Fluvial sediment pathways enlightened by OSL bleaching of river sediments and deltaic deposits

Abstract

Abstract. While a number of studies have investigated bleaching of the optical signals of sediments in rivers and deltas, unified trends and mechanisms for bleaching in these settings remain unresolved. Here, we explore the bleaching of the optically stimulated luminescence (OSL) signal of quartz sediments in a large fluviodeltaic system across time and space, by comparing residual doses of sand and silt from the modern Mississippi River channel with estimated residual doses of sand isolated from Late Holocene Mississippi Delta mouth bar and overbank deposits. Further insight is obtained from a comparison of burial ages of paired quartz sand and silt of Mississippi Delta overbank deposits. Contrasting some previous investigations, we find that the bleaching of the OSL signal is at least as likely for finer sediment as for coarser sediment of the meandering Mississippi River and its delta. In addition we find an unexpected spatiotemporal pattern in OSL bleaching of mouth bar sand deposits. We suggest this may be caused by changes in upstream pathways of the meandering channel belt(s) within the alluvial valley, or by distributary channel and coastal dynamics within the delta. Our study demonstrates that the degree of OSL bleaching of sand in a large delta can be highly time- and/or space-dependent. Silt is shown to be generally sufficiently bleached in both the modern Mississippi River and associated paleo-deposits regardless of age, and may provide a viable option for obtaining OSL chronologies in megadeltas. In addition to informing dating approaches, our work contributes to initiatives to use luminescence signals to fingerprint sediment pathways within river channel networks and their deltas.

Refining the late-Holocene coastline and delta development of the northern Yangtze River delta: Combining historical archives and OSL dating

“…The D e distributions for all 24 samples presented in combined radial and kernel density estimate plots are shown in Figures 5 and S2, S3 and S4, available online, which were generated by the R package ‘Luminescence’ of the abanico plot (Kreutzer et al, 2012). Two groups of ages reproduced by the CAM and MAM models are generally consistent within the experimental errors (Table 1 and Figure 6), indicating that most of the 45–63 μm quartz samples were well bleached in the area (Chamberlain et al, 2018b; Chamberlain and Wallinga, 2018; Nian et al, 2018a, 2018b). At least to some extent, some samples showed that the CAM D e values are higher than the MAM D e values, especially for relative young samples (<500 years) (Figure 6).…”

Luminescence as a Sediment Tracer and Provenance Tool

“…This observation is puzzling, as finer grains should spend more time in suspension and consequently are exposed to light for a longer duration than are coarser grains (Gray & Mahan, ). However, differences in bleaching by grain size are not ubiquitous, as some researchers have found that finer grains have lower residual doses (Fuchs et al, ; Hu et al, ; Schielein & Lomax, ) and there are cases where all grain sizes seem adequately bleached (e.g., Chamberlain & Wallinga, )…”