1. Introduction
Global tectonics combined with Gondwanan glaciation confounds the subdivision of the Carboniferous and also complicates global correlations. Four Carboniferous stages, including the Serpukhovian of the Mississippian and the Moscovian, Kasimovian and Gzhelian of the Pennsylvanian still do not have Global Stratotype Sections and Points (GSSPs). Four Task Groups were therefore established ten years ago to search for their candidate GSSPs worldwide.
Marine Carboniferous sediments are well developed and widely distributed in South China. Sections with continous carbonate-dominated successions are especially well exposed in Guizhou Province of South China, among which the most representative section is the Naqing section in Luosu, Luodian of Guizhou. It is a candidate section for the GSSPs of the global Serpukhovian, Moscovian, Kasimovian and the Gzhelian stages at present, of which abundant conodonts and foraminifers have been densely studied in the last decade (Wang & Qi, Reference Wang and Qi2003, Reference Wang and Qi2007; Qi & Wang, Reference Qi and Wang2005; Qi et al. Reference Qi, Wang, Wang, Ueno and Wang2007, Reference Qi, Wang, Wang, Lane, Richards, Ueno and Groves2009, Reference Qi, Lambert, Barrick, Groves, Wang, Hu, Wang, Wang, Qi, Groves and Barrick2010a , Reference Qi, Wang and Lambert2010b , Reference Qi, Wang, Richards, Groves, Ueno, Wang, Wu, Hu, Wang, Qi, Groves and Barrick2010c , Reference Qi, Wang, Lambert, Barrick, Wang, Hu and Wang2011, Reference Qi, Hu, Barrick, Wang and Lin2012; Wang et al. Reference Wang, Qi and Wang2008, Reference Wang, Qi, Lambert, Wang, Wang, Hu, Lin and Chen2011; Barrick et al. Reference Barrick, Qi, Wang and Wang2010; Groves et al. Reference Groves, Wang, Qi, Richards, Ueno and Wang2012). The Naqing section is a relatively deep-water section of slope to basin facies containing abundant conodonts, but its foraminifers are not abundant enough for the study of the correlation of the conodont succession with the foraminiferal succession. The other sections of shallower water facies including the Yashui section, the Luokun section, the Dianzishang section, the Narao section and the Fengting section have therefore been studied in recent years.
The Dianzishang section was measured and described by the Guizhou Geological Survey during the mapping project for the 1:200000 geological map of the Wangxingren region (Bureau of Geology and Mineral Resources of Guizhou Province, 1987), while its microfossil succession has been little studied. A preliminary conodont succession and biostratigraphy from lower Visean to uppermost Moscovian in this section is reported in this paper.
The Visean–Moscovian duration not only contains several important stage boundaries, but also records several important geological and biotic events such as initiation of the Late Palaeozoic ice age and Middle Carboniferous mass extinction. The conodont zonation documented here provides the high-resolution time frameworks required for future studies concerning the above events.
2. The studied section, geological and stratigraphic settings
The Dianzishang section (25° 49′ 18″ N, 105° 52′ 35″ E) is located in Shazi, Zhenning, Anshun, Guizhou Province, a distance of 40 km from Zhenning County and 50 km from the city of Anshun. The section can be conveniently accessed by highway from Guiyang and Anshun (Fig. 1). It is part of the eastern limb of the Douluo anticline, which lies within the NW Shuicheng–Ziyun deformation zone (Wang, Reference Wang2000). Palaeogeographically, the section was situated on a middle-slope of the platform south of Upper Yangtze Old Land. A succession of sediments from the Visean to the Moscovian is well exposed, except for a 10 m covered interval of middle Bashkirian age. The Dianzishang section is mainly composed of greyish-black to black, thin- to medium-bedded packstone, wackestone and chert, intercalated with thick bedded grainstone but includes minor shale and slope breccias or slump deposits. This distinctive lithological succession is usually termed the ‘Black Zone’ in the Langdai–Luodian sedimentary zone.
Figure 1. Location map of the Dianzishang section.
The Dianzishang section can be subdivided into two parts (Fig. 2). The lower part is called the Xiaoxibian section, with a thickness of 80.08 m, and includes the beds from Visean to Bashkirian age. The upper part is called the Dalubian section, with a thickness of 94.44 m, and includes the beds from Bashkirian to Moscovian age. About 10 m of section between the lower part and the upper part are covered.
Figure 2. Photographs showing the Dianzishang section. (a, b) Upper part of the section (Dalubian section); and (c, d) lower part of the section (Xiaoxibian section).
3. Conodont biostratigraphy and correlation
The Dianzishang section is composed of typical middle- to upper-slope sediments that mainly contain microfossils such as conodonts and foraminifers. Only conodonts are considered in this paper.
A total of 56 conodont species/subspecies (including more than 10 undetermined forms) belonging to 14 genera are identified (Fig. 3). Eleven conodont zones (sections 3.a.1–3.a.2, 3.b.1, 3.c.1–3.c.3, 3.d.1–3.d.5) are recognized from base to top, which are easily correlated with those of the Naqing section in South China, Russian and North American sections, as well as other important sections in the world (Fig. 4).
