Stratygrafia syluru w obszarze nadbałtyckim Polski na podstawie wierceń

Abstract

SILURIAN STRATIGRAPHY IN THE PERIBALTIC AREAS OF POLAND, BASED ON DRILLING DATA

Summary

In the Peribaltic areas of Poland the Siurian deposits have so far been encountered in 50 bore holes made in an area stretching from Darłowo in the west, as far as Lake Okrągłe in the east (Fig. 1). In the individual drill sections the Upper Silurian deposits are strongly reduced and eroded. At many places, the erosion surface of Permian reached down to the Wenlockian deposits, or to the lower Siedlce beds with Pristiograptus bohemicus (B a r r.).
So far, neither Carboniferous and Devonian deposits nor the uppermost Silurian deposits that correspond to the Podlasie stage have been encountered in the area considered. It can hardly be assumed that so great gaps were formed here only due to the pre-Permian denudation. It may well be that this area was being uplifted throughout the whole period, from Upper Silurian to Carboniferous, and that here no marine sedimentation tock place. As proved by the recent drillings made in the region of Kołobrzeg and Chojnice, a Devonian basin stretched at that time only south-west of the Lębork and Darłowo. On the other hand, in the vicinity of Darłowo, Łeba and Wejherowo and within the area situated more to the east, no Devonian particularly, however, no Lower Devonian basin existed. Thus, a considerable gap between the Ludlovian and Permian deposits may have developed already at the close of the Ludlovian, after the sedimentation of shallow pelecypod-brachiopod, subordinately also ostracod facies of Beyrichia limestone type (A. Martinsson, 1965). It is also possible that at that time arenaceous deposits were laid down, resembling those of Downtonian type, or of the Ovöd Ramsasa series, which underwent a pre-Permian erosion.
At the end of the Ludlovian sedimentation, i.e, at the close of the Whitcliffian stage (C. H. Holland, 1965) strong Young Caledonian orogenic movements took place in Wales. They were responsible for an uplifting of the continent throughout a vast area, and for a withdrawal of the marine basin. Phenomena of considerable regressions are observed also in Scania, and more to the east – in the Peribaltic area, as well as in the northern and north-eastern regions of the country.
In Poland, the Ludlovian basin was preserved only in the central part of the country, and to the north-east of the Świętokrzyskie Mts. In the lows of this basin, clay deposits with graptolites were sedimented, resembling those of the Podlasie beds from Ruda Lubycka beds, or littoral deposits, similar, to the Upper Rzepin beds from the northern part of the Świętokrzyskie Mts. (Tab. 2), were laid down. The deposits are younger than those of the British Ludlovian, and older than the  deposits of the West-European Gedinian. The present author referred them to the Podlasie stage. Basin of the Podlasie stage was also connected with the Rhineland area and, to the south-east, with the Wolhynia and Podolia. This is evidenced by the graptolite facies ascertained in the bore holes Ruda Lubycka and Rawa Ruska that, more to the east, pass into calcareous, near-shore facies commonly known to occur in the Dniester and Sbrutsh river areas.
It results from the preliminary correlations that in the Podolia area the Skala beds correspond to the Upper Siedlce beds (H. Tomczyk, 1962), and the Borshtshev beds – to the Podlasie stage. The upper deposits of the Czortkov beds already contain such trilobites as Warburgella and Acastella that, according to E. Tomczykowa (1962), prove a good connection with the Gedinian deposits of the Bostów beds in the Świętokrzyskie Mts.
As compared with the Bohemian Silurian, a correlation between the equivalents of the British Ludlovian and those occurring at the boundary of the Kopanina and Pridoli beds is highly difficult. The lower horizons of the Pridoli beds are characterized by other graptolites (L. Teller, 1964) than the Lower Podlasie beds. In addition, the top of the Kopanina  beds does not reveal the presence of such trilobites as Acaste, Acastella prima, A. spinosa and Scotiella, which can be correlated with the top of the British Ludlovian (J. Shergold, 1967).
Au interpretation of correlation between the Polish and British Silurian deposits, proposed by the present author, is given in Tab. 2.