青海湖现代三角洲沉积特征及形成控制因素

青海湖是中国内陆最大的高原微咸水断隐湖泊，是研究现代湖三角洲沉积的理想地区，按河流与湖水动相互作用的强弱关系，将其三角洲为2种类型：鸟足形（河探型建设性）三角洲、扇形（河浪探型）三角洲和平直滨岸形（浪控型破坏性）三角洲，前者沿青海湖断隐盆地长轴发布，是湖区最大和最典型三角洲，后者沿盆地短轴分布，形成规模小且发育不齐全，鸟足形三角洲发育完整的三角洲平原、三角洲前缘和后三角洲有个亚相，其中三角洲平原亚相由分流河道、废弃河道、洪泛平原、泥沼、沿岸沙坝和风成沙丘组成，三角洲前缘亚相由河口沙坝、水下分流河道、分流间湾和三角洲前缘席状砂组成，与国内外其它湖三角洲相比，以发育沿岸沙坝和风成沙丘为其特征；平直滨岸形三角洲主要由三角洲平原部分构成，三角洲前缘亚相不发育（属滨岸沉积）；湖泊三角洲的形成受气候、构造、地形、河流作用与湖泊作用相对强度以及注入河水与盆地湖水在河口地区的混合等因素控制。

Sedimentary Characteristics of Modern Lacustrine Deltas in Qinghai Lake and Their Controlling Factors

The Qinghai Lake is an inland intermountain rift-subsidence lake basin.Based on strong or weak relations between river and lake energies,the modern lake deltas are divided into three types,that is,bird-foot delta (river-dominated constructive delta),fan delta (river and wave-dominated delta) and smooth coast delta (wave-dominated destructional delta).The first type is formed along the long axis of the basin,and is the biggest and a fine type of delta in the lake.The other two are distributed along the short axis with a smaller scope and an incomplete growth.The bird-foot delta has the three complete subfacies of delta plain,delta front and prodelta.The subfacies of the delta plain consist of microfacies of distributary channel,discarded channel,flood plain,swamp,longshore bar and aeolian dune.The subfacies of the delta front is subdivided into four microfacies of river-mouth bar,subaqueous distributary channel,distributary internal zone and prodelta sheet sand.Compared with other lake deltas in China and abroad,the deposits in the delta of Qinghai Lake are featured by its better developed longshore bar and aeolian microfacies.The smooth coast delta mainly consists of delta plain and lack of delta front.The development of the deltas is mainly controlled by climate,tectonic setting,topography,relative intensity between river and lake energies,and the mixed flow of injected river water and lake water in the river mouth region.