Journal of Asian Earth Sciences 118 (2016) 101–110

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Journal of Asian Earth Sciences

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Integrated biochronology for marine faunas of Guizhou Province, South China ⇑ Zuoyu Sun a,b, , Dayong Jiang a, Cheng Ji c, Weicheng Hao a a Laboratory of Orogenic Belt and Crustal Evolution, Ministry of Education, and Department of Geology and Geological Museum, Peking University, Yiheyuan Street 5, Beijing 100871, PR China b State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Science), Nanjing 210008, PR China c Key Laboratory of Economic Stratigraphy and Palaeogeography, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China article info abstract

Article history: The Middle and Upper Triassic marine deposits of Guizhou Province, which yielded exceptionally well- Received 10 November 2015 preserved vertebrate faunas, are further investigated. New age-diagnostic conodonts and ammonoids Received in revised form 28 December 2015 from six measured sections, together with already published data, allow us to construct an integrated Accepted 5 January 2016 biochronology straddling strata from the upper (, ) to the Available online 6 January 2016 basal Xiaowa Formation (, Upper Triassic). Age constrains for those fossil Lagerstätten are now dated to the substage and zone levels: the Panxian Fauna, within the conodont Nicoraella kockeli Zone Keywords: and broadly coexisted with the ammonoid ‘Schreyerites’ binodosus, is suggested as latest Pelsonian (mid- Biochronology dle Anisian) in age; the Xingyi Fauna is assumed to be not younger than the middle Longobardian (Late Marine vertebrate faunas Triassic ) because the conodont Paragondolella inclinata with free-blade and the ammonoid Haoceras Guizhou Province xingyiensis are recorded from slightly younger strata; the conodont Paragondolella auriformis and the South China ammonoid Trachyceras multituberculatum and Austrotrachyceras triadicum clearly indicate that the Guanling Fauna is not older than Julian (early Carnian) in age (time interval between Aon Zone or Aonoides Zone). With the new biostratigraphic data, a relative sequence and correlation of the Middle Triassic vertebrate faunas from Guizhou (South China) and Monte San Giorgio (Southern Alps, Switzerland/Italy) is proposed. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction Xiaowa Formation, near Xinpu of Guanling County. The Panxian Fauna appeared in publication slightly later (Wang et al., 2001), The Middle and Upper Triassic marine deposits of Guizhou Pro- and came from the Guanling Formation (Anisian, Middle Triassic) vinces, South China, have traditionally yielded fossil fishes and rep- near Xinmin of Panxian County. Many new finds of tiles (Young, 1958, 1965a, 1965b; Su, 1959). However, these (referred to as ‘China’s good-luck monsters’ by the National Geo- isolated materials with ambiguous provenance (localities and/or graphic Magazine) from these Lagersttätten have attracted stratigraphies) drew little attention of the scientific community increased attention from both scientists and the public. Many until the end of the last century (Lin and Rieppel, 1998; Rieppel, research groups, from China and overseas, have carried out exten- 1998, 1999, 2000). The boom was fueled by the discoveries and rel- sive studies and produced numerous publications that greatly evant researches of two new Lagerstätten with exceptionally pre- enhanced our knowledge of , systematics, evolution served vertebrate fossils (i.e., the Anisian Panxian Fauna and the and paleobiogeography of these ‘sea monsters’ (Benton et al., Carnian Guanling Fauna), besides the already known Ladinian/ 2013 and references therein). Meanwhile, relevant fundamental early Carnian Xingyi Fauna that is famous for the pachypleurosaur work concerning their age determination, faunal composition, sed- Keichousaurus (Fig. 1a and b). Among the above three, the Guanling imentology and taphonomy have also been improved (Wang et al., Fauna was first discovered in 1999 (Li, 1999; Liu, 1999) in the 2008 and references therein; Motani et al., 2008; Jiang et al., 2009; Zou et al., 2015). Age determinations of those Lagerstätten dated back to ⇑ Corresponding author at: Laboratory of Orogenic Belt and Crustal Evolution, 1958 when C.C. Young considered Keichousaurus hui as Ladinian Ministry of Education, and Department of Geology and Geological Museum, Peking (Middle Triassic) in age based on its evolution level among the University, Yiheyuan Street 5, Beijing 100871, PR China. Pachypleurosauria (Young, 1958). Wang et al. (1998), on the basis E-mail address: [email protected] (Z. Sun). http://dx.doi.org/10.1016/j.jseaes.2016.01.004 1367-9120/Ó 2016 Elsevier Ltd. All rights reserved. 102 Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110

