PURBECKIAN LIMNIC OSTRACODA REWORKED IN THE EARLY MIOCENE MARINE DEPOSITS OF THE VIENNA BASIN, SLOVAKIA
Roč.17,č.1-2(2010)
Burdigalian clays with thin silty tempestites layers outcropped near the village Cerová have been investigated for its abundant neritic/bathyal vertebrate and invertebrate fauna.
Among the Miocene marine neritic ostracoda, we have found well-preserved limnic Mesozoic ostracods
Cetacella armata Martin, 1958, Cypridea ex gr. tumescens (Anderson, 1939), Cypridea cf. altissima Martin 1940, Mantelliana perlata Wienholz, 1968, Theriosynoecum forbesii (Jones, 1885), Darwinula sp. These taxa were a part of the limnic Mesozoic ostracod fauna wide-spread over the world, which disappeared in the Europe with marine Aptian transgression and was replaced in the Late Cretaceous by new and modern ostracod taxa (Babinot et al., 1996).
A presence of Theriosynoecum forbesii (Fig. 1A) confirms that these limnic ostracods were reworked to the Early Miocene deposits from the Late Jurassic/Early Cretaceous deposits of the Theriosynoecum forbesii Zone, equal to the Tithonian/Berriasian age. In the lithostratigraphical division, this zone corresponds to Purbeck and lower Hastings Groups known from the southern England and north-western France (Horne 1995).
With a respect to this biostratigraphical attribution, this discovery induces a paleogeographical problem on a source geological unit because no limnic Late Jurassic/Early Cretaceous deposits have been found in the Central Europe till now. The eastern edge of the Bohemian Massif can be regarded as the most possible source, which was at this time emerged land (Fig. 1B). Unfortunately preserved Late Jurassic/Early Cretaceous deposits are of marine origin and a lack of the Purbeckian limnic deposits is underlined by Lower Cretaceous regression and karstification of the older deposits. Moreover, well-preserved ostracod valves without any marks of transport-related holes and smoothening of the ornamentation, and a relatively large distance of the deposition area from the Bohemian Massif make this “source” questionable, even impossible. Perfect preservation requires a transport on a short distance from the neighboring geological units. Central Western Carpathian geotectonic units can be hardly accepted as a possible source, due their continual and fully marine Late Jurassic–Early Cretaceous sedimentary sequence. The only source of the Purbeckian deposits, which could be partially emerged in that time, can be situated in the Outer Western Carpathians, however this limnic deposits
were completely eroded.
Paleogeography; Purbeckian; Theriosynoecum forbesii Zone; Vienna Basin
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