GLACIAL HISTORY OF THE SOUTHERN SIDE OF THE CENTRAL ALPS, ITALY

The area covers the sub-alpine valleys between Lago d’Orta, to the east, and Lago d’Iseo, to the east and the corresponding morainic amphitheatres of the high Po plain. Geological mapping was carried out at a 1:10,000 scale in order to allow detailed geological reconstruction.

On the high Po plain the boundaries of many ice advances can be distinguished that moved out of subalpine valleys and reached the plain beyond. The different valleys experienced different glacial histories so that the alloformations described from different basins cannot be directly correlated. In the Verbano amphitheatre it is possible to distinguish 13 glaciations. The oldest is of Pliocene age and the youngest is of Late Pleistocene age.

In the Lario amphiteatre it is impossible to say how many glacial episodes are represented. It is possible to recognize 4 alloformations (related to 4 glaciations), 4 formations (containing tills from 4 glaciations) and 1 allogroup (more than 1 glaciation). Concerning the age of these glaciations the two oldest are Pliocene and the youngest is Late Pleistocene. The Sebino amphitheatre is very regularly shaped. At least 7 glaciations are recognizable in this area.

The survey of the area provides evidence that correlations cannot be established by using elevation or position of the deposits.

Between the Pliocene glacial episodes (about 2.4 Ma BP) and Holocene, glacigenic deposits have been subjected to alternating weathering (warm conditions) and strong erosion (cold phases). The erosion and subsequent slope movements have determined: the intense fragmentation of the deposits and the burial of glacial deposits by up to several meter thick slope deposits. For these reasons the glacial maximum (MEG) is discontinuous and doubtful. Another obstacle preventing the reconstruction of the MEG is that the area has been subsequently affected by tectonic events including uplifting, subsidence, thrusting and lateral displacements.

The LGM glacial deposits are principally distinguished by a poorly-developed weathering profile, well-preserved landforms and no loess cover. It must be emphasised that the LGM mapped using these criteria, does not correspond to previous authors' Würm limit. The Würm in older maps was regarded as more extensive.