大型坳陷湖盆浅水辫状河三角洲沉积特征及模式:以鄂尔多斯盆地陇东地区延长组为例

浅水三角洲是当今沉积学研究热点和油气勘探重点对象。鄂尔多斯盆地陇东地区三叠系延长组发育了大型浅水辫状河三角洲,并在其中发现了丰富的油气资源。在大量野外露头、岩心和地球物理资料分析的基础上,明确鄂尔多斯盆地延长组具有利于浅水辫状河三角洲发育的大型坳陷湖盆地质背景,形成的辫状河三角洲具有粒度较粗、塑性岩屑较多、成分和结构成熟度较低、发育交错层理和间断正韵律、水下分支河道多叉、砂厚、延伸远等沉积特征。鄂尔多斯盆地浅水辫状河三角洲沉积时期,沉积区距物源区相对较近,河道宽深比较大,发育浅水沉积构造和沉积韵律,构造活动和湖平面变化共同控制了三角洲的发育,形成了"小平原、大前缘"的浅水辫状河三角洲沉积体系。

Sedimentary characteristics and model of shallow braided delta in large-scale lacustrine: An example from Triassic Yanchang Formation in Ordos Basin

The research and exploration of shallow delta have been paid much attention in recent years.A large shallow braided delta developed in Longdong Area of southwestern Ordos Basin.Based on some outcrop,core,logging,seismic data from Triassic Yanchang Formation in Ordos Basin,it is suggested that the geological setting of Ordos Basin is favorable for the formation of shallow braided delta during the period of Yanchang Formation.The shallow braided delta is characteristics of coarse grain size,many soft lithoclasts,low content and texture maturity,many cross beddings,normal cycles,many distributary channels,thick sandbodies,distal extension etc.During the sedimentation of the shallow braided delta in southwestern Ordos Basin,the sediment center was near to provenance,the width to depth ratio of the channel was big and shallow water sedimentary structures were developed.The development of the braided shallow delta was controlled by the tectonic activities and lake level changes and therefore,the shallow braided delta in southwestern Ordos Basin was formed in the form of small plain and large delta front.