Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Contents lists available at ScienceDirect

Palaeogeography, Palaeoclimatology, Palaeoecology

journal homepage: www.elsevier.com/locate/palaeo

Palaeovegetation and palaeoclimate changes across the Triassic–Jurassic T transition in the Sichuan Basin, China ⁎ ⁎ Liqin Lia,b, Yongdong Wanga, , Wolfram M. Kürschnerc, Micha Ruhld, Vivi Vajdab, a State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, and Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, East Beijing Road 39, Nanjing 210008, China b Department of Palaeobiology, Swedish Museum of Natural History, Frescativägen 40, Stockholm 10405, Sweden c Department of Geosciences, University of Oslo, P.O.Box 1047, Blindern, 0316 Oslo, Norway d Department of Geology & Irish Centre for Research in Applied Geosciences (iCRAG), Trinity College Dublin, The University of Dublin, College Green, Dublin 2, Ireland

ARTICLE INFO ABSTRACT

Keywords: The Triassic–Jurassic transition interval is marked by enhanced biotic turnover rates in both marine and ter- T–J transition restrial realms. However, limited data from Asia hampers the understanding of global ecosystem response to the Terrestrial response end-Triassic mass extinction event. Here, we present significant vegetation and climate changes across the Palynology Triassic–Jurassic transition in the eastern Tethys region (southern China). A detailed palynological study was Eastern Tethys performed from the Qilixia section of the Sichuan Basin, China, spanning the Upper Triassic (Norian–Rhaetian) Xujiahe Formation (Xujiahe Formation) to the Lower Jurassic (Hettangian–Sinemurian) (lower Zhenzhuchong Formation). Five Zhenzhuchong Formation palynological assemblages reveal significant ecosystem fluctuations across the Triassic–Jurassic transition. Our study indicates a lowland fern flora and a warm and humid climate in the Late Triassic (Norian to Rhaetian), interrupted by a cooler interval at the Norian–Rhaetian transition, and followed by a mixed mid-storey forest under cooler and drier condition in the latest Rhaetian. This is followed by a fern-dominated lowland vegetation and a warmer and drier climate during the Triassic–Jurassic transition, and a flora with abundant cheirolepid conifers in the Hettangian–Sinemurian. These long term changes in vegetation and inferred climatic conditions are comparable with records from the western Tethyan realm, and possibly reflect global terrestrial environ- mental changes associated with Central Atlantic Magmatic Province volcanism during the Triassic–Jurassic transition.

1. Introduction across the T–J transition (Lucas and Tanner, 2015; Barbacka et al., 2017), while others present major turnovers (McElwain et al., 2007). The Triassic–Jurassic (T–J) transition interval is characterized by a Macroflora records from East Greenland and southern Sweden showa major mass extinction, one of the five largest Phanerozoic extinctions in dramatic plant species-level decline of > 80%, with the Late Triassic Earth history (Sepkoski Jr., 1996; McGhee Jr. et al., 2013). Major biotic Lepidopteris flora being replaced by the Early Jurassic Thaumatopteris turnover occurred in both marine and terrestrial realms (McElwain flora (Harris, 1937; Lundblad, 1959; McElwain et al., 1999, 2007; et al., 1999, 2007; Pálfy et al., 2000; Hallam, 2002; Hesselbo et al., Kustatscher et al., 2018). On the Southern Hemisphere record, the 2002; Olsen et al., 2002; van de Schootbrugge et al., 2009; Lindström Triassic seed-fern dominated flora was replaced by a more complex et al., 2012). The emplacement of the Central Atlantic Magmatic Pro- flora with conifers (Cheirolepids), Bennettitales, and new seed-ferns vince (CAMP) volcanism, with emissions of CO2, CH4, SO2 and Hg, has during the Early Jurassic (Turner et al., 2009). been considered as a main trigger for the severe environmental changes The significant palynofloral changes reported for the T–J transition leading to the end-Triassic biotic crisis (Götz et al., 2009; Deenen et al., across both hemispheres (Larsson, 2009; Turner et al., 2009; Vajda and 2010; Schoene et al., 2010; Ruhl et al., 2010, 2011; Greene et al., 2012; Bercovici, 2014; Lindström, 2016) may be globally correlated, and Percival et al., 2017; Panfili et al., 2019; Lindström et al., 2019). possibly represent a global vegetation response to climatic and en- The response of the terrestrial vegetation to this event is debated vironmental changes at that time. In European successions, Rhaetian with some authors suggesting that no abrupt floral extinction took place palynological assemblages are characterized by the abundance of the

⁎ Corresponding authors. E-mail addresses: [email protected] (L. Li), [email protected] (Y. Wang), [email protected] (W.M. Kürschner), [email protected] (M. Ruhl), [email protected] (V. Vajda). https://doi.org/10.1016/j.palaeo.2020.109891 Received 18 March 2020; Received in revised form 28 June 2020; Accepted 29 June 2020 Available online 05 July 2020 0031-0182/ © 2020 Elsevier B.V. All rights reserved. L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 1. Location of the Qilixia Section at Xuanhan, northeastern Sichuan Basin, and the geological map of the study area. A) Latest Triassic palaeomap indicating the study area (after Li et al., 2017); B) Geographical range of the Sichuan Basin; C) Geological map of the studied section and adjacent area (after Wang et al., 2010). gymnosperm pollen Ricciisporites tuberculatus, followed by a fern spore preceding the end-Triassic mass extinction event in the Sichuan Basin, spike across the T–J transition, and high abundances of Classopollis SW China (Li et al., 2016, 2018). (Cheirolepidiaceae) in the Lower Jurassic successions (Götz et al., 2009; In the northeastern Sichuan Basin, the Upper Triassic Xujiahe and Larsson, 2009; van de Schootbrugge et al., 2009; Bonis et al., 2009, the Lower Jurassic Zhenzhuchong formations are well exposed and 2010; Pieńkowski et al., 2012; Vajda et al., 2013). A fern spike was also continuously developed, yielding diverse fossil plant remains (Ye et al., identified within the Triassic–Jurassic sedimentary succession inthe 1986; Wang et al., 2010). The Upper Triassic Dictyophyllum–Cla- Newark Basin, North America, followed by the dominance of Classo- thropteris macroflora of the Xujiahe Formation is replaced by theLower pollis meyeriana in the Lower Jurassic successions (Olsen et al., 2002; Jurassic Ptilophyllum–Coniopteris flora in the Zhenzhuchong Formation Whiteside et al., 2007). Rhaetian palynofloras from the Southern (Ye et al., 1986), and the Upper Triassic Dictyophyllidites–Kyrtomispor- Hemisphere (New Zealand) are dominated by lycophyte spores and is–Ovalipollis–Ricciisporites palynological assemblage is replaced by the corystosperm pollen, followed by a high abundance of bryophyte spores Lower Jurassic Dictyophyllidites–Classopollis–Cycadopites assemblage (Lu in the uppermost Rhaetian, elevated osmundaceous fern spore abun- and Wang, 1987; Wang et al., 2010). Previous palynological and mac- dance in the Hettangian, and abundant Classopollis occurrence in the rofloral studies dated the Xujiahe Formation as Norian to Rhaetian in Sinemurian (Akikuni et al., 2010; de Jersey and McKellar, 2013). Si- age (Ye et al., 1986; Lu and Wang, 1987; Wang et al., 2010; Li et al., milar stratigraphical abundance patterns were observed in eastern 2016, 2018). The Sulcocythere–Oncocythere–Darwinulla ostracod as- Australian records across the T–J transition, with abundant fern and semblage and the Burmesia–Myophora (Costatoria) Yunnanophor- bryophyte spores in the uppermost Rhaetian, and common cheir- us–Pemophorus–Weiyuanella bivalve assemblages of the Xujiahe For- olepidiacean pollen occurrences in the Hettangian and Sinemurian (de mation also indicate a Norian to Rhaetian age (Wei, 1982; Gou, 1998; Jersey and McKellar, 2013). Thus, across both hemispheres, vegetation Wang et al., 2010). Macrofloral and palynological assemblages (Dic- turnover was accompanied by the dominance of ferns and fern allies tyophyllidites–Classopollis–Cyathidites–Cycadopites), and bivalves (Mar- during the T–J transition, followed by a widespread proliferation of garitifera, Qiyangia, Pseudocardinia) in the Zhenzhuchong Formation Cheirolepidiaceae conifers in the aftermath of the end-Triassic biotic suggest an Early Jurassic age (Ye et al., 1986; Wang et al., 2010). A crisis. Recent studies suggested an increased abundance of aberrant recent magnetostratigraphical study suggests that the Xujiahe Forma- spores and pollen during the end-Triassic mass extinction, indicating tion spans from 207.2 Ma to 201.3 Ma at the Qilixia section, and the genetic disruption of land plants because of CAMP-related extreme Triassic–Jurassic boundary was placed between the Xujiahe and environmental stress (Kürschner et al., 2013; Lindström et al., 2019). Zhenzhuchong formations (Li et al., 2017). This refined framework Much emphasis has been placed on the European and North allows further studies on changes in vegetation patterns and continental American Triassic–Jurassic terrestrial successions. However, evidence ecosystem conditions across the T–J transition in the East Asia region. from the eastern Tethys region (Asia) is still sparse, with only sys- In this study, we present detailed Upper Triassic to Lower Jurassic tematic studies reporting on e.g. palaeobotany, palynology, bivalve palynological data and a palynostratigraphical framework from the stratigraphy and palaeoclimate in the Junggar Basin, NW China (Lu and Qilixia section in Xuanhan County, northeastern Sichuan Basin, China, Deng, 2005, 2009; Deng et al., 2010; Sun et al., 2010; Sha et al., 2011, and further interpret the ecosystem changes during this interval of 2015); palynostratigraphy in the Tarim Basin, NW China (Peng et al., global biological crisis, providing new evidence from the eastern Tethys 2018); Late Triassic terrestrial palynology and ecosystem variation realm for investigating the terrestrial environmental background of the

