Study On Middle Permian Brachiopod Biostratigraphy And Community In Lower Member Of Longge Formationhami,Rongma,Tibet

The paper collects a lot of materials about paleontology.It analyzes brachiopod fossils from section 002 of the lower member of Longge formation in Rongma,Tibet.In the study area,it establishes the branchiopod assemblages in Permian,and compares with the brachiopod assemblages in South China.Based on the study of buried characteristics?combination features?output layers and lithologic characteristics of brachiopod fossils in the study area,it establishes three brachiopod communities and corresponds benthic niche contrast,and discusses the sedimentary environment.In this paper,it can obtain the following points:1.According to the study of 502 fossil specimens in section 002 of Longge formation in Rongma,Tibet,Brachiopods were identified 28 genera,32 species,produced 7 fossil plates,which greatly enriches brachiopods fossil content in the study area in Permian.2.On the basis of brachiopods identification,according to the features?abundance ratio?diversity of brachiopod fauna,and combines with Periodic analysis of brachiopod evolution developments,it can be established two assemblages from bottom to top:Urushtenia chaoi Ching-Neoplicatifera elongata Huang(U-N)Assemblage;Tyloplecta richthofeni Chao-Cryptospirifer omeishanensis Huang(T-C)Assemblage;Through a detailed study of typical molecular in this two brachiopod assemblages and the overall portfolio outlook,and extensive comparison with some related fossils home and abroad,it makes a clear sense of the times of each assemblages,and enriches strata contents in the study area.3.According to a comprehensive analysis of output layers?buried characteristics?fossil composition?individual paleoecology?lithology of brachiopod fossils in the study area,it can be established three brachiopod communities:Neoplicatifera-Chonetinella(N-C)Community?Tyloplecta-Spiriferellina(T-S)Community?Cryptospirifer(C)Community.And the study of ecological environment of the three communities shows that N-C Community and T-S Community are a products of the low energy environment,and C Community is a product of high energy environment,Comparison of benthic niche displays that the brachiopod communities in the study area is located in the benthic niche BA2-BA3,the water depth is about 10-60m.4.According to longitudinal changes of benthic niche of the three communities,combining the analysis of cross-section sedimentary to explore the relation between relative sea-level change and the replace of brachiopods community.In the study area,the lower member of Longge formation has undergone a sea-level rising phase,which shows that the main factor affecting the community replacement is water depth,and in addition to global sea level change,regional tectonic movement also has an important influence on relative sea-level changes.