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Upper Cretaceous (Campanian) Transgressive Deposits From Mikulić Potok, Medvednica Mt., Ne Croatia

A Gosau-type transgressive succession, typical for the area of the Inner Dinarides, is exposed at Mikulić potok on the Medvednica Mt. (NE Croatia). The succession records a continental- to-marine transition consisting of basal conglomerates, shallow-marine sandstones and carbonates, followed by shales and pelagic Scaglia-type limestones (CRNJAKOVIĆ, 1979). The carbonate deposits with rudists form lens-like bodies, which are laterally enveloped by siliciclastics. They consist of a mixture of fine-grained siliciclastic detritus and carbonate grains with predominance of toppled rudist shells and their fragments. The depositional environment is determined as subtidal with predominate siliciclastic sedimentation. Siliciclastic deposits generally do not contain any macrofossils. Exceptions can be found in the lower part of the succession with findings of inoceramid shells. Within siliciclastic–carbonate deposits rudists (hippuritids) are present, which are characteristic for relatively deeper subtidal with absence of shallowing-upward cyclicity, as well as relatively deeper and more open subtidal without influence of terrigenous input from emerged areas. The depositional setting of the investigated locality may be considered as a result of a relatively rapid sea-level rise with tectonic influence in the background. The result was a relatively short period of shallow-water sedimentation without repetition of peritidal conditions during a period of relatively rapid deepening. Transgression, which generally extended from north towards the southeast of the Inner Dinarides and covered different types of tectonically uplifted and eroded paleorelief, ranging from predominantly carbonate to siliciclastic deposition (MORO et al., 2016). Presumably, at this locality paleorelief was low and the transgressive succession started with clastic deposits. When subtidal paleonvironment became relatively more open and distant the transgressive succession characterize carbonate sedimentation with rudist communities. Transgressive successions with similar vertical exchange of lithotypes have been studied at other localities (MORO et al., 2016) with Gosau-type transgressive successions, where first appearance of rudists is connected with establishment of carbonate sedimentation.

Gosau-type deposits, transgression, siliciclastics, carbonates, rudists

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