Sedimentary Records Of Paleoflood In The Linhe Reach Of The Yellow River Over The Last 30 Ka

Understanding the frequency and intensity of paleoflood is critical for revealing long term hydrological response to climate change,and is a hot topic in recent day.The houtao basin is an important alluvial region as a sequence of frequent channel swinging,containing lots of hydrological information,is an ideal area for reconstructing paleoflood sequence.This study uses 20-m-deep core(identified as HDZ04)to analysis grain size and chemical characters.Combining with the Optical Stimulated Luminescence(OSL)dating,we reconstruct paleoflood sequence in the Linhe reach of the Yellow River over the last 30 ka.Compared with regional paleoenvironment,we discuss the relationship between paleoflood and climate change.Preliminary conclusions and results are as follows:(1)According to the grain size and element results,we find the sediment mainly contains sand and silt,the average grain size changes between 6.98-328.56 ?m,kurtosis changes between 0.62-3.25,sorting changes between 0.51-2.64,skewness changes between-0.65-0.19.The intensity of element K,Ca,Al and Si show similar trend,Fe,Zn and Rb show similar trend,S rand Y show similar trend,Zr and Mo show similar trend.(2)According to the sand contents,P95,end member results and ln(Zr/Ti),we find 20.41-12.90 m the grain size contains 80% sand,P95 is about 300 ?m,the two coarser end member content is more than 60%,and ln(Zr/Ti)is higher.12.9-10.01 m the grain size contains 0-98% sand,P95 changes between 0-600 ?m,the two coarser end member changes between 0-1,and ln(Zr/Ti)is lower;10.01-8.25 m the grain size contains 0-12% sand,P95 changes between 0-150 ?m,the two coarser end member is about 0,and ln(Zr/Ti)is about-1;8.25-5.50 m the grain size contains more than 70% sand,P95 changes at 200 ?m,the two coarser end member is about 1,and ln(Zr/Ti)changes at-1-1.8;5.50-0 m the grain size,P95 changes,the two coarser end member,and ln(Zr/Ti)decreases quickly.(3)According to the grain size,chemical results and age dates,we construct the paleoflood sequence over the last 30 ka in the Linhe reach of the Yellow River.The super-paleoflood since 30 ka occurs at ~23 ka and ~13 ka.30-12 ka is marked by high frequent and high intense paleoflood,The Holocene(12-0 ka)was marked by low frequent and low intense paleoflood,seven episodes of increased flood in the middle Yellow River since middle and late Holocene occurs at 6.27-5.16,4.5-3.9,3.6-2.44,1.94-1.47,~0.38 ka,the largest paleoflood peaks at 3.6-2.44 ka,three episodes of decreased flood occurs at 5.16-4.5,3.9-3.6,1.47-0 ka.The Early Holocene(12-8.5 ka)is marked by little paleoflood,during the Middle Holocene(8.5-3.0 ka),the paleoflood frequency and intensity increase slightly,The Late Holocene(3.0-0 ka)is marked by sharp increase in the frequency and intensity of paleoflood.(4)Compared with the regional paleoenvironmental records,we find the paleoflood scarely occurrs at warm and dry climate stage,while moderate frequent and intense paleoflood mainly occurs at the warm and humid climate stage,High frequent and intense paleoflood occurs mainly at cold and dry climate stage.What's more,super-paleoflood clusters at climate transition stages in the upper and middle Yellow River.