Environmental Impacts of Early Jurassic Large Igneous Province Volcanism in the Northwestern Tethys Ocean

A series of global climate perturbations characterize the transition from the late Pliensbachian to the early Toarcian (~183 Ma) stage, with global marine extinctions and carbonate factory collapses identified at the Pliensbachian/Toarcian Boundary event (Pl/To) and the Toarcian Ocean Anoxic Event (T-OAE). Both events are marked by significant negative carbon isotope excursions (CIE) (~ -3.5 to ~ -6), which closely align with eruptions of the Karoo-Ferrar Large Igneous Province (LIP). Moroccan Dades Valley (DV) field sites document a highly expanded Early Jurassic section that spans both the Pl/To and the T-OAE, in a carbonate ramp setting along the tropical Central High Atlas Basin. Each event is accompanied by a regional carbonate factory collapse, but in contrast to many other studied sections lithologic evidence of anoxia is absent. Here we integrate sedimentological, stable isotope, and elemental analysis (XRF, LA-ICP-MS) to better understand how these events relate to extinctions in this proximal margin marine depositional setting. We identified CIEs in the DV sites preceding each carbonate factory collapse and associated extinction, consistent with previous research in the area. Trace element proxy analyses and previously documented sedimentological data show an influx of terrestrial sediment immediately following each CIE. Based on K/Al, the intervals of terrestrial sediment influx may have been driven by increased chemical weathering due to a more humid local hydroclimate. This sediment influx is accompanied by a rapid increase in the Al-normalized concentrations of P, Ba, Zn, Cu, and Ni in marls, consistent with increased marine nutrient levels. Redox-sensitive trace element concentrations (Mo, U, V) in both deep ramp carbonates and shallow water oolites do not noticeably change across either CIE interval. These data suggest that anoxia was not a local extinction mechanism during the Pl/To and T-OAE, unlike in other areas of the Tethys Ocean. Elemental data suggest that eutrophication driven by increased continental weathering, along with a more intense regional hydroclimate, may have been a significant factor driving regional extinctions. These data highlight the regional variations in environmental changes and extinction mechanisms throughout the Pliensbachian-Toarcian transition.