MERCURY AS A PROXY FOR LARGE IGNEOUS PROVINCE VOLCANISM: A COMPARISON OF MESOZOIC EVENTS

Mass extinction events and other episodes of palaeoceanographic and palaeoclimatic upheaval, such as Oceanic Anoxic Events (OAEs), have punctuated global climate throughout the Phanerozoic Aeon. Many of these events have been causally linked with the formation of Large Igneous Provinces (LIPs), which represent the geologically abrupt emplacement of millions of cubic kilometres of igneous material. This relationship is indicated by the coincidence in the determined ages of many LIPs with the apparent ages of environmental perturbation, and from the sedimentary record, where stratigraphic horizons recording palaeoclimatic events commonly also record perturbations in sedimentary proxies for volcanism. A number of recent studies have highlighted elevated Hg/TOC (mercury/total organic carbon) in sedimentary archives recording mass extinctions. As one of the main natural sources of mercury to the modern environment is volcanic outgassing, such Hg/TOC excursions have been used to support a precise temporal link of many major environmental perturbations with LIP volcanism. However, questions remain regarding the influence of both volcanic and sedimentary processes on any Hg record of LIP volcanic activity. Here, new Hg/TOC data are presented from records of the end-Triassic extinction and Late Cretaceous OAE 2, which are associated with notably different styles of LIP volcanism. End-Triassic LIP volcanism was subaerial, and likely featured the generation of additional thermogenic volatiles, whereas LIP volcanism during OAE 2 was predominantly subaqueous. The new Hg/TOC trends are also compared with those of the Toarcian (Early Jurassic) OAE to investigate possible sedimentary influences on the preservation of volcanic Hg signals. Comparing the Hg records of multiple events is crucial to further understanding of the controls on Hg/TOC as a volcanic proxy, as well as the processes governing relationships between different environmental perturbations and the formation of LIPs.