Acta Musei Moraviae

Contribution to lithology of the Cretaceous formations at the Bystrý potok section near Trojanovice (Silesian Unit, Outer Western Carpathians, Czech Republic)

Zone of natural outcrops of Cretaceous sediments of the Silesian Unit on the Czech territory (Outer Western Carpathians) was studied in the Bystrý potok stream by Trojanovice, between Velká Stolová near Frýdlant n. O. and Noříčí Hora near Frenštát p. R. The section consist of pelitic deposits of the Lhoty Formation, the Mazák Formation and the lower part of the Godula Formation. The thickness of the section is 323 m.

The upper part of the Lhoty Formation represents the facies of grey clayey limestones and spotted claystones. According to planktonic foraminifera and noncalcareous dinocysts it can be assigned to the Late Albian. Uppermost part of the Lhoty Formation (an 11 m thick) consist of light grey, noncalcareous claystones with several thin horizons of dark grey claystones. Based on dinocysts they are Early to Middle Cenomanian in age.

In the overlying beds variegated deposits of the Mazák Formation follows. Red claystones are dominant. They are intercalated with greenish-light grey claystones. The red and light colours of the claystones indicate the definitive creation of oxic conditions in the Silesian Basin. The variegated pelitic deposits are

there approximately in the central part of their extent divided by a set of deposits of sandy flysch. In the sandy flysch, both greenish-grey sandstones and grey white siliceous sandstones occur. The latter sandstones correspond to the Ostravice Sandstone. According to only sporadically occurring dinocysts, the Mazák Formation in the studied section belongs from Late Cenomanian to Coniacian age.

Grey claystones prevail in the overlying strata. Those are usually intercalated with thinner or thicker layers of at first red grey, then upwards of brown grey to reddish-brown grey claystones. In the set of the mentioned pelitic deposits, two more conspicuous layers of a sandy flysch appear (the lower one of the thickness of 38 m, the upper of the thickness of 13 m). This part is correlated with the lower part of the Godula Formation. Based on palynomorphs, these deposits belong to the Coniacian to Early Campanian. Layers of variegated claystones disappear at the top of the pelitic sequence. The grey claystones are

replaced by green grey one and the number of sandy layers increases. Higher, a sandy flysch of the middle part of Godula Formation sets on.