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Jurassic - Early Cretaceous radiolarian stratigraphy of the Danubian nappes (eastern Serbia)

The Danubian nappes of eastern Serbia belong to a much larger Dacia Mega-Unit. The Dacia Mega-Unit actually comprises different allochthonous smaller units in East and South Carpathians. These units are considered to be parts of the European continent that were detached from it during Jurassic rifting in the domain of the Alpine Tethys (Schmid et al., 2008). Some of these units were separated from Europe by oceanic lithosphere of the Ceahlau-Severin oceanic domain, while other units, including the Danubian nappes were just later scraped off the European margin due to strong coupling of the orogenic wedge and the foreland (Ziegler et al., 1995). According to Schmid et al. (2008), the Danubian nappes were detached from the Moesian foreland. Together with more internal units located underneath the Transilvanian Basin and outcropping in the North Apuseni Mountains (Tisza Mega-Unit ; Haas & Pero, 2004), they invaded the Carpathian embayment in Cenozoic times (i.e. Royden, 1988 ; Csontos & Vörös, 2004 ; Horváth et al., 2006) and finally docked with the European foreland during the Miocene. In eastern Serbia, the Mesozoic successions of the Danubian nappes are exposed along the valley of the Danube River. Our knowledge on Mesozoic microfauna from the Danubian nappes is still insufficient. Particularly scarce are published data on Jurassic – Early Cretaceous microfauna on which this study concentrates. Data on radiolarian assemblages are available for locality Sviniţa in Romania (Dumitrica, 1995), which is located in the vicinity of our sections in Serbia. The information on Jurassic – Early Cretaceous Radiolaria from eastern Serbia presented here comes from a few sections which crop out along the road Dobra – Boljetinsko brdo. In the studied area, Jurassic sedimentation began with clastic deposits that transgressively overlie Permian rocks. Two considerably different successions were studied above the Lower Jurassic quartz sandstone and conglomerate. The first succession, exposed between tunnels no 17 and 21 (22°00.1’E, 44°36.1’N), is over 150m 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 ; 22°01.0’E, 44°34.1’N) indicates deposition on a pelagic plateau. This section is much more condensed, not exceeding 20m 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 Maiolicalimestone of the Southern Alps. Up to several meters thick slumped levels are common in this Lower Cretaceous limestone. In addition to these two sections, several short sections in the upper part of the Maiolica limestone and in the overlying Barremian marls and marly limestones were sampled for radiolarians and stable carbon isotope analyses. The interest of precise stratigraphic studies is based on the fact that, according to the recent geotectonic interpretations (e.g., Schmid et al., 2008), the study area actually represents the easternmost part of the Alpine Tethys. Radiolarian dating has been undertaken primarily to elucidate the rifting history in this domain. Post-rift sedimentary successions of a deep basin and a pelagic plateau have been distinguished. 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.

Radiolaria; Jurassic; Early Cretaceous; the Danubian Nappes; eastern Serbia

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