Studies On The Fauna And Its Palaeobiogeography Of Late Ordovician Yingan Fm In Kalpin Area, Northwest Tarim

The Ordovician strata is outcropped well in Kalpin area of Xinjiang.The Yingan formation with abundant graptolite,trilobite,brachiopod and other fossils of late Ordovician is preserved well.Recently,the coral and stromatoporoid fossils are d iscovered in the top layer.Through the field route investigation and precision formation survey,the Yingan formation was decomposed in the study area of Yimugantawu range and Kalpintag range.Based on the research result,the Yingan group is divided into upper and lower segments.The lower segment lithology which is mainly for marlite and mudstone indicates that the early stage is given priority to with shallow sea shelf facies.The upper segment is mainly bioclastic limestone showing the late stage appeared platform edge facies.Through comprehensive studing on graptolite,trilobite,brachiopod and coral fossils,three graptolite zones are established in the lower segment.These are Climacograptus spiniferus,Orthograptus quadrimucronatus and Amplexograpts disjunctus yangtzensis zone.Besides,the Agetolites—Heliolite assemblage is also established in the upper segment.Combining stratigraphic palaeobios studing,the author discusses the age ascription of Yingan formation in this paper,And believes that the lower segment with Aijiashan deposition belongs to early Kaiti period and the upper segment with Q iantangjiang deposition belongs to late Kaiti period.On the basis of studing on palaeogeographic areal-type of graptolite,trilobite and coral,the paleontological community geographic division is not obvious.It is with transition characteristic between North China and Middle China.