Currently, it is believed that volcanogenic outgassing of CO 2 during Karoo-Ferrar igneous province eruptions caused prolonged global warming and a multiphased extinction event during the Pliensbachian–Toarcian interval of the Early Jurassic. Warmer water temperatures are thought to have caused a release from the methane hydrate reservoir and global marine anoxia in the Early Toarcian (dubbed the Toarcian oceanic anoxic event). Recently, the timing and geographic extent of these events have been questioned, with emphasis placed on regional conditions in the Tethys Ocean area rather than global controls. Our study compares paleontological and geochemical data from western North America with previously established correlative data in Europe to provide a perspective on the duration, extent, and controlling mechanisms of this Early Jurassic extinction event. Our data indicate that during Pliensbachian–Toarcian time, concurrent with Karoo-Ferrar magmatism: (1) there were six globally correlative intervals of taxonomic diversity decline that constitute evidence of a multiphased extinction event; (2) there was a major disruption in the long-term δ 13 C profile (~3‰–7‰), suggesting volcanogenic CO 2 outgassing as a preeminent factor driving global warming and mass extinction; (3) there was a large negative excursion in the Early Toarcian δ 13 C profile in two successions on Haida Gwaii (formerly known as Queen Charlotte Islands), Canada, suggesting global methane release; and (4) the northeast Panthalassa Ocean did not contain anoxic water during the Early Toarcian. Although the Toarcian oceanic anoxic event does not appear to have globally affected every marine environment in the same manner, it is possible that local anoxic water masses occurred in restricted basins outside the Tethys Ocean area.

Abstract The Late Palaeozoic period was an important time in Earth history, primarily as a result of the formation of Pangea and the Gondwana glaciations that had direct influences in high latitudes and indirect, but no less important, effects in low latitudes. This study documents and interprets the isotopic record for the Early–Middle Permian in northern Gondwana from detailed fieldwork in the Venezuelan Andes. Sr-isotope dating of well-preserved brachiopod shells suggests a Kungurian age from samples located within the middle part of the Palmarito Formation. δ 13 C data show a long-term trend through the section towards more positive values, but with some very negative δ 13 C values suggesting carbonates affected by pedogenic processes. In the middle part of the succession, major excursions in δ 13 C and δ 18 O show a strong connection with glacial–deglacial events during the Early–Middle Permian. Overall results presented here fill an important gap in the regional palaeogeography and, therefore, have significant implications for the palaeoclimate and palaeoceanography of this Late Palaeozoic time.