青海湖现代滨岸沉积微相及其特征

Sedimentary Characteristics and Microfacies of Shore Zone in Qinghai Lake

本文将青海湖滨岸带沉积划分为沿岸砾沙坝、泥坪、沙滩、砾石滩、泻湖和水下风沙堆积六个微相。与国内外其它湖泊滨岸沉积相比，以发育沿岸砾沙坝和水下风沙堆积为其特征。其中规模较大的沿岸砾沙坝和沙滩分布于地形坡度不大（坡度１０°±）和波浪、沿岸流及风力作用强烈的滨岸地区，粒度概率曲线以推移和跳跃总体为主、悬移组份含量少和跳跃总具双跳跃式为特征，垂向层序由分选差（δ１＞１）的上部粗碎屑物与分选好（δ１＜１）的下部细碎屑物构成反韵律层；砾石滩主要分布于冲积扇或扇三角洲入湖地带和湖蚀岸边，以砾石均匀、磨圆较好、绝大多数砾石长轴平行湖岸线和最大扁平面倾向湖方向且倾角８°±为特征；泥坪主要分布于湖水动力弱、无大河流注入的湖湾、湖岸地形平缓以及坝后湖水滞流地带；水下风沙堆积以分选好、磨圆好、石英表面具风蚀凹坑、概率曲线呈上凸和双跳跃式总体以及粒度参数δ１＜１、Ｓｋ＝－０．１５～０．２１、Ｋｇ＝０．７５～１．１３和Ｍｄ＝０．２２～０．０２３ｍｍ为特征。本文对丰富湖泊沉积相内容具有一定意义。

The shore zone in Qinghai Lake is divided into six sedimentary microfacies:longshore bar,mudflat,sand beach,shingle beach,lagoon and subagueous aeolian.Compared with othe lakes in China and abroad,the deposits in the shore zone of Qinghai Lake are featured by their better developed longshore bar and subaqueous aeolian;A large scale of longshore bar and sand beach are distributed in the shore zone of small slope(slope 10°±)and strong wave,longshore current and wind action.There are characteristics of main traction and saltation parts (two parts of saltation) and little suspended load in their grain-size probability curve.The vertical sequences are reversed rhythmite of poorly sorted (δ 1>1) overlying coarse grained clastics and well-sorted (δ 1<1) underlying fine-grained clastics;The shingle beach distributes mainly in the erosion coast and the areas from alluvial fan or fan delta into the lake.The gravels are homogenous size and well psephicity,the long axis of most gravels parallel the lake strandline,the maximam flat surface tend to lake and the dip angle is about 8°±;The mudflats mainly distribute in the lakebay,level lakeshore and stagnant area behind longshore bar;The characteristics of subagueous aeolian have well sorted (δ 1<1),well psephicity,deflation hollows of quartz surface,S k=-0.15-0.21,K g=0.75-1.13,M d=0.22～0.023 mm,convex upward and two parts of saltation in the grain size probability curve.