Available online at www.sciencedirect.com Progress in Natural Science 18 (2008) 1549–1556 www.elsevier.com/locate/pnsc A new section of Kaili Formation (Cambrian) and a biostratigraphic study of the boundary interval across the undefined Cambrian Series 2 and Series 3 at Jianshan, Jianhe County, China with a discussion of global correlation based on the first appearance datum of Oryctocephalus indicus (Reed, 1910) Yuanlong Zhao a,*, Jinliang Yuan b, Shanchi Peng c, Loren E. Babcock d, Jin Peng a,e, Qingjun Guo f, Jihpai Lin d, Tongshu Tai g, Ruidong Yang a, Yuxian Wang a a College of Resource and Environment Engineering, Guizhou University (Caijiaguan Campus), Guiyang 550003, China b Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China c State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China d School of Earth Sciences, Ohio State University, Columbus, OH 43210, USA e Department of Earth Sciences, Nanjing University, Nanjing 210093, China f State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China g Agency of Natural Protected Area of Gedong Fossil Fauna, Kaili 556000, China Received 15 March 2008; received in revised form 4 May 2008; accepted 14 May 2008 Abstract A trilobite biostratigraphic study of a new section of the Kaili Formation at Jianshan, Chuandong Village, Jianhe County, Guizhou is reported. Additional occurrences of key species associated with the Ovatoryctocara granulata–Bathynotus holopygus Zone and the overlying Oryctocephalus indicus Zone that were originally defined from the trilobite assemblages at the Wuliu- Zengjiayan section of the Kaili are reported from this new section. The first appearance datum (FAD) of Oryctocephalus indicus occurs at the 44.52 m above the base of the unit. Based on study of abundant specimens (n = 800) from the Kaili Formation, we argue that Oryctocephalus indicus is a widespread taxon with a global distribution. O. reticulatus (Lermontova, 1940) from themiddlepartoftheKounamkites Zone of the Amganian Stage in the Molodo River region of Siberia and O. americanus (Sundberg and McCollum, 2003) from Nevada, North America are similar to representatives of O. indicus which occur in the O. indicus Zone of the Kaili Formation. O. reticulatus and O. americanus are here synonymized with O. indicus (Reed, 1910). This study strengthens the Wuliu-Zengjiayan section of the Kaili Formation as a candidate section for a Global Stratotype for the base of the unnamed Cambrian Series 3. Ó 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved. Keywords: Jianshan section; Kaili Formation; Boundary; Cambrian Series 3; Guizhou China 1. Introduction The Kaili Formation in eastern Guizhou records both * Corresponding author. the mass extinction of redlichiid trilobites in the lower por- E-mail address: [email protected] (Y. Zhao). tion of the unit and the radiation of the ptychopariid and 1002-0071/$ - see front matter Ó 2008 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved. doi:10.1016/j.pnsc.2008.05.020 1550 Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556 corynexochid trilobites in the middle to upper portion of the unit. Due to its significance of documenting one of the most important trilobite faunal turnovers [1], the first appearance datum (FAD) of Oryctocephalus indicus at the Wuliu-Zengjiayan section of the Kaili Formation has been proposed as a candidate section for a Global Strato- type Section and Point (GSSP) for the base of the undefined Cambrian Series 3 [2–4]. However, several colleagues [5–7] have subsequently proposed alternative sections and/or tie-points for the base of Cambrian Series 3. Oryctocephalus indicus (Reed, 1910) is abundant in the Kaili Formation of the Kaili region in southeastern Guiz- hou. A total of 800 specimens of O. indicus were collected. Through detailed examination, some discrepancy was found among well preserved and poorly preserved speci- mens from this deep water environment. O. reticulatus (Lermontova, 1940) from the middle part of the Kounamk- ites Zone of the Amganian Stage in the Molodo River region of Siberia and O. americanus (Sundberg and McCol- lum, 2003) from Nevada, North America, are similar to poorly preserved O. indicus from the deeper water environ- ment of the Kaili Formation. They show the second and third transglabellar furrows (S2 and S3) which are not connected or are connected with shallower transglabellar Fig. 1. Map of geographical locations, transportation of Jianshan section of Kaili Formation and geology of Kaili Formation in Jianhe area, eastern furrows. Therefore, we argue that