Relikty tekstur okruchowych i struktur sedymentacyjnych najniższej części anhydrytu dolnego (A1d, cechsztyn) w okolicach Mieroszyna, Pomorze Gdańskie

A b s t r a c t.The Lower Werra Anhydrite (A1d) of the Pomerania region, northern Poland (Southern Permian Zechstein Basin of Europe), overlies directly the Zechstein Limestone (Ca1) and is 50-170 metres thick.The lowermost element of this lithostratigraphic member (Beds A1d-1) is only 8-11 metres thick and has been usually considered as an apparently uniform unit of indistinctly bedded-to-massive, coarsely crystalline, nodular anhydrite.However, the pervasive diagenetic fabrics of this unit significantly overprint the syn-sedimentary features of the pre-existing deposit.A careful examination of the A1d-1 core material and formation scanner images from Mieroszyno region, north-eastern Pomerania, reveals common relics of breccia-conglomerate textures, slump-like deformations, and steeply inclined stratifications.These relict features demonstrate effects of partial destruction, reworking, and some transportation of the primary sulphate-carbonate (?) sediments (e.g.gypsum palisade beds, carbonate-sulphate stromatolites) prior to their burial and diagenetic transformations (e.g.recrystallization, anhydrite nodule development).It is concluded that the processes of evaporitic crust cracking, rip-up clast formation, storm surges, and local slope failure were the principal forces that modified the surface of the initial evaporite accumulations.The inclined heterolithic stratification composed of repetitive sulphate-carbonate couplets displays effects of partial destruction (abrasion and dissolution) of the primary palisade gypsum and a short-distance redeposition of the resultant detrital crystalline material.This pattern of sedimentation is attributed to repetitive seasons of fair weather and storm conditions, which also implied water salinity changes.Relics of coarse breccia/conglomerate fabrics and slump-style deformations of the lower intervals of Beds A1d-1 document the processes of cannibalization of the initial fair-weather coastal sebkha in the course of an evaporative drawdown followed by a marine ingression.The elongate, ridge-like accumulation of the A1d-1 Beds coincides with the prominent Mieroszyno anhydrite ridge which, enclosing the complete profile of the Lower Werra Anhydrite deposits.Both sediment accumulations follow a zone of gentle basin floor slope breaks that are potentially related to a fault system.