Reefs — Evaporites Relations in Late Permian of Western Poland

Peryt, Tadeusz M.; Dyjaczynski, Kazimierz

In West Poland, isolated bryozoan reefs located in the basinal facies of the Zechstein Limestone (carbonate member of the first evaporite cyclothem of the Zechstein) are sealed by evaporites and are important gas reservoirs. The current concept assumes that the initiation of the reef growth was controlled by the inherited relief: the elevations became the loci of the intensive local carbonate production (the reefs are a dozen to 90 m thick), and over the large area in the region the regime was hostile for net carbonate production and hence condensed sequences (often less than 1 m thick) were deposited in the major part of the basin. The concept is supported by very successful exploration history. The reefs are covered by anhydrite deposits (40 m thick or less) of the first cyclothem, and in the basins adjacent to the reefs thicker halite deposits occur; the evaporite deposition led thus to the elimination of the pre-existing relief by the end of the first evaporite cyclothem. The evaporite deposits form thick (up to 300 m) sulphate platform system that subsequently controlled the facies pattern and hydrocarbon potential of the Main Dolomite (carbonate member of the second evaporite cyclothem of the Zechstein). 3-D seismic data indicate that the history of evaporite deposition of the sulphate platform system is quite complex, there were several phases of chloride deposition (and not just one, as previously assumed) separated by sulphate deposition, and the boundaries of salt basins and sulphate platforms were changing in time and space.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013