2 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Triassic–Jurassic transition. At least 250 sporomorphs were, where possible, counted in each sample, using an Olympus BX41 light microscope. Palynomorph images 2. Geological background and stratigraphy were collected on a Zeiss Imager, Z2 microscope and an AxioCam HRc imaging system. Percentages of spore and pollen taxa were calculated During the Late Triassic to Early Jurassic, the Sichuan Basin was based on the sum of total sporomorphs. Palynological assemblages were located at the western margin of the South China block, at low–middle identified by stratigraphically-constrained cluster analysis (CONISS), latitudes, in the eastern Tethyan region (Li et al., 2017; Pole et al., using the Tilia software (Grimm, 2004). Observed spores and pollen 2018; Fig. 1A). The basin was formed as a result of early Paleozoic were assigned to botanical groups to aid interpretation of the vegeta- craton depression and late Paleozoic–Middle Triassic craton rifting tion history, based on published in situ spore and pollen affinity studies (Wang et al., 2010). The basin is flanked to the west by the Longmen (e.g. Van Konijnenburg-Van Cittert, 1971, 1978, 1993, 2002; Litwin, Shan orogenic belt (located along the eastern border of the Tibetan 1985; Balme, 1995; Wang, 1999, 2002; Wang and Mei, 1999; Wang Plateau), to the southeast by the Xuefengshan intercontinental tectonic et al., 2015). deformation, to the north by the Micangshan and Dabashan uplift belts, In order to constrain Late Triassic–Early Jurassic palaeoclimate and to the southwest by the Emei-Liangshan fault-fold belt (Fig. 1B; variations within the Sichuan Basin, two different methods were ap- Wang et al., 2010). plied: 1) the Sporomorph EcoGroup (SEG) model established by Abbink The Precambrian to Middle Triassic marine strata are well devel- et al. (2004), which is based on the quantitative compositions of dif- oped in the adjacent mountain areas, while the Upper Triassic to Lower ferent ecological groups; and 2) the Principal Components Analysis Jurassic terrestrial lacustrine–fluvial to coal-swamp sediments are (PCA) within CANOCO (Lepš and Šmilauer, 2003), which transforms mainly distributed in the eastern and northeastern margin of the basin relative abundances of sporomorphs into environmental variables. (Wang et al., 2010; Li et al., 2018). This change from marine to con- tinental environments is due to the collision of the South China block 4. Results with North China and other Asian plates during the Middle–Late Triassic (Wang et al., 2010). The overlying Jurassic and Cretaceous 4.1. Palynological assemblages terrestrial red beds are preserved in the central and western areas of the basin (Wang et al., 2010). Thirty of the studied 131 samples were productive, containing di- The Qilixia section (31°11′49″N, 107°44′37″E) is the best-exposed verse and well-preserved palynomorphs (Fig. 2). A total of 145 species succession of Upper Triassic–Lower Jurassic sequences in the north- in 66 genera of spore and pollen were identified in the samples from the eastern Sichuan Basin. It is located at the Ecengshan Anticline, in the Xujiahe and Zhenzhuchong formations (Figs. 2–7; Appendix A). Trilete core of which is the Middle Triassic Leikoupo Formation, while the fern spores (10–80%), bisaccate conifer pollen (4–62%) and mono- Upper Triassic Xujiahe Formation and the Lower–Upper Jurassic strata sulcate pollen (1–38%) are the dominant elements through the entire are exposed at the eastern and western flanks of the anticline (Fig. 1C). section (Fig. 2; Appendix B). Five assemblages were distinguished based At the Qilixia Section, the Middle Triassic marine Leikoupo Formation on the palynomorph taxonomic composition, combined with abun- is unconformably overlain by the non-marine Upper Triassic Xujiahe dance variations, and CONISS results and visual inspection of the data Formation, which in turn is conformably overlain by the non-marine (Fig. 2). In ascending stratigraphic order, the assemblage features are Lower Jurassic Zhenzhuchong Formation (Fig. 2). The Xujiahe Forma- summarized as: tion is about 500 m thick and comprises sandstones, siltstones, mud- stones and coal beds, yielding diverse and rich plant fossils, and is di- 4.1.1. Palynological Assemblage 1 (PA1) vided into seven lithological members (Wang et al., 2010; Fig. 2). Stratigraphic interval: Member I of the Xujiahe Formation (Samples Members I, III, V and VII mainly comprise fine-grained sandstones, QLX-1 to QLX-3; Fig. 2; Appendix B). mudstones and coal, hosting abundant plant fossils, representing flood Characteristics: A dominance of trilete spores (57–62%) over gym- plain-lacustrine deposits; Members II, IV and VI represent fluvial-deltaic nosperm pollen grains (38–42%) (Fig. 2; Appendix B). Dictyophyllidites deposits, with the lithology largely characterized by medium- to coarse- and Concavisporites are the most dominant fern spores (14–16%) (Fig. 2; grained sandstones (Wang et al., 2010; Li et al., 2016; Fig. 2). The Appendix B). Bisaccate conifer pollen (13–24%) and monosulcate Zhenzhuchong Formation is about 174 m thick and lithologically pollen related to cycadophytes/ginkgophytes (10–15%) dominate the composed of a thin basal bed of conglomerate and siliceous sandstones pollen component (Fig. 2; Appendix B). PA1 furthermore comprises followed by feldspathic sandstones, siltstones, and several thin coal abundant Concavisporites (C. toralis, C. bohemiensis, C. kermanense), beds in the lower part (Fig. 2). Recently reported hummocky/swaley Dictyophyllidites (D. harrisii, D. charicis), and Cycadopites, common cross-bedding, heterolithic bedding and the presence of the trace fossil Chasmatosporites, low abundance of Annulispora, Ovalipollis and Quad- Skolithos within the sediments of the Xujiahe and Zhenzhuchong for- raeculina, presence of Kyrtomisporis, Lunzisporites and Aratrisporites mations suggest a wave-dominated coastal plain environment with (Fig. 3). frequent storm activities (Pole et al., 2018). Stratigraphic significance: In the eastern Tethys region, another well-exposed terrestrial Triassic–Jurassic sequence has been system- 3. Materials and methods atically studied in the Junggar Basin, NW China, for detailed palyno- logical and palaeobotanical stratigraphy (e.g. Lu and Deng, 2005, 2009; A total of 131 rock samples were collected from the Xujiahe Huang, 2006; Deng et al., 2010; Sun et al., 2010; Sha et al., 2011). The Formation and lower part of the Zhenzhuchong Formation at the Qilixia combined Junggar and Sichuan basins records form an integrated section in the northeastern Sichuan Basin (Fig. 2). Samples were pre- stratigraphic reference framework for the eastern Tethys region. Paly- pared in the palynological laboratory of the Nanjing Institute of nological Assemblage 1 can be correlated with the Norian palynoflora Geology and Palaeontology, Chinese Academy of Sciences (NIGPAS). of the Huangshanjie Formation in the Junggar Basin, NW China, with About 30 g of each sample was crushed into small fragments, and many common elements, including Dictyophyllidites, Concavisporites, subsequently treated twice alternately with cold HCl (30%) and cold HF Cyclogranisporites, Osmundacidites, Apiculatisporis, Baculatisporites, Ly- (38%), to remove the carbonate and silicate minerals, respectively. The copodiacidites, Camarozonosporites, Annulispora, Asseretospora, Kraeuse- residue was washed with water until a pH of 7 was reached, and sieved lisporites, Aratrisporites, Taeniaesporites, Alisporites, Paleoconiferus, Chas- through a 10 μm mesh. Slides were mounted using glycerin jelly and matosporites, Cycadopites and Ovalipollis (Qu and Wang, 1990; Ashraf sealed with paraffin wax. All the permanent slides are housed at et al., 2001). NIGPAS. Age: The above taxa, together with the absence of Classopollis,

3 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 2. Upper Triassic–Lower Jurassic lithological column and palynostratigraphic diagram of the Qilixia section. Geological age frame is after Li et al. (2017). indicate a Late Triassic, most possibly Norian age. Ovalipollis and Taeniaesporites (Lu and Deng, 2005; Huang, 2006; Deng et al., 2010)(Fig. 2). However, spores Concavisporites, Dictyophyllidites, 4.1.2. Palynological Assemblage 2 (PA2) Cyclogranisporites, Granulatisporites and Cyathidites are more abundant Stratigraphic interval: Member II ~ V of the Xujiahe Formation in the Xujiahe Formation than the Haojiagou Formation, while Ara- (Samples XHQL-37 to QLX-12; Fig. 2; Appendix B). trisporites and Alisporites are less common (Lu and Deng, 2005; Deng Characteristics: A slightly lower average abundance of spores et al., 2010)(Fig. 2). Members II ~ V of the Xujiahe Formation at the (35–77%), followed by gymnosperm pollen grains (average ~ 44%) Qilixia section and the lower Haojiagou Formation of the Junggar (Fig. 2; Appendix B). Dictyophyllidites and Concavisporites are the Basin, also share the occurrence of many macroplant fossil taxa, e.g. dominant spore genera (average ~ 11%), bisaccate conifer pollen Neocalamites, Dictyophyllum, Cladophlebis kaoiana, Podozamites, Pityo- (average ~ 19%) and cycadophytes/ginkgophytes monosulcate pollen phyllum and Cycadocarpidium (Deng et al., 2010; Table 1). The im- (average ~ 20%) are more abundant compared to PA1 (Figs. 2 and 4; portant taxa Dictyophyllum and Clathropteris within the Xujiahe For- Appendix B). Observed miospore genera, which do not occur in the mation of the Sichuan Basin is, however, less common in the Haojiagou younger palynological zones, include Sphagnumsporites, Biretisporites, Formation (Junggar Basin), while Danaeopsis, typical for the Junggar Undulatisporites, Cibotiumspora, Triancoraesporites, Leptolepidites, Lopho- Basin is absent from coeval strata at the Qilixia section (Ye et al., 1986; triletes, Apiculatisporis, Conbaculatisporites, Neoraistrickia, Camar- Deng et al., 2010; Sun et al., 2010; Wang et al., 2010)(Table 1). These ozonosporites, Canalizonospora, Kyrtomisporis, Kraeuselisporites, Trizo- differences divide the floras into two separate floristic regions, theso nites, Marattisporites, Laevigatosporites, Aratrisporites, Cordaitina, called South China Floristic Region represented by the Late Triassic Chordasporites, Ovalipollis and Verrumonocolpites (Fig. 2). “Dictyophyllum–Clathropteris flora” (the typical Xujiahe Flora in the Si- Stratigraphic significance: Palynological Assemblage 2 can be cor- chuan Basin) and the North China Floristic Region represented by the related with the palynological assemblage from the lower Haojiagou Late Triassic “Danaeoposis–Bernoulia flora (the typical Haojiagou flora Formation in the Junggar Basin, both assemblages show common oc- in the Junggar Basin) (Sun et al., 1995; Deng et al., 2010; Wang et al., currence of Dictyophyllidites, Concavisporites, Annulispora, Alisporites, 2010). Cycadopites, Chasmatosporites and Quadraeculina; presence of Age: The abundance of Dictyophyllidites (D. harrisii, D. charicis), the Lycopodiacidites, Neoraistrickia, Kraeuselisporites, Aratrisporites, moderately abundant Cycadopites and Concavisporites (C. toralis, C.