Figure 3. Conodont range chart for the Dianzishang section: (a) Visean–Serpukhovian; (b) Serpukhovian–Bashkirian–Moscovian; (c) Moscovian; and (d) Moscovian–Kasimovian.
Figure 4. Conodont zones of the Dianzishang section and their correlations.
3.a. Visean
3.a.1. Gnathodus praebilineatus Zone (DZSC2.0–27.6; Fig. 5)
The base of this zone is marked by the First Appearance Datum (FAD) of Gnathodus praebilineatus Belka, Reference Belka1985 and its top by the FAD of G. bilineatus remus Meischner & Nemyrovska, Reference Nemyrovska1999 or G. bilineatus romulus Meischner & Nemyrovska, Reference Nemyrovska1999. Presently, the base of this zone is not recognized in the Dianzishang section. This zone is characterized by the occurrence of G. praebilineatus, associated with other common forms such as Gnathodus delicatus Branson & Mehl, Reference Branson and Mehl1938, G. girtyi girtyi Hass, Reference Hass1953, G. girtyi meischneri (Austin & Husri, Reference Austin, Husri, Bouckaert and Streel1974), Lochriea comutata (Branson & Mehl, Reference Branson and Mehl1941) and Pseudognathodus homopunctatus (Ziegler, Reference Ziegler1960). This zone is the highest conodont zone in the Lower Visean. Previously, this zone has only been recognized in North Africa (Nemyrovska et al. Reference Nemyrovska, Perret-Mirouse and Weyant2006). It can be roughly correlated with the Hindeodus scitulus – Apatognathus scalenus Zone in North America (Lane & Brenckle, Reference Lane, Brenckle and Heckel2001).
Figure 5. Visean – lower Bashkirian interval in the Dianzishang section, Zhenning, Guizhou, South China. (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, catalogue numbers 155794–155808.) (a) Lochriea comutata (Branson & Mehl, Reference Branson and Mehl1941) oral view, sample DZSC7.70, cat. no. 155794; (b) Lochriea saharea Nemyrovska, Perret & Weyant, Reference Nemyrovska, Perret-Mirouse and Weyant2006, oral view, sample DZSC7.70, cat. no. 155795; (c, d) Gnathodus praebilineatus Belka, Reference Belka1985, oral views, (c), sample DZSC49.00, (d), sample DZSC64.40, cat. no. 155796, 155797; (e) Lochriea costata (Pazukhin & Nemirovska in Kulagina et al. Reference Kulagina, Rumyantseva, Pazukhin and Kotchetkova1992), oral view, sample DZSC57.80, cat. no. 155798; (f) Lochriea monocostata (Pazukhin & Nemirovska in Kulagina et al. Reference Kulagina, Rumyantseva, Pazukhin and Kotchetkova1992) oral view, sample DZSC57.80, cat. no. 155799; (g) Pseudognathodus homopunctatus (Ziegler, Reference Ziegler1960) oral view, sample DZSC7.70, cat. no. 155800; (h) Gnathodus bilineatus bilineatus (Roundy, Reference Roundy1926) oral view, sample DZSC57.80, cat. no. 155801; (i) Declinognathodus noduliferus noduliferus (Ellison & Graves, Reference Ellison and Graves1941) oral view, sample DZSC59.40, cat. no. 155802; (j, k) Lochriea ziegleri Nemirovskaya, Perret-Mirouse & Meischer, 1994, oral views, (j), sample DZSC49.00, (k) sample DZSC59.40, cat. no. 155803, 155804; (l) Gnathodus bilineatus bollandensis Higgins & Bouckaert, Reference Higgins and Bouckaert1968, oral view, sample DZSC59.40, cat. no. 155805; (m) Gnathodus bilineatus remus Meischner & Nemyrovska, Reference Nemyrovska1999, oral view, sample DZSC64.40, cat. no. 155806; (n) Declinognathodus cf. lateralis (Higgins & Bouckaert, Reference Higgins and Bouckaert1968) oral view, sample DZSC61.80, cat. no. 155807; (o) Gnathodus postbilineatus Nigmadganov & Nemirovskaya, Reference Nigmadganov and Nemirovskaya1992, oral view, sample DZSC61.80, cat. no. 155808.
3.a.2. Gnathodus bilineatus Zone (DZSC27.6–49.0)
The base of this zone is marked by the FAD of Gnathodus bilineatus remus or G. bilineatus romulus and its top by the FAD of Lochriea nodosa (Bischoff, Reference Bischoff1957). L. nodosa has not yet been found in the Dianzishang section. Other commonly associated forms are G. bilineatus bilineatus (Roundy, Reference Roundy1926), G. delicatus, G. praebilineatus, and L. comutata (Branson & Mehl, Reference Branson and Mehl1941). This zone is the lowest conodont zone in the upper Visean. It is also recognized in the Naqing section from Guizhou, South China (Y. P. Qi, unpub. Ph.D. thesis, Graduate University of Chinese Academy of Sciences, 2008) and the Genicera (= Alba) Formation from the Cantabrian Mountains, Spain (Nemyrovska, Reference Nemyrovska2005). It can be correlated with the G. bilineatus bilineatus Zone and L. mononodosa (Rhodes, Austin & Druce, Reference Rhodes, Austin and Druce1969) zone from the Verkhnyaya Kardailovka section, South Urals (Nikolaeva et al. Reference Nikolaeva, Gibshman, Kulagina, Barskov and Pazukhin2002) and the lower part of the G. girtyi collinsoni Zone from the Asbian of Britain and Ireland (Higgins, Reference Higgins1975, Reference Higgins, Higgins and Austin1985).
