论中国前寒武纪地质时代及年代地层的划分

本文讨论了前寒武纪地质时代和年代地层划分的原则和命名,提出建立隐生宙、原生宙和显生宙。隐生宙包括冥古代和太古代;原生宙分始元代、中元代和新元代。划分中的重要改变是根据新的年龄值数据将五台群归入太古代,将长城系底界改为1700Ma;并根据蠕虫-须腕动物群的出现,将震旦纪归入古生代。文中还阐述了作者对前寒武纪时代划分的新观点。

PRECAMBRIAN GEOCHRONOLOGIC AND CHRONOSTRATIGRAPHIC SUBDIVISION OF CHINA

This paper contains a brief review and discussion of the principle and terminology of Precambrian geochronometry and chronostratigraphy. Three eons,Cryptozoic,Proterozoic and Phanerozoic, are recommended, with boundaries selected at 2500 and 740 Ma. The Cryptozoic comprises Hadean and Archaean eras, divided at 3800 Ma.The Proterozoic eon includes three eras, Palaeoprotozoic, Mesoprotozoic and Neoprotozoic, delimited at 1700 and 1050 Ma. The Archaean and the Palaeoprotozoic are subdivided into regional chronostratigraphic units without rank designation, while the Mesoprotozoic and Neoprotozoic contain four divisions of system rank, including the youngest (850-740 Ma)unnamed unit. Substantial changes consist in the transfer of Wutaian into Archaean and the alteration of lower limit of Changchengian system from 1850 to 1700 Ma, both based on new interpretation of isotopic dating. The lower limit of the Sinian is changed to the base of Nantuo tillite ( 740 Ma ) , coping with the world-wide major glaciation inPrecambrian history, and the Sinian is transferred to the Palaeozoic on account of discovery in basal Sinian of annelids and sabellidids. The first appearance of stromatolites ( indicating life ) , of eucaryotes ( about 1700 Ma), of megaalgae ( about 1400 Ma ) and their thriving (about 1050 Ma) cope all well with boundaries in the time scale. Special sedimentary types reflecting major changes in atmosphere and hydrosphere composition seem also to show a good correlation.