Sedimentary Evolution Of The Xujiayao Site

The origin and evolution of ancient humans has always been one of the important research contents of paleoanthropology and Quaternary geology.The Xujiayao site is an important part of the ancient human ruins culture in North China,and it plays an important role in the evolution of Paleolithic and ancient humans.The Xujiayao site includes the 73113 location and the 74093 location.Since the excavation of the site,different scholars have used different experimental methods to measure the site and the relationship between the historical stage of the site's cultural layer and the location of the cultural layer.The position of the cultural layer expresses different viewpoints,and the age of the acquired sites ranges from six to seventy years to four hundred and fifty thousand years.For the burial position of the cultural layer,some scholars believe that it is buried in the Muhewan layer,that is,in the lacustrine sediments,and some scholars believe that it belongs to river deposits.It can be seen that the stratigraphic accumulation in the site is very complicated.If we want to obtain accurate chronological judgment,the premise is to clarify the order of accumulation and evolution of the stratum,and to figure out which stage of the historical evolution of the site's cultural layer.Through the field investigation of the site,it is found that the location of the cultural layer is located in the sedimentary layer of the lake.It should be located at the top of the lake layer,below the erosion surface,and the thickness is about 2.7m.Above the erosion surface,it is a loess layer of sand and fine gravel conveyed by flowing water.As far as the site profile is concerned,the stacking sequence from bottom to top is the lake layer-the erosion surface-the loess layer transported by the water stream.Above the erosion surface,the accumulation environment of the site profile is changed from lake to flowing water.The gravel in the loess is poorly rounded,and the direction and inclination of the abrasive surface are also very messy.This is obviously different from the riverbed gravel that has been eroded and transported for a long time.The lithologic composition and the gravel deposits in the upper reaches of the Liyigou The lithology is quite similar.We analyze the flooding formed on the piedmont alluvial fan,which is formed by the rapid accumulation of mountain floods and seasonal water from the valleys.Therefore,we need to further verify the evolution process of the overall sedimentary environment of the region,so as to more accurately locate the buried position of the cultural layer of the site.Field field investigations revealed that the lower gray-green lake layer and the middle-upper yellow-green lake sedimentary layer of the site section are two sets of marking layers in the area,which can be traced from the downstream to the upstream along the Liyigou.The midstream and site profiles were sampled and a total of four sections were used for magnetic susceptibility and particle size analysis.The significance of the magnetic susceptibility to the sedimentation of the lacustrine facies is very obvious,and the difference in the particle size distribution map between the lacustrine sediments and the river deposits is more prominent.Among them,the magnetic susceptibility curve shows that the Xujiayao section 1 is 7.6-13.1m deep,the Xujiayao section 2 is 3-15.6m deep,and the Xujiayao section 3 is stacked at depth 1.3-28.3m.A thick lacustrine sedimentary layer,in which the peak of magnetic susceptibility at the depth of 5.5m and 6.2m of the Xujiayao section represents two volcanic clastic layers,and the peak of magnetic susceptibility at the depth of 13.3m and 27.8m in the Xujiayao section It represents the volcanic debris layer produced by two volcanic eruptions.The particle size distribution of individual samples in each layer of the profile shows that the single-peak size of the particle size distribution at the 1,2,and 3 sections of the Xujiayao section is more obvious,showing good lacustrine sedimentary characteristics.Among them,the Xujiayao section is 2m deep and the Xujiayao section is 3m deep and 11 m in the lacustrine sedimentary layer.There is a thin layer of gravel.The double-peak(multi-peak)of the particle size distribution above the lake layer is more obvious,indicating the characteristics of typical river sediments,which means that the sedimentary environment of the section has changed above the erosion surface,and both accept the front of the valley from the upper reaches of the valley.Flood accumulation.This is consistent with the situation when we inspected the profile of the site.Therefore,we judged that the cultural layer of the Xujiayao site was formed when the ancient lake was on the verge of extinction and the accumulation of pre-mountain alluvial deposits.