A New Section of Kaili Formation (Cambrian)

Home , Bathynotus, Jianhe County, Kaili Formation, Oryctocephalus, Ovatoryctocara, Taijiang County

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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 specimens 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 environment 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 kueichouensis, 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 indicus (Reed, 1910) granulata Tchernysheva, 1962 have also been suggested as key species for defining the base of Cambrian Series 3 The FAD of Oryctocephalus indicus (Reed, 1910) was [5,20]. At present, the controversy about the use of O. indi- first proposed as a marker of the base of the traditional cus as a defining mark of the base of Cambrian Series 3 Middle Cambrian of China by Yuan et al. [13]. Sundberg concerns its geographical range. A global distribution is and McCollum also consider that the FAD of Oryctoceph- key for correlation of the global boundary between Cam- alus indicus occurs above the traditional Lower-Middle brian Series 2 and Series 3. Cambrian boundary. The redlichiids Redlichia or Olenellus and Bathynotus were confined to intervals below the 3.1. Oryctocephalus reticulatus (Lermontova, 1940) boundary in both South China and Western North Amer- ica, providing a stratigraphic tie-point for correlating the Oryctocephalus reticulatus was established by Lermont- Lower-Middle Cambrian boundary of both regions ova in 1940 according to specimens from Siberia, Russia [6,14]. The proposal that the FAD of O. indicus should (Fig. 5d and e). The species specimens were figured in many define the base of the Cambrian Series 3 has been accepted Russian language publications [21–24], especially in mono- by many scholars, including those from the International graphs of oryctocephaliids [25]. Based on these documents, Cambrian Subcommission [7,15–19]; although Arthrico- the species described occur in the middle part of Kounamkites cephalus chauveaui Bergeron, 1899 and Ovatoryctocara Zone of Amganian Stage near the Molodo River of Siberia, 1552 Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556

Fig. 3. Trilobites from the Bathynotus holopygus-Ovatoryctocara granulata Assemblage-zone in the Kaili Formation in the Jianshan section, Chuandong, Guizhou Province, China. Specimens are deposited in the Palaeontological Museum of Guizhou University, Guiyang, China. (a) Chittidilla (Diandongaspidella) brevis Lu and Zhang in Zhang et al., 1980; dorsal exoskeleton, GJCJ-29.50-2; (b) Olenoides hubeiensis (Sun, 1984); pygidium, GJCJ- 35.50-6; (c) Nangaops brevis Yuan and Sun in Zhang et al., 1980; dorsal exoskeleton, GJCJ-20.80-6; (d) Probowmania (P.) balangensis Yuan and Zhao in Yuan et al., 1997; dorsal exoskeleton, GJCJ-32.30-4; (e) Ovatoryctocara granulata Chernysheva, 1962, dorsal exoskeleton, GJCJ-32.00; (f) Oryctocephalops guizhouensis Zhao and Yuan, 2002. Dorsal exoskeleton, GJCJ-43.65-5; (g and h) Bathynotus kueichouensis Lu, 1964; (g) dorsal exoskeleton, GJCJ-30.15-4; (h) dorsal exoskeleton, GJCJ-34.60-5. Scale bars are 5 mm except those in (e and f) which are 2 mm.

