The malacological record from the Middle Pleistocene Pianico-Sellere Basin(Bergamo, northern Italy)

摘要

Non-marine molluscan assemblages from the Pianico-Sellere Basin (southern Alps, northern Italy) have been known since the 19th century. In the present work, new records of freshwater molluscs from the Middle Pleistocene varved lacustrine Pianico Formation are highlighted. Mollusc remains are mainly found in slump deposits, detrital layers and very fine-grained calcitic layers intercalated in the varve succession. Five molluscan assemblages from the Pianico Formation were selected to describe the palaeoenvironment of the sedimentary succession. The assemblages are characterized by freshwater molluscs which proved to be significant for palaeoenvironmental and biostratigraphical reconstructions. Stream and marginal lacustrine conditions are recognized throughout the sedimentary succession and a palaeoclimatic trend, from temperate (corresponding to the well known "Pianico interglacial phase") to cool/cold phase, is detected. The palaeoclimatical meaning of the molluscan assemblages is related to the palaeotemperature curve deduced by pollen analysis on the same stratigraphical succession. The occurrence of an extinct representative of the thermophilous genus Tanousia Servain (Gastropoda, Hydrobiidae) is noteworthy, since this taxon provides good information about palaeoecology and biochronology.