Paleoenvironmental significance of Middle-Upper Pleistocene alluvial and lacustrine deposits of Mercuri basin (souther Italy).

The late Quaternary evolution of the Mercure paleolacustrine basin (Lucanian Apennines, southern Italy) was reconstructed through a multidisciplinary approach. In particular, here are presented the results of stratigraphical, geomorphological and palynological analysis of the fluvio-lacustrine sedimentary succession, which is Middle-Upper Pleistocene in age. The Mercure paleolacustrine basin, about 50 km2 wide, is located at the Calabria-Lucania boundary. The modern valley floor lies at 300 m asl and the sorrounding mountain tops reach 2000 m to the south and 1300/1500 to the north of the basin. The reconstruction of the sedimentary succession of the Mercure basin allows the definition of three main phases of the basin filling which occurred during the Middle-Upper Pleistocene time. The first sedimentary phase (Middle Pleistocene) is characterised by alluvial facies, which grade basinward into deltaic and lacustrine deposits. The second phase of filling (Middle-Upper? Pleistocene) consists of alternating sand-silty deposits passing upward to carbonate silts. After a dissecting phase, probably occurred during the Last Glacial Period, less widespread alluvial deposition took place at the basin margin; in particular the Upper Pleistocene deposits are telescopically inset within previous valley-side perched alluvial and lacustrine terraces, preserved as hanging remnants, gently sloping basinward. Pollen analysis was performed on the carbonate silts of the second filling phase. Two outcrops of about 12 and 16 metres were sampled at Zarafa and Sorgente Mercure. They represent the slopes of lacustrine terraces whose tops is now located up to 600 m asl. On the whole, pollen spectra reveal the existence of a very luxuriant oak forest, with Carpinus and Ulmus as main secondary elements, typical of a warm-humid interglacial period. The constant presence of Zelkova in the deciduous forest and the co-existence of Abies and Fagus in the highest forested belt suggests a late-Middle Pleistocene age for this interglacial association. In particular this interglacial should correspond to IS 7 or 5. An interglacial period corresponding to stage 9 was recognised at Acerno in the Picentini massif (Munno et al., 2001). Here the forest association was not very different but the presence of Cedrus suggests an older age for this paleolake. No other exemples of stage 7 or 5 are available in southern Apennines paleolakes.