Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

J Žítt, Č Nekovařík, L Hradecká

Late Cretaceous nearshore environments and taphocoenoses in the surroundings of Brandy's nad Labem (Bohemian Cretaceous Basin, Czech Republic)

Journal of the Czech Geological Society, volume 43 (1998), issue 3, 175 - 186


  Abstract

A study of the Late Cretaceous localities Černá skála and Martinov situated north to northwest of Brandýs nad Labem in central Bohemia (Fig. 1) applied new data on sedimentation and faunal taphocoenoses of the area. Both localities are situated on or near the exhumed bedrock elevations of assistant Upper Proterozoic rocks.
Cretaceous deposits at Černá skála were originally exposed in quarry which is now abandoned and partly infilled. These old sections are, unfortunately, poorly known and no adequate description was given. It seems, however, that basal coarse psephites, composed of disintegrated silicite, overlain by glauconitic claystones to siltstones and locally the limestones were developed here. The only source of data is represented by old museum collections of fossils. In the District Museum Praha-východ at Brandýs nad Labem there is collection containing at least 12 species with prevailing oysters Amphidonte (Amphidonte) haliotoideum (Sowerby), A. (A.) sigmoideum (Reuss), Rastellum diluvianum (Linné), R. carinatum (Lamarck) and Pycnodonte (Phygraea) vesiculare (Lamarck) (syn. Ostrea hippopodium), and numerous guards of Praeactinocamax plenus (Blainville) (Fig. 3). Remains of strongly glauconitic sediment adhere to large specimens of P. (P.) vesiculare which contain phosphatized invertebrate coprolites and late Cenomanian foraminiferal assemblage with Gavelinella cenomanica. Some P. plenus guards are coated by phosphatic crusts. All features indicate here a distinct condensed horizon. Samples of Cretaceous sedimentary rocks (Fig. 4) taken from agricultural soils nearby the Černá skala elevation show sedimentary environments with varying influence of currents, scour and lag deposit formation.
At the Martinov locality, about 0.5 m thick section of Cretaceous sediments covering the Proterozoic grey wacke bedrock was recently studied. Thin basal glauconitic sandstone with disseminated coarse silicite cobbles rapidly passes into a lag deposit formed of oysters [A. (A.) haliotoideum, R. diluvianum, R. carinatum] (Figs. 5-7). The convex-up orientation of small isolated right valves of A. (A.) haliotoideum and convex-down orientation of large valves of R. diluvianum and R. carinatum (Fig. 6) indicates conditions with slight bottom currents. In upper parts of the section the amount of clay substance increases showing calmer conditions in deeper sea. The age of sequence is late Cenomanian (Gavelinella cenomanica), probably older than the plenus-event. Old Museum collections (Brandýs nad Labem) contain a set of fossils (about 33 species) in which Synhelia gibbosa and P. plenus are most significant. These fossils indicate former presence of slightly younger deposits which are now absent at the locality.

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ISSN: 1802-6222

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