Fig. 1. (a) Geographic map and (b) Simplified lithostratigraphic log of the Triassic marine vertebrate faunas in Guizhou Province, South China and its adjacent area; (c–e) showing the localization of measured sections. (1) Zhuganpo section, Yongningzhen, Guanling County, Guizhou Province (GLZ); (2) Xiaowa section, Xinpu, Guanling County, Guizhou Province (GLX); (3) Yangjuan-Chupiwa section, Xinmin, Panxian County, Guizhou Province (YC); (4) Zhachong section, Changdi, Luoping County, Province (LPZ); (5) Shijiangjun section, Banqiao, Luoping County, Yunnan Province (LPS); (6) Niubudai section, Banqiao, Luoping County, Yunnan Province (LPN). of the presence of the conodont Paragondolella polygnathiformis establish an integrated biochronology that extends across the Tri- 3 m above the Keichousaurus bed of the type locality, assigned assic marine vertebrate faunas mentioned above. Such an inte- the Xingyi Fauna as early Carnian, rather than late Ladinian as pro- grated biochronology is in part calibrated with the relevant data posed in earlier work (Young, 1958, 1965a; Su, 1959; Dong, 1980). from the Middle Triassic succession of Monte San Giorgio (South- However, complex tectonic condition around the type locality of ern Alps, Switzerland/Italy) (Stockar et al., 2012) and also GSSPs the Xingyi Fauna makes Wang et al. (1998)’s conclusion question- of the Ladinian and Carnian (Brack et al., 2005; Mietto et al., able. The ammonoid biostratigraphy of the laterally equivalent sec- 2012). Thus, the Triassic marine vertebrate Lagerstätten of Guizhou tions that do not yield fossiliferous layers (Wang, 1983; Xu et al., Province are now dated to the substage and zone levels and are 2003) suggested an early-middle late Ladinian age and was preliminarily correlated to analogous faunas of Monte San Giorgio. recently in part confirmed by ammonoids directly collected during Meanwhile, their stratigraphy and fauna composition is also a large scale yet bed-by-bed excavation of the fossiliferous layers improved following Benton et al. (2013) and Tintori et al. (2014) (Zou et al., 2015). Meanwhile, a rather broad age assignment of with new data from the joint excavations held by Peking Univer- the Xingyi fauna to the Ladinian–Carnian is still held by some sity, Beijing, University of California, Davis, USA, and Università researchers (Benton et al., 2013), which to some extent blurs the degli Studi di Milano, Italy during 2004–2014. age difference between the Xingyi Fauna and the younger Guanling Fauna. The Guanling Fauna in the basal Xiao Formation was corre- lated to lower Carnian (Upper Triassic) based on (Hao 2. Palaeogeographical setting et al., 2003; Xu et al., 2003) or middle Carnian (Upper Triassic) based on conodonts (Wang, 2000; Chen and Wang, 2002; Sun During the Triassic Period the southwestern corner of Guizhou et al., 2003) and ichthyoliths (Chen and Cuny, 2003). Sun et al. Province (i.e., the study area in the present paper) was located at (2006, 2014) presented conodont biostratigraphic data from the the south-west platform margin of the Yangtze Platform between upper Guanling Formation near the type locality of the Panxian the Khamdian (Kangdian) Old Land and the Nanpanjiang Basin Fauna and referred it to the conodont Nicoraella kockeli Zone, indi- (also named the Youjiang depression in some Chinese references). cating a Pelsonian (Middle Anisian) age. The Yangtze Platform almost extended across the entire Yangtze Herein, we integrate new conodont and ammonoid data from plate (west from the present South China Sea to the Longmen Shan, six measured sections, together with already published data, to north from near the Vietnamese border, and beyond the valley of Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110 103 the Yangtze River) and the Nanpanjiang Basin developed in the layers, equal to beds 77–91 of Motani et al. (2008) and Cy 10–13 of border region between Yunnan, Guizhou and Guangxi provinces Sun et al. (2006), are a ca. 2 m thick interval of dark gray to black and adjacent areas in northern Vietnam (see Fig. 1 in Enos et al., laminated lime or dolomitic mudstones with rich organic matters 1998). As a stable palaeogeographic element from the Late Protero- and at least five bentonite layers of variable thickness. Vertically, zoic to Middle Triassic the Yangtze Platform was characterized by eight vertebrate-bearing beds (Motani et al., 2008) are identified shallow-water carbonate deposits, whereas the Nanpanjiang Basin and have previously been lumped as follows: Lower Reptile Hori- was dominated by basinal deposits (i.e., relatively deep-water car- zon (layers 77 and 79), Middle Reptile Horizon (layers 81, 84, bonates and turbite sequences) with small isolated platforms. 