解读国际地层委员会2004年前寒武纪地层表及2004—2008年参考方案

UNSCRAMBLE THE ISC 2004 AND SPECIAL REFERENCE TO PRECAMBRIAN FROM 2004 TO 2008

国际地层委员会前不久公布了2 0 0 4年“国际地层表”,并专门提出了“2 0 0 4—2 0 0 8年前寒武纪年表参考方案”。在2 0 0 4年版“国际地层表”中,新建了埃迪卡拉系,其时限从6 30 Ma至5 4 2 Ma。“2 0 0 4—2 0 0 8年前寒武系划分参考方案”指出应该根据唯一客观的物理标准——现存的岩石记录,对前寒武纪地质年表重新进行界定。前寒武纪的地层界线应标定于地层记录中的关键事件或转变点上,以突出反映地球系统演化的巨变。在介绍有关埃迪卡拉系的背景、地质特征和时限的同时,对“参考方案”中有关前寒武系划分原则和具体划分方案的新思路进行了介绍和评述,对“参考方案”中值得商榷的问题进行了初步分析。

'International Stratigraphic Chart' (GSC) (2004) proposed by Gradstein (Chair of ICS) et al. has been published in the paper 'A new Geologic Time Scale,with special reference to Precambrian and Neogene'. A new Ediacaran System is set up in the new International Stratigraphic Chart. The Ediacaran Period is the last geologic period of the Neoproterozoic age, just before the Cambrian. It ranges from approximately 630 to 542 million years before the present. In the paper, Gradstein and others also suggest a special reference to Precambrian from 2004 to 2008. They point out that “the Precambrian time scale should be redefined in terms of the only objective physical standard-the extant rock record. Boundaries should be placed at key events or transitions in the stratigraphic record, to highlight important milestones in the evolution of our planet.” We firstly introduce the concept, feature and time range of the new Ediacaran Period. Then the new ideas including subdivision principle, criterion and scheme of the above-mentioned reference to Precambrian are briefly made known. Furthermore, a preliminary discussion has been done on some consultable problems in the special reference, and some suggestions are provided for our establishing the Chinese Precambrian Time Scale.