Tracing provenance and pathways of late Holocene fluvio-deltaic sediments by heavy-metal spatial distribution (Po Plain-Northern Apennines system, Italy)

The bulk geochemistry of 435 near-surface sediment samples from the southern Po Plain was used to identify the major sources of sediment delivered through distinct tracts of the routing system, from the Apenninic catchments to the Po Delta and the Adriatic coast. Sediment composition from the downstream reaches of the Po River and 23 Apenninic channel-levee river systems is fingerprinted by distinctive heavy-metal (chromium and nickel) concentrations, which vary primarily as a function of the local ultramafic rock contribution. For any constant provenance domain, fine-grained (floodplain) sediments are invariably enriched in trace metals relative to their coarser-sized, channel-related counterparts, thus reflecting hydraulic sorting by crevasse and overbank processes. Once the geochemical signatures of fluvial end-members are established, the relative contribution of the individual detrital sources to the downstream segments of the system can be assessed. Through an example from a multi-sourced supplied system, we outline the reconstruction of source-rock lithology and sediment pathways by combined sedimentological and geochemical studies as the basis for reliable estimates of sediment budgets in a source-to-sink context.