Utwory ilaste górnego cechsztynu w rejonie Lubina

Wojciech Salski




The paper deals with a lithologic-petrographical characteristic of the Zechstein clay deposits that occur in the Lubin region, within the area of the Fore-Sudetic monocline. Depending on the accepted subdivisions, the deposits are referred either to the Upper Zechstein, or are thought to be an equivalent of Aller cyclothem. The series characterized by a varying thickness (from 15 m to 45 m) rests on a thick anrhydirite complex that also belongs to the Zechstein, but is overlain with the Buntsandstein deposits. The clay deposits, red-brown in colour, display changing amounts of arenaceous and  carbonate admixtures, and considerable textural and structural differentiation. Lithologic petrographical observations allow to distinguish in the Upper Zehstein clay series several rock types, as follows:
1 ­– red-brown clay shales, hard, compact, having distinct lamination and parting, pelitic texture, and parallel fine-laminated structure;
2 ­– claystones characterized by brecciated structure, consisting mainly of hard, sharp-edged claystone fragments, chaotically disseminated in the clay mass; these deposits, typical of the series under discussion, are considerably wide-spread;
3 ­– clay marls and marly claystones revealing fine-grained texture and chaotic structure, are built up of red-brown, clayey substance, and of cartbonates represented mainly by dolomites;
4 – gypseous caystones connected with the bottom part of the day series; they consist of clayey substance that bears numerous gypsum crystals.
An unusually diversed gypsum mineralization, connected with both syngenetic and epigenetic  processes, is here a typical phenomenon of the whole clay shale series. Gypsum occurs here in the shape of irregular concentrations, numerous veins, in the stratified form and as the main rock-forming component.
In the lower part of the clay deposits an interbedding of carbonate rocks occurs, particularly characteristic of the Lubin region. It consists of porous and cavernous limestones or dolomites, 0,5–8,0 m in thickness. In vertical section these deposits reveal a changing position, as compared with the contact between clay shales and anhydrite shales; locally, they disclose traces of weathering and erosion. The southern boundary of this interbedding is, defined by some sub-Tertiary outcrops, or fault lines in other directions, the interbedding gradually passes into a gypsum or anhydrite bank. A number of interesting tectonical phenomena can be observed within the day shale series. These express themselves in the form of numerous sliding surfaces and as a squeezing-out of strata. In addition tectonic breccia consisting of sharp edged fragments and lumps of sandstones, cemented thy clay material is found, too. At the bottom of the clay deposits there appears a disturbance connected with the hydration of anhydrites.
The series under consideration is characterized by a considerable lithological variability that resulted in different development of clay rocks. The presence of these rocks in the deposits of intraformational breccia points to several periods of erosion of the deposits altered, before, diagenetically. These phenomena, and the occurrence of the deposits of both chemical and elastic origins prove a transition character of this series from Zechstein to Buntsandstein sedimentary conditions.

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