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Comparison of OSL ages from young dune sediments with a high-resolution independent age model

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Costas, I. , Reimann, T. , Tsukamoto, S. , Ludwig, J. , Lindhorst, S. , Frechen, M. , Hass, H. C. and Betzler, C. (2012): Comparison of OSL ages from young dune sediments with a high-resolution independent age model , Quaternary Geochronology .
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Abstract:

Optically stimulated luminescence (OSL) dating of very young sediments (<100 a) is challenging due to the low signal-to-noise ratio of the natural OSL signal. Young samples are furthermore very sensitive to thermal transfer or insufficient resetting of the luminescence signal during sediment transport. In this study, a series of aerial images of a migrating sand dune were used to cross validate OSL ages for the last ~100 years. The investigated dune is situated on the northern part of the island of Sylt (southern North Sea). Based on several aerial images and the internal architecture of the dune obtained by ground penetrating radar (GPR), an age model has been developed to attribute sedimentary-architectural elements of the dune to time. The annual rate of dune migration is calculated to around 4.7 m/a. Along a 245 m transect oriented parallel to the direction of dune movement, 13 samples for OSL dating were collected at equidistant locations. This transect covers the time span between 1920 and 2010 AD. Sand-sized quartz (150-250 μm) was used for determining the equivalent dose (De) applying a SAR protocol. Results show that the oldest OSL age appeared to be 160±20 a whereas the modern analogue was dated to 34±3 a. In comparison with the aerial images, the OSL ages show a systematic overestimation of 20-40 a for the very young samples (<80 a). This offset is negligible for older samples but a substantial error in these younger ages. This overestimation seems to be due to combination of small thermal transfer of 4-12 mGy during preheat and incomplete bleaching in Medium OSL component which caused a residual dose of about 15 mGy. The contribution of Medium component cannot be removed by an early background subtraction approach.

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