Lopingian brachiopods from the Abadeh section (Central Iran) and their biostratigraphic implications

The Abadeh section is one of the most important Neotethyan sections, as it records a continuous marine sedimentary succession across the Permian-Triassic boundary. Although this succession yields a rich brachiopod fauna, this has never been studied in detail. Instead, most of the studies carried out so far have been focused on the position of the Permian-Triassic boundary, which is still debated. Here, we present a systematic study of the brachiopod fauna from the Hambast Formation, which comprises 30 species of the orders Productida, Orthotetida, Orthida, Athyridida and Spiriferida. Brachiopod biodiversity is relatively high and constant in the Wuchiapingian part of the section. But in Changhsingian, just a single species occurs: Paracrurithyris pygmaea. Also, species of bivalves of the genus Claraia occur within an upper Griesbachian bed of the Elikah Formation. Using the Unitary Associations method, we compared the stratigraphic distribution of the brachiopods in the Abadeh section with those in the Julfa section, another important Permian-Triassic succession in North-West Iran. Based on this analysis, three Wuchiapingian brachiopod biozones and one Changhsingian brachiopod biozone have been detected and correlated to the conodont biozonation; these biozones are the Araxilevis intermedius-Leptodus nobilis Biozone, the Permophricodothyris ovata-Araxathyris quadrilobata Biozone, and the Haydenella kiangsiensis-Transcaucasathyris minor Biozone in the Wuchiapingian, and the Paracrurithyris pygmaea Biozone in the Changhsingian. Most of the biozones can be correlated through Iran and Transcaucasia, showing the potential of brachiopods for correlation at a regional scale in the Upper Permian.