MERCURY CONCENTRATIONS AND ISOTOPES AS TRACERS OF CAMP IN TRIASSIC-JURASSIC STRATA FROM MULLER CANYON, NEVADA
Recent high-resolution age dating indicates that the end-Triassic mass extinction coincided with the eruption of the Central Atlantic Magmatic Province (CAMP), and the release of CO2 and other volatiles to the atmosphere has been implicated in the extinction. However, the timing of global marine biotic recovery versus the CAMP eruptions is still uncertain. To better resolve this timing, we use Hg concentrations and stable Hg isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic-Jurassic strata from Muller Canyon, Nevada, both Hg concentrations and Hg/TOC ratios rise within the extinction interval and peak just before the appearance of the first Jurassic ammonite. Mercury anomalies persist in association with a depauperate earliest Jurassic fauna, but disappear before significant pelagic and benthic faunal recovery begins. Within the extinction and depauperate intervals, Hg isotopes display no significant mass independent fractionation (MIF), a signature consistent with a volcanic origin for the Hg in these strata. In contrast, strata below and above these intervals display measurable Hg-MIF, similar to signatures observed in modern coastal and oceanic sediments. If the Hg anomalies are volcanic in origin, as suggested by the isotopic evidence, then significant biotic recovery did not begin until the CAMP eruptions ceased. These data not only provide new insight into the timing of biotic recovery following the end-Triassic mass extinction, but support the use of Hg concentrations, Hg/TOC ratios, and Hg isotopes as fingerprints for CAMP (or any large igneous province) in sedimentary successions that largely lack datable ash beds.