Stratygrafia i mikrofauna górnego cenomanu niecki północno-sudeckiej

Abstract

Stratigraphy and microfauna of the Upper Cenomanian in the North Sudetic Basin The stratigraphy of the Cenomanian of the North-Sudetic Basin was elaborated by J. Milewicz (1958, 1961, 1965), and J. Milewicz, M. Podemski and E. Witwicka (1968). These authors distinguished the basal sandstone member, unfossiliferous or containing a very poor fauna, and the upper member consisting of marls and marly limestones with rare fossils. These marls were assigned to the Lower Turonian — Actinocamax plenus zone. A new profile of the Cretaceous rocks at Raciborowice near Bolesławiec in the eastern part of the basin comprises the both lithostratigraphic members. The Cenomanian rocks are underlain by dolomitic marls of the Roth (Fig. 1). The lower member consists of coarse-grained quartz sandstones containing glauconite, 13-15 m thick (layer 1). The sandstones are overlain by marls and grey marly clays, containing 15—35 per cent CaCO(3), with rare pelecypod shells and a rich microfauna. The thickness of the marls ranges from 28 to 31 m (layers 2—4). Radiolaria are numerous in the middle part of the marls, and sponge spicules in their upper part. The uppermost layer in the described profile consists of calcareous marls containing a Turonian microfauna (layer 5). The microfauna assemblages show little variability. Benthic foraminifers, chiefly arenaceous, predominate in the Cenomanian marls. Planktonie foraminifers are numerous only in the middle part of the marl member (layer 3) where they are accompanied by radiolaria. The Turonian marls contain a benthic, chiefly calcareous foraminiferal assemblage (Fig. 2). The stratigraphic ranges of the foraminiferal species present in the profile at Raciborowice (Table 1) permit to determine the age of the described beds. The presence of index species Rotalipora cushmani (Morrow), Cibicidoides gorbenkoi Akimec, Hagenovella advena (Cushman), Pseudovalvulineria cenomanica (Brotzen) , Ps. globosa (Brotzen) , Ps. berthelini (Kellex), Galvelinella baltiea ( Brotzen ) and Discorbis sanjarensis Lipnik (Fig. 3), permits to assign the marls described as layers 2—4 to the Upper Cenomanian, and the- marls described as layer 5 to the Lower Turonian (Fig. 1). The lower boundary of the Turonian is well marked by the appearance of the planktonie form Praeglobotruncana Helvetica (Bolli). The marls containing radiolaria described as layer 3 (Fig. 1) may correspond to the radiolarian horizon known from the Upper Cenomanian of the Carpathians and Alps. This horizon has a great importance for regional correlation. Its formation was probably related with a period of increased content of Si02 in marine water due to intense volcanic activity. Radiolarites and radiolaria shales occur in the Outer Carpathians in Cenomanian beds of all flysch units in Poland (L. Koszarski, W. Nowak and K. Żytko 1959, F. Bieda et al. 1963, S. Alexandrowicz 1966) and also in Roumania (T. Neagu 1968). In the Inner Carpathians the radiolarites are present in the Pieniny Klippen Belt in Poland and Slovakia (J. Salaj 1961, O. Samuel 1962, S. Alexandrowicz 1966). In the individual profiles the radiolarian horizon is accompanied by Pseudovalvulineria cenomanica (Brotzen) and Rotalipora cushmani (Morrow). The marls with sponge spicules (layer 4) may be compared with the spongiolites known at the Cenomanian-Turonian boundary in Northern Bohemia, in the Intra-Sudetic Basin and in the area of Drezden (J. Soukup 1949, J. Dvorak 1955, K. Trôger 1956). The numerous occurrences of sponges are related with the zones Actinocamax plenus and Inoceramus labiatus. The stratigraphie correlation of the Upper Cretaceous rocks in the North Sudetic Basin leads to the conclusion, that the marly complex overlying at Raciborowice the coarse-grained sandstones is corresponding to the Actinocamax plenus zone (J. Milewicz 1965). This zone contains foraminifers characteristic for the Cenomanian in its lower part, and characteristic for the Turonian in its upper part (J. Magné and J. Polvêche 1961).