Trunk river and tributary interactions recorded in the Pleistocene–Holocene stratigraphy of the Po Plain (northern Italy)

Tributary rivers can contribute significantly to alluvial-plain construction by supplying large volumes of clastic material. Their relation the main axial river strongly influences sediment deposition and preservation. The Po Plain is fed River a dense network transverse tributaries draining nearby Alpine Apennine chains. Stratigraphic, sedimentological, petrographic geochemical analyses on 38 cores permitted detailed differentiation sedimentary units. deposits are vertically stacked channel-belt sand bodies with high contents quartz–feldspar metamorphic rock fragments, combined chromium levels. These bodies, 20 30 km wide, replaced southward finer-grained that represent distal tributary-rivers system. sands, confined in narrow ribbons, show lower contents, abundant lithics In last 870 kyr, boundary between delivery systems shifted along north–south axis response distinct controlling factors. A northward shift channel belt, possibly related tectonic event, recorded across regional unconformity dating Marine Isotope Stage 12/11 transition. High supply rates during glacial-lowstand periods widened belt towards domain for few kilometres. Last Glacial Maximum body, wide 40 m thick, progressively narrowed after glacial culmination. During Holocene, patterns became avulsive distributive. Narrow belts (<3 km) formed branches, swamp poorly drained-floodplain muds were preserved interfluvial areas. Activation deactivation branches resulted sharp narrowing widening area available Apennine-rivers sedimentation. This work provides insights into tributary-trunk relations which control grain-size distribution compositional characters subsurface deposits.