Paleogeographic and paleodrainage changes during Pleistocene glaciations (Po Plain, Northern Italy)

The Po Basin, a Pliocene marine gulf between the Alps and the Apennines, was filled progressively from west to east and finally capped by fluvial sediments during the Pleistocene. By ~ 1.25 Ma, a meandering trunk river (paleoDora Baltea) reached westernmost Lombardia (Cilavegna); at ~ 1 Ma, the paleoAdda, entering the plain through the Como Valley, joined the paleoTicino in the Milano area. The coastline was directed NNE/SSW, and the open sea persisted east of ~ 10°E. Metamorphiclastic prodelta sediments of the Alpine trunk river reached central Lombardia (Pianengo) by MIS 36 and eastern Lombardia (Palosco) at MIS 31. Trunk-river delta foresets accumulated rapidly in easternmost Lombardia (Ghedi) during the Jaramillo. Fluvial sedimentation, continuous at Pianengo since MIS 28, eventually reached Ghedi at MIS 22. In this time interval, the embayment secluded between the prograding trunk-river delta and the Southalpine front was progressively filled by Southalpine fan deltas.With the onset of major Alpine glaciations in the late Matuyama, detrital supply increased markedly and fluvial deposits spread all over Lombardia. Because of outward growth of Alpine fans, the paleoDora Baltea was replaced at Cilavegna by the paleoSesia and paleoToce. Milano lay in the paleoAdda braidplain. Southalpine alluvial fans reached as far south as Pianengo. The paleoOglio glacier exited Lake Iseo at Cremignane.In the early Brunhes, accumulation rates markedly dropped in Lombardia; carbonaticlastic paleoPiave turbidites accumulated rapidly at Venezia, capped by the prograding paleoPo delta and finally by fluvial paleoBrenta–Bacchiglione deposits. Subsequently, accumulation rates decreased further, and paleosols developed during stages of prolonged exposure. The paleoTicino continued to flow southwest of Milano, where detritus from the paleoOlona is documented locally. PaleoAdda sediments were deposited at Milano and sedimentaclastic detritus at Trezzo up to a few meters from ground surface, indicating that the final shift of River Adda to the Lecco branch of Lake Como was a very recent event. The paleoOglio exited Lake Iseo in its present position. At Ghedi the paleoChiese was replaced by the paleoAdige, and finally re-established before development of a paleosol overlain by topmost Pleistocene marsh deposits (MIS 2).This study indicates new guidelines for studies of drainage evolution, and more in general of depositional architecture in foreland basins.