3.b. Serpukhovian
3.b.1. Lochriea ziegleri Zone (DZSC49.0–59.4; Fig. 5)
The base of this zone is marked by the FAD of Lochriea ziegleri (Nemirovskaya et al. Reference Nemirovskaya, Perret-Mirouse and Meischner1994) and its top by the FAD of L. cruciformis (Clarke, Reference Clarke1960) (Qi & Wang, Reference Qi and Wang2005). L. cruciformis has not yet been found in the Dianzishang section. Other commonly associated forms are Gnathodus bilineatus bilineatus, G. bilineatus remus, G. delicatus, G. praebilineatus, L. comutata, L. costata Pazukhin & Nemirovska in Kulagina et al. Reference Kulagina, Rumyantseva, Pazukhin and Kotchetkova1992, L. monocostata Pazukhin & Nemirovskaya in Kulagina et al. Reference Kulagina, Rumyantseva, Pazukhin and Kotchetkova1992 and L. mononodosa. This zone is the lowest conodont zone in the Serpukhovian. It is also recognized in the Naqing section from South China, Cantabrian Mountains from Spain, Moscow Basin from Russia, South Urals, Donetz Basin and various locations in Eurasia (Nemirovskaya et al. Reference Nemirovskaya, Perret-Mirouse and Meischner1994; Skomposki et al. Reference Skomposki, Alekseev, Meischner, Nemirovskaya, Perret-Mirouse and Varker1995; Nikolaeva et al. Reference Nikolaeva, Gibshman, Kulagina, Barskov and Pazukhin2002; Nemyrovska, Reference Nemyrovska2005; Qi & Wang, Reference Qi and Wang2005; Y. P. Qi, unpub. Ph.D. thesis, Graduate University of Chinese Academy of Sciences, 2008). This zone is coeval with the lower part of G. girtyi simplex – Kladognathus Zone in Britain and Ireland (Higgins, Reference Higgins1975, Reference Higgins, Higgins and Austin1985) and the uppermost G. bilineatus Zone to lower part of Cavusgnathus naviculus Zone from North America (Lane & Straka, Reference Lane and Straka1974; Lane & Brenckle, Reference Lane, Brenckle and Heckel2001).
3.c. Bashkirian
3.c.1. Declinognathodus noduliferus Zone (DZSC59.4–68.5; Figs 5, 6)
The base of this zone is marked by the FAD of Declinognathodus noduliferus noduliferus (Ellison & Graves, Reference Ellison and Graves1941) and its top by the FAD of Idiognathoides sulcatus sulcatus Higgins & Bouckaert, Reference Higgins and Bouckaert1968 (Wang & Qi, Reference Wang and Qi2003). Other commonly associated forms are D. cf. lateralis (Higgins & Bouckaert, Reference Higgins and Bouckaert1968), D. marginodosus (Grayson, Reference Grayson1984), D. noduliferus bernesgae Sanz-Lopez, Blanco-Ferrera, Garcia-Lopez & De Posada, Reference Sanz-López, Blanco-Ferrera, Sánchez De and García-López2006, D. noduliferus inaequalis (Higgins, Reference Higgins1975) and D. noduliferus noduliferus, together with a few Gnathodus bilineatus bilineatus, G. bilineatus bollandensis Higgins & Bouckaert, Reference Higgins and Bouckaert1968, G. bilineatus remus, G. bilineatus romulus, G. postbilineatus Nigmadganov & Nemirovskaya, Reference Nigmadganov and Nemirovskaya1992, Lochriea comutata, L. monocostata, L. mononodosa and L. ziegleri. The ranges of species of Gnathodus and Lochriea extend only to the bottom or middle part of this zone in the Dianzishang section. This zone is widespread over the world in the areas which were not strongly affected by the Middle Carboniferous eustatic event and where the Middle Carboniferous boundary deposits do occur (Nemyrovska, Reference Nemyrovska1999; Nemirovska & Alekseev, Reference Nemirovskaya and Alekseev1994; Lane & Straka, Reference Lane and Straka1974; Higgins, Reference Higgins1975, Reference Higgins, Higgins and Austin1985; Wang et al. Reference Wang, Lane, Manger and Wang1987; Perret, Reference Perret1993).
