Journal of Paleontology, 92(3), 2018, p. 398–411 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.152


Middle Ordovician actinocerid nautiloids (Cephalopoda) from Xainza County, Tibet, western China, and their paleogeographic implications


Xiang Fang,1,2 Tingen Chen,1 Clive Burrett,3,4 Yongsheng Wang,5 Yonggui Qu,5 Chunzi Zheng,5 Yunbai Zhang,1 Yuandong Zhang,1* and Wenjie Li1,2


1CAS Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China ⟨xfang@nigpas.ac.cn⟩, ⟨chenten40@163.com⟩, ⟨ybzhang@nigpas.ac.cn⟩, ⟨ydzhang@nigpas.ac.cn⟩,


⟨wjli@nigpas.ac.cn⟩ 2University of Chinese Academy of Sciences, Beijing 100049, China 3School of Physical Sciences, University of Tasmania, Tasmania 7001, Australia ⟨cfburrett@gmail.com⟩ 4Palaeontological Research and Education Centre, Mahasarakham University, Mahasarakham 44150, Thailand 5Jilin Institute of Geological Survey, Changchun 130061, China ⟨jlwangysh@163.com⟩, ⟨596089519@qq.com⟩, ⟨zheng_czi@163.com⟩


Abstract.—Actinocerid nautiloids from the Lhasai Formation in the Xainza region are studied systematically for the first time. The nautiloids are identified as Middle Ordovician in age based on stratigraphic correlations with those from North China, Sibumasu, North Australia (northern Gondwana), and North America (Laurentia). A cluster analysis shows strong affi- nities between the actinocerid nautiloids of the Lhasa Terrane and those of the Himalaya, North China, and Sibumasu ter- ranes. Our results support Middle Ordovician paleogeographic reconstructions that place North China rather than South China much closer to Australia. Nine species assigned to six genera of Meitanoceratidae, Wutinoceratidae, Armenoceratidae, Ormoceratidae, and Discoactinoceratidae are described in detail: Pomphoceras nyalamense (Chen, 1975), Pomphoceras yaliense (Chen, 1975), Wutinoceras cf. W. foerstei (Endo, 1930), Mesowutinoceras giganteum Chen in Chen and Zou, 1984, Armenoceras tani (Grabau, 1922), Armenoceras teicherti Endo, 1932, Armenoceras xizangense new species, Deiroceras glo- bosom Zou and Shen in Chen and Zou, 1984, and Discoactinoceras cf. D. multiplexum Kobayashi, 1927.


UUID: http://zoobank.org/ba851fea-e107-4754-a0f4-a70744e325ab Introduction


Ordovician cephalopods of the Xainza region, North Tibet, were first reported by the Tibet Geological Bureau General Survey Team (1980) during mapping of the Shigatse geological map sheet. Subsequently, many Ordovician cephalopods from this region were described by Lai (1982a, b), Chen (1986, 1987), Li and Cheng (1988), and in a series of works by Cheng et al. (2005a, b, c, 2006). However, most of the recorded taxa were from the Upper Ordovician Keerduo and Gangmusang forma- tions, which are both suggested as of Sandbian–Katian age by Xia (1983; Fig. 1.1), based on the outcrops mainly in the Xainza region. There is no conclusive evidence about the Middle Ordovician strata and the corresponding fossils in the Xainza area, northern Tibet (Cheng et al., 2004; Zhang et al., 2004). We have recovered nine species of actinocerid nautiloids,


including one new species, from the Lhasai Formation, Middle Ordovician in Lhasai, Xainza County, northern Tibet. This is the first detailed taxonomic description of Middle Ordovician nautiloids from Xainza, which allows for more detailed strati- graphic correlation and better paleogeographic assessments.


* Corresponding author Geological setting


The Xainza region is located in the northern part of the Lhasa Terrane, which is separated from the Himalaya Terrane by the Yarlung-Zangbo suture to the south and from the Qiangtang Terrane by the Bangon-Nujiang suture to the north (Fig. 1.2; Zhang et al., 2010). The Middle Ordovician Lhasai Formation was first introduced during the geological investigations by the Jilin Institute of Geological Survey (Zhang et al., 2003) in the Lhasai section, eastern Xiongmei town, in the sparsely popu- lated northern part of Xainza County. The Ordovician in this section is represented, in ascending order, by the Middle Ordovician Lhasai Formation, the Middle to Upper Ordovician Keerduo and Gangmusang formations, and the overlying Silurian strata. Among them, in the Lhasai Formation, abundant cephalo-


pods, brachiopods, sponges, bryozoans, and conodonts are recorded (Qu et al., 2002, 2004; Zhang et al., 2003; Zheng, 2005), indicating a Middle Ordovician age. The unit is lithos- tratigraphically divided into three parts: (1) the lower part, consisting of limestone intercalated with some purple thin- bedded, silty, micritic limestone, with abundant cephalopods; (2) the middle part, consisting of limestone intercalated with


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