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1 2005

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Mid-Cretaceous spicule-rich turbidites in the Silesian Nappe of the Polish Outer Carpathians : radiolarian and foraminiferal biostratigraphy

Bąk M., Bąk K., Ciurej A.

Geological Quarterly

2005

Vol. 49, No. 3

275--290

Spicule-rich turbidites are widespread in mid-Cretaceous deep-water flysch of the Subsilesian and Silesian units in the Polish Outer Carpathians. The spicule-richmaterial with an admixture of numerous radiolarian and foraminiferal particles was supplied, together with siliciclastic material, from shallow environments, mostly from the northern margin of the Carpathian Basin. We present new data on the age of these deposits in the Silesian Nappe, where they are distinguished as the Mikuszowice Cherts. This unit is composed of mediumand thick-bedded siliciclastic to calcareous turbidites including bluish cherts in their middle and upper parts and of thin non-calcareous hemipelagic shales.We have studied radiolaria and foraminifera from hemipelagic sediments and spicule-rich turbidites, from two continuous sections in the Barnasiówka Range (BeskidWyspowyMts.) that included theMikuszowice Cherts (31 m thick) and their transition into the surrounding units. The age of the Mikuszowice Cherts was determined taking into account the following radiolarian datum events: (1) the occurrence of Praeconocaryomma lipmanae in the entire unit, (2) the FO (first occurrence) of Hemicryptocapsa tuberosa in the upper part of the unit, (3) the FO of Amphipyndax stocki close to the upper boundary of the unit, (4) the FO of Hemicryptocapsa prepolyhedra in the lowermost part of the overlying Barnasiówka Radiolarian Shale Formation. These datum events appear successively in theWestern Tethys successions within the Rotalipora cushmani planktonic foraminiferal Zone, which corresponds to the middle and upper Cenomanian (except for its uppermost part). The foraminiferal assemblages, in which such taxa as Rotalipora cf. cushmani, R. cf. greenhornensis, whiteinellids and Uvigerinammina praejankoi successively appear, confirm the mid-late Cenomanian age of the spicule-rich turbidites in the Silesian Nappe.