Journal of Earth Science  2017, Vol. 8 Issue (4): 595-613   PDF    
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Conodont and Ammonoid Biostratigraphies around the Permian-Triassic Boundary from the Jianzishan of South China
Ruoyu Bai, Xu Dai, Haijun Song    
State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China
Abstract: Conodonts and ammonoids have played significant roles in the Permian-Triassic timescale. In order to uncover the nature of the Permian-Triassic mass extinction and subsequent recovery, we studied conodont and ammonoid biostratigraphies around the Permian-Triassic boundary from Jianzishan of Hubei, South China. A total of four conodont zones and two ammonoid beds are recognized. In ascending order, the conodont zones are Late Changhsingian Clarkina changxingensis Zone, Clarkina yini Zone and Griesbachian Hindeodus parvus Zone, Hindeodus postparvus Zone; the ammonoid beds are Late Griesbachian Ophiceras beds and Early Dienerian Ussuridiscus varaha beds. At Jianzishan, Ophiceras beds are stratigraphically younger than Hindeodus parvus Zone, but it is likely to be the same level with Hindeodus postparvus Zone. The Lower Dienerian in Bed 8 in this section is characterized by ammonoid Ussuridiscus varaha beds, which is associated with many Late Griesbachian conodonts including Hindeodus postparvus, Hindeodus praeparvus, Hindeodus typicalis, Hindeodus pisai, Hindeodus latidentatus, Hindeodus parvus, Hindeodus anterodentatus and Isarcicella turgida, indicating these conodont species could pass through the Griesbachian-Dienerian boundary and occurred in the Early Dienerian oceans.
Keywords: Permian-Triassic    conodont    ammonoid    South China    stratigraphy    
0 INTRODUCTION

The Permian-Triassic mass extinction has been considered as the most severe biodiversity crisis in the Phanerozoic, which wiped out over 90% of marine species (Song et al., 2013; Erwin, 1994). Many hypothesis have been proposed to interpret the culprits of this catastrophic event, including the eruption of Siberian Traps (Wignall, 2001; Campbell et al., 1992), the elevated continental weathering (Song et al., 2015; Algeo and Twitchett, 2010), global warming (Joachimski et al., 2012; Sun Y D et al., 2012), ocean acidification (Clarkson et al., 2015; Liang, 2002), and ocean anoxia (Grasby et al., 2012; Song et al., 2012; Wignall and Twitchett, 1996). Biotic recovery following the Permian-Triassic mass extinction event has been taken more seriously in recent years, however, the tempo and mechanism are still in controversial. Some taxa such as conodonts, ammonoids and foraminifers began to recover in the Early Triassic (Brosse et al., 2013; Song et al., 2011; Brayard et al., 2009; Orchard, 2007). In contrast, other taxa such as corals and other reef building taxa seem to have a prolonged delay in recovery till Middle Triassic (Chen and Benton, 2012; Kiessling et al., 2002). In order to better understand these puzzling questions from the Permian-Triassic transition and its aftermath, a high-resolution biostratigraphy is essential. Both conodonts and ammonoids are important index fossils in the Permian and Triassic timescale for their abundance, extensive distribution and high evolutionary rates.

Conodonts did not suffer a seriously affection during the Permian-Triassic mass extinction event, yet the biostratigraphic resolution has been higher than that before the event (Clark, 1987), suggesting this kind of index fossil is able to establish a more accurate biostratigraphic frame during the crisis interval. Accordingly, conodonts from the Permian-Triassic transition have been widely studied around the world, including South China (Brosse et al., 2015; Jiang et al., 2014, 2011, 2007; Zhang N et al., 2014; Sun D Y et al., 2012; Zhang K X et al., 2009; Yin et al., 2001), North America (Paull, 1988; Clark, 1959), Alps (Chen et al., 2016; Perri and Farabegoli, 2003), Himalayas (Krystyn et al., 2003; Orchard and Krystyn, 1998), Australia (Metcalfe et al., 2013, 2008), Russia (Shigeta et al., 2009; Zakharov et al., 2005) and Japan (Xia et al., 2004). Research history of the Permian-Triassic conodonts in South China can trace back to 1970s, 40 years so far. Wang and Wang (1976) first documented the Triassic conodonts faunas in Everest. Yin et al. (1988) proposed that the first occurrence (FO) of Hindeodus parvus, which was first reported at Meishan Section by Zhang (1987), is a suitable marker for the base of Triassic. Since then, studies on conodont zones of the Permian-Triassic transition bloomed in South China. For example, Meishan Section of Zhejiang is the Global Stratotype Section and Point (GSSP) for the Permian-Triassic boundary (Yin et al., 2001) and has been discriminated 13 conodont zones (Zhang et al., 2009). Besides, 8 conodont zones have been recognized at the Shangsi Section (Jiang et al., 2011). Furthermore, abundant Permian-Triassic sections of shallow platform facies has been widely studied, including Yangou Section (Sun D Y et al., 2012), Cili Section (Wang L N et al., 2016; Wang Q X et al., 2009), Dawen Section (Liu et al., 2007), Dajiang Section (Jiang et al., 2014), Heping Section (Lehrmann et al., 2003) and Langpai Section (Ezaki et al., 2008). Meanwhile, Early Triassic conodont biostratigraphic work has been done quite well in South China, e.g., Chaohu Section (Zhao et al., 2005a), Qingyan Section (Ji et al., 2011), Bianyang Section (Yan et al., 2013), Guandao Section (Wang et al., 2005), Jiarong Section (Chen et al., 2015), Mingtang Section (Liang et al., 2016) and other sections in Guangxi area (Yan et al., 2015).