Figure 6. Lower Bashkirian – lower Moscovian interval in the Dianzishang section. (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, catalogue numbers 155809–155824.) (a) Idiognathoides corrugates Harris & Hollinsworth, Reference Harris and Hollingsworth1933, oral view, sample DZSC61.80, cat. no. 155809; (b) Idiognathoides sinuatus Harris & Hollingsworth, Reference Harris and Hollingsworth1933, oral view, sample DZSC68.50, cat. no. 155810; (c) Idiognathoides postsulcatus Nemyrovska, Reference Nemyrovska1999, oral view, sample ZXC−18.60, cat. no. 155811; (d) Idiognathoides sulcatus sulcatus Higgins & Bouckaert, Reference Higgins and Bouckaert1968, oral view, sample ZXC−18.60, cat. no. 155812; (e) Neognathodus symmetricus (Lane, Reference Lane1967) oral view, sample ZXC−20.00, cat. no. 155813; (f) ‘Streptognathodus’ expansus (primitive form) Igo & Koike, Reference Igo and Koike1964, oral view, sample ZXC−16.60, cat. no. 155814; (g–i) ‘Streptognathodus’ expansus Igo & Koike, Reference Igo and Koike1964, oral views, (g) sample ZXC−11.80, (h, i) sample ZXC−12.10, cat. nos 155815–155817; (j–l) ‘Streptognathodus’ suberectus Dunn, Reference Dunn1966, oral views, (j) sample ZXC−11.80, (k, l) sample ZXC−12.10, cat. nos 155818–155820; (m) Neognathodus kanumai Igo, Reference Igo1974, oral view, sample ZXC−16.60, cat. no. 155821; (n) Declinognathodus marginodosus (Grayson, Reference Grayson1984) oral view, sample ZXC−10.30, cat. no. 155822; (o, p) Neognathodus bothrops Merrill, Reference Merrill1972, oral views, (o) sample ZXC−10.30, (p) sample ZXC−8.50, cat. nos 155823, 155824.
3.c.2. Neognathodus symmetricus Zone (DZSC68.5–ZXC−16.6; Fig. 6)
The base of this zone is marked by the FAD of Neognathodus symmetricus (Lane, Reference Lane1967) and its top by the FAD of N. bassleri (Harris & Hollingsworth, Reference Harris and Hollingsworth1933). N. bassleri has not yet been found in the Dianzishang section. Other commonly associated forms in this zone are Declinognathodus marginodosus, D. noduliferus inaequalis, D. noduliferus noduliferus, Idiognathoides corrugatus Harris & Hollingsworth, Reference Harris and Hollingsworth1933, Id. postsulcatus Nemyrovska, Reference Nemyrovska1999, Id. sinuatus Harris & Hollingsworth, Reference Harris and Hollingsworth1933, Id. sulcatus sulcatus, Streptognathodus sp. and Idiognathodus sp. This zone can be correlated with the N. symmetricus Zone to I. primulus – N. symmetricus Zone at the Naqing section (Wang & Qi, Reference Wang and Qi2003; Wang et al. Reference Wang, Qi, Wang and Wang2004). It is coeval with the same zone in North America (Lane & Straka, Reference Lane and Straka1974; Barrick et al. Reference Barrick, Lambert, Heckel and Boardman2004) and the Neognathodus askynensis – N. symmetricus Zone in South Urals, Russia (Nemirovska & Alekseev, Reference Nemirovskaya, Perret-Mirouse and Meischner1994; Kulagina et al. Reference Kulagina, Pazukhin, Davydov, Puchkov, Kulagina, Nikolaeva and Kochetova2009).
3.c.3. ‘Streptognathodus’ expansus (primitive form) Zone (ZXC−16.6 – −12.1; Fig. 6)
The base of this zone is marked by the FAD of ‘Streptognathodus’ expansus (primitive form) and its top by the FAD of ‘S.’ expansus Igo & Koike, Reference Igo and Koike1964. Other commonly associated forms are Declinognathodus marginodosus, Idiognathoides corrugatus, Id. postsulcatus, Id. sinuatus and Id. sulcatus sulcatus. This zone can be correlated with the ‘Streptognathodus preexpansus’ Zone from the Naqing section (Qi et al. Reference Qi, Wang, Lambert, Barrick, Wang, Hu and Wang2011) and the Idiognathoides sulcatus parva Zone in Western Europe (Higgins, Reference Higgins1975, Reference Higgins, Higgins and Austin1985), and it can be roughly correlated with the Idiognathodus sinuosus Ellison & Graves, Reference Ellison and Graves1941 Zone in Russia and North America (Lane & Straka, Reference Lane and Straka1974; Nemirovska & Alekseev, Reference Nemirovskaya and Alekseev1994; Nemyrovska, Reference Nemyrovska1999; Wang & Qi, Reference Wang and Qi2003; Kulagina et al. Reference Kulagina, Pazukhin, Davydov, Puchkov, Kulagina, Nikolaeva and Kochetova2009). It is also coeval with the previously established Idiognathoides sulcatus parva Zone in the Naqing section (Wang et al. Reference Wang, Qi, Wang and Wang2004). (Note that ‘Streptognathodus preexpansus’ is a new and unpublished species, here identified as ‘Streptognathodus’ expansus (primitive form).) ‘Streptognathodus’ expansus (primitive form) is used here to replace the unpublished species name and the name of the conodont zone.)