85), and Upper Reptile Horizon (layers 87, 89, 90). Further details However, during the Middle and Upper Triassic under the influence concerning horizons, assemblages and palaeoenvironment changes of the Indosinian Orogeny the Yangze Platform was progressively of the Panxian Fauna have been described exhaustively on the drowned, and many intraplatform basins developed from west to basis of the finds of fishes and reptiles during bed-by-bed excava- northwest when the Npanjiang Basin encroached northward tions (see Motani et al., 2008; Sun et al., 2008; Jiang et al., 2009). (Enos et al., 1998; Lehmann et al., 2005). Correspondingly, several The Luoping Fauna, mainly outcropping around Dawazi village of intraplatform basins of the study area provided a suitable environ- Luoping County (Yunnan Province) in the upper Guanling Forma- ment for the preservation of fossil Lagerstättes, including the Panx- tion, was also assigned to the conodont Nicoraella kockeli Zone ian, Xingyi and Guanling faunas (see Fig. 1 in Benton et al., 2013). (Zhang et al., 2009). In contrast, it is more extensive and spectacu- Therein, black rock series (so called black ‘‘shale”) yielded those lar, including and fishes as the most common fossils, fossil fishes and reptiles, having developed in a succession of shal- followed by marine reptiles, bivalves, gastropods, echinoderms, low water carbonates with evaporites or with intermittent terrige- brachiopods, conodonts, foraminifers and plants (Hu et al., 2011). nous influx (Guanling, Yangliujing, Zhuganpo and Xiaowa Further details of the Luoping Fauna are described by Hu et al. formations) (Wang et al., 2009). (2011) and relevant research advances have been thoroughly reviewed by Benton et al. (2013). The Yangliujing Formation generally corresponds to ‘the 3. Stratigraphy and relevant marine vertebrate Lagerstätten Member III of the Guanling Formation’ adopted by Zhang et al. (2009) and is herein constrained to include the massive dolomites, We herein investigated Middle and Upper Triassic deposits with as suggested by Chen and Wang (2009). It is strongly dolomitized the marine vertebrate-bearing levels, mainly distributed in Panx- and traditionally conceived as the Ladinian evaporative tidal sedi- ian, Pu’an, Wusha, Anlong, Xingyi, Qinglong and Guanling of west- ments that comprises medium- to thick-bedded dolostones or cal- ern Guizhou Province, and Luoping and Fuyuan of eastern Yunnan cite dolostones intercalated with pseudomorphs of gypsum- and Province, South China (Fig. 1c, d, e; Wang et al., 2001; Sun et al., evaporate-solution breccias. 2006). To well illustrate the stratigraphy of these Lagersttätten, a The Zhuganpo Formation can be lithologically subdivided into composite lithologic succession (Fig. 1b), which straddles the Tri- three members: (1) laminated dolomitic in the lower assic vertebrate Lagersttätten mentioned above, is constructed Member; (2) bioclastic limestones with chert concretions in the and four vertebrate-bearing rock units (i.e., Guanling Formation, middle Member; (3) nodular limestones in the upper Member. Yangliujing Formation, Zhuganpo Formation and Xiaowa Forma- Marine have been recovered from both lower and mid- tion) are in detail clarified below. dle members. Liu et al. (2002a) reported the marine reptile Dingx- The Guanling Formation generally represents the Anisian iaosaurus luyinensis from the upper Yangliujing Formation near the deposits and mainly comprises clastic rocks and carbonates. It type locality of the Xingyi Fauna, and Sun et al. (2005a, 2005b) can be subdivided into two members, of which the lower member reported a thalattosaur and lariosaur from the upper Gejiu Forma- contains yellow-green fine sandstones, silty mudstones and mud- tion (near Niubudai Village, Banqiao Town, Luoping County, Yun- stones intercalated with muddy dolomites interpreted to reflect a nan Province). Judged by the lithology and rock sequence, the transition from restricted-evaporitic tidal flat to shallow marine layers of the laminated dolomitic limestones yielding Dingxi- facies, whereas the upper member comprises light-gray to dark- aosaurus luyinensis from Xingyi and that yielding the thalattosaur gray nodular micritic limestones, muddy limestones and cherty and lariosaur from Luoping should be assigned to the lower