华中西南区一条国际前寒武系与寒武系界线层型补充剖面

1992年，全球前寒武系与寒武系界线层型剖面和层型点确定在加拿大纽芬兰东南幸运角剖面，并以遗迹化石带Trichophycus pedium的底作为前寒武系与寒武系的分界点。但是，幸运角剖面主要是以硅质碎屑岩相为主，难以与含有丰富小壳化石和具有可对比的稳定同位素资料的碳酸盐相界线剖面进行对比。为此，提出我国云南会泽大海附近的一条以碳酸盐相为主的剖面作为全球前寒武系与寒武系界线层型剖面的补充剖面。理由是（1）在大海剖面上，震旦系灯影组白岩哨段、待补段和下寒武统牛家菁组的中谊村段，大海段之间为整合接触；（2）早寒武世早期地层单元含有丰富的小壳化石并且可划分出4个小壳化石组合带；（3）利用碳同位素资料可以将大海剖面与许多其它剖面相当地层对比；（4）著名的梅树村剖面离大海剖面不远，它们均含有丰富的小壳化石和遗迹化石，两者易于对比。文章进一步认为寒武系的下界放在第I小壳化石组合带（Anabarites trisulcatus-Protohertzina anabarica）的底，相当于大海剖面11层的底。

A SUPPLEMENTAL PRECAMBRIAN-CAMBRIAN BOUNDARY GLOBAL STRATOTYPE SECTION IN SW CHINA

Since 1992, the siliciclastic Fortune Head section(southeastern Newfoundland, Canada) and the base of the Trichophycus pedium trace fossil zone have together served as the Precambrian Cambrian(PreC C) boundary global stratotype section and point(GSSP). However, the fact that the Fortune Head section consists mainly of siliciclastic rocks makes it difficult to correlate this section with boundary sections consisting mainly of carbonate rocks, which contain abundant small shelly fossils(SSFs) and can also be correlated using stable carbon isotope data. We propose that a predominantly carbonate section near the town of Dahai, eastern Yunnan Province, southwestern China, be designated a supplementary stratotype for the PreC C boundary GSSP, for the following reasons:(1) the Dahai section is continuous, consisting of the Neoproterozoic Baiyanshao and Daibu members conformably overlain by the Early Cambrian Zhongyicun and Dahai members and Shiyantou Formation; (2) the Early Cambrian units contain abundant SSFs representing four assemblage zones; (3) the Dahai section can be correlated with numerous other sections using stable C isotopic chemostratigraphy; (4) the famous Meishucun section, located not far from Dahai, contains both abundant SSFs and trace fossils and can be readily correlated with the SSF rich Dahai section. We further propose that the base of the Cambrian System be placed at the base of the first SSF assemblage zone(the Anabarites Protohertzina Zone), which in the Dahai section coincides with the base of Bed 11.