Pelitic facies above the sandstone body of Příhrazské skály Rocks, NE Bohemia (lithology and calcareous nannofossil biostratigraphy)


Lilian Švábenická, Jaroslav Valečka

Geoscience Research Reports 44, 2011 (GRR for 2010), pages 50–56
Map sheets: Sobotka (03-34)

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Lithology and calcareous nannofossils were studied in the pelitic facies above the quartzose sandstone body of the Příhrazské skály Rocks, Jizera development of the Bohemian Cretaceous Basin, NE Bohemia. Material was obtained from the Mužský Muž-1 borehole drilled in 2010. Two layers of regional correlation importance were recognized: 1. layer with rusty orange-coloured clayey flasers in the uppermost part of quartzose sandstones designated as "Upper Red Layer" (Čech 2009), 2. layer of firm gray marlstone above the body of quartzose sandstone of the Příhrazské skály Rocks (in niveau of 2.0-3.6 m above it) that could be correlated with the similar layer recorded in the same level 8-14 km far to SE. Lithostratigraphically, quartzose sandstones are correlated with the Teplice Formation and the overlying pelites already with the Březno Formation. The layer of firm gray marlstone may be compared with the Rohatce Member. Nannofosils were present in the interval of 3.90- 9.20 m. According to the presence of Broinsonia parca expansa, transitional forms of genera Quadrum-Micula and absence of Helicolithus trabeculatus sediments are correlated with the upper part of UC9c zone, Lower Coniacian. In the depth of 9.20 m, nannofossil assemblage is characteristic by common Marthasterites furcatus accompanied by Kamptnerius magnificus. In overlying sediments, both species occur only in low numbers. This level probably recorded the top of interval with common occurrence ("acme") of M. furcatus, that was described in the uppermost Turonian and Lower Coniacian (Švábenická 2010). The transitional forms of genera Quadrum-Micula and questionable specimens of IMicula cf. adumbrata are discussed. Deposition of the quartzose sandstone body of the Příhrazské skály Rocks spans the time interval of "acme" Marthasterites furcatus (upper part) that is correlated with the Turonian-Coniacian boundary and lowermost Coniacian.