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. Reconstructing sediment pathways in fluvial and deltaic systemsbeyond instrumental records is challenging due to a lack of suitablemethods. Here we explore the potential of luminescence methods for suchpurposes, focusing on bleaching of the optically stimulated luminescence(OSL) signal of quartz sediments in a large fluviodeltaic system across timeand space. We approach this by comparing residual doses of sand and siltfrom the modern Mississippi River channel with estimated residual doses ofsand isolated from Late Holocene Mississippi Delta mouth bar and overbankdeposits. Further insight is obtained from a comparison of burial ages ofpaired quartz sand and silt of Mississippi Delta overbank deposits.In contrast to some previous investigations, we find that the bleaching of theOSL signal is at least as likely for finer sediment as for coarser sedimentof the meandering Mississippi River and its delta. We attribute this to thedifferences in light exposure related to transport mode (bedload vs.suspended load). In addition, we find an unexpected spatiotemporal pattern inOSL bleaching of mouth bar sand deposits. We suggest this may be caused bychanges in upstream pathways of the meandering channel belt(s) within thealluvial valley or by distributary channel and coastal dynamics within thedelta. Our study demonstrates that the degree of OSL signal bleaching ofsand in a large delta can be highly time- and/or space-dependent. Silt isshown to be generally sufficiently bleached in both the modern MississippiRiver and associated paleo-deposits regardless of age, and silt may therefore provide aviable option for obtaining OSL chronologies in megadeltas. Our workcontributes to initiatives to use luminescence signals to fingerprintsediment pathways within river channel networks and their deltas and alsohelps inform luminescence dating approaches in fluviodeltaic environments.

Seeking enlightenment of fluvial sediment pathways by optically stimulated luminescence signal bleaching of river sediments and deltaic deposits