3.d. Moscovian
3.d.1. ‘Streptognathodus’ expansus Zone (ZXC−12.1 – −1.3; Figs 6–8)
The base of this zone is marked by the FAD of ‘Streptognathodus’ expansus. The top of this zone is defined as the FAD of Diplognathodus ellesmerensis (Qi et al. Reference Qi, Wang, Lambert, Barrick, Wang, Hu and Wang2011), but D. ellesmerensis has not yet been found in the Dianzishang section. Other commonly associated forms are Idiognathoides corrugatus, Id. fossatus (Branson & Mehl, Reference Branson and Mehl1941), Id. lanei Nemirovskaya, Reference Nemirovskaya1978, Id. postsulcatus, Id. sinuatus, Id. sulcatus sulcatus, Neolochriea glaber (Wirth, Reference Wirth1967), Neol. hisaharui Mizuno,1997, Neognathodus bothrops Merrill, Reference Merrill1972, N. caudatus Lambert, Reference Lambert, Sutherland and Manger1992, N. kanumai Igo, Reference Igo1974, ‘S.’ suberectus (Dunn, Reference Dunn1966), Gondolella spp., Idiognathodus spp. and Streptognathodus spp. This zone is also recognized in the Naqing section (Qi et al. Reference Qi, Wang, Lambert, Barrick, Wang, Hu and Wang2011). It is coeval with the previously established conodont zones in the Naqing section such as ‘S.’ expansus and Id. ouachitensis zones (Wang et al. Reference Wang, Qi, Wang and Wang2004) and the ‘S.’ expansus, Id. ouachitensis and Diplognathodus coloradoensis zones (Wang et al. Reference Wang, Qi and Wang2008). It can also be correlated with ‘S.’ expansus, Idiognathoides tuberculatus-Id. fossatus and Declinognathodus marginodosus zones in the Donets Basin, Ukraine (Nemyrovska, Reference Nemyrovska1999), Declinognathodus marginodosus Zone in South Urals, Russia (Nemirovska & Alekseev, Reference Nemirovskaya and Alekseev1994; Nemyrovska, Reference Nemyrovska1999; Kulagina et al. Reference Kulagina, Pazukhin, Davydov, Puchkov, Kulagina, Nikolaeva and Kochetova2009), Idiognathodus klapperi, Idiognathoides convexus and Id. ouachitensis zones in North America (Lane, Reference Lane, Sutherland and Manger1977; Lane et al. Reference Lane, Baesemann, Brenckle and West1985) and the ‘S.’ expansus–‘S.’ suberectus Zone in Nevada, USA (Dunn, Reference Dunn1970).
Figure 7. Upper Visean – middle Moscovian interval in the Dianzishang section. (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, catalogue numbers 155825–155836. (a–g) Gondolella spp. lateral views, (a, c) sample ZXC−1.30, (b) sample ZXC−5.00, (d, f, g) sample ZXC 28.30, 5, sample ZXC−10.30, cat. nos 155825–155831; (h) Mestognathodus beckmani Bischoff, Reference Bischoff1957, latero-oral view, sample DZSC42.50, cat. no. 155832; (i, j) Mesogondolella clarki (Koike, Reference Koike1967) oral views, (i), sample ZXC 28.30, (j), sample ZXC−1.30, cat. nos 155833, 155834; (k) Mesogondolella donbassica Kossenko, Reference Kossenko1975, oral view, sample ZXC−1.30, cat. no. 155835; (l) Mesogondolella subclarki Wang & Qi, Reference Wang and Qi2003, oral view, sample ZXC−1.30, cat. no. 155836.
Figure 8. Lower–upper Moscovian interval in the Dianzishang section. (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, catalogue numbers 155837–155851. (a–f) Idiognathodus spp. oral views, (a) sample ZXC−2.60, (b) sample ZXC 20.50, (c) sample ZXC 38.40, (d) sample ZXC 4.00, (e, f) sample ZXC 28.30, cat. nos 155837–155842; (g) Swadelina sp. 2 Barrick, Qi & Wang, Reference Barrick, Qi, Wang and Wang2010, oral view, sample ZXC 38.40, cat. no. 155843; (h–j) Idiognathodus podolskensis Goreva, Reference Goreva and Menner1984, oral views, (h,i), sample ZXC 38.40, (j) sample ZXC 20.50, cat. nos 155844–155846; (k) Idiognathoides fossatus (Branson & Mehl, Reference Branson and Mehl1941) oral view, sample ZXC−0.20, cat. no. 155847; (l) Idiognathodus amplificus Lambert, Reference Lambert, Sutherland and Manger1992, oral view, sample ZXC−1.30, cat. no. 155848; (m) Neognathodus caudatus Lambert, Reference Lambert, Sutherland and Manger1992, oral view, sample ZXC−8.50, cat. no. 155849; (n) Neolochriea hisaharui Mizuno, Reference Mizuno1997, oral view, sample ZXC−6.00, cat. no 155850; (o) Neolochriea nagatoensis (Igo & Koike, Reference Igo and Koike1965) oral view, sample ZXC 4.00, cat. no. 155851.
