Skondensowane profile wapienia cechsztyńskiego w północnej części monokliny przedsudeckiej

Abstract

Przedstawiono charakterystykę mikrofacjalną i geochemiczną skondensowanych profili wapienia cechsztyńskiego w północnej części monokliny przedsudeckiej i porównano je z profilami kompletnymi wewnętrznej części zbiornika. Stwierdzono, że profile skondensowane w zasadzie powstały w okresie osadzania się kompletnej sekwencji wapienia cechsztyńskiego. Wyniki badań wskazują, że profile skondesowane świadczą o płytkim, często supralitoralnym, środowisku sedymentacji, natomiast profile kompletne powstały w środowisku nieco głębszym. Omówiono znaczenie wapienia cechsztyńskiego dla analizy paleotektonicznej permu na obszarze północnej monokliny przedsudeckiej oraz przedyskutowano pewne implikacje paleogeograficzne i paleotektoniczne.

CONDENSED PROFILES OF THE ZECHSTEIN LIMESTONE IN THE NORTHERN PART OF THE FORE-SUDETIC MONOCLINE

During the sedimentation of the Zechstein Limestone (Ca1), the areas of northern part of the Fore-Sudetic monocline and southern part of the Szczecin trough (Fig. 1) constituted a part of the basinal zone (T. M. Peryt, 1978a; T. M. Peryt, T. S. Piątkowski, R. Wagner, 1978). The Zechstein Limestone in this zone is characterized by the often micritic development and thickness of about 5 m (T. M. Peryt, 1978a), although in the studied area the profiles of regressive sequences of microfacies, typical for the nearshore area of the Zechstein Limestone basin (T. M. Peryt, 1978a~) were also found. They have thickness'liiimilar to that in the nearshore area (e.g., Pogorzela region - T. M. Peryt, A. Protas, 1978) or diminished to less than 2.5 m, usually about 2.0 m, although the profiles only several cm thick were also recorded (Fig. 1). The profiles of diminished thickness are condensed ones, and they are subject of the present paper. They ,quite often contain at the bottom the Kupferschiefer that is 2–80 cm thick in the case of profiles of thickness more than 1.50 m and is less than 15 cm in profiles of smaller thickness.

In the present paper the micrafacies development and geochemical characteristics are shown in several instances and the condensed sequences of the Zechstein Limestone are compared with those of the thickness typical for the basinal zone (Fig. 2–5, table 1–3, Plates I–IV). It was stated that the deposits of the condensed profiles of the Zechstein Limestone originated in the shallow marine environment (comp. Fig. 6) temporarily being subaerially exposed. The deposits of the complete sequences of the Zechstein Limestone originated in a little deeper environment (Fig. 6) but the depth of water most probably did not exceed several tens of metres. The condens'ed sequences originated during the deposition of the complete sequences of the Zechstein Limestone typical for the depressions within the basinal zone except of the profiles of thickness several tens of cm that characterize the areas in which the accumulation took place during the sedimentation of the upper part of the Zechstein Limestone only. The Bechstein Limestone in the condensed sequences shows the regressive sequence of microfacies.

The development of the lower part of the Zechstein Limestone indicates the subtidal sedimentary environment, although considerably shallower when compared with that of the complete profiles, while the development of the upper part of the Zechstein Limestone indicates the percitidal, very often stipratidal sedimentary environment. The development of the uppermost part of the Zechstein Limestone and of the overlying the lowermost part of the Lower Anhydrite of the thickness at least several tens of cm indicate the supratidal sedimentation in a sabkha environment.

It was demonstrated that the Zechstein Limestone in the northern part of the Fore-Sudetic monocline is the exceptionally sensitive indicator of changes in sedimentary environment and it is therefore of great importance for the paleotectonical analysis. The results of studies testify to the activity of studied area (expressed in vertical movements) during the sedimentation of the Zechstein Limestone. The studied area was divided into many blocks in a different degree elevated in relation to the neighbouring blocks with the amplitudes of their elevation reaching several tens of metres. The rates of subsidence of these blocks were very changeable, in many cases being equal to the rates of sedimentation.

When possessing good well control it is possible to state the small sizes of the blocks but, nevertheless, some regional zones of evident predominance of elevated blocks can be distinguish (comp. Fig. 7). When compared with the zones of elevations in the Saxonian, the area of elevations during the Zechstein Limestone is broader, the areas elevated during the Saxonian being as a rule elevated also during the sedimentation of the Zechstein Limestone. The zones of elevations in the higher horizons of the Werra and in the Stassfurt show some correlation with the areas elevated during the Zechstein Limestone as well (Fig. 7).