COMPARATIVE ANALYSIS OF SEDIMENTARY MERCURY GEOCHEMICAL RECORDS FROM LAND TO OPEN OCEAN DURING THE TRIASSIC-JURASSIC TRANSITION

The Triassic-Jurassic (T-J) transition is associated with one of the largest mass extinctions of the Phanerozoic, the end-Triassic mass extinction (ETE). Hypothesized drivers of this extinction have ranged from extreme temperature change, ocean acidification, eutrophication and enhanced reducing conditions in the oceans (i.e., extent of anoxic and euxinic conditions increased), to an extraterrestrial impactor. More recently, emphasis has been placed on the role of the Central Atlantic Magmatic Province (CAMP), which may have erupted voluminous amounts of climate-altering gases into the atmosphere, leading to a multitude of environmental feedbacks, ultimately stressing life on Earth. It has been suggested that sedimentary mercury (Hg) geochemistry has pinpointed the eruptive events associated with pulses of CAMP emplacement during the ETE. Both Hg concentration and Hg/TOC anomalies are interpreted as the outcome of increased atmospheric fallout of CAMP-derived gaseous Hg. This is problematic because other common secondary environmental processes, not directly related to volcanism, such as changes in weathering, wildfires, redox, and other biogeochemical feedbacks may also be responsible for sedimentary Hg enrichments.

Here, we generated new concentration data of Hg and pyrite from open Panthalassa (Wrangell Mountains, Alaska) and the restricted Laurasian Sea (United Kingdom) to explore potential local vs. regional environmental effects within the Hg cycle. Our comparative study provides a critical opportunity to distinguish the underlying controls of the T-J Hg cycle driving observed enrichments. Our data suggest that the T-J sedimentary Hg enrichments were dependent on a combination of local redox variability, weathering intensity and soil destabilization, detrital input, wildfires, and aridification, which is contrary to the current interpretation of direct volcanogenic outgassing as the primary or dominant source. Moreover, there is no distinct evidence for enhanced atmospheric fallout of Hg at either study locality. Combined with a global compilation, mostly shallow-water marginal and terrestrial locations, these data suggest a greater influence on the Hg cycle from many other secondary processes rather than a direct influence from CAMP-related volcanism.