4 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 3. Representative taxa of the Palynological Assemblage 1 (PA1) from the Xujiahe Formation in the Qilixia section. A) Sphagnumsporites clavus (Balme 1957) Huang, 2000, sample: QLX-1(1); B) Toroisporis minoris (Nakoman 1966) Sun et He 1980, QLX-1(3); C–D) Dictyophyllidites harrisii Couper 1958, C. QLX-1(1), D. QLX-1(4); E) Concavisporites toralis (Leschik 1955) Nilsson 1958, H. QLX-1(3); F) Dictyophyllidites charicis Zhang 1984, QLX-1(1); G) Granulatisporites triconvexus Staplin 1960, QLX-1(4); H) Granulatisporites granulatus Ibrahim 1933, QLX-2(1); I) Acanthotriletes microspinosus (Ibrahim 1933) Potonié et Kremp 1955, QLX-1(1); J) Osmundacidites granulata (Maljavkina 1960) Zhou 1981, QLX-2(1); K) Lunzisporites lunzensis Bharadwaj et Singh 1964, QLX-1(1); L, O) Acanthotriletes aculeatus (Verbitzkaya 1962) Zhang 1965, L. QLX-1(4), O. QLX-1(1); M) Osmundacidites alpinus Klaus 1960, QLX-1(1); N, S, V) Cycadopites parvus (Bolkhovitina 1953) Pocock 1970, N. QLX-1(3), S. QLX-1(1), V. QLX-1(3); P) Apiculatisporis spiniger (Leschik 1955) Qu 1980, QLX-1(1); Q) Kyrtomisporis laevigatus Mädler 1964, QLX-1(3); R) Annulispora folliculosa (Rogalska 1954) de Jersey 1959, QLX-1(3); T) Araucariacites australis Cookson 1947, QLX-1(3); U) Platysaccus queenslandi de Jersey 1962, QLX-1(1); W) Piceites enodis Bolkhovitina 1956, QLX-2(1). bohemiensis, C. kermanense), the low abundance of Asseretospora, PA2. This age assignment is consistent with magnetostratigraphical age Annulispora, Quadraeculina and Lunzisporites, the presence of Ovalipollis interpretations, which suggest the Norian–Rhaetian boundary to be and the absence of Classopollis, combining the palynological and mac- located within the Member II of the Xujiahe Formation (Li et al., 2017; rofloral correlation with the lower Haojiagou Formation of the Junggar Fig. 2). Basin, suggest a Late Triassic (possibly late Norian–Rhaetian) age for

5 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 4. Representative taxa of the Palynological Assemblage 2 (PA2) from the Xujiahe Formation in the Qilixia section. A) Leiotriletes adnatus (Kosanke 1950) Potonié et Kremp 1955, QLX-11(1); B) Toroisporis minoris (Nakoman 1966) Sun et He 1980, QLX-7(7); C, E) Dictyophyllidites mortoni (de Jersey 1959) Playford et Dettmann 1965, C. QLX-7(7), E. QLX-7(7); D) Concavisporites toralis (Leschik 1955) Nilsson 1958, XHQL-44(1); F) Lophotriletes microsaetosus (Loose 1932) Potonié et Kremp 1955, QLX-7(7); G) Cyclogranisporites arenosus Mädler 1964, QLX-8(2); H) Osmundacidites wellmanii Couper 1953, QLX- 9(2); I) Planisporites dilucidus McGregor 1960, QLX-12(2); J) Angiopteridaspora denticulata Chang 1965, QLX-9(2); K) Apiculatisporis clematisi de Jersey 1968, QLX- 10(6); L) Anapiculatisporites spiniger (Leschik 1955) Reinhardt 1962, L. QLX-11(1); M) Conbaculatisporites pauculus Bai et Lu 1983, QLX-10(6); N) Neoraistrickia taylorii Playford et Dettmann 1965, XHQL-38(4); O) Neoraistrickia gracilis Shang 1981, QLX-8(2); P) Lycopodiacidites rudis (Leschik 1955) Li et Shang 1980, QLX-9(2); Q) Annulispora folliculosa (Rogalska 1954) de Jersey 1959, XHQL-40(1); R) Quadraeculina anellaeformis Maljavkina 1949, QLX-7(7); S) Annulispora minima Zhang 1990, XHQL-41(1); T) Asseretospora gyrata (Playford et Dettmann 1965) Schuurman 1977, QLX-8(2); U) Asseretospora parva (Li et Shang 1980) Pu et Wu 1985, QLX-8(2); V) Chasmatosporites minor Nilsson 1958, QLX-7(7); W) Chasmatosporites apertus (Rogalska 1954) Nilsson 1958, QLX-7(7); X, Z) Cycadopites follicularis Wilson et Webster 1946, QLX-9(2); Y) Cycadopites reticulata (Nilsson 1958) Arjang 1975, X. QLX-7(7), Z. XHQL-40(2); AA) Cycadopites parvus (Bolkhovitina 1953) Pocock 1970, XHQL- 38(5); BB) Vitreisporites pallidus (Reissinger 1950) Nilsson 1958, XHQL-40(2).

4.1.3. Palynological Assemblage 3 (PA3) Cheirolepid Classopollis pollen first appear in this zone (Figs. 2 and 5; Stratigraphic interval: Member VII of the Xujiahe Formation Appendix B). Among the spores, the Dicksoniaceae/Cyatheaceae re- (Samples XHQL-89 to XHQL-92; Fig. 2; Appendix B). lated Cyathidites spore is the dominant type (Fig. 2, Appendix B). The Characteristics: Predominance of gymnosperm pollen grains observed Acanthotriletes, Converrucosisporites, Annulispora, In- (average ~ 79%) and a lower relative abundance of spores aperturopollenites and Protopicea spores and pollen are absent from (average ~ 21%) (Fig. 2; Appendix B). The pollen assemblage is younger palynological zones (Fig. 2). dominated by a high abundance of bisaccate conifer pollen Stratigraphic significance: Palynological Assemblage 3 can be (average ~ 33%) and monosulcate pollen (average ~ 31%), compared with the palynological assemblage of the upper Haojiagou

6 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 5. Representative taxa of Palynological Assemblage 3 (PA3) of the Xujiahe Formation in the Qilixia section. A) Monosulcites enormis Jain 1968, XHQL-89(3); B) Monosulcites fusiformis (Nilsson 1958) Lei 1981, XHQL-92(4); C–D) Quadraeculina minor (Pocock 1970) Xu et Zhang 1980, C. XHQL-92(3), D. XHQL-91(1); E) Pinuspollenites divulgatus (Bolkhovitina 1956) Qu 1980, XHQL-89(3); F) Quadraeculina anellaeformis Maljavkina 1949, XHQL-89(1); G, J) Alisporites parvus de Jersey 1962, G. XHQL-91(1), J. XHQL-89(5); H) Pinuspollenites alatipollenites (Rouse 1959) Liu 1982, XHQL-91(1); I) Pseudopinus pectinella (Maljavkina 1949) Bolkhovitina 1956, XHQL-92(2); K) Protopodocarpus sp., XHQL-91(1); L) Classopollis annulatus (Verbitzkaja 1962) Li 1974, XHQL-92(3).

Formation in the Junggar Basin, both with abundance of Alisporites, Aratrisporites in the Member VII of the Xujiahe Formation (Sichuan Quadraeculina, Cycadopites and Chasmatosporites; the common occur- Basin). The macroflora in Member VII of the Xujiahe Formation rence of Cyathidites; and the presence of Annulispora, Asseretospora, (Table 1) resembles the one in the upper Haojiagou Formation of the Lycopodiacidites, Cerebropollenites and Classopollis (Lu and Deng, 2005; Junggar Basin, with common taxa including: Neocalamites, Clathropteris, Huang, 2006; Deng et al., 2010; Sha et al., 2011). The palynological Cladophlebis, Podozamites, Pityophyllum and Cycadocarpidium (Ye et al., assemblages between the two basins differ, with the higher abundance 1986; Wang et al., 2010; Deng et al., 2010). of Dictyophyllidites and Concavisporites, and lower content of Age: The abundance of Cycadopites, Cyathidites, Chasmatosporites,

7 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 6. Representative taxa of the Palynological Assemblage 4 (PA4) from the Zhenzhuchong Formation in the Qilixia section. A) Dictyophyllidites charicis Zhang 1984, XHQL-101(4); B) Dictyophyllidites harrisii Couper 1958, XHQL-94(5); C) Concavisporites toralis (Leschik 1955) Nilsson 1958, XHQL-99(1); D–F) Cyathidites minor Couper 1953, D. XHQL-104(1), E-F. XHQL-99(1); G) Cyathidites mesozoicus (Thiergart 1949) Potonié 1955, XHQL-101(4); H) Pinuspollenites minutus (Zaklinskaja 1957) Sung et Zheng 1978, XHQL-99(1); I) Pinuspollenites alatipollenites (Rouse 1959) Liu 1982, XHQL-95(2); J) Pinuspollenites divulgatus (Bolkhovitina 1956) Qu 1980, XHQL-103(2); K, M) Alisporites bilateralis Rouse 1959, K. XHQL-94(2), M. XHQL-101(4); L) Classopollis annulatus (Verbitzkaja 1962) Li 1974, XHQL-99(1); N) Alisporites parvus de Jersey 1962, XHQL-102(1); O) Cycadopites reticulata (Nilsson 1958) Arjang 1975, XHQL-103(2). and Quadraeculina, the lower abundance of Dictyophyllidites and the common occurrence of Dictyophyllidites and Concavisporites, a de- Concavisporites, the appearance of Classopollis, and stratigraphic corre- creased content of Chasmatosporites and Quadraeculina, and the dis- lation to the upper Haojiagou Formation of the Junggar Basin, are in- appearance of the Triassic taxa Kraeuselisporites (Lu and Deng, 2005, dicative of a latest Triassic (late Rhaetian) age for PA3. 2009; Deng et al., 2010; Sha et al., 2011)(Fig. 2; Appendix B). The main differences between the two assemblages from the base Zhenzhuchong Formation and the lower Badaowan Formation, is that the spore com- 4.1.4. Palynological Assemblage 4 (PA4) ponent of the former is largely dominated by Cyathidites, while the Stratigraphic horizon: Base of the Zhenzhuchong Formation latter is instead dominated by Asserotospora and Densoisporites (Lu and (Sample No: XHQL-94 ~ XHQL-104; Fig. 2; Appendix B). Deng, 2005, 2009; Deng et al., 2010)(Fig. 2). With regard to the plant Characteristics: Low diversity in spores and pollen, both at a genera fossil record, the successions in both basins witness the appearance of and species level; a high dominance of spores (average ~ 52%, up to Todites princeps (Deng et al., 2010; Table 1). ~79%), with a highly elevated abundance of Cyathidites Age: The strong dominance of Cyathidites, the common occurrence (average ~ 39%), abundant bisaccate conifer pollen (average ~ 36%), of Classopollis, Dictyophyllidites and Concavisporites, the low abundance the common occurrence of Classopollis (average ~ 6%), and less of Quadraeculina, presence of Chasmatosporites and appearance of the abundant monosulcate pollen (average ~ 5%) (Figs. 2 and 6, Appendix plant macrofossils Todites princeps, support a Triassic–Jurassic transi- B). Anapiculatisporites, Osmundacidites, Lycopodiacidites, Klukisporites, tional age. Protopodocarpus, Podocarpidites, and Protoconiferus occur in PA4, but disappear in subsequent palynological zones in the studied succession (Fig. 2). 4.1.5. Palynological Assemblage 5 (PA5) Stratigraphic significance: Palynological Assemblage 4 can be cor- Stratigraphic interval: Lower part of the Zhenzhuchong Formation related with sporopollen assemblages in the lower Badaowan (Samples XHQL-115 to XHQL-128; Fig. 2; Appendix B). Formation of the Junggar Basin. Both assemblages are dominated by a Characteristics: Dominance of Cyathidites (average: ~39%) and a few genera of fern spores, with an increased abundance of Cyathidites, significant increase in Classopollis (average: ~23%), followed by

8 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 7. Representative taxa of the Palynological Assemblage 5 (PA5) of the Zhenzhuchong Formation in the Qilixia section. A) Dictyophyllidites harrisii Couper 1958, XHQL-125(3); B–C) Cyathidites mesozoicus (Thiergart 1949) Potonié 1955, B. XHQL-115(1), C. XHQL-115(5); D) Cyathidites minor Couper 1953, XHQL-115(4); E) Cyathidites australis Couper 1953, XHQL-127(2); F) Pinuspollenites alatipollenites (Rouse 1959) Liu 1982, XHQL-102(1); G) Podocarpidites minisculus Singh 1964, XHQL-115(1); H) Alisporites parvus de Jersey 1962, XHQL-102(1); I–J) Cycadopites follicularis Wilson et Webster 1946, I. XHQL- 125(3), J. XHQL-125(3); K) Cycadopites deterius (Balme 1957) Pocock 1970, XHQL-125(3); L) Cycadopites parvus (Bolkhovitina 1953) Pocock 1970, XHQL-122(1); M–N) Classopollis annulatus (Verbitzkaja 1962) Li 1974, XHQL-127(1); O–eS) Classopollis minor Pocock et Jansonius 1961, O-R. XHQL-125(3), S. XHQL-125(4).