Ammonoid nearly died out during the Permian-Triassic mass extinction, but recovered rapidly, only ca. one million years after the extinction event, with extremely high origination and extinction rates during the Early Triassic (Brayard et al., 2009). Combining the widely distribution with highly turnover rates, ammonoid has been used to be a perfect index fossil since the nineteenth century (Waagen, 1895; Griesbach, 1880). Afterwards, numerous contributions from worldwide on the Early Triassic ammonoids were published, such as South China (Mu et al., 2007; Chao, 1959), Greenland (Spath, 1930), USA (Brayard et al., 2013; Smith, 1932), Spiti (Brühwiler et al., 2012a) and Salt Range (Brühwiler et al., 2012b), which lead to high-resolved ammonoid biozonations and possibility of worldwide correlation. In South China, the first Early Triassic ammonoids fauna was found near Guiyang (Tien, 1933), including several species of Ophiceras, which indicated a Late Griesbachian age. Then, Chao (1959) documented a diverse and well preserved ammonoids fauna from Luolou Formation of Guangxi. Since then, several Early Triassic ammonoids faunas were described (Mu et al., 2007; Tong et al., 2004; Xu, 1988). Unfortunately, most of these specimens were terribly preserved. Accordingly, the taxonomy, biostratigraphy and biodiversity were suspicious. Recent studies from Guangxi and Guizhou provide a good ammonoid biostratigraphic frame based on well preserved specimens, with four Induan ammonoid beds, i.e., Late Griesbachian Ophiceras beds, Early Dienerian Proptychites candidus beds and Late Dienerian Clypites beds (Brayard and Bucher, 2008; Brühwiler et al., 2008).

The correlations between the Permian-Triassic conodont zones and ammonoid beds have been done, but most of which are from different geological sections (e.g., Kolar-Jurkovšek and Jurkovšek, 2015; Wu et al., 2014; Ogg, 2012; Kozur, 2003). In contrast, conodont and ammonoid collections from the same section play a significant role in improving the accuracy of correlation (e.g., Komatsu et al., 2016; Zakharov and Kozur, 2010; Shigeta et al., 2009; Orchard, 2008; Orchard and Krystyn, 1998). In order to better understand the temporal distribution of conodont zones and ammonoid beds during the Permian-Triassic interval, we studied conodonts and ammonoids synchronously at the Jianzishan Section from Hubei, South China.

1 GEOLOGICAL SETTING

The Jianzishan (30 9′58.08ʺN, 109 0′27.5ʺE) Section is situated near Ruiping countryside of Lichuan, South China (Fig. 1). The Late Permian to the Early Triassic successions, being composed of Changxing and Daye formations, are well exposed in the Jianzishan Section. The upper Changxing Formation (Fig. 2c) consists of 6.7 m thick-bedded flinty bioclastic limestone, yielding well-diversified Permian-type biota, dominated by calcareous sponges, calcareous algae, gastropods, corals, brachiopods and foraminifers, representing a shallow-water carbonate platform facies. The lowermost part of the Daye Formation is characterized by thick-bedded microbialites (Fig. 2d), which is extensively expanded in the lowermost Triassic strata of the Yangtze carbonate platform (Yang et al., 2015, 2011; Jiang et al., 2014), yielding rare fossils, e.g., foraminifers and small gastropods. The overlying strata consist of medium-bedded limestone alternating with yellow shale (Figs. 2e, 2f, 2g), with abundant brachiopods (e.g., Lingula sp.), ammonoids as well as bivalves (e.g., Claraia sp., Pteria sp.), suggesting an outer platform facies.

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Figure 1. (a) Schematic map showing the studying sites (modified after Feng et al., 1997 and Lehrmann et al., 1998); (b) paleogeographic map illustrating the position of South China during the end-Permian extinction (modified after Scotese, 2001). NPJB. Nanpanjiang Basin.
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Figure 2. Outcrop photographs from the Jianzishan Section. (a) The panorama of the Jianzishan Section. (b) Permian-Triassic boundary in Jianzishan Section. (c) Bioclastic limestone in the Changxing Formation in Bed 1. (d) Microbialites in the Daye Formation in Bed 2. (e) Yellow shale in the Daye Formation in Bed 6 to Bed 7. (f) Thin to medium-bedded limestone interbedded with yellow shale in the Daye Formation in Bed 8. (g) Thin-medium bedded limestone in the Daye Formation in Bed 9 to Bed 11.
2 MATERIALS AND METHODS

In this study, conodonts and ammonoids in the upper Changhsingian and Induan succession at Jianzishan have been investigated bed-by-bed. In total of 48 conodont samples (each ~2 kg) and 31 ammonoid fossils were collected from Chang-xing and Daye formations, in which 17 conodont species (1 572 specimens) and 5 ammonoid species (31 specimens) were identified (Plates 14).