Zhu- micritic limestones with bands of dolomites. The base of the Guan- ganpo Formation (Sun, 2006) and referred to the reptile layers ling Formation is well defined by the occurrence of the typical below the Xingyi biota (see Fig. 3 of Benton et al., 2013). The type coarse-grained tuff (traditionally called green pisolite), a laterally locality of the Xingyi Fauna is located near Lüyin Village (Dingxiao, traceable lithostratigraphic marker, whereas the top is defined as Xingyi City of Guizhou Province), where the fossil-bearing interval the occurrence of the thick-bedded, massive dolomites (i.e., the is ca. 3 m thick, comprising gray to gray dark thin-bedded muddy base of the overlying Yangliujing Formation). From the upper limestones (i.e., the traditional Keichousaurus beds, equal to the Guanling Formation, two Anisian (Middle Triassic) marine verte- Lower Assemblage of the Xingyi Fauna of Ji et al., 2012). Laterally, brate faunas discovered, i.e. the Panxian Fauna and the Luoping the equivalent fossiliferous layers geographically extend to Wusha Fauna, respectively. The former is geographically restricted and Anlong of Guizhou Province, and Luoping and Fuyuan of Yun- between Xinmin (around Yangjuan and Chupiwa villages) of Panx- nan Province (Fig. 1d; Wang et al., 2001; Jiang, 2002). Our field ian County and Qingshan (near Xindian and Xuepu villages) of examinations of those localities confirmed that the Xingyi Fauna Pu’an County (Fig. 1c). Stratigraphically, it lies about 50 m below comes from the middle Zhuganpo Formation (Fig. 2b and c), which the bottom of the Yangliujing Formation at the Yangjuan- is dominated by bioclastic limestones with chert concretions. It Chupiwa section (Fig. 2a). The Panxian Fauna has yielded a remark- should be pointed out that Wang et al. (2009) wrongly referred able assemblage of marine reptiles, including the the Xingyi Fauna to the lowest Zhuganpo Formation and Benton , Phalarodon and Xinminosaurus, the nothosaurid et al. (2013) wrongly referred it to the upper part of the Zhuganpo sauropterygians Nothosaurus and Lariosaurus, and some unique lin- Formation. The Xingyi Fauna has yielded diverse fossil reptiles and eages like the protorosaur , the Qiano- fishes, of which fossil reptiles include pachypleurosaurid Keic- suchus, the unarmored placodontid Placodus, the eosauropterygian housaurus, pistosauroid Yunguisaurus and Wangosaurus, notho- Wumengosaurus (Jiang et al., 2009 and references therein) and the saurid Nothosaurus and Lariosaurus, placodontid Glyphoderma, saurosphargid Largocephalosaurus (Li et al., 2013) as well as unde- thalattosaur Anshunsaurus, Guizhouichthyosaurus and scribed pachypleurosaurid sauropterygian. The vertebrate-bearing Qianichthyosaurus, and protorosaur Tanystropheus and Macrocne- 104 Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110

Fig. 2. An integrated biochronology straddling the Middle and Upper Triassic marine vertebrate faunas in Guizhou Province, South China and its adjacent area. (a) Yangjuan- Chupiwa section, Xinmin, Panxian County, Guizhou Province (YC), with conodont data partly from Sun et al. (2006, 2014); (b) Zhuganpo section, Yongningzhen, Guanling County, Guizhou Province (GLZ), with conodont data partly from Sun et al. (2005c); (c) Niubudai composite section, Banqiao, Luoping County, Yunnan Province; (d) Xiaowa section, Xinpu, Guanling County, Guizhou Province, with ammonoid data from Hao et al. (2003); (e) type locality of Keichousaurus hui Young, 1958, Luyin, Dingxiao, Xingyi County, Guizhou Province, with conodont data from Wang et al. (1998). Abbreviations: Nc., Nicoraella; Ng., Neogondolella; Pg., Paragondolella. Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110 105 mus (Ma et al., 2013, 2015 and references therein; Yang et al., level have been erected for reptiles, of which the ichthyosaurs 2014); fossil fishes include Sinoeugnathus kueichowensis Su, 1959, Guizhouichthyosaurus, Guanlingsaurus and Qianichthyosaurus, tha- orientalis (Su, 1959), Asialepidotus shingyiensis Su, lattosaurs Anshunsaurus, Xinpusaurus and Miodentosaurus, pla- 1959 (=Guizhouella analilepida Liu, 2003 in Liu et al., 2003 codontid sauropterygians Sinocyamodus and Psephochelys, and an =Guizhoueugnathus analilepida (Liu, 2004)), Guizhouamia bellula ancestral (Jiang et al., 2005 and reference Liu et al., 2002b, Xingyia gracilis Liu, 2003 in Liu et al., 2003, therein; Cheng et al., 2007; Li et al., 2008) are valid for sure, while Guizhouniscus microlepidus Liu, 2003 in Liu et al., 2003, Brachyso- the taxonomic statuses of the rest e.g. the ichthyosaur Typicu- mus minor (Liu, 2004), Thoracopterus wushaensis Tintori