Beijing Mountain Of Debris Flow Deposits TL Dating Research

The age of ancient debris flow events not only is the foundation of revealing the geography environment change of active debris flow areas, but the key to research the ancient debris flow evolution and its interaction mechanism. Although thermo luminescence dating has been widely used in Quaternary research as the important dating technique, but its application in the study of debris flow deposits is less. The outstanding problem of TL technique been applied to ancient debris flow deposits is that the mechanism of debris flow luminescence dating is unclear, and research in this area rarely reported.First, the TL residual background of the modern debris flow surface material of KeTai, XiBaiLianYu and BaiLongTan Gully, which in MiYun Reservoir upstream Basin of Beijing, was studied using the TL technology. The results reveal that the residual background is8.81-28.5ka in this basin. Shows even the surface material is partial bleaching and has a larger residual background, so the residual background should be considered when using debris flow material to date.Then, the changes of TL signal along the ditch of the modern debris flow material of KeTai and XiBaiLianYu Gully, which in White River Basin, was studied. The research indicates that the TL signal of debris flow materials reduced obviously in the process of flow. The average residual background of the provenance, circulation area and the accumulation area is respectively25.15ka,23.43ka and15.93ka. And due to the light fading,the surface sample’s background radiation less than the sample5-10cm from the surface.Finally, using the thermo luminescence technology to measure three profile of ancient debris flow deposits in Qingshui River Basin of Beijing. Age of the ancient debris flow profile obtained after subtracting the11.2ka residual background which derived from the preliminary work. The age of the HongShuiKou profile range from46.0ka B.P.to32.5ka B.P., and it is in the later period of Late Pleistocene; The age of the LingShan profile range from264.0ka B.P.to146.6ka B.P., and it is in late Middle Pleistocene; The age of the ZhaiTang reservoir above profile range from214.9ka B.P.to69.4ka B.P., and it is in late Middle Pleistocene to the early period of Late Pleistocene. For HongShuiKou profile and LingShan profile, the trend with depth of U, Th and K contents and annual dose is consistency, and the age increase with the increasing depth. But the trend with depth of U, Th and K contents and annual dose of ZhaiTang reservoir above profile is inconsistent, and the luminescence age presences reverse phenomenon.