Journal of Paleontology, 91(1), 2017, p. 12–24 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2016.122


Depauperate fusulinid faunas of the Tengchong Block in western Yunnan, China, and their paleogeographic and paleoenvironmental indications


Yukun Shi,1,2 Hao Huang,3 and Xiaochi Jin3


1School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China ⟨ykshi@nju.edu.cn⟩ 2State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Science, Nanjing


210000, China 3Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China ⟨geohaohuang@gmail.com⟩, ⟨jinxchi@cags.ac.cn⟩


Abstract.—New samples of fusulinids collected in the Tengchong Block, western Yunnan, China, are systematically studied and presented here. The fusulinid fauna from the Xishancun section in the Shanmutang area is dominated by Chusenella and Nankinella, whereas that from the Shuangheyan area is composed mainly of Chusenella and Schwagerina. Both faunas are dated as Roadian–Capitanian (middle Permian). These new findings are integrated with fusulinid taxa reported earlier from the block to demonstrate the taxonomic features and paleogeographic significance of Permian fusulinids. The low generic diversity through early and middle Permian and the paucity of middle Permian neoschwagerinids and verbeekinids in the block confirm its Gondwana-affinity attributes. Moreover, the Permian fusulinids of the Tengchong Block are depauperate; i.e., consisting of a limited number of species with abundant individuals. This particular feature commonly suggests an inhospitable environment, and carbonates of varied facies containing these faunas in the Tengchong Block suggest a facies-independent factor as the reason, most likely the relatively low temperature of seawater.


Introduction


The Tengchong and Baoshan blocks, in the western Yunnan of Southwest China, are considered to beGondwana derived,mainly on the basis of their Permo-Carboniferous Gondwana-affinity sediments (diamictites, pebbly mudstones) and fossils (cool- to cold-water faunas;Wang, 1983; Jin, 1994, 1996, 2002;Wopfner, 1996; Fig. 1). Both blocks have been suggested to have been at the northern margin of Gondwana during the Permo-Carboniferous glaciation and detach thereafter (e.g., Wopfner, 1996; Shi and Archbold, 1998; Ueno et al., 2003; Wang et al., 2013). The carbonate deposition starting in the late early Permian marks the rapid climate amelioration after the glaciation (Jin et al., 2011). The continuation of the carbonate environment resulted in the formation of Permian (to Triassic) carbonate successions. The understanding of the remarkable climate transition in


the Tengchong Block is mainly attributed to the work since the 1980s. Geological mapping and a few studies on Carboniferous and Permian strata in the Tengchong Block have discovered a number of fossils and accumulated important geological data (e.g., Geological Survey of Yunnan, 1979, 1985, 1986; Sheng and He, 1983; Fan, 1993; Nie et al., 1993; Yang, 1998; Jin, 2002). The brachiopods, bryozoans, crinoids, and small corals reported from the late Carboniferous–early Permian clastic sediments indicated a cool climate, whereas the fusulinids discovered from the Permian carbonates suggested somewhat warmer water (Nie et al., 1993; Jin, 2002; Duan et al., personal communication, 2005; Shi et al., 2008; Jin et al., 2011). Nevertheless, among these fossils, only limited materials have


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been illustrated and described (e.g., Sheng and He, 1983; Fan, 1993; Nie et al., 1993; Yang, 1998; Shi et al., 2008); thus most of these reported data are unexaminable for further discussions concerning paleoecology and paleobiogeography. In particular, although fusulinid foraminifera have long been recognized as an environment-sensitive indicator (e.g., Thompson, 1948; Ross, 1967, 1995; Rui, 1981; Leven, 1993), the fusulinids in the Tengchong Block were not systematically studied until several years ago (Shi et al., 2008). During recent years, we have conducted several field trips in


the Tengchong Block and discovered a considerable number of fusulinid fossils. According to the results of our studies, the early Permian fusulinids are dominated by Eoparafusulina,and the middle Permian fusulinids are dominated by Chusenella and Monodiexodina. These genera have also been found inmany other Gondwana-derived blocks although with specific distinctions (Shi et al., 2008). In 2010 and 2013, more middle Permian fusulinid specimens were found in both northern and southern regions of the Tengchong Block. This paper describes these newly discovered fossils and discusses their particular taxonomic features. In conjunction with previously reported data, these new materials are then used to unravel the paleogeographic and paleoenvironmental details of the Tengchong Block.


Geologic setting


The Tengchong Block is bounded by the Nujiang fault zone on the east. Its west boundary is hard to define due to the lack of available data, although it has been suggested to lie roughly


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