Graptolite fauna of the Hungshihyen Formation (Early Ordovician), eastern Yunnan, China

Abstract

Ordovician graptolite-bearing strata in eastern Yunnan were deposited in nearshore, shallow-water environments. Graptolites are systematically described from three sections through the Hungshihyen Formation in eastern Yunnan Province, China: (1) Hongshiya section near Ercun village, Kunming; (2) Liujiang section, Luquan; and (3) Guihuaqing Reservoir section, Luquan. The graptolite fauna, characterized by the predominance of deflexed forms, includes ten species in two genera: Baltograptus turgidus (Lee), B. varicosus (Wang), B. yunnanensis (Li), B. calidus (Ni), B. enshiensis (Ni), Baltograptus sp. cf. B. deflexus (Elles & Wood), Baltograptus sp. cf. B. bolivianus (Finney & Branisa), Baltograptus sp. A, Baltograptus sp. B and Corymbograptus v-fractus minor (Li). A detailed morphological study of these southern Chinese graptolite faunas suggests that Baltograptus wudingensis (Li) is a junior synonym of B. turgidus (Lee); Baltograptus kunmingensis (Ni) is a junior synonym of B. varicosus (Wang); and Baltograptus triangulatus (Ni) is a junior synonym of B. yunnanensis (Li). The B. varicosus Biozone is newly recognized within the middle part of the Hungshihyen Formation, replacing the former Didymograptus deflexus Biozone. This interval is well correlated to the Baltograptus jacksoni Biozone in Britain, the Tetragraptus akzharensis, ‘Baltograptus cf. deflexus’ and Didymograptus bifidus (lower part) biozones in NW Argentina (eastern Cordillera), and the Acrograptus filiformis and Didymograptellus eobifidus biozones in northern Guizhou, South China. Accordingly, the interval is of mid-Floian age, rather than late Floian as previously proposed.

云南东部含奥陶纪笔石的地层沉积于近岸浅水环境。对云南省东部Hungshihyen组的三个剖面的笔石进行了系统描述：（1）昆明二村附近的红石崖剖面; （2）鹿泉的柳江剖面;（3）鹿泉的Guihuaqing水库剖面。该笔石动物群的特点是下弯的类形为主，包括两个属十个种：Baltograptus turgidus (Lee)、 B. varicosus (Wang)、B. yunnanensis (Li)、 B. calidus (Ni)、 B. enshiensis (Ni)、 Baltograptus sp. cf. B. deflexus (Elles & Wood)、 Baltograptus sp. cf. B. bolivianus (Finney & Branisa)、Baltograptus sp. A、 Baltograptus sp. B 和 Corymbograptus v-fractus minor (Li) 。这些中国南方笔石动物群的详细形态学研究表明，Baltograptus wudingensis（Li）是B. turgidus（Li）的异名; Baltograptus kunmingensis（Ni）是B. varicosus（Wang）的异名; Baltograptus triangulatus（Ni）是B. yunnanensis （Li）的异名。在Hungshihyen组的中部新近建立了B.varicosus生物带，取代以往的Didymograptus deflexus生物带。这个层段可以与英国的Baltograptus jacksoni生物带、阿根廷西北部的Tetragraptus akzharensis、‘Baltograptus cf. deflexus’ 和Didymograptus bifidus （下部）生物带以及贵州北部的Acrograptus filiformis 和 Didymograptellus eobifidus 生物带相对比。因此，该层段应是弗洛阶中期，而非以往所认为的弗洛阶晚期。

Key words:

• Graptolite
• Early Ordovician
• Hungshihyen Formation
• Yunnan
• South China.

Acknowledgements

We thank Chen Xu and Jörg Maletz for helpful discussions and comments, and Blanca Toro, Bernie Erdtmann and Song Yanyan for discussions and help in the field. Financial support from the National Natural Science Foundation (41172034, 41221001) and the Ministry of Science and Technology (2011ZX05008-001-10) is acknowledged.