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Plate1. SEM photographs of the key conodont elements from Jianzishan. 1–2. Hindeodus anterodentatus (Dai and Zhang, 1989); 1. JZS-11+0.4, lateral view; 2. JZS-6+1.2, lateral view. 3–4, 8. Hindeodus latidentatus (Kozur, Mostler and Rahimi-Yazd, 1975); 3. JZS-1-D+2.0, lateral view; 4. JZS-1-D+1.5, lateral view; 8. JZS-4+0.1, lateral view. 5, 9. Hindeodus parvus (Kozur and Pjatakova, 1976); 5. JZS-2+1.2, lateral view; 9. JZS-6+1.2, lateral view. 6. Hindeodus eurypyge (Nicoll et al., 2002); JZS-2+0.5, lateral view. 7. Hindeodus cf. typicalis; JZS-2+0.5, lateral view. 10. Hindeodus pisai (Perri and Farabegoli, 2003); JZS-1-C+0.8, lateral view. 11. Hindeodus postparvus (Kozur, 1989); JZS-6+1.9, lateral view. 12, 16–17. Hindeodus praeparvus (Kozur, 1996); 12. JZS-6+1.2, lateral view; 16–17. JZS-2+0.5, lateral and upper view. 13–15. Hindeodus typicalis (Sweet, 1970); 13. JZS-1-D+1.5, lateral view; 14. JZS-1-D+0.5, lateral view; 15. JZS-1-C+0.8, lateral view. 18. Isarcicella turgida (Kozur, Mostler and Rahimi-Yazd, 1975); JZS-6+1.2, lateral and upper view.
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Plate2. SEM photographs of the key conodont elements from Jianzishan. 1–3. Clarkina yini (Mei et al., 1998); 1. JZS-1-D+1.0, upper view; 2. JZS-1-D+1.0, upper view; 3. JZS-1-D+2.0, latteral and upper view. 4–5. Clarkina changxingensis (Wang and Wang, 1981); 4. JZS-1-D+1.0, latteral and upper view; 5. JZS-1-A+0.5, upper view. 6–8. Clarkina carinata (Clark, 1959); JZS-8+1.3, upper view. 9–13. Clarkina deflecta (Wang and Wang, 1981); 9. JZS-1-A+2.0, upper view; 10. JZS-1-D+0.5, upper view; 11. JZS-1-D+2.0, upper view; 12. JZS-1-B+0.5, upper view; 13. JZS-1-A+0.5, upper view.
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Plate3. SEM photographs of the key conodont elements from Jianzishan. 1, 4. Clarkina changxingensis (Wang and Wang, 1981); 1. JZS-1-B+0.5, latteral and upper view; 4. JZS-1-D+1.0, latteral and upper view. 2–3. Clarkina planata (Clark, 1959); 2. JZS-8+1.3, latteral and upper view; 3. JZS-13+0.75, latteral and upper view. 5. Clarkina cf. tulongensis; JZS-13+0.75, latteral and upper view.
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Plate4. Photographs of the ammonoid elements from Jianzishan. 1. Ophiceras sp. indet.; JZS-6+1.4. 2. Vishnuites pralambha (Diener, 1897); JZS-8+1.05. 3. Jieshaniceras guizhouensis (Zakharov and Mu in Mu et al., 2007); JZS-8+0.65. 4. Ussuridiscus varaha (Diener, 1895); JZS-8+0.85. 5. Hubeitoceras yanjiaensis (Xu, 1988); JZS-8+0.45.

Both limestones and shales were collected to extract conodonts. Shale samples were processed using redox reaction of hydrogen peroxide with sodium dithionite until all samples were broken apart. Carbonate samples were dissolved in 10% acetic acid after coarsely crushing into ~2 cm3 size fragments. After filtered through 20-mesh and 160-mesh sieves, the residues were separated in 2.78–2.80 g/mL heavy liquid. Conodonts were selected carefully under a stereomicroscope from those sieved insoluble residues and well preserved conodonts were picked out to photograph by a scanning electronic microscope (Quanta200, SU8010) at the State Key Laboratory of Biogeology and Environmental Geology in China University of Geosciences (CUG), Wuhan.

Ammonoid samples were collected by mechanically decomposing decimeter-sized blocks from respective beds. Mechanical techniques, including pneumatic air scribe and electrical scribe, were later performed in the laboratory to work out morphologic details facilitating species-level identification. Specimens were photographed by Canon 70D camera with a micro lens EF 100 mm f/2.8.

3 CONODONT ZONATION

Abundant conodont fossils were recovered from Changhsingian and Induan at Jianzishan including 17 species in 2 genera, i.e., Clarkina changxingensis, C. deflecta, C. parasubcarinata, C. praedeflecta, C. yini, C. taylorae, C. planata, C. cf. tulongensis, C. carinata, Hindeodus eurypyge, H. praeparvus, H. typicalis, H. pisai, H. latidentatus, H. postparvus, H. parvus, H. anterodentatus and Isarcicella turgida. Four conodont zones were recognized, including two Changhsingian zones Clarkina changxingensis Zone and Clarkina yini Zone, two Griesbachian zones Hindeodus parvus Zone and Hindeodus postparvus Zone.

3.1 Clarkina changxingensis Zone

Lower limit: the bottom of this zone can't be recognized for the lower part of Jianzishan Section is covered; Upper limit: the FO of Clarkina yini. Associated taxa include Clarkina changxingensis, C. deflecta, C. parasubcarinata, C. praedeflecta, Hindeodus eurypyge, H. praeparvus, H. typicalis, H. pisai and H. latidentatus.

Clarkina changxingensis Zone was first established by Wang and Wang (1981) and termed as the Clarkina deflecta-Clarkina changxingensis assemblage from Changxing Formation at Meishan Section in South China. The age of this zone is recognized as Late Changhsingian (Wang and Wang, 1981). Clarkina changxingensis Zone has been found in Meishan (Yuan et al., 2014; Zhang et al., 2009; Mei et al., 1998), Xinmin (Zhang et al., 2014), Yangou (Sun D Y et al., 2012), Ganxi (Nafi et al., 2006) and Daijiagou (Yuan et al., 2015) of South China; Ubara, Gujo-hachiman and Tenjinmaru of Japan (Xia et al., 2004); Julfa of Iran (Ghaderi et al., 2014); Spiti of India (Orchard and Krystyn, 1998) and Transcaucasia of Russia (Zakharov and Kozur, 2010).

Correlated ammonoid zones include Rotodiscoceras-Pleuronodoceras Zone at Shangsi Section of South China (Lai et al., 1996); entire Paratirolites trapezoidalis Zone and lower part of Paratirolites waageni Zone in Julfa of Iran (Ghaderi et al., 2014).

3.2 Clarkina yini Zone

Lower limit: the FO of Clarkina yini; Upper limit: the base of the microbialite. Associated taxa include Clarkina changxingensis, C. deflecta, C. yini, Hindeodus eurypyge, H. praeparvus, H. typicalis, H. pisai and H. latidentatus.

Clarkina yini Zone was first established by Mei et al. (1998) and termed as the Clarkina yini-Clarkina zhangi assemblage from Changxing Formation at Meishan Section in South China. The age of this zone is recognized as Late Changhsingian (Mei et al., 1998). Clarkina yini Zone has been reported in Meishan (Yuan et al., 2014; Zhang et al., 2009; Jiang et al., 2007; Yin et al., 2001; Mei et al., 1998), Xinmin (Zhang et al., 2014), Yangou (Sun D Y et al., 2012), Ganxi (Nafi et al., 2006), Daijiagou (Yuan et al., 2015), Shangsi (Jiang et al., 2011), Bianyang (Yan et al., 2013), Daxiakou (Zhao et al., 2013) of South China, Ubara, Gujo-hachiman and Tenjinmaru of Japan (Xia et al., 2004), Wenbudangsang of Tibet (Wu et al., 2014) and Julfa of Iran (Ghaderi et al., 2014).

