G-OJP, not Tethyan records. This pattern highlights significant G-OJP re-emphasises limited potential submarine eruptions cause except areas very source. The absence clear peaks basal strata (or anywhere outside Pacific) does support intense HALIP time, suggesting was more volcanically active when commenced. Thus, mantle were likely played role initiating than thermogenic volatiles HALIP. A transient pulse HALIP-related subaerial and/or volatile early–middle part potentially evidenced widespread time (including Arctic), might prolonged event. non-volcanic these later influxes cannot be excluded. These findings challenge previous suggestions CO2 incapable carbon-cycle alone, highlight need further investigations establish whether high volume/emplacement rate (potentially an order magnitude greater other LIPs) made it unique case stands contrast provinces where crucial.