Upper Permian reef complex in the basinal facies of the Zechstein Limestone (Ca1), western Poland

Stromatolite and bryozoan build-ups from the Werra Cycle (Zechstein) of the Southern Permian Basin of Europe meet all definitions given by various authors for reefs and they commonly occur at the shelf edge. In a few places, including western Poland, they are also recorded in the basinal facies. The main part of the reef is formed by fragmented bryozoan zoaria. The reef biota are a typical bryonoderm association indicating cool-water and cold-water environments. A characteristic feature is a large amount of fragmented skeletal remains lacking rigidity. The main part of the reefs is built of rudstones, and only stromatolitic crusts form massive constructions. Remarkable is the mechanism of the origin of clearly morphologically separated reef constructions from the remains of a relatively low potential of fossilization. Zones built of crushed remains dominate over parts representing massive constructions. The colonization of the substrate began very early, as indicated by the interbedding of breccia and bioclastic carbonates in the lowermost part of the Zechstein Limestone in some reef sections. The Zechstein Limestone reefs of western Poland abound in the hemispheroid (botryoid) aragonitic cement that is otherwise common for the Zechstein reefs. The abundance of the cement recorded in Permian reefs is interpreted as the result of an unusually high saturation state of surface seawater because of a number of factors, including prolific carbonate precipitation due to the occasional upwelling of warmer saline waters on shelf environments in the stratified Zechstein Basin. The pervasive carbonate precipitation in the reef area contrasts with a restricted carbonate precipitation in the adjoining basin where very thin sequences have accumulated. Copyright (c) 2012 John Wiley & Sons, Ltd.