Assemblages of molluscs from Sulisławice (Małopolska Upland, southern Poland) and their significance for interpretation of depositional conditions of calcareous tufas in small water bodies

Small water bodies, occurring behind barriers across valleys, create very advantageous conditions for the sedimentation of calcareous tufas. These sediments usually contain rich and diversified malacocoenoses. The composition and structure of these associations are closely linked to environmental changes during the accumulation of the sediments. At the Sulisławice locality, the remnants of two barriers, composed of hard, calcareous tufa, were found. Behind them, sequences of granular, calcareous tufas were preserved, forming terraces, elevated up to 3 m above the level of the present stream bed. The age of the sediments was obtained from radiocarbon dating and is referable to the Atlantic Phase. The rich malacofauna, occurring in these tufas, permitted the recognition of four types of faunistic association, in a sequence that corresponds to phases in the development of the water bodies. Three of them are characterised by the dominance of aquatic species and permit the reconstruction of specific features of the body of water. In the fourth association, terrestrial species predominate. A detailed, malacological analysis was the basis for a model of the evolution of the water bodies, occurring behind the barriers. The model is more widely applicable to the sediments of similar origin, frequently found in upland regions of Poland and other parts of Europe.