monosulcate pollen grains (average: ~20%) and bisaccate conifer 4.2. Palaeovegetation reconstruction pollen (average: ~11%) (Figs. 2 and 7, Appendix B). Stratigraphic significance: Palynological Assemblage 5 shows a For the reconstruction of the vegetation aspect across the large similarity with those from the middle to upper Badaowan Triassic–Jurassic transition in the Sichuan Basin, palynological data Formation of the Junggar Basin, with the dominance of Cyathidites have been interpreted relative to the parent-plant record, following the among spores, the common occurrence of Cycadopites, an increased botanical affinity of the principal dispersed spore and pollen genera abundance of Classopollis and a lower relative abundance of (Table 2), this is in combination with the coeval macrofloral fossil re- Dictyophyllidites and Concavisporites spores compared with the pre- cord (Table 1). Palynological assemblages are interpreted to reflect the ceding assemblages (Lu and Deng, 2009; Deng et al., 2010; Sha et al., flora of the hinterland of the basin(Muller, 1959; Traverse, 2007). 2011)(Fig. 2). An important common macroplant fossil within this Diverse plant groups are recognized for the Late Triassic–Early Jurassic stratigraphic level in both basins is Coniopteris (Deng et al., 2010; in the Xuanhan area, including ferns, conifers, cycadophytes/ginkgo- Table 1). phytes, seed ferns, lycopsids, mosses and horsetails (Table 2; Fig. 8). Age: The co-dominance of Cyathidites and Classopollis, the low They vary considerably in abundance in different intervals. abundance of Concavisporites, and the presence of Dictyophyllidites, Chasmatosporites, Quadraeculina, and presence of the macroplant fossil 4.2.1. Late Triassic (Norian) taxa Coniopteris, indicate an Early Jurassic (Hettangian–Sinemurian) The Late Triassic (Norian) palynoflora can be described as a lowland age. mire forest. Ferns were the most dominant type (53–55%), represented

9 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Table 1 Upper Triassic–Lower Jurassic palynological assemblages and the coeval macroplant fossil taxa from the Qilixia section.

Horizon Palynological assemblages Megaplant fossil taxa

Lower Zhenzhuchong Formation PA5 Ferns: Todites princeps, Coniopteris sp. (Early Jurassic) Cycadophytes: Zamites sp., Bucklandia sp. Ginkgophytes: Ixostrobus groenlandicus Conifers: Podozamites sp. Base of Zhenzhuchong Formation PA4 Horsetails: Equisetites sp. (T–J transition) Ferns: Todites princeps, Coniopteris sp. Conifers: Podozamites sp. Member VII of Xujiahe Formation PA3 Horsetails: Equisetites scanicus, Neocalamites carcinoides, Schizoneura sp. (late Rhaetian) Ferns: Todites kwanguyuanensis, Cynepteris lasiophora, Clathropteris tenuinervis, Cladophlebis cf. kaoiana Seed ferns: Ptilozamites chinensis Cycadophytes: Zamites sinensis, Pterophyllum angustum, P. costa, Ctenis yamanarii, Nilssonia furcata, Anthrophyopsis venulosa, Cycadolepis corrugata, Vardekloeftia sulcata Ginkgophytes: Baiera elegans, Ixostrobus sp. Conifers: Pityophyllum nordenskioildi, Podozamites distans, P. cf. issykkulensis, P. mucronatus, Elatocladusi sp., Schizolepis gracilis, Cycadocarpidium Members II-V of Xujiahe PA2 Horsetails: Annulariopsis cf. inopinata, Neocalamites carcinoides Formation (late Ferns: Todites kwangyuanensis, Cladophlebis cf. kaoiana, Dictyophyllum nathorsti, Clathropteris meniscioides Norian–Rhaetian) Seed ferns: Ptilozamites sp., Ctenozamites cycades Cycadophytes: Pterophyllum sp., Nilssonia sp., Zamites sp., Ctenis denticulata, C.? mirabilis, Anthrophyopsis venulosa Ginkgophytes: Baiera sp., Ixostrobus sp., Stachyopitys sp. Conifers: Pityophyllum sp., Cycadocarpidium swabii, Podozamites distans, Nagatostrobus linearis Members I of Xujiahe Formation PA1 Horsetails: Neocalamites sp. (Norian) Ferns: Leptopteris sp., Dictyophyllum sp., Phlebopteris sp. Conifers: Podozamites sp.

Note: The megaplant fossil taxa are mainly based on Ye et al. (1986), Wang et al. (2010) and newly found plant fossil collections during recent field survey.

by Dipteridaceae/Matoniaceae (17–26%), and include the common areas. The mid-canopy cycadophytes/ginkgophytes trees were also occurrence of Cyatheaceae/Dicksoniaceae (11–18%), as well as the less common (9–15%) in this vegetation, as well as seed ferns (< 5%) abundant Marattiaceae, Osmundaceae, Pteridaceae, and Gleicheniaceae (Fig. 8). (Fig. 8). These ferns, combined with a few lycopsids, mosses and The macroflora within the same interval (Member I of the Xujiahe horsetails, likely comprised the ground cover vegetation. The upper Formation) shows a dominance of horsetails (Neocalamites) and ferns canopy conifer trees (19–27%) mainly consist of Pinaceae (7–16%), (Leptopteris, Dictyophyllum, Phlebopteris), with only few conifers Araucariaceae (5–8%), Podocarpaceae (2–3%) and a few Taxodiaceae (Podozamites)(Huang, 1995; Table 1). Both the macroflora and paly- (Fig. 8). Conifer pollen may have been transported from the highland noflora are indicative of a lowland ground cover and bush landscape in

Table 2 Botanical affinity and classification of the SEGs for dispersed Upper Triassic–Lower Jurassic miospores from the Qilixiasection.

Botanical affinity Sporomorph genera SEG Ecological remarks

Horsetails Calamospora Lowland Wetter, warmer Ferns (Dipteridaceae/ Matoniaceae) Dictyophyllidites, Concavisporites Ferns (Dipteridaceae) Granulatisporites, Apiculatisporis, Kyrtomisporis, Canalizonospora, Conbaculatisporites, Converrucosisporites Ferns (Osmundaceae) Biretisporites, Osmundacidites, Baculatisporites Ferns (Pteridaceae) Asseretospora Ferns (Marattiaceae) Angiopteridaspora, Toroisporis, Marattisporites Ferns Leiotriletes, Triancoraesporites, Punctatisporites, Lophotriletes, Cyclogranisporites, Lunzisporites, Planisporites, Anapiculatisporites, Klukisporites, Laevigatosporites Ferns (Dicksoniaceae) Cibotiumspora, Undulatisporites Lowland Drier, warmer Ferns (Dicksoniaceae/ Cyatheaceae) Cyathidites Cycadophytes Cycadopites, Monosulcites Cycads Chasmatosporites Gymnosperms Verrumonocolpites Conifers (Cheirolepidiaceae) Classopollis Ginkgophytes Monosulcites minimus Lowland Drier, cooler Conifers (Araucariaceae) Araucariacites Lowland Wetter, cooler Conifers (Taxodiaceae) Inaperturopollenites, Cerebropollenites Conifers (Pinaceae) Piceites, Pinuspollenites Upland Conifers (Podocarpaceae) Podocarpidites, Protopodocarpus, Quadraeculina, Taeniaesporites, Platysaccus Conifers Protopinus, Pseudopinus, Pseudopicea, Protoconiferus, Paleoconiferus, Protopicea Pinaceae / Cycads Ovalipollis Gymnosperm Cordaitina, Chordasporites Mosses Sphagnumsporites, Annulispora River Lycopsids Leptolepidites, Acanthotriletes, Neoraistrickia, Lycopodiacidites, Lycopodiumsporites, Aratrisporites, Camarozonosporites, Trizonites, Kraeuselisporites Seed ferns Vitreisporites, Alisporites

Note: This summary is mainly based upon published references on the botanical affinity of dispersed spores and ecology of Mesozoic plants: e.g. Van Konijnenburg- Van Cittert, 1971, 1978, 1993, 2002; Litwin, 1985; Balme, 1995; Wang, 1999, 2002; Wang and Mei, 1999; Deng, 2002; Abbink et al., 2004; Wang et al., 2005, 2015.

10 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 8. Late Triassic–Early Jurassic palaeovegetation reconstruction of the Xuanhan region, Sichuan Basin, China. this geographic region for the Norian. dominant vegetation groups, and Cheirolepidiaceae plants were present (Fig. 8). Ferns decreased sharply in abundance at this time, the typical 4.2.2. Late Triassic (late Norian–Rhaetian) Triassic Dipteridaceae/Matoniaceae plants were less common than The Norian–Rhaetian palynoflora was similar to the slightly older earlier, while seed ferns became more abundant (Fig.8). Norian palynoflora, but with a higher abundance of mid-canopy trees Palaeobotanical studies indicated that, the flora was richer in (represented by cycadophytes/ginkgophytes and seed ferns) as re- ginkgophytes (Baiera, Ixostrobus), conifers (Pityophyllum, Podozamites, corded in the sedimentary successions of Member II (Fig. 8). Ferns, Elatocladus, Schizolepis, Cycadocarpidium) and seed ferns (Ptilozamites); especially the Dipteridaceae/Matoniaceae (up to 40%), were relatively whereas ferns (Todites, Cynepteris, Clathropteris, Cladophlebis), horsetails common in the younger strata of this stratigraphic interval (Member III- (Equisetites, Neocalamites, Schizoneura) and cycadophytes (Zamites, V) (Fig. 8). Conifers became however more common (up to 30%) in Pterophyllum, Ctenis, Nilssonia, Anthrophyopsis, Cycadolepis, strata of the younger Member V (Fig. 8). Vardekloeftia) were less common (Ye et al., 1986; Huang, 1995; Wang Fossil macrofloral assemblages of this time interval are mainly et al., 2010)(Table 1). composed of ferns (Todites, Cladophlebis, Dictyophyllum nathorsti, Clathropteris), cycadophytes (Pterophyllum, Nilssonia, Zamites, Ctenis, 4.2.4. Triassic–Jurassic transition Anthrophyopsis) and horsetails (Annulariopsis, Neocalamites), with a few Our palynofloral analysis shows that across the Triassic–Jurassic conifers (Pityophyllum, Cycadocarpidium, Podozamites, Nagatostrobus), transition, a lowland mire vegetation covered the landscape again. ginkgophytes (Baiera, Ixostrobus, Stachyopitys) and seed ferns Ferns were the most dominant (average 52%, up to 80%), characterized (Ptilozamites, Ctenozamites) being present (Ye et al., 1986; Huang, 1995; by a significant content of Cyatheaceae/Dicksoniaceae (18–59%), and Wang et al., 2010)(Table 1). to a lesser extent Dipteridaceae/Matoniaceae and Marattiaceae (Fig. 8). Seed ferns were still common, Cheirolepidiaceae increased in abun- 4.2.3. Latest Triassic (late Rhaetian) dance, whereas cycadophytes/ginkgophytes and conifers decreased in The latest Triassic palynoflora was likely comprised of a mixed abundance relative to previous times (Fig. 8). forest with more canopy trees and less ground cover ferns. Conifers Macroplant fossil records within this interval are less rich, mainly (15–45%) and cycadophytes/ginkgophytes (25–38%) were the most featured by a few ferns (Todites, Coniopteris) and conifers (Podozamites)