Correlated ammonoid zones include entire Stoyanowites dieneri Zone and lower part of Abichites stoyanowi Zone in Julfa of Iran (Ghaderi et al., 2014).

The absence of Hindeodus changxingensis Zone and associated conodont species like Clarkina meishanensis probably results from depositional hiatus that is widely recognized in the shallow-water facies of Yangtze Platform (Jiang et al., 2014; Yin et al., 2014). Therefore, we believe this hiatus at the base of the microbialite in Jianzishan is similar with that in Dajiang (Jiang et al., 2014) and Cili (Wang et al., 2016). Although the FO of Hindeodus parvus was at 0.5 m above the base of Bed 2, Sample JZS-2+0.5, we put the Permian-Triassic boundary at the base of the microbialite, as well as the upper limit of the Clarkina yini Zone and the lower limit of the Hindeodus parvus Zone.

3.3 Hindeodus parvus Zone

Lower limit: the base of the microbialite which has already discussed in Clarkina yini Zone; Upper limit: the upper limit can not be defined accurately. Comparing with the other microbialites sections, e.g., Langpai Section (Ezaki et al., 2008), Dajiang Section (Jiang et al., 2014), Dawen Section (Chen et al., 2008) and Gaohua Section (Wang et al., 2016), we roughly put the upper limit of Hindeodus parvus Zone above the microbialites in Bed 4. Associated taxa include Hindeodus latidentatus, H. parvus, H. pisai, H. typicalis and H. praeparvus.

Hindeodus parvus Zone is the oldest conodont zone in Triassic, and is widely distributed in Meishan (Yuan et al., 2014; Zhang et al., 2009, 2007; Yin et al., 2001), Xinmin (Zhang et al., 2014), Yangou (Sun D Y et al., 2012), Daijiagou (Yuan et al., 2015), Shangsi (Jiang et al., 2011), Bianyang (Yan et al., 2013), Jiarong (Chen et al., 2015), Daxiakou (Zhao et al., 2013) and Dajiang (Jiang et al., 2014) of South China; Wenbudangsang of Tibet (Wu et al., 2014); Lukač of Slovenia (Kolar-Jurkovšek et al., 2011); Transcaucasia of Russia (Zakharov and Kozur, 2010) and Spiti of India (Orchard and Krystyn, 1998).

Correlated ammonoid zones include middle part of Ophiceras Zone in Shangsi of South China (Jiang et al., 2011; Lai et al., 1996; Li et al., 1986), Otoceras latilobatum-Otoceras woodwardi Zone in Selong of Tibet (Wang and Wang, 1995), middle part of Otoceras concavum Zone in Arctic Canada (Orchard and Tozer, 1997) and upper part of Otoceras latilobatum Zone in Spiti of India (Orchard and Krystyn, 1998).

3.4 Hindeodus postparvus Zone

Lower limit: FO of Hindeodus postparvus without the presence of Isarcicella isarcica and Isarcicella staeschei; Upper limit: FO of Sweetospathodus kummeli which are not found at this section. Associated taxa: Hindeodus praeparvus, H. typicalis, H. pisai, H. latidentatus, H. parvus, H. postparvus, H. anterodentatus, I. turgida, Clarkina planata and C. cf. tulongensis.

Hindeodus postparvus was first established by Kozur (1989) based on the elements from the Ophiceras commune Zone at Nevada. Hindeodus postparvus Zone has been found in Lukač of Slovenia (Kolar-Jurkovšek and Jurkovšek, 2015; Kolar-Jurkovšek et al., 2011), Wenbudangsang of Tibet (Wu et al., 2014) and Spiti of India (Orchard and Krystyn, 1998).

Correlated ammonoid zones include upper Ophiceras tibeticum Zone in Spiti of India (Orchard and Krystyn, 1998), Ophiceras commune Zone in Moorman Ranch of Nevada (Kozur, 1989).

4 AMMONOID BEDS

Abundant ammonoid fossils were collected from Lower Daye Formation at Jianzishan including 6 species, i.e., Ophiceras sp. indet., Ussuridiscus varaha, Jieshaniceras guizhouensis, Vishnuites pralambha, Hubeitoceras yanjiaensis and Koninckites sp. indet.. Two ammonoid beds were recognized, including one Griebachian bed Ophiceras beds and one Dienerian bed Ussuridiscus varaha beds (Fig. 3).

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Figure 3. Conodonts and ammonoids distribution across the Permian-Triassic transition at Jianzishan Section. H.-Hindeodus, C.-Clarkina, I.-Isarcicella, U.-Ussuridiscus, C.Z.-conodont zone, A.B.-ammonoid beds.
4.1 Ophiceras Beds

This zone is characterized by the occurrence of Ophiceras sp. indet., which is seriously squashed and represent a Late Griesbachian age in Tibet, Canada, Spiti, Chaohu and Meishan (Figs. 4, 5).

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Figure 4. Comparison of the Induan conodont zones and ammonoid beds between Jianzishan Section and other areas in South China. H.-Hindeodus, C.-Clarkina, I.-Isarcicella, Ns.-Neospathodus, Sw.-Sweetospathodus, C.Z.-conodont zone, A.B.-ammonoid beds.
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Figure 5. Correlation of the Induan conodont zones and ammonoid beds of Jianzishan Section with other regions in the world. H.-Hindeodus, C.-Clarkina, I.-Isarcicella, Ns.-Neospathodus, Sw.-Sweetospathodus, A.F.-Ambitoides fuliginatus, C.Z.-conodont zone, A.B.-ammonoid beds.

