Study On Late Carboniferous-early Permian Aniushan Formation And Fusulinids Fauna In The Bayan Obo Area, Inner Mongolia, China

Carboniferous-Permian is an important orogenic period in the world sincePhanerozoic. During this period, climate changed violently and global cold eventoccurred frequently. Three biogeographic realms, e.g. Northern biogeographic realm,Cathaysian-Tethyan biogeographic realm and Gondwana biogeographic realm.Paleo-Asian Ocean located in the north part of Cathaysian-Tethyan biogeographicrealm。 And its closure time has been argued for many years, and become one of hottopocs in the geology circle. Most researchers consider that Paleo-Asian Ocean closedat the end of Permian or in the Early Triassic, forming the Xar Moron River-Yanjisuture zone. Recently, the eastward termination of the Xar Moron River suture zonehas been located along the Wangqing-Hunchun area. However, is still debatedlocation of the suture zone in central Inner Mongolia. On the Carboniferous-Permianstratigraphic regionalization, the debate is about the stratigraphic belonging of theInner Mongolia Grasslands–Songhua River stratigraphic region.To solve these problems, this thesis reinvestigates the type section of AmushanFormation in Bayan Obo, Inner Mongolia. The authors identified the fusulinidsfossils and compared their ultramicrostructures under the SEM. Besides, byanalysising the LA-ICP-MS zircon U-Pb dating of clastic rocks from the interbed offusulinids fossils, was discussed the sediment provenance of the sandstone from theAmushan Formation.The fusulinids fossils from the Amushan Formation consist of11species of6genera (including2indeterminate species). They are Ozawainella vozhgalicaSafonova, O. crassiformis Putrja, Schubertella obscura Lee et Chen, Triticitesohioensis Thompson, T. sinuosus Rosovskaya, T.sp., Quasifusulina spatiosa Sheng, Q. brevituba Zhu, Q. longissima Moeller, Sphaeroschwagerina moelleri (Rauser),Pseudoendothyra sp.. The fusulinid fossils assemblage from Amushan Formation iscomposed mainly of spieces of the Family Schwagerinidae, together with a smallamount of Schubertella and Ozawainella. Most of these species are wide distributed,in North American, Russian, Mid-Asian, Tarim, North China, South China, NortheastChina (including Inner Mongolia, Jilin and Heilongjiang Province). The present fossilassemblage belongs to the Sphaeroschwagerina zone, which is equivalent to theSphaeroschwagerina sphaerica-Pseudoschwagerina uddeni fossil zone established byZhang (2010) in west Guizhou or the Sphaeroschwagerina moelleri subzone ofSphaeroschwagerina zone established by Zhu (1987) in Wulan, Qinghai Province,China. Its geological age might be Asselian (Early Permian). By observing thefusulinids fossils under the SEM, we found that tectum and keriothecas on thespirotheca have similar ultramicrostructure in different fusulinids spieces.The detrital zircons from Amushan Formation is354-479Ma,934-1941Ma and2330-2688Ma in age. The presence of934-1941Ma zircons shows the character ofthe Jiamusi–Mongolia Block. Provenance analysis indicates that the sedimentprovenance of Amushan Formation is derived from Jiamusi-Mongolia Block. Thus, inthe period of Late Carboniferous-Early Permian, the study area belongs to theJiamusi-Mongolia Block. Considering on the study of the fusulinid geography, theInner Mongolia Grasslands-Songhua River stratigraphic region where the AmushanFomation distributed should be assigned to Jiamusi-Xingmeng stratigraphicsuperregion.