11 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

(Ye et al., 1986; Wang et al., 2010)(Table 1). Paleoconiferus, while fern spores Concavisporites, Dictyophyllidites and Cyathidites mark high negative scores on the axis 2 (Fig. 9). Most of 4.2.5. Early Jurassic (Hettangian–Sinemurian) Mesozoic ferns are considered to favor relatively warm conditions (Van During the Early Jurassic, ferns remained the most abundant paly- Konijnenburg-Van Cittert, 2002; Wang, 2002). Therefore, the second nomorph (and likely vegetation) type, but with a lower abundance of axis is interpreted to reflect temperature (Fig. 9). 31–72%, mainly consisting of Cyatheaceae/Dicksoniaceae and only a Relative temperature and humidity changes inferred from the limited abundance of Dipteridaceae/Matoniaceae (Fig. 8). Conifers in- sample scores on the two axes are shown in Fig. 10. The scores on axis 1 creased in abundance, represented by Cheirolepidiaceae (up to 36%), show negative values in the Xujiahe Formation, and turn to positive and Pinaceae (Fig. 8). Cycadophytes/ginkgophytes were also common values within the uppermost Xujiahe and lower Zhenzhuchong forma- in the flora (9–31%), whereas seed ferns were less abundant (Fig. 8). tions, suggesting a more humid climate during the Norian to Rhaetian, Fossil macrofloral assemblages in the Zhenzhuchong Formation are and drier conditions in the late Rhaetian to Hettangian–Sinemurian characterized by the abundance of ferns (Todites, Coniopteris) and cy- (Fig. 10). The strong negative loadings on the axis 2 in the Member I, cadophytes (Zamites, Bucklandia), especially the rise of Dicksoniaceae III-V of the Xujiahe Formation and lower Zhenzhuchong Formation, (Coniopteris), the less common occurrence of ginkgophytes (Ixostrobus) indicate warmer climate during the Norian, Rhaetian, and Hettan- and conifers (Podozamites), and a decline of seed ferns (Huang, 2000; gian–Sinemurian periods; whereas the high positive values on axis 2 in Wang et al., 2010)(Table 1). the Member II and VII of Xujiahe Formation, reflect cooler intervals in the Norian–Rhaetian transition and late Rhaetian (Fig. 10).

4.3. Palaeoclimate variations 4.3.2. Sporomorph EcoGroup analysis result The SEG model was first utilized for the Late Jurassic–Early Previous palaeobotanical studies suggested the dominance of ferns Cretaceous palynological records from NW Europe (Abbink et al., and the abundance of cycadophytes throughout the Triassic–Jurassic 2004). Considering climate and environment conditions in the Sichuan transition, inferring a generally warm and humid tropical-subtropical Basin during the Triassic–Jurassic transition, some of the palynomorphs climate (Huang, 1995, 2000; Wang et al., 2010). To reveal palaeocli- in this study were re-grouped, e.g. the Coastal Araucariaceae and mate changes and variations in more detail, the Principal Components Cheirolepidiaceae pollen in Abbink et al. (2004) were regrouped as Analysis (PCA) and Sporomorph EcoGroup (SEG) analysis (Abbink Lowland elements (Table 2). Spores and pollen encountered in the et al., 2004) were performed in this study based on detailed palynolo- studied section were assigned to three SEG groups, the Lowland SEG, gical records. Upland SEG and River SEG (Table 2). Obviously, elements attributed to the Lowland SEG show a marked dominance, especially the warmer 4.3.1. Principal components analysis result Lowland elements; the River SEG and Upland SEG are less abundant The PCA ordination diagram based on the relative abundance of (Fig. 10). This implies that, the study area was generally marked by a spore and pollen genera shows that, axis 1 accounts for 40.4% of var- prevailing warm and humid lowland lake-marsh ecosystem during the iance in the sporomorph spectra, axis 2 accounts for 13.1% (Fig. 9). Late Triassic to Early Jurassic period, but likely with several palaeo- Two main ordination axes represent the largest variance in palynolo- climatic fluctuations superimposed on that. gical composition controlled by environmental/climatic changes. The The stronger occurrence of warmer Lowland ecosystems, ex- xerophytic Classopollis pollen (Alvin, 1982) and hygro-mesophytic Cy- emplified by peaks in the Lowland warm/cool ratio, as captured in athidites spores (Wang et al., 2005) have the highest positive loadings sedimentary strata from the members IV-V of the Xujiahe Formation on axis 1, whereas the moisture-loving fern spores, e.g. Concavisporites, and lower Zhenzhuchong Formation, suggests relatively warmer cli- Dictyophyllidites, Osmundacidites, Granulatisporites and Punctatisporites, mate during the Rhaetian and Early Jurassic (Fig. 10). During deposi- load on the negative sides of axis 1, with this the first axis can be ex- tion of sedimentary strata of Member VII of the Xujiahe Formation, both plained as reflecting humidity (Fig. 9). On the positive side of the axis 2, the warmer Lowland SEG and the Lowland warm/cool show minimum temperate conifer bisaccate pollen (Wang et al., 2005) have high scores, values, inferring cooler condition in the late Rhaetian (Fig. 10). The represented by e.g. Pinuspollenites, Alisporites, Quadraeculina and decreased abundance of wetter Lowland elements and valley values in Lowland wet/dry ratios, in the uppermost Xujiahe and lower part of the Zhenzhuchong Formation, are suggesting drier conditions from the late Rhaetian to the Early Jurassic (Fig. 10).

5. Discussion

5.1. Palaeovegetation turnover across the Triassic–Jurassic transition

The present study indicates significant vegetation changes from the Late Triassic to the Early Jurassic in the Sichuan Basin. The Late Triassic (Norian–Rhaetian) fern (mainly Dipteridaceae/Matoniaceae) domi- nated lowland forest with abundant cycadophytes and conifers, evolved to a mixed forest with more cycadophytes, ginkgophytes and conifers in the late Rhaetian. Most interestingly, the significantly dominant fern vegetation (represented by Cyatheaceae/Dicksoniaceae and Dipteridaceae/Matoniaceae) that characterized the Triassic–Jurassic transition interval, was replaced by a flora with co-dominance of Cyatheaceae/Dicksoniaceae and Cheirolepidiaceae in the Hettangian–Sinemurian (Fig. 8). The observed vegetation turnover is similar to the changes reported from other sites. The Triassic–Jurassic transitional interval is also Fig. 9. Principal component analysis (PCA) ordination plot of Upper Triassic to marked by a significant relative increase in ferns in hinterlands, re- Lower Jurassic sporomorph relative abundances at the Qilixia section. presented by a spore spike as observed in geographically widespread

12 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Fig. 10. Late Triassic–Early Jurassic PCA and SEG curves, and palaeoclimate implications for the Xuanhan region, Sichuan Basin, China. sedimentary records, from North America (Olsen et al., 2002), Europe subtropical–tropical climates, while some cheirolepids were likely (Bonis et al., 2009; Larsson, 2009; Mander et al., 2010; Vajda et al., coastal plants that could tolerate seasonal droughts and saline influence 2013; Vajda and Bercovici, 2014), Asia (Lu and Deng, 2009), Australia (Alvin, 1982). Recent studies show that cheirolepids can locally dom- and New Zealand (Akikuni et al., 2010; de Jersey and McKellar, 2013). inate in disturbed ecosystems after mass extinction events (Tosolini This spike in fern vegetation predominance was also followed by a et al., 2015). The widespread proliferation of Cheirolepidiaceae forests dominance of Cheirolepidiaceae in the Hettangian to Early Sinemurian during the Early Jurassic, maybe explained by their polyploidy me- in Europe, Australia and New Zealand (Bonis et al., 2010; Akikuni et al., chanism which make them more tolerant to stressed environments 2010; de Jersey and McKellar, 2013). during the Triassic–Jurassic biotic crisis (Kürschner et al., 2013). The increased spore abundances at Triassic–Jurassic transition are observed across both hemispheres, inferring global environmental and 5.2. Climate changes across the Triassic–Jurassic transition climatic changes in favor of spore-producing plants. It is likely in re- sponse to CAMP volcanism induced changes in atmospheric CO levels, 2 PCA and SEG analysis suggest warm and humid climatic conditions as well as terrestrial soil and freshwater acidification (van de in the northeastern Sichuan Basin during Norian to Rhaetian, inter- Schootbrugge et al., 2009; Pieńkowski et al., 2012). rupted by a cooler interval at the Norian–Rhaetian transition. This was Cheirolepidiaceae was one of the most common conifers in the followed by cooler and drier conditions in the latest Triassic, and sig- Mesozoic, occupying a wide range of habitats. It's generally considered nificantly warmer and drier conditions during the Triassic–Jurassic to be xerophytic and thermophilous shrubs and trees occurring in transition and Early Jurassic (Fig. 10).

