Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography

Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography

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Accepted Manuscript Full length article Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography Jingfang Bo, Xunlian Wang, Jinhan Gao, Jianxin Yao, Genhou Wang, Engang Hou PII: DOI: Reference:

S1367-9120(17)30223-7 http://dx.doi.org/10.1016/j.jseaes.2017.05.006 JAES 3071

To appear in:

Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

24 February 2017 27 April 2017 6 May 2017

Please cite this article as: Bo, J., Wang, X., Gao, J., Yao, J., Wang, G., Hou, E., Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography, Journal of Asian Earth Sciences (2017), doi: http://dx.doi.org/10.1016/j.jseaes.2017.05.006

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Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography

Jingfang Bo a,b, Xunlian Wang b, Jinhan Gao b*, Jianxin Yao a*, Genhou Wangb, Engang Hou b

a

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR

China b

School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083,

PR China

Corresponding author: Jianxin Yao in Institute of Geology, Chinese Academy of Geological Sciences, Baiwanzhuang Street,

Beijing

100037,

PR

China.

E-mail

address:

[email protected],

[email protected]; Phone numbers: 13691576369, +86 10 68995116. Jianhan Gao at School of Earth Sciences and Resources, China University of Geosciences (Beijing), Xueyuan Road 29, Beijing 100083, PR China. E-mail address: [email protected]; Phone numbers: 13801125030, +86 10 82323488.

Abstract: Upper Triassic reef corals from the Riganpeicuo Formation in northern

Tibet

represent

important

scleractinian

coral fauna that

help

explain

the

palaeobiogeography of the eastern Tethys region during the Late Triassic period. The corals were discovered in bedded limestone in patch reefs or biostromes of the Renacuo area. In this paper, 15 genera and 25 species are identified and categorized, the systematic composition of these corals and their relationships with other Triassic coral faunas are also discussed. The results show that these corals are composed of the typical elements of the western Tethys, with the following genera and species that are endemic to China: Radiophyllia cf. astylatus, Margarosmilia zogangensis and Conophyllopsis qamdoensis, and the genera Retiophyllia, Margarosmilia, Hydrasmilia, Procyclolites, Pamiroseris, Araiophyllum, Stylophyllopsis, Stylophyllum and Guembelastraea provide important links to the Tethys province. The coral fauna also highlights the connection between the Qiangtang terrane and the Songpan-Ganzi fold belt, but shows that the areas are distinct from the Himalayan terrane. It has been interpreted that the Qiangtang terrane and the Songpan-Ganzi fold belt were in the vicinity of the gradually-closed Paleo-Tethys Ocean, which resulted in the free transmigration of the benthonic organisms of these areas. On the other hand, the Himalayan terrane was separated from the Qiangtang terrane by a wide ocean--meso Tethys during the Late Triassic period, which made it impossible for the benthonic organisms on both flanks to freely migrate toward the opposite continental margins.

2

Upper Triassic reef coral fauna in the Renacuo area, northern Tibet, and its implications for palaeobiogeography

Jingfang Bo a,b, Xunlian Wang b, Jinhan Gao b*, Jianxin Yao a*, Genhou Wangb, Engang Hou b

a

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037,

PR China b

School of Earth Sciences and Resources, China University of Geosciences,

Beijing 100083, PR China

Abstract: Upper Triassic reef corals from the Riganpeicuo Formation in northern Tibet represent important scleractinian coral fauna that help explain the palaeobiogeography of the eastern Tethys region during the Late Triassic period. The corals were discovered in bedded limestone in patch reefs or biostromes of the Renacuo area. In this paper, 15 genera and 25 species are identified and categorized, the systematic composition of these corals and their relationships with other Triassic coral faunas are also discussed. The results show that these corals are composed of the typical elements of the western Tethys, with the following genera and species that 3

are endemic to China: Radiophyllia cf. astylatus, Margarosmilia zogangensis and Conophyllopsis qamdoensis, and the genera Retiophyllia, Margarosmilia, Hydrasmilia,

Procyclolites,

Pamiroseris,

Araiophyllum,

Stylophyllopsis,

Stylophyllum and Guembelastraea provide important links to the Tethys province. The coral fauna also highlights the connection between the Qiangtang terrane and the Songpan-Ganzi fold belt, but shows that the areas are distinct from the Himalayan terrane. It has been interpreted that the Qiangtang terrane and the Songpan-Ganzi fold belt were in the vicinity of the gradually-closed Paleo-Tethys Ocean, which resulted in the free transmigration of the benthonic organisms of these areas. On the other hand, the Himalayan terrane was separated from the Qiangtang terrane by a wide ocean--meso Tethys during the Late Triassic period, which made it impossible for the benthonic organisms on both flanks to freely migrate toward the opposite continental margins.

Key words: Upper Triassic, Scleractinian coral fauna, Renacuo area, Northern Tibet, Palaeobiogeography

*Corresponding author. E-mail: [email protected], [email protected]

1.

Introduction 4

The period of recovery and proliferation of reef ecosystems that occurred during the Middle and Late Triassic was characterized by the rise of reefs dominated by scleractinian corals and coralline sponges (Flügel, 2002; Lehrmann et al., 2006; Yin and Song, 2013; Peybernes et al., 2015). Late Triassic scleractinian corals are well known in the reef and reef-related settings of the Tethys, especially in the Alpine regions of central Europe (Turnšek and Ramovs, 1987; Roniewicz and Stanley, 2013; Tosti et al., 2014), and the research on Triassic scleractinian corals in these areas has been carried out for over 160 years (e.g. Reuss, 1854; Frech, 1890; Volz, 1896; Melnikova, 1975, 1996; Roniewicz, 1989, 2011; Roniewicz et al., 2007). However, the study of Late Triassic reef corals in China only began in the past century and has received considerably less attention. The Late Triassic scleractinian corals of China have been collected mainly in Tibet, and in the adjacent areas of Sichuan, Yunnan, Qinghai, and Xinjiang; they are mostly distributed on both sides of the Bangong LakeNujiang – Changning – Menglian collision zone (Bo et al., 2017). Tibet is an ideal region for research on Late Triassic reef corals, due to the wide distribution of the Triassic marine strata and the abundant scleractinian fossils that are well preserved in the Upper Triassic strata (Liao and Xia, 1994); it is the key area connecting the Tethyan realm (Wang et al., 2009; Fan et al., 2017). Some research was performed on the biostratigraphy and general paleontological taxonomy of Triassic scleractinian corals in Tibet, and a number of Triassic scleractinian coral reefs were found in eastern Tibet (such as those discovered in Dênqên, Riwoqê, Chamdo, Jomda, Chagyab, Konjo, Zogang, and Markam), southern Tibet (Nyalam and Tingri), and the central region (Lhünzhub, Coqên, and Nagqu). The corals bear 5

a taxonomic relationship to faunas from the western Tethys, as well as from the Pamirs and Timor. Past investigations of these Late Triassic corals emphasized the coral fauna composition, diversity and their strong Tethyan character (Yoh, 1965, 1982; Wu, 1975; Liao and Li, 1979; Liao, 1982; Deng and Zhang, 1984a, 1984b; Xia and Liao, 1986; Yoh and Liao, 1986; Deng, 1990; Liao and Xia, 1994; Ji et al., 2010a; Liao and Deng, 2013; Huang et al., 2014). Nevertheless, there is no comprehensive study on Upper Triassic reef corals from northern Tibet, although some researchers have reported recently on areas such as the Guoganjianian mountain in Gêrzê (Ji et al., 2010b) and the purported Zhanjin Formation in Gêrzê (Bo et al., 2015; Luo et al., 2015). In order to ascertain the features of the Late Triassic scleractinian coral fauna in northern Tibet, provide the basis for the stratigraphic division and correlation of the Triassic strata, inquire into the plate tectonics and paleobiogeography of the eastern Tethys, and establish the relationship of the Triassic scleractinian corals fauna between the eastern Tethys and the western Tethys, we collected more than 128 specimens of the scleractinian corals from the Renacuo area in the northern Tibet. We describe and illustrate in detail 15 genera and 25 species in accordance with their corallite structure, morphology of the septa, and typology of the growth forms, and compare the coral faunas from the Himalayan terrane, Lhasa terrane, Qiangtang terrane and Songpan-Ganzi fold belt. Moreover, we also discuss the biogeographic characteristics of these regions during the Late Triassic period.

2.

