关于中国新元古界划分几个问题的讨论

Discussion on the New Subdivision of the Neoproterozoic in China

2001年4月正式出版的《中国地层指南及中国地层指南说明书》(修订版)中将新元古界从二分变为三分,自下而上分别为青白口系、南华系和震旦系。本文首先介绍了震旦系重新定义的背景和必要性。由于近些年国际末元古界分会酝酿在新元古代末期新建一个系,而多数学者的意见是该系的下界应置于冰碛层之上,即大致相当于我国陡山沱阶的底部。鉴于此,在1999年12月初断代工作组会议期间,晚前寒武系工作组的与会专家一致认为,有必要对震旦系重新定义,并决定将原震旦系解体,原上统代表重新定义的震旦系,原下统独立新建一个系,命名为“南华系”。由于震旦系的再分,新元古界也从二分变为的三分,重新界定的震旦系包括原上震旦统灯影组和陡山沱组,南华系包含了原下震旦统南沱组和莲沱组。笔者认为南华系标准剖面的候选剖面应具备下列基本条件:①上覆有震旦系下部陡山沱组及其相当层位的地层,该地层与南华系顶部地层之间沉积记录的缺失应是最少的;②剖面中应包括寒冷性气候的冰川沉积记录,虽然在全国性南华系地层对比中,冰成岩层不是绝对的对比标志,但为有利于全球对比,我国南华系候选标准剖面应将冰成岩层包括其内;③剖面中应出露莲沱组(约750Ma)或与其时代相近层位(休宁组、志棠组等)之下的一套地层,这套地层与莲沱组之?

According to the ' China Stratigraphic Guide and Exposition on China Stratigraphic Guide (Revised Edition)' published by the China Stratigraphic Commission in 2001, the Neoproterozoic Era is subdivided into the current three systems from the previous two, in ascending order, the Qingbaikou, Nanhua and Sinian Systems. In this paper, the background and necessity of the new subdivision are firstly introduced. It is known that a new system of the terminal Proterozoic will be set up, which is suggested by the International Terminal Proterozoic Stratigraphic Subcommission. The upper boundary of the new system corresponds to the bottom of the Cambrian System, and the lower boundary will be set up at the top of the glacial bed, which is equal to the Nantuo Formation of the Three Gorges of South China. The new China Stratigraphic Commission has decided that the previous Sinian System would be subdivided into two systems, i. e. , the new Sinian System including the Dengying and Doushantuo Formations of the previous Upper Sinian Series, and the Nanhua System containing the Nantuo and Liantuo Formations of the previous Lower Sinian Series. In this paper some principle and procedure for establishing the Nanhua type section are also proposed. The author points out that a candidate section should posses the following features: ① The strata is overlain by the Doushantuo Formation or beds of the same age and there is less sedimentary absence between them. ② In order for a global Stratigraphic correlation, glacial sedimentary records should be included in the section. ③ The beds that are overlain by the Liantuo Formation or the corresponding strata should be developed in the section, and there is no longer sedimentary gap between the beds and overlying Liantuo Formation and the bottom time boundary of the beds is not younger than 800 Ma or older than 850Ma. ④ There are some good regional, national and even global Stratigraphic correlation markers, and the lithology, geochronology and paleontology are well studied.⑤Good outcrop, communication, environment and successive section.