engleski

The Permian-Triassic sedimentary sequences in the External Dinarides (Croatia)

The External Dinarides, ca 700 km long geotectonic unit along the coastal Croatia, started to develop as a part of the Carboniferous to Early Permian epeiric platform along northern Gondwana accumulating shallow marine carbonates and terrigenous clastics. In the Middle-Late Permian this primary setting was punctuated by intermittent rift-related extensional tectonism that started to break the platform into several horsts and grabens. As a consequence, the lithofacies of the Middle-Late Permian-Early Triassic sediments differentiated according to the ancient tectonic settings with respect to such topographic contrast. The Mts. Velebit formed on the Permian submarine horsts with the dominant carbonate deposition. Approximately 900 m thick sequence, mostly dolomites with rare relicts of thin limestone lenses, accumulated without terrigenues input. Long lived shallow carbonate sedimentation has a characteristic of deposition in a restricted, low energy platform interior with the occasional appearance of reefal structures consisting dominantly of sponges, Shamovella (Tubiphytes) microbial problematica and brachiopods. The whole sequence was intensively dolomitised. The thorough dolomitisation of a thick sequence (with only lenses of limestone left undolomitised) suggest possible dolomitisation due to thermal convection on an isolated platform. The Velebit carbonate platform was isolated from the main carbonate platforms in the Southern Alps and experienced continuous carbonate sedimentation from the Permian to Early Triassic. Some Permian inter-platform grabens (e.g., the Gorski Kotar Region to the NW of Mts. Velebit.) were filled with clastics prior to the onset of the dominant Early Triassic carbonate deposition. The Gorski Kotar sequence consists of a thick siliciclastics intercalated with re-sedimented carbonates, such as carbonate megabreccia and carbonate turbidites. These characteristics suggest the filling of a depression with land-derived material associated with the destruction of fringing carbonate hights. The high flux of siliciclastics punctually filled grabens that led the disappearance of a depression and intermittent deposition of red terrigenous clastics onto the former isolated platform carbonates, as observed in the upper portion of the Velebit Formation. The rift-related tectonics was inherited into the Middle Triassic. The extensionally disintegrated domains formed the huge isolated platform to build a foundation of the future Adriatic Carbonate Platform.

Permian sedimentary sequence; External Dinarides; Croatia

nije evidentirano