Geology and tectonic setting

6

The scleractinian corals analyzed in the present paper were collected from the Renacuo area in Tibet, China (Fig. 1). The fossils were found in the limestones of the Riganpeicuo Formation (X: 251167.67, Y: 3626597.93, Z: 4960 m) of the Donggou section in Gêrzê county and in the Zishicuo section in Rongma county (X: 324817, Y: 864450, Z: 5007 m). The Renacuo area, the research location of this study, was located on the southern margin of the southern Qiangtang terrane during the Triassic period. The southern Qiangtang terrane in northern Tibet was located between the Longmu Co-Shuanghu Suture Zone and the Bangong-Nujiang Suture Zone (Yang et al., 2017) (Fig. 2), which became a new part of the Tethys Ocean in the Late Triassic after the closure of the ancient Tethys during the period from the Late Permian to the Triassic. It is a very important tectonic belt that contains the evolutionary information of the Tethys Ocean from multiple periods (Mo et al., 2006; Wang et al., 2009; Peng et al., 2014). In the Late Triassic, with the extension of the Qiangtang terrane, the carbonate sediments of the Upper Triassic Riganpeicuo Formation were developed in the southern Qiangtang terrane, which had unconformable contact with the overlying Sewa Formation (lower-middle Jurassic) and unconformity with the underlying Longe Formation (Permian) (Hou et al., 2014a). The Upper Triassic organic reefs are well developed in the Riganpeicuo Formation (Fig. 3). The reef-building organisms consist of scleractinian corals, calcispongiae, calcareous algae, and other reef-inserted organisms such as foraminifera, brachiopods, bivalves, gastropods, echinoderms, and bryozoans (Hou et al., 2014a). The carbonate in the Riganpeicuo Formation may be divided into 5 sedimentary facies based on the characteristics of the rocks and combination type, namely, debris littoral facies, restricted platform facies, open platform 7

facies, platform edge shallow facies, and platform edge reef facies. The Z values of the salinity (from 126.32 to 135.37) indicate that the paleoseawater in the Renucuo area of the Gêrzê ranged from normal marine to hypersaline, and the average temperature of the paleoseawater was 22.4ºC according to the analysis of the C and O isotopes (Hou et al., 2013). The sedimentary environment of the Riganpeicuo Formation in the Renacuo area was the epicontinental sea sedimentary environment in a warm and humid climate. More information on the geological situation and the origin and fauna composition of the Riganpeicuo Formation was documented by Chen (2007), Bo (2014) and Hou (2014b). Furthermore, Hou et al. (2013, 2014a) and Hou (2014b) presented information on the coral-bearing beds of the Riganpeicuo Formation and geological investigations on the Late Triassic reefs of northern Tibet. Flügel (1982, 2002) and Martindale et al., (2015) reported on the general aspects of the formation in the Upper Triassic reef facies in the Tethys realm. All the specimens and thin sections described and illustrated here are stored in the Teaching and Research Section of the Earth Sciences and Resources School at the China University of Geosciences, Beijing. The fossil specimens were sliced into thin sections and illustrated with the aid of a camera lucida attached to a microscope.

3.

Upper Triassic reef corals from the Renacuo area in Tibet

3.1 Occurrence of the corals Scleractinian corals from the Upper Triassic Riganpeicuo Formation in the Renacuo area were abundant and diverse. Fifteen genera and 25 species are described and illustrated in 8

detail in this paper. In this fauna, Remimaniphylliidae is the dominant family, and the representative genera of Margarophylliidae and Stylophyllidae are present. The species of Retiophyllia are the most abundant, accounting for about 30% of the coral fauna. The endemic characteristic is not obvious. These coral fossils collected from the Riganpeicuo Formation in the Renacuo area are characterized by more phacelloid colonial forms and fewer solidary and massive colonial forms; they are also characterized as pseudo-meandroid colony and thamnasterioid colony in regards to their morphological and structural features. The corallite transverse diameter is generally smaller than that of the homogeneity from other places. Intracalicinal budding is the main reproduction type. Their skeletal structural features include an epithecal wall that is developed in most of the corals, and the wall is generally better preserved. The septothecal wall and parathecal wall are developed in a few corals; the septa are compact and their lateral faces decorate a small number of granules. Falculate pennulae and pennular septa appear in several of the corals. The septa generally show a radial symmetry and the endothecal dissepiment generally exists in individuals. The synapticulae are only developed in a few of the species. The columella structures are non-existent or only weakly developed (Table 1).

3.2 Biostratigraphy The corals from the studied area are similar to the Late Triassic reef corals reported from Europe and Asia. In addition, the majority of the corals in the study area can be compared with those in the Upper Triassic strata in the western Tethys (northern Calcareous Alps, Austria, Southern Alps, Slovenia, Italy, and Greece), especially the Julian Carboate Platform 9

in Slovenia (Table 2). Because of the similar living environment in this period, reef coral fauna and coral reefs of different sizes were distributed in the Tethys realm. Specifically, Furcophyllia septafindens (Volz), Hydrasmilia fossulata Turnšek and Senowbari-Daryan, Guembelastraea guembelii Laube, Hydrasmilia ornamenta Turnšek and Senowbari-Daryan, Margarosmilia zieteni (Klipstein), and Araiophyllum triasicum Cuif, have been found in the Carnian strata of Italy, Turkey, Slovenia, and Greece. Parathecosmilia sellae (Stoppani) has been reported in the Carnian-Norian Strata of the Julian Carboate Plateform in Slovenia and the Dachsterin Formation of Austria. Guembelastraea aff. guembelii (Laube) and Conophyllopsis qamdoensis Deng and Zhang were found in the Norian strata of the northern Alps in Austria,

and the Bolila Formation of Tibet. Pokljukosmilia tuvalica Turnšek,

Retiophyllia defilippi (Stoppani), and Retiophyllia paraclathrata Roniewicz have been reported in the Norian-Rhaetian strata of Slovenia and the St. Cassian Formation and Calcare di Zu Formation in Italy. Retiophyllia gracilis Roniewicz has been found in the Rhaetian strata of the Zlambach Beds in Austria and the northern Alps.

3.3 Implications to palaeobiogeography The Triassic corals in the Qinghai-Tibet Plateau are mainly distributed in the Himalayan terrane, Lhasa terrane, Qiangtang terrane and Songpan-Ganzi fold belt from south to north (Bo et al., 2017). The Himalayan terrane was located in the southern hemisphere from the Ordovician to the Late Cretaceous periods, was relatively stable, and drifted to the north as a whole block during the Ordovician to the Middle Triassic periods; the northward movement of the Himalayan terrane was accelerated in the Late Triassic and Late Cretaceous periods 10

(Zou et al., 2016). The Lhasa terrane was part of the Gondwana continent in the early Late Permian period and separated from the Gondwana continent at the end of the Permian period, becoming an independent terrane drifting toward ancient Asia (Li et al., 2014). In the Early Cretaceous, the eastern part of the Lhasa terrane collided with the Qiangtang terrane, and the Lhasa terrane was completely proliferated to Eurasia and formed the Bangong - Nujiang collision zone in the early Late Cretaceous period (Zhu et al., 2013). The Qiangtang terrane was almost a continuous deposition during the Paleozoic to the Jurassic periods, in which the local uplift and magmatic volcanic activity only appeared in the northern region during the Permian and the Triassic periods (Fu et al., 2010). The Qiangtang terrane began to drift northward rapidly from the late Carboniferous period, accreted to the ancient Asian continent and formed the Jinshajiang-Lancangjiang Belt during the Late Permian-Early Triassic period (Feng et al., 2013; Cheng et al., 2013). The Songpan-Ganzi fold belt was a large triangular deformation area surrounded by the North China craton, Yangtze craton, and Qiangtang-Changdu terrane, it had stayed in continent island arc setting during most of its geological history (Su et al., 2005). The outcropped main stratum of the Songpan-Ganzi was a Middle-Upper Triassic complex deformation flysch, the Paleozoic strata were only exposed in the inner marginal areas of the Songpan-Ganzi, and the provenance of sediments was mainly from theYangtze craton (Deng et al., 2010). During the Triassic period, the ocean’s warm current was mainly concentrated near the equator. The western Pacific’s warm current was bounded by the equator, and moved in the clockwise direction in the northern region and in the counterclockwise direction in the southern region towards the higher latitude region (Martindale et al., 2015). The Arctic cold 11

flow moved southward and Antarctic cold flow moved northward, forming a circulation of cold and warm currents at 30 ° N and 30 ° S by the confluence with the warm currents from the Tethyan and Eastern Pacific ocean, respectively (Taskyn et al., 2014; Frankowiak et al., 2016); these flows provided favorable conditions for the growth and propagation of coral fauna in the Himalayan terrane, Lhasa terrane, Qiangtang terrane and Songpan-Ganzi fold belt.. Therefore, the study on the Upper Triassic coral fauna of the Renacuo area is of great significance for clarifying the coral fauna relationships between the Qiangtang terrane, Lhasa terrane, Himalayan terrane, and Songpan-Ganzi fold belt, and it helps to further define the palaeogeographic positions of these four regions. Wide-ranging coral genera from the Triassic, such as Distichophyllia, Retiophyllia, Margarophyllia, and Pamiroseris, are found in the Himalayan terrane, Lhasa terrane, Qiangtang terrane, and Songpan-Ganzi fold belt (Table 3). In addition to the above widely distributed genera of the Tethys, the coral fauna in the Himalayan region is distinctly different from the other 3 regions. However, the coral fauna in the Qiangtang region presented a certain degree of similarity with the coral fauna in the same period of the Songpan-Ganzi fold belt and Lhasa terrane. For example, Conophyllopsis qamdoensis Deng and Zhang and Distichophyllia norica xizangensis Deng and Zhang are endemic to China, and found in both the Qingtang terrane and Songpan-Ganzi fold belt; Volzeia cf. degeensis Deng and Zhang from the Qiangtang terrane appears to have a certain affinity with Volzeia degeensis Deng and Zhang from the Songpan-Ganzi fold belt; Distichophyllia gigas (Vinassa de Regny) and Margaraphyllia stylophylloides (Vinassa de Regny), collected from the Qiangtang terrane and Lhasa terrane, have consistent features 12

except for the size of the corallites in these two terranes (Bo, 2014). We can provide a further explanation of the palaeobiogeography of the four regions during the Late Triassic period (Fig. 4). The Qiangtang terrane and Songpan-Ganzi fold belt were in the vicinity of the gradually closed Paleo-Tethys Ocean, which resulted in the free transmigration of the benthonic organisms. The Himalayan terrane was located on the southern side of the Meso-Tethyan Ocean (Feng et al., 2013), which can be interpreted as a terrane belonging to Gondwana that was separated from the Qiangtang terrane, Lhasa terrane, and Songpan-Ganzi region by a wide ocean--meso Tethys that made it impossible for benthonic organisms on both flanks to freely migrate toward the opposite continental margins. The location of the Lhasa terrane and its relationship with the other blocks requires further exploration.

