AN EARLY HETTANGIAN CORAL REEF IN SOUTHERN FRANCE: IMPLICATIONS FOR THEEND-TRIASSIC REEF CRISIS

摘要

The oldest known Jurassic coral reef is exposed in the Ardeche region ofsouthern France. This reef site, consisting of at least three reefal bodies, isof early Hettangian age and thus immediately postdates the end-Triassicmass extinction, which is well known for its catastrophic effect on reefbuilding. Bulk carbonate carbon isotopes of the limestones below the reefare likely to record environmental perturbations subsequent to the massextinction. The main reef is surprisingly well developed (20 m inthickness, 200 m in lateral extent) and composed of at least four generaand six species of corals—not only holdover genera from the Triassic, butalso one newly evolved genus (Phacelophyllia), contributed to reefconstruction. Just like their latest Triassic counterparts, the reef isdominated by phaceloid corals with a considerable contribution ofmicrobialite. The reef predates similarly well developed structures byalmost ten million years. The shelf setting of the reef renders it unlikelythat refuges around oceanic islands are needed to explain survival ofcorals across the end-Triassic mass extinction.