Facies variability in the Cambrian deposits from the Kościerzyna and Gdańsk sections (Pomeranian Caledonides foreland, northern Poland) : a comparative study

The origin of Cambrian clastics occurring in the marginal part of the East European Craton, in the foreland of the Pomeranian Caledonides is discussed. They were deposited in an epicontinental sea influenced by tides and storms. The first Lower Palaeozoic transgressive-regressive (T-R) cycle spans the Lower and most of the Middle Cambrian. The maximum transgression in the craton-margin part (Kościerzyna section) is marked by submarine erosion and a very low deposition rate around the Lower/Middle Cambrian boundary. The condensed deposit is a limestone - shell hash packstone with phosphatized mudstone clasts. In the inner part of the craton (Gdańsk section), the condensed deposit is represented by mudstones and heterolithic deposits with iron ooids. Transgressive phase deposits of the first T-R cycle from the Kościerzyna section are 323.5 m thick, while regressive phase deposits - 273.7 m thick. In the Gdańsk section the thicknesses are of 113.0 and 218.8 m, respectively. Deposits of the first T-R cycle of northern Poland and the Polish part of the Baltic Sea are overlain by those of the second T-R cycle, which, when complete, comprise the uppermost Middle Cambrian, Upper Cambrian and Lower Tremadoc. In both the sections discussed, deposits of the second T-R cycle were almost completely removed by pre-Arenig erosion. Facies analysis of deposits of the first T-R cycle from the Kościerzyna and Gdańsk sections shows that the source areas of terrigenous material, during both transgressive and regressive phases of this cycle, were elevated zones of the East European Craton.