GENERATION OF PRIMARY SYLVITE: THE FLUID INCLUSION DATA FROM THE UPPER PERMIAN (ZECHSTEIN) EVAPORITES, SW POLAND

Abstract

The chemical composition of primary inclusions in sedimentary halite from the Polish Zechstein salt deposits (Upper Permian), which represent deposition in salt lagoon to salt pansalina conditions of two evaporitic units of the Stassfurt and Leine cyclothems, contains evidence that the included brines belong to the Na-K-Mg-Cl-SO 4 (SO 4-rich) type. They differ from the brines typical for other Zechstein salts by having an elevated potassium content, which produced primary sylvite (daughter crystals in inclusions), caused by redeposition of locally generated potassium salts during inflow of fresh seawater into the sedimentary basin. The homogenization temperature of primary inclusions in halite with sylvite daughter crystals reflects the increased temperature (53-60 °C) of basin brines, caused by a greenhouse effect due to density stratification of the brines. Isotopic composition of the anhydrite (sulphur: 9.4-13.30‰ Canyon Diablo Troilite (CDT); oxygen: 9.44-10.41/oo Standard Middle Ocean Water (SMOW), as well as the bromine content in halite (49-77 ppm) indicated that these salts had a marine origin and were deposited at an elevated temperature, from concentrated seawater with a high potassium content, that favoured precipitation of primary sylvite.