扬子区震旦纪地层序列和南、北方震旦系对比

198 2年“晚前寒武纪地层分类命名会议”决议“震旦系是青白口系之上的晚元古代最上部的一个年代地层单位 ,以三峡地区的剖面为代表 ,暂以莲沱组底界为底界”。但从区域性对比和同位素年代地层学分析 ,莲沱组底至黄陵花岗岩的侵蚀面之间有约 10 0 Ma的沉积缺失 ,莲沱组和南沱组也不能代表 75 0～ 6 6 0 Ma间的沉积历史。峡东地区震旦系下部地层不完整是显而易见的。本文赞同修订震旦系的含义 ,以下冰碛层 (古城组或铁丝坳组 )之底为震旦系的底界 ,年龄为 70 0 Ma。朝鲜飞浪洞组可与古城组、大塘坡组和南沱组对比 ,祥原系及辽南、徐淮地区的相当地层属“南华冰期”前的沉积地层。建议震旦系之下至青白口系顶 (85 0 Ma)之间建立辽南系 ,从而完善我国晚元古代年代地层框架

THE SINIAN STRATIGRAPHIC SEQUENCE OF THE YANGTZE REGION AND CORRELATION TO THE LATE PRECAMBRIAN STRATA OF NORTH CHINA

As decided by the meeting on the division and nomenclature of the Late Precambrian strata (China) in 1982, “the Sinian is an uppermost chronostratigraphic unit of the Upper Proterozoic overlying the Qingbaikou System and represented by the section of the eastern Yangtze Gorges and temporarily using the basd of the Liantuo Formation as its basal boundary”. However, there is a sedimentary interval at about 100 Ma between the erosion surface of the Huangling Granite (about 850 Ma) and the base of the Liantuo Formation (about 750 Ma). Also, the Nantuo Formation can not represent the sedimentary history from the top of the Liantuo Formation to the base of the Doushantuo Formation because the Gucheng Formation (“small tillite”) and Datangpo Formation (interglacial sediments) occurred between the Liantuo Formation and the Nantuo Formation in Changyang, Hubei and the East Guizhou West Hunan region. The incompletion of the Lower Sinian strata in the section of the eastern Yangtze Gorges is obvious. Therefore, we agree to revising the primary definition of the Sinian, i.e. regarding the beginning of the “small glacial age” sediments as the basal boundary of the Sinian System and the age is about 700 Ma. The Pirandon Formation of the Southern Pyongyang Depression, D. P. R. Korea, with a sequence from the “small ice age” sediment to interglacial sediment to the major tillites should be correlated with the Gucheng, Datangpo and Nantuo Formations. Consequently, the Late Precambrian strata underlie the Pirandon Formation, and its corresponding strata in South Liaoning and Xuzhou Huainan district, China, should be the sedimentary strata before the Nantuo glacial epoch. We agree to establishing a new system level stratigraphic unit, i.e. the South Liaoning (Liaonanian) System, to represent a phase of geological history between 850 and 700 Ma.