Middle-Late Triassic sedimentological history in northern Montenegro: From the drowning of the Ravni Carbonate Ramp to the Wetterstein Carbonate Platform evolution

The localities Kovčezi, Brvenica, Jugovo and Vrbica (Pljevlja and Žabljak regions) preserve the depositional history of the Middle Triassic to early Late Triassic in the northern Montenegro. The sedimentological evolution, geodynamic history of the East Bosnian-Durmitor megaunit allows reconstructing from the Late Anisian break-up unconformity, i.e. the formation of a Horst-and-Graben structure to the onset and demise of the Early Carnian Wetterstein Carbonate Platform. All the studied sections record the geological history from the drowning of the shallow-water Ravni Carbonate Ramp in the late Pelsonian (Middle Anisian) to the demise of the Wetterstein Carbonate Platform around the Julian 1/2 boundary (Early Carnian) and the aftermath of carbonate production in the latest Carnian. During the middle Anisian, shallow-water limestone formation (Ravni Carbonate Ramp) changed rapidly to deposition of deep-water limestones forming a drowning unconformity. Contemporaneously with the demise of the shallow-water ramp a first horst-and-graben topography was formed, subsequently followed by a volcanic event. The demise and drowning of the Ravni Carbonate Ramp are related to the initial of the opening of the Neo-Tethys Ocean east of the present day Inner Dinarides. The late Pelsonian continental break-up and opening of the Neo-Tethys Ocean triggered formation of a Horst-and-Graben topography and a rapid decrease of shallow-water carbonate production throughout the Dinarides like elsewhere in the Western Tethys Realm. During this tectonostratigraphic event sedimentation changed rapidly from shallow-water carbonates to deep-water limestones. Later, around the middle/late Illyrian boundary the onset of volcanism (its cause remain unclear in the moment) in the Outer Dinarides resulted in the formation of a second unconformity. The first event can be traced everywhere in the Western Tethys Realm, but a second Horst-and-Graben topography was only formed in the Outer Dinarides. During latest Anisian to Early Carnian times a period of tectonic quiescence followed. Sedimentation is characterized by deep-water volcaniclastics, siliceous limestones or radiolarites, often intercalated with volcanic ash layers. Only in the short time interval of the early Late Ladinian in some regions shallow-water carbonates were formed. Generally deep-water conditions prevailed until the Early Carnian, when the situation changed and the Wetterstein Carbonate Platforms started to evolve on the late Anisian horsts. During the Early Carnian these Wetterstein Carbonate Platforms prograded towards the late Anisian grabens, but were not able to fill these depressions. Short-living intraplatform basins therefore remain, and can be traced between the prograding platforms. These earned depressions could not be filled by carbonates, because the evolution of this platform cycle ended abruptly around the Julian 1/2 boundary, in addition, these platforms were uplifted and during the Carnian deeply eroded.