Mollusc assemblages from Subatlantic oxbow lake deposits in the Szreniawa River valley near Słomniki (Miechów Upland, southern Poland)

Abstract

A rich mollusc fauna was found in the sediments filling the ancient oxbow lake developed on the floodplain of the Szreniawa River in the environs of Miechów (near Topola village). The sediments represent the Subatlantic phase of the Holocene. Their stratigraphic position was confirmed by radiocarbon dates. The oxbow under study is filled with organic sediments (peats), organic-mineral (peaty muds), and carbonate deposits (calcareous muds) with the maximum thickness of 1.5 m. The variation in mollusc assemblages provided the basis for the reconstruction of environmental changes that took place over about 2,000 years, from the moment of oxbow emergence up to its complete filling. Within that sequence, it is possible to distinguish two principal intervals. The older interval corresponds to the period of a small water body functioning there. The malacofauna present in this interval shows the prevalence of aquatic and hygrophilous species. The younger phase corresponds to the period of accumulation of calcareous muds with predominance of open-country and xerophilous taxa. The collected materials also made it possible to determine the characteristics of the malacofauna diversification within the oxbow itself, and it showed the distinctiveness of environmental features in its central part and in marginal parts.