13 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

The cooling event at the Norian–Rhaetian transition is supported by 6. Conclusions the occurrence of the fossil wood Xenoxylon in Member II of the Xujiahe Formation from the NW Sichuan Basin (Tian et al., 2016). This scenario 1) Detailed palynological study of the Xujiahe and Zhenzhuchong is consistent with the western Tethys studies, which also revealed a formations at the Qilixia section was carried out in the Sichuan Basin of cooling interval during the Norian–Rhaetian transition, as indicated by southern China, eastern Tethys region. Five palynological assemblage higher oxygen isotope (δ18O) records from conodont apatite (Trotter zones were distinguished, spanning Norian to Hettangian–Sinemurian. et al., 2015). The climate change across the Norian–Rhaetian boundary 2) This allows for an Upper Triassic–Lower Jurassic chronostrati- may be caused by emplacement of large volcanic event, although no LIP graphic framework to be established for the study area. It sheds new dated to this time is known to date (Rigo et al., 2020). light on the palaeovegetation and palaeoclimate changes across the A cooler and drier condition in the latest Triassic has also been re- Triassic–Jurassic transition in the eastern Tethyan realm, and links it to vealed by palynological data from Hechuan region in the southern global change events at the Triassic–Jurassic transition. Sichuan Basin (Li et al., 2018). Recent sedimentary and biomarker 3) The Norian–Rhaetian lowland fern ground cover forest with studies suggested increased wildfire activity during the Triassic–Jur- common mid-storey cycadophytes and canopy conifers, was replaced assic transition within the Sichuan Basin (Pole et al., 2018; Song et al., by a mixed gymnosperm forest with increasing the portions of mid- 2020), possibly as a result of the warmer and drier climate during this storey and canopy trees in the latest Triassic. During the interval. Detailed palynological study from the Junggar Basin revealed Triassic–Jurassic transition, vegetation was strongly dominated by a warmer climate during the earliest Jurassic relative to the Late ferns. The dominance of Dipteridaceae/Matoniaceae ferns in the Late Triassic (Lu and Deng, 2009; Deng et al., 2010). The observed palaeo- Triassic was replaced by Cyatheaceae/Dicksoniaceae ferns during the climate changes across the Triassic–Jurassic transition in the eastern Triassic–Jurassic transition. This fern dominated flora was followed by Tethys likely reflect (global) climatic fluctuations at this time. a co-dominance of ferns and cheirolepid conifers in the Pioneering palynological studies in northwestern and central Hettangian–Sinemurian time-interval. Europe, western Australia and northeastern Greenland (Hubbard and 4) With this, an overall warm and humid climate is thought to have Boulter, 1997, 2000), suggested a strong cooling event immediately prevailed during the Late Triassic–Early Jurassic in the Sichuan Basin. A prior the Triassic–Jurassic boundary, and preceding a period of greatly cooling event at the Norian–Rhaetian transition was revealed. An decreased humidity. High-resolution palynological data from two im- abrupt and short cooler and drier interval likely occurred in the latest portant Triassic–Jurassic boundary sections in Europe (Hochalplgraben Triassic, coinciding with the end-Triassic mass extinction event. This in Austria and St. Audrie's Bay in UK) showed a warming trend from the was followed by a warmer and drier climate during the Triassic to the Jurassic, interrupted by a cooler period in the latest Triassic–Jurassic transition, overall representing global climatic Rhaetian, which was observed from the Schattwald beds in the Eiberg changes associated with the Triassic–Jurassic ecosystem crisis. Basin, Austria, and the upper Lilstock Formation (Langport Member) and the basal Blue Lias Formation at St Audries Bay, UK (Bonis and Declaration of Competing Interest Kürschner, 2012). This cooler period onsets and coincides with the end- Triassic mass extinction event (Bonis and Kürschner, 2012). We declare that we do not have any commercial or associative in- 18 Furthermore, oxygen-isotope (δ O) analyses of fossil-calcite from terest that represents a conflict of interest in connection with the work the uppermost Rhaetian at St. Audrie's Bay show elevated values at this submitted. time, reflecting lower seawater temperatures relative to the succeeding lower Hettangian (Korte et al., 2009). Chemo-, bio-, magnetostrati- Acknowledgements graphic and astrochronological constraints suggest that, most of the (basalt) surface magmatic emplacement associated with CAMP, coin- Thanks to Xiaoping Xie (Qufu Normal University), Ning Tian cided with the end-Triassic mass extinction interval, as recognized in (Shenyang Normal University), Zikun Jiang (Chinese Academy of marine sedimentary strata (Deenen et al., 2010; Whiteside et al., 2010; Geological Sciences), Ning Lu, Chong Dong, Mike Pole, Ning Zhou, Korte et al., 2019; Panfili et al., 2019). The CAMP event was thus co- Xiaoqing Zhang, Aowei Xie and Pengcheng An (Nanjing Institute of inciding with the Schattwald Beds in the Eiberg Basin and the strati- Geology and Palaeontology, Chinese Academy of Sciences) (NIGPAS) 18 graphic interval marked by elevated δ O values in fossil calcite in the for their field assistance. We are also grateful to Zhaosheng Liu Bristol Channel Basin (St. Audrie's Bay). Magneto- and biostratigraphic (NIGPAS) for his aid during the early stage of this work. Limei Feng correlation to the here studied terrestrial successions of the Sichuan (NIGPAS) is thanked for laboratory analysis. Two anonymous reviewers Basin suggest that this main pulse of CAMP basalt emplacement also are acknowledged for their constructive feedback and suggestions. This directly coincides with the cooler climatic conditions evidenced by the work was co-sponsored by the National Science Foundation of China changes in the composition of the palynological assemblages. Bentho- [NSFC 41702004, 41790454, 41572014, 41688103], the Strategic planktonic studies from the Austrian Alps also indicate that, cooling Priority Program (B) of CAS [XDB18000000, XDB26000000], the State episodes may have occurred in the latest Triassic (Late Rhaetian) Key Laboratory of Palaeobiology and Stratigraphy [20172103, (Clémence et al., 2010). 20191103], the Swedish Research Council (VR 2019-4061). L. Li ac- This global response in vegetation and climate may suggest that, the knowledges funding from the Chinese Academy of Sciences for her CAMP emplacement, with a significant influx 2of SO and sulphate visiting researcher work at the Swedish Museum of Natural History, aerosols into atmosphere, causing an initial cooling at the latest Sweden. Triassic, and was later outpaced by global warming from elevated The following are the supplementary data related to this article. carbon release in the earliest Jurassic (Sigurdsson, 1990; McElwain et al., 1999; Olsen, 1999; Tanner et al., 2001, 2004; Guex et al., 2004; References Deenen et al., 2010; Ruhl et al., 2010; Steinthorsdottir et al., 2011; Bond and Grasby, 2017). Abbink, O.A., Van Konijnenburg-Van Cittert, J.H.A., Visscher, H., 2004. A sporomorph The CAMP-related sulphuric emissions, heavy metal concentrations, ecogroup model for the Northwest European Jurassic - Lower Cretaceous I: Concepts poisoning of ecosystems, widespread anoxia, seawater acidification and and framework. Netherlands J. Geosci./Geol. Mijnbouw 83, 17–38. https://doi.org/ 10.1017/S0016774600020436. rapid climate change might have been the trigger for the collapse of Akikuni, K., Hori, R., Vajda, V., Grant-Mackie, J.A., Ikehara, M., 2010. Stratigraphy of ecosystems, leading to the latest Triassic extinction (Tanner et al., 2001, Triassic–Jurassic boundary sequences from the Kawhia coast and Awakino gorge. 2004; Guex et al., 2004; Deenen et al., 2010; Bartolini et al., 2012). Murihiku Terrane, New Zealand. Stratigr. 7, 7–24. Alvin, K.L., 1982. Cheirolepidiaceae: Biology, structure and paleoecology. Rev. Palaeobot.

