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Lower Triassic) Journal of Earth Science, Vol. 29, No. 4, p. 824–836, August 2018 ISSN 1674-487X Printed in China https://doi.org/10.1007/s12583-018-0795-3 A Taxonomic Re-Assessment of the Novispathodus waageni Group and Its Role in Defining the Base of the Olenekian (Lower Triassic) Zhengyi Lyu1, Michael J Orchard1, 3, Zhong-Qiang Chen2, Laishi Zhao*1, Lei Zhang1, Xiumei Zhang1 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China 2. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China 3. Natural Resources Canada, Geological Survey of Canada, Vancouver, BC, V6E4S6, Canada ABSTRACT: Lower Triassic conodont biostratigraphy has been well studied around the world in the past decades, but the Induan-Olenekian boundary (IOB) remains undecided. The Novispathodus waa- geni group has been taxonomically re-assessed based on abundant new materials from the Jianshi and Chaohu sections, South China. New study shows that Nv. waageni typically possesses: (1) an approx- imately equi-dimentional P1 blade element, (2) an accurate upper profile with denticle height descend- ing in both directions, (3) a denticulated posterior edge (lower denticles posterior of the highest den- ticle), and (4) a round basal cavity outline. Of the three proposed subspecies of the waageni species, both Nv. waageni waageni (Sweet, 1970) and Nv. w. eowaageni (Zhao and Orchard, 2005) are valid, and the former differs clearly from Nv. w. eowaageni in having (1) a slightly higher length/height ratio (holotype=1.30 : 1.23), (2) a thicker blade, sometimes with medial thickening, (3) fewer (broader) den- ticles per unit length, (4) generally recurved denticles, not straight and upright, (5) highest denticles closer to posterior, (6) common differentiation of a posterior cusp, and (7) more sinuous basal profile, with increased posterior upturning. A third subspecies illustrated as Nv. waageni n. subsp. A sensu Goudemand, 2014 is not conspecific with older individuals of Nv. w. eowaageni, and also cannot be as- signed to the Nv. waageni group. Abundant new materials demonstrate a clear ontogenic process for Nv. w. eowaageni, indicating that Nv. w. eowaageni occurring in the Induan−Olenekian boundary (IOB) succession is rather stable. Small, earlier individuals (i.e., those from Bed 225 in Jianshi) are referred to as Nv. w. eowaageni Morphotype A, and are thought to have likely evolved from Ns. dieneri Morpho- type 3, and to be the precursor of mature elements of Nv. w. eowaageni. The first appearance datum of Nv. w. eowaageni therefore is an ideal mark defining the IOB. KEY WORDS: Lower Triassic, evolutionary lineage, Novispathodus waageni eowaageni, Induan- Olenekian boundary, South China. 0 INTRODUCTION has been well accepted as a guide to determine stratigraphic Since 1960s, the International Commission on Stratigra- resolution for the Triassic. phy has worked to establish the global stratotype section and The Triassic contains three series and seven stages. The point (GSSP) for each stage for stratigraphic division and cor- Lower Triassic includes the Induan and Olenekian stages. The relations around the world. Conodont biostratigraphic study base of the Induan is also the Permian-Triassic boundary (PTB) established the age of strata and enabled intercontinental strati- (Yin et al., 2001). Orchard (2010) reviewed the distribution of graphic correlations through their global distribution, rapid conodont faunas across each of the stage boundaries within the evolution, and abundant occurrence in marine strata. Conodonts system. Of these, the GSSP for the base of the Induan (also the therefore are widely used as an important index fossil in strati- base of the Triassic) was selected in the Meishan Section, graphic division and correlations from the Cambrian to Triassic. Changxing County, Zhejiang Province, South China (Yin et al., In particular, conodonts also have a crucial role in providing a 2001), in which the first appearance of conodont Hindeodus precise Triassic timescale (Orchard, 2016), and their zonation parvus marks the PTB, which is calibrated to the base of Bed 27c (Chen et al., 2015b; Yin et al., 2001). In contrast, the *Corresponding author: [email protected] Induan-Olenekian boundary (IOB), the second GSSP of the © China University of Geosciences and Springer-Verlag GmbH Lower Triassic series, remains undefined. Growing evidence Germany, Part of Springer Nature 2018 shows that conodonts are very abundant across this stage boundary, and may potentially define the IOB (Orchard, Manuscript received June 3, 2018. 2007b). In particular, conodont elements of Novispathodus Manuscript accepted July 10, 2018. waageni group occur in the boundary beds worldwide (Fig. 1), Lyu, Z. Y., Orchard, M. J., Chen, Z.