Biostratigraphic and paleoenvironmental evaluation ofthe pilot sections NE of the Libuňka Fault according to the study of calcareous nannofossils, Jizera Development of the Bohemian Cretaceous Basin, NE Bohemia


Lilian Švábenická

Geoscience Research Reports 46, 2013 (GRR for 2012), pages 77–84
Map sheets: Sobotka (03-34)

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Nannoplankton biostratigraphy and paleoenvironmental interpretations were made from the pilot sections situated NE from the Lužice Fault between sites of Turnov and Trosky in the Bohemian Paradise area, Jizera Development ofthe Bohemian Cretaceous Basin, NE Bohemia. Nannofossils with Lithastrinus septenarius and Marthasterites furcatus indicated UC9a zone that is correlated with the stratigraphical interval from the uppermost part of Middle Turonian to lower part of Upper Turonian. Nannofossil content and their preservation state are evidently depended on facial character of deposits. Claystones of pelagic facies provided relatively abundant and medium well preserved nannofossils wheras overlying sandstones of flyschoid facies yielded scarceand heavily etched specimens. Biostratigraphic validity of the M. furcatus and L. septenarius in the secondarily modified assemblages is discussed. Their presence in taphocoenoses may be influenced post mortem both by follow-up diagenetic processes and facial character of deposits. Selective dissolution of nannofossils may be also caused by the release of carbon dioxide during oxidation of organic matter that is present in abundance especially in flyschoid facies. The precise stratigraphic evaluation of deposits that contain the secondarily impoverished nannofossil assemblages is therefore problematic.