O. reticulatus and Guizhou, China. Notes of illustration about legends in ascending order: O. americanus should be synonymized with O. indicus which Ptbnb3 = Third member of the Proterozoic Banxi Group; Z1n = Nantuo occurs in deeper water environments. Because the water Sandstone Bed of the Lower Sinian Nantuo Formation; Z1nn = Glacial depth of Siberian and North American deposits bearing Drift Bed of the Lower Sinian Nantuo Formation; Z2d = Upper Sinian Oryctocephalus is deeper than that of the Kaili Formation Doushantuo Formation; Z2lc = Upper Sinian Liuchapo Formation; Z lc+d = Upper Sinian Liuchanpo Formation and Dengying (or Tongy- at Balang, Guizhou, the small discrepancy in morphology 2 ing) Formation; e1n = Lower Cambrian Niutitang Formation; may be related to taphonomic differences between the dee- e1b = Lower Cambrian Bianmachong Formation; e1p = Lower Cambrian per water environment and shallower environments. The Balang Formation; e1ts = Lower Cambrian Tsinghsutung Formation; FAD of O. indicus (Reed, 1910) in South China, Siberia e1–2k = Lower-Middle Cambrian Kaili Formation; e2j = Middle Cam- of Russia and North America is coincident with that in dif- brian Jialao Formation; e2–3ls = Middle-Upper Cambrian Loushankuan Formation. ferent Cambrian realmsand, this is also consistent with a turning point in trilobite evolution. Therefore, O. indicus is an important trilobite for the definition and correlation (the lowermost 83 m), the frequency of limestone–marl- of global stratigraphic boundary between Cambrian Series stone interbred decreases away from the base, and is dom- 2 and Cambrian Series 3 [8–10]. inated by calcareous mudrocks in the middle portion with During an excursion in 2006, a new well-exposed section increasing limestone and marlstone content in the upper of the Kaili Formation at Jianshan was located. This study portion (69–80 m above the base). Trilobites are common provides a detailed trilobite biostratigraphy from the lower locally, but the species richness is not as high as reported two thirds of the unit. The acritarch biostratigraphy and from the Wuliu-Zengjiayan section [11]. Trilobite zonation chemostratigraphy of this section will be addressed is adapted from the work done at the Wuliu-Zengjiayan elsewhere. section [12]. In the Ovatoryctocara granulata–Bathynotus holopygus Zone (see Fig. 3), the trilobite assemblage is 2. Jianshan section of Kaili Formation characterized by the occurrences of Bathynotus kueichou- ensis, Oryctocephalops guizhouensis, Ovatoryctocara granu- The section (site 3 in Fig. 1) is located along a ridge of lata, Nangaops brevis and N. elongatus. In the overlying Jianshan Mountain, which is 1.5 km west of Chuandong Oryctocephalus indicus Zone (Fig. 2), the trilobite Village. The Kaili Formation here is more than 200 m in assemblage contains abundant Oryctocephalus indicus, thickness and both the lower contact with the underlying Miaobanpoia triangulata, Euarthricocephalus (E.) taijiang- Tshinghsutung Formation and the upper contact with the ensis, Danzhaiaspis elongatus, Metabalangia yupingensis, overlying Jialao Formation are exposed. The Jianshan sec- Xingrenaspis xingrrenensis, Eosoptychopara (Danzhaina) tion is ca. 8 km NE of Wuliu-Zengjiayan section (site 1 in coina, Majiangia majiangensis, Kutsingocephalus qiannanen- Fig. 1). The Kaili Formation at this locality is mainly com- sis, Douposiella guizhouensis and Pagetia sp. Detailed prised of silty shale. In the studied interval of the section ranges of key species are shown in Fig. 4 (see Fig. 3). Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556 1551 Fig. 2. Trilobites from the Oryctocephalus indicus Zone of Kaili Formation, in the Jianshan section, Chuandong, Guizhou Province, South China. Specimens are deposited in the Palaeontological Museum of Guizhou University, Guiyang, China. (a) Oryctocephalus(O) latilimbatus Zhao and Yuan, 2002, cranidium, GJCJ-61.60-7; (b–c) Oryctocephalus indicus (Reed, 1910); (b) cranidium, GJCJ-55.90-15; (c) dorsal exoskeleton, GJCJ -58.20-3; (d) Euarthricocephalus (E.) taijiangensis Zhao and Yuan 2002, dorsal exoskeleton, GJCJ -46.45-2; (e) Pagetia taijiangensis Yuan and Zhao in Yuan et al., 1997, dorsal exoskeleton, GJCJ-62.50-35; (f) Majiangia majiangensis Lu and Qian, 1983, cranidium, GJCJ-67.80-7; (g) Kaotaia (K.) globosa Chang and Zhou in Lu et al., 1974; cranidium, GJCJ-70.65-8; (h) Danzhaiaspis quadratus Yuan and Zhou in Zhang et al., 1980; dorsal exoskeleton, GJCJ-70.60-23. Scale bars are 2 mm except those in (g and h) which are 5 mm. 3. On Oryctocephalus