Skala magnetostratygraficzna dla utworów czerwonego spągowca, cechsztynu i pstrego piaskowca z obszaru Polski

Jerzy Nawrocki



Magnetic polarity scale for the Rotliegend, Zechstein and Buntsandstein of Poland is based on the results of paleomagnetic investigation of 566 hand samples coming from Polish Lowland (11 boreholes, Fig. 1) and 45 hand samples taken from the North Sudetic and Intrasudetic Basins. Only samples with characteristic directions of first and second cathegory of the reliability [3,9] were taken into account to construct the scale. This selected set consists of the data derived from 250 hand samples. Unfortunately, the sedimentation rate of investigated rocks is very poorly known. It was assumed that sandy rocks were accumulated two times faster than fine grained and carbonate rocks. Polarity of the first, second and third Zechstein cycles is almost completely uncertain. This fact is related to bad paleomagnetic properties of those sediments. The end of the Kiaman reversed magnetization epoch (i.e. Illawarra Reversal [2]) is situated in the stratigraphic gap that separates Lower and Upper Rotliegend rocks of Polish Basin [11]. This interpretation differs from Menning's solution [8] in which the Illawarra Reversal is situated in the lower part of Upper Rotliegend and corresponds to the Lowermost Tatarian. In the light of magnetostratigraphic data obtained from another sedimentary basins, where normal polarity zones occur already in Murgabian rocks [5], the solution presented here (Fig. 2) seems to be more adequate. The magnetostratigraphic data sets from Pakistan [4], China [5] and Transcaucasia [7] indicate that two or three significant normal polarity intervals occur in the time from Murgabian stage to the end of Permian. Two distinct normal polarity intervals occur in the Upper Rotiegend sediments from Poland. This fact, although the sedimentation rate of that rocks is very poorly known, seems to support the thesis about late Permian age of the oldest Zechstein cycle. The polarity patern observed in the Buntsandstein sediments is very close to the graph obtained in the Canadian Arctic section [10]. The most probable correlation between Polish Permian-Lower Triassic formations and sections from another basins is presented in Fig. 3.