干旱地区河流扇三角洲-河流扇演替模式:来自黄羊泉扇的启示

Arid Fluvial Fandelta-Fluvial Fan Transition:Implications of Huangyangquan Fan Area

通过地表实地踏勘和浅层探槽解释,结合卫星照片解译,参考第四纪和历史地理研究结果,对准噶尔盆地西北缘黄羊泉扇的沉积特征及其第四纪以来的演变进行了分析.黄羊泉扇是一个发育在内陆干旱地区、以河流沉积为主的河流扇,扇体平面上呈上细下粗的"葫芦型",可以划分为上扇、中扇和扇缘3个相带,沉积物具有由上扇向扇缘变细的趋势.扇上沉积动力以河流为主,缺乏泥石流沉积,但扇面活动水道不发育,大多数河道为偶尔才有径流通过的暂时性河道,风对扇表面的沉积物有明显的改造作用.黄羊泉扇扇缘发育4种不同的终止方式,一部分进入艾里克湖,一部分终止在沼泽地带,一部分在小型湖泊边缘消失,一部分受地形阻挡终止,与经典冲积扇和扇三角洲都不完全相同.结合前人历史地理研究成果认为第四纪以来黄羊泉扇所在的古玛纳斯湖出现过6次高湖平面,在30 ka以前,黄羊泉扇体一直处于古玛纳斯湖包围中,形成黄羊泉扇三角洲.直到30~10 ka期间才由于湖泊水位下降,扇体逐步出露形成河流扇.研究建立了黄羊泉扇随着湖平面升降从河流扇三角洲不断演化为河流扇的沉积模式,表明黄羊泉扇目前正处于河流扇三角洲沉积体系向河流扇沉积体系演变的过渡阶段.

This study focuses on the sedimentary characteristics of Huangyangquan fan through field investigation and trench excavation combined with satellite image interpretation and Quaternary geological as well as historical geography analysis.The authors suggest that the Huangyangquan fan is a fluvial fan developed in the inland arid area of northwestern Junggar basin margin,which is a gourd in plan metric shape and can be divided into three parts,namely,upper fan,middle fan and fan margin.The fan is dominated by fluvial deposits but not debris flow deposits.The channel is most of ephemeral with minor intermittent channel.The effect of wind on the sediment of fluvial fan surface is obvious.The fan is terminated in 4 types as into Eric lake,to the marshes,to the shore of small lakes and to an terrain block,these are all different to either of normal alluvial fan or fan deltas.Research shows that the ancient Manas lake appeared six times high level in the Quaternary.Before 30 ka,the fan was surrounded by ancient Manas lake as a fluvial fan delta system,after that time it changed gradually to be an fluvial fan due to the lake level down.The depositional model has been built based the historical geography research results to interpret the evolution of the fan from fluvial fan delta to fluvial fan system,and it shows the present Huangyangquan fan is in the transition period from fan delta to fluvial fan system.