Conodont biostratigraphy, carbonate microfacies and climate changes during the Late Devonain (Frasnian–Famennian) in the Preslavtsi 2 well (Moesian Terrane, NE Bulgaria)

Five conodont zones (falsiovalis, rhenana, triangularis, marginifera, and praesulcata) were recognized within the Upper Devonian carbonate sequence in the Preslavtsi 2 well from the Moesian Terrane in NE Bulgaria. Microfacies study indicates a climate change (from the Subtropical Arid to the Warm Temperate Climatic Zones) recorded in the Frasnian–Famennian succession. Thus, during the Givetian and early Frasnian, sedimentation took place in an arid tidal flat setting, where microbial mats and lagoon carbonates have been formed. In the late Frasnian, a transgression, followed by a rapid regression was recorded that are presumably related to the Late Devonian Kellwasser event. At the beginning of the Famennian, a climate change has occurred and various shallow- and open-marine carbonates have been formed under warm temperate climate conditions.