论大巴山地区的临湘组

我国上扬子地区奥陶系宝塔组与五峰组之间的介壳相地层历来存在两个岩性组:一个是临湘组,岩性为绿灰色瘤状灰岩,另一个是涧草沟组,岩性为灰黄色砂质页岩.二者均曾建立Nankinolithus带。1975年以后,涧草沟组一名被广泛引用于大巴山地区,意指宝塔组顶部瘤状泥灰岩以上的黄绿或桔黄色页岩,厚仅数十厘米.本文以五个实测地层剖面为例,从岩性特征和化石内容论证大巴山地区原宝塔组顶部的瘤状泥灰岩实与其上的原涧草沟组页岩为一套独立的岩性地层单元,符合临湘组的概念,故改大巴山地区的涧草沟组为临湘组。并据化石与国内外相当地层进行对比.

ON LINXIANG FORMATION IN THE DABA MOUNTAINS

The shelly facies between Baota Formation and Wufeng Formation of the Ordovician in the upper Yantze area used to be called Linxiang Formation or Jian-tsaokou Formation.The former is composed of the greenish-grey warty marlites and the later consists of the greyish-yellow sandy shales.The "Jiantsaokou Formation" has been widely used in the study of the Daba Mountains since 1975.It is defined ag the yellowish-green or orange shale of several centimeters in thichness.It contains Nankinolithus and lies over the uppermost warty marlites of so-called Baota Formation.Taking the five surveyed sections as examples, this paper expounds and proves that the top marty marlites of so-called Baota Formation formed an independent lithostratic unit in terms of the features and the contents of fossils. This accords with the conception of Linxiang Formation.Its lithologic characteristics and fossil assemblage correspond to those of Linxiang Formation in the upper Yangtze area.Therefore, the uppermost warty marlites should be separated from so-called Baota Formation in the Daba Mountains. They should be combined with the Tiant-saokou Formation and named Linxiang pormation.They can also be correlated with the upper ordovician horizons of other parts in China or in other countries.