Sedimentary Mercury Enrichments as a Tracer of Large Igneous Province Volcanism

Abstract

Volcanic activity associated with the emplacement of Large Igneous Provinces (LIPs) has been linked to most Phanerozoic extinctions/episodes of major environmental change. In recent years, mercury (Hg) enrichments and elevated mercury/total organic carbon (Hg/TOC) ratios have been increasingly utilized as a marker of volcanism in sedimentary records deposited distally from LIPs. The proxy is based on the premise that volcanism is a major natural source of the element to the atmosphere, and that it was especially important prior to anthropogenic emissions. To date, end-Permian and end-Triassic records illustrate the strongest use of Hg as a marker of volcanic activity, supplemented by the use of Hg isotopes and other evidence for LIP eruptions and volatile emissions. Sedimentary records of several other events also document Hg enrichments in at least one region, suggestive of a regional- or global-scale perturbation to the Hg cycle at those times, potentially linked to volcanism. The Cenomanian– Turonian Oceanic Anoxic Event 2 appears to be the exception, with strata documenting peaks in Hg/TOC in a small minority of studied records, suggesting that there was only a minimal perturbation to the Hg cycle at that time. Even for events where a global Hg-cycle perturbation apparently occurred, varying Hg enrichments documented from individual archives of the same event indicate that the complex biogeochemical cycling of mercury can result in a strong influence of local/regional aquatic, biological, or sedimentary processes on the precise signature of any worldwide disturbance. Of additional intrigue is an apparent lack of correlation of Hg and Hg/TOC with other volcanic proxies such as osmium isotopes, suggesting that the two systems record different aspects of LIP volcanism and emplacement. Recent studies are beginning to investigate these above complexities, but further work is needed to fully explore the nuances of Hg in the geological record, and how it can be best employed as a proxy for LIP volcanism.