Sedimentological and palaeontological features of an ancient alluvial plain in the Lucca Basin (Central Italy)

The multidisciplinary analysis of the deposits outcropping in the Nuova Lam Quarry (Lucca, Central Italy) permitted a palaeoenvironmental reconstructi on which differs considerably from those traditionally proposed for the con tinental deposits present in this area and hitherto interpreted as lacustri ne. The sequence described here is interpreted as an alluvial plain deposit . Five main associations of lithofacies have been recognised and referred t o different subenvironments. Backswamp deposits crop out in the basal part. They indicate the presence of ponds periodically affected by crevasse spla y processes and phases of subaerial exposure, which caused the formation of immature soils. An avulsion process, which gave rise to two main fluvial c hannels can be detected in the uppermost part of the sequence. A new avulsi on caused a return to a backswamp zone. The investigated sequence is an exa mple of aggradation of an ancient alluvial plain under humid climatic condi tions as suggested by pollen analysis. The sequence studied makes part of c ontinental deposits whose age has long been a matter of debate. The finding of astragali of very rare Pliotragus ardeus in the first channel deposits, along with some freshwater molluscs, allows to assign the sequence studied to the Villafranchian (Middle Pliocene-Lower Pleistocene).