An interesting sedimentary succession with accumulation of coprolites, oysters and worms (Plaňany, Bohemian Cretaceous Basin)


Jiří Žítt

Geoscience Research Reports 34, 2001 (GRR for 2000), pages 25–27
Map sheets: Nymburk (13-14)

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A new section across the Late Cretaceous rocks was recently studied in the gneiss-amphibolite-migmatite quarry at Plaňany near Kolín, central Bohemia. Cretaceous sediments cover the abraded surface of crystalline basement and their succession consists of three lithologies. Unit 1 is formed by sandstone with densely packed large oysters in its topmost part. This oyster bed most probably represents a secondary accumulation due to the winnowing of softer sediment particles. Belemnite praeactinocamax plenus (BLAINV.) occurs rarely together with the oysters. The overlying lithological Unit 2 represents coprolitic calcareous sandstone with abundant oysters (dominated by oysters similar to Gryphaeostrea canaliculata (Sowerby) but probably belonging to new species, see Záruba in this Journal) and thick tubes of worms (Protula planianica ZIEGLER). Sharp lower boundary of this bed and taphonomic features of organic remains indicate an abrupt change of sedimentary conditions. Deposition of Unit 2 probably started as a rapid short-distance redeposition of the roughly coeval low-energy deposits. Some macrofauna (the above mentioned worms) may represent more autochthonous component of the resulting taphocoenosis. In the top parts of Unit 2, the sedimentation gradually changes, showing more quiet conditions of in situ deposition of the overlying sponge-containing spiculite siltstone of Unit 3.