Stratigraphy of the Krš Gradac section (SW Serbia)

Abstract

In the Krs Gradac section (near to Sjenica, SW Serbia), a transition of a carbonate platform to basin facies are outcropped: Norian-lower Liassic shallow-water carbonates, middle Liassic-lower Dogger Ammonitico Rosso facies, and upper Bathonian into lowermost Cretaceous deep-water radiolarites in which the carbonate graded bed and mass flow layer are intercalated. The presence of a lower Dogger condensed sequence with the Bajocian protoglobigerinid event was hitherto not evidenced. It is documented that components of a graded bed are of extrabasinal (upper Triassic-lower Tithonian carbonate platform sediments) and intrabasinal (radiolarite, meta-andesite) origin, indicating a tectonic event not older than the early Tithonian. This tectonic event caused the fracturing of the carbonate platform, also partly basinal area. Consequently, the age of the graded bed is not older than the lower Tithonian. In the uppermost radiolaritic sediments in the Krs Gradac section (?middle-upper Tithonian-lowermost Cretaceous), a mass flow layer appears, which contains clasts of intrabasinal origin - different radiolarites, siliceous radiolarian argillites (some of which are unconsolidated with washed radiolarians and sponge spicules in a ferruginous sediment), sandstone grains, etc. The mass flow event is estimated as Berriasian. In the Krs Gradac radiolarite succession, the authors recognized two deep-water formations, an older one, upper Bathonian-lower Tithonian, between hardground (Dogger) and a graded bed, and a younger formation, which started with a graded bed. This formation, according to its stratigraphic position, corresponds to ?middle-upper Tithonian-lowermost Cretaceous.