Stratigraphic range of the pelitic and flyschoid facies under the Hrubá Skála sandstones (Bohemian Cretaceous Basin, Teplice Formation) ofthe Příhrazské skály, Hrubá Skála and Prachovské skály Cliffs (NE Bohemia)


Jaroslav Valečka, Lilian Švábenická

Geoscience Research Reports 45, 2012 (GRR for 2011), pages 44–50
Map sheets: Sobotka (03-34)

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Macrofossil and nannofossil biostratigraphy in the underlying strata of quartzose Hrubá Skála sandstones in the areas of the Příhrazské skály Cliffs, Hrubá Skála Cliffs and Prachovské skály Cliffs proved a diachronous onset of deposition of this sandstone body. In the Příhrazské skály Cliffs the base of this body belongs to the lowermost part of acme Marthasterites furcatus (important event in the Bohemian Cretaceous Basin), which lies in the uppermost Turonian or at the Turonian- Coniacian boundary. In the Prachovské skály Cliffs its base is younger, lying in the Lower Coniacian: this is suggested by the occurrence of inoceramid species Cremnoceramus deformis erectus (Meek), C. waltersdorfensis hannovrensis (Heinz) and acme M. furcatus already in the underlying strata. It is supposed that the onset of the deposition of the Hrubá Skála sandstones shifted in geological time (from the uppermost Turonian to Lower Coniacian) from the WNW (Příhrazské skály Cliffs) to the ESE (Prachovské skály Cliffs) with the influx of sandy detritus from the N and NW. This phenomenon was probably influenced by changeable paleocurrents in this part of the Bohemian Cretaceous Basin. The upper boundary of the Hrubá Skála sandstones is nearly isochronous across the whole body.