Optical Dating Of Young Fluvial Sediments(<1 Ka) In North Tianshan

The accurate dating of young?<1 ka?fluvial sediments has always been a difficulty in the study of luminescence dating.Timing of young sediments,especially for samples from late Holocene or even at centennial and millennium scale,can probably reflect the latest environmental,climatic and geological events in the history of human activities.However,for young fluvial fine-grained sediments,it is widespread that mineral particles are poorly bleached before burial.And quartz grains are dim,which is particularly prominent for samples in western China.Hu and Li?2018?introduced simplified small aliquot standardized growth curve?SSA-SGC?procedure to date young samples with dim and poorly bleached quartz grains.The most obvious advantage of this method is saving time and improving the proportion of effective data.The universality of this method needs to be verified.In addition,in the arid and semi-arid areas of central and western China,where there is lack of fine-grained sediments for conventional OSL dating,most of the sediments are mainly gravels,which puts forward higher requirements for the selection of materials.OSL dating of rock surface has attracted much interest over the past few years and great progress has been made in the fields of geology,geomorphology and archaeology.It is also considered to have potential in some special areas where traditional dating methods are not available.Therefore,could this method be used to date fluvial terrace gravels?The study of modern zero-age sediment samples is of great significance to exam the process of luminescence dating and physical models.At the same time,it is of great significance to analyze the degree of bleaching?resetting to zero?of samples in different sedimentary environments.In this paper,the equivalent doses of modern riverbed and low terrace silty sand samples in gully were measured by quartz simplified small aliquot standard growth curve?SSA-SGC?procedure.In addition,using different procedure,the difference on daylight bleaching between modern riverbed cobbles with various sediments environments and geometric properties,and residual dose of top and bottom surface of cobbles were reported,to explore possibility of luminescence dating to fluvial clastic sediments.The following preliminary understanding was obtained:?1?The residual dose of silt quartz samples in modern river bed was only 0.1±0.11Gy?⁵0 a?,and the deposition age of T1 terrace was about 400 years age.The quartz SSA-SGC procedure has obvious advantages for the dating of young samples with poor bleaching and weak signal.?2?By comparing the IRSL₅₀ and post-IR IRSL signals of different surface slices of different cobbles,it is found that the flat light-colored granite gravels,with the deposit environmrnt of less sediment matrix,particle support structure,and well sorting and rounding,are easier to bleach.?3?There are obvious differences of bleaching between the top and bottom surface of modern riverbed and terrace gravels.And the top surface is a better choice for the luminescence dating of gravels.?4?The depth profiles of four different temperature signals of light colored granite gravel samples in manas river point bar were established.For the top surface of grevals with sufficient bleaching,the bleaching depth of IR50 signal can reach about 10 mm,and the depth of pIRIR₁₁₀,pIRIR₁₇₀ and pIRIR₂₂₅ signals are at least about 3.5 mm,2.5 mm and 1.5 mm respectively.?5?The residual dose of IRSL₅₀ signal of the top and bottom surface are respectively⁰.4 Gy and⁰.7 Gy,suggesting residual age are about 60 and 100 years,respectively;The residual dose of post-IR IRSL₁₇₀ signals of the surface of the top and bottom are respectively¹.1 Gy and¹.4 Gy,suggesting residual age are about 160 and 200 years,respectively.