3.4 Systematic palaeontology Since all the specimens were recrystallized, the microarchitecture of the menianae was not preserved. We only included the familial rank classification, avoiding all higher-rank units, because the state of the higher level systematic classification of Triassic corals of the Order Scleractinia is not finalized or fully understood. The following abbreviations are for the dimensions given in this manuscript: D: Diameter of a solitary corallite or corallites in fasciculate colony or cerioid colony (mm). C-C: Distance between 2 adjacent corallites in fasciculate colony or cerioid colony (mm). S1-S6: Number of septa cycles. 13

Order Scleractinia Bourne, 1900 Genus Furcophyllia Stolarski et al., 2004 Type species: Montlivaltia septafindens Volz, 1896 Remarks: Furcophyllia was established by Stolarski et al. (2004, p. 530) according to the neotype collected from the Dolomite Mountains in Italy and it was assigned to an informal category of the scleractiniamorphs. It is believed that the genus was characterized by its unusual increase mode of its septal apparatus despite the similarity of the external form to ordinary scleractinian corals. This genus is not comparable to other taxa described in the Triassic, due to its unique increase mode of its septal apparatus that occurs in the form of bunches called “septal brooms.” Furcophyllia septafindens (Volz, 1896) (Fig. 5, K, L) 1896 Montlivaltia septafindens Volz; p. 44, pl. 3, figs. 22-25. 2004 Furcophyllia septafindens (Volz); Stolarski et al., p. 530, figs. 1-2. Description: This solitary coral is oval in its cross section with an average diameter of about 5.6 mm×7.6 mm. The epithecal wall is thickened by the peripheral borders of the thin and densely-crowded septa. The septa are thin and abundant, densely arranged, easily-confused, and differentiate into branching septal sets. All the septa and septal branches have approximately the same thickness in the cross section. Multiple, centripetal, and usually alternating bifurcations of the lower-cycle septa exist. Spike-like projections can be seen in the lateral faces of some septa. The septa converge at a 2-mm-long and 0.2-mm-wide linear 14

calyx hole. The endotheca is composed of abundant small, thin dissepiments. Remarks: The specimen described here is similar to the neotype collected from the Dolomite Mountains in Italy (Stolarski et al., 2004, p. 530, figs. 1-2) except for the smaller diameter. Moreover, in contrast to the Furcophyllia shaitanica found in Pamir (Melnikova and Roniewicz, 2007, p. 402, figs. 3A-C, F; 4A), the latter does not have a linear calyx hole in its central part. Genus Hydrasmilia Turnšek and Senowbari-Daryan, 1994 Type species: Hydrasmilia rhytmica Turnšek and Senowbari-Daryan, 1994 Remarks: Hydrasmilia was established by Turnšek and Senowbari-Daryan (1994, p. 482) based on the specimens collected from Hydra Island, Greece, and was assigned to Procyclolitidae by Vaughan and Wells. Roniewicz (2011, p. 424) noted that this genus cannot be assigned to the Procyclolitidae, due to the lack of pennular septa. However, because the specimen collected from Turkey (Roniewicz, 2011) was preserved in poor condition, the attribution of this genus has not been determined. Because of the poor preservation of these fossils, the attribution of the genus was not discussed in this paper. Hydrasmilia fossulata Turnšek and Senowbari-Daryan, 1994 (Fig. 5, A-B, D, F, H-I) 1994 Hydrasmilia fossulata Turnšek and Senowbari-Daryan; p. 482, pl. 8, figs. 1-5. Description: Phaceloid colony with rhythmical thickenings of the corallites are observable in the longitudinal section. The corallites are roundish to oval in the cross section, with the diameters ranging from 2.3 mm to 5.7 mm, and the distances between 2 adjacent corallites range from 2.4 mm to 4.7 mm. The epithecal wall is thin. The septal apparatus is thin and 15

compact, equal in thickness, and subradially symmetric with few lateral granulations. The columella is parietal. The endotheca is composed of vesicular dissepiments, and the budding type is intracalicular. Remarks: Three species of Hydrasmilia were described by Turnšek and Senowbari-Daryan (1994) when they established Hydrasmilia: H. rhythmica, H. fossulata, and H. ornamenta. The specimen in this paper is smaller in diameter than H. fossulata (Turnšek and Senowbari-Daryan, 1994, p. 482, pl. 8, figs. 1-5); it differs from H. rhythmica in its more densely-arranged septa, elongated calyx cups, and rhythmical thickenings in the longitudinal section. The specimen is different from H. ornamenta because the septal lateral edge is richly decorated in the latter. The specimen in this paper is similar to the H. laciana collected from Austria and described by Roniewicz (2011, p. 424, fig. 6A), except that H. laciana has fewer septa. Hydrasmilia ornamenta Turnšek and Senowbari-Daryan, 1994 (Fig. 5, C, E, G, J) 1994 Hydrasmilia ornamenta Turnšek and Senowbari-Daryan; p. 482, pl. 9, figs. 1-4. Description: The phaceloid colony has irregular roundish or irregular oval corallites in the cross section, and the diameters of the corallites range from 3.5 mm to 5.7 mm. The distances between 2 adjacent corallites range from 3.8 mm to 5.8 mm. The epithecal wall is thickened by the stereome and connected with the original parts of the septa. The septa are compact, subequal in thickness, and subradially symmetric with abundant lateral ornamentations that look like thorns. The endotheca is composed of vesicular dissepiments, and the budding is intracalicular. Less obvious rhythmical thickenings of the corallites are observable in the 16

longitudinal section. Remarks: The specimen in this paper is smaller in diameter than the specimen of H. ornamenta (Turnšek and Senowbari-Daryan, 1994, p. 482, pl. 9, figs. 1-4). It differs from the specimen of H. fossulata in that it has more septal lateral decorations, and it differs from H. rhythmica in that its epithecal wall is thickened by the stereome and connected to the original parts of the septa as well as more ornaments of septa lateral edges. The specimen in this paper is similar to the H. laciana described by Roniewicz (2011, p. 424, fig. 6A), except that H. laciana has fewer septa. Family Stylophyllidae Volz, emended by Cuif, 1976 Genus Stylophyllopsis Frech, 1890 Type species: Stylophyllopsis polyactis Frech, 1890 Stylophyllopsis cognata Melnikova, 1979 (Fig. 6, A-B, G) 2001 Stylophyllopsis cognata Melnikova; pl. 3, fig. 2. Description: This specimen is a phacelloid colony. The corallites are roundish in the cross section with an average diameter of 3 mm. The wall is epithecal. The septa are differentiated into 4 cycles and arranged radially. S1 reach nearly to the axial center, S2 are thinner and shorter than S1, and the lengths of S2 are about 3/4 of S1. S3 and S4 are approximately 1/3 and 1/4 the length of S1, respectively. The inner septal margin is dissociated into septal spines. The distal edge is coarsely denticulate, and the columella is papillar. The endotheca is formed by large, densely-packed dissepiments. Remarks: The specimen in this paper must be Stylophyllopsis because of the point-linear 17

arrangement of the septa and papillar columella. In addition, its features are consistent with those of the specimen collected from Pamir and described by Melnikova (2001) in terms of the arrangement mode, number, and structure of the septa (except that the distribution of the corallites of the former is not as dense as that of the latter). It differs from the type species S. polyactis in that the latter is solitary and has abundant thin radial elements with fenestrae. Genus Stylophyllum Reuss, 1854 Type species: Stylophyllum polyacanthum Reuss, 1854 Stylophyllum sp. (Fig. 6, C-E, H) Description: The phaceloid colony has medium-sized corallites that are distributed loosely and arranged messily. The corallites are roundish or oval in the cross section, with an average diameter ranging from 1.5 mm to 3 mm, and the C-C ranges from 3 mm to 5.5 mm. The septal spines are free or incompletely joined to form rudimentary septal blades. The septal cycle and hexameral arrangement are not easily identified. The septa have a zigzag or moniliform pattern with well-developed granules on the septal lateral edge of the corallites. The septa are separated into many discrete fragments in the corallites’ axial region and are arranged in strange combinations of polycentric radial and vermicular patterns. Remarks: The septa of the specimen in this paper are discontinuous or isolated into septal spines. Few of them connect into flakes. Therefore, it should be classified into Stylophyllum. Since the features of the septa merged together, this specimen is similar to Astraeomorpha pratz Volz, but the latter is a massive colony.