et al., sichthyosaurus, Panjiangsaurus and Cymbospondylus still need to 2012 (=Potanichthys xingyiensis Xu et al., 2012), Peripeltopleurus be clarified (Jiang et al., 2005). Further details of the Guanling exquisitus (Xu et al., 2015) and also several undescribed Fauna are in detail described by Wang et al. (2008). of (Brough, 1939), Marcopoloichthys (Tintori et al., 2008) and Fuyuanperleidus (Geng et al., 2012). However, most of these taxa were erected on specimens collected by amateurs, thus 4. An integrated bio-chronostratigraphy their precise provenance (concerning localities, horizons and assemblages) are elusive. Recently, bed-by-bed excavations of the Six sections, straddling strata that range from the upper Guan- Xingyi Fauna has been carried out since August of 2011 at the ling Formation to the lower Xiaowa Formation (see details in Nimaigu Village (Wusha District, Xingyi City, Guizhou Province). Fig. 1c–e), were measured and over 550 conodont samples were Thus, for the first time the vertebrate-bearing layers of the Xingyi collected with an average sampling rate of 1 sample/m and each Fauna are completely measured and 28 distinguishable layers about 2 kg in weight. The vertical sequences of the biochronologi- (layer 26 to layer 53) with ca. 5 m thick in sum are counted. cally significant conodont occurrence and, to a lesser extent, Vertebrate-bearing layers are described in detail, concerning the ammonoid occurrence, are recognized and laterally correlated lithology and the finds of fossil reptiles by Ji et al. (2012) and Ma (Fig. 2). et al. (2013) and fossil fishes herein. Lithologically, from bottom At the Yangjuan-Chupiwa section, exposed near Yangjuan Vil- to top, layers 26–34 consist of dark gray, thin bedded limestones lage, Xinmin District, Panxian County (starting at N25°3104800, intercalated with argillaceous banded limestones; layers 35–44 E1045305100 and ending at N25°3104400, E104°5304600), conodonts comprise medium bedded limestones intercalated with marls, are outstandingly differentiated in the upper Guanling Formation: and layers 45–53 are gray, medium-thick bedded limestones inter- its basal part is characterized by species of the platform-less gon- calated with dark gray medium-thin bedded marls, indicating a dollellid Nicoraella, viz. Nicoraella germanica, Nicoraella kock- transition from anoxic bottom water conditions (lagoon) to pelagic eli and Nicoraella parabudaensis, whereas species of the platform conditions (open sea). Two different vertebrate fossil assemblages gondollellid genera Neogondolella and Paragondolella dominate were recognized in the Xingyi Fauna: the Lower Assemblage (lay- the upper part (Figs. 2a and 3; Sun et al., 2006, 2009, 2014). Due ers 26–41) is dominated by Keichousaurus together with fishes to the lack of Nicoraella kockeli, the basal 21.0 m, which contains Asialepidotus and Habroichthys and the ichthyosaurs are not Nicoraella germanica, are attributed to late Bithynian (Kozur, recorded as yet, while the Upper Assemblage (layers 42–53) is 1989). The first occurrence (FO) of undoubted specimens of Nico- characterized by the presence of the ichthyosaurs Guizhouichthyo- raella kockeli was recorded at meter 21.0 and approximates the saurus and Qianichthyosaurus associated with the oldest species of base of the Pelsonian (middle Anisian) according to Kovács and ‘‘flying” fish Thoracopterus. Thus, concerning fossil component, the Kozur (1980) and Kozur (2003). The FO of Neogondolella constricta Lower Assemblage is more analogous to the slightly older fossil cornuta at meter 71.0 suggests the base of the Illyrian (late Anisian) vertebrate fauna in the Lower Meride of Southern Alps because this conodont event corresponds broadly to the base of the (Stockar et al., 2012), but the occurrence of the ichthyosaurs Guiz- ammonoid Trinodosus Zone in Western Tethys (Kovács et al., 1994; houichthyosaurus and Qianichthyosaurus and the thalattosaur Xin- Muttoni et al., 1998; Meco, 1999). A rich ammonoid bed, contain- pusaurus and Anshunsaurus in the Upper Assemblage displays a ing ‘Schreyerites’ binodosus, occurs at meter 34.7, about 2 m below close affinity to the younger Guanling Fauna (Carnian, Late Trias- the fossil-bearing layers of the Panxian Fauna. ‘Schreyerites’ bino- sic; Jiang et al., 2005). Moreover, Xinpusaurus, Guanlingsaurus and dosus is typical of the latest Pelsonian in the Tethyan Realm Qianichthyosaurus show strong phylogenetic relationship close to (Vörös, 1987; Mietto and Manfrin, 1995; Vörös and Pálfy, 2002), the taxa Nectosaurus, Shonisaurus and Toretocnemus from eastern although its taxonomic assignment at the