Zechstein PZ3/PZ4 cyclothems boundary in the Inowrocław salt dome according to archival photographs of the "Solno" mine - an interpretation of local sedimentation conditions in the central part of the Polish Zechstein Basin

Abstract

Three decades ago in the exposures of the Inowrocław "Solno" salt mine, mud cracks at the top of Brown Zuber complex (Na3t) of the PZ3 Zechstein cyclothem were observed and documented in photographs. Brown Zuber complex is covered by the layer of Underlying Halite which is the first member of the PZ4 Zechstein sequence. The contact between Brown Zuber and Underlying Halite is clearly delineated. In some exposures a thin (1-2 cm) layer of anhydrite appears indicating the episode of dilution of brines in the sedimentation basin. Sometimes the thin (10 cm) layer of red or dark red salt occurs between the mud cracks on the top of Brown Zuber and a typical Underlying Halite. Probably the layer was created as a result of salt dissolving within the upper part of zuber and re-sedimentation. Documented features provide the evidence of the short episode of subaerial exposure of the basin bottom and of the discontinuities during sedimentation in this area. They also provide new information on paleogeographic conditions of Na4a0 salt sedimentation.