Durham Research Online Deposited in DRO: 06 September 2019 Version of attached le: Accepted Version Peer-review status of attached le: Peer-reviewed Citation for published item: Rong, Jia-Yu and Aung, Kyi Pyar and Zhan, Ren-Bin and Huang, Bing and Harper, David A.T. and Chen, Di and Zhou, Hang-Hang and Zhang, Xiao-Le (2020) 'The latest Ordovician Hirnantia brachiopod fauna of Myanmar : signicance of new data from the Mandalay Region.', Palaeoworld, 29 (1). pp. 1-30. 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Durham University Library, Stockton Road, Durham DH1 3LY, United Kingdom Tel : +44 (0)191 334 3042 | Fax : +44 (0)191 334 2971 https://dro.dur.ac.uk The latest Ordovician Hirnantia brachiopod Fauna of Myanmar: Significance of new data from the Mandalay Region Jia-Yu Rong a *, Kyi Pyar Aung b, Ren-Bin Zhan a, Bing Huang a, David A.T. Harper c, Di Chen d, Hang-Hang Zhou e, Xiao-Le Zhang a a State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China b Department of Geology, Taunggyi University, Southern Shan State, Myanmar c Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK d School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China e University of Science and Technology of China, Hefei 230026, China * Corresponding author. E-mail address: [email protected] Abstract A new, latest Ordovician brachiopod fauna is systematically described from the Hwe Mawng Purple Shale Member (Hirnantian) of the Naungkangyi Group of Pa-thin area, Mandalay Region, Myanmar, revealing one of the most diverse representatives of the typical Hirnantia Fauna. Rhynchonelliformean, craniiformean and linguliformean brachiopods studied belong to 23 genera and a few indeterminate taxa, among which the most abundant genus Kinnella, along with the four common genera or subgenera (Paromalomena, Pseudopholidops, Coolinia, and Dalmanella), and other genera (such as Cliftonia, Draborthis, Hindella, Hirnantia, Leptaena, Mirorthis, Plectothyrella, Pseudopholidops, Skenidioides, and Xenocrania) are recorded for the first time. This high diversity Hirnantia Fauna represents an ecological differentiation within the benthos of the Sibumasu Terrane during the end 1 Ordovician global crisis. The palaeoeco-unit named herein as the Kinnella-Paromalomena community is assigned to lower BA3. This paper includes a taxonomic revision with the following conclusions: 1) Sinomena Zeng et al. and Yichangomena Zeng et al. are treated as junior synonyms of Eostropheodonta Bancroft; 2) Hubeinomena Zeng et al. is regarded as a juvenile form of Coolinia Bancroft; 3) Paramirorthis Zeng et al. is considered an immature growth stage of Mirorthis Zeng; 4) Shanomena Cocks and Fortey is treated as a junior synonym of Paromalomena Rong; 5) Scenidium? medlicotti Reed is redesignated as the type species of Kinnella Bergström to replace Hirnantia? kielanae Temple. The distribution of the Hirnantia Fauna in Myanmar, Thailand and western Yunnan of the Sibumasu Terrane highlights the distinctive nature of the Mandalay fauna, and the analysis of the Hirnantia Fauna of Sibumasu shows that Sibumasu was not located far from the South China and Lhasa palaeoplates during late Middle and Late Ordovician. Keywords: Latest Ordovician; Hirnantia brachiopod Fauna; Myanmar; faunal cluster analysis 1. Introduction It has been more than 100 years since Reed (1915) first described shelly fossils originally collected by officers of the Indian Geological Survey, at the end of the nineteenth century, from the basal Panghsa-pye Formation (partly Hirnantian) in Northern Shan State, Myanmar. These fossils, collected from a poorly accessible locality, were considered a typical representative of the Hirnantia Fauna (Temple, 1965), and were later revised by Cocks and Fortey (2002), although Hirnantia itself was not present. In January 2017, the present authors (Rong, J.Y. and Zhan, R.B.) visited the Mandalay Region at the invitation of the Geological Survey of Myanmar; and a large number of shelly fossils from the Hwe Mawng Purple Shale Member (Hirnantian) of the Naungkangyi Group were collected in the Pa-thin area (Fig. 1). The brachiopods are the most abundant and predominant elements, comprising about 97% of the whole fauna and containing 23 named 2 genera along with a few indeterminate species which are described and/or illustrated herein. The nature and relationship of the Hirnantia Fauna of Myanmar are analyzed. The Hirnantia fauna in various regions of the Sibumasu Terrane is briefly reviewed. The Hirnantia Fauna has been documented from many plates or terranes throughout the world, including Africa, Avalonia, Baltica, European Peri-Gondwana (e.g., Carnic Alps, Armorica, Sardinia, Spain, and Portugal), the Kazakhstanian terranes, marginal Laurentia, Perunica, San Juan in the Argentinian Precordillera, Sibumasu, South China, Lhasa (central Xizang), and a few others. It is known to be, geographically, the widest distributed brachiopod fauna in Phanerozoic (Rong et al., 2017). 