Ophiceras has been reported widely in South China. Tien (1933) reported Ophiceras beds from the lower part of Daye Formation near Guiyang, which is characterized by Ophiceras sinesis, Ophiceras tingi and Ophiceras cf. demissum. The Ophiceras beds found in Jianzishan correlates with the Tien's Ophiceras beds. The Ophiceras Zone at Meishan Section of Zhejiang (Yin et al., 2001; Wang, 1984) and Qinglongshan Section of Jiangsu (Wang, 1984) are defined by the occurrence of Ophiceras, which also correspond to Ophiceras beds of Jianzishan Section. The Ophiceras-Lytophiceras Zone from Chaohu characterized by the occurrences of Ophiceras sp., Lytophiceras sp., Ophiceras demissum, Kymatites? sp. and Lytophiceras? sp. (Tong et al., 2004), also correlates to Ophiceras beds in Jianzishan. Ophiceras beds from Laren and Shanggan (Guangxi), defined by the occurrence of Ophiceras sp. indet., which might be juvenile individuals of Ophiceras sinesis indicates a Late Griesbachian age (Brühwiler et al., 2008).

4.2 Ussuridiscus varaha Beds

Ussuridiscus varaha beds is characterized by the occurrences of Ussuridiscus varaha, Jieshaniceras guizhouensis, Vishnuites pralambha, Hubeitoceras yanjiaensis and Koninckites sp. indet., which can correspond to the Proptychites candidus beds (Brühwiler et al., 2008; Tozer, 1994), and accordingly indicates an Early Dienerian age.

Ussuridiscus varaha has been found in South China (Brühwiler et al., 2008; Xu, 1988), South Primorye (Shigeta et al., 2009), Salt Range (Ware et al., 2015) and Spiti (Ware et al., 2015). Only in South Primorye (Shigeta et al., 2009), few specimens occurred in Late Griesbachian while most of them occurred in Early Dienerian. Ussuridiscus varaha has a wide extent in the Early Dienerian strata of South China, e.g., Xiaohe Section of Hubei (being assigned as 'Koninckites' (Xu, 1988)), Jieshan Section of Guizhou, Jinya, Waili, Shanggan, and Yu-ping sections of Guangxi (Brühwiler et al., 2008). Although Proptychites candidus has not been found at Jianzishan, we found Jieshaniceras guizhouensis, Vishnuites pralambha and Hubeitoceras yanjiaensis, which are typical forms in Proptychites candidus beds (see Brühwiler et al., 2008). In summary, Ussuridiscus varaha beds indicates an Early Dienerian age.

5 COMPARISON BETWEEN CONODONT AND AMMONOID BEDS AT JIANZISHAN

At Jianzishan, Ophiceras sp. indet. occurs in the upper part of Bed 6 and lower part of Bed 7 whereas Hindeodus parvus Zone occupies mainly microbialites part from Bed 2 to Bed 4. Hindeodus postparvus first occurs in the 1.4 m above the base of Bed 6 at Jianzishan, which is only 0.5 m above the base of Ophiceras beds (Fig. 3). Stratigraphically, Ophiceras beds is above Hindeodus parvus Zone. Although the upper limit of Hindeodus parvus Zone can not be recognized definitely at Jianzishan for the absence of Isarcicella isarcica and Isarcicella staeschei, it is clear that Ophiceras beds are younger than Hindeodus parvus Zone at Jianzishan but are comparable to Hindeodus postparvus Zone.

As we have discussed above, Ussuridiscus varaha beds indicate Early Dienerian in age. At Jianzishan, Ussuridiscus varaha beds co-occurs with conodonts Clarkina carinata, Clarkina planata, Hindeodus postparvus, Hindeodus praeparvus, Hindeodus typicalis, Hindeodus pisai, Hindeodus latidentatus, Hindeodus parvus, Hindeodus anterodentatus and Isarcicella turgida (Fig. 3), suggesting these conodont species could pass through the Griesbachian-Dienerian boundary and appeared in Early Dienerian strata. In fact, co-occurrence of Clarkina carinata and Clarkina planata and some Dienerian conodont species, e.g., Neospathodus kummeli and Neospathodus dieneri has been reported in many areas, such as Meishan (Zhang et al., 2007), Sichuan Basin (Jiang et al., 2000) and Nantuowan (Zhao et al., 2005b) of South China, Selong of Tibet (Wang and Wang, 1995), Guling of Spiti (Krystyn et al., 2004), and Wapiti Lake, Yukon Territories and Canadian Arctic of Canada (Orchard and Zonneveld, 2009; Orchard, 2007). Accordingly, the viewpoint that all hindeodid conodonts disappeared at the top of the Griesbachian stage (Kozur, 1998) is likely to reflect a local phenomenon.

6 CONCLUSION

A systematic study of conodont and ammonoid sequences at Jianzishan provides new information for the timescale from Late Changhsingian to Early Dienerian of Upper Yangtze Platform. Four conodont zones are identified from Late Changhsingian to Griesbachian, in ascending order, they are Clarkina changxingensis Zone, Clarkina yini Zone, Hindeodus parvus Zone and Hindeodus postparvus Zone. Two ammonoid beds are recognized including Late Griesbachian Ophiceras beds and Early Dienerian Ussuridiscus varaha beds. Stratigraphically, Ophiceras beds are younger than Hindeodus parvus Zone, but are likely to be the same level with Hindeodus postparvus Zone, suggesting a Late Griesbachian age. At Jianzishan, Lower Dienerian is characterized by ammonoid Ussuridiscus varaha beds, which is associated with Hindeodus postparvus, Hindeodus praeparvus, Hindeodus typicalis, Hindeodus pisai, Hindeodus latidentatus, Hindeodus parvus, Hindeodus anterodentatus, Isarcicella turgida, Clarkina carinata and Clarkina planata, indicating that these conodont species could pass through the Griesbachian-Dienerian boundary and occurred in younger strata. Both conodont zones and ammonoid beds are correlated very well with other sections in South China and other regions around the world.

