Study On The Burial Age Of ²⁶Al/¹⁰Be At The Bottom Of The Beihai Formation In The Nandujiang River Basin, Qiongbei

Geochronology is the foundation of geoscience research.Stenographic dating provides data support for the study of tectonic movement and geographic evolution.Due to the limitation of dating materials and dating range,accurate determination of the early and mid-Pleistocene stratospheric ages has always been a difficult problem in the field of Quaternary Geology,and is also a hot topic of current research.Since 1980s,accelerated mass spectrometry(AMS)technology has been greatly developed.Now it can accurately measure the concentration of low abundance ²⁶Al and ¹⁰Be nuclide pairs.The introduction of isometric burial dating method further improves the dating accuracy and application range.The age range of ²⁶Al/¹⁰Be burial dating method is 0.3-5Ma,and the dating materials are easy to available,which compensates for the shortcomings of other Quaternary dating methods.At present,the²⁶Al/¹⁰Be buried dating method has been improved by leaps and bounds in the application of dating technology in ancient human research,geomorphological evolution and climate change.In this paper,the Nandu River Basin of the Beihai formation as the specific dating object,²⁶Al/¹⁰Be buried dating method of the application of dating technology.It is of great significance to select the Beihai formation as the marker formation to carry out applied research of the ²⁶Al/¹⁰Be buried dating method.First,the Beihai formation is a series of brown-red and brown-yellow sand gravel layers distributed in Beihai,Guangxi,Leizhou Peninsula,Guangdong and Northern Hainan Island.It is the most widely distributed Quaternary stratum along the coastal area of South China,and it is a marker stratum for the study of geological geomorphology and environmental evolution in the area,accurate strati graphic age is the basis for the study of tectonic movement and geographic evolution in this area.Second,at present,the ²⁶Al/¹⁰Be burial dating method is mostly applied to the related research in high-altitude areas,and in recent years,the research cases of applying this dating method in low altitude areas have gradually increased.However,there are few studies on the Middle Pleistocene strati graphic are in low latitude and low altitude areas.Samples of this paper were gathered from the gravel layer at the bottom of the Beihai formation,with a total of 10 samples,including 9 gravel samples and 1 quartz sand sample.Comprehensive use of simple burial dating and isometric buried dating method to determine the bottom of the Beihai formation ²⁶Al/¹⁰Be burial age,and collect and organize the existing age data of the formation,compared with the burial age of this paper and cross-validation,so as to determine the age of the Beihai formation.On this basis,the significance of age results to the environmental evolution and tectonic movement of the study area is considered.The conclusions of this article are as following:1.The burial age of quartz sand samples at the bottom of the Beihai formation was calculated by simple burial dating method,and the minimum burial age of the layer was 0.67±0.38Ma.For the accuracy and credibility of this era,we have the following conclusion:First,the use of low AMS energy resulting in minimal test accuracy,resulting in a larger analysis error.Second,the depth of the sample burial is less than10m,the age results may be influenced by the generation of nuclides after burial,so that the age of burial is less than the actual burial age of the sample.On this basis,the simple burial age obtained in this paper is cross-compared with the age data already available in the formation,and the actual age of the sample should be greater than0.7±0.1Ma.2.According to the principle of ²⁶Al/¹⁰Be isometric burial dating,select the appropriate study area,and on the basis of a detailed study of the geological features in the study area,exclude the possibility of complex exposure-burial history of the sample,and the AMS test results show that the sample contains a higher concentration of Al and Be.The above two points verify the applicability of the ²⁶Al/¹⁰Be buried dating method in low latitudes and low altitudes,expand the application range of the method,and provide experience and reference for the future application of the method in low latitudes and low altitudes.3.Through the study of the late new generation formations in Nandu River basin,the causes of the Xiuying formation and the Beihai formations are clarified,the hybrid clay layers of Xiuying formation are lake phase or coastal and shallow sea sedimentation,the Beihai formations belong to river sedimentation,the two formations are falsely integrated contact,and iron weathering crusts remain at the junction of the formation of the Beihai formations.Based on the age results of this paper,it can be inferred that the environment of the area changed considerably in the period from about 0.7±0.1Ma,that is,after the crust lifted,large areas of water disappeared and rivers began to develop.