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780


Journal of Paleontology 89(5):768–790


three genera reach their prominent peaks all in the sample W-6-1 (Table 1). It should also be noted that the sample W-6-1 was collected from a storm-generated layer (bioclastic packstone), which means the abnormal abundance of the three facies-indicating genera in this sample was caused by the intermingling of fossils removed from the shallower water. Hence, we conclude that the Periodon, Protopanderodus and Costiconus biofacies are shallower than the ancient sea depth of Wuhai (Fig. 5). Spinodus spinatus, another facies indicator, shows a regular stratigraphic occurrence through the two investigated sections (Table 1). This taxon was interpreted as mesopelagic and to be restricted to platform edges or to adjacent deep-water basinal environments (Zhang, 1998a). The abun- dance of Spinodus spinatus in our sections apparently has not been affected by the mixture of shallow water conodonts, and this suggests Spinodus spinatus most likely inhabited this environment (Fig. 5). Therefore, a Spinodus biofacies is recognized in the studied sections. This conclusion is in agreement with the Ordovician paleo-tectonic regimes distinguished in the North China (Feng et al., 1998).


Conclusions


The conodont biostratigraphy and biofacies of the Klimoli and Wulalike formations of the Wuhai area in Inner Mongolia, North China, were investigated. The middle Darriwilian and earliest Sandbian conodont faunas of this area comprise species typical of the cold/deep water fauna known from Baltoscandia, South China, and Tarim. The presence of several pandemic and endemic stratigraphically diagnostic taxa make the regional and global correlations relatively straightforward and reliable. Moreover, abundant facies-dependent conodonts can be used for biofacies discrimination. Middle Darriwilian and earliest Sandbian conodont zones


and subzones are well documented both in the Wolonggang and Hatuke Creek sections. These biostratigraphic units are the Dzikodus tablepointensis Zone, the Eoplacongathus suecicus Zone (subdivided into the Pygodus lunnensis and P. anitae Subzones), the P. serra Zone (only the Yangtzeplacognathus foliaceus Subzone was recognized), and the P. anserinus Zone, in ascending order. The zones and subzones of Wuhai area are comparable to the intervals from the Eoplacognathus pseudoplanus Zone to the Pygodus anserinus Zone of the standard zonation in Baltoscandia, the Dzikodus tablepointensis


Zone to the Yangtzeplacognathus jianyeensis–Pygodus anserinus Zone in South China and the Histiodella holodentata Zone to the Pygodus anserinus Zone in Tarim. The biostrati- graphic units in the present study also correlate with the interval from the Histiodella holodentata–Tangshanodus tangshanensis Zone to the middle Tasmanognathus sishuiensis Zone in the platform facies of North China. The Dzikodus tablepointensis Zone to the Eoplacognathus suecicus Zone of the Wolonggang Section correspond to the upper Periodon macrodentatus Zone and the P. zgierensis Zone in western Newfoundland. Based on the stratigraphic distribution characteristics of


four well-known depth-dependent genera, the Spinodus bio- facies was discerned in our studied successions. The lithology, and the conodont association of open-sea taxa with epi- and mesopelagic lifestyle indicate a slope environment, which agrees with the Ordovician paleo-tectonic regimes of the North China.


Systematic paleontology


All figured specimens in this paper are housed in the School of Earth Sciences and Resources, China University of Geosciences (Beijing), with the prefix CUGB. Collection numbers of all illus- trations shown in Figures 6 to 9 are prefixed CUGB-jxch. Most of the conodont species recovered from our samples are considered adequately described in previous publications, and only selected taxa are included in the descriptions. Taxa documented herein are alphabetically listed according to their generic assignment, with family level and higher classification omitted.


Genus Dzikodus Zhang, 1998 Type species.—Polonodus tablepointensis Stouge, 1984.


