Exploring the use of mercury in reconstructing the environmental impacts of Large Igneous Provinces

Thesis

Large Igneous Provinces (LIPs) represent geologically rapid emplacements of vast quantities of igneous material into/onto Earth’s crust. There is a marked correlation in the known ages of LIPs and Mesozoic extinctions and other environmental perturbations, suggesting a possible causal link between these events. However, uncertainties in matching LIP basalt ages to the stratigraphic record of Mesozoic events mean that a sedimentary tracer of volcanism would better indicate a precise coincidence between the two phenomena. Mercury (Hg) has shown potential as such a proxy. Volcanism is a major source of Hg to the natural environment, and its relatively long atmospheric residence time (0.5–2 years) allows global distribution of the element before it is deposited to sediments. However, questions remain about how the manner of LIP emplacement might influence its impact on the Hg cycle, as well as how sedimentary processes may locally overprint any global signal. Here, the Hg records of three Mesozoic events are investigated: the end-Triassic extinction (TJ: ~201.5 Ma), Cretaceous Oceanic Anoxic Event 2 (OAE 2: ~94 Ma), and the latest Cretaceous (K–Pg: ~67–66 Ma). These events coincided with markedly different LIPs: OAE 2 with multiple submarine LIPs; the K–Pg and TJ with subaerial LIPs; with the TJ also featuring release of additional thermogenic volatiles from intrusion of organic-rich lithologies by LIP sills. Additionally, mercury is used with osmium and carbon isotopes to study the temporal relationships between volcanism, weathering, and the carbon cycle during the Toarcian Oceanic Anoxic Event (~183 Ma). This work highlights the links between LIP volcanism and other surface processes, and shows that subaerial LIPs featuring thermogenic emissions are most likely to perturb the global Hg cycle, with the record of such perturbations dependent on the nature of the sedimentary archive.

Authors: Percival, L

• Alternative title: Mercury as a tracer of Large Igneous Province volcanism
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Palaeoclimate; Geochemistry; Mercury; Volcanism; Mass extinctions
• Subjects: Volcanology; Mercury Geochemistry; Palaeoclimate