7 TAXONOMIC NOTES 7.1 Conodont

A total of 17 species in 2 conodont genera are identified in the Permian-Triassic interval of Jianzishan Section in this study and here we illustrate some key conodont specimens.

Genus Clarkina Kozur, 1989

Type species: Gondolella leveni Kozur, Mostler and Pjatakova, 1975.

Clarkina changxingensis(Wang and Wang), 1981

Pl. 2, Figs. 4–5; Pl. 3, Figs. 1, 4

1981 Neogondolella subcarinata changxingensis Wang and Wang, Pl. 1, Figs. 13–16.

1995 Clarkina changxingensis (Wang and Wang); Wang, Pl. 1, Fig. 1.

1998 Clarkina changxingensis changxingensis (Wang and Wang); Mei et al., Pl. 1, Figs. B–D, F–H, K; Pl. 2, Fig. G.

2002 Clarkina changxingensis changxingensis (Wang and Wang); Wu et al., Pl. 1, Fig. 9.

2007 Clarkina changxingensis (Wang and Wang); Ji et al., Pl. Ⅳ, Fig. 8.

2007 Neogondolella changxingensis Wang and Wang; Jiang et al., Pl. 1, Figs. 11–18.

2007 Neogondolella changxingensis changxingensis Wang and Wang; Zhang et al., Fig. 4, Fig. 1.

2008 Clarkina changxingensis changxingensis (Wang and Wang); Chen et al., Pl. 1, Figs. 4a–5b.

2010 Clarkina changxingensis (Wang and Wang); Shen and Mei, Figs. 8.1a–8.15b.

2014 Clarkina changxingensis (Wang and Wang); Yuan et al., Pl. 4, Figs. 1–20, 22–24; Pl. 5, Figs. 1–12.

2014 Clarkina changxingensis (Wang and Wang); Jiang et al., Pl. 6, Fig. 4.

Description: The P1 element is characterized by an elongate platform of the drop-shaped morphotype whose widest point is in the middle or posterior portion. Denticles decreasing distinctly in size and height toward the posterior. Cusp is erect to reclined, as high as or slightly higher and larger than the posterior denticles and sometimes fused with the posteriormost denticles. Lower part of the carina is fused and the platform margin is upturned.

Remark: Clarkina taylorae is differentiated from Clarkina changxingensis by a posterior brim, largely discrete denticles and prominent cusp on the posterior end of the platform. Comparing with Clarkina zhangi, Clarkina changxingensis has a broader platform and smaller cusp.

Occurrence: 46 specimen from JZS-1-A+0.5 to JZS-1-E+1.2 in Jianzishan Section. From Clarkina changxingensis Zone to Clarkina yini Zone.

Clarkina yiniMei, 1998

Pl. 2, Figs. 1–3

1998 Clarkina yini Mei et al., Pl. 4, Figs. L–N.

2000 Clarkina changxingensis yini Mei et al.; Wang and Zhu, Pl. 1, Figs. 5, 10.

2004 Clarkina changxingensis yini Mei et al.; Wang and Xia, Figs. 2, 4.

2006 Clarkina changxingensis yini Mei et al.; Nafi et al., Figs. 5.9–5.13.

2006 Neogondolella yini (Mei et al.); Luo et al., Pl. 1, Fig. 25.

2007 Neogondolella yini (Mei et al.), Jiang et al., Pl. 1, Figs. 19–20, 22–23.

2007 Clarkina yini Mei et al.; Ji et al., Figs. 4, 10.

2007 Neogondolella yini (Mei et al.); Zhang et al., Figs. 4, 5.

2010 Clarkina yini Mei et al.; Shen and Mei, Figs. 11.1a–11.10b.

2011 Neogondolella yini (Mei et al.); Jiang et al., Pl. 5, Fig. 10.

2014 Clarkina yini Mei et al.; Yuan et al., Pl. 6, Figs. 1–20.

2015 Clarkina yini Mei, Wardlaw et al., Pl. 1, Figs. 12–13.

Description: The P1 element is characterized by a relatively arched platform of the drop-shaped morphotype whose widest point is in the middle or posterior 1/3 portion. Platform narrows gradually anterior portion, posterior platform is much flattened and rounded. Denticles decreasing gradually in size and height toward the posterior until the cusp, which is erect to slightly reclined and terminally located.

Remark: Clarkina yini is distinguishable from Clarkina changxingensis mainly by the slightly larger cusp and the much flattened posterior platform.

Occurrence: 1 specimen from JZS-1-D+1.0 in Jianzishan Section. Clarkina yini Zone.

Clarkina cf.tulongensis

Pl. 3, Figs. 5

Description: The P1 element is characterized by an arched platform of the wedge-shaped morphotype whose widest point is in posterior portion. Platform narrows gradually anterior portion and posterior platform is approximate square. Carina is composed of discrete denticles. Posterior part of carinata is divaricate and on either side of posterior part of the carina develops a denticle.

Remark: Carina is divaricate in the posterior which is similar to Clarkina tulongensis while the either side of posterior part of the carina develops a denticle instead of a fused carina is quite different led to the definition of Clarkina cf. tulongensis.

Occurrence: 1 specimen from JZS-13+0.75 in Jianzishan Section.