18

Family Zardinophyllidae Montanaro-Gallitelli, 1975 = Pachythecaliidae Cuif, 1975 Genus Radiophyllia Deng, 2006 Type species: Radiophyllia astylatus Deng, 2006 Radiophyllia cf. astylatus Deng, 2006 (Fig. 7, B) Cf. 2006 Radiophyllia astylatus Deng; p. 36, pl. 2, figs. 7-8, pl. 3, figs. 1-6. Cf. 2013 Radiophyllia astylatus Deng; Liao and Deng, p. 31, pl. 4, figs. 1-3. Description: This solitary coral is roundish in the cross section with a diameter of 17.8 mm. The epithecal wall is thin, and the radial elements are compact and straight. The septa are differentiated into 4 cycles and wedge-shaped. S1 reach nearly to the axial center, S2 are thinner and shorter than S1, and the lengths of S2 are about 5/6 of S1. S3 are approximately 1/3 of the length of S1, and the lengths of S4 are about 1/3 of S3. The septal lateral edge is not smooth and small granules can be observed if one looks carefully. No dissepiment or axial structure can be found. Remarks: We have only 1 cross section of this specimen, and its morphological characteristics are similar to those of the R. astylatus collected from Tianyang, Guangxi (Deng, 2006; Liao and Deng, 2013). The difference lies in the 4 cycles of the septa of the former and the 6 cycles of the septa of the latter. Other species, such as the R. stylatus and R. pygmaeus described by Deng (2006), Liao and Deng (2013) are different from our specimens. R. stylatus has a developed axis structure, and the corallites of the R. pygmaeus are smaller (2 mm-3 mm). Both of the other species have fewer septa with obvious ornaments observed on the septal lateral edges. 19

Family Guembelastraeidae Cuif, 1977 Genus Guembelastraea Cuif, 1976 Type species: Isastrea guembelii Laube,1865 Guembelastraea guembelii (Laube, 1865) (Fig. 6, F, J, L) 1865 Isastraea gümbeli Laube; p. 263, pl. 7, fig. 2. 1896 Isastraea gümbeli Laube; Volz, p. 50, pl. 4, figs. 1-5. 1975 Isastraea guembelii Laube; Cuif, p. 102-104, pl. 14, figs. 1-6. 1976 Guembelastraea guembelii (Laube); Cuif, p. 105-108, pl. 8, figs. 1-6. 1984 Guembelastraea guembelii (Laube); Ramovš and Turnšek, p. 175, pl. 3, figs. 3-5. 1990 Guembelastraea guembelii (Laube); Riedel, p. 61, pl. 11, fig. 3. 1993 Guembelastraea guembelii (Laube); Zamparelli, p. 252, pl. 3, figs. 1-3. 1997 Guembelastraea guembelii (Laube); Turnšek, p. 99, pl. 99. Description: This colonial specimen is cerioid with pentagonal to hexagonal corallites in the cross section. D = 3.5 mm-4.1 mm. C-C = 3 mm-5.4 mm. The septotheca is made up of the peripheral septal borders and usually thickened by the stereome. The radial elements are compact. The septal lateral edge is in the form of concave pennulae with its margins directed upward. The septa are differentiated into 5 cycles and radially symmetric. The original parts of S1 are thick, extending to the center; they gradually thin, and S2 reach nearly to the center. S3 are about 2/3 of S1’s length and S4 are about 1/2 of S1’s length. S5 are thin, incomplete, and poorly developed. The dissepiments and columella are not present. The thick wall is actually made of 2 opposite septa connected directly at the center and this wall delimits the 20

parridal daughter corallites. Remarks: The specimen in this paper differs from the type specimen collected from St. Cassian described by Laube (1865, p. 263, pl. 7, fig. 2) in that it has a thicker septotheca. It is different from the G. guembelii collected in Turkey (Cuif, 1976, p.105-108, pl.8, figs. 1-6) in that the latter develops remarkable falculate pennulae. In addition, the G. ramosa collected from the Mailonggang Formation in Tibet (Liao and Xia, 1994, p. 97, pl. 15, figs. 2-5) includes fewer dissepiments, fewer cycles of septa, and less septal lateral ornamentation than this specimen. Guembelastraea aff. guembelii (Laube, 1865) (Fig. 6, I, K) 2011 Guembelastraea aff. guembelii (Laube); Roniewicz, p. 422, fig. 7A. Description: There is only 1 cross section of this cerioid colony which composed of several of corallites. The irregularly-polygonal corallites in the cross section have an average diameter of 4.9 mm, and the C-C is about 4 mm. The septotheca is complete and polygon-shaped. The septa are thicker at the original part and become thinner at the axis. S1 are the thickest, extending to the axis, and S2 and S3 are shorter and thinner in decreasing series. Alternate dentations have developed on the lateral faces of the septa. The columella is absent, and the budding type is unknown. Remarks: The characteristics of our specimen, such as its polygonal corallites, lack of any columella, and alternate dentations developed on the septal flanks, are similar to those of the G. guembeli collected from St. Cassian and described by Laube (1865, p. 263, pl. 7, fig. 2). The differences lie in the septotheca thickened by the stereome of the former and the greater 21

number of septa in the latter. The specimen examined differs in 2 taxonomically important features from the G. pamphylliensis collected from the Taurus Mountains, Turkey, and described by Cuif (1976, p. 108, pl. 9, fig. 2-4): a weak development of the alternate dentations (in the G. pamphylliensis, the pennular covering is dense on the septal flanks), and the septa are thicker at the original part and become thinner at the axis (these are rod-like in the G. pamphylliensis). In addition, this specimen is consistent with the G. aff. guembelli collected from Austria by Roniewicz (2011, p. 422, fig. 7A). Family Conophyllidae Alloiteau 1952 Genus Araiophyllum Cuif, 1975 Type species: Araiophyllum triasicum Cuif, 1975 Araiophyllum triasicum Cuif, 1975 (Fig. 8, A-C, K; Fig. 9, B) 1975 Araiophyllum triassicum Cuif; p. 110-115, pl. 16, figs. 1-7. 1989 Araiophyllum triassicum Cuif; Turnšek and Buser, p. 86, pl. 7, figs. 1-2. 1993 Araiophyllum triassicum Cuif; Cuif and Gautret, p. 407-408, figs. 1-4. 1997 Araiophyllum triassicum Cuif; Turnšek, p. 20, pl. 20. Description: The colony is phaceloid with cylindric corallites. The average diameter of the corallites ranges from 2.6 mm to 4.3 mm, and the C-C ranges from 3.6 mm to 4.8 mm. The septa are winding and porous and decorated with numerous lateral granules. Rough dentations occurred on the septal edge. The epitheca is so poorly preserved so that the septa are naked. The synapticulae are present, and the budding type is intracalicular. The axis structure cannot be easily distinguished. 22

Remarks: The size and morphological characteristics of the specimen are basically consistent with the monotype collected from the Taurus Mountains (Cuif, 1975), except for the particularly prominent dentations that occurred on the septal edge. In addition, due to the recrystallization of the specimen, the axis structure cannot be easily distinguished. Family Margarophylliidae L. Beauvais, 1980 Genus Margarosmilia Volz, 1896 Type species: Montlivaltia zieteni Klipstein, 1843 Margarosmilia zogangensis Deng and Zhang, 1984 (Fig. 8, D-F; Fig. 9, J) 1984a Margarosmilia zogangensis Deng and Zhang; p. 268, pl. XV, figs. 1a-b. 1994 Margarosmilia zogangensis Deng and Zhang; Liao and Xia, pp. 65-66, pl. LXⅥ, figs. 2-3. 2013 Margarosmilia zogangensis Deng and Zhang; Liao and Deng, p. 62, pl. 26, figs. 1-2. Description: The colony is fasciculate with irregularly oval calices ranging from 2.6 mm×5.45 mm to 3.25 mm×7.65 mm in diameter, and the C-C ranges from 4.1 mm to 4.7 mm. The wall is epithecal. The costosepta are densely arranged and form a long fusiform shape in the cross section. The septa are differentiated into 4-5 cycles and bilaterally symmetric. S1 extend to the corallite’s center but do not co-mingle. The lengths of S2 are approximately 5/6 of S1, S3 are 1/2 of S2 in length, and approximately 24 in number. S4 are about 1/4 of S1. The septal faces are covered with small granules that project laterally. The endotheca is composed of vesicular dissepiments, and the columella is absent. The budding type is intracalicular. 23

