Seesaw longitudinal–transverse drainage patterns driven by Middle and Late Pleistocene climate cycles in the foreland basin of the south-eastern European Alps

Abstract

The multi-proxy sediment provenance analysis of two sedimentary successions (GER1 core, 130 m long, and CB core, 103 m long) provides new data for detecting the temporal and spatial variations in fluvial drainage patterns and landscape evolution of the Venetian Plain (NE Italy) in relation to Middle–Late Pleistocene climate fluctuations. Detailed petrographic analyses, compared to present-day river signatures, highlight compositional variations of the sediments, providing crucial information for detecting the depositional histories of the two sites, which lie about 15 km apart, and considering a source-to-sink multi-source context. The successions span from a cold phase older than MIS 9/11 to MIS 1, and are chronostratigraphically well correlated from the MIS 7.3 marine transgression. Despite belonging to the same alluvial system since the Last Glacial Maximum, the GER1 and CB cores show different depositional histories during previous Marine Isotopic Stages, starting at least from MIS 8 (i.e., ca 300–250 ka). A glacial interval older than MIS 9/11, is encountered only within records of the GER1 core. Due to its composition and the particularly coarse grain size, it represents a key element for detecting the depositional dynamics of megafans during past climate oscillations. Conversely, the presence of sediments not fully ascribable to any of the present-day catchment suggests the existence of a trunk paleo-river, longitudinal to the foreland axis, flowing from west to east along the Po Plain and occasionally draining the Venetian Plain. A causal relationship between prograding mechanisms of transverse alluvial megafans and Pleistocene climate variations is detected, taking into account responses of local alluvial systems to glaciers' development, sediment yield from the orogenic hinterland, and sea-level lowstands and highstands. A focus on glacial termination phases allows identification of two additional incised valleys, established at the end of the pre-MIS 9/11 glaciation and of MIS 6.