Russia. Comparison of specimens of O. indicus (formally and pygidia from the Amecephalus arrojosensis Zone of the O. indicus latus) from the Kaili Formation with pictures of Emigrant Formation of Split Mountain and the Goldfield O. reticulatus in monographs of oryctocephaliids suggests Hills of western Nevada, USA. The Amecephalus arrojosen- that there is no discrepancy: these specimens previously sis Zone lies just below the Oryctocephalus indicus Zone. assigned to Oryctocephalus reticulatus may be the synonym A. arrojosensis differs from Oryctocephalus indicus (Reed, of Oryctocephalus indicus (Reed, 1910) [9,10]. In 2005 and 1910) in having only one transglabellar furrow (S1) and 2007, separately in Guiyang, China and Moscow, Russia, two pairs of pygidial marginal spines. However, close scru- authors had examined in detail many specimens of O. retic- tiny of the cranidia of A. arrojosensis (Sundberg and McCol- ulatus from Siberia, and reached the conclusion that some lum, 2003, pl. 4, Figs. 1–4) [6] under magnification reveals specimens among O. reticulatus should be assigned to that there are two more pairs of very shallow transglabellar Oryctocephalus indicus. Those cranidia have subcylindrical furrows (S2 and S3). The same shallow transglabellar galbella with 3 pairs of shallower transglabellar furrows as furrows may also be seen in Oryctocephalus indicus (Reed, same as those of O. indicus (latus) from the Kaili Formation 1910) from China (pl. 18, Fig. 4; pl. 20, Figs. 5 and 6; pl. [9,10]. Recently this view has been accepted by many scholars 22, Fig. 5) [11], including specimens from the base of the Ory- [26–28]. According to Russian documents, Ovatoryctocara ctocephalus indicus Zone at the Pingzhai section in Danzhai granulata Tchernysheva, 1962 also occurs in lower part of County (Fig. 5i), about 80 km to the southwest of the Balang the Amganain stage. If the FAD of Oryctocephalus indicus section, where the deposits of the Kaili Formation represent lies at the base of the international Cambrian Series 3, based deeper water environments of the outer shelf to slope [29–31]. on the criterion of the boundary between Oryctocephalus These specimens of O. indicus have as same diagnosis as indicus Zone and Ovatoryctocara granulata–Bathynotus those from North America [6,11]. We consider that Orycto- holopygus Zone in South China, then the boundary between cephalus americanus Sundberg and McCollum 2003 may rep- Cambrian Series 2 and Series 3 would replace the lower part resent a primitive form of Oryctocephalus indicus (Reed, of the Kounamkites Zone within the Amganian Stage in 1910). Therefore, Oryctocephalus americanus Sundberg and Siberia, Russia (Table 1). McCollum, 2003 should be a synonym of O. indicus. Because the biostratigraphic sequences of the O. indicus Zone of both 3.2. Oryctocephalus americanus Sundberg and McCollum, 2003 South China and western North America may completely correlate, the boundary between Cambrian Series 2 and Oryctocephalus americanus Sundberg and McCollum, Series 3 replaces the boundary between the Olenellus and 2003 (Fig. 5a–c) was erected based on specimens of cranidia Amecephalus arrojosensis zones of North America (Table 1). Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556 1553

Fig. 4. Trilobite distribution in the interval from 0 to 83 m above the base of Kaili Formation, (more than 200 m in thickness), Chungdon, Jianhe (formally Taijiang), Guizhou, China.

3.3. Oryctocephalus indicus (Reed, 1910) from the Kaili in eastern Guizhou, South China, but the thickness of the Formation Kaili Fm. varies from 50 m to 326.2 m. The stratigraphic interval of O. indicus (sensu lato) ranges from 64.8 m to Previously, specimens of Oryctocephalus indicus (Reed, 87.59 m at Balang, Jianhe County [8,11], only slightly more 1910) from South China were erroneously identified as than 10 m in the Zupin Zhenyuan area of eastern Guizhou, new species, Oryctocephalus incurvus Lu and Chien, 1974 where the Kaili Formation is just over 60-m thick [35,36]. [32,33] (p. 101, pl. 39, Fig. 8 and p. 270, pl. 96, Figs. 13 Therefore the stratigraphic interval of O. indicus range is and 14), but in 1997 were revised as O. indicus (Reed, a direct ratio of the total thickness of the Kaili Formation 1910) [13,34]. At the same time, the FAD of O. indicus at each locality. In eastern Guizhou, O. indicus has not only (Reed, 1910) was first proposed to mark the base of the tra- a long stratigraphic range but is also abundant, with up to ditional Middle Cambrian in China. Subsequently, the six individuals per 20 cm2 at the Wuliu-Zengjiayan section. FAD of this species was proposed to define the base of At present, we have collected over 800 specimens of O. indi- the Taijiangian [15]. Oryctocephalus indicus (Reed, 1910) cus (sensu lato) in eastern Guizhou. Previously, with diag- has a wide distribution in the Kaili Formation of south- nosis of fixigena width, glabellar tapering, length of eastern Guizhou. The Kaili Formation is well developed thoracic pleural spines and pygidial marginal spines O. 1554 Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556

