Bivalves and brachiopods near the Permian-Triassic boundary from the Bükk Mountains (Balvany-North section, Northern Hungary).

In the Bükk Mountains the Upper Permian is represented by the Nagyvisnyó Limestone Formation, which contains very rich marine assemblages. It is overlain by the Gerennavár Limestone Formation (uppermost Permian - Lower Triassic) which records the effects of the Permo-Triassic mass extinction with a dramatic decrease in diversity and abundance of fossils. The basal Gerennavár Limestone Formation is represented by a clayey marl unit (Basal beds) deposited in a quiet, low-energy marine environment below the fair-weather wave-base, whose maximum thickness, about one meter, is recorded in the Bálvány-North section. From this locality a relatively diversified and abundant marine benthonic assemblage has been collected, and is here described. Bivalves are represented by: Bakevellia cf. ceratophaga (Schlotheim), ? Pterinopectinidae gen. et sp. indet., Eumorphotis lorigae sp. n., the most abundant species, Entolium piriformis (Liu) and Pernopecten latangulatus Yin. Brachiopods are less frequent, and the following four species have been determined: Spinomarginifera sp., Orthothetina ladina (Stache), Ombonia tirolensis (Stache) and Crurithyris tschernyschewi Likharew. An exact age of this fauna, based on conodonts, is not yet available, but the strong affinities with those of the lower Tesero Member (Dolomites) and the Lower Kathwai Member (Pakistan) suggest an uppermost Permian age (? Hindeodus praeparvus Zone). If so, the Bálvány-North section becomes one of the few in the world which record the last bioevents of the Palaeozoic.