genus level seems to Panthalassa, respectively (Jiang et al., 2004; Maisch et al., 2008). be problematic (Mietto and Manfrin, 1995; Tatzreiter and Balini, Thus, it is possible that Xingyi Fauna displays a transition of marine 1993). Thus, the upper Guanling Formation ranges from the late reptile faunas from Tethyan affinity to much more pelagic forms. Bithynian to early Illyrian, and the Anisian/Ladinian boundary Southwestern China in the eastern Tethys was open in the south- enters the overlying Yangliujing Formation (Sun et al., 2006). east to Panthalassa through the Nanpanjiang Basin during the late Chen and Wang (2009) recorded a conodont assemblage with Ladinian, earlier than previously thought (, Lehmann Neogondolella trammeri, Neogondolella alpine alpine, Neogondolella et al., 2005). constricta cornuta, and Neogondolella constricta postcornuta from The Xiaowa Formation lithologically comprises condensed the basal Yangliujing Formation. A similar conodont fauna was black fine-grained clastic deposits (bioclastic micrites, siltstones known from the Anisian/Ladinian boundary interval (generally and silty shales) intercalated with thin-bedded or laminated marl- ranging from ammonoid Reitzi Zone to Curionii Zone, late stones and manganiferous mudstones. The basal Xiaowa Forma- Anisian-early Ladinian in age) at the Bagolino section of Northern tion, about 30 m thick, was well exposed at the Xiaowa section Italy (the Global boundary Stratotype Section of the Ladinian (Xinpu, Guanling County), where the Guanling Fauna which is Stage) (Brack et al., 2005) and the Felsöörs section of the Balaton characterized by rich marine reptiles and pelagic crinoids (Fig. 2d). Highland, Hungary (Kovács et al., 1994). The conodont Paragondo- It was first excavated near Xinpu of Guanling County, thereafter at lella inclinata, ranging from early Longobardian (late Ladinian, Mid- Liangshui of Qinglong County (Fig. 1e), and geographically covers dle Triassic) to late Julian (Carnian, Late Triassic) (Kovács, 1983), an area of about 200 km2 (Wang et al., 2008). At the Xiaowa sec- was recorded from the upper Longtou Formation (Yang et al., tion, the fossiliferous layers are a ca. 5.5 m interval of gray thin- 1995) within platform-margin deposits of the Yangtze Platform, a bedded argillaceous limestones, about 4.4 m above the base of lateral equivalent of the Yangliujing Formation. Thus, the Yangliu- the Xiaowa Formation. Since 1999, more than 20 taxa at the genus jing Formation can be biochronologically constrained between 106 Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110

Fig. 3. Selected age-diagnostic conodonts from measured sections, straddling strata from the upper Guanling Formation to the basal Xiaowa Formation, in SW Guizhou and its adjacent area. 1, Nicoraella germanica,90, sample YC6/1.0. 2–4 Nicoraella kockeli 2, 110, sample YC23/8.0; 3, 120, sample YC25/0.0; 4, 170, sample YC15/3.0; 5, Neogondolella constricta cornuta 85, sample YC29/3.0; 6–8 Gladigondolella sp. 6, 54, sample GLZ4/47.3; 7, 45, sample GLZ1/3.9; 8, 63, sample GLZ1/3.86. 9 Budurovignathus sp. 36, sample LPZ5/13.5. 10–13 Paragondolella foliata inclinata 10, 20, sample LPS1/0.0; 11, 36, sample LPZ2/4.0; 12, 30, sample LPZ2/4.0; 13, 50, sample LPZ3/2.4; 14, 15 Paragondolella tadpole 14, 30, sample LPZ5/13.5; 15, 40, sample LPZ6/6.9; 16, 17 Paragondolella polygnathiformis 16, 20, sample LPZ6/6.9; 17, 20, sample LPS7/5.8; 18–22 Paragondolella auriformis 18, 70, sample LPN10/10.0; 19, 45, sample LPN9/3.5; 20, 35, sample LPN9/2.0; 21, 60, sample GLX0/-3.0; 22, 70, sample GLZ7/3.3. Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110 107

Illyrian of late Anisian and Longobardian of late Ladinian. However, (Kovács, 1983; Krystyn, 1983). Paragondolella auriformis is a typi- massive dolomites with the lack of index fossils allows any further cally Tethyan species and first occurs in the Aonoides Zone biochronostratigraphic subdivision of the Yangliujing Formation (Krystyn, 1983). The pelagic conodont association with Paragondo- impossible. lella auriformis, Paragondolella polygnathiformis s.s., Paragondolella The Zhuganpo section, the type-section of the Zhuganpo Forma- tadpole and species of Gladigondolella corresponds to the ammo- tion, outcropping along the 301 highroad between Yongningzhen noid Austriacum Zone (Krystyn, 1983; Chhabra and Kumar, 1984; and Xinpu, Guanling County, Guizhou Province (Fig. 1e), and three Mastandrea, 1995), whereas a similar conodont assemblage lack- of its laterally correlatable sections from Luoping County, Yunnan ing Gladigondolella species was recorded at the basal Xiaowa For- Province (Fig. 