Comparative Study On Equivalent Particle Size Of Sediments In Landslides And Lakes

With the development of optical stimulated luminescence(OSL)methods,OSL dating has been successfully applied in the lake sediments.Dammed lake sediments caused by landslide are similar to general lake sediments,existed in a problem that the quartz incompletely faded.Meanwhile,there was a controversy in the grain-size of the quartz to date accurately in the dammed lake sediments.The dammed lake sediments is different from general lake sediments.Owing to its lake shape narrow,influenced easily by debris flow and fluvial deposits from hill and ditch.Meanwhile,due to water-level fluctuation in lake and the flood events.The dammed lake sediments including silty-fine sand and medium-coarse sand.We can reconstruct the age of dammed lake,by OSL dating those interlayer caused by the above events during the period of dammed lake existting.Previously research shows that medium-grained quartz faded better than fine-grained quartz in dammed lake sediments.The grain-size of silty fine sand and medium-coarse sand interlayer in dammed lake sediments is relatively coarser.So we can further compare the equivalent dose of medium-grained quartz with coarse-grained quartz in dammed lake sediments.A representative geomorphic feature is valley and basin in the upper reaches of the Yellow River.Giant and large landslides has blocked Yellow River many times in Jishi Valley,there were many dammed lake sediments in Xunhua basin.In three profiles dammed lake sediments of the Xunhua basin,we have collected silty-fine sand and medium-coarse sand sediments OSL samples.In the base of depositional environment analysis including sedimentary profile describes,grain size,scanning electron microscopy,Using the single aliquots regenerative protocol(SAR)of Germany Freiberg instrument,By comparing the equivalent dose of medium-grained(38-63 ?m)quartz with coarse-grained(90-150 ?m)quartz in silty-fine sand five samples and medium-grained(38-63 ?m)quartz with coarse-grained(90-150 ?m)quartz,coarse-grained(200-300 ?m)quartz in medium-coarse sand four samples.The conclusions are obtained from the experimental results.(1)Analyzing the distribution of equivalent dose value by histogram,radiation figure and clarke division method;Selecting of equivalent dose from Mean age model,Central age model,Minimum age model and Zhang Jia Fu age model.For silty-fine sand samples faded completely in the landslide dammed lake sediments,getting similar equivalent dose in the error range from the four age model;for those samples poorly faded,getting equivalent dose faded completely by Minimum age model.(2)Silty-fined sand samples in the landslide dammed lake sediments,medium-grained(38-63 ?m)quartz,coarse-grained(90-150 ?m)quartz,can get similar equivalent dose in the error range,so medium-grained(38-63?m)quartz,coarse-grained(90-150 ?m)quartz can get similar OSL age.(3)MEP-2,MEP-3 sample taken from sand lens,Through comparisons of the equivalent dose of the medium-grained(38-63 ?m)quartz,coarse-grained(90-150 ?m)quartz,coarse-grained(200-300 ?m)quartz,if we can extract medium-grained(38-63?m)quartz or coarse-grained(200-300?m)pure quartz form those sample,we can choose(38-63?m)quartz,coarse-grained(90-150 ?m)quartz,coarse-grained(200-300?m)get OSL age.(4)In combination with scanning electron microscope in quartz,medium-coarse sand samples in the landslide dammed lake sediments,two samples MEP-4,MEP-5 belong to near-source dammed lake sediments,there exists a problem that the quartz incompletely faded.Through comparisons of the equivalent dose value of the medium-grained(38-63?m)quartz,coarse-grained(90-150?m)quartz,coarse-grained(200-300?m)quartz,we get the smallest equivalent dose of the coarse-grained(200-300 ?m)quartz.So we can choose coarser-grained quartz to OSL dating for near-source lake sediments.