-Q., et al., 2018. A Taxonomic Re-Assessment of the Novispathodus waageni Group and Its Role in Defining the Base of the Olenekian (Lower Triassic). Journal of Earth Science, 29(4): 824–836. https://doi.org/10.1007/s12583-018-0795-3. http://en.earth-science.net A Taxonomic Re-Assessment of the Novispathodus waageni Group and Its Role in Defining the Base of the Olenekian 825 and they are a product of rapid evolution, and thus are strong 1 GEOLOGICAL AND STRATIGRAPHIC SETTINGS candidate index fossils for precisely defining the IOB. The restudied conodont specimens were extracted from The conodont segminate element Nv. waageni was first the samples collected from both the West Pingdingshan Section established from the Mianwali Formation of Salt Range, west- of Chaohu area, Anhui Province and the Jianshi Section of ern Pakistan (Sweet, 1970), and later has been widely reported western Hubei Province, South China (Fig. 2). The Chaohu from around the world, as shown in Figs. 1 and 2. area was located in a deep part of carbonate ramp on the north- As a result of its global distribution, the first appearance of ern margins of the Lower Yangtze Platform, while the Jianshi Nv. (previously Neospathodus) waageni sensu lato has been area was situated on the relatively shallower part of a carbonate widely accepted as a stratigraphic mark defining the IOB (Tong ramp on the northern margin of the Yangtze Platform during and Zhao, 2011; Krystyn et al., 2007; Zhao et al., 2007; Tong et the Permian-Triassic transition (Feng et al., 1997; Chen et al., al., 2004, 2003). Two candidate sections for the GSSP of the 2011; Lyu et al., 2018; Fig. 2). Both sections yield abundant IOB have been proposed on this basis: the West Pingdingshan conodont fossils throughout the entire Lower Triassic (Lyu et Section in Chaohu, Anhui Province, China where the first ap- al., 2018; Zhao et al., 2008a, b, 2007). The Chaohu Section has pearance datum (FAD) of Nv. waageni eowaageni has been been extensively studied since 1980s (Zhao et al., 2008a, b, proposed to define the boundary (Zhao et al., 2013, 2008a, b, 2007, 2005a, b, 2004, 2003; Tong et al., 2005, 2004; Ding, 2007; Tong and Zhao, 2011; Tong et al., 2004), and the Mud 1983). Zhao et al. (2007, 2005a) established eight conodont Section in Spiti, India (Krystyn et al., 2007, 2005; Orchard, zones for Lower Triassic succession in Chaohu. The continuous 2007a; Orchard and Krystyn, 2007). A third candidate section, conodont zonation has become an important reference for the in Nammal, Pakistan, has recently been proposed on the basis Lower Triassic stratigraphic correlations around the world. The of ammonoids (Ware et al., 2017). Uppermost Permian through Lower Triassic successions of the To date, many subspecies or variant forms of Nv. waageni Jianshi Section has been well studied by systematically sam- have been proposed and illustrated, and this has led to tax- pling for conodont biostratigraphy, and a total of nine conodont onomic uncertainty within the group, masked evolutionary zones has been established (Lyu et al., 2018; Fig. 3). traits of those important taxa, and thus prevented precise defi- nition of the IOB. Recently, Goudemand (2014) assigned va- 2 CONODONTS ACROSS THE INDUAN-OLENEKIAN riant forms to Nv. waageni and Nv. waageni eowaageni, and BOUNDARY questioned the utility of the latter subspecies in defining the Novispathodus waageni has been reported worldwide after IOB. Accordingly, a reappraisal of taxonomy and evolutionary its first report from Salt Range, western Pakistan (Sweet, 1970) lineage of Nv. waageni group is essential to provide better un- (Fig. 1). Later, two subspecies: waageni waageni and waageni derstanding of conodont evolutions across the IOB, and to offer eowaageni were established from Nv. waageni species popula- a reliable definition for its GSSP. tion based on materials obtained from Chaohu area (Zhao et al., Figure 1. Global occurrences of the Novispathodus waageni group during the Induan-Olenekian transition (Early Triassic) (base map after Scotese, 2014). Codes for fossil localities: 1. South Primorye, Russia (Shigeta et al., 2009); 2. northern Japan (Takahashi et al., 2009); 3. Southwest Japan (Isozaki, 1997); 4. Chaohu, Anhui, South China (Zhao et al., 2008a); 5. Hubei, South China (Lyu et al., 2018; Zhao et al., 2013); 6. Guizhou, southwestern China (Chen et al., 2015a; Ji et al., 2011; Jiang, 1980); 7. Guangxi, South China (Yang et al., 1986); 8. northeastern Vietnam (Maekawa et al., 2016); 9. Timor (Sweet, 1970); 10. Malay Peninsula (Metcalfe, 1990); 11. West Malaysia (Koike, 1982); 12. Northwest Tibet, China (Wu et al., 2007); 13. Afghanistan (Sweet, 1970); 14. northern Iran (Horacek et al., 2007); 15. United Arab Emirates (Clarkson et al., 2013); 16. Oman (Baud et al., 2012); 17. Salt Range, Pakistan (Shigeta et al., 2009); 18. Spiti, India (Orchard and Krystyn, 2007; Krystyn, 2005; Krystyn et al., 2004); 19. Kashmir, India (Bhatt et al., 1999); 20. Nepal (Hatleberg and Clark, 1984); 21. southern Tibet, China (Wang, 1995; Wang and Wang, 1976); 22. western Australia (Metcalfe et al., 2013); 23. Nevada, America (Clarkson et al., 2013); 24. Idaho/Utah, America (Clarkson et al., 2013; Solien, 1979); 25.
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