A deep-marine record of early Paleozoic mercury deposition from the Road River Group of northern Yukon, Canada

Mercury (Hg) enrichments in fine-grained sedimentary rocks have been widely applied as proxies for large-scale volcanism, particularly in association with models linking mass extinctions or global anoxic events to large igneous provinces (LIPs). For example, transient spikes in Hg/total organic carbon (Hg/TOC) ratios have recently been identified from Ordovician-Silurian boundary sections in South China and Nevada, as well through proposed anoxic events such as the upper Cambrian (Furongian) Steptoean Positive Carbon Isotope Excursion (SPICE) event in Newfoundland. These highly focused studies highlight relationships between Hg/TOC enrichments and proposed global environmental perturbations, but there has been little effort to develop long-term background records of Hg enrichments from single depositional basins or critical evaluations of Hg host phases in ancient marine deposits. Here we present over 500 measurements of coupled Hg, TOC, Fe speciation, bulk mineralogy, and major and trace element geochemistry from the ~2.5 km thick upper Cambrian-Middle Devonian Road River Group of north-central Yukon, Canada. Fine-grained carbonate and siliciclastic strata of the Road River Group are interpreted as slope to basin-floor deposits accumulating in an intra-platform setting. Integrated over the entire early Paleozoic record, these geochemical data reveal remarkable enrichments in Hg/TOC across the majority of the Ordovician Period, which are largely uncorrelated with host phase, TOC, detrital material, redox conditions, and/or other lithological indicators. Critically, these data support previous and recently published datasets that call for elevated global rates of Ordovician magmatism, but call into question whether Hg/TOC enrichments are always coincident with LIP events.