| Volcanic activity and ancient human activity relics in the Datong-Yangyuan basin.The dating of the Datong volcano and the Xujiayao ruins has not yet been revealed.Although different scholars have done a lot of research on the dating of Datong volcano and Xujiayao site,there are still many disputes because of the differences in understanding of strataum,sampling locations and dating methods.The Datong volcanic activity and the age of Xujiayao site still need further discussion.The Datong-Yangyuan basin in the quaternary period has developed loess-paleosurface sedimentary layer,lacustrine layer and volcanic layer.In this paper,after estimating the formation age,photoluminescence dating samples were collected on the basis of analyzing the formation,and the estimated age of the formation was compared with the photoluminescence dating results.Finally,the dating results of Datong volcano and Xujiayao site were obtained.Through field survey and laboratory experiment analysis,the Jinshan volcanic lava layer in the Datong volcanic group is located under the L1 loessial layer and in the S1 ancient loessial layer,and the volcanic eruption age is estimated to be between 100,000 and 140,000 years.The volcanic lava layer of Heishan is approximately the same as that of Jinshan,but the volcanic lava layer of Heishan tends to be located in the upper part of L1 loess,so its age may be younger than that of Jinshan.There are few loess layers above the Cetian reservoir-Yujiazhai volcano,or incomplete remains,but there are still loess layers below the lava layer,which is consistent with L1 loessial layer.The Chenzhuang formation is a fluvial horizontal sand layer with an ancient lake facies layer,which is located in the center of the ancient lake.The test results of photoluminescence samples collected in Datong volcanic area show that Jinshan volcano in Datong volcano is respectively 80,000±13,700 years old and 128,800±11,200 years old.Montenegro volcano is 69,600±93,000 years old.The age of Cetian reservior-Yujiazhai volcano was 97,000±10,500 years.The volcanic eruption time recorded in the Chenzhuang formation is 132,100±15,300 years.Therefore,by comparing the estimated formation age and photoluminescence dating results,we draw the following conclusions:although there are many volcanoes in Datong area,the Datong volcano is uniformly active and has the same activity cycle.The study captured two similar periods of volcanic activity,the more recent one between 69,000 and 97,000 years ago and the other between 129,000 and 132,000 years ago.Field investigation at Xujiayao site revealed that from the entire stratigraphic section,the lacustrine layer is below.Unlike the previous understanding,the cultural layer is not located in the lacustrine layer,nor is it directly connected to it.The cultural layer is a pale yellow clay layer above the lacustrine layer.The continuous river facies in the area have a uniform texture and a very fine surface sand layer.This layer indicates that the area has undergone a period of time to change from a large lake to a river,was then exposed to the surface and deposited under the loess-like rust.The fine sand layer with good horizontal stratification is above the cultural layer,and the alluvial gravel layer is above that These two layers have been observed and measured to have high magnetic susceptibility and contain fine volcanic magnetic minerals by observation and measurement.Combined with the release of 117,900±5,200 years old from the lower layer sand light[1],the last volcanic eruption was 69600±9,300 years old.According to this,the age of the Xujiayao site is around 100,000 years old. |
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