Microfacies of the Silurian/Devonian boundary interval in the Gorna Vrabcha 2 section (Morava Unit, SW Bulgaria) – preliminary results

This study is focused on the sedimentary strata of the Silurian/Devonian boundary interval in the Gorna Vrabcha section 2 from the Morava Unit (SW Bulgaria). Four microfacies types have been distinguished and described: Bioclastic wackestone/packstone (MFT 1), Bioclastic packstone with clayey mudstone laminae (MFT 2), Bioclastic mudstone (MFT 3) and Homogeneous mudstone (MFT 4). They are respectively interpreted as formed in various high- and low-energy open-marine environments. Thus, during the Přídolí and at the begging of the Lochkovian sedimentation occurred in an open-marine setting located between the fair-weather wave base and the storm wave base (MFT 1 and MFT 2), that was often affected by storms and storm-related currents. Later, during the Lochkovian, a calm and relatively deep-water environment predominated (MFT 3 and MFT 4) and was most probably located below the storm wave base. Based on the obtained microfacies data and depositional setting interpretations a deepening trend of sedimentary basin during the Přídoli–early Lochkovian time have been suggested.