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 was especially important prior to anthropogenic emissions. To date, end-Permian and end-Triassic records illustrate the strongest use of Hg as a volcanic proxy; aided by supporting evidence (including Hg isotopes) for LIP eruptions and/or volatile emissions. Sedimentary records of several other events also document Hg enrichments in at least one region, suggesting regional or global Hg-cycle perturbations potentially linked to volcanism at those times. The Cenomanian-Turonian Oceanic Anoxic Event appears to be an exception, with Hg/TOC peaks documented in a small minority of studied records, suggesting minimal Hg-cycle disturbance at that time. Even for events that apparently featured a global-scale Hg-cycle perturbation, variable Hg enrichments across individual archives of that same crisis indicate that the complex biogeochemical cycling of the element can strongly influence local/regional aquatic, biological, or sedimentary processes to alter the precise signature of any worldwide disturbance. Recent studies are beginning to investigate these 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.

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

“…Mercury is chiefly emitted as a gaseous elemental species that typically has a residence time of 0.5-2 years in the stratosphere, enabling worldwide distribution before the element is ultimately deposited in sediments (Schroeder and Munthe, 1998;Ericksen et al, 2003;Selin et al, 2009). The global distribution of volcanic mercury has led several studies of geological events associated with LIPs to utilise sedimentary concentrations of the element as a proxy for the volcanism (see reviews by Grasby et al, 2019;Percival et al, 2021). This approach includes normalising sedimentary mercury concentrations against total organic carbon (TOC) content to account for the association of the element with organic compounds when it is deposited in sediments (Sanei et al, 2012, and references therein).…”

Tracing North Atlantic volcanism and seaway connectivity across the Paleocene–Eocene Thermal Maximum (PETM)

“…A widely used volcanic proxy is mercury (Hg) contents in sedimentary records (Grasby et al, 2019;Percival et al, 2021). Volcanic emissions are a primary source of gaseous Hg 0 that is rapidly dispersed through the atmosphere (Pyle and Mather, 2003).…”

Volcanism and carbon cycle perturbations in the High Arctic during the Late Jurassic – Early Cretaceous

“…Despite a number of caveats and considerations, Hg enrichment in the sedimentary record has been used as a proxy for volcanic eruptions, as volcanism is one of the major natural sources of Hg to the atmosphere (e.g. Sanei et al, 2012;Grasby et al, 2019;Percival et al, 2021b;Edwards et al, 2021). We investigate two sections from the East and West coast of Spitsbergen in the Svalbard archipelago, and two localities from Axel Heiberg Island in the Canadian Arctic, to determine if Hg is elevated across CIEs and contemporaneous with LIP activity in the Arctic.…”

“…Whilst volcanism is generally regarded as a major control on Hg in the geological record, a number of other processes can affect concentrations of this element in sedimentary rocks (see overviews by Sanei et al, 2012Sanei et al, , 2015Grasby et al, 2013Grasby et al, , 2019Percival et al, 2021b). Although Hg is dominantly sequestered with OM in oxygenated marine conditions, Hg may occasionally be removed and buried via other pathways that are partially controlled by ambient redox conditions.…”