寒武纪年代地层的研究现状和研究方向

全球寒武系的底、顶界层型已被确定 ,但寒武系内的统和阶一级的全球标准划分尚待进行。介绍了国际地层委员会寒武系分会有关建阶的意见和推荐的 13个分阶的层位 ;同时介绍了劳亚大陆新近提出的 4统 6阶的年代地层划分方案。回顾了我国的建阶过程 ,指出我国现有的阶一级单位实质上仍然是岩石地层单位 ,具有建立在单位层型上、底界被粗略界定因而时间意义不明确、对比性差、与岩石地层单位重名和不利于竞争国际标准阶和GSSPs等一系列缺点。在湘西、黔东地区新建的 5个阶可取代我国现有的中—晚寒武世年代地层系统。建议暂将我国寒武系划分为 3统和 9个阶 ,即 :下寒武统梅树村阶、筇竹寺阶、沧浪铺阶和龙王庙阶 ;中寒武统台江阶和王村阶 ;上寒武统酉水阶、瓦儿岗阶和桃源阶。

Cambrian Chronostratigraphy Research: Present and Tendency

The current study on Cambrian chronostratigraphy in the world, especially in North America, and the tendency of searching for the formally accepted stages and series, as well as the efforts of the International Subcommission on Cambrian Stratigraphy and its Cambrian Subdivision Working Group for Cambrian subdivision are reviewed. The history of proposing the existfing Chinese stages shows that the concepts of those stages, as originally understood, are actually of lithostratigraphy than chronostratigraphy. Because the existing Chinese stages are directly introduced from the same named lithstratigraphical units, such as formations, all the stages are, therefore, defined by the unit rather than boundary stratotypes. Because of the use of endomic taxa in generic levels, the boundaries of the existing Chinese stages have never been precisely defined. Such boundaries have little international or intercontinental correlation potential. To replace the existing Middle Upper Cambrian stages that erected from the shallow water platform sequences in North China, 5 new statotype based stages are proposed based on the slope facies sequences in western Hunan and eastern Guizhou areas of the Jiangnan Slope Belt. At present, we consider to subdivide the Chinese Cambrian into 3 series and 9 stages. As the four existing Lower Cambrian stages, the Meishucunian, the Chiungchussuan, the Tsanglanpuan, and the Longwangmiaoan have been restudied recently, they are now tentatively retained for the Lower Cambrian Series. The Middle Cambrian Series includes two stages: the Taijiangian and the Wangcunian. They are proposed respectively in this issue, and recently by Peng et al. (1998). The Upper Cambrian Series comprises four stages: the Youshuian, the Waergangian and the Taoyuanian, all of which are also proposed by Peng et al .(1998).