Ewolucja basenu cechsztyńskiego w Polsce

Ryszard Wagner

Abstract


 Dokonano analizy podziału litostratygraficznego cechsztynu oraz jego położenia w tabeli chronostratygraficznej, z której wynika, że osady te tworzyły się w ostatnich 5 mln lat górnego permu. Prześledzono rozwój basenu cechsztyńskiego w Polsce i dokonano analizy paleotektonicznej. Wydzielono trzy główne rejony, różniące się stabilnością, tempem subsydencji i ewolucją basenu: 1 - względnie stabilny obszar platformy prekambryjskiej, 2 - bruzdę środkowopolską z maksymalnym tempem subsydencji rzędu 300 m/mln lat, 3 - labilną platformą waryscyjską. W obrębie tych rejonów wyróżniono jednostki tektoniczne niższego rzędu. Rozpatrzono problemy dziedziczenia późnowaryscyjskich ruchów tektonicznych w rozwoju basenu cechsztyńskiego.

 

THE EVOLUTION OF THE ZECHSTEIN BASIN IN POLAND

 

Litho- and chronostratigraphic investigations have shown that the Zechstein represents the uppermost

Permian sediments - that conform most probably with Upper Tatarian on the East-Europen Platform (Tab. 1). The time of its sedimentation was probably not longer than 5 my.

The maximum subsidence rate in the Polish basin was as high as 300 m/my. Based on the palaeothickness and facies maps of the Zechstein Basin in Poland was investigated. The palaeothickness map of the whole Zechstein (Fig. 5) was interpreted from the palaeotectonic point of view. Based on these researches three basic regions, differentiated by stability, subsidence rate and basin evolution have been distinguished. They were as follows: the Precambrian Platform, the Mid-Polish Furrow and the Variscan Platform.

The Precambrian Platform area was characterized in the Zechstein by remarkable stability, the lack of marked depressions and large sizes of distinguished structural units. The subsidence was weak about

50 m/my - and was compensated by the sediments. The arrangement and magnitude of stable and labile zones in the Zechstein showed remarkable concurrence main tectonic units of the East-Europen Platform. Based on changes in facies and thickness some crossing tectonic directions influencing the shape and evolution of the basin have been distinguished. The NW-SE directions parallel to the Teisseyre-Tornquist Zone (the T - T Zone) dominate in the south-western part of the Precambrian Platform.

The N - S directions of dubious origin occur in the axis of the Baltic Bay. The subparallel directions and the NE - SW directions perpendicular to the edge of the Precambrian Platform are observed in the depressions of the Mazury and Radom - Lublin lands. They are most likely the older tectonic directions rejuvenated in the Hercynian stage.

Mid-Polish Furrow and adjacent structural slopes was in the Zechstein an area of maximum subsidence. The subsidence rate, often compensated by sediments was as high as 300 m/my. Continuous downwarping movements (since the Upper Rotliegendes) enabled the sedimentation of the fullest in Europe, 1500 m thick Zechstein sequence of devoid of diastems and erosion gaps. In the uppermost Zechstein a unique zuber lithofacies was formed. The NW - SE tectonic directions (parallel to the T – T Zone) prevail in the Mid-Polish Furrow. Only in the northern and southern parts of the area the subparallel directions are observed. The arrangement of tectonic directions and high subsidence in this zone resulted from its particular tectonic location - between the Precambrian Platform edge and the Variscan folding front.

The Variscan Platform is characterized by lower subsidence rate (about 100 m/my) with its high differentiation. This differentiation manifests itself in a mosaic arrangement of facies zones and more or less labile zones that results probably from the heterogeneity of the Variscan tectogen. A distinct genetic relationship between both the Zechstein and Upper Rotliegendes structural units particularly that of the Wolsztyn Ridge and the Silesia Furrow is evident. The NW - SE tectonic directions connected with the Variscan tectogen dominate in the northern part of the area. In the southern part (the Sudetic - Silesia Terrace) the subparallel directions appear - probably the Caledonian ones rejuvenated in the Hercynian stage.

The main features of the Zechstein Basin on the Paleozoic Platform were inherited after the Upper

Rotliegendes basin which was shaped as a result of the Late Variscan Saalian phase. Strong downwarping movements at the boundary of the Rotliegendes and Zechstein caused expansion of the basin on the Precambrian Platform. This event made the base frames of the posterior Mesozoic basin.

 


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