14 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Palynol. 37, 71–98. https://doi.org/10.1016/0034-6667(82)90038-0. Van Konijnenburg-Van Cittert, J.H.A., 1971. In situ gymnosperm pollen from the Middle Ashraf, A.R., Wang, Y.D., Sun, G., Li, J., Mosbrugger, V., 2001. Palynostratigraphic Jurassic of Yorkshire. Acta Bot. Neerl. 20, 1–97. analysis of the Huangshanjie, Haojiagou and Badaowan formations in the Junggar Van Konijnenburg-Van Cittert, J.H.A., 1978. Osmundaceous spores in situ from the Basin (NW China). In: Sun, G., Mosbrugger, V., Ashraf, A.R., Wang, Y.D. (Eds.), The Jurassic of Yorkshire, England. Rev. Palaeobot. Palynol. 26, 125–141. https://doi. Advanced Study of Prehistory Life and Geology of Junggar Basin, Xinjiang, China. org/10.1016/0034-6667(78)90009-X. Proc Sino-German Cooperation Symp Prehistory Life and Geology of Junggar Basin, Van Konijnenburg-Van Cittert, J.H.A., 1993. A review of the Matoniaceae based on in situ Xinjiang, China. Urumqi, pp. 40–64. spores. Rev. Palaeobot. Palynol. 78, 235–267. https://doi.org/10.1016/0034- Balme, B.E., 1995. Fossil in situ spores and pollen grains: An annotated catalogue. Rev. 6667(93)90066-4. Palaeobot. Palynol. 87, 81–323. https://doi.org/10.1016/0034-6667(95)93235-X. Van Konijnenburg-Van Cittert, J.H.A., 2002. Ecology of some Late Triassic to Early Barbacka, M., Pacyna, G., Kocsis, A.T., Jarzynka, A., Ziaja, J., Bodor, E., 2017. Changes in Cretaceous ferns in Eurasia. Rev. Palaeobot. Palynol. 119, 113–124. https://doi.org/ terrestrial floras at the Triassic-Jurassic Boundary in Europe. Palaeogeogr. 10.1016/S0034-6667(01)00132-4. Palaeoclimatol. Palaeoecol. 480, 80–93. https://doi.org/10.1016/j.palaeo.2017.05. Korte, C., Hesselbo, S.P., Jenkyns, H.C., Rickaby, R.E.M., Spötl, C., 2009. 024. Palaeoenvironmental significance of carbon- and oxygen-isotope stratigraphy of Bartolini, A., Guex, J., Spangenberg, J.E., Schoene, B., Taylor, D.G., Schaltegger, U., marine Triassic–Jurassic boundary sections in SW Britain. J. Geol. Soc. Lond. 166, Atudorei, V., 2012. Disentangling the Hettangian carbon isotope record: Implications 431–445. https://doi.org/10.1144/0016-76492007-177. for the aftermath of the end-Triassic mass extinction. Geochem. Geophys. Geosyst. Korte, C., Ruhl, M., Pálfy, J., Ullmann, C.V., Hesselbo, S.P., 2019. Chemostratigraphy 13, 1–11. https://doi.org/10.1029/2011GC003807. across the Triassic–Jurassic boundary. In: Sial, A.N., Gaucher, C., Ramkumar, M., Bond, D.P.G., Grasby, S.E., 2017. On the causes of mass extinctions. Palaeogeogr. Ferreira, V.P. (Eds.), Chemostratigraphy across Major Chronological Boundaries, First Palaeoclimatol. Palaeoecol. 478, 3–29. https://doi.org/10.1016/j.palaeo.2016.11. edition. Geophysical Monograph 240 John Wiley & Sons, Inc, pp. 185–210. https:// 005. doi.org/10.1002/9781119382508.ch10. Bonis, N.R., Kürschner, W.M., 2012. Vegetation history, diversity patterns, and climate Kürschner, W.M., Batenburg, S.J., Mander, L., 2013. Aberrant Classopollis pollen reveals change across the Triassic/Jurassic boundary. Paleobiology 38, 240–264. https://doi. evidence for unreduced (2n) pollen in the conifer family Cheirolepidiaceae during the org/10.1666/09071.1. Triassic–Jurassic transition. Proc. R. Soc. B 280, 20131708. https://doi.org/10.1098/ Bonis, N.R., Kürschner, W.M., Krystyn, L., 2009. A detailed palynological study of the rspb.2013.1708. Triassic–Jurassic transition in key sections of the Eiberg Basin (Northern Calcareous Kustatscher, E., Ash, S.R., Karasev, E., Pott, C., Vajda, V., Yu, J., McLoughlin, S., 2018. Alps, Austria). Rev. Palaeobot. Palynol. 156, 376–400. https://doi.org/10.1016/j. Flora of the Late Triassic. In: Tanner, L.H. (Ed.), The Late Triassic World. Earth in a revpalbo.2009.04.003. Time of Transition. Topics in Geobiology 46 Springer, Cham, Switzerland, pp. Bonis, N.R., Ruhl, M., Kürschner, W.M., 2010. Climate change driven black shale de- 545–622. https://doi.org/10.1007/978-3-319-68009-5_13. position during the end-Triassic in the western Tethys. Palaeogeogr. Palaeoclimatol. Larsson, L.M., 2009. Palynostratigraphy of the Triassic–Jurassic transition in southern Palaeoecol. 290, 151–159. https://doi.org/10.1016/j.palaeo.2009.06.016. Sweden. GFF 131, 147–163. https://doi.org/10.1080/11035890902924828. Clémence, M.E., Gardin, S., Bartolini, A., Paris, G., Beaumont, V., Guex, G., 2010. Bentho- Lepš, J., Šmilauer, P., 2003. Multivariate Analysis of Ecological Data Using CANOCO. planktonic evidence from the Austrian Alps for a decline in sea-surface carbonate Cambridge University Press, Cambridge. https://doi.org/10.1017/ production at the end of the Triassic. Swiss J. Geosci. 103, 293–315. https://doi.org/ CBO9780511615146. 10.1007/s00015-010-0019-z. Li, L.Q., Wang, Y.D., Liu, Z.S., Zhou, N., Wang, Y., 2016. Late Triassic palaeoclimate and de Jersey, N.J., McKellar, J.L., 2013. The palynology of the Triassic–Jurassic transition in palaeoecosystem variations inferred by palynological record in the north-eastern southeastern Queensland, Australia, and correlation with New Zealand. Palynology Sichuan Basin, China. PalZ 90, 327–348. https://doi.org/10.1007/s12542-016- 37, 77–114. https://doi.org/10.1080/01916122.2012.718609. 0309-5. Deenen, M.H.L., Ruhl, M., Bonis, N.R., Krijgsman, W., Kürschner, W.M., Reitsma, M., van Li, M.S., Zhang, Y., Huang, C.J., Ogg, J., Hinnov, L., Wang, Y.D., Zou, Z.Y., Li, L.Q., 2017. Bergen, M.J., 2010. A new chronology for the end-Triassic mass extinction. Earth Astronomical tuning and magnetostratigraphy of the Upper Triassic Xujiahe Planet. Sci. Lett. 291, 113–125. https://doi.org/10.1016/j.epsl.2010.01.003. Formation of South China and Newark Supergroup of North America: Implications for Deng, S.H., 2002. Ecology of the Early Cretaceous ferns of Northeast China. Rev. the Late Triassic time scale. Earth Planet. Sci. Lett. 475, 207–223. https://doi.org/10. Palaeobot. Palynol. 119, 93–112. https://doi.org/10.1016/S0034-6667(01)00131-2. 1016/j.epsl.2017.07.015. Deng, S.H., Lu, Y.Z., Fan, R., Pan, Y.H., Cheng, X.S., Fu, G.B., Wang, Q.F., Pan, H.Z., Shen, Li, L.Q., Wang, Y.D., Vajda, V., Liu, Z.S., 2018. Late Triassic ecosystem variations inferred Y.B., Wang, Y.Q., Zhang, H.C., Jia, C.K., Duan, W.Z., Fang, L.H., 2010. The Jurassic by palynological records from Hechuan, southern Sichuan Basin, China. Geol. Mag. system of northern Xinjiang, China. University of Science and Technology of China 155, 1793–1810. https://doi.org/10.1017/S0016756817000735. Press, Hefei (in Chinese and English). Lindström, S., 2016. Palynofloral patterns of terrestrial ecosystem change during the end- Götz, A.E., Ruckwied, K., Pálfy, J., Haas, J., 2009. Palynological evidence of synchronous Triassic event - A review. Geol. Mag. 153, 223–251. https://doi.org/10.1017/ changes within the terrestrial and marine realm at the Triassic/Jurassic boundary S0016756815000552. (Csővár section, Hungary). Rev. Palaeobot. Palynol. 156, 401–409. https://doi.org/ Lindström, S., van de Schootbrugge, B., Dybkjær, K., Pedersen, G.K., Fiebig, J., Nielsen, 10.1016/j.revpalbo.2009.04.002. L.H., Richoz, S., 2012. No causal link between terrestrial ecosystem change and Gou, Z.H., 1998. The bivalve faunas from the Upper Triassic Xujiahe Formation in the methane release during the end-Triassic mass extinction. Geology 40, 531–534. Sichuan Basin. Sediment. Facies Palaeogeogr. 18, 20–31 (in Chinese with English https://doi.org/10.1130/G32928.1. abstract). Lindström, S., Sanei, H., van de Schootbrugge, B., Pedersen, G.K., Lesher, C.E., Tegner, C., Greene, S.E., Martindale, R.C., Ritterbush, K.A., Bottjer, D.J., Corsetti, F.A., Berelson, Heunisch, C., Dybkjær, K., Outridge, P.M., 2019. Volcanic mercury and mutagenesis W.M., 2012. Recognising ocean acidification in deep time: An evaluation ofthe in land plants during the end-Triassic mass extinction. Sci. Adv. 5, eaaw4018. evidence for acidification across the Triassic-Jurassic boundary. Earth-Sci. Rev. 113, https://doi.org/10.1126/sciadv.aaw4018. 72–93. https://doi.org/10.1016/j.earscirev.2012.03.009. Litwin, R.J., 1985. Fertile organs and in situ spores of ferns from the Late Triassic Chinle Grimm, E.C., 2004. Tilia and Tilia. Graph V.2.0.2. Illinois State Museum, Springfield, Formation of Arizona and New Mexico, with discussion of the associated dispersed USA. spores. Rev. Palaeobot. Palynol. 44, 101–146. https://doi.org/10.1016/0034- Guex, J., Bartolini, A., Atudorei, V., Taylor, D., 2004. High-resolution ammonite and 6667(85)90030-2. carbon isotope stratigraphy across the Triassic–Jurassic boundary at New York Lu, Y.Z., Deng, S.H., 2005. Triassic–Jurassic sporopollen assemblages on the southern Canyon (Nevada). Earth Planet. Sci. Lett. 225, 29–41. https://doi.org/10.1016/j.epsl. margin of the Junggar Basin, Xinjiang and the T–J boundary. Acta Geol. Sin. 79, 2004.06.006. 15–27 (in Chinese with English abstract). Hallam, A., 2002. How catastrophic was the end-Triassic mass extinction? Lethaia 35, Lu, Y.Z., Deng, S.H., 2009. Palaeoclimate around the Triassic–Jurassic Boundary in 147–157. https://doi.org/10.1111/j.1502-3931.2002.tb00075.x. southern margin of Junggar Basin. Journal of Palaeogeography (Chinese Edition) 11, Harris, T.M., 1937. The fossil flora of Scoresby Sound, East Greenland. Part 5: 652–660 (in Chinese with English abstract). Stratigraphic relations of the plant beds. Medd. Grønland 112, 1–114. Lu, M.N., Wang, R.S., 1987. Pollen and spore assemblages and distribution characteristics Hesselbo, S.P., Robinson, S.A., Surlyk, F., Piasecki, S., 2002. Terrestrial and marine ex- from Late Triassic to Early Jurassic epoch in Sichuan Basin. In: Collections of tinction at the Triassic–Jurassic boundary synchronized with major carbon-cycle Petroleum Stratum Paleontology Conferences. Geological Publishing House, Beijing, perturbation: A link to initiation of massive volcanism? Geology 30, 251–254. pp. 207–212 (in Chinese). https://doi.org/10.1130/0091-7613(2002)030<0251:TAMEAT>2.0.CO;2. Lucas, S.G., Tanner, L.H., 2015. End-Triassic nonmarine biotic events. J. Palaeogeogr. 4, Huang, Q.S., 1995. Paleoclimate and coal-forming characteristics of the Late Triassic 331–348. https://doi.org/10.1016/j.jop.2015.08.010. Xujiahe stage in northern Sichuan. Geol. Rev. 41, 92–99 (in Chinese with English Lundblad, A.B., 1959. Rhaeto-Liassic floras and their bearing on the stratigraphy of abstract). Triassic-Jurassic rocks. Stockholm Contrib. Geol. 3, 83–102. Huang, Q.S., 2000. Early Jurassic flora and paleoenvironment in Daxian and Kaixian Mander, L., Kürschner, W.M., McElwain, J.C., 2010. An explanation for conflicting re- counties, north border of Sichuan Basin, China. Earth Sci. J. China Univ. Geosci. 26, cords of Triassic–Jurassic plant diversity. Proc. Natl. Acad. Sci. U. S. A. 107, 221–228 (in Chinese with English abstract). 15351–15356. https://doi.org/10.1073/pnas.1004207107. Huang, P., 2006. Sporopollen assemblages from the Haojiagou and Badaowan formations McElwain, J.C., Beerling, D.J., Woodward, F.I., 1999. Fossil plants and global warming at at the Haojiagou section of Ürümqi, Xinjiang and their stratigraphical significance. the Triassic–Jurassic boundary. Science 285, 1386–1390. https://doi.org/10.1126/ Acta Micropalaeontol. Sin. 23, 235–274 (in Chinese with English summary). science.285.5432.1386. Hubbard, R.N.L.B., Boulter, M.C., 1997. Mid Mesozoic floras and climates. Palaeontology McElwain, J.C., Popa, M.E., Hesselbo, S.P., Haworth, M., Surlyk, F., 2007. 40, 43–70. Macroecological responses of terrestrial vegetation to climatic and atmospheric Hubbard, R.N.L.B., Boulter, M.C., 2000. Phytogeography and paleoecology in western change across the Triassic/Jurassic boundary in East Greenland. Paleobiology 33, Europe and eastern Greenland near the Triassic-Jurassic boundary. Palaios 15, 547–573. https://doi.org/10.1666/06026.1. 120–131. https://doi.org/10.1669/0883-1351(2000)015<0120:PAPIWE>2.0. McGhee Jr., G.R., Clapham, M.E., Sheehan, P.M., Bottjer, D.J., Droser, M.L., 2013. A new CO;2. ecological-severity ranking of major Phanerozoic biodiversity crises. Palaeogeogr.

