Provenance discrimination of fine sediments by mid‐infrared spectroscopy: Calibration and application to fluvial palaeo‐environmental reconstruction

Determining sediment provenance allows a better understanding of fluvial palaeo‐dynamics, and identifying involved watersheds, at broad spatio‐temporal scales. Conventional approaches for source identification are usually based on the physical, mineralogical, geochemical, magnetic or isotopic properties of sediments. Rapid, non‐destructive and, in well‐established contexts, highly accurate, mid‐infrared spectroscopy is an alternative method for investigating sediment sources. The present research objectives are: (i) to use the mid‐infrared spectroscopy method to discriminate the provenance of fine sediments, by applying discriminant analysis on a large set of reference samples from three different watersheds in the Upper Rhine area (associated with the Rhine, Ill and Vosges tributaries); (ii) to clarify whether the provenance spectra signatures are influenced by riverine depositional contexts (bars versus banks) and, to some extent, by grain size and/or high organic matter content; and (iii) to apply the mid‐infrared spectroscopy – discriminant analysis method to a study of fluvial palaeo‐dynamics and determine the provenance of palaeo‐channel infillings. Three main sedimentary sources, divided into eight sub‐categories, have been characterized by 196 modern reference samples from 78 collecting sites. Discriminant analysis displayed a strong separating power by classifying correctly the origin of samples without any inter‐group overlap, independently from the geomorphological context (bar or bank) and associated slight changes in organic matter contents or grain size. Mid‐infrared spectroscopy – discriminant analysis investigations of the palaeo‐channel infill, complemented by radiocarbon dates and mineralogical data, allowed reconstructing general trends for the local morpho‐sedimentary dynamics over the last ca 12 millennia.