Remarks: The irregularly oval calices of the specimen described here are similar to those found in specimens collected from Zogang, Tibet (Deng and Zhang, 1984a; Liao and Xia, 1994; Liao and Deng, 2013) except for the smaller diameter and shorter S2. Margarosmilia zieteni (Klipstein, 1843) (Fig. 8, G, I-J, L; Fig. 10, K) 1986 Margarosmilia zieteni (Klipstein); Xia and Liao, p. 40, pl.Ⅰ, figs. 7-9. 1994 Margarosmilia zieteni (Klipstein); Liao and Xia, p. 64, pl.Ⅳ, figs. 1, 2. 2013 Margarosmilia zieteni (Klipstein); Liao and Deng, p. 62, pl. 23, figs. 8. Description: The colony is fasciculate. The corallites are monocentric and occasionally double-centric. Roundish or oval calices in the cross section have diameters ranging from 3.7 mm to 6.5 mm, and the C-C ranges from 3.1 mm to 5.9 mm. The septal apparatus is differentiated into 4-5 cycles and slightly bilaterally symmetric. S1-S3 are subequal in thickness and fusiform in shape, and have few granules on the septal flanks. S1 extend to the axis, S2 are slightly shorter than S1, and S3 are 2/3 of S1 in length. S4 taper, and S5 are rudimentary (they are short and spiny). The epithecal wall is thin, and the endotheca is composed of vesicular dissepiments. The columella is absent, and the budding is intracalicular. Remarks: The characteristics of the specimen are consistent with the specimens found from the Mailonggang Formation in Lhünzhub, Tibet (Xia and Liao, 1986; Liao and Xia, 1994; Liao and Deng, 2013), except for the smaller diameter (the latter is 6 mm-10 mm). Genus Thamnomargarosmilia Melnikova, 1996 Type species: Thamnomargarosmilia prima Melnikova, 1996 24

Thamnomargarosmilia sp. (Fig. 7, A, C; Fig. 8, H; Fig. 9, K; Fig. 10, L) Description: The colony is phaceloid-thamnasterioid. The oval calices have a diameter of about 12 mm, and the epithecal wall is thin. The septal apparatus is septocostal and biseptal. S1 and S2 cannot be distinguished easily, as they extend to the axis and form a weak axis structure. The other septa are shorter and thinner in decreasing series. The endotheca is dissepimental. Remarks: Due to the typical biseptal elements and the approximate thamnastraeoid features, the specimen here can be assigned to Thamnomargarosmilia. It differs from the type species T. Prima (Melnikova, 1996, p. 12, pl. 2, fig. 1; Melnikova, 2001, p. 56, pl. 17, fig. 1) in the obvious biseptal elements of the former and the marginal intracalicular budding type of the latter. Since there is only one specimen, this species is undefined. Genus Conophyllopsis Deng and Zhang, 1984 Type species: Conophyllopsis qamdoensis Deng and Zhang, 1984 Conophyllopsis qamdoensis Deng and Zhang, 1984 (Fig. 7, D-G; Fig. 9, A) 1984a Conophyllopsis qamdoensis Deng and Zhang; p. 265, pl.Ⅹ, figs. 1a-c. 1994 Conophyllopsis qamdoensis Deng and Zhang; Liao and Xia, p. 57, pl. LXⅧ, figs. 4, 5. 2013 Conophyllopsis qamdoensis Deng and Zhang; Liao and Deng, p. 82, pl. 37, figs. 1-3. Description: The colony is phacelloid and composed of cylindrical corallites that are perhaps connected at the lateral surfaces. The corallite diameters range from 1.5 mm to 2 mm, 25

and the C-C ranges from 1.6 mm to 2.6 mm. The septa are thin and compact, with sparse granules on the septal flanks, and are differentiated into 3-4 cycles; there are approximately 48 in number and they are radially symmetric. S1 extend to the axis, S2 are shorter than S1, S3 are usually 1/2 of S2 in length, and S4 are almost hidden in the epithecal stereome. The broad endotheca is composed of vesicular, well-developed dissepiments. The epithecal wall is thin, and the increase mode is extracalicular. Weakly-developed clintheriform columella can be observed in some of the corallites. Remarks: The specimen in this paper differs from the speciemens collected from the Bolila Formation in Chamdo, Tibet (Deng and Zhang, 1984a; Liao and Xia, 1994; Liao and Deng, 2013) in that the latter has a larger corallite diameter (3 mm-5 mm) than this specimen. Family Coryphylliidae Beauvais, 1981 emended Roniewicz and Stanley, 2009 Genus Pokljukosmilia Turnšek, 1989 Type species: Pokljukosmilia tuvalica Turnšek, 1989 Pokljukosmilia cf. tuvalica Turnšek, 1989 (Fig. 9, D-E, G-I) Cf. 1989 Pokljukosmilia tuvalica Turnšek; p. 85-86, pl. 5, figs. 1-5, pl. 6, fig. 1-3. Cf. 1991 Pokljukosmilia tuvalica Turnšek; Ramovš and Turnšek, p. 185, pl. 7, fig. 3-4. Cf. 1997 Pokljukosmilia tuvalica Turnšek; Turnšek, p. 156, pl. 156. Description: The colony is phaceloid. The oval corallites have an average diameter of their long axis ranging from 2 mm to 5 mm. The epitheca is pellicular, and the axial fossula is elongated. The septa are not abundant and are thin and differentiated into 3-4 size cycles. S1 and S2 are subequal in thickness, with granulation on the septal sides. The endotheca is 26

dissepimental. There is no columella, and the mode of reproduction is unknown. Remarks: Pokljukosmilia has only one species as P. tuvalica by now. The specimen in this paper differs from the monotype collected from Pokljuka Mountain in that it has smaller corallites (5-6 mm in diameter of the latter). In addition, the S1 and S2 of our specimen are thickened by the stereome, while all the septa of P. tuvalica in the same thickness. Genus Khytrastrea Roniewicz and Stanley, 2013 Type species: Khytrastrea silberlingi Roniewicz and Stanley, 2013 Khytrastrea sp. (Fig. 9, C, F) Description: It is a solitary coral. The corallite is roundish in the cross section with a diameter of about 5.5 mm. The septal sides have dense and sharp granulations. S1 and S2 are slightly thicker than the remaining cycles and thickened as there is a fusiform in the adaxial part and a tapering toward the inner margin. The endotheca is composed of vesicular dissepiments. The wall is composed of epitheca and the peripheral parts of the septa. There is no columella. Remarks: As S1 and S2 of this specimen are thickened as fusiform in the adaxial part and taper toward the inner margin, it can be assigned to Khytrastrea. It differs from the K. silberlingi and K. cuifiamorpha (Roniewicz and Stanley, 2013, pp. 946-947) and K. ominensis (Stanley and Onoue, 2015, p.8, fig. 5a-k) in that these 3 species have larger numbers of thinner septa. However, we only have 1 cross section and the external form is unclear; this species is in open nomenclature. Family Reimaniphylliidae Melnikova 1975 = Distichophylliidae Beauvais 1980 27

Genus Paracuifia Melnikova, 2001 Type species: Protoheterastraea magnifica Melnikova, 1984 Paracuifia sp. (Fig. 11, B) Description: This colonial coral tends to be a pseudomeandroid and slightly bifurcating colony growth. The corallites are irregular ovals in the cross section (D=5.5 mm-12 mm). The septa are abundant and thin and subequal in thickness. The distal lateral edges of the septa faces decorate granules. S1 and S2 reach the axial part, but do not form an axial structure. The epitheca is thin. Remarks: Paracuifia was established by Melinikova (2001) based on specimens collected from Pamir. Paracuifia is incomparable to other colonial corals in the Triassic as large and irregular corallites tend to be pseudomeandroid. The specimen described here differs from the species illustrated by Melnikova (2001, pl. 11, fig. 5) in that numerous and thinner septa of our specimen. It differs from P. smith and P. anomala established by Caruthers and Stanley (2008, p. 474) who collected the specimens from Alaska in that these species have fewer septa. It is different from P. jennieae (Caruthers and Stanley, 2008, p.474, fig. 2.10, 2.15, 2.16, 2.17, 2.21) in that the latter forms a single sinuous elevated meander without adjacent counterparts. In addition, the diameter of our specimen is larger than those of the 3 species described by Caruthers and Stanley (2008). Genus Retiophyllia Cuif, 1966 1972 Archaeophyllia Beauvais, p. 310 1975 Paradistichophyllum Melnikova, p. 89 28

