TIMING AND ALTERNATIVE ECOSYSTEM STATES FOLLOWING THE END-TRIASSIC MASS EXTINCTION (NEVADA, PERU, ENGLAND): INSIGHTS FROM HG ANOMALIES AND THEIR RELATIONSHIP TO THE CENTRAL ATLANTIC MAGMATIC PROVINCE (Invited Presentation)

The end-Triassic mass extinction overlapped 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 more uncertain. Here, we use Hg concentration, Hg/TOC ratios, and Hg isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. We have measured Hg anomalies associated with the Triassic-Jurassic (T-J) transition in Nevada, Peru, and England, and others have recently reported Hg anomalies in additional T-J successions, indicating a global signal. In T-J strata, Hg and Hg/TOC levels are low prior to the extinction, rise sharply in the extinction interval, peak just prior to the appearance of the first Jurassic ammonite, and remain above background in association with a depauperate (low diversity) earliest Jurassic fauna. The return of Hg to pre-extinction levels is associated with a significant pelagic and benthic faunal recovery. Thus, we conclude that significant biotic recovery did not begin until CAMP eruptions ceased. We also report the existence of mass independent fractionation (MIF) of Hg isotopes prior to the extinction and following the start of the recovery, whereas intervening strata record the lack of MIF, consistent with a dominantly geogenic source for Hg. Furthermore, the initial benthic recovery involved an alternative ecosystem state—the expansion of a siliceous sponge-dominated ecosystem across shallow marine environments (e.g., Nevada, Peru, Morocco, Austria)—before carbonate dominated benthic ecosystems recovered. Carbonate system did not recover for ~1 million years following the last eruption of CAMP, longer than the typical duration considered for ocean acidification events, implying other factors may have played a role in carbonate ecosystem dynamics after the extinction.