Alluvial sand composition as a tool to unravel the Late Quaternary sedimentation of the Modena Plain, northern Italy

The Modena alluvial plain is located on the northern side of the northern Apenninesfold-and-thrust belt, where streams draining the chain flow toward the northeastinto the Po River. The alluvial plain is characterized by a spectacular abundanceof archaeological sites of various ages and can be considered a natural laboratory forthe reconstruction of the recent sedimentary evolution of the Po Plain. Detailed modalanalyses of modern sands of the Modena Plain streams indicate that the provenancesignal can be distinguished on the basis of key components, such as quartz, feldspar,carbonate, and lithic fragments. The compositional fields of the streams depend onthe extent of the watershed, the recycling of older fluvial sediments, and the sedimentinput from tributary streams.The modal analyses demonstrate that sand composition of the major rivers (Panaroand Secchia) has not changed during the Holocene, when sediment production,storage, and dispersal were probably dominated by colluvial aggradation in an environmentcharacterized by dense vegetation cover.In the late Pleistocene, fluvial sands were characterized by higher feldspar contentscompared with modern and Holocene sands. This feldspar abundance couldreflect a high-frequency signal in sediment supply rates linked to secular variationsof weathering processes, and it reveals the strong denudation and sediment removalconditions of the last glacial stage (15–18 ka).The implication of this study is that provenance of Holocene sediments now buriedin the floodplain can be determined by a simple comparison with modern sandcomposition. Sand composition studies may represent a useful tool to reconstruct thePleistocene-Holocene fluvial sediment supply and the evolution of human settlementsas function of climate and drainage system changes.