Bryozoans (trepostomes and fenestellids) in the Zechstein Limestone (Wuchiapingian) of the North Sudetic Basin (SW Poland : palaeoecological implications

A recently investigated Zechstein Limestone (Ca1, Wuchiapingian) bryozoan fauna from the Polish part of the Southern Permian Basin (SW Poland) is dominated volumetrically and taxonomically by fenestellids. In total six species from five genera are recognized, comprising two species of trepostomes belonging to Dyscritella Girty, 1911 and four fenestellids attributed to Kingopora Morozova, 1970, Kalvariella Morozova, 1970, Acanthocladia King, 1849 and Spinofenestella Termier and Termier, 1971. The greatest biodiversity of the bryozoans in the Ca1 profiles studied is within the slope facies where large, fan-shaped and funnel-shaped reticulate fenestellid colonies up to 10 cm high dominate. In contrast, bryozoans in the marginal (proximal) parts of the basin mostly comprise trepostomes, represented by encrusting plate-like or coil-shaped colonies of Dyscritella Girty, and commonly broken branched colonies of Acanthocladia King. The changes in the biotic composition of the bryozoans and the presence of a dominant colony growth form in the stratigraphical profile of the Ca1 reflect the depositional environment and water energy. These factors stimulate the successive stages of the development of the biota and their settlement, marked by the rich productid-fenestellid assemblages typical of the offshore setting, with the maximum depth in the middle part of the Ca1 in the Grodziec Syncline. The proximal tempestites and foreshore facies of the upper part of the Ca1 (Leszczyna Syncline) terminate the sedimentary cycle of the Ca1, with the remnant, broken bryozoans of Acanthocladia and fenestellids. The relationship between the taxonomic composition, colony growth-patterns, associated biota, and sedimentary structures points to slow sedimentation rate on slope and basin floor of the Ca1 carbonate platform. The fenestellids which are dominated in the studied biota by the reticulate and pinnate colonies of Spinofenestella, Kingopora, Kalvariella and Acanthocladia mark a close palaeogeographical link with the Zechstein (Ca1) bryozoans of Great Britain, Germany and the southern Baltic region.