EVALUATING SEDIMENTARY MERCURY CONCENTRATIONS ACROSS THE LATE DEVONIAN FRASNIAN-FAMMENIAN MASS EXTINCTION EVENT FROM THE MICHIGAN AND APPALACHIAN BASINS

Over the last decade, massive volcanism has been linked to all mass extinction events during the Phanerozoic. Flood basalts and large igneous provinces (LIPs) have the capacity to release enormous amounts of climate-altering gases into the ocean/atmosphere systems and drive biogeochemical feedbacks that also result in the deterioration of the local and global environment. The Late Devonian Frasnian-Fammenian (F-F) mass extinction event (~372 Ma) is one of the five largest extinction events of the Phanerozoic and has recently been linked to the emplacement of multiple LIPs. In some of these F-F sedimentary successions mercury (Hg) enrichments are preserved, suggesting volcanic episodes where Hg is released and subsequently accumulated in sediments. Other F-F successions, however, do not display Hg anomalies, thereby challenging the notion that LIP emplacement played a major role in the extinctions. Furthermore, as supported here, sedimentary Hg anomalies are not exclusively associated with volcanogenic outgassing. Other mechanisms such as increased weathering, enhanced wildfires, and changes in local redox conditions or mineral assemblages can also change the Hg content of sediments.

We have generated sedimentary Hg content data from three study sites in the Michigan Basin (MB) and one study site in the Appalachian Basin (AB) to test the hypothesis that massive volcanism played a role in the F-F extinction. We present these Hg data from an intra- and inter-basin transect in the Late Devonian North American sea: the proximal basin margin, intermediate lower slope, and distal basin center in the MB, and one site closer to the open Rheic Ocean in the AB. These sites primarily contain organic matter-rich shales and include the Norwood, Paxton, and Lachine members of the Antrim Shale Formation in the MB, and the Chattanooga Shale in the AB. Important to the Hg proxy, local redox has been constrained with iron speciation data at all the study sites. Preliminary data from the AB suggest that Hg is primarily hosted in pyrite, indicating a local redox control on Hg contents, rather than increased volcanogenic inputs. After determining the mechanisms behind Hg accumulation in the MB, we will compare our datasets to available Hg data from around the world and examine the role of massive volcanism during the F-F extinction events.