浙江常山黄泥塘全球层型剖面的中奥陶世疑源类

浙江常山黄泥塘剖面在1996-1997年被国际奥陶系分会和国际地质科学联合会(IUGS)确立为全球中奥陶统达瑞威尔阶(Dariwillian)层型剖面,从该剖面宁国组Azygograptus suectcus-Exigraptus clavus笔石带至Undulograptus sinicus笔石亚带下部的页岩及灰岩中获得丰富的,保存不很好的疑源类化石,它们包含26个形态属,41个已知种和12个未定名种.该宁国组疑源类组合极少有环冈瓦纳古陆的“冷水“类型,根据疑源类类型在地层柱的首次出现,可划分两个与Azygograptus suecicus和Undulograptus austrodentatus笔石带相吻合的疑源类生物地层单元,结合中国南方在奥陶纪的古地理位置加以讨论,当前疑源类组合表明,中奥陶世环冈瓦纳古陆的“冷水“洋流至下扬子区已很微弱.

MIDDLE ORDOVICIAN ACRITARCHS FROM THE GLOBAL STRATOTYPE SECTION OF HUANGNITANG IN CHANGSHAN, ZHEJIANG, CHINA

The Huangnitang section-located in the Changshan County of Zhejiang Province- includes the Global StratotypeSection and Point (GSSP) of the upper Middle Ordovician Darriwilian Stage. Abundant, though not especially well preservedacritarchs have been obtained from the Ninguo Formation, specifically from the biostratigraphic interval comprising theAzygograptus suecicus and Exigraptus clavus graptolite zones (lower Middle Ordovician: Dawanian) and the succeedingDarriwilian Arienigraptus zhejiangensis and lower part of the Undulograptus sinicus graptolite subzones. The acritarchassemblage of the Ninguo Formation, thus sampled, consists of 26 genera, 41 known species, and 12 unnamed species; itcontains a paucity of Perigondwanan "cold water" forms. The assemblage is divisible into two successive biostratigraphicunits, based on acritarch first appearances and coinciding generally with the Azygograptus suecicus and Undulograptusaustrodentatus graptolite zones respectively. Taking into account the known acritarch distributions and the inferredpalaeogeography of South China, a cool oceanic current from Perigondwana affected the upper Yangtze region, but, to a muchlesser degree, the lower Yangtze region and the Jiangshan-Changshan-Yushan (JCY) area.