New Record of Fossil Wood Xenoxylon from the Late Triassic in the Sichuan Basin, Southern China and Its Paleoclimatic Implications
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PALAEO-07681; No of Pages 11 Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2016) xxx–xxx Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo New record of fossil wood Xenoxylon from the Late Triassic in the Sichuan Basin, southern China and its paleoclimatic implications Ning Tian a,c,d, Yongdong Wang b,c,⁎,MarcPhilippee,LiqinLib,h, Xiaoping Xie f,ZikunJiangg a College of Paleontology, Shenyang Normal University, Shenyang 110034, China b Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China c State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS), Nanjing 210008, China d Key Laboratory for Evolution of Past Life in Northeast Asia, Ministry of Land and Resources, Shenyang 110034, China e Laboratoire de Géologie de Lyon, Université Claude Bernard Lyon 1 and CNRS, Campus de la DOUA, Bâtiment, Darwin A, 69622 Villeurbanne Cedex, France f College of Geography and Tourism, Qufu Normal University, Rizhao 276826, China g Chinese Academy of Geological Sciences, Beijing 100037, China h University of Chinese Academy of Sciences, Beijing 100049, China article info abstract Article history: Fossil wood is one of the significant proxies for terrestrial paleoclimate and paleogeographical reconstruction in Received 6 October 2015 Earth history. Abundant and diversified Mesozoic fossil woods are well recorded in China; however, Triassic fossil Received in revised form 21 January 2016 wood is very scarce. Here, we report a new fossil wood from the Late Triassic Xujiahe Formation (Norian to Accepted 3 February 2016 Rhaetian) in Guangyuan of northern Sichuan Basin, southwestern China. The fossil wood material consists of Available online xxxx two well-preserved specimens yielding secondary xylem with distinct growth rings. Bordered pits on the radial tracheid walls are mostly contiguous, biseriate alternate, locally uniseriate and strongly flattened. Cross-fields Keywords: Xenoxylon show a large window-like pore. This anatomy is typical for the important fossil wood morphogenus Xenoxylon Late Triassic Gothan, and, based on a novel combination of radial and cross-field pitting type and ray height, a new species, Xujiahe Formation Xenoxylon guangyuanense sp. nov. is recognized. The finding of this new fossil wood taxon contributes to a better Paleoclimate understanding of the yet poorly documented Xenoxylon early radiation during the Late Triassic, as well as of the Sichuan Basin origin of X. meisteri group, a peculiar endemic group which diversified in Far-East Asia from the Triassic to the Southern China Early Cretaceous. Xenoxylon is a paleobiogeographically significant genus, being bound to cooler and/or wetter climates of Northern Hemisphere throughout its Late Triassic–Late Cretaceous range. The occurrence of Xenoxylon in the Sichuan Basin of southern China may indicate a short-term cooling event, sandwiched within a period during which warm and wet climate conditions largely prevailed over lower latitude regions of the Northern Hemisphere. Such a cooling event in the Sichuan Basin which was located at a low paleolatitude on the eastern rim of Tethys may be in accordance in time with the temperature decline event in Norian– Rhaetian boundary uncovered by oxygen isotope (δ18O) record in Italy of the western rim of Tethys. © 2016 Elsevier B.V. All rights reserved. 1. Introduction documented in both the northern and southern phytoprovinces of China (Zheng et al., 2008; Wang et al., 2009; Yang et al., 2013). Howev- Currently, the understanding of Mesozoic climates is mainly based er, Triassic fossil wood records are very scarce and limited in this coun- on marine paleoclimatic information; however, detailed information try. Here we report a new fossil conifer wood taxon recently collected on the climatic evolution of continental interiors is relatively rare, al- from the continental Triassic in the Sichuan Basin of southern China at though much wanted. Fossil wood is an important component of plant a low paleolatitude with implications for paleoclimate shift. remains, and plays a significant role in reconstructing the terrestrial Late Triassic floras of the Sichuan Basin have been well known in vegetation, paleoclimate and paleoenvironment in the geological past China for a long time (e.g. Schenk, 1883; Sze and Lee, 1952). In particu- (Creber and Francis, 1999; Uhl, 2006). Rich and diversified fossil wood lar, the floral composition and paleoenvironmental significance of the records are documented from China, ranging in age from the Late plant remains from the Upper Triassic Xujiahe (=formerly Hsüchiaho) Carboniferous to the