震旦系在北方的一个完整剖面

<正> 前几年,辽东半岛南部(下称辽南)晚前寒武纪地层层序被认为是衔接青白口系与震旦系之间的过渡层。换言之,青白口系与震旦系之间有一段地层缺失,缺失的地层由辽南

A complete Sinian section in North China

The Precambrian strata of the southern LiaoJong Peninsula are divided into the Yongning, Xihe, Wuhangshan and Jinxian Groups. They were considered as the transitional strata between the Qing-baikou and Sinian Systems several years ago, but recently have been considered to be equivalent to the combination of the Qingbaikou and Sinian Systems. A new sequence of Late Precambrian age in this area is proposed here, which is a complete sequence and may be represented by the Haidaozi-Yuanjia-gou profile section in Fuxian of Liaoning and divided, in ascending order, into the Xihe Series (including the Yongning, Diaoyutai, Nanfen, and Qiaotao Formations) and the Wuhangshan Series (including the Gaojiatun, Wall and Jinjia Formations). The Ycngning Formation in the lowermost part of this sequence overlies unconformably the Anshan, Liaohe and Xiangyangsi Groups. This unconformity resulted from the Xiangyangsi Orogeny. The Jinjia Formation in the uppermost part underlies disconfor-mably the Lower Cambrian Jianchang Formation. This disconformity shows the Jixian Movement. This sequence may range in age from 700 Ma (the lower limit of the Yongning Formation) to 570 Ma (the upper limit of the Jinjia Formation) based on foss sabellids and was dated at 658±13 Ma by K-Ar age dates from the glauconite in the upper part of the Qiaotau Formation and 660 to 670 Ma based on glauconite in the Diaoyutai Formation exposed in Jinlin. Thus, the Xihe and Wuhangshan Series should be Sinian. The Haidaozi-Yuangjiagou protila section in Fuxian of Liaoning is, therefore, a complete section of the Sinian System in northern China and is of important significance. It may be used not only to solve the relation between the Sinian and Qingbaikou Systems but also to provide a solid fundamental data for redefining the Sinian and Qingbaikou Systems in China.