中国华北地台区寒武系与奥陶系的分界并简述有关三叶虫

Cambrian-Ordovician boundary in the North China platform With descriptions of trilobites

本文提出了华北地台区较完整的晚寒武世及早奥陶世三叶虫组合带序列,并记述了一些寒武系与奥陶系界线附近的有关三叶虫。据本区笔石与三叶虫动物群层位关系的研究,表明特马豆克阶的底界应在笔石 Dictyonema flabelliforme sociale-Staurograptus 带之下的三叶虫 Richardsonella (Richardsonel fa)-Troedssonia组合带的底部。鉴于本区这一实证,国际寒武系与奥陶系的分界,似也应划在 Mictosaukia 组合带与 Richardsonella (Richardsonella)-Troedssonia 组合带之间。

The boundary between the Cambrian and Ordovician sys terns is a moot question, challenged internationally by those who are engaged in the study of the Cambrian and Ordovician stratigraphy. The major disagreement involves wheter the Cambrian-Or-dovician boundary should be placed at the base of Tremadoc or much higher, at the mid-Tremadoc or nearthe base of Arenig. The first opinion has been unanimously accepted by Cheese stratigraphers, however, the base of the Tremadoc is selected for the base of the Ordovician.The late Cambrian Fengshan Formation and the Tremadoc Yeli Formation are conformable in the North China platform and include a record of continuous trilobite succession across the Cambrian-Ordovician boundary. In sections of southern Jilin, interbed-ded linestones and shales contain rich platform trilobite faunas which give complete succession of North China zones. The stratigraphic relationship between graptolites and tri lobites shows that the base of the Tremadoc lies below Dictyonema flabelliforme sociale-Staurograptus zone at the base of Richaidsonella (Richardsonella)-Troedssonia Assemblage Zone. It seems reasonable to conclude that the Camdrian-Ordovician boundary should be drown between the Mictosaukia and Richardsonella (Richardsonella)-Troedssonia assemdlage zones.