An Investigation Of The Early Carboniferous Rugose Coral Fauna And Its Biostratigraphic Significance In Riwancaka Formation,Gêrzê,Tibet

Carboniferous Marine system in Qiangtang Basin,Tibet is well developed.In particular,there are abundant fossils in the lower carboniferous system.In this paper more than 36 rugose corals collected from the Gangmacuo area of Gêrzê,Tibet are identified,the rugose corals of 8 genera and 15 species are systematically described.Rugose corals collected from Riwancaka Formation in the Gangmacuo area of Gêrzê,Tibet including Arachnolasma aichiapinense Fan,Arachnolasma chabugense Fan,Arachnolasma sp.indet 1,Arachnolasma sp.indet 2,Axophyllum jamdaense Fan,Clisiophyllum cf.subimbricatum Thomson,Clisiophyllum sp.indet,Dibunophyllum cf.turbinatum M.Coy,Dibunophyllum sp.indet 1,Dibunophyllum sp.indet 2,Diphyphyllum gerzeense Fan,Kueichouphyllum heishikuanense Yü,Kueichouphyllum sinense Yü,Neoclisiophyllum jamdaense Fan,Slimoniphyllum cf.retiforme Fan &Chen.The rugose coral fauna of Riwancaka Formation in Gangmacuo area of Gêrzê,Tibet is a kind of mixed fauna.The triple-zoned corals are taking the role,meanwhile,the large sized solitary corals with double-zoned characteristic are well developed in the study area.With acknowledge of rugose corals and its cenozone distribution,the Kueichouphyllum heishikuanense-Arachnolasma chabugense assemblage zone is established to represent the Riwancaka Formation,which divided into 2 assemblage subzone,the one layered at lower part is Kueichouphyllum heishikuanenseAxophyllum jamdaense assemblage subzone and the other layered at upper part is Arachnolasma chabugense-Clisiophyllum cf.subimbricatum assemblage subzone.The former is comparable with Arachnolasma sinense-Heterocaninia tholusitabulata subzone of Yuanophyllum fossil zone of Hunan province and PseudodorlodotiaZunyiphyllum assemblage zone of Gêrzê,Tibet,while,the later is comparable with Neoclisiophyllum yengtzeense-Koninckophyllum stellatum subzone of Yuanophyllumfossil zone of Hunan province and Yuanophyllum-Aulinia assemblage zone of Gêrzê,Tibet.It can be found that the age of the Kueichouphyllum heishikuanenseArachnolasma chabugense assemblage zone belong to upper part of Visean,Lower Carboniferous.The fauna from Riwancaka Formation is a combination of warm-water type fossils,which shows that it has the affinity with Yangtze block.