Fig. 5. Oryctocephalus indicus (Reed, 1910) from the Kaili Formation, Guizhou Province, China, the Emigrant Formation, Split Mountain section, Nevada, USA and the Kuonamka Formation, Siberia, Russia. Specimens with prefix USNM are deposited in the National Museum of Natural History of the United States; those with prefix GTB, P, GJCJ in the Palaeontological Museum of Guizhou University, Guiyang, China, and those with K-2-31 and 15/13a separately from Molodo River Section by Igor Korovnikov provided and Egorova et al. (a–c) Specimens from Split Mountain Nevada, USA formerly assigned to O. americanus Sundberg and McCollum, 2003; (a) cranidium, USNM41964(in Sundberg and McCollum, 2003, pl. 4, Fig. 2); (b) cranidium, USNM410808; (c) cranidium, USNM517587(in Sundberg and McCollum, 2003, pl. 4, Fig. 3); (d) specimen from Molodo River section, Siberia, formerly assigned to O. reticulatus (Lermontova, 1940), K-2-31; (e) specimens from Siberia, Russia, by Egorova et al. (1976; pl. 49, Fig. 14, pl. 51, Fig. 4), 15/13a; (f–i) specimens from the Kaili Formation, formerly assigned to O. indicus latus Zhao and Yuan, 2002; (f) cranidium P4-2-120 from Pingzhai section at Danxhai County; (g) cranidium, GTB-17-1-121, the holotype of O. indicus latus Zhao and Yuan (in Yuan et al., 2002, pl. 20, Fig. 4) from Wuliu-Zengjiayan section at Balang, Jianhe County; (h) cranidium, GTB13-3-188 from Wuliu-Zengjiayan section; (i) cranidium, GJCJ-55.90-15 from Jianshan section at Chuandong, Jianhe County. All scale bars are 1 mm. indicus (sensu lato) was subdivided three subspecies: O. criteria of biotic evolution, the FAD of various organisms indicus indicus, O. i. latus, and O. i. kobayashi [11], but is often consistent with an equivalent period of biotic these fine differences among the O. indicus indicus, O. i. evolution. This is the fundamental principle of biostrati- latus, and O. i. kobayashi could easily be explained by tec- graphical division. Therefore GSSPs should be established tonic distortion or ontogeny. Therefore these subspecies that reflect important biotic events over geological time. have been synonymized as O. indicus [8]. Perhaps more The FAD of Oryctocephalus indicus (Reed 1910) in dif- error could be the results of over-splitting of O. indicus into ferent Cambrian faunal realms is precisely consistent with subspecies, adding ambiguities to the species definition. such a biotic turning point, including mass extinctions of As mentioned above Oryctocephalus indicus (Reed, 1910) the redlichiid trilobites Redilichia, Bathynotus, Olenellus not only has a widespread distribution in Asia (Himalaya, and the corynexochid trilobite Arthricocephalus at the ter- Korea, South China), North America (western United States mination of Cambrian Series 2, which the FAD of O. indi- of America) [14,37], and Siberia, Russia, but also has distinct cus immediately overlies [2,9–13] as well extinction of some morphological features that may be easily recognized by acritarch taxa [38,39]. Above the FAD of O. indicus, many both specialists and non-specialists. Furthermore, the FAD new trilobite taxa occur, representing the beginning of a of O. indicus always occurs above the extinction events of prosperous period for the corynexochida and ptychopari- redlichiids in Asian and Siberian faunal realms and of olenel- ida. Previously, the boundary between Cambrian Series 2 lids in the North American faunal realm. Therefore, it is an and Series 3 was set between the Anabaraspis Zone of the ideal guide species for marking the base of Cambrian Series 3. Toyonian Stage and the Oryctocara Zone of the Amganian Stage in Siberia. However, due to the occurrence of O. indi- 4. Division of Cambrian Series 3 related to biotic evolution cus in the Kounamkites Zone [8,10,25,26], the boundary should be re-placed at the FAD of O. indicus within the The chronostratigraphic division is consistent with evo- Kounamkites Zone. This change places two different trilo- lutionary and environmental changes on Earth. Based on bite assemblages above and below the new boundary, Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556 1555

