Unconformity Between Ordovician And Sinian In Bashenkaogong Area,Altun Mountains,and Its Geological Significance

In the research area,there are two kinds of contact relationship.One is angle unconformity,the other is fault.The reason for the lost of Cambrian is that the research area was a uplift platform in that time.The research area is in northern Altun mountains.Because of the poor environment and bad traffic condition,it is one of the most unexplored regions in the west of China.Cambrian and Ordovician source rock play the role of chief source rocks in Tarim Basin.At the same time,they are also good reservoir.According to statistics,there are 82 wells which have drilled Ordovician.So,the study is very important for the exploration of southeastern Tarim basin.This paper focuses on the study of Ordovician field profile.After the analysis of sedimentary faces,the lithoface paleogeography can be inferred.It should be helpful for the further exploration.The results of this paper are showing as followed:The sedimentary model changes from shoreland,carbonate platform to shallow sea.Unconformity between Ordovician and Sinian tells that the research area was under the condition of uplifting during Cambrian.The Cambrian was weathered and denuded.Transgression started in Ordovician.The transgression is also proved by the correlation of middle and east areas of Tarim basin.Kumuqibalake formation belongs to the face of turbidite fan in middle Ordovician.It should be formed at the slope of basin'boundary.