毛不拉孔兑流域河岸沙丘粒度与地球化学元素的动态时空分异

Spatial distribution characteristics of grain size and geochemical elements of surface sediments in the Mu Bulag River

通过对不同年份库布齐沙漠毛不拉孔兑流域河岸沙丘地表沉积物样品进行粒度、化学元素分析,获得其粒度和元素组成特征及其变化:2019年和2013年样品粒度组成均以极细沙和粉沙为主,含量占70%以上,峰度呈窄峰,分选较好,表现为典型风成特性。但2019年较2013年粒径组成变粗,分选性变好;化学元素组成上以Si、Al为主,与上陆壳平均化学元素组成相比,2019年较2013年大部分化学元素亏损程度加大。A-CN-K图解揭示了2个年份内流域河岸沙丘地表物质化学风化程度均很低,处于较弱的去Na、Ca阶段,其他元素未发生明显的化学风化或迁移;对于不同河流断面,2019年和2013年的样品均表现出自河流上游至河流中下游,粒度组成变细,峰度变窄,分选性变好,风成特性更明显。与上陆壳平均化学元素组成相比,2013年4个断面样品的元素变化趋势一致性较2019年更明显。在流域尺度上,不同年份河岸沙丘地表沉积物样品理化特征具有较大相似性,其原因与母岩,以及在风水交互作用下地表物质呈现一定的动态平衡有关。

Riparian dunes are ubiquitous in the main deserts all over the world,and their uniqueness is promin-ently reflected in the wind-water geomorphic process.In this study,the characteristics and variations of particle size and element composition were obtained through the analysis of the particle sizes and geochemical ele-ments in the surface sediments from the Mu Bulag River located in the Hobq Desert.For characteristics of the particle size composition,the samples collected in 2013 and 2019 were extremely fine sand and dust sand,which accounted for more than 70%with narrow kurtosis and good sorting.These results of the sediments dis-played typical aeolian characteristics.However,the samples collected in 2019 presented a coarser particle size and better sorting compared with that obtained in 2013.The Si and Al were the dominant elements for chemic-al composition in the sediments.Considering the average chemical composition of the upper continental crust(UCC),the loss of most chemical elements in 2019 were higher than with that in 2013.The A-CN-K diagrams revealed that the chemical weathering degree was low in the surface materials of riparian dunes in the basin,in-dicating a weak stage of removing Na and Ca,while other elements experienced unremarkable chemical weath-ering or migration.As for the samples from different river sections in both 2013 and 2019,the particle sizes be-longed to finer with narrower kurtosis and better sorting,and thus the aeolian characteristics were more obvi-ous from the upper to the middle and lower reaches of the river.Compared with the average chemical composi-tion of the UCC,the consistency of element changes trends of samples in four sections in 2013 was more re-markable.For the basin scale,the physical and chemical characteristics of surface sediments of riparian dunes in different years showed great similarities,and these results can be attributed to the influences of parent rocks and the dynamic balance in surface materials under the alternate action of wind and water.