Zarys rozwoju basenu czerwonego spągowca na obszarze Niżu Polskiego

Jędrzej Pokorski



The Rotliegendes was divided into lower and upper part and correlated with the Autunian and Saxonian with reference to lithological features. Five diastrophic-sedimentary cycles were differentiated in the Rotliegendes: 2 or 3 in the Autunian and 2 in Saxonian. The Autunian/Saxonian boundary coincides with the main Saalian subphase and it is interpreted as isochronous. The Saxonian diastrophic-sedimentary megacycles I and II, related to the main and last Saalian subphases, respectively, are discussed in the paper (Figs. 1 and 4). The Rotliegendes/ Zechstein boundary is delineated at the base of the Capper Shale horizon or Basal Limestone deposits.
In the earliest Autunian, sedimentation of clastic deposits was continuing in Late Carboniferous intermontane basins (Mid-Sudetic and North Sudetic basins). At that time, a depression (Zielona Góra basin), at first very narrow, appeared in the contact zone of Variscan internides and externides. It seems that the remaining parts of the Polish Lowlands were subjected to up lift and erosion. Before the end of the Autunian, the Zielona Góra and Sudetic basins became infilled with volcanogenic and clastic rocks. The Poznań graben from external arc of Variscan internides became infilled with mainly pyroclastic deposits. An highland with local volcanic centers appeared in the Wolsztyn area. In central parts of the Polish Lowlands is inferred presence of a basin infilled with pyroclastic and siltstone-sandy deposits (Figs. l and 2).
The tectonic framework of the Polonian Basin, determined by Variscide front zone and tectonic fracture zone of the Teisseyre-Tornquist line, originated in result of tectonic movement of the main Saalian subphase.
The area of Variscan internides was the main source of detrital material. Fluvial sedimentation was prevailing in inner zone of the externides (Wrocław Plain and Zielona Góra Depression Highland). A belt of horst-like elevations separated by tectonic troughs, named Wolsztyn Dissected Highland, was being formed in external zone of the externides.
The second megacycle is characterized by widening and connecting of basins which were previously partly or completely isolated. The Polonian Basin became connected with the German, turning into vast depression weakly differentiated in morphology and the sedimentary environment of the inland sabkha of playa type. Shallow but vast basins resembling Zechstein, especially PZ1 basins in morphogenetic features, have originated in the area of the pre-Vendian Platform. Peneplenization of alimentary areas and leveling of morphology of sedimentary basins in this area resulted in appearance of eolian deposits in marginal zones. The Saxonian ends with that stage of continental-desert conditions.

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