堰塞湖沉积物粒度特征分析——以岷江上游叠溪古堰塞湖为例

对叠溪149个古堰塞湖沉积物样品作了物质组成分析、粒度参数计算和概率累积曲线的统计,结合有关资料对比分析了不同沉积环境中沉积物的粒度特征。结果显示湖相沉积上游段的沉积物主要是粉砂质砂和砂质粉砂,中游和下游段的沉积物较细,主要是黏土质粉砂和粉砂。受河流扰动的影响,湖相沉积上游段沉积物的粒径较粗,平均粒径在4～6φ之间,多为负偏度,峰态宽平,分选性差;中游和下游段的平均粒径在6～8φ之间,均为正偏度,峰态中等,沉积物的分选比上游段好。堰塞湖沉积物是由三个或四个粒度次总体组成,其中上游段沉积物含有4个次总体,中游和下游段含有3个次总体,受物源区的控制,上游段中推移总体的含量远大于中、下游段。这些特征均表明堰塞湖上游段沉积物的搬运方式和沉积环境与中、下游段明显不同。与其他环境中的沉积物相比,堰塞湖沉积物的截点偏细,跃移组分分选性最差。

Grain Size Characteristics of Sediments in a Dammed Lake: A case study of the Diexi Ancient Dammed Lake upstream of the Minjiang River

Material composition analysis, parameter calculation and statistics determined from log-probability curves were carried out on 149 samples collected from the Diexi ancient dammed lake upstream of the Minjiang River. Grain-size characteristics in different sedimentary environments were analyzed using related data, showing that upstream sediments in the lacustrine deposit are mainly composed of silty sand and sandy silt. However, midstream and downstream sediments are finer, consisting of clayey silt and silt. Because of disturbance by the river, upstream lacustrine sediments are coarser, with mean particle size between 4 to 6 φ, with negative skewness, wide, flat kurtosis and poor sorting. Midstream and downstream sediments are relatively fine (average particle size 6-8 φ), with positive skewness, medium kurtosis and better sorting. The sediments in the dammed lake are made up of three or four separate log-normal populations, depending on their location. Sediments in the upstream deposit consist of four log-normal populations; midstream and downstream sediments comprise three log-normal populations. The amount of surface creep population is largely provenance-controlled, with a larger percentage of this population upstream than midstream or downstream, indicating obviously different transport mode and sedimentary environments. Notable features of these sediments compared to other sedimentary environments are the poorly sorted saltation population and a truncation point toward finer sizes.