MERCURY CHEMOSTRATIGRAPHY THROUGH THE CRETACEOUS-PALEOGENE BOUNDARY IN THE HELL CREEK REGION OF MONTANA AND ITS RELATIONSHIP TO DECCAN VOLCANISM

Despite substantial research, the exact mechanisms and causes of the end-Cretaceous mass extinction are still unresolved. Most research points to either the Chicxulub impact, Deccan traps (DT) eruptions, or both, as the likely culprit ­— since both events could have caused extensive environmental changes leading to mass extinction. Since the pacing of the eruptions, currently being refined via high-precision ⁴⁰Ar/³⁹Ar geochronology, may have been a factor in the both the extinction and recovery, there is a need for a tracer to construct a relative timeline with high precision—making it more useful to compare with biological and paleoenvironmental records.

This study uses mercury (Hg) concentration as one such signal. 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 global dispersion and deposition. Parallel analysis of other compositional data (e.g., Al and TOC) facilitates recognition of possible biases from e.g. biotic or clay adsorption effects. Hg chemostratigraphy in the Hell Creek region of Montana, where a high-resolution chronostratigraphy through the Cretaceous-Paleogene boundary (KPB) mass extinction and recovery interval has been established, will allow us to directly compare the pacing of DT eruptions with biological and paleoenvironmental records and evaluate the role the eruptions had on the extinction event.

We will present Hg concentration data spanning the KPB from two stratigraphic sections in the Hell Creek region. We see multiple peaks in Hg concentration, including one within centimeters of the KPB, in both localities. The origin of these peaks is uncertain, however those very close to the boundary can be linked with local or Deccan volcanism, or potentially with the Chicxulub impact. Later peaks in the Paleogene are also noted, which presumably are solely of volcanic origin. This is the first set of results from an ongoing project creating a high resolution Hg record through the entire DT eruptive interval.