Biostratigraphic, palaeoenvironmental and palaeobiogeographic implications of bryozoan fauna from the Upper Devonian sequences of Armenia

Abstract

This paper presents the first contribution to the study of bryozoans from the Frasnian–lower Famennian successions of Armenia. The latter were examined in two distinct localities (Ertych and Noravank) of Central Armenia; abundant fragments of branched ramose and encrusting bryozoans were observed in them, belonging to the orders Trepostomata and Cryptostomata. Their taxonomic assessment led us to recognize four species: two cryptostomes – Euthyrhombopora tenuis Ernst et al., 2017 and Bigeyella indigena (Morozova and Weiss in Morozova et al., 2002) from the Noravank section (Frasnian) – and two trepostomes – Eostenopora sp. and Eridotrypella sp. from the Ertych section (lower Famennian). No cystoporate and fenestrate bryozoans were observed. The identified bryozoans are characteristic of shallow marine or middle shelf paleoenvironments. The presence of Euthyrhombopora tenuis and Bigeyella indigena suggests palaeobiogeographic affinities to contemporary faunas from Iran and Poland, respectively. In addition to our results, an overview of previously published data reveals that the upper Famennian assemblages of bryozoans from the Lesser Caucasus contain more endemic species than those known from the Frasnian and the lowermost Famennian.