3.d.2. Mesogondolella donbassica – Mesogondolella clarki Zone (ZXC−1.3–11.2; Figs 7–9)
The base of this zone is marked by the FAD of Mesogondolella donbassica Kossenko, Reference Kossenko1975 or M. clarki (Koike, Reference Koike1967) and its top by the FAD of Idiognathodus podolskensis Goreva, Reference Goreva and Menner1984 (Wang et al. Reference Wang, Qi and Wang2008; Y. P. Qi, unpub. Ph.D. thesis, Graduate University of Chinese Academy of Sciences, 2008). Other commonly associated forms are I. amplificus Lambert, Reference Lambert, Sutherland and Manger1992, I. obliquus Kossenko in Kozitskaya et al. Reference Kozitskaya, Kossenko, Lipnjagov and Nemirovskaya1978, I. praeobliquus Nemyrovska, Perret-Mirouse & Alekseev, Reference Nemyrovska1999, M. subclarki Wang & Qi, Reference Wang and Qi2003, Neolochriea glaber, Gondolella sp. and I. sp. This zone is also recognized in the Naqing section, and can be roughly correlated with the Streptognathodus transtivus, Neognathodus bothrops, N. medadultimus and Streptognathodus concinus– Idiognathodus robustus zones in Russia (Kulagina et al. Reference Kulagina, Pazukhin, Davydov, Puchkov, Kulagina, Nikolaeva and Kochetova2009), and with the N. bothrops Zone, N. caudatus Zone and the lower part of the N. asymmetricus Zone in North America (Barrick et al. Reference Barrick, Lambert, Heckel and Boardman2004; Wang & Qi, Reference Wang and Qi2003; Wang et al. Reference Wang, Qi and Wang2008).
Figure 9. Lower Moscovian – lower Kasimovian interval in the Dianzishang section. (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, catalogue numbers 155852–155869. (a–d) Idiognathodus spp. oral views, (a) sample ZXC 31.80, (b) sample ZXC 4.00, (c) sample ZXC 28.30, (d) sample ZXC 20.50, cat. nos 155852–155855; (e) Transitional form from Idiognathodus praeobliquus Nemyrovska, Perret-Mirouse & Alekseev, 1999 to Idiognathodus obliquus Kossenko in Kozitskaya et al. Reference Kozitskaya, Kossenko, Lipnjagov and Nemirovskaya1978, oral view, sample ZXC 28.30, cat. no. 155856; (f) Idiognathodus obliquus Kossenko in Kozitskaya et al. Reference Kozitskaya, Kossenko, Lipnjagov and Nemirovskaya1978, oral view, sample ZXC−0.20, cat. no. 155857; (g) Idiognathoides planus Furduj, Reference Furduj and Einor1975, oral view, sample ZXC 2.50, cat. no. 155858; (h–j) Idiognathodus swadei Rosscoe & Barrick Reference Rosscoe and Barrick2009a , oral views, sample ZXC 67.80, lower Kasimovian cat. nos 155859–155861; (k) ‘Streptognathodus’ suberectus Dunn, Reference Dunn1966, oral view, sample ZXC 38.40, cat. no. 155862; (l–n) Transitional forms from Idiognathodus swadei Rosscoe & Barrick Reference Rosscoe and Barrick2009a to Idiognathodus turbatus Rosscoe & Barrick Reference Rosscoe and Barrick2009a , oral views, sample ZXC 48.00, cat. nos 155863–155865; (o–r) Idiognathodus juveniles, oral views, sample ZXC 67.80, lower Kasimovian cat. nos 155866–155869.
3.d.3. Idiognathodus podolskensis Zone (ZXC 11.2–38.4; Figs 7–9)
The base of this Zone is marked by the FAD of Idiognathodus podolskensis and its top by the FAD of any species of Swadelina. Other commonly associated forms are I. amplificus, I. planus Furduj, 1979, I. praeobliquus, I. obliquus, Mesogondolella clarki, M. donbassica, M. subclarki, Neolochriea glaber, Neolochriea nagatoensis (Igo & Koike, Reference Igo and Koike1965), Gondolella sp. and Idiognathodus spp. This zone is also recognized in the Naqing section, and can be roughly correlated with the I. podolskensis Zone, N. inaequalis Zone and N. roundyi Zone in Russia, the upper part of the N. asymmetricus Zone and the N. roundyi Zone in North America (Wang & Qi, Reference Wang and Qi2003; Wang et al. Reference Wang, Qi and Wang2008).
3.d.4. Swadelina fauna Zone (ZXC 38.4–48.0; Fig. 8)
The base of this Zone is marked by the FAD of any species of Swadelina, while its top is marked by the FAD of Idiognathodus swadei Rosscoe & Barrick, Reference Rosscoe and Barrick2009a . This zone is characterized by the appearance of Swadelina sp. 2 Barrick, Qi & Wang, Reference Barrick, Qi, Wang and Wang2010 in the Dianzishang section. Other forms in this zone are Gondolella spp. and Idiognathodus spp. Even though the taxonomy of Swadelina, Idiognathodus and Gondolella from the Moscovian in South China are not fully understood at the species level, the Swadelina fauna Zone in the Dianzishang section can be correlated with the beds that yield the latest Moscovian Swadelina fauna worldwide (Lambert et al. Reference Lambert, Heckel and Barrick2003; Wang & Qi, Reference Wang and Qi2007; Barrick et al. Reference Barrick, Qi, Wang and Wang2010; Goreva & Alekseev, Reference Goreva and Alekseev2010; Nemyrovska, Reference Nemyrovska2011).
