Palaeogeographic and palaeoclimate factors of salinity fluctuations in the eastern part of the Late Permian (Zechstein) European Basin: case study from the salt basin in Poland

Abstract

AbstractA study of the bromine content and facies in the salt successions (representing PZ1, PZ2 and PZ3 cycles) from the Late Permian (Zechstein) salt basin in Poland evidences fluctuations in mother brine concentrations. The study indicates that the local (better recorded in facies of the shallow basin and its margins) and regional changes were the result of Late Permian climate variations and eustatic sea-level rises and drops.The observed trend for a lowering of brine concentration is attributed to more humid climate periods accompanied by frequent rainy seasons. Such a change from arid to more humid climatic conditions was observed in all three studied cycles, proving the variations of a dominant warm and dry climate, assumed for the inner part of the Pangea supercontinent in the Late Permian. The coastal zone of the Pangea supercontinent was more affected by the atmospheric perturbations, which were more frequent at the boundary between the continent and the ocean. The intracontinent areas were characterized with a more stable climate, thus interpreted by the authors, that the climate changes in the successions coming from the inner part of such intracontinental basin, far from the continent coasts (as the Polish part of the European Permian Basin) as the evidence for climate instability in the whole Zechstein period. The authors recorded the climate fluctuations in an area, which should be characterized with the most constant climate, particularly during the evaporite deposition. The prolonged more rainy periods that succeeded the warm and arid periods were recorded in the central part of the continent.Eustatic sea-level fluctuations, responsible for large changes in brine concentrations, became independent from the climatic variations. Sea-level rises initiated huge marine water input and caused extreme refreshing of the bottom salt brine in deep-water basin parts. Two such events were registered in salts of the PZ1 cycle, and a further three in the evaporite succession of the PZ3 cycle. A single rapid drop in sea-level, resulting from a postulated tectonic close of the narrow North Atlantic seaway that conducted ocean water to the evaporite basin, was detected in the lower part of the PZ2 salt succession. This caused the evaporite basin cutoff, its successive desiccation and, consequently, the production of potash-bearing salts.