engleski

Sedimentological characteristics and facies analyses of Istrian flysch deposits (Dinaric foreland, Croatia)

Istrian Foreland basin was formed during the Eocene period in collisional processes between the Adria microplate and the Euroasian plate in migrating Dinaridic foredeep depozones in front of the migrating Dinaridic wedge. The Istrian foreland basin fill consists of Foraminiferal limestones, Transitional beds (Globigerina marls) and Istrian flysch which represent the lower, middle and the upper unit of the Underfilled peripheral foreland basin. The Istrian Flysch is well investigated and described in many aspects, like mineralogical composition, paleontological data and paleotransport directions. In contrast, available information about the sedimentology and facies analysis of these deposits is sparse. The aim of this research is to present new sedimentological data about these deposits and to shed some light about the environmental conditions and depositional mechanisms of Istrian flysch deposits. Furthermore, the goal is to define the Litostratigraphic units of the clastic part of the Istrian Foreland basin fill (Globigerina marls and Istrian flysch). The Istrian Flysch deposits are characterized by the alternation of hemipelagic marls and gravity-flow deposits. The gravity-flow deposits are 5-40 cm thick beds of turbidites, developed mostly as laminated and cross-rippled sandstone beds (shale-sandstone/siltstone couplets without a Bouma a division). Complete Ta-e Bouma sequences are rare. Sandstones are of mixed carbonate-siliciclastic composition. The monotonous succession of marls and mixed carbonate-siliciclastic sandstones is intercalated with several thick carbonate beds composed of breccias, conglomerates, bioclastic arenites/siltites and marls. They show a significant thickness, occasionally more than 10 m. These carbonate beds (megabeds) are interpreted as complex packages of debrite and turbidite origin. Some of them thin out and pinch out laterally, but the thicker ones are continuous over distances of more than 10 km. The distinct packages within the Istrian flysch are interpreted as deposits of deep sea environments, either distal fan or base of the slope. Studied sedimentological sections will be presented here as well as the facies analysis. The contact between the Istrian flysch and the underlying Cretaceous carbonates is presented here for the first time. Furthermore, some limestone layers within the Istrian flysch succession are interpreted as a short return of carbonate sedimentation within the foredeep basin. Although there are many open questions on the more precise correlation of the recorded sedimentary collumns, the information presented here can be used for a reconstruction of the dynamic environments of the Istrian foredeep sedimentation.

turbidites, foreland basin, Istria

nije evidentirano