engleski

Jurassic-Lower Cretaceous facies and biostratigraphy of the Danubian nappes (eastern Serbia)

In eastern Serbia, the Mesozoic successions are exposed along the valley of the Danube River. They represent the Danubian nappes which belong to a much larger Dacia Mega-Unit. It was a part of the European continent detached from it during Jurassic rifting in the easternmost domain of the Alpine Tethys and docked again to the European foreland during the Miocene. Three sections with Jurassic–Early Cretaceous deposits crop out along the road Dobra – Boljetinsko brdo. In the studied area, Jurassic sedimentation began with clastic deposits that transgressively overlie Permian rocks. Three considerably different successions were studied above the Lower Jurassic quartz sandstone and conglomerate. The first succession, exposed between tunnels no 17 and 21, is over 150 m thick and typical of a deep-water basin. The following units occur in stratigraphic order: red shale with intercalations of thin beds of nodular limestone ; white marly limestone that transits upwards into well-bedded limestone with subordinate marly interlayers ; thin-bedded green and upsection red calcareous radiolarite ; indistinctly bedded grey marly limestone ; well-bedded reddish limestone with chert nodules and interlayers of dark red shale. Several breccia and calcarenite beds are interstratified in the last unit. The second succession (exposed at tunnel no 10) indicates deposition on a pelagic plateau. This section is much more condensed, not exceeding 20 m in total thickness. The predominant facies is red nodular limestone of Rosso Ammonitico type. Rare chert nodules and layers exist only in the middle part of the section. Slumped beds and intraformational conglomerates occur in the upper half. Both sections continue with a thick succession of light grey micrite with chert nodules that closely resembles the Maiolica limestone of the Southern Alps. Up to several meters thick slumped levels are common in this Lower Cretaceous limestone. The third succession (exposed at tunnel no 13) is also condensed (total thickness 17m) and indicates deposition on a pelagic plateau. This section is characterized by a thin, but rather conspicuous interval of alternating green, violet and red radiolarites. The first section represents a deeper basin, whereas the other two were deposited on a pelagic plateau. These successions indicate a typical horst-and-graben topography, well known from other domains of the Alpine Tethys. The topographic difference was apparently diminished by the Early Cretaceous, when Maiolica type limestone became ubiquitous as is now confirmed also with radiolarians.

Jurassic; Lower Cretaceous; eastern Serbia; radiolarians

nije evidentirano