Type species: Retiophyllia frechi Roniewicz, 1989 Retiophyllia gracilis Roniewicz, 1989 (Fig. 11, C-F, H; Fig. 12, A) 1989 Retiophyllia gracilis Roniewicz; p. 58, pl. 9, fig. 9; pl. 10, fig. 2; pl. 13, fig. 3. 1998 Retiophyllia gracilis Roniewicz; Roniewicz and Michalik, p. 396; fig. 1.1. Description: The colony is a phaceloid coral composed of cylindrical corallites. In the cross section, the corallites are subcircular in shape, with diameters ranging from 2 mm to 3 mm. The C-C ranges from 2.7 mm to 3.7 mm. The epitheca is relatively thick. The radial elements are zigzag, subequal in thickness, and rather thin. The septal apparatus is differentiated into 3 cycles. The S1 approach the axis but do not co-mingle. S2 are slightly shorter than S1 and are about 4/5 of S1. S3 are about 1/2 of S1. Spiny granules on septal flanks can be observed. There is no columella. Big vesicular dissepiments are developed in the peripheral part of the corallites, and clathrate dissepiments are developed in the axial part. The budding type is intracalicular. Remarks: The characteristics of this specimen are basically the same as those of the R. gracilis (Roniewicz, 1989) collected from the Zlambach Beds, except for the smaller diameter. Retiophyllia cf. gracilis Roniewicz, 1989 (Fig. 11, A, G; Fig. 12, C-E) Cf. 1989 Retiophyllia gracilis Roniewicz; p. 58, pl. 9, fig. 9; pl. 10, fig. 2; pl. 13, fig. 3. Cf. 1998 Retiophyllia gracilis Roniewicz; Roniewicz and Michalik, p. 396; fig. 1.1. Description: The colony is phaceloid with roundish or oval corallites in the cross section, 29

and the diameter of the corallites ranges from 0.9 mm to 2.1 mm, and the C-C ranges from 1.9 mm to 2.5 mm. The epitheca is pellicular. The endotheca is about 0.4 mm thick and composed by costoseptal and vesicular dissepiments. The radial elements are thin and zigzag and subequal in thickness with granulations developed on the septal flanks. The septal apparatus is differentiated into 3-4 cycles and radially symmetric. The S1 approach the axis. S2 are slightly shorter than S1, and S3 are usually 1/2 of S1 in length. S4 are incompletely developed and protrudes slightly from the wall. There is no columella. Big vesicular dissepiments have developed in the peripheral part of the corallites, and clathrate dissepiments have developed in the axial part. The budding type is intracalicular. Remarks: The specimen here differs from the R. gracilis of the Zlambach Beds (Roniewicz, 1989) in terms of its smaller diameter, longer septa, and more abundant ornaments on the septal flanks. Retiophyllia? sp. (Fig. 13, E-F) Description: The colony is phaceloid with roundish corallites in the cross section, the diameter of the corallites ranges from 2 mm to 3 mm, and the C-C is 4 mm. The epitheca is pellicular. The radial elements are thin and zigzag, subequal in thickness, with granulations developed on the septal flanks. The septal apparatus is differentiated into 3-4 cycles; there are 48 in number and they are radially symmetrical. S1 approach the axis. S2 are slightly shorter than S1 and S3 are usually 1/2 of S1. S4 are incompletely developed and protrudes slightly from the wall. There is no columella. The budding is intracalicular. Remarks: The specimen in this paper is similar to the R. tolminensis collected from Turkey 30

and described by Turnšek (1997, p. 184, pl. 184), but the dissepimental endotheca cannot be distinguished due to recrystallization. We consider this a suspected species. Retiophyllia clathrata (Emmrich, 1853) (Fig. 12, F; Fig. 13, A, C) 1890 Thecosmilia clathrata Emmrich; Frech, p. 15-16, pl. 4, figs. 1-5, 7-11. 1974 Retiophyllia clathrata (Emmrich); Roniewicz, p. 108, pl. 4, fig. 1, pl. 5, fig. 3, textfig. 7. 1987 Retiophyllia clathrata (Emmrich); Turnšek and Ramovš, p. 40, pl. 10, figs. 1-5. 1997 Retiophyllia clathrata (Emmrich); Turnšek, p. 178, pl. 178. Description: The colony is fasciculate with oval corallites in the cross section. The average diameter of the corallites is about 2.5 mm-4 mm, and the C-C is 3 mm-6 mm. The costosepta are compact, straight, and fusiform, and a few granules decorate the septa flanks. The arrangement of the septa apparatus is bilaterally symmetric, differentiated into 4 cycles, and subequal in thickness. S1 reach the center but do not co-mingle. The remaining septa are shorter in decreasing series. A circular stereome endotheca lies in the inner part of the corallites, which occurs as a result of the thick parts of the costosepta laterally anastomosing with each other. This endotheca separates the costal region and septal region. The wall is pellicular epithecal or bilaminar. The dissepiments are developed. The budding type is intracalicular. Remarks: The specimen here is consistent with the R. clathrata described by Turnšek and Ramovš (1987) in terms of its oval corallites and stereome endotheca, except for the smaller corallites (which are 5 mm-8 mm in diameter of the latter). It differs from the R. clathrata 31

collected from the Tatra Mountains (Roniewicz, 1974) in the few ornaments on the lateral faces of the septa. Moreover, it is similar to R. paraclathrata in accordance with the circular stereome endotheca composed of the thick parts of the costosepta that laterally anastomosed with each other. However, the corallites of R. paraclathrata are roundish in the cross section and their septa with abundant granulations. Retiophyllia paraclathrata Roniewicz, 1974 (Fig. 12, B; Fig. 13, D) 1974 Retiophyllia paraclathrata Roniewicz; p. 108-109, pl. 4, fig. 2, pl. 5, figs. 1-2, textfig. 8. 1987 Retiophyllia paraclathrata Roniewicz; Turnšek and Ramovš, p. 41, pl. 10, figs. 6-7. 1997 Retiophyllia paraclathrata Roniewicz; Turnšek, p. 183, pl. 183. Description: The colony is fasciculate and composed of cylindrical corallites. In the cross section, the corallites have an average diameter of 2.6 mm, and the C-C is 2.8 mm. The arrangement of the septa apparatus is radially symmetric and differentiated into 3 cycles. The costosepta are fusiform. S1 are the bluntest; it extend to the axis but do not co-mingle. The remaining septa are shorter in decreasing series. Thick and strong falculate pennulae are developed on the septal lateral edges. A circular stereome endotheca lies in the inner part of the corallites, which occurs as a result of the thick parts of the costosepta laterally anastomosing with each other. This separates the costal region and septal region. The wall is pellicular epithecal or bilaminar. There is no columella, and the mode of reproduction is unknown. Remarks: The characteristics of the specimen in this paper are consistent with those of the 32

R. paraclathrata collected from the Tatra Mountains (Roniewicz, 1974), except for the more abundant ornaments on the lateral faces of the former and the greater diameter of the latter (4 mm-5 mm). Retiophyllia multigranulata (Melnikova, 1967) (Fig. 12, G) 2001 Margarosmilia multigranulata (Melnikova); pl. 16, fig. 3. Description: The morphogenesis of corallum is unknown. The corallite is oval in the cross section with a diameter of about 2.5 mm. The epitheca is pellicular. The septal apparatus is arranged in radially symmetric and differentiated into 4 cycles. The septa are fusiform, with the maximum width in the wall area and getting thinner in the axial part. S1 are the bluntest and the remaining septa are shorter in decreasing series. S4 protrude slightly from the wall. Remarkable pennulea have developed on the septal flanks. Horizontal elements are presented as several rows of dissepiments that fill in the spaces between septa, forming an external wall with large dissepiments. The axial structure cannot be observed. Remarks: The characteristics of the specimen in this paper are the same as the Margarosmilia multigranulata collected from the Pamir region (Melnikova, 2001). However, it should be assigned to Retiophyllia because of the circular stereome endotheca lying in the inner part of the corallites, which occurs as a result of the thick parts of the costosepta laterally anastomosing with each other and separating the costal region and septal region. Retiophyllia defilippi (Stoppani, 1865) (Fig. 10, A-C, H-I, M) 1987 Retiophyllia defilippi (Stoppani); Turnšek and Ramovš, p. 40-41, pl. 11, figs. 1-3. 33

1997 Retiophyllia defilippi (Stoppani); Turnšek, p. 179, pl. 179. Description: Phaceloid colony with irregularly branched corallites, and appears triangular, polygonal or irregularly prolonged in the cross section. The diameter of the corallites ranges from 2.2 mm to 6.3 mm, and the C-C ranges from 2.9 mm to 4.2 mm. The septa are compact, thin, zig-zagging, and differentiated into 5 cycles with the same thickness. The granulous decorations developed on the septa lateral faces. Septal apparatus is arranged in subradially symmetric. S1 approximately extend to the axis, but do not co-mingle. The remaining septa are shorter in decreasing series. Horizontal elements are presented as several rows of dissepiments that fill in the spaces between septa, forming an external wall zone and an inner endothecal zone in the axial cavity. The columella is absent. The budding is intracalicular. Remarks: The characteristics of the specimen in this paper are consistent with those of the R. defilippi described by Turnšek and Ramovš (1987), such as the irregular corallites and polygonal or irregular prolongation, except for the larger corallites of the latter (which are 7 mm-9 mm in diameter). Genus Parathecosmilia Roniewicz, 1974 Type species: Rhabdophyllia sellae Stoppani, 1862 Parathecosmilia sellae (Stoppani, 1862) (Fig. 10, F-G; Fig. 13, G) 1890 Thecosmilia sellae Stoppani; Frech, p. 17, pl. 4, fig. 12. 1974 Parathecosmilia sellae (Stoppani); Roniewicz, pp. 110-111, p1. 6, figs. 1-3, p1. 7, figs. 1-2, texefigs. 9-10. 1987 Parathecosmilia sellae (Stoppani); Turnšek and Ramovš, p. 38, p1. 8, figs. 3-5. 34

