晚奥陶世五峰期扬子板块沉积模式

本文从沉积相分析及稀土元素地球化学特征来探讨扬子板块在晚奥陶世五峰期的沉积模式,认为五峰期扬子板块南部为古陆,东西北为断续分布的碳酸盐岩台地、生物礁和隆起区所环绕,中部为半封闭的浅水滞流海盆,稀土元素分析表明扬子扳块中部广泛分布的五峰组形成于陆浅海而非深海小洋盆。

Sedimentary Environment Pattern of Yangtz Plate in Wufeng Age of Late Ordovician

Strata of Wufeng age are widely distributed in Yangtze Plate,and our sedimental types can be recognized from east to west, i.e., Yushan, Yuqia.Yichang and Hanyuan type. Yichang type is characterized by graptolite black shales Wufeng Formation Two different opinions about the sedimental environment of Wufeng Formation have been arguing in recent years: i.e., shallow sea deposits or deep sea deposits. Based on the paleontology, petrogrphic characteristics,especialy the analyses of the rare earth elements, the authors concluded that the graptolite black shales of Wufeng Formation were deposited in a epicontinemal shallow restricted basin. Yushan type consists mainly of micritic limestone, bird-eye limestone and shales bearing abundant algae, corals, brachiopods, trilobites. This type constructs some isolated carbonate reef platformes staning on the southeast margin of the restricted basin. Between the restricted basin and carbonate reef platformes, there is a depression trough filled by shallow water flysch deposits called Yuqian Formation or Changwu Formation. Hanyuan type developed in the west part of Yangtze Plate and consists of carbonate rocks and black shales, representing another type of reef carbonate platform and ramp.