Characteristics of the petrology and stratigraphy in the Qingshuigou of South Qilian mountains

The Ordovician Yanchiwan Formation spreads out with the NWW-SEE direction in the belt of Qingshuigou in South Qilian mountains.It is made up with a set of deep celadon fine clastic turdidite sequence and abyssal mudstone that form the flyth formation by combining with the different proportion repetion eath other.Its main rocks is the metamorphic pelitic siltstone, the feldspathic quartz wacke,the fine sandial feldspathic quartz siltstone,the feldspathic wacke and the sericite quartz phyllite etc.It is not developing that the middle grain sequence lamination and the crossing lamination that indicate this formation's sequence is reversal and the northern rocks is older than the sou thern rocks.The Bouma Sequence is not integrated in this formation,it has three types:ABDE type,rhythmic one and simple one. By research kinds of information in Yanchiwan Formaion,such as the macro petrological characteristics,basic sequence,sedimentary structure,turbidity pertrological characteristics grain size curve's characteristics,the strace element and the rare-earth element's index,authors consider that this formation formed at the middle for facies and carry for facies of the bathyal-abyssal facies's turbidity current sedimentary.