EGU2020-3737
https://doi.org/10.5194/egusphere-egu2020-3737
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Illuminating the speed of sand – quantifying sediment transport using optically stimulated luminescence

Jürgen Mey1, Wolfgang Schwanghart1, Anna-Maartje de Boer2, and Tony Reimann2
Jürgen Mey et al.
  • 1Institute of Environmental Sciences and Geography, University of Potsdam, Potsdam, Germany (juemey@uni-potsdam.de)
  • 2Netherlands Centre for Luminescence Dating, Soil Geography and Landscape group, Wageningen University, Wageningen, The Netherlands

Sediment burial dating using optically stimulated luminescence (OSL) is a well-established tool in geochronology. Yet, an important prerequisite for its successful application is that the OSL signal is sufficiently reset prior to deposition. However, subaqueous bleaching conditions are vastly understudied, for example the effect of turbidity and sediment mixing on luminescence bleaching rates is only poorly established. The possibility that slow bleaching rates may dominate in certain transport conditions led to the concept that OSL could be used to derive sediment transport histories. The feasibility of this concept is still to be demonstrated and experimental setups to be tested. Our contribution to this scientific challenge involves subaquatic bleaching experiments, in which we suspend saturated coastal sand of Miocene age in a circular flume and illuminate for discrete time intervals with natural light. We further record the in-situ energy flux density received by the suspended grains in the UV-NIR frequency range by using a broadband spectrometer with a submersible probe.

Our analysis includes pre-profiling of each sample following a polymineral multiple signal protocol (Reimann et al., 2015), in which we simultaneously measured the quartz dominated blue stimulated luminescence signal at 125°C (BSL-125) and the K-feldspar dominated post-infrared infrared stimulated luminescence signal at 155°C (pIRIR-155). Preliminary results from the flume experiments show that the bleaching rates are indeed slow, differ for both signals and that the pIRIR155 seem to bleach faster than the BSL125. Besides the good prospects of acquiring a new tool for quantifying sediment transport, these results might have potentially far-reaching implications regarding the preferred target mineral for OSL dating in fluvial settings.  

How to cite: Mey, J., Schwanghart, W., de Boer, A.-M., and Reimann, T.: Illuminating the speed of sand – quantifying sediment transport using optically stimulated luminescence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3737, https://doi.org/10.5194/egusphere-egu2020-3737, 2020

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  • CC1: Comment on EGU2020-3737, Harrison Gray, 08 May 2020

    This is cool work! One quick question about your experiment. Do you think the lower density of feldspar allows the sand grains to, on average, stay higher in fluid suspension than the denser quartz grains? Maybe the feldspar grains are better able to reach the surface and this is why the pIR155 decreases faster than BSL?

    • CC2: Reply to CC1, Sebastien Huot, 09 May 2020

      good idea you raised, Harrison. My personal and unsuccessful experience, from enriching myself while panning for gold only yielded dirt! You need a big rig, to separate minerals by density, with a water flow. Unless I got it wrong.

      from the data shown here, they showed that the transmitted wavelength spectrum, through the suspended sediment, shifts toward longer wavelength (red), as the suspension load increases. That UV, then blue light gets cut off rather quickly. On the one hand, quartz bleaches very quickly... as long as there is UV in the light spectrum. blue also helps. On the other hand, feldspars fairly poorly, under UV illumination.

      I would bet what money I have left on a spectral shift, rather than a density difference, to explain the difference in bleaching rates.

    • AC1: Reply to CC1, Jürgen Mey, 09 May 2020

      Thanks for that question! We cannot rule out effects of the density difference of qtz and fsp. However, this difference is quite small, between 0.03 - 0.1 g cm-3, depending on the chemistry of the fsp in our sample. In principle we could translate this density difference into a depth difference and compare the difference of the energy flux density received by the qtz vs. that for the fsp. My guess is that this is very small.

    • AC2: Reply to CC1, Tony Reimann, 10 May 2020

      Hi Harrsion,

      good question! So far, we mainly discuss grain-size as being transport depth dependent. My guess is that the grain-size effects will be the main control of the average transport depth, thus in my mind grain size will overwhelm mineralogy seperation.

      Regarding the bleaching difference between quartz and feldspar I agree with Sebastian. Our interpretation is that it is related to blocking UV and blue components from the light spectrum plus the quartz OSL trap being insensitive to bleaching with longer wavelenghts photons. In theory (and literature from the 80ies and 90ies) there has been speculate quit a bit already about the better potential of feldspars for dating sub-aquatic bleached deposits. So far, there is not much experimental proof of this hypothesis. This could be one but it is a bit too early to state that with certainty.

      Best and stay safe! Tony

  • CC3: Comment on EGU2020-3737, Harrison Gray, 11 May 2020

    Thanks for the answers all. This is very interesting work. I am looking forward to hearing more!

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