Table 1 Chart of boundary correlation between Cambrian 2 Series and Series 3 from South China, Siberia, Russia and North America

which belong to the different periods of biotic evolution; for the base of Cambrian Series 3. Trilobite assemblages above this boundary Oryctocephalus flourishes, Bathyno- occurring below and above the FAD of O. indicus have dis- tus, Oryctocephalops, Ovatoryctocara are quite common tinct disparity, which is coincident with a mass extinction below this boundary. This lower assemblage including the of trilobite taxa at the traditional Early-Middle Cambrian LAD of redlichiids in Siberia and the LAD of olenellids boundary, providing an excellent basis for global correla- in North America coincides with the redlichiid extinction tion of this important stratigraphic boundary. event, which defines the base of Cambrian Series 3 globally. The largest negative d13C excursions known from the Acknowledgements Cambrian occur at the proposed position of the base of Cambrian Series 3 [40–43]. This indicates the coincidence This work was supported by National Natural Science of perturbations in the carbon cycle, as reflected by d13C, Foundation of China (Grant Nos. 40672018 and with periods of biotic evolution in Cambrian realms. This 40762001), the Foundation of the Mobile Project of Sci- chemostratigraphical maker is present in the Great Basin ence and Technology of Guizhou Province (Grant No. and southern Canadian Rockies of Laurentia, and also in Gui Ji. 2007-4004), the Foundation of the Governor of South China and Siberia, making it a significant reference Guizhou Province (Gui E. 2006–7), the Key Project of datum for global correlation of the base of Cambrian International cooperation of Guizhou Science and Tech- Series 3 (Table 1). nology (Gui. Co. G. [2008]700110]), and the Alexander von Humboldt Foundation. The authors thank graduate 5. Conclusions students Yang Hong, Yao Lu, Chen Xin, and Li Binxia at Guizhou University for their assistance in the field work. The Jianshan section, located 8 km away from the Special thanks are go to Igor Korovnicov (Institute of highly fossiliferous Wuliu-Zengjiayan section at Balang, Petroleum Geology and Geophysics, Siberian Branch of Jianhe of eastern Guizhou, South China contains key trilo- Russian Academy of Sciences) for providing the bite species that allow a wide correlation of the major Cam- photographs of specimens collected from the Kuonamka brian faunal realms of the world. It is a good parastrotype Formation at the Molodo River, Siberia, Russia, and to for defining the base of global Series 3 of the Cambrian Dr. Robert R. Gaines (Pomona College, USA) for English System. If the view that O. reticulates and O. americanus writing of this manuscript. should be synonymized with O. indicus is accepted, then precise correlation of boundary between Cambrian Series 2 and Series 3 among South China, Siberia, North America References can be achieved. As documented here, Oryctocephalus indicus (Reed, 1910) is an excellent guide species to mark the [1] Taylor JF. History and status of the biomere concept. Memoirs Ass Aust Palaeontol 2006;32:247–65. base of Cambrian Series 3. At the present time, the [2] Zhao Y, Yuan J, Zhu L, et al. An advance in the research of the Wuliu-Zengjiayan section of Kaili Formation appears to Lower-Middle Cambrian boundary in South China and its prospects. be the most viable candidate for establishing the GSSP J Stratigr 2001;25(Suppl.):383–90, [in Chinese]. 1556 Y. Zhao et al. / Progress in Natural Science 18 (2008) 1549–1556

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