International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

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Demise of the Wetterstein Carbonate Platform and onset of the Dachstein Carbonate Platform recorded in deep-water successions of the East Bosnian–Durmitor megaunit (Pliješevina, northern Montenegro, Dinarides)

Published: Dec 2023

Pages: 443 - 458

DOI: https://doi.org/10.31577/GeolCarp.2023.26

Authors: MILICA MRDAK, EVA WEGERER, MILAN SUDAR, NEVENKA DJERIĆ, MARTIN ĐAKOVIĆ, HANS-JÜRGEN GAWLICK

Abstract: During the latest Ladinian to earliest Carnian, the Wetterstein Carbonate Platform evolution led to the formation of the first rimmed platforms in the Western Tethys Realm after the Permian/Triassic mass extinction. The overall demise of the Wetterstein Carbonate Platform is related to the Lunz event (Reingraben event, Mid-Carnian Pluvial Episode or Mid-Carnian Wet Intermezzo – Julian 2). However, several questions remain open when comparing the platform demise in the Eastern Alps, the Southern Alps, and the Western Carpathians (ALCAPA) with its demise in the Dinarides/Albanides/Hellenides, where these siliciclastics are practically unknown, except the Outer Dinarides in Croatia or Montenegro (High Karst). Prior to the drowning of the Wetterstein Carbonate Platform in the ALCAPA region with siliciclastics, the platform emerged due to a sea-level drop around the Julian 1/2 boundary (Carnica event). The underfilled accommodation space between the platforms is characterized by restricted deep basinal areas with deposition of organic-rich siliceous limestones, followed by the deposition of fine-grained siliciclastics (Reingraben claystones). In contrast to the ALCAPA region a long-lasting stratigraphic gap is common in the Carnian in the Dinarides/Albanides/Hellenides. Carbonate deposition resumed during the Late Carnian after the demise and uplift of the Wetterstein Carbonate Platform. In northern Montenegro, near the village Pliješevina, the final demise of the Wetterstein Carbonate Platform around the Julian 1/2 boundary can be dated by conodont faunas (Carnica conodont zone) in a newly detected Carnian basinal sequence. Above the fine-grained resediments of the Wetterstein Carbonate Platform (Zlošnica Formation), less then 3 m of grey “filament”- and radiolarian-rich biomicrites were deposited, followed upsection by a ~6 m-thick sequence of siliceous claystones, black cherts and silicified volcanic ashes (Džegeruša Formation). The carbonate-free intercalated metabentonites of Julian 2 to Tuvalian age are composed of (biogenic) quartz, and clay minerals of the mica-group (mainly illite), montmorillonite, the smectite group, and mixed layer clay minerals. A controversially discussed environmental change around the Julian 1/2 boundary resulted in the demise of the Wetterstein Carbonate Platform and carbonate deposition was replaced by deposition of siliciclastics. Carbonate production reflecting the onset of a precursor of the Dachstein Carbonate Platform evolution started again during the latest Carnian as dated by conodonts.

Keywords: Triassic, Carnica event, clay mineralogy, conodont biostratigraphy, Neo-Tethys

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