First record of a Middle Jurassic macrofauna from the Brnjica (NE Serbia): stratigraphy, palaeoecology and correlation with adjacent regions

The Middle Jurassic sediments of the Getic of Carpatho-Balkanides in the trans-border area of Serbia and Romania are insufficiently studied. This zone is composed mainly of pre-Jurassic metamorphic rocks and the Upper Jurassic/Lower Cretaceous limestones. The palaeontological and sedimentological study of the Middle Jurassic deposits of the Brnjica River (Carpatho-Balkanides), which is one of the rare well-exposed outcrops, is being carried out for the first time. The dominant lithologies are grey and yellow sandy limestones and marly limestones with intercalations of reddish shales characterized by low-diversity fossil assemblages dominated by molluscs. Eleven bivalve taxa are determined for the first time in the studied area. Litho-and biofacies analysis in the marine Jurassic strata are reported based on bivalve assemblages with additional data from brachiopods, ammonites and microfossils. The age of the fossil association is determined as the Upper Bajocian and Bathonian based on two brachiopod species Cymathorhynchia quadriplicata and Torquirhynchia asymmetrica. The first is reported from the Middle and the Upper Bajocian sediments and has a wider palaeobiogeographical distribution, while the latter is exclusively described from the Upper Bajocian and Bathonian of the Serbian Carpatho-Balkanides. Most of the collected bivalves have a wider stratigraphic extent. Retroceramus cf. obliquus and Plagiostoma rigidula have up to now been known from the Bajocian stage. The determined macrofauna is compared with the Middle Jurassic fauna of adjacent regions of Hungary, Romania and Bulgaria, and show strong affinity to those of the northern margins of Tethys. By the end of the Bathonian, the depositional environment has changed from shallow-marine to deep-marine, suggesting a drowning of the carbonate platform