Biostratigraphy and microfacies of the pelagic carbonates across the Jurassic/Cretaceous boundary in eastern Serbia (Stara Planina–Poreč Zone)

Abstract

Integrated micropaleontological and microfacies studies on Tithonian and Berriasian pelagic carbonates of the Stara Planina–Poreč Zone (eastern Serbia) provided a new knowledge on the stratigraphic ages, depositional settings and lateral correlation with the Western Balkan Unit in Bulgaria. A total of forty calpionellid species, nineteen benthic foraminiferal species, and fourteen species of calcareous dinoflagellates have been identified in the Rosomač section in eastern Serbia. Calpionellid zones Chitinoidella, Crassicollaria, Calpionella, and Calpionellopsis have been recorded. Calcareous dinoflagellate zonation consists of Parastomiosphaera malmica, Colomisphaera fortis, and Stomiosphaerina proxima zones. The Rosomač Limestones are assigned to the Upper Tithonian and Lower Berriasian and the Ržana Clayey Limestone Beds to the Upper Berriasian. Seven distinct microfacies have been identified at the Rosomač section in eastern Serbia. Two of them, MF 1 calpionellid mudstones and MF 2 calpionellid wackestones, characterize the basinal depositional zone. Five microfacies belong to the slope facial zone, including the toe of the slope. These are: MF 3 Saccocoma wackestones, MF 4 wackestones with bioclasts, MF 5 intraclast-bioclastic grainstones, MF 6 bioclast-intraclastic floatstones, and MF 7 bioclast-intraclastic rudstones. Vertical microfacies distributions are directly correlated with the calpionellid and calcareous dinocyst zonations in sections in Serbia and Bulgaria. The pelagic carbonates in the Tithonian/Berriasian boundary interval were deposited under slope conditions at Rosomač section, and under basinal conditions at Barlya section in western Bulgaria.