Frasnian-Famennian brachiopod extinction and recovery in Southern Poland

The new trench Z−17 situated in the Dębnik anticline (Cracow Region, southern Poland) exposed strata representing the Frasnian–Famennian boundary interval. The latest Frasnian crisis interval is characterized by the fauna of Ryocarhynchus tumidus interval consisting of the nominal species, Barroisella campbelli, Biernatella polonica, and representives of Lingulipora, Athyris, ?Retichonetes, Longispina, Cyrtospirifer and Warrenella. The first brachiopods that appears immediately above the F–F boundary in the survival interval include the unidentified rhipidomellid, Praewaagenoconcha cf. speciosa, and Pampoecilorhynchus geniculatus sp. nov. The fauna in the succeeding layer is dominated by P. geniculatus and Cyrtospirifer minor. The earliest Famennian repopulation assemblage consists of representatives of Barroisella, ?Rhyssochonetes, Praewaagenoconcha, Nigerinoplica, Schizophoria, unidentified rhipidomellid, Pampoecilorhynchus geniculatus sp. nov., Chapinella striata sp. nov., Crinisarina angelicoides, and Cyrtospirifer minor. Low diversity and low frequency brachiopod assemblages consisting of stunted specimens characterize the succeeding brachiopod intervals spanning the remainder of the Palmatolepis triangularis Zone. Basinal dysoxia prevailed in the region for the duration of Pa. triangularis Zone. Resumption of aerobic bottom−water conditions is marked by the appearance of brachiopods of the Dmitria gibbosa interval (Pa. crepida Zone). Resumption of favorable environmental conditions during the recovery interval is marked by an increase in brachiopod diversity recording the beginning of a strong post−extinction rediversification of the fauna.