Brachiopod faunas from the basinal facies of southeastern Thuringia (Germany) before and after the Hangenberg crisis (devonian–carboniferous boundary)

Abstract

Upper Famennian–Tournaisian (Hastarian) brachiopods from the deep-water, mixed siliciclastic–carbonate Gleitsch Formation (Breternitz and Pfaffenberg members) of southeastern Thuringia (mainly from the Saalfeld area, Germany) are described systematically. A new Tournaisian rhynchonellide genus (Thuringorhynchus gen. nov.) and four new Tournaisian species are described (Productina saalfeldensis sp. nov., Thuringorhynchus pseudoequitans gen. et sp. nov., Cleiothyridina pfaffenbergensis sp. nov., and Crassumbo germanicus sp. nov.). Moreover, the lectotype of “Lingularia” straeleni (Demanet, 1934), from the Tournaisian of Belgium, is selected. Prior the Hangenberg Crisis, the brachiopod assemblage (10 species) of the Breternitz Member (upper and uppermost Famennian) is strongly dominated by species belonging to smooth to poorly ornamented rhynchonellide genera (Hadyrhyncha, Novaplatirostrum, Rozmanaria, and rozmanariid? gen. indet.) notably reported from Laurussia and the northern margin of Gondwana. The onset of the Hangenberg Crisis is marked by an anoxic black shale horizon at the top of the Breternitz Member followed by the siltstones and turbiditic sandstones of the Obernitz Member; both horizons did not yield brachiopods. A completely changed, more diverse brachiopod assemblage (15 species) existed in the Pfaffenberg Member (Tournaisian, lower Hastarian), which also included a basal 20 cm “topmost Famennian” (according to the current, soon abandoned definition of the Carboniferous base using Siphonodella sulcata as criterion), but clearly dated as upper Protognathodus kockeli Zone). Small-sized productidines (Productina) and spir-iferides (Crassumbo, Texathyris?) dominate; a probable complete turnover is recorded among the Rhynchonellida (Thuringorhynchus). The rapid recovery after the drastic Hangenberg extinction event includes species belonging to pre-existing genera and to new ones.