Marine biotic events in the Lopingian succession and latest Permian extinction in the Southern Alps (Italy)

Abstract

The Upper Permian in the eastern Southern Alps consists of an overall transgressive sedimentary succession of continental red beds (Val Gardena Sandstone), which are overlain and interfingered by the marine Bellerophon Fm, consisting of sulphate evaporites, dolomites and neritic limestones. In the western Dolomites, a key-area for analyzing the stratigraphic framework and biotic events connected with the Permian-Triassic boundary and related mass extinction studies, the Bellerophon Fm is followed by oolitic limestone of the Werfen Fm, where the end-Permian mass extinction and the erathem boundary, located a few centimetres and few metres respectively above the formational contact. The marine events presented here are located in three historical sections in the western Dolomites (Bletterbach, Seceda-Monte Balest, and Putia). Bioevents mostly concern brachiopod and cephalopod assemblages, discussed herein in terms of biodiversity changes and bio-chronostratigraphic value. Recent data on cephalopod and conodont biostratigraphy have improved significantly the chronostratigraphic framework of the upper part of the succession and its correlation with other Tethyan localities. As far as concerns nautiloids, the Tirolonautilus beds (T. crux and Tirolonautilus sebedinus lineage zone) are Changhsingian in age; while, all the Comelicania-bearing brachiopod beds are late Changhsingian in age. The extinction pattern of the Dolomites is compared with that which occurred in the GSSP Meishan (South China) section. In both regions, the main extinction phase is probably synchronous, whereas the ultimate extinction of relicts is slightly diachronous. However, in the Dolomites the extinction seems to have been more catastrophic, because of the lack of the Chinese prelude phase, which is also characterized by miniaturization. On the other hand, the supposed coeval Dolomites assemblages have a high biodiversity, both in richness and abundance, and include gigantic brachiopod species