15 L. Li, et al. Palaeogeography, Palaeoclimatology, Palaeoecology 556 (2020) 109891

Palaeoclimatol. Palaeoecol. 370, 260–270. https://doi.org/10.1016/j.palaeo.2012. Sun, G., Meng, F.S., Qian, L.J., Ouyang, S., 1995. Triassic floras. In: Li, X.X., Zhou, Z.Y., 12.019. Cai, C.Y., Sun, G., Ouyang, S., Deng, L.H. (Eds.), Fossil Floras of China through the Muller, J., 1959. Palynology of recent Orinoco Delta and shelf sediments. Micropaleont. Geological Ages. Guangdong Science and Technology Press, Guangzhou, pp. 5, 1–32. 305–342. Olsen, P.E., 1999. Giant lava flows, mass extinctions, and mantle plumes. Science 284, Sun, G., Miao, Y.Y., Mosbrugger, V., Ashraf, A.R., 2010. The Upper Triassic to Middle 604–605. https://doi.org/10.1126/science.284.5414.604. Jurassic strata and floras of the Junggar Basin, Xinjiang, Northwest China. Olsen, P.E., Kent, D.V., Sues, H.D., Koeberl, C., Huber, H., Montanari, A., Rainforth, E.C., Palaeobiol. Palaeoenviron. 90, 203–214. https://doi.org/10.1007/s12549-010- Fowell, S.J., Szajna, M.J., Hartline, B.W., 2002. Ascent of dinosaurs linked to an 0039-8. iridium anomaly at the Triassic–Jurassic boundary. Science 296, 1305–1307. https:// Tanner, L.H., Hubert, J.F., Coffey, B.P., McInerney, D.P., 2001. Stability of atmospheric doi.org/10.1126/science.1065522. CO2 levels across the Triassic/Jurassic boundary. Nature 411, 675–677. https://doi. Pálfy, J., Mortensen, J.K., Carter, E.S., Smith, P.L., Friedman, R.M., Tipper, H.W., 2000. org/10.1038/35079548. Timing the end-Triassic mass extinction: First on land, then in the sea? Geology 28, Tanner, L.H., Lucas, S.G., Chapman, M.G., 2004. Assessing the record and causes of Late 39–42. https://doi.org/10.1130/0091-7613(2000)28<39:TTEMEF>2.0.CO;2. Triassic extinctions. Earth-Sci. Rev. 65, 103–139. https://doi.org/10.1016/S0012- Panfili, G., Cirilli, S., Dal Corso, J., Bertrand, H., Medina, F., Youbi, N., Marzoli, A.,2019. 8252(03)00082-5. New biostratigraphic constraints show rapid emplacement of the Central Atlantic Tian, N., Wang, Y.D., Philippe, M., Li, L.Q., Xie, X.P., Jiang, Z.K., 2016. New record of Magmatic Province (CAMP) during the end-Triassic mass extinction interval. Glob. fossil wood Xenoxylon from the late Triassic in the Sichuan Basin, southern China and Planet. Change 172, 60–68. https://doi.org/10.1016/j.gloplacha.2018.09.009. its paleoclimatic implications. Palaeogeogr. Palaeoclimatol. Palaeoecol. 464, 65–75. Peng, J., Li, J., Li, W., Slater, S.M., Zhu, H., Vajda, V., 2018. The Triassic to Early Jurassic https://doi.org/10.1016/j.palaeo.2016.02.006. palynological record of the Tarim Basin, China. Palaeobiodiv. Palaeoenviron. 98, Tosolini, A.M.P., McLoughlin, S., Wagstaff, B.E., Cantrill, D.J., Gallagher, S.J., 2015. 7–28. https://doi.org/10.1007/s12549-017-0279-y. Cheirolepidiacean foliage and pollen from Cretaceous high-latitudes of southeastern Percival, L.M.E., Ruhl, M., Hesselbo, S.P., Jenkyns, H.C., Mather, T.A., Whiteside, J.H., Australia. Gondwana Res. 27, 960–977. https://doi.org/10.1016/j.gr.2013.11.008. 2017. Mercury evidence for pulsed volcanism during the end-Triassic mass extinc- Traverse, A., 2007. Paleopalynology. Springer, Dordrecht, The Netherlands. tion. Proc. Natl. Acad. Sci. U. S. A. 114, 7929–7934. https://doi.org/10.1073/pnas. Trotter, J.A., Williams, I.S., Nicora, A., Mazza, M., Rigo, M., 2015. Long-term cycles of 1705378114. Triassic climate change: A new δ18O record from conodont apatite. Earth Planet. Sci. Pieńkowski, G., Niedźwiedzki, G., Waksmundzka, M., 2012. Sedimentological, palyno- Lett. 415, 165–174. https://doi.org/10.1016/j.epsl.2015.01.038. logical and geochemical studies of the terrestrial Triassic–Jurassic boundary in Turner, S., Bean, L.B., Dettmann, M., McKellar, J.L., McLoughlin, S., Thulborn, T., 2009. northwestern Poland. Geol. Mag. 149, 308–332. https://doi.org/10.1017/ Australian Jurassic sedimentary and fossil successions: Current work and future S0016756811000914. prospects for marine and non-marine correlation. GFF 131, 49–70. https://doi.org/ Pole, M., Wang, Y.D., Dong, C., Xie, X.P., Tian, N., Li, L.Q., Zhou, N., Lu, N., Xie, A.W., 10.1080/11035890902924877. Zhang, X.Q., 2018. Fires and storms—a Triassic–Jurassic transition section in the Vajda, V., Bercovici, A., 2014. The global vegetation pattern across the Cretaceous- Sichuan Basin, China. Palaeobiol. Palaeoenviron. 98, 29–47. https://doi.org/10. Paleogene mass extinction interval: A template for other extinction events. Glob. 1007/s12549-017-0315-y. Planet. Change 122, 29–49. https://doi.org/10.1016/j.gloplacha.2014.07.014. Qu, L.F., Wang, Z., 1990. Triassic palynological assemblages in North Xinjiang. In: Vajda, V., Calner, M., Ahlberg, A., 2013. Palynostratigraphy of dinosaur footprint-bearing Institute of Geology, Chinese Academy of Geological sciences and Research Institute deposits from the Triassic–Jurassic boundary interval of Sweden. GFF 135, 120–130. of Petroleum Exploration and Development, Xinjiang Petroleum Administration https://doi.org/10.1080/11035897.2013.799223. (Ed.), Permian to Tertiary strata and palynological assemblages in the North of van de Schootbrugge, B., Quan, T.M., Lindström, S., Püttmann, W., Heunisch, C., Pross, J., Xinjiang. China Environmental Science Press, Beijing, pp. 37–56 (in Chinese with Fiebig, J., Petschick, R., Röhling, H.-G., Richoz, S., Rosenthal, Y., Falkowski, P.G., English abstract). 2009. Floral changes across the Triassic/Jurassic boundary linked to flood basalt Rigo, M., Onoue, T., Tanner, L.H., Lucas, S.G., Godfrey, L., Katz, M.E., Zaffani, M., Grice, volcanism. Nat. Geosci. 2, 589–594. https://doi.org/10.1038/ngeo577. K., Cesar, J., Yamashita, D., Maron, M., Tackett, L.S., Campbell, H., Tateo, F., Wang, Y.D., 1999. Fertile organs and in situ spores of Marattia asiatica (Kawasaki) Harris Concheri, G., Agnini, C., Chiari, M., Bertinelli, A., 2020. The Late Triassic Extinction (Marattiales) from the Lower Jurassic Hsiangchi Formation in Hubei, China. Rev. at the Norian/Rhaetian boundary: Biotic evidence and geochemical signature. Earth- Palaeobot. Palynol. 107, 125–144. https://doi.org/10.1016/S0034-6667(99) Sci. Rev. 204, 103180. https://doi.org/10.1016/j.earscirev.2020.103180. 00025-1. Ruhl, M., Veld, H., Kürschner, W.M., 2010. Sedimentary organic matter characterization Wang, Y.D., 2002. Fern ecological implications from the Lower Jurassic in Western Hubei, of the Triassic–Jurassic boundary GSSP at Kuhjoch (Austria). Earth Planet. Sci. Lett. China. Rev. Palaeobot. Palynol. 119, 125–141. https://doi.org/10.1016/S0034- 292, 17–26. https://doi.org/10.1016/j.epsl.2009.12.046. 6667(01)00133-6. Ruhl, M., Bonis, N.R., Reichart, G.J., Damsté, J.S.S., Kürschner, W.M., 2011. Atmospheric Wang, Y.D., Mei, S.W., 1999. Fertile organs and in situ spores of a matoniaceous fern from carbon injection linked to End-Triassic mass extinction. Science 333, 430–434. the Lower Jurassic of West Hubei. Chin. Sci. Bull. 44, 1333–1337. https://doi.org/10. https://doi.org/10.1126/science.1204255. 1007/BF02885857. Schoene, B., Guex, J., Bartolini, A., Schaltegger, U., Blackburn, T.J., 2010. Correlating the Wang, Y.D., Mosbrugger, V., Zhang, H., 2005. Early to Middle Jurassic vegetation and end-Triassic mass extinction and flood basalt volcanism at the 100 ka level. Geology climatic events in the Qaidam Basin, Northwest China. Palaeogeogr. Palaeoclimatol. 38, 387–390. https://doi.org/10.1130/G30683.1. Palaeoecol. 224, 200–216. https://doi.org/10.1016/j.palaeo.2005.03.035. Sepkoski Jr., J.J., 1996. Patterns of Phanerozoic extinction: A perspective from global Wang, Y.D., Fu, B.H., Xie, X.P., Huang, Q.S., Li, K., Li, G., Liu, Z.S., Yu, J.X., Pan, Y.H., data bases. In: Walliser, O.H. (Ed.), Global Events and Event Stratigraphy. Springer, Tian, N., Jiang, Z.K., 2010. The terrestrial Triassic and Jurassic Systems in the Berlin, Heidelberg, pp. 35–51. https://doi.org/10.1007/978-3-642-79634-0_4. Sichuan Basin, China. University of Science and Technology of China Press, Hefei (in Sha, J.G., Vajda, V., Pan, Y.H., Larsson, L., Yao, X.G., Zhang, X.L., Wang, Y.Q., Cheng, Chinese and English). X.S., Jiang, B.Y., Deng, S.H., Chen, S.W., Peng, B., 2011. The Stratigraphy of the Wang, Y.D., Li, L.Q., Guignard, G., Dilcher, D.L., Xie, X.P., Tian, N., Zhou, N., Wang, Y., Triassic−Jurassic boundary successions of the southern margin of Junggar Basin, 2015. Fertile structures with in situ spores of a dipterid fern from the Triassic in northwestern China. Acta Geol. Sin-Engl. 85, 421–436. https://doi.org/10.1111/j. southern China. J. Plant Res. 128, 445–457. https://doi.org/10.1007/s10265-015- 1755-6724.2011.00410.x. 0708-9. Sha, J.G., Olsen, P.E., Pan, Y.H., Xu, D.Y., Wang, Y.Q., Zhang, X.L., Yao, X.G., Vajda, V., Wei, M., 1982. Late Triassic and Jurassic Ostracods in Sichuan Province, in: Continental 2015. Triassic–Jurassic climate in continental high-latitude Asia was dominated by Mesozoic Stratigraphy and Paleontology in the Sichuan Basin. Sichuan People’s obliquity-paced variations (Junggar Basin, Urumqi, China). Proc. Natl. Acad. Sci. U. Publishing House, Chengdu, pp. 346–363 (in Chinese). S. A. 112, 3624–3629. https://doi.org/10.1073/pnas.1501137112. Whiteside, J.H., Olsen, P.E., Kent, D.V., Fowell, S.J., Et-Touhami, M., 2007. Synchrony Sigurdsson, H., 1990. Assessment of atmospheric impact of volcanic eruptions. GSA between the Central Atlantic magmatic province and the Triassic–Jurassic mass-ex- Special Papers 247, 99–110. https://doi.org/10.1130/SPE247-p99. tinction event? Palaeogeogr. Palaeoclimatol. Palaeoecol. 244, 345–367. https://doi. Song, Y., Algeo, T.J., Wu, W.J., Luo, G.M., Li, L.Q., Wang, Y.D., Xie, S.C., 2020. org/10.1016/j.palaeo.2006.06.035. Distribution of pyrolytic PAHs across the Triassic-Jurassic boundary in the Sichuan Whiteside, J.H., Olsen, P.E., Eglinton, T., Brookfield, M.E., Sambrotto, R.N., 2010. Basin, southwestern China: Evidence of wildfire outside the Central Atlantic Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions di- Magmatic Province. Earth-Sci. Rev. 201, 102970. https://doi.org/10.1016/j. rectly linked to the end-Triassic mass extinction. Proc. Natl. Acad. Sci. U. S. A. 107, earscirev.2019.102970. 6721–6725. https://doi.org/10.1073/pnas.1001706107. Steinthorsdottir, M., Jeram, A.J., McElwain, J.C., 2011. Extremely elevated CO2 con- Ye, M.N., Liu, X.Y., Huang, G.Q., Chen, L.X., Peng, S.J., Xu, A.F., Zhang, B.X., 1986. Late centrations at the Triassic/Jurassic boundary. Palaeogeogr. Palaeoclimatol. Triassic and Early–Middle Jurassic Fossil Plants from Northeastern Sichuan. Anhui Palaeoecol. 308, 418–432. https://doi.org/10.1016/j.palaeo.2011.05.050. Science and Technology Publishing House, Hefei (in Chinese with English summary).

16