Studying The Small Shelly Fossils Of Lower Cambrian In Guizhou Province, Yangtze Platform

This paper mainly focuses on the Small Shelly Fossils(SSFs) of Guizhou Yangtze platform strtigraphic district through Gezhongwu section of Zhijin and Yankong section of Jinsha. The study shows that the base Cambrian of Guizhou are rich in the SSFs, including 32 genera and 33 species, including 1 similar ity species, 2questions species and 10 undetermined species. It is noted that spherical SSFs were first discovered in the base of N iutitang Formation from Jinsha. These spherical SSFs are mainly consisted of unicell or multi-cell structure, and indentified as Olivooides pearformis and the remaining Phylum, C lass, Order, Genus and Species uncertain, and enlarged the composed components of SSFs. SSFs mainly live in the normal sea where temperature, salinity, clear water and hydrodynamic are suitable for them. However, they are extremely sensitive in environment, and the composed components will change along with the environment changes. Combined with fossil assemblages and lithology, our studies show that: Gezhongwu Formation and the underlying Dengying Formation, the overlying N iutitang Formation are para-unconformable contact, and Gezhongwu Formation belong to Anabarites trisulcatus-Protohertzina anabarica Assemblage Zone、Siphogonuchites triangularis-Halkieria uncostattus Assemblage Zone, and missing third fossil assemblage zone, the zone I are interpreted as Jinningian, and the zone II and the horizon under the N i-Mo ore bed of N iutitang Formation are interpreted as Meishucunian. The base of N iutitang Formation and the underlying Dengying Formation is also para- unconformable contact in Yankong section of Jinsha. The SSFs of base of N iutitang Formation belong to Heraultipegma yunnanensis Zone, and missing zone I and II, with the horizon under the N i-Mo ore bed of N iutitang Formation are interpreted as mid-to-late Meishucunian.The study of SSFs from Guizhou is not only enriched fossil assemblage of Niutitang biota, and providing an important basis for revealing living environment of SSFs, but also shed a light on the origin and evolution of early metazoan and embryology. At the same time, it also provides important fossil evidence for the accurate division and correlation of the base Cambrian from Guizhou.