Utwory pogranicza cyklotemów PZ1 i PZ2 cechsztynu w kłodawskim wysadzie solnym (środkowa Polska)
Abstract
Deposits from the transition of Zechstein PZ1 to PZ2 cyclothems in the Kłodawa salt dome (central Poland).
A b s t r a c t. The possible occurrence of the Oldest Halite (Na1) unit of the Zechstein PZ1 cyclothem in the Kłodawa salt dome was a discussed matter for many years. Profiling and sampling of the evaporite Zechstein succession (a transition of PZ1 to PZ2 cyclothems) visible in a corridor of the “Kłodawa” Salt Mine at the mining level –650 m, located near the NE marginal pillar of the dome, were done in 2011. The studied section includes rock salt, shale, sulphate and carbonate rocks inclined at 60–90o to the NE and represents a normal succession of the PZ1 and PZ2 cyclothems. The normal succession of the top part of the PZ1 cyclothem consists of two lithological units: 1) rock salt complex (extending over a distance of ca. 5.8 m), defined as the Oldest Halite (Na1) lithostratigraphic unit, and 2) anhydrite bed, c.a. 1.3 m thick, distinguished as the Upper Anhydrite (A1g). These deposits are overlain by 4 lithological units, considered as
those creating the normal sequence of the lower part of the younger PZ2 cyclothem. The first one is a dolomitic shale bed, ca. 3.7 m thick, defined as the Stink Shale (T2). It is overlain by a dolomite layer, 0.3–0.5 m thick, representing the Main Dolomite (Ca2), and by an anhydrite series, over 17 m thick, attributed to the Basal Anhydrite (A2). The studied section ends with a rock salt complex, ca. 4 m
thick, interpreted as the Older Halite (Na2). The bromine (Br) content in both salt units is relatively low: 81–86 ppm (7 samples) in the Na1 unit and 54–77 ppm (4 samples) in the Na2 unit, with a distinct upward-increasing trend in the latter. Similar low Br values and their distribution trends were characteristic for the top of the Na1 standard bromine curve in Poland and for the lower part of such curve for the Na2 salts. This geochemical similarity could support a proper stratigraphic position of both units. The analysed section
was interpreted as a tectonic slice or intrusion, composed of Na1 rock salt overlain with the younger A1g sulphate, incorporated within the folded complex of Na2 rock salt. Such image confirms the current opinion of a more complicated internal structure of the so-called “marginal anticlines” within the Kłodawa dome, composed of intensively folded both salt units. It also documents that the oldest Zechstein evaporites (chlorides and sulphates) could occur above within the dome section than was stated earlier.
A b s t r a c t. The possible occurrence of the Oldest Halite (Na1) unit of the Zechstein PZ1 cyclothem in the Kłodawa salt dome was a discussed matter for many years. Profiling and sampling of the evaporite Zechstein succession (a transition of PZ1 to PZ2 cyclothems) visible in a corridor of the “Kłodawa” Salt Mine at the mining level –650 m, located near the NE marginal pillar of the dome, were done in 2011. The studied section includes rock salt, shale, sulphate and carbonate rocks inclined at 60–90o to the NE and represents a normal succession of the PZ1 and PZ2 cyclothems. The normal succession of the top part of the PZ1 cyclothem consists of two lithological units: 1) rock salt complex (extending over a distance of ca. 5.8 m), defined as the Oldest Halite (Na1) lithostratigraphic unit, and 2) anhydrite bed, c.a. 1.3 m thick, distinguished as the Upper Anhydrite (A1g). These deposits are overlain by 4 lithological units, considered as
those creating the normal sequence of the lower part of the younger PZ2 cyclothem. The first one is a dolomitic shale bed, ca. 3.7 m thick, defined as the Stink Shale (T2). It is overlain by a dolomite layer, 0.3–0.5 m thick, representing the Main Dolomite (Ca2), and by an anhydrite series, over 17 m thick, attributed to the Basal Anhydrite (A2). The studied section ends with a rock salt complex, ca. 4 m
thick, interpreted as the Older Halite (Na2). The bromine (Br) content in both salt units is relatively low: 81–86 ppm (7 samples) in the Na1 unit and 54–77 ppm (4 samples) in the Na2 unit, with a distinct upward-increasing trend in the latter. Similar low Br values and their distribution trends were characteristic for the top of the Na1 standard bromine curve in Poland and for the lower part of such curve for the Na2 salts. This geochemical similarity could support a proper stratigraphic position of both units. The analysed section
was interpreted as a tectonic slice or intrusion, composed of Na1 rock salt overlain with the younger A1g sulphate, incorporated within the folded complex of Na2 rock salt. Such image confirms the current opinion of a more complicated internal structure of the so-called “marginal anticlines” within the Kłodawa dome, composed of intensively folded both salt units. It also documents that the oldest Zechstein evaporites (chlorides and sulphates) could occur above within the dome section than was stated earlier.