1997 Parathecosmilia sellae (Stoppani); Turnšek, p. 149, pl. 149. Description: The colony is phaceloid. The corallites are irregularly roundish in the cross section with diameters ranging from 2.3 mm to 4.4 mm, and the C-C ranges from 3.5 mm to 5. 5mm. The wall is parathecal, thin, or epithecal. The specimen is poorly preserved and the outer part of the septa is naked. The costosepta are compact, straight, and differentiated into 3-4 cycles; there are approximately 31-41 in number, and they are radially symmetric. S1 approach the center, and the number is 6. S2 are shorter than S1. S3 are about 1/2 of S1 in length. Granulations can be observed in the septal lateral edges. Weak Peneckiella-type dissepiments and vesicular dissepiments can be observed in the longitudinal section. The budding type is intracalicular. Remarks: The specimen in this paper differs from the P. sellae collected from Splevta in the Alps (Turnšek, 1997) because of the irregularly roundish corallites in the cross section. Parathecosmilia aff. sellae (Stoppani, 1862) (Fig. 10, D-E, J; Fig. 13, B) aff. 1974 Parathecosmilia sellae (Stoppani); Roniewicz, p. 110-111, p1. 6, figs. 1-3, p1. 7, figs. 1-2, Textfigs. 9-10. aff. 1987 Parathecosmilia sellae (Stoppani); Turnšek and Ramovš, p. 38, p1. 8, figs. 3-5. aff. 1997 Parathecosmilia sellae (Stoppani); Turnšek, p. 149, pl. 149. Description: The colony is phaceloid. The corallites are cylindrical with diameters ranging from 2.2 mm to 3.3 mm, and the C-C ranges from 3.5 mm to 5.5 mm. The wall is parathecal, thin, or epithecal, and usually poorly preserved so that the outer parts of the septa are naked. The costosepta are compact, straight, and differentiated into 3-4 cycles; there are 35

approximately 31-42 in number, and they are radially symmetric. S1 approach the center, and the number is 6. S2 are shorter than S1. S3 are about 1/2 of S1 in length. Granulations can be observed in the septal lateral edges. Weak Peneckiella-type dissepiments and vesicular dissepiments can be observed in the longitudinal section. The increase of the corallites occurred through the budding from the lateral edge. Remarks: The specimen here differs from P. sellae (Turnšek, 1997) in the reproduction mode of the lateral increase.

4.

Conclusions

Fifteen genera and 25 species were identified, described, and illustrated based on the above discussion and the study of the new materials available from the Renacuo area of northern Tibet. The Late Triassic reef coral fauna from the Riganpeicuo Formation in the Renacuo area is dominated by Remimaniphylliidae, associated with Margarophylliidae, Stylophyllidae, and Zardinophyllidae, of which the colonial forms (phaceloid, massive, pseudo-meandroid, and thamnasterioid) strongly dominate the solitary forms. The majority of the corals in the study area can be compared with those in the Upper Triassic strata in the western Tethys (northern Calcareous Alps, Austria, Southern Alps, Slovenia, Italy, and Greece), especially the Julian Carbonate Platform in Slovenia. A comparison of the coral faunas in the Qiangtang terrane, Songpan-Ganzi fold belt, Himalayan terrane, Lhasa terrane, and western Tethys reveals that the fauna in the Qiangtang region was distinctly different from that found in the Himalayan region, appeared to be close to the fauna found in the western Tethys, and presented a certain 36

degree of similarity with the coral fauna in the same period of the Songpan-Ganzi fold belt and Lhasa terrane. A further analysis of the four regions during the Late Triassic period shows that the Qiangtang terrane and Songpan-Ganzi fold belt were in the vicinity of the gradually closed Paleo-Tethys Ocean, resulting in the free transmigration of the benthonic organisms of these areas. The Himalayan terrane was located on the southern side of the Meso-Tethyan Ocean, which was separated from the Qiangtang terrane, Lhasa terrane, and Songpan-Ganzi fold belt by a wide ocean-meso Tethys, which made it impossible for benthonic organisms on both flanks to freely migrate toward the opposite continental margins. The location of the Lhasa terrane and its relationship with the other regions requires further exploration.

Acknowledgements

We would like to express our appreciation to Deng Zhanqiu and Liao Weihua, researchers at the Nanjing Institute of Geological Paleontology, Chinese Academy of Sciences, for their guidance and help during the identification of the coral fossils. Our sincere thanks to Professor Jean-Piere CUIF (Sciences de la Terre, Universite Paris Sud) for providing the important literatures. This work was supported by the China Geological Survey (Grant Nos.: 1212011121271, 1212011121244), the Ministry of Science and Technology of the People’s Republic of China (Grant No.: 2015FY310100), and the National Natural Science Foundation of China (Grant No.: 41472030). Lastly, we would like to thank Accdon for its linguistic assistance during the preparation of this manuscript.

37

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47

All figure captions: Fig.1. Map showing the sample locality of the scleractinian corals from the Renacuo area in northern Tibet.

Fig. 2. Tectonic framework of the Tibetan Plateau (modified from Liu et al., 2016) KSZ: Kunlun-Qaidam Suture Zone, JSZ: the Jingsha Suture Zone, LSSZ: the Longmu Co-Shuanghu Suture Zone, BNSZ: the Bangong-Nujiang Suture Zone, YZSZ: the Yarlung Zangbo Suture Zone.

Fig. 3. Stratigraphic columnar sections showing the major lithostratigraphic units of the Riganpeicuo Formation in the Renacuo area (modified from Hou et al., 2015)

Fig. 4. Late Triassic paleogeographic map showing the possible paleo-position of the Himalayas terrane, Lhasa terrane, Qiangtang terrane, Songpan Ganzi fold belt (modified from Flügel et al., 2002; Boucot et al., 2013; Feng et al., 2013; Martindale et al., 2015). Hi: the Himalayas terrane, Lh: the Lhasa terrane, QT: the Qiangtang terrane, SP: the Songpan Ganzi fold belt, SC: the South China Block.

Fig. 5. Corals of the genus Furcophyllia and the genus Hydrasmilia. A-B, D, F, H-I, Hydrasmilia fossulata Turnšek and Senowbari-Daryan; A, transverse thin section; B, longitudinal thin section showing rhythmical thickenings of the corallites; D, thin-septal corallite in transverse section; F, intracalicular budding; H, I, longitudinal 48

thin section and its fragment showing abundant dissepiments. A, F, J171-35; B, D, H-I, J171-33. C, E, G, J, Hydrasmilia ornamenta Turnšek and Senowbari-Daryan; C, a corallite showing the epithecal wall thickened and connected to the original parts of the septa; E, two carallites showing abundant lateral septal granulations; G, transverse thin section; J, longitudinal thin section. J171-34. K, L, Furcophyllia septafindens (Volz); K, transverse thin section showing septal brooms; L, transverse thin section showing linear calyx hole in the central part. J169-2. Scale bars: A-B, E, G-J, L, 2 mm; C, D, 0.5 mm; F, K, 1 mm.

Fig. 6. Corals of the family Stylophyllidae and the family Guembelastraeidae. A-B, G, Stylophyllopsis cognata Melnikova; A, transverse thin section; B, G, a corallite and its enlarged view. T139-2. C-E, H, Stylophyllum sp.; C, showing the budding type, D, partial transverse thin section showing roundish corallites, E, longitudinal thin section showing the colonial type; H, a corallite with moniliform septa. C, D, H, T90-6; E, T90-7. F, J, L, Guembelastraea guembelii (Laube); F, transverse thin section; J, a corallite showing completely developed septal apparatus; L, longitudinal thin section. T134-1. I, K, Guembelastraea aff. guembeli (Laube); I, transverse thin section; K, a corallite showing alternate dentations on the lateral faces of the septa. J168-15. Scale bars: A, D-F, I, K-L, 2 mm; B, 1 mm; C, G, H, J, 0.5 mm.

Fig. 7. Corals of the family Margarophylliidae and the family Zardinophyllidae. A, C, Thamnomargarosmilia sp.; A, transverse thin section; C, a corallite showing septal 49

apparatus. T113-1. B, Radiophyllia cf. astylatus Deng; transverse thin section. J170-9. D-G, Conophyllopsis qamdoensis Deng and Zhang; D, partial transverse thin section showing corallites connected at the lateral surfaces; E, a corallite showing septa apparatus; F, longitudinal thin section showing the extracalicular budding and abundant dissepiments; G, phaceloid colony in longitudinal thin section. J171-31. Scale bars: A-C, 2 mm; D, F, 0.5 mm; E, 0.2 mm; G, 1 mm.

Fig. 8. Corals of the family Conophyllidae and the family Margarophylliidae. A-C, K, Araiophyllum triasicum Cuif; A, roundish corallites in transverse thin section; B, C, corallites showing winding and porous septa; K, longitudinal thin section. T80-5. D-F, Margarosmilia zogangensis Deng and Zhang; D, transverse thin section showing long fusiform septa and abundant vesicular dissepiments; E, showing the colonial type; F, transverse thin section showing irregularly oval calices. J171-6. G, I-J, L, Margarosmilia zieteni (Klipstein); G, transverse thin section; I, longitudinal thin section; J, L, corallites of this phaceloid coral showing vesicular endotheca and pellicular wall (arrows); J170-8. H, Thamnomargarosmilia sp.; longitudinal thin section showing vesicular marginal and tabuloid internal dissepiments. T113-1. Scale bars: A, B, L, 1 mm; C, J, 0.5 mm; D-I, K, 2 mm.

