LARGE, RAPID EARLY TRIASSIC SULFUR ISOTOPE SHIFTS RECORDED IN MARINE CARBONATES FROM THE WESTERN U.S

The Early Triassic records the ~5 My aftermath and delayed biological recovery from the end-Permian mass extinction (~252 Ma). Large perturbations of several isotope systems (C, O, S, Sr, U) have been widely documented from Lower Triassic marine successions. The Early Triassic marine S-isotope record has been of recent interest due to newly published data from South China indicating large magnitude variability. Here, we present a biostratigraphically controlled S-isotope record for the Early Triassic from marine carbonates from the western U.S., to better understand the timing and magnitude of the S-isotope excursions. Our data indicate three large (>20‰), rapid positive S-isotope shifts, which occur with similar timing as the South China record, indicating a global signal. Our data expands on the existing Early Triassic S-isotope record by providing additional sample resolution across the transition between the Smithian and Spathian stages (~250 Ma), where we observe some of the highest S-isotope values for the Phanerozoic, followed by a return to normal marine values by the middle to late Spathian (~248 Ma). As with the South China record, our data show a coupling of the C-and S-isotopic records, indicating contemporaneous global burial of isotopically light organic C and pyrite-S in anoxic environments. The timing of the positive S-isotope shift is inconsistent, however, with other globally distributed, regional marine redox proxy records (e.g., pyritic organic-rich shales). The Smithian-Spathian transition is associated with decreased seawater temperatures following an extremely warm period indicated from conodont oxygen isotopes, a positive carbonate C-isotope shift, and conodont and ammonoid extinctions. The extraordinary S-isotope increase across this transition suggests a sudden and major paleoceanic upheaval preceded the complete global recovery of marine ecosystems.