Cenozoic (Zheng et al., 2008). For Mesozoic fossil Formation in Guangyuan region of the northern Sichuan Basin, have wood, the Jurassic and Early Cretaceous records are abundant and well been investigated in detail (Lee, 1964; Yang, 1978; Huang, 1995; Wu, 1999). Fossil plants of the Xujiahe flora are mostly represented by fo- liage impressions or compressions. In this flora, the cycadophytes are ⁎ Corresponding author at: Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China. the dominant group, yielding diverse bennettitalean taxa (e.g. E-mail address: [email protected] (Y. Wang). Pterophyllum, Anomozamites and Otozamites). Ferns, including http://dx.doi.org/10.1016/j.palaeo.2016.02.006 0031-0182/© 2016 Elsevier B.V. All rights reserved. Please cite this article as: Tian, N., et al., New record of fossil wood Xenoxylon from the Late Triassic in the Sichuan Basin, southern China and its paleoclimatic implications, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2016), http://dx.doi.org/10.1016/j.palaeo.2016.02.006 2 N. Tian et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2016) xxx–xxx Dictyophyllum and Clathropteris, are the second most diverse group County (Fig. 1). Fossil woods from Yangliu and Gongnong Towns (Wang et al., 2010; Wang et al., 2015). Sphenophytes, pteridosperms, are not structurally preserved. conifers and ginkgoales are also present in this flora (Lee, 1964; Wu, The fossil wood specimens were collected from the Upper Triassic 1999; Wang et al., 2010). Compared to leaf impressions or compres- Xujiahe Formation, a coal-bearing sequence consisting of alternating sions, structurally preserved fossil wood remains are rarely documented deposits of mudstones and gray-yellow sandstones (Fig. 2). This forma- in this flora. Although a wood fragment was briefly noted from the tion crops out well in the Sichuan Basin, i.e. in the Guangyuan, Hechuan, Upper Triassic in western Sichuan Basin (Qian et al., 2010), no detailed Xuanhan, Daxian and Kaixian regions (Liu, 1982; Wang et al., 2010). information was provided regarding its systematic identification and In the Guangyuan region, the Xujiahe Formation consists of four affinity. lithological members, representing deltaic estuary sandbars and delta During a recent field survey in Guangyuan region of northern Si- plain swamp sedimentary environments, yielding diverse and well- chuan Basin, several fossil wood specimens were collected from the preserved plant fossil remains (Lee, 1964; Wang et al., 2010, 2015). Upper Triassic Xujiahe Formation. Among them, a new conifer wood The specimens studied here occurred in the gray-yellowish sandstone taxon, Xenoxylon guangyuanense sp. nov. was recognized, representing of the Xujiahe Formation Member 2, in Gaoyang Town (Fig. 2). The the first identified Triassic fossil wood data from the Sichuan Basin, Xujiahe Formation is dated as Norian to Rhaetian according to the asso- thus providing welcome evidence about the early radiation of the ciated invertebrate faunal assemblages (e.g. bivalves, ostracodes, genus Xenoxylon in Far-East Asia. As the wood taxon Xenoxylon is an in- conchostraceans) (Chen et al., 1979; Wei, 1982; Gou, 1993, 1998)and dicator of cool and/or wet climatic conditions (Philippe and Thévenard, palynological evidence (Liu, 1982; Lu and Wang, 1987; Liu et al., 1996; Amiot et al., 2011), the occurrence of this taxon at the low 2015a, 2015b). It is tentatively proposed that the Norian–Rhaetian paleolatitudes of southern China may document a short cool climatic boundary occurred in Member 1 of the Xujiahe Formation (Lu et al., event under the generally warm and humid climate that otherwise 2013). Hence the age of the Member 2 may represent early Rhaetian prevailed. age. The fossil flora of the Xujiahe Formation is paleobiogeographically considered as a typical hygrophilous “Dictyophyllum–Clathropteris” southern flora, dominated by ferns, cycads and bennettitales, with a 2. Geological setting, material and methods high occurrence frequency of sphenophytes (e.g. Neocalamites), pointing to humid climate conditions (Wang et al., 2010). Totally six fossil wood specimens were collected from three lo- For anatomical studies, the fossil wood specimens were cut trans- calities in Guangyuan city, northern Sichuan Province, including versely, longitudinally/radially and tangentially in order to prepare Gaoyang Town of Wangcang County (32°16′57.2″N, 106°16′43.1″ thin sections by standard methods (Hass and Rowe, 1999). These thin E), Xiaotangzi Village of Gongnong Town (32°29′20″N, 105°50′38″ sections were observed under light microscope for anatomical charac- E) and Yangliu Village of Yangjiayan Town (32°28′47″N, 105°46′ ters. Photographs were taken with Scope Image 9.0 (H3D) Software 15″E) (Fig. 1).