CSDMS 2014 annual meeting poster Harrison Gray
An iterative bleach-and-mix model for the change in luminescence signal with cumulative sediment transport.
Abstract:
Optically Stimulated Luminescence (OSL) dating is one member of a family of dating techniques that rely on sufficient sunlight exposure (bleaching) to remove a previously obtained signal. Sunlight exposure occurs during sediment transport from original erosional source to depositional sink and the presence of this signal bleaching is well-documented in the literature, yet, the mechanics of sunlight exposure in geomorphic systems has been unexplored. Since this bleaching of luminescence signal is a function of geomorphic variables such as transport rate, mechanism, and sediment flux, there exists potential to quantify these processes through measurement of the luminescence signal at various locations within a geomorphic system.
Here, I present a simple model demonstrating the predicted change in luminescence signal for a package of sediment with a homogeneous initial signal that is iteratively bleached at the surface and re-mixed. The model does not attempt to directly model a specific geomorphic environment, but is a starting point for predicting the magnitude and dispersion of luminescence signal values throughout a geomorphic system.
Initial model results demonstrate that the mean luminescence signal should decrease in a power law fashion asymptotically approaching zero with each mixing event. The standard deviation of the sediment package increases rapidly during the early mix and bleach iterations before leveling off and decreasing toward zero as the majority of the sediment reaches a homogeneously bleached state. Introducing a sediment flux into and out of the sediment package alters the geometry of the package and therefore the efficiency of bleaching causing the mean and standard deviation to approach steady-state values. This may suggest that the luminescence signals measured from sediment in transport act as a proxy for volumetric sediment fluxes. Combining this model with landscape evolution models may help predict the luminescence signal for fluvial networks which may in turn assist in provenance studies.
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