Pestre vrstvy svrchni kridy v basskem vyvoji slezske jednotky

A zone of the Chlebovice Conglomerate passing upwards in the Baška Formation is exposed in a stream-bed of the Ondřejnice River in the environs of the municipality of Hukvaldy. The formation belongs to the Baška development of the Silesian Unit. The section studied and documented attains a thickness of about 82 m. The section begins with a thick layer of boulders composed of the Štramberk-type limestone. In the overlying layers of this block accumulation, frequent layers of carbonate conglomerates with well-rounded pebbles alternate with layers of laminated siltstones and sandstones, and higher in the section occur laminated marly limestones. Upwards, the grain size and the thickness of conglomerate layers diminish. This part represents the Chlebovice Conglomerate. In the upper part of the section, the silicification of pelitic deposits is obvious, and the amount of layers of slab-like limestones decreases. Some of the fine-grained conglomerates and slab-like sandstones may also pass upward in a silicite. This part can be attributed to the Baška Formation. Siltstones, claystones and grey limestones prevail higher in the section, accompanied by calcareous silicified sandstones typical of the Baška Formation. Intercalations of red-coloured sediments appeared in the middle part of the claystone interval.
Red intercalations contain high proportion of hematite (11%) and goethite (20%). Mineralogically anomalous strata contain rich manganese oxide mineralization: birnessite, Cu-asbolan, and todorokite. Mn oxides are very finely dispersed. In the studied samples, some pseudomorphs of Mn oxides after Mn-rich carbonates were also detected.
In thin sections of limestones, planktonic foraminifera species Whiteinella archaeocretacea Pessagno (= Whiteinella gigantea (Lehmann)), Heterohelix Ehrenberg, and Hedbergella Brönnimann et Brown indicate the uppermost Cenomanian to the lowermost Turonian Whiteinella archaeocretacea biozone. Diversification of planktonic foraminifera increases in the upper part of the section. Species such as Whiteinella, Heterohelix, Hedbergella, Dicarinella cf. canaliculata (Reuss), and ?Helvetoglobotruncana helvetica (Bolli) were identified there. The last mentioned index species proved the Lower Turonian.
Lithology, mineralogy and stratigraphic position of the claystones and silicites at the Ondřejnice section correspond to the description of the uppermost part of the Barnasiówka Formation in the Polish part of the Silesian Unit.