Acme Marthasterites furcatus as a good marker for the Turonian-Coniacian boundary and Lower Coniacian, Jizera development of the Bohemian Cretaceous Basin

Geoscience Research Reports 50, 2017, pages 111–116

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Published online: 29 June 2017

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Abstract

Nannoplankton study and its biostratigraphic interpretation contributed to the geological research in the vicinity of Dolní Bousov, SW part of the Jizera development of the Bohemian Cretaceous Basin (BCB) (Havlíček et al. 2017). The acme M. furcatus (1-3 specimens in 1 field of view of the microscope) helped to recognize the Turonian-Coniacian boundary interval and the Lower Coniacian, and facilitated to classify rocks into the lithostratigraphic units.
Terrain was mostly covered by Quaternary deposits and isolated outcrops occurred only on rare occasions. Rocks were sampled mainly from the manual soil-sounding. Grey and green-grey claystones with silty admixture and grey marly claystones provided relative rich, medium well preserved and diversified nannofossil assemblages with marker species Broinsonia parca expansa, Zeugrhabdothus biperforatus, Marthasterites furcatus and Eiffellithus nudus (Fig. 2). Stratigraphically significant Polycyclolithaceae Quadrum gartneri, transitional forms Quadrum-Uniplanarius and Quadrum-Micula, and Micula adumbrata occurred irregularly. Scarce Micula staurophora was recorded in only sample.
Nannofossil assemblages indicated following stratigraphic horizons (Tab. 1):
UC9c zone (lower part) with sporadic occurrence of Broinsonia parca expansa and Marthasterites furcatus, upper Upper Turonian, Teplice Formation.

1. UC9c, acme Marthasterites furcatus, Turonian-Coniacian boundary to lower Lower Coniacian, transitional interval between the Teplice and Březno formations, equivalent of the Rohatce Member. Strata provided scarce inoceramid fauna.
2. UC9c zone (upper part) with few B. parca expansa, transitional forms of Quadrum-Uniplanarius and Micula adumbrata, and with distinct quantitative fall of M. furcatus (1-5 specimens in 10 fields of view of microscope). Interval may be correlated with the overlie of acme M. furcatus, Lower Coniacian, Březno Formation.
3. UC10 zone with sporadic Micula staurophora, the uppermost part of Lower Coniacian up to Lower-Middle Coniacian boundary interval, Březno Formation.
Biostratigraphic interpretations followed the UC zones by Burnett (1998), acme M. furcatus by Švábenická (2012), and the regional lithostratigraphic units of the BCB respect the classification of Čech et al. (1980). Distribution of nannofossil marker species, biostratigraphic interpretation and photodocumentation are presented.
This study is dedicated in memoriam to co-author Pavel Havlíček, who died in November, 27. Pavel Havlíček, specialist in Quaternary geology made the geological research and mapping in 2015 and 2016 in this field and overgave samples for nannofossil study.

 

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