Geochemical and foraminiferal records of environmental changes during the Zechstein Limestone (Lopingian) deposition in Northern Poland

Abstract

The entire Zechstein Limestone section of the Zdrada IG 8 borehole (Northern Poland) is composed of oncoid packstone that is accompanied by stromatolites in the upper part of the unit. Deposition of the Zechstein Limestone occurred in persistently subtidal environments, above the storm wave base, in mostly dysoxic conditions, and thus these conditions did not differ essentially from those characteristic for the Kupferschiefer strata. The previous supposition of vadose diagenesis is not confirmed by the isotopic study of calcite that showed its clearly marine values (average d¹³C and d¹⁸O values of +5.1 ±0.6‰ and –0.5 ±0.7‰, correspondingly) that are compatible with contemporaneous Lopingian deposits. The faunal restriction and the predominance of lagenids in the foraminiferal assemblage of the Zechstein Limestone indicate continual dysaerobic conditions and elevated salinity of seawater. The calculated palaeotemperature of the seawater was within the range from 23 to 33°C (or higher), and slightly (by ca. 1.5°C) decreased at the end of the Zechstein Limestone deposition.