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

Abstract

Abstract. Reconstructing sediment pathways in fluvial and deltaic systems beyond instrumental records is challenging due to a lack of suitable methods. Here we explore the potential of luminescence methods for such purposes, focusing on bleaching of the optically stimulated luminescence (OSL) signal of quartz sediments in a large fluviodeltaic system across time and space. We approach this 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. In contrast to 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. We attribute this to the differences in light exposure related to transport mode (bedload vs. suspended load). 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 signal 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 silt may therefore provide a viable option for obtaining OSL chronologies in megadeltas. Our work contributes to initiatives to use luminescence signals to fingerprint sediment pathways within river channel networks and their deltas and also helps inform luminescence dating approaches in fluviodeltaic environments.

Determining the Age of Terrace Formation Using Luminescence Dating—A Case of the Yellow River Terraces in the Baode Area, China

“…Actually, previous investigations have demonstrated that the residual dose of modern fluvial sand samples from the middle reaches of the Yellow River are only 0.1 to 2.4 Gy, and have a large scatter, with OD values up to 90% [18,20,55]. The small residual doses of the modern fluvial sand samples are also confirmed by those of modern analogues from different rivers in the world (e.g., [56][57][58][59]). These suggest that the effect of the residual dose on the old samples from the terrace deposits in this study are insignificant.…”

Integrating geochronologic and instrumental approaches across the Bengal Basin

“…Grall et al, 2018), accretion (e.g. Chamberlain et al, 2017), and determining the timing and pathways of active river channels (e.g. Allison et al, 2003 ;Sincavage et al, 2018).…”

“…The low formation and preservation of peat in the Bengal Basin is a direct consequence of the system's sedimentary processes and environmental conditions. Three principal factors play a role: (i) a lack of available accommodation due to the high sediment yield (Chamberlain et al, 2017); (ii) remineralization and flushing under the highly seasonal climate (Allison et al, 2003); and (iii) a lack of preservation due to laterally mobile channel belts in upstream regions of the delta (Wilson and Goodbred, 2015). Foremost, the widespread, seasonal deposition of siliciclastic sediment limits the concentrated accumulation of organic matter.…”

“…This low organic-toclastic ratio is a function of sediment yield (Figure 3), because mineral sediment aggrades more rapidly and is therefore more efficient at filling accommodation than organic deposits (i.e. peat) that grow slowly in situ (Chamberlain et al, 2017). Overall, the sediment yield of the Bengal Basin throughout the Holocene has been exceptionally high relative to many deltas (Goodbred and Kuehl, 2000a), because it is fed by two of the rivers draining the rapidly uplifting Himalayas and the powerful erosive and transport engine of the Southeast Asian Monsoon (Goodbred and Kuehl, 2000b).…”

Chronostratigraphy of a 1.5±0.1 Ma composite sedimentary record from Colônia basin (SE Brazil): Bayesian modeling based on paleomagnetic, authigenic 10Be/9Be, radiocarbon and luminescence dating

“…Incomplete reset ("bleaching") of OSL signal before deposition of quartz grains can lead to residual doses and age overestimation. However, studies about OSL signals of quartz from water-laid sediments (e.g Hu et al, 2010;Chamberlain and Wallinga, 2019). show that silt grains are relatively well-bleached and suitable for luminescence dating.…”