Provenance of Holocene sediments from the Venetian-Paduan area (NE Italy) by elemental and Pb-Sr isotopes analyses.

This study investigates a set of sediment samples from the easternmost sector of the Po Valley (north of the present-day Po River course), an area filled during the Holocene by alluvia from two interfering fluvial systems (Po and Adige). The investigated samples represent a subset of a wider collection already characterized through X-ray fluorescence (XRF) and classified for their provenance on the basis of the geochemical composition following the criteria reported in Natali & Bianchini (2017). In this work, these samples were analyzed for their trace elements composition by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), and for lead (Pb)-strontium (Sr) isotope ratios by Thermal Ionization Mass Spectrometry (TIMS). The ICP-MS data show a lower dispersion and higher consistency with respect to XRF data, as highlighted by the distribution of siderophile and chalcophile elements, leading to a better discrimination of the sediments provenance for the two river systems (i.e., Adige and Po) in the study area, and a reclassification of some samples. The Sr and Pb isotopic composition of the investigated samples show a variability consistent with the provenance discrimination obtained by the ICP-MS data, and provide further information on the sediment’s sources. The obtained isotopic ratios were compared with those of ore deposits from the whole Alpine arc (Giunti, 2010; Artioli et al., 2016) to find a link between different source lithologies and alluvial sediments. Sediments with Po River geochemical affinity show a Pb isotope composition consistent with that of ore deposits from western Alps, whereas sediments with Adige geochemical affinity show a Pb isotopic signature compatible with the Valsugana and Southalpine ore deposits. Furthermore, the application at a regional scale of these new tracers, allowed to better constrain the geochemical and isotopic features of Po and Adige sources, and to identify further differences in Po affinity sediments settled in various sectors of the easternmost Padanian plain. In particular, sediments with Po affinity from the northern side of the present-day Po River course (Veneto region, this work) show intermediate geochemical features between those of Adige affinity and Po sediments collected from the southern side (Emilia-Romagna region, Ciarpaglini, 2021), the latter representing the Holocene sedimentary deposit with the most genuine signature of the Po River basin source rocks.