JoP Vol. 89 No. 5

774

Journal of Paleontology 89(5):768–790

boundary of theD. tablepointensis Zone at the last occurrence of Yangtzeplacognathus crassus (Chen and Zhang, 1993), and the upper boundary at the First Occurrence (FO) of E. suecicus, but the base of this zone is a little higher than the FO of the zonal species. Unlike Zhang’sdefinition, we place the base of the D. tablepointensis Zone at the FO of the nominate species because of the absence of Y. crassus at the Wolonggang Section. In view of the low conodont abundance under the sample W-2-2 (the FO sample of D. tablepointensis), the lower limits of the D. tablepointensis Zone of the Wolonggang section and in south-central China are probably very close. Zhang (1998a) correlated the D. tablepoinetnsis Zone with the upper part of Acrograptus ellesae graptolite zone and the Nicholsonograptus fasiculatus graptolite zone, which coincide with the middle and upper parts of time slice 4b of Webby, Cooper, Bergström, and Paris (2004). A late Kundan age for the zone was suggested (Zhang, 1998a; Löfgren, 2004), and this corresponds to the middle part of Stage slice Dw 2 (middle Darriwilian) of Bergström et al., (2009).

Eoplacognathus suecicus Zone.—This zone occupies the inter- val between about 104m to 185m above the base of the Wolonggang Section. The zonal species, first described by Bergström (1971), is widely distributed in Baltoscandia (Bergström, 1971, 1983; Lindström, 1971; Dzik, 1976, 1994; Löfgren, 1978, 1994, 2000a; Bagnoli and Stouge, 1997; Zhang, 1998a, 1999; Rasmussen, 2001; Viira et al., 2001), North America (Harris et al., 1979; Pyle and Barnes, 2003), North China (An et al., 1983;An and Zheng, 1990; Wang et al., 2014), South China (An, 1987; Ding et al., 1993; Zhang, 1998a; Wu et al., 2010) and New Zealand (Zhen et al., 2011a). Bergström (1971) proposed an E. suecicus Subzone that occupies the lowermost part of the Middle Ordovician Pygodus serra zone in Europe. Later, Löfgren (1978) established the separate E. suecicus Zone underlying the P. serra Zone in Jämtland, Sweden. Zhang (1998a) redefined this zone as the interval between the FO of E. suecicus Bergström, 1971 and the FO of Yangtzeplacognathus foliaceus (Fåhræus, 1966), and confined it to the Aserian. Bergström et al. (2009) dated this zone as the upper part of Dw 2. Zhang (1998d) subdivided the E. suecicus Zone into two subzones, the lower P. lunnensis Subzone and the upper P. anitae Subzone. The base and top of the P. lunnensis Subzone were defined by the FOs of P. lunnensis Zhang, 1998 and P. anitae Bergström, 1983. The lower and upper boundaries of the P. anitae Subzone were taken as the FOs of P. anitae and Yangtzeplacognathus foliaceus. Such subdivisions have been generally accepted (e.g., Löfgren and Zhang, 2003; Bergström, 2007b; Agematsu et al., 2013; Wang et al., 2013b). The E. suecicus Zone of the Wolonggang Section can also be sub- divided into the same two subzones as those were proposed by Zhang (1998d).

Pygodus lunnensis Subzone.—This level is represented by a diverse assemblage recovered from sample W-6-1. Being the most diverse one in the Wolonggang section, this sample includes 26 species, Ansella jemtlandica, Bergstroemognathus sp., Besselodus semisymmetricus (Hamar, 1966), Cornuodus longibasis, Costiconus ethingtoni, Drepnodus arcuatus Pander, 1856, D. reclinatus (Lindström, 1955), Drepanoistodus

basiovalis, Dzikodus tablepointensis, Eoplacognathus suecicus, Erraticodon hexianensis An and Ding, 1985, Gen. et sp. indet., Onyxodus acuoliratus Watson, 1988, Panderodus sulcatus (Fåhræus, 1966), Periodon hankensis, P. macrodentatus, P. zgierzensis Dzik, 1976, Phragmodus polonicus, Plectodina onychodenta An and Xu, 1983, Polonodus

sp.,

Protopanderodus caleatus Bagnoli and Stouge, 1997, P. cooperi, P. graeai (Hamar, 1966), P. varicostatus, Pygodus lunnensis, and Spinodus spinatus. The subzone index is the most distinctive species of this assemblage, along with several other biostratigraphically important species, including Plectodina onychodenta, Periodon zgierzensis, Phragmodus polonicus and Panderodus sulcatus. Although P. lunnensis has previously been reported only from Sweden (Zhang, 1998d; Zhang and Sturkell, 1998; Bergström, 2007b) and Thailand (Agematsu et al., 2013), and was also recorded as Polonodus magnum Albanesi 1998 from Argentina (Albanesi et al., 1998; Ortega, 2007), it is a potentially important age-diagnostic taxon in deep-water Darriwilian bio-realms.

Pygodus anitae Subzone.—This subzone is ranging from 128m to 185m above the base of the Wolonggang Section, and is characterized by the occurrence of P. anitae along with 23 other species, including Ansella crassa, A. jemtlandica, A. nevadensis (Ethington and Schumacher, 1969), Besselodus semisymmetricus,

Cornuodus longibasis, Costiconus

ethingtoni, Dapsilodus viruensis, Drepnodus arcuatus, D. reclinatus, Dzikodus tablepointensis, Eoplacognathus suecicus, Panderodus gryphus (An, 1985), Panderodus sulcatus, Periodon hankensis, P. macrodentatus, P. flabellum, P. zgierzensis, Phragmodus polonicus, P. sp., Plectodina onychodenta, Protopanderodus cooperi, P. varicostatus and Spinodus spinatus. Most concurrent species, including all of the biostratigraphically important species, of this Subzone extend from the underlying P. lunnensis Subzone. Compared to P. lunnensis, its proposed descendent P. anitae has a much wider geographic range, being recorded from Baltoscandia (Bergström, 1983; Zhang, 1998d; Zhang and Sturkell, 1998; Bergström, 2007b) , North China (Wang and Luo, 1984; An and Zheng, 1990), Argentina (Ottone et al., 1999; Albanesi and Ortega, 2002; Ortega et al., 2007), Russia (Melnikov, 1999), Tarim (Zhao et al., 2000) and New Zealand (Zhen et al., 2011a). The subzonal species stratigraphically ranges from the upper E. suecicus Zone to the lower part of the Y. foliaceus Subzone of the P. serra Zone (Löfgren, 1978; Zhang and Sturkell, 1998), but does not co-occur with P. serra. The P. anitae-yielding sample HT-1-1 at the base of the Hatuke Creek Section is included into the P. anitae Zone because no Y. foliaceus has been found in it.

Pygodus serra Zone.—P. serra (Hadding, 1913), one of key species in global Ordovician conodont biostratigraphy, was recovered from two samples (HT-3-1 and HT-5-2) in the lower part of the Wulalike Formation of the Hatuke Creek Section and is associated with ten other species, including Besselodus semisymmetricus, B. variabilis (Webers, 1966), Coelocerodontus trigonius, Cornuodus longibasis, Costiconus ethingtoni, Drepanodus reclinatus, Periodon aculeatus Hadding, 1913, P. hankensis, P. flabellum and P. zgierzensis.

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