Phenomenal Diachroneity in the Upper Boundary of the Lower Ordovician Hunghuayuan Formation in the Upper Yangtze Region, South China
详细信息
- 责任者：Liao Hanqing (School of Earth and Space Sciences ; Peking University ; Beijing 100871 ; China) ; Liu Jianbo
- 刊名：Acta Palaeontologica Sinica
- 出版年：2013
- 卷期：52(1)
- 关键词：红花园阶 ; Honghuayuanian Stage ; 穿时性 ; diachronism ; 扬子地区 ; Yangtze Region
- 页码：p.18-34
- 图表：illus., 63 refs.
- 分类号：1200
- issnNo：ISSN0001-6616
- isbnNo：CN32-1188/Q
摘要
During early Floian ( Early Ordovician ) time , extensive shallow-marine carbonates ( named the Hunghuayuan Formation ) were deposited on the Yangtze platform , which were gradually replaced by the deposition of terrigenous clastics and mixed carbonate-siliciclastic sediments later.In the meantime , the biodiversity of the marine biota increased rapidly , and reached its first acme in the middle Floian.Thus , further studies on the lithostratigraphic and chronostratigraphic successions of the upper Hunghuayuan Formation is necessary , as there are still some ongoing debates over its diachroneity. Diverse conodont faunas recovered from the studied sections ( Honghuayuan of Tongzhi and Houtan of Xishui , northern Guizhou Province , Gudongkou of Xingshan , western Hubei Province , and Wentang of Zhangjiajie , northwestern Hunan Province ) indicate that three conodont biozones could be recognized from the Hunghuayuan Formation , i.e. , the Serratognathus diversus Biozone , the Prioniodus honghuayuanensis-Oepikodus communis Biozone , and the Oepikodus evae Biozone. The top of the Hunghuayuan Formation , marked by the vanishing surface of medium-to thick-bed-ded lime grainstones in the Upper Yangtze region is substantially diachronous from the S.diversus to the O.evae biozones.The upper boundary of the formation in most part of the Upper Yangtze platform is in the P.honghuayuanensis-O.communis Biozone.However , this part of the formation gets progressively younger ( in the O.evae Biozone ) towards the northern and southern marginal areas of the Yangtze platform.The upper boundary of the formation on the western platform which is in close association to the depositional area of terrigenous clastics lies within the S.diversus Biozone.The spatial distribution of this phenomenal diachroneity in the upper boundary of the Hunghuayuan Formation of the Upper Yangtze platform was possibly controlled by a rapid eustatic sea-level rise as well as an increase in the terrigenous supply due to erosion from the western areas.
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