Fig. 9. Corals of the family Margarophylliidae, the family Conophyllidae, and the family Coryphylliidae. A, Conophyllopsis qamdoensis Deng and Zhang; showing weakly-developed clintheriform columella (arrow). J171-31. B, Araiophyllum 50

triasicum Cuif; longitudinal thin section. T80-5. C, F, Khytrastrea sp.; C, transverse thin section; F, enlarged view of this solitary coral. T0-43. D-E, G-I, Pokljukosmilia cf. tuvalica Turnšek and Buser; D, transverse thin section; E, G-H, three corallites showing the enlongated axial fossula and the septal apparatus; I, longitudinal thin section showing the colonial type. J171-8. J, Margarosmilia zogangensis Deng and Zhang; transverse thin section. J171-6. K, Thamnomargarosmilia sp.; showing typical biseptal elements. T113-1. Scale bars: A, C, E-H, 0.5 mm; B, G, I, 1 mm; D, J-K, 2 mm.

Fig. 10. Corals of the family Remimaniphylliidae and the family Margarophylliidae. A-C, H-I, M, Retiophyllia defilippi (Stoppani); A, transverse thin section showing irregular corallites; B, enlarged view of the dotted box in A showing the details of septa; C, enlarged view of longitudinal thin section showing the horizontal elements; H, longitudinal thin section; I, a corallite showing several rows of dissepiments; M, intracalicular budding. T0-19. D-E, J, Parathecosmilia aff. sellae (Stoppani); D, transverse thin section; E, longitudinal thin section; J, showing thin epithecal. J170-6. F-G, Parathecosmilia sellae (Stoppani); F, view of a normal corallite showing thin wall; G, longitudinal thin section. T134-2. K, Margarosmilia zieteni (Klipstein); partial transverse thin section. J170-8. L, Thamnomargarosmilia sp.; partial transverse thin section. T113-1. Scale bars: A, D-E, G-H, K-M, 2 mm; B-C, F, I-J, 0.5 mm.

Fig. 11. Corals of the family Remimaniphylliidae (1). A, G, Retiophyllia cf. gracilis 51

Roniewicz; A, transverse thin section showing abundant connecting processes; G, enlarged view of corallite showing details of the septal apparatus. J171-21. B, Paracuifia sp.; transverse thin section. T11-1. C-F, H, Retiophyllia gracilis Roniewicz; C, longitudinal thin section; E, transverse thin section; D, F, H, three corallites of this phaceloid coral showing the details of septa apparatus. J168-10. Scale bars: A, D, F-H, 0.4 mm; B, C, E, 2 mm.

Fig. 12. Corals of the genus Retiophyllia. A, Retiophyllia gracilis Roniewicz; intracalicular budding. J168-10. B, Retiophyllia paraclathrata Roniewicz; transverse thin section. J171-4. C-E, Retiophyllia cf. gracilis Roniewicz; C, longitudinal thin section showing the colonial type; D, enlarged view of C showing abundant dissepiments; E, transverse thin section showing roundish corallites. J171-21. F, Retiophyllia clathrata (Emmrich); a corallite showing a circular stereome endotheca. J168-3. G, Retiophyllia multigranulata (Melnikova); corallite with completely developed septal apparatus. J170-11. Scale bars: A, 0.4 mm; B, F, 1 mm; C-E, 2 mm; G, 0.2 mm.

Fig. 13. Corals of the family Remimaniphylliidae (2). A, C, Retiophyllia clathrata (Emmrich); A, transverse thin section showing oval corallites; C, corallite with completely developed septal apparatus. J168-3. B, Parathecosmilia aff. sellae (Stoppani); a fragment of the transverse thin section. J170-6. D, Retiophyllia paraclathrata Roniewicz; a corallite showing completely developed septa apparatus. 52

J171-4. E-F, Retiophyllia? sp.; E, longitudinal thin section showing phaceloid colonial type; F, a corallite showing the details of septa. J168-2. G, Parathecosmilia sellae (Stoppani); transverse thin section. T134-2. Scale bars: A, 2 mm; B, D, 0.5 mm; C, E, G, 1 mm; F, 0.2 mm.

All tables’ titles,descriptions and footnotes: Table 1 A list of the coral species from the Riganpeicuo Formation, and their abundance, growth form, type of colony, and ornamentation (special structures) of the septa.

Table

2

Coral

species

of the

Riganpeicuo

Formation and

their

other

Formations/localities in China and the Tethys province. Abbreviations: JPL, Jiapila Formation (China); BLL, Bolila Formation (China); JCP, Julian Carboate Plateform (Slovenia); CAS, St. Cassian Formatin (Italy) ; CDZ, Calcare di zu Formation (Italy), DAC, Dachstein Formation (Austria); ZLA, Zlambach Beds (Austria); PAN, Pantokrator limestone (Hydra, Greece); CAL, Calcareous (northern Alps); C, Carnian; N, Norian; R, Rhaetian.

Tabel 3 Genera spectra of the Late Triassic coral faunas from the Himalayan terrane, Lhasa terrane, Qiangtang terrane, and Songpan-Ganzi fold belt. The data are related to coral faunas from the Songpan-Ganzi terrane, Himalayan terrane, and Lhasa terrane using the research found in Bo et al. (2017). 53

Explanation:

genera represented by rare corals of 1-2 species;

represented by about 3-5 species of corals; species.

54

genera

genera represented by more than 5

Taxa

Order Scleractinia Bourne, Genus Furcophyllia 1900 Furcophyllia Stolarski et al., 2004 Genus Hydrasmilia septafindens (Volz, 1896) Hydrasmilia fossulata Turnšek and Hydrasmilia ornamenta Turnšek Senowbari-Daryan, 1994and Family Turnšek Senowbari-Daryan, 1994and Genus Paracuifia Remimaniphylliidae Senowbari-Daryan, 1994 Paracuifia sp. Melnikova, 2001 1974 Genus Retiophyllia Cuif, gracilis 1966Retiophyllia Retiophyllia cf. gracilis Roniewicz, 1989 Retiophyllia Roniewicz, 1989? sp. Retiophyllia clathrata Retiophyllia (Emmrich, 1853) Retiophyllia paraclathrata Roniewicz, defilippi multigranulata 1974Retiophyllia (Melnikova, Genus 1865) Parathecosmilia (Stoppani, 1967) Parathecosmilia sellae Roniewicz, 1974 Parathecosmilia aff. (Stoppani, 1862) Family Guembelastraeidae sellae (Stoppani, 1862) Genus Cuif, 1977 Guembelastraea Guembelastraea Cuif, 1976 Guembelastraea guembelii (Laube, 1865) aff. Family Conophyllidae guembelii (Laube, 1865) Genus 1952Araiophyllum Alloiteau, Araiophyllum triasicum Cuif, 1975 Family Cuif, 1975Margarophylliidae Margarosmilia L. Genus Beauvais, 1980 Margarosmilia Volz, 1896 Margarosmilia zogangensis Deng zieteni and Genus (Klipstein, 1843) Zhang, 1984 Thamnomargarosmilia Thamnomargarosmilia Genus 1996 Conophyllopsis sp. Melnikova, Conophyllopsis Deng and Zhang, 1984 Family qamdoensis Coryphylliidae Deng and Genus Pokljukosmilia Beauvais, 1981 Zhang, 1984 Pokljukosmilia cf. Turnšek, 1989 GenusTurnšek,Khytrastrea tuvalica 1989 Khytrastrea sp. 2013 Roniewicz et Stanley, Family Stylophyllidae Genus Stylophyllopsis Volz, emend. Cuif, 1976 Stylophyllopsis cognata Frech, 1890 Genus 1979Stylophyllum Melnikova, Stylophyllum sp. Reuss, 1854

Fossil abundance

Growth form

Type of colony

Ornamentation (special structures)

+

solitary

++++ ++++

colonial colonial

phaceloid phaceloid

granulation granulation

+

colonial

pseudomeandroid

granulation

++ ++ ++ ++ ++ ++ ++

colonial colonial colonial colonial colonial unknown colonial

phaceloid phaceloid phaceloid fasciculate fasciculate phaceloid

granulation granulation granulation granulation pennules pennules granulation

++ ++

colonial colonial

phaceloid phaceloid

granulation granulation

+ +

colonial colonial

cerioid cerioid

pennules pennules

++++

colonial

phaceloid

porous

++ ++

colonial colonial

fasciculate fasciculate

granulation granulation

++

colonial

phaceloid-thamnasterioid

granulation /

++

colonial

thamnasterioid phaceloid thamnasterioid

biseptal granulation

granulation

thamnasterioid thamnasterioid phaceloid thamnasterioid

+++

colonial

++

solitary

+

colonial

phaceloid

porous

++

colonial

phaceloid

moniliform

55

ttttttthththamnasterioid

granulation granulation

Family Zardinophyllidae Genus Radiophyllia Montanaro-Gallitelli, 1975 Radiophyllia cf. Deng, 2006

++

solitary

astylatus Deng, 2006

56

granulation

Highlights



First systematic description of the Upper Triassic reef coral fauna in northern Tibet.



Tethys-type scleractinian corals occurring in the Renacuo area of the Qiangtang terrane.



A new perspective on the palaeogeographic positions of the Qiangtang terrane, Lhasa terrane, Himalayan terrane and Songpan-Ganzi fold belt.

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