1d), were investigated. Similar conodont biostrati- mation of the Xiaowa section, Guanling County. graphic sequences occur in all these sections, allowing a reliable Age-diagnostic ammonoids are discontinuously present in the lateral correlation of the vertical sequence of bio-events Zhuganpo and Xiaowa formations: at the Zhachong section, the (Fig. 2b, c, e). Paragondolella inclinata and Gladigondolella sp. pre- ammonoid Haoceras xingyiensis occurs more than 10 m above the dominate in the lower Zhuganpo Formation (Figs. 2b, c and 3; fossil-bearing interval of the Xingyi Fauna. Haoceras xingyiensis Sun et al., 2005c). There are several morphotypes of Paragondolella was originally erected by Zou et al. (2015) from the interval which inclinata with variations in their blade-height and in the develop- directly overlies the Xingyi Fauna at Nimaigu section, Wusha, Xin- ment of the anterior platform. The relatively primitive Paragondo- gyi, Guizhou Province. The Haoceras xingyiensis Zone is referred in lella inclinata with a low blade and having no free-blade appears at part to the lower Sutherlandi Zone of the North American, middle meter 3.86. The free-bladed forms of Paragondolella inclinata occur Longobardian (late Ladinian, Middle Triassic) in age (Zou et al., at meter 43.0. Paragondolella inclinata evolved from Paragondolella 2015). The Ammonoid genus Trachyceras was recorded at and excelsa during the Early Longobardian in Western Tethys (Kovács above meter 161.0 in the upper Zhuganpo Formation at the Niubu- and Kozur, 1980; Kovács, 1983). The FO of the free-blade forms dai section, however, its first occurrence remains uncertain. Similar of Paragondolella inclinata is hitherto known with ammonoid Dax- simplified ornamentation suggests a lateral correlation with atina in North America (Orchard et al., 2002). The FO of Paragondo- Trachyceras beds of Zou et al. (2015). Species of Trachyceras, with lella polygnathiformis sensu strictu, having geniculation points on complex ornamentation that is comparable to Trachyceras species both platform margins (Orchard et al., 2002), occurs at meter of the second or third Carnian Zon (Aon Zone or Aonoides Zone) 68.6. The alleged Paragondolella polygnathiformis recorded at meter in the Tethyan successions, are recorded from the basal Xiaowa 3.86 (Sun et al., 2005c) was re-investigated and assigned to Formation at Xiaowa and Nimaigu sections of Guizhou (Hao Paragondolella langdaiensis (Yang et al., 2002) due to its slender, et al., 2003; Xu et al., 2003; Zou et al., 2015), and Niubudai and elongate unit, posteriorly protruded keel and far posteriorly Caizitang sections of Yunnan (Li et al., 2013). At the Xiaowa section located pit. Paragondolella polygnathiformis s.s. is characterized by of Guanling County, the basal Xiaowa Formation (Sun et al., 2003; a geniculation point or an abrupt anterior step on both anterior lat- Hao et al., 2003) containing the ammonoids Trachyceras multituber- eral margins and the presence of this feature on only one of the culatum and Austrotrachyceras triadicum associated with the con- anterior margins is typical of the transitional forms between odont Paragondolella auriformis, is assumed comparable to the Paragondolella inclinata and Paragondolella polygnathiformis s.s. Aon Zone-Aonoides Zone. Thus, the Zhuganpo Formation com- from the latest Ladinian (Krystyn, 1983; Orchard et al., 2002; prises the Longobardian (late Ladinian) and the early Julian (early Mietto et al., 2012). Traditionally, the occurrence of Paragondolella Carnian), and the basal Xiaowa Formation covers the late early Car- polygnathiformis s.s. in the west Tethys realm has been considered nian, comparable to the ammonoid Aon Zone-Aonoides Zone. to be coincident with the base of the ammonoid Trachyceras aon Subzone (generally regarded as the first representative of the genus), previously proposed as the base of the Carnian. However, 5. Age constrains and correlations of analogous fossil the range of Paragondolella polygnathiformis s.s. was recorded Lagerstätten below the FAD of Trachyceras aon or Trachyceras (Mosher, 1968; Kozur, 1989; Gallet et al., 1998) and into the Daxatina canadensis With the new integrated biochronological data, age constraints Subzone (Mietto et al., 2012; Orchard et al., 2002). At the GSSP for those marine vertebrate faunas, from the upper Guanling For- Prati di Stuores/Stuores Wiesen, Paragondolella polygnathiformis s. mation to the basal Xiaowa Formation, are defined to the sub- s. was recorded 70 cm above the first occurrence of Daxatina stage and zone level and are generally correlated to analogous canadensis, while