Zechstein marine deposits in the Wleń Graben (North Sudetic Synclinorium, SW Poland) : new insights into the palaeogeography of the southern part of the Polish Zechstein Basin

This paper presents the results of sedimentological studies of Zechstein marine deposits occurring in the Wleń Graben, a tectonic unit located in the southeastern part of the North Sudetic Synclinorium (NSS; Western Sudetes, SW Poland). Owing to poor exposure, small thickness, and lack of palaeontological data, the stratigraphy and age of these rocks were determined solely on the basis of analogies with adjacent areas. New findings described here, including faunal remains (remains of bivalves, including Liebea sp.), geopetal structures, clastic fills of halite crystals, moulds and bioturbation, shed new light on the environmental interpretations of the Zechstein in this part of the NSS. It should be assumed that at least two types of deposit may be assigned to the marine Zechstein in the Wleń Graben area, namely sparitic and microsparitic dolomite (PZ3) and the overlying deposits of the heterolithic series (PZt). These deposits were formed during the late Zechstein transgression, when the study area was in the marginal southwesternmost part of a newly formed shallow-marine bay of the Polish Zechstein Basin. In the central part of the present-day Wleń Graben, a shallow-marine bay (lagoon?) was dominated by carbonate sedimentation. A north-dipping mud plain, periodically flooded by a shallow sea, occurred in the southern part of the area. The paper summarises the present state of research on Permian deposits in the Wleń Graben, the first comprehensive lithostratigraphic scheme is suggested, and a new concept of the palaeogeographic evolution of the area in the Early and Late Permian is proposed.