2. Geological setting The Lower Paleozoic rocks of Myanmar mainly outcrop on the Shan Plateau (Aye Ko Aung and Cocks, 2017), where the Ordovician–Silurian boundary strata are widely distributed and usually well exposed. The locality yielding the Hirnantia Fauna is exposed along a poorly paved country road, about 40 km east of Mandalay City in the Pa-thin area of Pyin Oo Lwin, Mandalay Region (GPS reading N21°56'24.5" and E96°30'11.2") (Fig. 1). The Hwe Mawng Purple Shale Member (Hirnantian), originally reported as the basal Panghsa-pye Formation (Reed, 1915; Cocks and Fortey, 2002), yielding the diverse Hirnantia fauna, is underlain and overlain conformably by graptolitic shales, i.e., the top Naungkangyi Group and the basal Panghsa-pye Formation respectively (Fig. 2). This 45 cm- thick member is composed mostly of light brown, medium- to thin-bedded silty mudstone intercalated with quartzose wacke (Fig. 3). The Hirnantia Fauna is encountered only in the silty mudstone, which generally lacks any macroscopic evidence of major disturbance of the substrate except for a few borings (2–3 mm in diameter), and thus may represent deposition in quiet shelf environments. The quartzose wacke consists of angular to subangular detrital grains, which are matrix supported and poorly sorted. Mineralogical and textural maturities of the wacke are both poor due to the presence of rare feldspar (approximately less than 2% of the whole contents) and a high content of groundmass, respectively. The rare occurrence of 3 quartzose wacke in the silty mudstone may suggest either a sudden shift from shelf environments into shallower-water settings (e.g., nearshore) due to regression or alternatively, disturbances of seabed (e.g., gravity flows). In the view of sedimentary and fossil evidence, the latter may be more likely. 3. Material and methods The Pa-thin area of the Mandalay Region, where the brachiopods were collected for this study, is located approximately 110 km southwest of the old site of the Northern Shan State reported by Reed (1915). Both sites belong to the Sibumasu Terrane. Among the associated fossils, surprisingly, trilobites, usually common or abundant associated with the Hirnantia Fauna elsewhere, are small in size and rare in both abundance and diversity. There are many co-occurring animal groups, including bivalves, bryozoans, crinoids (debris), gastropods, hyolithids, machaeridians, ostracods, trilobites, and a few others, but they are much fewer than the brachiopods. All the fossils studied are preserved as moulds. The preservation is good, but the matrix is rather coarse, fragile and easily broken because of the deep weathering and unconsolidated matrix. To display external and internal morphologies in detail, latex casts are needed, although it is challenging to strengthen fossils prior to casting. PVB ethanol solution (a mixture of PVB powder and ethanol) and latex solutions I and II were employed for this purpose. The latex solution was prepared by mixing the commercially available product MOLD BUILDER and water at a volumetric ration of 1:5 (I) and 1:2 (II). A total of 1221 specimens were examined in this study. To test the sampling sufficiency, we have counted the number of specimens of each species and proceeded with individual rarefaction analysis using the software PAST (Hammer et al., 2001) with steps of 10. The result clearly shows that the curve reaches a nearly horizontal threshold, which indicates that our sample size is sufficient (Fig. 4). 4 All specimens illustrated herein are housed in Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences (catalogue with NIGP as a prefix of registered numbers). 4. Age determination The bed yielding the brachiopods in the Pa-thin area can probably be correlated with that near the base of the Pangsa-pye Formation in the Northern Shan State (Reed, 1915; Cocks and Fortey, 2002). It is further confirmed by graptolites from the underlying and overlying shales based on Xu Chen’s identification. The graptolites underneath the Hirnantia Fauna in the Mandalay Region include Metabolograptus extraordinarius, Normalograptus pseudovenustus, Koreanograptus acanthus and others, indicating a level of the M.