Conodont Biostratigraphy and Age Determination of the Lower-Middle Triassic Boundary in South Guizhou Province, China

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	Conodont Biostratigraphy and Age Determination of the Lower-Middle Triassic Boundary in South Guizhou Province, China
	Yao, JX (Yao Jianxin); Ji, ZS (Ji Zhansheng); Wang, LT (Wang Liting); Wang, YB (Wang Yanbin); Wu, ZJ (Wu Zhenjie); Liu, DY (Liu Dunyi); Wu, GC (Wu Guichun); Zhang, JW (Zhang Jianwei); Li, SP (Li Suping)
刊名	ACTA GEOLOGICA SINICA-ENGLISH EDITION
	2011
卷号	85 期号:2 页码:408-420
关键词	L-M Triassic Qingyan Stage conodont biostratigraphy isotope chronology South China
ISSN号	1000-9515
英文摘要	The demarcation of the Lower Middle Triassic boundary is a disputed problem in global stratigraphic research. Lower Middle Triassic strata of different types, from platform to basin facies, are well developed in Southwest China. This is favorable for the study of the Olenekian-Anisian boundary and establishing a stratotype for the Qingyan I Stage. Based on research at the Ganheqiao section in Wangmo county and the Qingyan section in Guiyang city, Guizhou province, six conodont zones have been recognized, which can be correlated with those in other regions, in ascending order as follows 1, Neospathodus cristagalli Interval-Zone; 2, Neospathodus pakistanensis Interval-Zone; 3, Neospathodus waageni Interval-Zone; 4, Neospathodus homeri-N. triangularis Assemblage-Zone; 5, Chiosella timorensis Interval-Zone; and 6, Neogongdolella regalis Range-Zone. An evolutionary series of the Early Middle Triassic conodont genera Neospathodus-Chiosella-Neogongdolella discovered in the Ganheqiao and Qingyan sections has an intermediate type named Neospathodus qingyanensis that appears between Neospathodus homeri and Chiosella timorensis in the upper part of the Neospathodus homeri-N. triangularis Zone, showing an excellent evolutionary relationship of conodonts near the Lower Middle Triassic boundary. The Lower Middle Triassic boundary is located at 1.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Qingyan section, whereas this bound is located 0.5 m below the top of the Ziyun Formation, where Chiosella timorensis Zone first appears in the Ganheqiao section. There exists one nearly 6-m thick vitric tuff bed at the bottom of the Xinyuan Formation in the Ganheqiao section, which is usually regarded as a lithologic symbol of the Lower Middle Triassic boundary in South China. Based on the analysis of high-precision and high-sensitivity Secondary Ion Mass Spectrum data,the zircon age of this has a weighted me (206)Pb/(238)U age of 239.0 +/- 2.9 Ma (2 sigma), which is a directly measured zircon U-Pb age of the Lower Middle Triassic boundary. The Ganheqiao section in Wan so county can therefore provide an excellent section through the Lower Middle Triassic because it is continuous, the evolution of the conodonts is distinctive and the regionally stable distributed vitric tuff near the Lower Middle Triassic boundary can be regarded as a regional key isochronal layer. This section can be regarded not only as a standard section for the establishment of the Qingyan Stage in China, but also as a reference section for the GSSP of the Lower Middle Triassic boundary.
学科主题	地层学与地史学
WOS关键词	PB
WOS研究方向	Geology
语种	英语
出版者	WILEY-BLACKWELL
WOS记录号	WOS:000289845800014
内容类型	期刊论文
源URL	[http://119.78.100.197/handle/2HKVOGP0/39360]
专题	中国地质调查局
作者单位	Guizhou Bur Geol & Mineral Resources, Guiyang 550004, Peoples R China
推荐引用方式 GB/T 7714	Yao, JX ,Ji, ZS ,Wang, LT ,et al. Conodont Biostratigraphy and Age Determination of the Lower-Middle Triassic Boundary in South Guizhou Province, China[J]. ACTA GEOLOGICA SINICA-ENGLISH EDITION,2011,85(2):408-420.
APA	Yao, JX .,Ji, ZS .,Wang, LT .,Wang, YB .,Wu, ZJ .,...&Li, SP .(2011).Conodont Biostratigraphy and Age Determination of the Lower-Middle Triassic Boundary in South Guizhou Province, China.ACTA GEOLOGICA SINICA-ENGLISH EDITION,85(2),408-420.
MLA	Yao, JX ,et al."Conodont Biostratigraphy and Age Determination of the Lower-Middle Triassic Boundary in South Guizhou Province, China".ACTA GEOLOGICA SINICA-ENGLISH EDITION 85.2(2011):408-420.