Post-Messinian drainage changes triggered by tectonic and climatic events (eastern Southern Alps, Italy)

Abstract

The Messinian–Quaternary history of tectonic and climatic control on sedimentation in the eastern Southern Alps, northern Italy, was reconstructed using an integrated petrographic and sedimentological analysis of five sedimentary successions. These units mainly consist of fluvial conglomerates of the Tagliamento sequence, deposited within the eastern Southern Alps since the Upper Miocene (“Messinian Salinity Crisis”). At that time, the closure of marine gateways between the Atlantic Ocean and the Mediterranean Sea caused a drop in sea level, causing exchanged fluvial erosion and widening of the Alpine catchments. Sediment composition in the Upper Miocene to Lower Pliocene units shows an abrupt change in the source areas: from sediments characterized by carbonate rock fragments to detritus rich in low-grade metamorphic grains. In spite of tectonic activity within the eastern Southern Alps, no major modifications in sediment supply took place during the Pliocene–Early Pleistocene time span. In the Middle Pleistocene the first major expansion of the Alpine glaciers triggered a change in drainage patterns and a marked increase in erosion rates. Predominantly climatic control on sedimentation in the Tagliamento basin and the erosion of the Carnic Alps produced sediments rich in quartz, siltstone and metamorphic rock fragments, deposited in the Upper Pleistocene unit and in modern river sediments.