Optical dating techniques

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The wavelength of the signal is allocated to the nature of the mineral: the OSL from quartz is typically measured in ultra-violet (340-370 nm wavelength), while quartz also emits in blue (460-500 nm wavelength) and in orange-red (600-650 nm wavelength; Huntley , when the mineral is stored within the host-rock), natural radiation generates the trapping of electrons and the build-up of a latent luminescence signal; ii) when a grain is produced by mechanical erosion and transported (at the Earth’s surface, in the air, or in a river), it is exposed to sunlight.

Released electrons can recombine with another kind of crystalline defects (“holes” reflecting electrons vacancies).

Ainsi, l’article souligne l’importance de la méthode pour les recherches en géomorphologie, notamment dans le cadre du développement de la géomorphologie quantitative.

Absolute dating methods have been developed over the last five decades (Jull and Scott, 2007).

This phenomenon is associated with a resetting (“zeroing”) of the dosimetric clock; iii) after one or several transport phases the grain is “definitively” buried under a sedimentary cover.

It is exposed again to radiation and accumulates trapped electrons.

Some of the traps are considered ‘unstable’ (“shallow traps”), which means that an electron inside will not remain trapped for the whole duration of burial.

On the contrary, defects situated deeper inside the lattice have a higher thermal lifetime.

Luminescence methods (TL and OSL) are based on the estimation of the impact of radiation on the crystalline structure of minerals while they are shielded from light (Aitken, 1985; Wintle, 1997; Aitken, 1998; Duller, 2004; Vandenberghe, 2004).

The main minerals studied are quartz and K-rich feldspar, which can be found in almost all sedimentary environments.

These procedures are described as clearly as possible in order to provide useful information for geomorphologists interested in the method, and illustrated by a case study that has involved luminescence dating of fluvial sands (samples LUM 975 and LUM 978) from the lower alluvial terrace of the Moselle River (M1 terrace as defined by S. However, it is essential to keep in mind that the protocols (preparation of the sediments, measurements) may vary from one laboratory to the other: the presentation does not aim to be exhaustive, but to reference the main procedures at each step of the dating.

Finally the paper reviews the recent applications of OSL dating in France, and assesses the potential of applying the luminescence dating technique to a range of geomorphic research.

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