更尕海现代碎屑物质粒度组成空间分异及其输入过程

SPATIAL GRAIN-SIZE DIFFERENTIATION AND INPUT PROCESSES OF THE CLASTIC SEDIMENTS OF GENGGAHAI LAKE IN THE GONGHE BASIN

文章分析了更尕海表层沉积、流域地表沉积、湖泊水体沉积以及岩芯沉积等的粒度组成,并比较了不同沉积类型之间有关的沉积动力联系。更尕海表层沉积具有4种类型的粒度分布模式,其粒度组成由两个端元组分(粗、细颗粒组分)或者二者的混合构成。湖泊现代沉积物表现出自西北向东南逐渐变细的趋势。粗颗粒组分主要由风力输入,反映了流域风场状况或风沙活动的强度(如尘暴事件);而细颗粒组分输入过程复杂,其环境意义需要进一步理解。更尕海沉积岩芯样品具有类似于湖泊表层沉积的粒度组成特征,然而其粗颗粒组分的变化可能还受控于湖泊水域面积的分异作用。未来的工作拟将在合理评价湖泊水位变化的基础上。

Mineral dust plays an important role in regulating the global climate system. The North Western China, one of the most significant sources for atmospheric mineral dust over the Northern Hemisphere, provides an ideal place for the research on aeolian activities and dust storms. In this study, we selected Genggahai Lake, a hydrologically closed lake in the Gonghe Basin, for investigations of the spatial differentiation of modern clastic deposits in the lake in order to understand the process of aeolian activities in the lake region and the mechanism responsible for the input of detrital materials into the lake. Different types of deposits were analyzed for grain size distribution including the lake surface sediments, catchment surface deposits, core sediments and suspended particulate materials in the lake water column. The data indicate that the lake surface sediments show four patterns of grain size distribution that consists of two end-members（fine-and coarse-grained components）or a mixture of the two end-members with various relative proportions. The surface sediments display an overall trend of decreases in the grain size from the northwest to the southeast that is consistent with the direction of prevailing winds in the study area in winters and springs. Taking grain size distributions of suspended particulates trapped in the lake water and modern aeolian dust collected at Lenghu into account, the coarse-grained component of the lake sediments was most likely transported to the lake by winds and thus is sensitive to aeolian activities, i. e., occurrence of dust storms. The transportation of the fine- grained component of the lake sediments is not clear because fine particles deposited in the lake are complex in origin. The grain size distribution of the core sediments is quite similar to that of the lake surface sediments, suggesting that the modern process of input of elastic materials into the lake could be applied to the past. More attention must be paid to the effect of changes in the lake level on grain size distribution of the surface sediments in the future studies in order to better constrain the implication of coarse particles in the core sediments.