VEGETATION CHANGE IN A CLIMATIC CYCLE OF EARLY PLEISTOCENE AGE IN THELEFFE BASIN (NORTHERN ITALY)

The Plio-Pleistocene deposits of the Leffe Basin in the Lombardian Pre -Alps in Italy, first investigated in quarry and lignite mine shafts b y Lona in 1950, were recently cored. The pollen record of part of this core reveals a sequence of four climatic cycles. One of them, which i s about -1.6 Ma old and particularly characteristic, is discussed here . A long interglacial stage can be identified by the dominance of poll en of deciduous trees of temperate climate. It clearly shows a forest succession of a mixed oak forest of dry-temperate climate, followed by a strong development of a Juglandaceae assemblage rich in Arcto-Terti ary elements, some of them indicating a wet climate. In particular, th e Carya peaks appear to be linked to a warm-temperate (14-16 degrees C mean annual temperature), humid, maritime climate with a long growth season, if we compare them with modern and fossil analogs. This stage is followed by a cooling leading to a long phase of wet coniferous for est. This forest succession is subsequently interrupted by a brief per iod of open vegetation, indicating a drier and colder, continental cli mate, followed by a new vegetational cycle. The climate evolution is d iscussed in comparison with other recent pollen successions of uppermo st Pliocene age in the Mediterranean area. The cycle described is esti mated to have lasted about 30 ka. The entire Leffe lacustrine successi on records eight climatic cycles of moderate amplitude. We suggest tha t this cyclicity has been induced by obliquity forcing. Correlation of the cold phases with the major glacial events of the Southern Alps, a s proposed by Venzo (1950) and Lona (1950), is excluded.