Research On Biological Fossils Assemblage And Environment Of Gezhongwu Formation,Zhijin Area,Guizhou

The discovery and researches of small shelly fossils play a significant role in early studies on epigenetic organism’s evolution and biological taxonomy because they are firstly appeared biological fossil with shell in early Cambrian. Large amount of small shelly fossils were discovered in phosphorus sequence on bottom of Cambrian in Yangtze region because of its special geological environment.Researches and studies on small shelly fossils are hot topics of paleontology.In this paper, we take Guizhou Zhijin Gezhongwu Formation as the standard section of early Cambrian, and numerous of small shelly fossils were discovered in the dolomitic phosphorite from bottom of the standard section. According to the assemblage characteristics of these small shelly fossils,we classified these fossils as Anabarites-Protohertzina anabarica and Siphogonuchites-Lapworthella Assemblage Zone, and no fossils classified to the 3rd Assemblage Zone. Considering the distribution status of lithology variation, and quantity of fossils affected by the environment changes, we affirmed the contact relation between black shale and dolomitic phosphorite is parallel unconformity. The corresponding geological period of this formation should be mid-late Meishucun stage, and the environment gradually turned to disadvantageous condition. We found that the chemical composition of fossils were affected to the chemical composition of surrounding rock, the original composition was difficult to confirm. Medullary cavity structure was found in Zhijinites fossils through microscopic observe, refer to protective shield of uncertain mollusks. Limited by research conditions, further researches still need to be done.Researches on small shelly fossils from Guizhou Zhijin Gezhongwu Formation provides evidences to study on morphological characteristics and living environment of different biological combination, and also provides fossil materials to origin and evolution of early epigenetic organism. Meanwhile, the research has significant effect on division of phosphoric rock series from early Cambrian formation in Guizhou and stratigraphic correlation between coeval rocks.