MERCURY CONCENTRATION AS AN INDICATOR OF DECCAN TRAPS VOLCANISM IN LATE CRETACEOUS AND EARLIEST PALEOGENE SEDIMENTS FROM THE HELL CREEK REGION, MONTANA

Despite decades of research, the exact cause of the end-Cretaceous extinction remains unknown. The dominant hypotheses point to either the Chicxulub bolide impact or Deccan Traps (DT) volcanism, or both, as the instigator of the ecological and environmental changes that led to the mass extinction. While the impact has been precisely dated, even the best dates for the DT volcanism have an uncertainty of 60,000 years, and there is a paucity of data from near the Cretaceous-Paleogene boundary. Moreover the cessation of volcanism remains undated, even in the relatively well-studied Western Ghats, as material has been lost due to erosion. The lack of clear chronology for the DT eruptions in the late Cretaceous and early Paleogene prevents direct correlation between the eruptions and ecological changes. As the pacing of the eruptions may have been a factor in the both the extinction and the recovery, there is a need for a signal to construct a relative timeline with high precision—making it more useful for comparison with biological and paleoenvironmental records. This study uses mercury (Hg) concentration as one such signal. Several recent studies (e.g. Font et al., 2016; Sial et al., 2016; Thibodeau et al., 2016) have used Hg concentration as an indicator of volcanism in marine deposits. Hg is ideal for this purpose, as volcanic eruptions are its most significant non-anthropogenic source. Additionally, it has an atmospheric residence time of about a year, making it capable of spreading globally and being preserved in distal sections. Hg also has several stable isotopes, and in the future, isotopic composition could be used to distinguish between local and DT volcanic sources.

We will present preliminary Hg concentration data from the fluvial and floodplain sediments of the Hell Creek region of northeastern Montana, and assess the feasibility of using the terrestrial Hg record as a proxy for DT volcanism. The Hell Creek region is the one of the best-studied terrestrial K-Pg localities in the world, and there is an abundance of paleontological, geochemical, and geochronological data that creates a highly-resolved record of ecological and environmental change. The Hg chemostratigraphy could allow us to directly compare the pacing of DT eruptions with these records and evaluate the role the eruptions had in the extinction event.