摘要
通过岩心观察、薄片鉴定、X衍射矿物分析,对鄂尔多斯盆地西南部刘家沟组重力流沉积的岩石类型及特征、成因进行研究.结果表明,刘家沟组取心段发育灰紫色粉砂岩、砾屑混积岩以及薄层黑色泥岩.粉砂岩主要组分为石英、岩屑、长石、泥晶方解石及杂基,具杂基支撑结构,发育沟模、粒序层理、火焰状构造、包卷层理、鲍马序列等浊流沉积特征,为浊积岩.砾屑混积岩发育大量砾屑及填隙物,填隙物由陆源碎屑颗粒、内碎屑及基质组成,发育泥质撕裂屑、基质支撑结构、颗粒无定向排列、与上下泥岩突变接触等沉积特征,为碎屑流沉积.研究认为,早三叠世勉略洋盆并未完全闭合,对鄂尔多斯盆地西南缘产生海侵影响,形成混积岩层,在正宁一带发育潟湖沉积,并存在斜坡,在C3钻井处发育碎屑流-浊流为主的重力流沉积.
Abstract
Through core observation,thin section identification,and X-ray diffraction mineral analysis,the rock types and characteristics,and the genesis were studied.The results show that the core section of Liujia-gou Formation develops grayish purple siltstone,rudaceous mixed rock and black mudstone.The siltstone was mainly composed of quartz,rock debris,feldspar,micrite calcite,and matrix,with a matrix-supported fabric,and developed turbidite sedimentary characteristics such as groove casts,graded bedding,flame structures,convolute bedding,and Bouma sequences,identifying it as turbidite.The mixed rock contained a large a-mount of gravel intraclast and interstitial material,with the latter composed of terrigenous clastic particles,in-traclasts,and matrix.It exhibited sedimentary characteristics such as muddy tear-shaped clasts,matrix-sup-ported structure,randomly oriented particles,and abrupt contact with the overlying and underlying mud-stones,suggesting it was debris flow deposition.The study suggests that the Mianlue Ocean during the Early Triassic was not completely closed and had a marine transgression impact on the southwestern margin of the Er-dos Basin,forming mixed rock strata.Lagoon sediments developed in the Zhengning area,with slopes pres-ent,and gravity flow sediments dominated by debris flow-turbidity current were developed at the place of Well C3.
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