at Spiti (India), Paragondolella polygnathiformis faunas from the Besano, San Giorgio Dolomite and Meride Lime- s.s. first occurs in the Upper Ladinian ammonoid Sutherlandi Zone stone formations of Monte San Giorgio (Southern Alps, Switzer- (Krystyn et al., 2004). At the Zhuganpo section, Paragondolella land/Italy) (Fig. 4). The Panxian Fauna, in the upper Guanling polygnathiformis s.s. first occurs in the middle unit of the Zhuganpo Formation (ca. 50 m below the overlying Yangliujing Formation), Formation, extending well below the FAD of Trachyceras and most is attributed to the middle Anisian (Pelsonian) Nicoraella kockeli probably entering the ammonoid Protrachyceras Zone (Wang, conodont Zone, broadly correlated with the ammonoid ‘Schreyer- 1983; Xu et al., 2003; Hao et al., 2003; Sun et al., 2005c), as is ites’ binodosus bed. The tuff layer in the fossil-bearing layers of the case in the Niubudai composite section (Fig. 2c). Wang et al. the Panxian Fauna yielded a U–Pb zircon age of 244.0 ± 1.3 Ma (1998) reported Paragondolella polygnathiformis s.s. 3 m above the (Wang et al., 2014). Thus, the Panxian Fauna is slightly older than Keichousaurus bed near the type locality of the Xingyi Fauna the world-famous Grenzbitumenzone Fauna of the Besano Forma- (Fig. 2e): such an interval can be laterally correlatable to the tion, which is ascribed to the ammonoid Reitzi Zone (late Illyrian, ammonoid Haoceras xingyiensis Zone at Nimaigu section (Wusha Late Anisian, calibrated with GSSPs of the Ladinian; Stockar et al., District, Xingyi City, Guizhou Province) and a Middle Longobardian 2012) with a U–Pb zircon age of 242.0 ± 0.6 Ma (Stockar et al., (late Ladinian) in age is suggested (Zou et al., 2015). Paragondolella 2012). Given the new integrated biochronology in the present tadpole (Fig. 3; Sun et al., 2003, 2005c) and Paragondolella auri- paper the reptile levels below the Xingyi fauna (Benton et al., formis (Fig. 3; Sun et al., 2003) appear at meter 135.1 and meter 2013), which occur in the lower Zhuganbo Formation (i.e., lami- 157.3, respectively. These two species are undisputedly Early Car- nated dolomitic limestones), is rectified to earliest Longobardian nian (Late Triassic) conodont genera. Paragondolella tadpole occurs (late Ladinian, Middle Triassic), broadly correlated to the con- in the ammonoid Nanseni Zone in North America (Orchard and odont Paragondolella constricta Zone. Such an unnamed vertebrate Tozer, 1997) and in the basal Aonoides Zone in West Tethys assemblage is assumed younger than that of the Lower Meride 108 Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110

Fig. 4. Simplified stratigraphic logs of Middle and Upper Triassic from both Guizhou Province (South China) and Monte San Giorgio area (South Alps, Switzerland/Italy) which yield exceptionally well-preserved vertebrate fossil Lagerstättes, and their possible correlations.

Limestone and thus vertebrate assemblages of early Ladinian Kalkschieferzone fauna, which is now assigned to early late Ladi- (Fassanian) in age are lacking in South China. The age of the Xin- nian with a U–Pb zircon age of 239.51 ± 0.15 Ma (Stockar et al., gyi Fauna, present in the middle Zhuganbo Formation (i.e., bio- 2012). The conodont Paragondolella auriformis and ammonoid clastic limestones with chert concretions), should be middle Trachyceras multituberculatum and Austrotrachyceras triadicum Longobardian (Late Ladinian, Middle Triassic), in that the con- from the basal Xiaowa Formation ascertain that the Guanling odont Paragondolella inclinata with free-blade and the ammonoid Fauna is younger than the first Carnian ammonoid zone, which Haoceras xingyiensis are recorded from the overlying strata, of suggested to correlate it with the Aon-Aonoides zones of the which the latter is referred in part to the lower Sutherlandi Zone Tethys realm (Hao et al., 2003; Li et al., 2013; Zou et al., 2015). of the North American scale (Zou et al., 2015). By contrast, Cassin Consequently, a time-spatial sequence of the Middle and Upper beds lies in Protrachyceras gredleri/Protrachyceras archelaus transi- Triassic vertebrate faunas of Western Guizhou (South China) tion Zone and Lower Kalkschieferzone Protrachyceras lies in and Monte San Giorgio (Southern Alps, Switzerland/Italy) is pre- archelaus Zone (Stockar et al., 2012). Thus, the Xingyi Fauan is liminarily illustrated in Fig. 2 pending much more integrated broadly coeval or slightly younger to that of the Lower bio-chronostratigraphic and geochronologic data. Z. Sun et al. / Journal of Asian Earth Sciences 118 (2016) 101–110 109

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