龙潭组的定义和时代

<正> 以往,由于岩石地层和年代地层概念上的混淆,在很长的一段时间内,习惯于用年代地层学的概念去修订岩石地层单位的定义,产生了一些不易解释或难以解决的矛盾,江苏南部地区龙潭组定义的修订就是一个例子。本文在回顾龙潭组定义变化过程的同时,试图通过宁镇山脉一条比较完整的剖面,来讨论它的定义、时代以及与其它地区“龙潭组”的对比问题。

Definition and age of the Lungtan Formation

The authors of the present paper consider the definition of the Lungtan Coal Series of J. S. Lee and S. Chu (1932) suitable for the Lungtan Formation. In this sense, the Lungtan Formation is a stratigraphic unit between the Permian Kufeng Formation and the Triassic Chinglung Limestone. "The upper part of the Formation consists of a black shale bearing impressions of marine fossils. Lower part essentially of dark grey and buff sandstones with patches or pockets of coa. intercalated in the upper part. Gigantopteris nicotianaefolia, etc. occur. The total thickness ranges from 80 to 100 metres."A recent research reveals that the age of the parastratotype of the Lungtan Formation in Fu-niushan. Zhenjiang, Jiangsu, as the other so-called Gigantopteris Coal Series in South China, ranges from the late Eatly Permian to the close of the period, and the main coal-bearing part in the stratotypical section in Lungtan is late Early Permian.The Permian coal-bearing formations in different localities of South China have their own local names and are not strictly synchronous, so the chronostratigraphic correlation of the coal-bearing formations is one of the most complex problems. Based on the recent researches, a scheme of correlation is proposed in fig. 5.