JoP Vol. 89 No. 5

Jing et al.—Ordovician conodonts from Wuhai area

The Pygodus serra Zone was erected by Bergström (1971) as coinciding with the stratigraphic range of P. serra, and its upper boundary was defined to the FO of P. anserinus Lamont and Lindström, 1957 and the disappearance of P. serra. Bergström (1971) further subdivided the zone into five subzones, namely Eoplacognathus suecicus, “E.” foliaceus, “E.” reclinatus, “E.” robustus and E. lindstroemi subzones. Löfgren (1978) amended the lower boundary of this zone to be the first appearance of “E.” foliaceus, with the subzones of this zone only being the upper four subzones. When the co-occurrence of P. serra and its descendent P. anserinus was found in Tarim (Bergström and Finney, 1999) and Baltoscandia (Bergström et al., 2000), the upper boundary of the zone was defined by the appearance of P. anserinus. Accordingly, the P. serra zone is limited into the interval between the FO of Y. foliaceus and the FO of P. anserinus. As summarized by Bergström (2007b), this zone has an extraordinarily wide geographic range, being known from numerous localities in Baltoscandia, British Isles, North America, Argentina, Australia, China, and other parts of the world. In China, the P. serra Zone has been extensively reported from North China (Wang and Luo, 1984), South China (An, 1987; Ding et al., 1993; Wang et al., 1995) and Tarim (Zhang and Gao, 1990; Zhou and Chen, 1992; Wang and Qi, 2000; Zhao et al., 2000; Zhen et al., 2011b; Wang et al., 2013d). This zone was correlated to the lower and middle parts of Dw 3 (Bergström et al., 2009).

Yangtzeplacognathus foliaceus Subzone.—The assemblage of this zone recovered from sample W-10-3 at 185m above the base of the Wolonggang section. The accompanying conodonts includes 12 species, namely Besselodus semisymmetricus, Coelocerodontus trigonius, Costiconus ethingtoni, Dapsilodus viruensis, Panderodus gryphus, Periodon aculeatus, P. flabellum, Protopanderodus calceatus, P. varicostatus, Pygodus anitae, Spinodus spinatus and Venoistodus balticus Löfgren, 2006. The Y. foliaceus Subzone (An, 1987; Chen and Zhang, 1984a, 1984b; Ding et al., 1993) was initially recognized as a range zone (An, 1981) in South China. Later, the Y. foliaceus Zone was widely used in the Guniutan Formation of South China (e.g., Zhang, 1998a; Wu et al., 2010; Heredia, Carlorosi, Mestre, and Soria, 2013). Considering that the Y. foliaceus Zone was normally recognized based upon the absence of P. serra beneath the Pygodus anserinus Zone, we adopt the zonal scheme of Baltoscandia and discriminate the Y. foliaceus Subzone in the study area. As mentioned above, the co-occurrence of Y. foliaceus and Pygodus anitae, along with the absence of P. serra suggest a horizon in the lower part of the Y. foliaceus Subzone.

Pygodus anserinus Zone.—The zonal species, an important age- diagnostic taxon like its ancestor P. serra, was recorded in three samples (HT-5-2, HT-6-1, and TH-6-2) in the middle and upper part of the Wulalike Formation of the Hatuke Creek Section. Associated species are Ansella jemtlandica, Besselodus semisymmetricus, Costiconus ethingtoni, Drepanodus arcuatus, D. reclinatus, Panderodus sulcatus, Periodon aculeatus, P. flabellum, P. hankensis, P. zgierzensis, Protopanderodus cooperi, P.

varicostatus, Pseudooneotodus mitratus (Moskalenko, 1973), Pygodus serra, Spinodus spinatus, and

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Venoistodus balticus. P. anserinus is a morphologically distinctive species with a stratigraphic range spanning the P. anserinus Zone and the lower A. tvaerensis Zone (Sweet, 1988). Like P. serra, P. anserinus is also a world-wide dis- tributed species. Around North China Platform, P. anserinus has a broader distribution than P. serra along the eastern and southeastern margin. The former species has been recovered from Longxian (Li and Yu, 1983; An and Zheng, 1990), Wuhai (Wang and Luo, 1984; An and Zheng, 1990), and Pingliang (An and Zheng, 1990; Finney et al., 1999; Wang, 2000; Wang, Bergström, Zhan, and Zhang, 2013a; Wang et al., 2013b). Bergström et al. (2000) identified an interval in the basal part of the P. anserinus Zone where P. serra and P. anserinus co-occur. Moreover, P. serra ranges well into the upper P. anserinus Biozone in the Saergan Formation at the Dawangou section of Tarim (Bergström and Finney, 1999; Zhen et al., 2011b). Zhang (1998d) differentiated two morphotypes of P. anserinus: the early form has denticles of the fourth row developed only on the distal part of the platform; the late form has a well-developed fourth row. Most Pa elements (Fig 9:13-16) of the P. anserinus from HT-6-1 and HT-6-2 are late form, only some (Fig 9:11) from HT-5-2 and a few (Fig 9:12) from HT-6-1 represent the early form. After analyzing the symbiotic relationship between conodonts and graptolites from the Yenwashan Formation at the Huangnitang Section (the GSSP section for the base of the Darriwilian), Zhen et al. (2009) concluded that a mixture of advanced and primitive forms together with the absence of P. serra and P. xinjiangensis Wang and Qi, 2001 suggests a correlation with the upper part of the P. anserinus Zone. Therefore, the sampling horizon of HT-5-2 is referred to the lower part of P. anserinus Zone which correlates with the upper part of Dw3 (Bergström, 2009), while those of HT-6-1 and HT-6-2 are assigned to the upper part of the P. anserinus Zone that corresponds to the lower part of the Sa1 (lower Sandbian) of Bergström et al. (2009).

Correlations

The conodont fauna of the Klimoli and Wulalike formations in the Wuhai area are generally similar to the coeval faunas of Baltoscandia (Löfgren, 1978; Löfgren and Zhang, 2003; Bergström, 2007b), South China (Zhang, 1998a) and Tarim (Zhou and Chen, 1992; Wang and Zhou, 1998; Zhen et al., 2011b). Moreover, the conodont fauna in the present study shares several stratigraphically diagnostic taxa with the coeval faunas of the North China Platform (An et al., 1983; An and Zheng, 1990; Wang et al., 2014) and Western Newfoundland (Stouge, 1984; Stouge, 2012). This makes it an effective link for biostratigraphical correlations both regionally and globally. The correlations are shown in Figure 4.

Baltoscandia.—Southern Sweden is the most intensively studied area in Baltoscandia for research on Ordovician conodonts. The Ordovician conodont biostratigraphy of Southern Sweden was first summarized by Lindström (1971) andBergström (1971),with only minor changes made by later conodont workers (e.g., Löfgren, 1978, 2000a, 2000b; Zhang, 1998c, 1998d). On the basis of mod- ernmultielement taxonomy, the vertical ranges and biostratigraphy of the early to middleDarriwilian conodonts from southern Sweden

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