Uppermost Permian Reefs in Skyros (Greece) and Sichuan (China): Implications for the Late Permian Extinction Event

Based on the comparison of Uppermost Permian reefs from the Palaeofusulina zone of Skyros Island (Skiathos series) of Greece, and the Changhsiang Formation of Sichuan, China, major criteria of very late Permian reefs are defined: Reefs are small-scaled stratigraphic reef mounds, composed of lens-like boundstone structures (saccoliths) and a great amount of bioclastic sediment. Relief of the buildups was low. Individual saccoliths are biostromes rather than bioherms. Coarse-grained reef talus is lacking. Calcisponges and sclerosponges as well as encrusters (Archaeolithoporella, Tubiphytes) are the principal framing and binding organisms. Taxonomic diversity and biofacies diversity are high. The reefs developed within shallow subtidal inner shelf environments. Latest Permian reefs differ in geometry, dimensions, construction and composition of calcisponge assemblages from earlier Late Permian reefs. There is no evidence for a change in diversity of calcisponge taxa or for a preferred impact of the Permian extinction event on the structure of very late Permian reef communities. The assumption of climate cooling as an explanation for the end-Permian crisis of the reef ecosystem is contradicted by the close association of green algae and reefs.