3.d.5. Idiognathodus swadei Zone (ZXC 48.0–65.0; Fig. 9)
The base of this zone, the latest Moscovian zone, is marked by the FAD of Idiognathodus swadei and its top is marked by the FAD of I. turbatus Rosscoe & Barrick, Reference Rosscoe and Barrick2009a . Although I. turbatus, the greatest-potential boundary marker for the base of global Kasimovian Stage, has not yet been found in the Dianzishang section, the morphology of juveniles of Idiognathodus (Fig. 9o–r) from sample ZXC 67.8 indicate a possible early Kasimovian age. We tentatively put the top of this zone at 65.0 m in this section. This zone is also recognized in the Naqing section (K. Y. Hu, unpub. Masters thesis, Graduate University of Chinese Academy of Sciences, 2012), and it can be correlated with the Idiognathodus sulciferus Zone in North America (S. J. Rosscoe, unpub. Ph.D. dissertation, Graduate Faculty of Texas Tech University, 2008) and I. arendti Subzone in Russia (Barskov, Reference Barskov1984; Barskov et al. Reference Barskov, Alekseev, Goreva, Kononova and Migdisova1984; Goreva & Alekseev, Reference Goreva and Alekseev2010).
4. Discussion
4.a. Visean–Serpukhovian boundary
The GSSP of the base of Serpukhovian has not yet been established, but the majority of the boundary Task Group members agree on using the FAD of Lochriea ziegleri in the evolutionary lineage L. nodosa – L. ziegler as the GSSP marker. The species is easy to identify, widely distributed and relatively abundant. These features indisputably indicate that Lochriea ziegleri is a perfect boundary marker despite its first occurrence being a little earlier than the traditionally defined Serpukhovian base (Qi, Wang & Luo, Reference Qi, Wang and Luo2004, Reference Qi, Wang and Lambert2010b , Reference Qi, Wang, Richards, Groves, Ueno, Wang, Wu, Hu, Wang, Qi, Groves and Barrick2010c ; Wang & Jin, Reference Wang and Jin2005; Y. P. Qi, unpub. Ph.D. thesis, Graduate University of Chinese Academy of Sciences, 2008). In the Dianzishang section, the first occurrence of Lochriea ziegleri is at 49.0 m in the lower part of the section (the Xiaoxibian section), which indicates the Visean–Serpukhovian boundary. Unfortunately, Lochriea nodosa, the ancestor of L. ziegleri, has not yet been found in this section.
4.b. Serpukhovian–Bashkirian boundary
The GSSP of the base of Bashkirian was established in 1996 in the Arrow Canyon section, Nevada, USA. The FAD of conodont species Declinognathodus noduliferus was selected as the marker of this boundary (Lane et al. Reference Lane, Brenckle, Baesemenn and Richards1999). In the Dianzishang section, the base of the Bashkirian lies at the first occurrence of Declinognathodus noduliferus noduliferus at 59.4 m of the lower part of the section (the Xiaoxibian section)
4.c. Bashkirian–Moscovian boundary
Presently, the definition of the base of Moscovian is still in dispute. Three candidates for the marker of this boundary have been proposed by the boundary Task Group (Groves & Task Group, Reference Groves2006): (1) the FAD of Declinognathodus donetzianus in the evolutionary lineage of Decl. marginodosus (Grayson) – Decl. donetzianus Nemirovska, Reference Nemirovskaya1990; (2) the FAD of Idiognathoides postsulcatus in the evolutionary lineage Id. sulcatus sulcatus Higgins & Bouckaert, Reference Higgins and Bouckaert1968 – Id. postsulcatus Nemyrovska, Reference Nemyrovska1999; and (3) the FAD of one of the members of the evolutionary lineage from primitive to advanced forms of Neognathodus nataliae. These candidates all have their limitations for the recognition of the Bashkirian–Moscovian boundary worldwide according to detailed studies of the conodonts in the Naqing section. A new candidate taxon has therefore been proposed: the FAD of Diplognathodus ellesmerensis (Qi et al. Reference Qi, Wang, Wang, Ueno and Wang2007, Reference Qi, Wang, Wang, Lane, Richards, Ueno and Groves2009, Reference Qi, Lambert, Barrick, Groves, Wang, Hu, Wang, Wang, Qi, Groves and Barrick2010a ; Y. P. Qi, unpub. Ph.D. thesis, Graduate University of Chinese Academy of Sciences, 2008; Wang et al. Reference Wang, Qi and Wang2008, Reference Wang, Qi, Lambert, Wang, Wang, Hu, Lin and Chen2011). The FAD of Diplognathodus ellesmerensis is very near a previously defined Moscovian base (the FAD of Declinognathodus donetzianus, Alekseev & Goreva, Reference Alekseev and Goreva2000). Because it is widely distributed and easy to identify, D. ellesmerensis should be a very suitable boundary marker. However, it is not easily recovered due to its small size. Furthermore, the evolutionary lineage of this species is not very clear and requires further investigation. These imperfections led to a dispute on the proposal to use D. ellesmerensis as the boundary marker (Groves & Task Group, Reference Groves2008). Recently, on the basis of detailed studies on