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.