青海湖北部冲积扇沉积特征、演化过程及控制因素

Sedimentary characteristics,evolution and controlling factors of the alluvial fans,the north of Qinghai Lake

冲积扇是重要的油气储集体,具有内部结构复杂、非均质性强的特点。通过野外剖面实测、遥感影像分析等方法,对位于青海湖北部的3个冲积扇(泉吉河扇、沙柳河扇和烂泥湾扇)进行沉积亚相的划分和沉积微相的识别。对于泉吉河扇和沙柳河扇,在扇根亚相中识别出辫状河道、主水道和主水道间微相,在扇中亚相中识别出辫状河道、心滩、漫流微相和低粘度碎屑流沉积,在扇缘亚相中识别出漫流微相和泥滩微相。烂泥湾扇发育2期泥石流作用和短暂的牵引流作用。根据沉积特征将沙柳河扇和泉吉河扇的沉积演化过程划分为4个阶段,分别为初次碎屑流沉积及主水道发育阶段、低粘度碎屑流沉积阶段、广泛的辫状河道发育阶段、河道迁移及三角洲发育阶段。将烂泥湾扇的沉积演化过程划分为3个阶段,分别为早期泥石流沉积阶段、间歇期牵引流沉积阶段和后期泥石流沉积阶段。研究结果表明,物源条件的差异是造成研究区3个现代冲积扇沉积特征差异的主要原因,气候条件中的湿度和风场对青海湖北部冲积扇的沉积也具有一定的控制作用。

Alluvial fans,which are important reservoirs for hydrocarbon accumulation,are characterized by complex internal structures and strong heterogeneity. Three alluvial fans(Quanjihe Fan,Shaliuhe Fan,Lanniwan Fan)developed in the north of Qinghai Lake were divided into several subfacies and several microfacies based on field surveys and analysis of remote sensing images. For Quanjihe Fan and Shaliuhe Fan,braided channel,main channel and interchannels were identified at the fan roots;braided channel,channel bars,sheet flood and noncohesive debris flow were identified at the fan middle;sheetflood and mudflat were identified at the fan margin. Two periods of debris flow and one short period of traction flow happened during the development of Lanniwan Fan. According to the sedimentary characteristics,the evolution processes of Shaliuhe Fan and Quanjihe Fan can be divided into 4 stages:the initial debris flow deposition and the development of main channel,noncohesive debris flow deposition,extensive development of braided channel and migration of channels and development of the delta. And the evolution processes of Lanniwan Fan can be divided into 3 stages:the early debris flow deposition,the intermittent traction flow deposition and the late debris flow deposits. The results show that the differences in provenance are the main causes for the differences in sedimentary characteristics for the 3 modern alluvial fans.And climatic factors,including humidity and wind field,control fan deposition too.