Abstract
Microbial deposits commonly occur at the transition between carbonate and sulphate facies, and they also abound in the uppermost part of the middle Wuchiapingian Zechstein Limestone in west Poland. These deposits occur as isolated reefs of the basinal zone and in the condensed sequences in most parts of the study area. The deposits of the latter category reflect evaporative drawdown, and the abrupt boundary between the carbonate and sulphate deposits in the basin suggests the nature of evaporites that start to precipitate as soon as they reach the saturation level. A few-metre-thick unit of mostly brecciated microbial deposits at the top, reefal portion of the Zechstein Limestone records extreme palaeoenvironmental events that occurred at the transition from carbonate to sulphate deposition. These events are related first to subaerial exposure of the reef, which lasted several 105 years and then to the Lower Anhydrite transgression.
Highlights
Carbonates preceding the vast accumulation of evaporites reflect changes in the basin hydrology and the degree of connection to the open sea
1) The thin (2.8–5.1 m) unit of brecciated limestones and subordinate dolomites at the top part of the Zechstein Limestone (Wuchiapingian) in the Jabłonna Reef in western Poland recorded a sudden sea level fall that resulted in a long subaerial exposure of the reef, followed by a slow brine-level rise
2) The highstand systems tract deposits of the Zechstein Limestone are followed by transgressive systems tract deposits of the Lower Anhydrite in the Jabłonna Reef
Summary
Carbonates preceding the vast accumulation of evaporites reflect changes in the basin hydrology and the degree of connection to the open sea. In the Late Permian Zechstein Basin – one of the saline giants (Warren 2016), microbial deposits abound in the uppermost part of the first Zechstein cycle carbonate of the middle Wuchiapingian age (Zechstein Limestone–Fig. 1) both in marginal and central parts of the basin (e.g., Smith 1958, 1980a; Smith and Francis 1967; Peryt and Piątkowski 1977; Peryt 1978; Füchtbauer 1980; Paul 1980, 1987, 1995; Pöhlig 1986; Becker 2002; Peryt and Peryt 2012; Hammes et al 2013). The Zechstein Group is divided into cycles reflecting progressive evaporation: at the base of a cycle are normal marine sediments; these are followed by sediments indicative of increasing salinity, first sulphates, chlorides and eventually potash salts (Richter-Bernburg 1955). The total stratigraphic thickness of the Zechstein deposits in the basin centre exceeds 1.5 km
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