Genus HindeodusRexroad and Furnish, 1964

Type species: Spathognathodus cristulus (Youngquist and Miller, 1949)

Hindeodus parvus(Kozur and Pjatakova), 1976

Pl. 1, Figs. 5, 9

1976 Anchignathodus parvus Kozur and Pjatakova, Figs. 1a, 1b, 1e, 1h.

1981 Hindeodus parvus (Kozur and Pjatakova); Matsuda, Pl. 5, Figs. 2–3.

1995 Hindeodus parvus (Kozur and Pjatakova); Kozur, Pl. 3, Figs. 1–4.

1995 Isarcicella parva (Kozur and Pjatakova); Zhang et al., Pl. 2, Fig. 14.

1996 Hindeodus parvus (Kozur and Pjatakova); Kozur, Pl. Ⅲ, Figs. 1, 3.

1998 Hindeodus parvus (Kozur and Pjatakova); Orchard and Krystyn, Pl. 6, Figs. 9, 16, 17, 20.

2002 Hindeodus parvus (Kozur and Pjatakova); Nicoll et al., Figs. 15, 16.

2002 Hindeodus parvus (Kozur and Pjatakova); Wu et al., Pl. 1, Figs. 6–7.

2003 Hindeodus parvus (Kozur and Pjatakova); Lehrmann et al., Fig. 7B.

2004 Hindeodus parvus (Kozur and Pjatakova); Kozur, Pl. 1, Figs. 3, 6–9.

2007 Hindeodus parvus (Kozur and Pjatakova); Jiang et al., Pl. 5, Figs. 1–7.

2008 Hindeodus parvus (Kozur and Pjatakova); Chen et al., Fig. 10: 1–13.

2013 Hindeodus parvus (Kozur and Pjatakova); Yan et al., Fig. 5: G–L, P, S, U.

2014 Hindeodus parvus (Kozur and Pjatakova); Jiang et al., Pl. 1: 4–5, Pl. 2: 3–18; Pl. 4: 6.

2015 Hindeodus parvus (Kozur and Pjatakova); Brosse et al., Fig. 4.

2015 Hindeodus parvus (Kozur and Pjatakova); Yuan et al., Pl. 5, Figs. 25–30, Pl. 6, Figs. 1–10.

Description: It is characterized by an asymmetrical large basal cavity. The cusp is at least twice as high as the denticles. Blade often bears 4–8 denticles and denticle tips in profile are pointed and rounded, with small triangular space between sthem. Posterior part of carina abruptly diminished and steeply inclined.

Remark: Hindeodus eurypyge is differentiated from Hindeodus parvus by thickened blade, chisel-like denticle tips and a rounded posterior margin.

Occurrence: 66 specimens from JZS-2+0.5 to JZS-11+0.4 in Jianzishan Section. From Hindeodus parvus Zone to Hindeodus postparvus Zone.

Hindeodus postparvus Kozur, 1989

Pl. 1, Fig. 11

1989 Hindeodus postparvus Kozur, p. 400.

1996 Hindeodus postparvus Kozur; Kozur, Pl. 2, Figs. 9–10.

1998 Hindeodus postparvus Kozur; Orchard and Krystyn, Pl. 6, Fig. 1.

2008 Hindeodus postparvus Kozur; Chen et al., Fig. 11: 6–12.

2015 Hin deodus postparvus Kozur; Brosse et al., Figs. 3H–3N.

Description: P1 element of Hindeodus postparvus is characterized by a wide cusp which is only slightly higher than the following denticles. Blade composes of 5–7 denticles. Denticles are strongly divergent in the posterior giving an arcuate to sloped profile.

Remark: Hindeodus postparvus can be distinguish from Hindeodus parvus by relatively low but broad cusp and strongly divergent posterior denticles.

Occurrence: 38 specimens from JZS-6+1.9 to JZS-11+0.4 in Jianzishan Section. 1 specimen from JZS-8+0.5 and 1 specimen from JZS-8+1.3 in JZS Section. From Hindeodus postparvus Zone to Early Dienerian.

7.2 Ammonoid

Order Ceratitida Hyatt, 1884

Family O phiceratidae Arthaber, 1911

Genus O phiceras Griesbach, 1880

Type species: Ophiceras tibeticum Griesbach, 1880.

Ophiceras sp. indet.

Pl. 4, Fig. 1

Description: Very badly preserved, all the specimens are squashed. Moderately evolute shell, with an invisible venter, because of strong flaser. Without any trace of ornamentation. Suture line is not preserved.

Remark: Most of the specimens assigned to Ophiceras that were described from South China were badly preserved, for example, Meishan (Wang, 1984) and Chaohu (Tong et al., 2004). The common features, evolute conch and without any ornamentation, demonstrate these specimens belong to Ophiceras, but this assignment without any degree of confidence.

Occurrence: 9 specimens from sample JZS-6+1.4; 3 specimens from sample JZS-6+1.5; 1 specimen from sample JZS-6+1.9 and 1 specimen from sample JZS-7+0.75. All the specimens occur in Ophiceras beds.

Genus Vishnuites Diener, 1897

Type species: Vishnuites pralambha Diener, 1897

Vishnuites pralambha Diener, 1897

Pl. 4, Figs. 2a–2b

1897 Xenaspis(Vishnuites) pralambha Diener, Pl. 7, Figs. 4–5.

1913 Vishnuites pralambha Diener; Diener, Pl. 3, Figs. 4a, 4b.

? 1959 Vishnuites marginalis Chao, Pl. 11. Figs. 17–18.

? 1988 Vishnuites huazhongensis Xu, Pl. 1, Fig. 8, text-Fig. 6.

? 1988 Vishnuites lichuanensis Xu, Pl. 1, Fig. 3, Pl. 2, Fig. 10, text-Fig. 7.

? 1988 Vishnuites marginalis Xu, Pl. 2, Fig. 1, text-Fig. 8.

? 1988 Vishnuites orientalis Xu, Pl. 2, Fig. 6, text-Fig. 9.

1988 Vishnuites yangziensis Xu, Pl. 1, Fig. 9, Pl. 2, Fig. 3, text-Fig. 10.

2007 Vishnuites wenjiangsiensis Zakharov and Mu in Mu et al., Figs. 3.12-17, 5.1.

2007 Vishnuites cf. yangziensis Zakharov and Mu in Mu et al., Figs. 5.2, 6.3, 6.4, 6.6, 6.8, 6.10, 6.12.

2008 Vishnuites pralambha Diener; Brühwiler et al., Pl. 1, Figs. 18–21.

Description: Moderately evolute compressed conch, with an acute venter. Convex flanks with the maximum whorl width near the middle flanks. Umbilicus broad and shallow, with a low wall, rounded umbilicus margin. Ornamentation consists fine growth lines. Suture line invisible.

