From deep-marine stratigraphic condensation to mass-transport deposition: Illyrian stepwise extension recorded in a red nodular limestone drowning sequence (Bulog Formation) of the Ravni Carbonate Ramp (Seljani area, Montenegro)

New biostratigraphic data obtained by studying ammonoids, calcareous algae, conodonts,
and foraminifera from the westernmost part of the East Bosnian – Durmitor mega-unit in
northern Montenegro, result in a detailed reconstruction of the Middle – Late Anisian (Pelsonian-
Illyrian) subsidence history related to tectonic motions. Two independent times of extension
with formation of a horst-and-graben structure and neptunian dikes can be distinguished.
During the first phase of extension, a rapid deepening of the footwall block during
late Pelsonian times can be recognized. The initial late Pelsonian deepening is characterized
by the formation of neptunian dikes in the older Pelsonian shallow-water limestones,
which are filled with open-marine red micrite showing a microfacies typical for shallow deepswells.
This initial phase is only preserved in the infilling of neptunian dikes and represents
the onset of the drowning sequence. The final late Pelsonian depositional deep-swell environment
is preserved in a level with stratigraphic condensation, but a deep-water microfacies.
The second (late Illyrian) deepening also resulted in the formation of neptunian dikes,
a horst-and-graben topography, and the mobilization of mass-transport deposits related to
the onset of intense volcanism.