Discussion on the Bottom of Nanhua System: Evidences from Sedimentology and Isotopic Geochronology
详细信息
- 责任者：Wang Zhengjiang (Chengdu Institute of Geology and Mineral Resources ; Ministry of Land and Resources ; Chengdu 610082 ; China) ; Xu Xiaosong
- 刊名：Advances in Earth Science
- 出版年：2013
- 卷期：28(4)
- 关键词：冰期 ; glacial stage ; 南华纪 ; Nanhua Period ; ICP—MS ; inductively coupled plasma mass spectroscopy
- 页码：p.477-489
- 图表：illus., 1 table, 46 refs.
- 分类号：1200
- issnNo：ISSN1001-8166
- isbnNo：CN62-1091/P
摘要
At present,it is far from to get an agreement on the subdivision and correlation of Nanhua System,the mainly origins of this dispute are from the different understand to the tectonic attribute and the top limit age of Banxi Group and its equivalents.For this reason,based on the survey of sedimentology,the isotopic geochronology was carried out on the Longli Formation section of Xiajiang Group in Dunzhai of Jinping county,the Gongdong Formation section of Danzhou Group in Piaoli of Longsheng county,and the Gongdong Formation section of Danzhou Group in Pingtan of Tongdao county.The sedimentary survey indicates that the transforming boundary between Banxi Period and Nanhua glacial Period are clear.The petrofacies,petrofabric,sedimentary structure,and sedimentary sequence are greatly different from the upper units to the lower units of the boundary,which suggest obviously this boundary had seen a important sedimentary and tectonic event.At the same time,the isotopic geochronology from the tuffite and tuffaceous rocks of the top units of the Banxi Period make clear that the top limit age of Banxi Group and its equivalents should be tend to 720 Ma,and similar to the onset age 718 Ma of Sturtian glacial epoch.Based on the evolution phases of sedimentary basin,the comparability of global paleoclimate change and the geochronologic data,therefore,it is feasible to settle the bottom of Nanhua System upon the bottom of sedimentary sequence of Jiangkou glacial epoch,and it is also reasonable to put the onset age of Nanhua glacial Period at 720 Ma for the time being,and which would,thus,provide the essential constraints of sedimentology and isotopic geochronology to select the GSSP of Nanhua System.
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