Journal of Paleontology, 89(5), 2015, p. 768–790 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2015.54


Ordovician (middle Darriwilian-earliest Sandbian) conodonts from the Wuhai area of Inner Mongolia, North China


Xiuchun Jing,1,2 Hongrui Zhou,1 and Xunlian Wang1,2


1School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China ⟨jxch@cugb.edu.cn⟩, ⟨zhouhr@cugb.edu.cn⟩ 2State Key Laboratory of Geobiology and Environmental Geology, China University of Geosciences, Beijing 100083, China ⟨wxl@cugb.edu.cn⟩


Abstract.—Forty-two conodont species belonging to 26 genera, which span the middle Darriwilian to the earliest Sandbian interval, are documented from theWolonggang and Hatuke Creek sections in theWuhai area of InnerMongolia, North China. This conodont fauna is dominated by cosmopolitan and widespread species and accompanied by several endemic taxa. Four conodont zones, the Dzikodus tablepointensis, Eoplacognathus suecicus, Pygodus serra,and P. anserinus Zones, and three subzones, the Pygodus lunnensis, P. anitae,and Yangtzeplacognathus foliaceus Subzones, are recognized. Because of its slope habitat, the conodont fauna ofWuhai area differs from the coeval faunas on the North China Platform, which reflect a shallower and warmer water environment, but is similar to the contemporaneous faunas in Baltoscandia, South China, and Tarim. Moreover, the studied sections share several stratigraphically diagnostic taxa with the counterparts of the North China Platform and Western Newfoundland, which makes it an effective link for biostratigraphic correlations both regionally and internationally. The stratigraphically regular occurrences of Spinodus spinatus, a good index of a deep-water environment, represent a Spinodus biofacies that agrees with the Ordovician paleo-tectonic regimes of North China.


Introduction


The Wuhai area, which is situated in the southwest of Inner Mongolia Autonomous Region (Fig. 1A), was in the marginal and deep part of the North China plate during Ordovician time (Feng et al., 1990, 1999; Feng et al., 2004; Feng et al., 1998; Fu and Zheng, 2001; Li et al., 2012). The Ordovician strata of the Wuhai area are biostratigraphically important because of the richness of their macrofaunas and microfaunas (e.g., Lu, 1954; Mu, 1959; Zhang, 1959; Zhang, 1962; Chen, 1976; Wang and Luo, 1984; An and Zheng, 1990). These fossiliferous Ordovician strata are nearly 1000mthick (An and Zheng, 1990) and are exposed around the town of Hainan. They represent continuous deposition on the western edge of the North China plate. Ordovician conodonts of the Wuhai area were first reported


by An et al. (1983), who described seven species from the Klimoli and Wulalike formations. Based on the findings, they made a correlation of Ordovician lithological successions between Wuhai and the North China Platform (An et al., 1983, table 13). Shortly afterward, Wang and Luo (1984) documented in more detail the Ordovician conodonts of the area, and recognized six Ordovician biostratigraphic units from the Zhuozishan Formation to the Sheshan Formation. An and Zheng (1990, p. 29–39) subsequently studied the Ordovician con- odonts from the Wuhai area in a comprehensively bed by bed recording of species. Most recently, Wang and colleagues (Wang et al., 2013b; Wang et al., 2013c) examined the conodont fauna of the Klimoli Formation in the Dashimen Section, which is approximately 20km south of the town of Wuhai, and


distinguished two conodont biozones in the Klimoli. In addition, the Ordovician conodont zonations of the Wuhai area were reported briefly in two other publications (Chen et al., 1984; Feng et al., 1998). These investigations have greatly improved our knowledge of Ordovician conodonts from marginal areas of the North China plate. However, most of these publications were written in the Chinese language, and the latest taxonomic and biostratigraphic views have not been represented. This makes those studies, which form the basis for the understanding of the Chinese Ordovician conodonts, not widely available or else inaccessible to international researchers. Therefore, we present this taxonomic and biostratigraphic study of this critical area in North China. During a field survey in August of 2011, limestone samples


were collected from two well-exposed sections of the Wuhai area (Fig. 1). These yielded well-preserved conodonts that span the middle Darriwilian to the earliest Sandbian. In the present study, we identify these conodonts and the conodont biostratigraphy, and discuss the paleoecology of this fauna.


Geological setting


The Wuhai area is 430km southwest of Hohhot (the capital city of Inner Mongolia Autonomous Region) and 140km northeast of Yinchuan (the capital city of Ningxia Autonomous Region) (Fig. 1B). It is located in a nearly south-north striking intracontinental deformation zone, which starts from the Zhuozishan Mountains to the north, goes along the Helanshan Mountains southward, and ends at the Liupanshan Mountains


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