柴达木盆地巨型沙波纹条带表层沉积物粒度和地球化学元素组成特征

Characteristics of grain size and geochemical elements composition of surface sediments of megaripple stripes in the Qaidam Basin

巨型沙波纹条带(Megaripple stripes,MRS)是一种巨型沙波纹在来流方向上呈条带状分布的纵向风成地貌,包括巨型沙波纹尺寸较大的巨型沙波纹走廊(Megaripple corridor,MRC)和尺寸相对较小的微床面形态走廊(Smaller bedform corridor,SBC)。采集柴达木盆地MRS表层沉积物样品共112个,对其物理性质(粒度特征)和化学性质(常量元素和微量元素)进行分析。结果表明:(1)柴达木盆地MRS表层沉积物中MRC的优势粒级为砾石(44.24%~50.19%)和极细沙(15.91%~20.42%),粒度分布呈双峰型;SBC的优势粒级为极粗沙(26.00%~35.90%)和细沙(14.80%~20.47%),粒度分布呈三峰型。(2)MRS分选很差,偏度以正偏为主,峰态为宽到很宽。(3)MRC和SBC各元素含量差异不大。常量元素以SiO2和Al2O3为主,含量分别在63%和10%左右;微量元素以Cr、Co、Mo和Ba为主。除Cr和Mo外其余元素均为迁移淋失的状态。(4)柴达木盆地MRS为寒冷干燥环境下的低等化学风化,处于大陆风化初期,化学风化侵蚀相对稳定。

Megaripple stripes(MRS)are an enigmatic eolian bedform pattern characterized by alternating megaripples corridor(MRC)and smaller bedform corridor(SBC),oriented crosswise to the prevailing wind direction.MRCs have taller bedforms,longer wavelengths,and coarser surface sediments compared with the intervening SBCs.MRSs are widely distributed across the middle and southern margins of the Qaidam Basin,Qinghai Province of China,but their comprehensive study remains limited.Analyzing MRS surface sediments can provide a reference for the subsequent study on its formation and evolution,along with the erosion and deposition processes of eolian sand.Herein,112 surface sediment samples were collected from the middle and southern margins of the Qaidam Basin.The physical(grain size characteristics)and chemical properties(major and trace elements)of these sediment samples were analyzed.The results of this study are as follows:(1)MRCs primarily consist of gravel and very fine sand,with gravel and very fine sand contents ranging from 44.24%to 50.19%and 15.91%to 20.42%.The grain size frequency curve of MRCs shows a bimodal distribution.Conversely,SBCs are primarily composed of very coarse and fine sands,varying from 26.00%to 35.90%and 14.80%to 20.47%.The grain size frequency curve of SBCs shows a trimodal distribution.(2)MRS sorting parameters are poor and exhibit positive and negative skewness but primarily positive skewness.MRS kurtosis is relatively wide to very wide.(3)There are no considerable differences in the content of chemical elements between MRCs and SBCs.The major elements of MRS primarily consist of SiO2 and Al2O3,with the highest SiO2 content of~63%and Al2O3 content hovering at~10%.The trace elements,such as Cr,Co,Mo,and Ba,play a dominant role compared to the upper continental crust,Cr and Mo elements show an enriched state,while other elements show signs of leaching.(4)MRS sedimentary environment in the middle and southern margin of the Qaidam Basin is cold and dry.These areas have experienced low chemical weathering,with relatively stable chemical weathering.Compositionally,they closely resemble the upper continental crust and are in the early stage of continental weathering.