鄂尔多斯盆地南缘岐山曹家沟奥陶系剖面地层和沉积特征

Ordovician stratigraphy and sedimentary characteristics of Caojiagou section in Qishan County,southern margin of Ordos Basin

陕西岐山曹家沟剖面位于鄂尔多斯盆地南缘,交通便利、出露良好、地层齐全、沉积类型多样,是一条重要的奥陶系剖面。对曹家沟剖面进行了详细介绍,下奥陶统冶里组以泥质白云岩为主,亮甲山组以含硅质团块晶粒白云岩为特征,发育叠层石,均为潮坪相沉积。中奥陶统马家沟组主要为中薄层—中厚层的粉细晶云岩、灰岩,属开阔台地—台地前缘斜坡相沉积,峰峰组主要为中薄层—纹层状白云岩,发育大量薄层的碳酸盐碎屑流和浊流沉积,属较深水的台地前缘斜坡相重力流沉积。上奥陶统平凉组为一套大陆斜坡相类复理石的韵律沉积,唐王陵组为大陆斜坡相泥石流环境下的冰水沉积,具有典型的冰坠石构造。

The Caojiagou section in Qishan County,Shaanxi Province is located in the southern margin of the Ordos Basin.The well-exposed section deposited complete Ordovician strata and developed various sedimentary types,and its location has convenient transportation.In this paper,the stratigraphy and sedimentary characteristics of the Caojiagou section are introduced in detail.The lower Ordovician Yeli Formation is mainly composed of argillaceous dolomite and Mount Liangjia Formation is characterized by crystal dolomite intercalated with siliceous mass and develops stromatolites,all of which belong to tidal flat facies.The Middle Ordovician Majiagou Formation consists of medium-thin and medium-thick layers of silty-fine dolomite and limestone,belonging to open platform and platform front slope facies deposits.The Fengfeng Formation is mainly composed of medium-thin layer laminated dolomite with a great quantity of thin carbonate debris flow and turbidity current deposits,which represent the gravity flow deposit of the front slope of the platform in the deep-water environment.The Upper Ordovician Pingliang Formation mainly consists of a set of flyschoid rhythmic deposits of the continental slope facies.The Tangwangling Formation represents the debris flow environment of the continental slop and develops the ice-water deposits with typical ice-rafted dropstones.