湖北宜昌震旦系-寒武系界线地层Micrhystridium regulare化石的发现及其地层意义

DISCOVERY OF MICRHYSTRIDIUM REGULARE FROM SINIAN-CAMBRIAN BOUNDARY STRATA IN YICHANG,HUBEI,AND ITS STRATIGRAPHIC SIGNIFICANCE

该文记述了国际前寒武系-寒武系界线层型候选剖面所在地,湖北宜昌震旦系-寒武系界线地层中发现的小刺球藻类化石Micrhystridium regulare,regulare,讨论了它们的产出层位及其归属,并对小刺球藻类化石在时间上、空间上的分布作了简要的归纳,最后提出了小刺球藻类化石在震旦系-寒武系界线地层的划分和大区域地层对比中重要的潜在作用。

This peper describes the fossil microalga Micrhystridium found in the Sinian--Cambrian boundarystrata in Yichang,Hubei,the candidate for the international stratotype of the Precambrian--Cambrianboundary. We found that the Sinian--Cambrian boundary strata, named the Yanjiahe Formation by Chen Ping (1984), are in disconformity with the overlying strata (Shuitsingto Formation) and inconformity with the underlying strata (Baimatuo Member) in the Yanjiahe area. For this reason, theYanjiahe Formation is revised and renamed the Yanjiahe Member, which belongs to the TongyingFormation and is early Early Cambrian (Meishucunian) in age. The chronological and geographical distribution of Micrhystridium are concisely discussed. Thefossils studied here are extremely similar to those discovered in Kuanchuanpu, Ningqiang of ShaanxiProvince (Yin Lei--ming, 1987) in many respects, such as their size, quantity and preservation, thelithologic characters, the features of fossil combination, and so on. These strong similarities reflectsimilar palaeoecological environment and evolutionary status of the organisms. These fossil microalgae are different from small shelly fossils in their extensive geographicaldistribution, which is not controlled by the characters of the sea--floor. For this reason, they areregarded as reliable in stratigraphic correlation to a greater extent. Those fossils have also been found in Shimen of Hunan Province and Qingzhen of GuizhouProvince. It is believed that Micrhystridium has a great potential in defining the Sinian-Cambrianboundary and in making correlations in different regions.