Stratigraficky nejmladsi vapnite nanofosilie v sedimentech ceske kridove panve

The youngest hithero known calcareous nannofossils of the Bohemian Cretaceous Basin were found in the area of Litoměřice, NW Bohemia. Rocks were sampled during the engineering-geological explorative works of landslide near Dobkovičky for the purpose to detect their origin (Figs 1 and 2, Table 1). The presence of nannofossils reliably distinguished sediments of the Bohemian Cretaceous Basin from the altered Tertiary volcaniclastics and Tertiary and Quaternary deposits that were macroscopically alike. Landslide was activated in June, 2013 and radically damaged the under construction body of high-way D8 Prague-Dresden.
Grey, whitish grey and light green-grey marly claystones of the Březno Formation provided well preserved nannofossils with biostratigraphic markers Lucianorhabdus cayeuxii and Micula concava indicating the Upper Coniacian with the questionable exceed into Santonian. Three following nannofossil associations were recognized: 1 - Micula staurophora, Lithastrinus septenarius and sporadic Marthasterites furcatus, UC10 zone; 2 - Lithastrinus grillii and Lucianorhabdus inflatus, zone UC11a-b zone; 3 - Lucianorhabdus cayeuxii, L. arcuatus, Micula concava and M. cubiformis, UC11c zone (Table 2). Moreover, the association No. 3 contains species their first occurrence is mentioned from the uppermost Coniacian - Cribrocorona gallica, Gartnerago clarusora, G. margaritatus, Staurolithites imbricatus, Tortolithus dodekachyleon, and Prediscosphaera cf. desiderograndis (Fig. 3). Abundance of nannofossils and their excelent preservation document shallow epicontinental sea of normal salinity. The quantitative fluctuations of Biscutm ellipticum and Helicolithus trabeculatus are recorded. These phenomena may reflect the paleoenvironmental changes connecting with the Coniacian-Santonian boundary interval. Distribution of nannofossil marker species, biostratigraphic interpretation and photodocumentation are presented. Macrofauna was not recorded.
Nannofossils were investigated from the isolated chip sampling and not from the continuous section. Deposits were sampled from three boreholes surrounding landslide, two manual soil-sounding and from the side minor scarp of the landslide. So, the presented data have only the informative character.

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