Remarks.—As summarized by Zhen and Percival (2004), the derivation of the genus Dzikodus has been taxonomically complex. Zhang (1998a) established Dzikodus to accommodate the Polonodus tablepointensis species group of Stouge (1984), the sinistral and dextral Pb elements of Dzikodus are unpaired and do not mutually form mirror images, unlike the situation in Polonodus. For Polonodus (inclusive of Dzikodus), Löfgren (1990) proposed a seximembrate species apparatus, one geniculate (M), and three ramiform (Sa, Sb, and Sd) elements in association with the two platform (Pa and Pb) elements. Zhang (1998a) documented the different growth stages of the


Figure 7. (1–5) Eoplacognathus suecicus Bergström, 1971; (1–3) Pa, upper view, from W-6-1, CUGB-jxch660, CUGB-jxch658, CUGB-jxch657; (4, 5) Pb, upper view; (4) from W-6-1, CUGB-jxch659; (5) from W-10-1, CUGB-jxch770. (6) Venoistodus balticus Löfgren, 2006; M, inner lateral view, from W-10-3, CUGB-jxch779. (7–9) Panderodus sulcatus (Fåhræus, 1966); (7) graciliform, lateral view, from W-9-2, CUGB-jxch761; (8) falciform, lateral view, from W-6-1, CUGB-jxch732; (9) arcuatiform, lateral view, from HT-6-1, CUGB-jxch833. (10, 11) Erraticodon hexianensis An and Ding, 1985; (10) Sc, lateral view, from W-6-1, CUGB-jxch655; (11) Sb, lateral view, from W-6-1, CUGB-jxch656. (12–14, 18, 23, 24) Phragmodus polonicus Dizk, 1978; (12–14) Pb, (12, 13) inner lateral view, from W-6-1, CUGB-jxch697 and CUGB-jxch696, (14) outer lateral view, from W-2-1, CUGB-jxch625; (18) Sb, inner lateral view, from W-1-2, CUGB-jxch620; (23, 24) Sc, inner lateral view; (23) from W-8-2, CUGB-jxch754; (24) from W-6-1, CUGB-jxch685. (15–17) Phragmodus sp. (15, 16) Sa, lateral view, from W-4-1, CUGB-jxch640, CUGB-jxch638; (17) Sb, from W-9-3, CUGB-jxch769. (19–22) Plectodina onychodonta An and Xu, 1983; (19–21) Pa, lateral view; (19) from W-6-1, CUGB-jxch653; (20) from W-8-1, CUGB-jxch745; (21) from W-7-1, CUGB-jxch733; (22) Sa, posterior view, from W-8-1, CUGB-jxch753. (25) Bergstroemognathus? sp.; Sb, posterior view, from W-6-1, CUGB-jxch654. (26–28) Protopanderodus calceatus Bagnoli and Stouge, 1997; (26) Pb, lateral view, from W-10-3, CUGB-jxch782; (27) Sc, lateral view, from W-10-3, CUGB-jxch785; (28) M, inner lateral view, from W-6-1, CUGB- jxch702. (29–35) Protopanderodus cooperi (Sweet and Bergström, 1962); (29) Pb, lateral view, from HT-6-1, CUGB-jxch836; (30, 31) Sa, lateral view, from W-6-1, CUGB-jxch678, CUGB-jxch725; (32, 33) Sb, lateral view; (32) from W-6-1, CUGB-jxch679; (33) from HT-6-1, CUGB-jxch837; (34, 35) Sc, lateral view, from W-6-1, CUGB-jxch718, CUGB-jxch720. (36) Protopanderodus graeai (Hamar, 1966); Sb, lateral view, from W-6-1, CUGB-jxch693. (37–41) Protopanderodus varicostatus (Sweet and Bergström, 1962); (37) Pb, lateral view, from HT-6-1, CUGB-jxch824; (38) M, inner lateral view, from HT-6-1, CUGB-jxch835; (39) Sb, inner lateral view, from W-9-2, CUGB-jxch760; (40, 41) Sc, lateral view; (40) from W-6-1, CUGB-jxch723; (41) from W-4-1, CUGB-jxch648. Scale bars represent 50 μm.


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