Study On Sr-Nd Isotope Of Different Size Red-clay In Jingning County And Jingchuan County On The Loess Plateau

The Loess Plateau aeolian sedimentary sequence in China include Quaternaryloess-paleosol sedimentary sequence and Neogene period red clay sedimentary sequence.As a continental deposit,it is the best evidence for studying global climate change.For the genesis of loess in the Loess Plateau,the predecessors have achieved quite good research results,and the origin of the red clay is considered to be consistent with the loess and belongs to aeolian sediments.In this study,Sr-Nd isotope tracing method was used to obtain the isotopic characteristics of different grades of Jingning and Jingchuan red clay in the Loess Plateau.The consistency or difference of the sources of red clay in the two regions was determined,which could reveal the source changes.Construction,climate or environmental factors,etc.Through the Sr-Nd isotope characteristics,we obtain the following conclusions:?1?The Sr-Nd isotope of Jingning red clay has a large range,which mainly reflects the change of material source.The three fractions of JingningCaihe red clay?5-28?m,28⁴5?m,>45?m?has a generally consistent source of material,<5?m is far-source substance from the westerly flow.?2?The Sr-Nd isotopes of Jingchuan red clay as a whole changed less than that of Jingning,indicating that its material source was relatively stable.<5?m of Jingchuan red clay belongs to the far-source component,which comes from the Gobi Altai Mountains with a large proportion of material.The sources of the three components?5-28?m,28 45?m,and>45?m?are substantially identical.?3?Jingchuan red clays on the east of liupan Mountain and Jingningcaihe red clays west sides of Liupan Mountain have different deposition times and the?_Nd result of the material sources.The main components of JingningCaihe red clay are derived from the provenance of the Qilian Mountains and the Qaidam Basin,and they were deposited by the flow around the northerly wind and the venturi effect,which are unstable.Therefore,the?_Ndreslut fluctuates greatly.The source of Juanchuan red clay mainly comes from the Qilian Mountain and Gobi Altai Mountain.The material input of Qilian Mountain increases,so the?_Ndd result becomes lower.<5?m of Jingchuan is a distant component,and the input of the source is stable.The proportion of the material from the Altai Mountains in Gobi is high,so the mean is slightly higher than the other three components.<5?m of the Jingningred clays is far-source substance from the westerly flow and venturi effect.Although it comes from a distant source,the difference in isotope characteristics from the other three particle sizes is not obvious.?4?Aboutthe changing characteristics of Jingningcaihered clay and Jingchuan red clay with time,the sedimentary age of Jingning red clay is14.10-9.7ma,while that of Jingchuan is 7.12-2.6ma.The inconsistency in the chronology leads to limited significance of the comparison,because the source of the red clay varies with the geological time.On the whole,the Sr-Ndisotopedigit characteristics of Jingning and Jingchuan sections are consistent with the changes of Qinan-Lingtai sections measured by predecessors during the period of 14.10-9.7Ma and 7.12-2.6Ma,indicating the reliability of the results of Sr-Nd isotope changes in this study.