Studies on applicability of terrace sediment dating by OSL, TL and ESR methods - Illumination tests and dating of age-known terrace sediments -
We investigate the applicability of the luminescence dating methods for terrace sediments based on the assumption of the complete optical bleaching of some radiation defects in quartz grains in the processes of erosion, transportation and/or sedimentation. At first, we have carried out illumination tests. The illumination tests show that the Ti signal is more light-sensitive than E1' and Al signals, and is bleached completely by illumination. This result shows that the TL consists of the light-sensitive component and the residual one, and that we can obtain the intensity of a light-sensitive component easily by illumination tests.Then, we tried to date late Quaternary marine/river terrace sediments, whose age had been already estimated from geological information, using OSL, TL of light-sensitive component and ESR Ti signal. Ages obtained by the OSL and TL methods are in good agreement with geologically estimated ages. We found that variation in pore water content over time was of major significance in age determinations for these sediments, on account of their history of deposition underwater, with subsequent uplift and drainage. However, the ESR method fails to date marine terrace sediment, because we were not able to determine how the bleaching of the ESR Ti signal proceeded in antiquity.Furthermore, we have carried out OSL dating of late Quaternary river terrace to verify its applicability. Samples from the recent riverbed show a weak OSL and gave very young ages. OSL ages obtained from sand-lenses in terrace gravel layers show a good agreement with ones estimated by stratigraphic data. OSL ages obtained from flood plain deposits are older than geologically estimated ages. This was attributed to the mixing of different age grains by incomplete optical bleaching due to the inundation process. Analyses of OSL from single quartz grains confirmed that these sediments were composed of grains having a wide range of palaeodoses. Therefore, we concluded that the OSL method is adaptable for marine and river terrace sediments, and that the TL method is probably appropriate for dating of the marine terrace sediments. Furthermore, the process in transportation and deposition of sediments should be considered for dating of sediments.
|optically stimulated luminescence (OSL)