鄂尔多斯盆地内部中二叠统石盒子组盒8下亚段砂岩中的风暴岩

Tempesitites in Lower Submember of Member 8 of Shihezi Formation (Middle Permain) in Ordos Basin

鄂尔多斯盆地内部中二叠统石盒子组盒8下亚段为浅灰白色、矿物成熟度和结构成熟度高的石英砂岩和岩屑石英砂岩,是盆地内天然气主要储产层之一,该亚段砂岩一般厚15～40 m,在某些井的岩芯中频频见到风暴岩。根据单层风暴岩的厚度、粒度、异地碳质泥岩和煤屑的含量、剖面结构特征,特别是丘状交错层理的发育程度、袋模构造存在与否及其发育规模,以及风暴岩叠加层的多寡等,可以大致划分出由不同风暴流能量(级)形成的三种风暴岩端元类型。(1)较高能量风暴流形成的风暴岩,层底表现为大型的袋(壶)模构造切入下伏石英砂岩层中,风暴岩层主要是碳质泥岩和浅黄色泥岩砾片,并混有多少不等的石英砂和煤屑。单层厚度一般为20～50 cm或更大,呈正粒序构造,常见为若干风暴岩的叠加层。(2)中等能量风暴流形成的风暴岩,表现为完整和不完整的风暴岩层序,其内或多或少含有碳质泥岩和煤屑,单层厚度常为10～40 cm,亦常见若干风暴岩层的叠置层。(3)较低能量风暴流形成的风暴岩,单层厚大致为5～10 cm,仅发育丘状和洼状交错层理,可以单层形式出现,亦可以是若干层的叠置层。盒8下亚段砂岩被不少研究者厘定为河流相和辫状河相,风暴岩的存在对重新认识盒8下亚段的古地理具有重要意义。

Lower submember of the 8th of middle Permain Shihezi Formation is quartz sandstone and lithic quartz-sandstone with higher compositional and textural maturity and light grey-white color,and is one of the main reservoirs in the basin with the thickness generally 1540 m,tempesitites frequently occur in some well cores.According to thickness of single tempesitite bed,grain size,fragment contents of external land carbonaceous mudstone and coal,profile feature,especially the scale of hummocky crossbedding and pot cast,and more or less of the stacked tempesitites and so on,three ended type tempesitites could be divided approximately by varying degrees of energy stone wave current in cores.（1） The tempesitite generated by higher energy storm wave current appeared large scale pot cast cute into the top of underlying quartz sandstone or lithic quartz-sandstone,the super stratum tempesitite consists of flaky conglomerate of carbonous and light yellow grey mudstones,mixed with some quartz and coal clastics,thickness of single bed the same as 2050 cm,some are too thick,graded bedding,and frequently show the stacked secession.（2）The tempesitites generated by the middle energy storm wave current show the integrated or non-integrated tempesitite sequence,with developed hummocky cross bedding,and contain more or less some carbonous mudstone and coal clastics,the thickness of single bed is always 1040 cm,and stacked sequence often occurred.（3） The tempesitite generated by lower energy storm wave current appeared the thickness about 510 cm,only develops the hummocky and swaley cross stratification,not only is single bed,but also stacked by several beds.Tempesitites frequently occur in quartzitic sandstones of Lower submember of the 8th is questioned to viewpoint of fluvial facies.