Exploring the multi-faceted potential of luminescence profiling via the portable reader in various fluvial depositional systems (NE France)

Along with the development of “classical” optically stimulated luminescence (OSL) dating, portable luminescence readers have been increasingly employed in a wide breadth of geomorphological settings over the last decade. Portable measurements of bulk samples along depth profiles yield infra-red and optically stimulated luminescence net intensities (IRSL/OSL). The signal build-up depends on (i) the burial duration of the sediment, (ii) the dose rate, (iii) the inherited dose at time of burial, (iv) the mineral composition and (v) the luminescence sensitivity of the minerals. In fluvial landscapes, however, the handful of existing case studies mostly focused on the sole identification of alluvium’s unconformities via luminescence profiling. We argue here that this approach shall go beyond the mere one- (or sometimes two-) dimensional sedimentary screening and steer towards the production of three-dimensional chronostratigraphical information.

This study presents the outcomes of a luminescence-profiling approach performed in a wide array of fluvial depositional systems located in the Upper Rhine Graben and the adjacent Vosges Mountains (NE France). They include:

• modern and historical overbank fines from the main stem (Rhine) and its tributaries (Bruche and Sauer Rivers);
• palaeomeanders and swale-and-ridge topography (Bruche);
• Holocene terrace deposits (Bruche);
• fluvio-glacial deposits (probably) from the Last Glacial Maximum (Cleurie Valley).

We thus explore the ability of the reader to measure signals of varying intensities in different morpho-sedimentary units of clearly distinct ages. The results globally show:

• a consistent pattern of downward increasing OSL/IRSL signal intensities, although some sharp contrasts (i.e., shifts of one order of magnitude in signal intensities) in some sequences could be identified (e.g., Rhine);
• a larger scatter of OSL/IRSL signal intensities in the sandy fraction than in the silty fraction, probably reflecting the influence of grain size on the signal accumulation (requiring further investigation);
• the potential of the portable reader as a rapid and efficient tool for tracing historical overbank fine deposition in floodplains.