Stratygrafia anhydrytów Stassfurt w okolicach Lubina i Sieroszowic

Jerzy Kłapciński




The present paper deals with a subdivision of the Stassfurt anhydrites that occur in the areas of Lubin and Sieroszowice. Stassfurt anhydrites are called basal anhydrites, as well. Drill cores from 14 wells (Fig. 1) were a basis for the stratigraphical elaboration of the anhydrites here considered. Structural differences observed on drill core surfaces of the Stassfurt anhydrites allowed to distinguish, in the series under discussion, the following members (Fig. 2): upper breccia of anhydrite and clay, upper cavernous anhydrites, lower breccia of anhydrite and clay, lower cavernous anhydrites, laminated anhydrites.
The laminated anhydrites, 4,0 –18,3 m in thickness, occur in the lowermost part of the basal anhydrites. They are alternately bedded by grey anhydrite laminae, and by dark grey dolomitic anhydrite with clay admixture (Table I, Figs. 3, 4 and 5, and Table II, Fig. 6). In the bottom part, the laminae usually disclose, anhydrite beads.
The laminate anhydrites are covered, with the lover cavernous anhydrites, 7,1–15,7 m in thickness (Table II, Figs. 7. and 8, and Table III, Fig. 9). On the drill core surfaces of these anhydrites  numerous caverns occur passing into narrow fissures that are filled in with clayey material, or are void. After sawing a core we can observe its smooth surfaces with some caverns completely filled in with grey clayey material. Hence, a conclusion may be drawn that the empty caverns occurring at the drill core surfaces, are secondary, mechanical phenomenon, and that clay material has been brought away by drill mud during drilling operations.
The lower breccia of anhydrite and clay, 0,3–2,0 m in thickness, is a successive member here (Table IV, Figs. 10 and 11). It consists of dark-grey clay, irregularly disseminated anhydrite fragments of various shapes, from several millimeters to some centimetres in diameter. Horizontal, cross and wavy beddings are stressed by 1 m thick white-grey anhydrite laminae that alternate with dark-grey clay laminae.
Last but one horizon in the Stassfurt anhydrites is represented by the upper cavernous anhydrites, 1,5–9,5 m in thickness (Table IV, Figs. 12 and 13). Like the lower cavernous anhydrites, they also reveal numerous caverns communicated with fine fissures.
The upper breccia of anhydrite and clay, 1–4,5 m in thickness, is the last member ending the sedimentation of the Stassfurt anhydrites (Table IV, Fig. 14). It contains more clay material than the lower breccia, and towards the top it grades into a salt clay, grey in colour.
Microscope analysis demonstrates that the basal anhydrites of the area in study are built up of columnar forms (0,01–0,6 mm) chaotically arranged, and of granular forms, 0,002–0,5 mm in diameter. In certain thin slides made of laminated anhydrites aphanite mass can be observed. Dolomite bands with grains from 0,002 to 0,01 mm m diameter are visible, too.
Comparing the basal anhydrites from the Lubin–Sieroszowice area with the basal anhydrite series elaborated by W. Jung (1960) in Germany, I think that the laminated anhydrites correspond to the zone a, and the lower cavernous anhydrites – to the zone b. The lower breccia  of anhydrite and clay, the upper cavernous anhydrites, and the upper breccia of anhydrite and clay – to the zone g. In the area of study, the Stassfurt anhydrites are from 21,3 to 33,0 m in thickness.



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