Bioevents at the Konkian/Sarmatian boundary (Northeastern Bulgaria) – a response to paleoclimatic changes

New outcrops of the Konkian part of the Euxinograd Formation, located between Briz beach and Trakata beach, have been studied. The section comprises an alternation of gray calcareous clays, laminated calcareous clays and limestones, whose age is determined by mollusks and diatoms and ranges from the Konkian to the Sarmatian. The studied sediments were deposited in a shallow-marine environment with frequent fluctuations of the sea level. The fossil diatom flora is characterized by a monotonous species composition. The presence of crushed diatom valves and a relatively abundant sand fraction suggest intermittent high water dynamics. Generally, the climate was warm, with at least three dry periods, during which the alkalinity and CaCO3 content increased significantly and the living conditions of the mollusks and diatoms deteriorated.