conodonts in the Bashkirian–Moscovian boundary interval in South China, a new conodont evolutionary lineage (from primitive form to advanced form in Streptognathodus expansus) was found (Qi et al. Reference Qi, Wang and Lambert2010a ). Streptognathodus expansus was named by Japanese conodont workers in 1964 (Igo & Koike, Reference Igo and Koike1964). According to the description and illustrations, the originally published specimens belong to the advanced form of this species. The newly discovered primitive form may need a new species/subspecies name. In the Naqing section, the FAD of Streptognathodus expansus is near the top of Bashkirian, 5.25 m lower than the FAD of Diplognathodus ellesmerensis. Compared to Diplognathodus ellesmerensis, Streptognathodus expansus is larger, more abundant and also widely distributed. Its lineage is very clear and easy to identify. This species might be an excellent candidate for the marker of the base of Moscovian (Qi et al. Reference Qi, Wang and Lambert2010a , Reference Qi, Wang, Lambert, Barrick, Wang, Hu and Wang2011). In this paper, the Bashkirian–Moscovian boundary is recognized at –12.0 m of the lower part of the section (the Dalubian section), which coincides with the FAD of Streptognathodus expansus.
4.d. Moscovian–Kasimovian boundary
The Working Group on the Moscovian–Kasimovian boundary proposed two potential biostratigraphic markers, Idiognathodus sagittalis Kozitskaya, Reference Kozitskaya, Kossenko, Lipnjagov and Nemirovskaya1978 in Kozitskaya et al. Reference Kozitskaya, Kossenko, Lipnjagov and Nemirovskaya1978 and Idiognathodus turbatus Rosscoe & Barrick, Reference Rosscoe and Barrick2009a , by which the base of the Kasimovian Stage can be marked and correlated globally (Ueno & Task Group, Reference Ueno2009). Idiognathodus sagittalis is based on material from the Donets Basin (Ukraine) and I. turbatus is based on material from mid-continent North America. A lineage from Idiognathodus swadei Rosscoe & Barrick, Reference Rosscoe and Barrick2009a to I. turbatus has been described from mid-continent North America (Rosscoe & Barrick, Reference Rosscoe and Barrick2009b ). Highly abundant conodonts have been recovered from the large collections of the Moscovian–Kasimovian boundary interval in the Naqing section, Guizhou of South China in recent years, among which many transitional morphotypes (similar to I. sagittalis) with rapid morphological transformation from I. swadei to I. turbatus are found. The important conodont evolutionary lineage from I. swadei to I. turbatus is therefore also confirmed in South China.
In the Moscow Basin, Goreva et al. (Reference Goreva, Alekseev, Isakova and Kossovaya2009, fig. 6L) illustrated a specimen as Idiognathodus turbatus that is similar to I. turbatus from the Naqing section. Their I. sagittalis, which occurs below I. turbatus, resembles the I. swadei – I. turbatus transitional forms from the Naqing section. Possibly, I. sagittalis may be the transitional form from I. swadei to I. turbatus. The FAD of I. turbatus in the I. swadei – I. turbatus lineage appears to be the only reasonable biostratigraphic marker for defining the Moscovian–Kasimovian boundary. Unfortunately, I. turbatus has not yet been found in the Dianzishang section, but several transitional forms (Fig. 9l–n) from I. swadei to I. turbatus were found in the upper part of this section and Idiognathodus juveniles (Fig. 5o–r) from sample ZXC 67.8 appear to be possible early Kasimovian morphotypes. We therefore tentatively put the Moscovian–Kasimovian boundary at a level of 65.0 m in the Dianzishang section.
5. Conclusion
The Dianzishang section is intermediate between the lower-slope to basin deposits at Naqing and the shallow-marine platform deposits at Yashui (Richards & Task Group, Reference Richards2010). Abundant conodonts and foraminifers are found in this section. The preliminary conodont succession including only 11 conodont zones and conodont biostratigraphy from lower Visean to uppermost Moscovian are summarized here, which are based on very coarse sampling of the section during the past few years. Additional sampling at finer stratigraphic intervals with larger sample sizes are therefore needed for a more detailed investigation. Studies on foraminiferal biostratigraphy and its correlation with conodont biostratigraphy are badly needed for accurate correlations between shallow-marine and deep-marine sections worldwide.
Acknowledgements
This work was supported by National Natural Science Foundation of China (Grant nos. 41072009, 40772005, 41290260, 40839904) and State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (Grant no. 20102105). This manuscript was greatly improved by comments from James E. Barrick from Texas Tech University, the anonymous referees and Dr Mark Allen, editor of Geological Magazine.
