中国科学院南京地质古生物研究所机构知识库

通过对湖南永顺和桃源4条中–上奥陶统剖面的牙形刺生物地层研究,在湘西北地区中、上奥陶统原先划分(Pygodus anserinus-Yangtzeplacognathus jianyeensis带和Pygodus serra生物带)的基础上,自下而上识别出:牯牛潭组顶部的Pygodus serra生物带(达瑞威尔阶上部)、大田坝组下部的Pygodus anseinus-Yangtzeplacognathus jianyeensis生物带(达瑞威尔阶顶部–桑比阶下部)、大田坝组中部的Baltoniodus variabilis生物带(桑比阶中部)、大田坝组上部的Baltoniodusalobatus生物带(凯迪阶下部–桑比阶上部),以及大田坝组顶部–宝塔组下部的Hamarodus brevirameus生物带(凯迪阶中部)。这一台地边缘相区的牙形刺生物地层序列与扬子台地中心相区的湖北宜昌、重庆石柱及南京江宁等地的牙形刺生物带几乎一致,与斜坡相区的牙形刺生物带也可以进行很好的对比,为台地边缘相区、中心相区以及斜坡相区地层精细对比提供了新的依据,也证明了湖南永顺、桃源(茅草铺)地区应属于扬子台地区。

This contribution documents the late Darriwilian to middle Katian conodonts recovered from four stratigraphic sections exposed in Yongshun and Taoyuan of Hunan Province, South China. Previously only two conodont biozones(i.e., Pygodus anserinus-Yangtzeplacognathus jianyeensis Biozone and Pygodu serra Biozone) were known from the stratigraphic interval in these areas of Hunan. In our study, five conodont biozones are recognized, including ascendingly the Pygodus serra Biozone in the top part of the Kuniutan Formation(late Darriwilian), the Pygodus anserinus-Yangtzeplacognathus jianyeensis biozones in the lower Datianba Formation(latest Darriwilian–early Sandbian), the Baltoniodus variabilis Biozone in the middle of Datianba Formation(middle Sandbian), the Baltoniodus alobatus Biozone in the upper of Datianba Formation(late Sandbian–early Katian), and the Hamarodus brevirameus Biozone in the Pagoda Formation-top part of the Datianba Formation(middle Katian). This conodont succession recognized in Hunan is almost identical to those established in other parts of the Yangtze Platform, particularly those from Yichang of Hubei Province, Shizhu of Chongqing and Jiangning of Nanjing. Therefore, the establishment of these biozones provides new crucial data for a precise correlation of the Middle–Upper Ordovician rocks in Hunan with those from the other well-studied areas on the Yangtze Platform of South China.