The timing of paleoenvironmental change and cause-and-effect relationships during the early Jurassic mass extinction in Europe

Abstract

The early Jurassic marine mass extinction is one of several crises thought to coincide with anoxia, transgression and warming caused by catastrophic release of gas hydrates. However, high-resolution study of expanded sections in Yorkshire, England, reveal that only the first of these factors is truly coincidental with extinction. The well known transgression and large, negative carbon isotope perturbation, attributed to massive release of methane from gas hydrates, occur after these events. The anoxic event is developed diachronously in the European area, with anoxia developing and fading away earlier in the Mediterranean region compared with the NW European record. However, for a brief interval (in the mid semicelatum Subzone), anoxia was simultaneously developed throughout the European region and it is this time that is marked by extinction of both benthic and pelagic marine fossils. The sea-level curve is also more complex than hitherto assumed, with a minor regression occurring late in the semicelatum Subzone, shortly after the extinction. The Toarcian crisis occurred during a phase of global warming, but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend.