Vegetation change in a climatic cycle of Early Pleistocene age in the Leffe Basin (Northern Italy)

Abstract

The Plio-Pleistocene deposits of the Leffe Basin in the Lombardian Pre-Alps in Italy, first investigated in quarry and lignite mine shafts by 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 is about −1.6 Ma old and particularly characteristic, is discussed here. A long interglacial stage can be identified by the dominance of pollen 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-Tertiary elements, some of them indicating a wet climate. In particular, the Carya peaks appear to be linked to a warm-temperate (14–16°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 forest. This forest succession is subsequently interrupted by a brief period of open vegetation, indicating a drier and colder, continental climate, followed by a new vegetational cycle. The climate evolution is discussed in comparison with other recent pollen successions of uppermost Pliocene age in the Mediterranean area. The cycle described is estimated to have lasted about 30 ka. The entire Leffe lacustrine succession records eight climatic cycles of moderate amplitude. We suggest that this cyclicity has been induced by obliquity forcing. Correlation of the cold phases with the major glacial events of the Southern Alps, as proposed by Venzo (1950) and Lona (1950), is excluded.