鄂尔多斯盆地大牛地气田下二叠统下石盒子组盒2及盒3段风暴岩研究

首次提出在鄂尔多斯盆地大牛地气田下二叠统下石盒子组盒2及盒3段发育风暴岩。前人认为该区盒2及盒3段为一套河流相沉积体系，而风暴岩的发现证明还广泛发育一套湖泊沉积。鄂尔多斯盆地大牛地气田盒2及盒3段沉积时期，湖泊水面广阔，地形平缓，总体水体较浅，为浅水湖泊环境，易产生风暴回流。根据岩心观察和粒度分析资料，研究区内发育丰富的浅湖风暴岩沉积构造，主要有截切构造、渠模、丘状交错层理和冲刷面等典型的风暴成因构造。粒度概率累积曲线也反映出重力流和牵引流兼有的复杂的水动力机制。研究区风暴岩理想的沉积单元从下至上可概括为“似鲍马序列”，即：A、递变层理和块状层理段；B、平行层理段；C、丘状交错层理和洼状交错层理段；D、波状层理段；E、泥岩段。风暴岩是湖泊发育的典型标志，所以风暴岩的提出对确定研究区的沉积相类型增加了新的认识，并且对下石盒子组的古地理恢复具有重要意义。

Researches on tempestites of the Member 2 and Member 3 of Lower Permian Xiashihezi Formation in DaniUdi Gasfield.Ordos Basin

This paper firstly proposed that tempestites were developed in the Members 2 and 3 of Lower Permian Xiashihezi Formation in the Daniudi Gasfield in the Ordos Basin.The previous studies indicated that the two members were dominated by fluvial sedimentary system.However,the discovery of tempestites proved that lacustrine facies was also developed in the study area.During the deposition of the Members 2 and 3,the lake was wide and shallow,the topography was gentle,and shallow lacustrine facies was developed.Storm currents are easily formed in this setting.On the basis of core observation and granularity analyses,sedimentary structures of tempestites were identified and they were widely developed in the study area.They include truncated structure,gutter cast,hummocky cross-bedding and scouring surface etc.The cumulative probability curves and sedimentary structures reflect that the transportation medium was characterized by the combination of tractive current and gravity flow.The ideal vertical sequence of the tempestites in the study area is a Bouma-like sequence,namely as:A,graded and massive bedding segment;B,parallel bedding segment;C,hummocky cross bedding segment;D,Ripple bedding segment;E,mudstone segment.The tempestite is a typical marker of lacustrine facies,therefore,the proposition of tempestites gives some new viewpoints in identifying sedimentary facies types of the study area and has an important significance for reconstructing the palaeogeography of the Xiashihezi Formation.