Microfacies, sea-level fluctuations and conodont biostratigraphy of Frasnian–Famennian carbonate sequences from the Preslavtsi-2 well (the Moesian Platform, NE Bulgaria)

The falsiovalis, rhenana, triangularis, marginifera and praesulcata conodont zones have been recognized within the Upper Devonian (Frasnian–Famennian) carbonate succession in the Preslavtsi-2 well from the Moesian Terrane in NE Bulgaria. Five microfacies types (MFT 1–5) are also distinguished and described within the Frasnian carbonate deposits: fenestral peloidal microbial bindstone (MFT 1a); fenestral microbial bindstone with porostromate microstructures (MFT 1b); paleosiphonoclad wackestone and packstone (MFT 2); bioclastic-peloidal packstone and grainstone (MFT 3); bioturbated wackestone to grainstone (MFT 4); and lithoclastic rudstone (MFT 5). They are interpreted as formed in arid peritidal and lagoon environments or deposited in deep-water setting, located below the storm wave base. A sea-level transgression is documented during the late Frasnian (Late rhenana Zone) corresponding to the Lower Kellwasser Event, which was followed by rapid regression. At the beginning of the Famennian, a climate change occurred when the Moesian Terrane was removed from the Subtropical Arid to the Warm Temperate Climatic Zone, when various shallow- and open-marine carbonates were formed under warm temperate climate conditions.