Late Anisian extension evidenced by mass-transport deposits and overlying deep-water carbonates and radiolarites in the Dinarides of northern Montenegro (Brvenica, East Bosnian-Durmitor megaunit)

A unique Middle to lower Upper Triassic carbonate-radiolarite succession with intercalated mass-transport deposits is presented from the East Bosnian-Durmitor megaunit in north Montenegro. The studied section Brvenica represents new evidence of late Illyrian extensional tectonics with breccia formation and a continous deepening trend throughout the late Illyrian to Early Ladinian. The upper Illyrian breccias of the Komarani Formation overlie the recrystallized shallow-water limestones of the Ravni Carbonate Ramp after a long-lasting gap (late Pelsonian to middle Illyrian). The breccia succession is characterized by a fining-upward trend. The component spectrum is dated with foraminifera and conodonts. The overlying red nodular limestones of the Bulog Formation are dated with conodonts and the upsection following silicified limestones and radiolarites with radiolarians. Whereas the late Pelsonian drowning event of the Ravni Carbonate Ramp is in many places described in the Dinarides and related to the early opening of the Neo-Tethys Ocean, the late Illyrian extensional event is still not fully understood and is rarely described. This second deepening event with the formation of a horst-and-graben topography is related to intense volcanism and a rapid deepening of the depositional realm. The described section fills an important gap of knowledge of the Middle Triassic geodynamic evolution in northern Montenegro.