Middle Triassic stepwise deepening and stratigraphic condensation associated with Illyrian volcanism in the Durmitor Mountain, Montenegro

Abstract

New biostratigraphic and microfacies data from the Durmitor Mt. in northern Montenegro result in a detailed reconstruction of the Middle Triassic depositional history with special emphasis on the Middle-Late Anisian stepwise deepening related to the opening of the Neo-Tethys Ocean and the intense Illyrian volcanism in the Dinarides. The continental break-up and early opening history of the Neo-Tethys Ocean is recorded in the Middle-Late Anisian drowning sequence of the Pelsonian shallow-water Ravni Carbonate Ramp. The first pulse in the late Pelsonian creates a horst-and-graben topography forming a classical break-up unconformity. In addition, shallow-water carbonate production decreased significantly, and deep-marine red nodular limestones (Bulog Formation) and related sedimentary deep-water successions deposited throughout the late Pelsonian – early/middle Illyrian, in cases up to the Ladinian, as proven by ammonoids and conodonts. In the Durmitor Mt., intense volcanism in the middle Illyrian created short-living islands surrounded by atolls with shallow-water carbonate production up to the late Illyrian, as proven by conodonts. The older break-up and volcanism related topography get destructed around the middle/late Illyrian boundary by a second pulse of extensional tectonics, and resulted in deposition of Mass Transport Deposits (MTDs) with reworked middle Anisian (Pelsonian) shallow- and deep-water limestones (Komarani Formation). The shallow-water limestones are dated by dasycladalean algae and foraminifera, while the deep-water limestones are dated by ammonoids and conodonts. From the late Illyrian onwards deposition is characterized first by red condensed limestones with ammonoid-rich Fossillagerstätten beds subsequently overlain by Ladinian condensed grey siliceous deep-marine limestones. In the Early Carnian first turbidites with shallow-water grains overlain by reefal float- and rudstones indicate the onset and progradation of the Wetterstein Carbonate Platforms. In contrast to the well-known Middle Anisian (late Pelsonian) drowning event in the Western Tethys Realm the middle-late Illyrian depositional history associated with the intense volcanism and extensional tectonics is not well understood. This knowledge gap is filled by precisely dated sedimentary successions in the Durmitor Mt. in northern Montenegro.