Remark: Vishnuites is characterized by a strongly acute venter in Ophiceratidae, while other genera share a rounded (Such as Ophiceras, Lytophiceras) or narrow rounded but never acute venter (Wordioceras, Shangganites). Numerous species of Vishnuites erected by Chao (1959), Xu (1988) and Mu et al. (2007) based on poorly preserved specimens from South China are considered to be synonyms of V. Pralambha (Brühwiler et al., 2008).

Occurrence: 1 specimen from sample JZS-8+0.45; 2 specimens from JZS-8+0.65; 2 specimens from JZS-8+1.05 and possibly in sample JZS-8+0.85. Ussuridiscus varaha beds.

Family Mullericeratidae Ware, Jenks, Hautmann & Bucher, 2011

Genus UssuridiscusShigeta et al., 2009

Type species: Meekoceras (Kingites) varaha. Diener, 1895

Ussuridiscus varaha (Diener), 1895

Pl. 4, Figs. 4a–4c

1895 Meekoceras(Kingites) varaha Diener, Pl. 1, Fig. 2.

1988 Koninckites hubeiensis Xu, Pl. 3, Figs. 8, 15; 451, text-Fig. 22.

1988 Koninckites lingyunensis Chao; Xu, Pl. 3, Fig. 5; Pl. 4, Fig. 1; 452, text-Fig. 24.

1988 Koninckites xiaohensis Xu, Pl. 1, Fig. 4; Pl. 2, Figs. 11, 13; text-Fig. 25.

? 2007 Hubeitoceras (?) wangi Zakharov and Mu in Mu et al., Figs. 13.17–13.19, 15.2–15.5.

2008 "Koninckites" cf. timorense Brühwiler et al., Pl. 3, Figs. 1–4; Pl. 4, Fig. 1.

2009 Ussuridiscus varaha Shigeta et al., Figs. 50.5, 50.6, 55–57.

Description: Involute extremely discoidal shell with a strongly compressed whorl section. Tabulate venter with a rounded ventral-lateral shoulder. Flanks is flat from the umbilical shoulder to approximately middle, while slightly converges from the middle to the ventral-lateral shoulder. Umbilicus very small. Surface is ornamented with fine density growth line, sometimes become low fold on the outer flanks, especially on the outer whorls of maturity specimens. Suture line is badly preserved, without any possibility to describe.

Remark: Our specimens display the same shell characters as the specimens from South Primorye (Shigeta et al., 2009). Xu (1988) reported an Early Triassic ammonoid fauna from Xiaohe Section, located in Lichuan. The species, identified as Koninckites, share no much difference. According to the definition of Ussuridiscus, proposed by Shigeta, Xu's Koninckites species should put into this genus.

Occurrence: 2 specimens from sample JZS-8+0.45 and possibly in sample JZS-8+0.85. Ussuridiscus varaha beds.

Family Proptychitidae Waagen, 1895

Genus Hubeitoceras Waterhouse, 1994

Type species: Koninckites yanjiaensis Xu, 1988

Hubeitoceras yanjiaensis (Xu), 1988

Pl. 4, Figs. 5a–5c

1988 Koninckites yanjiaensis Xu, Pl. 3, Figs. 12–13.

2008 Hubeitoceras yanjiaensis (Xu); Brühwiler et al., Pl. 4, Figs. 3–6.

Description: Involute extremely discoidal shell with a strongly compressed whorl section. Rounded venter without ventrolateral shoulders. Convex flanks with the maximum whorl width near the inner third of flanks. Small umbilicus with rounded shoulders. Ornamentation consists slight trace of small folds. Sub-triangular first and second lateral saddles, the third lateral saddle very broad with a sub-tabulate top. The bottom of lobes not clear.

Remark: Our specimen share no difference from the juvenile specimens described by Brühwiler et al. (2008), which display a flanks slightly converging towards venter, while maturity specimens share a more flatten flanks.

Occurrence: 1 specimen from JZS-8+0.45. Ussuridiscus varaha beds.

Family Flemingitidae Hyatt, 1900

Genus JieshanicerasBrühwiler et al., 2008

Type species: Jieshaniceras guizhouensis Brühwiler et al., 2008

Jieshaniceras guizhouensis(Brühwiler et al.), 2008

Pl. 4, Fig. 3.

2007 Wordioceras aff. Wordiei Spath, Zakharov and Mu in Mu et al., Figs. 6.7, 6.9, 6.11, 7.1, 7.2, 8.

2007 Wordieoceras guizhouensis Zakharov and Mu in Mu et al., Figs. 7.3, 9.1, 9.2.

2008 Jieshaniceras guizhouensis (Zakharov and Mu); Brühwiler et al., Pl. 6, Figs. 1–4.

Description: Moderately evolute extremely discoidal shell with a strongly compressed whorl section. Rounded venter with inconspicuous ventrolateral shoulders. Convex flanks with the maximum whorl width near the mid-flanks. Shallow umbilicus with rounded shoulders. Ornamentation consists fine and curving growth lines and small folds, which is pronounced near the middle flanks and disappeared toward umbilicus and venter. Suture line not clear.

Remark: Our specimens completely fit with the description of Brühwiler et al. (2008). But without suture line, this assignment is not very confident.

Occurrence: 1 specimen from JZS-8+0.45 and 2 specimens from JZS-8+0.65. Ussuridiscus varaha beds.

ACKNOWLEDGMENTS


We thank Lirong Yang, Enhao Jia, Fengyu Wang, and Yuxuan Wang for help in the field, Lei Liang and Kui Wu for laboratory assistance. We are also grateful to Haishui Jiang and Arnaud Brayard for their suggestions on the identification of conodonts and ammonoids. This study was supported by the State Key R & D Project of China (No. 2016YFA0601100), the National Natural Science Foundation of China (Nos. 41622207, 41302271, 41530104), and the 111 Project (No. B08030). This is a contribution to the IGCP-630. The final publication is available at Springer via http://dx.doi.org/10.1007/s12583-017-0754-4.


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