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Pisolite Facies in the Wuchiapingian Isolated Reefs of Western Poland


Lloyd Pray contributed greatly to our understanding of spectacular facies of carbonate grains named pisoliths recorded in Upper Guadalupian facies of New Mexico and Texas through the initiation of, and participation in, fine detailed research conducted by Mateu Esteban in mid-seventies. These grains occur in the back-reef facies of the Capitan Limestone of the Gudalupe Mountains. Remarkably similar grains have been encountered in the topmost part of the Upper Permian Zechstein Limestone (Ca1) of western Poland in a slightly different paleogeographical situation, namely occurring in the isolated reefs developed in the basin facies. The occurrence of these reefs is related to an intra-basin ridge surrounded by Upper Rotliegend sedimentary basins within the Southern Permian Basin. On uplifted tectonic blocks isolated reefs developed in Wuchiapingian times. Lateral persistence of biofacies units distinguished in the Zechstein below the Werra Anhydrite suggests that the individual reefs had similar depositional histories. The general shallowing-upward nature of Zechstein Limestone deposition resulted in that in the upper part of the Zechstein Limestone stromatolites abound. Further sea-level fall resulted in subaerial exposure of considerable parts of the Zechstein Limestone in the Wolsztyn-Pogorzela High. The topmost unit of Ca1 is stromatolitic–pisolitic carbonate, mostly dolomite, a few metres thick. In some cases the unit shows brecciation. It is often composed of stromatolites (both planar and microdomal), fenestral peloidal dolomites, pisoids and calcrete. Occasionally intraformational tepees were recorded. This lithologic association shows remarkable similarities to the back-reef facies of the Capitan Limestone of the Gudalupe Mountains, New Mexico and Texas. In particular, co-occurrence of tepee structures, pisoids and fenestral peloidal dolomite strongly suggests a peritidal environment characterized by intense precipitation from very shallow hypersaline waters at a topographic high both in the Capitan Reef Complex and the Zechstein isolated reefs of western Poland. The paleogeographical context of both these areas is different. There existed an evaporitic lagoon separated from a more open marine area in the Capitan Reef Complex in contrast to the basal Zechstein of western Poland where the highs on which the reefs have developed were encircled by an evaporitic basin during the origin of pisoid facies.