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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Assemblages and Paleoclimate Implications of the Middle and Late Jurassic Floras in Western Liaoning, China 348 Zikun Jiang 1,2 , Yongdong Wang 1 , Ning Tian 1,2 1. Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Nanjing 210008, China 2. Graduate School of Chinese Academy of Sciences, Beijing 100049, China(E-mail: zikunjiang@hotmail.com) The Jurassic system is well developed and exposed in vast areas of western Liaoning, China, and is characterized by a series of terrestrial pyroclastic rocks, yielding diverse fossil organisms such as plants, spores and pollen, bivalves, insects, and vertebrate fauna (e.g. birds and dinosaurs). The Middle Jurassic system in this region includes two formations from the ascending order, i.e. the Haifanggou Formation and the Tiaojishan Formation (=Lanqi Formation). The Tiaojishan For- mation is represented by intermediate extrusive and pyroclastic rocks, with intercalations of basic volcanic and sedimentary rocks. The Upper Jurassic system is represented by the Tuchengzi Formation, which consists of gray purple, purple-red shales, sandstones with large crossing-beddings. It is disconformably underlain by the Tiaojishan Formation and unconformably overlain by the Lower Cretaceous Yixian Formation. Recent isotope analysis investigations show that the geological age of these formations are debated, i.e. the late middle Jurassic to Late Jurassic for the Tiaojishan Formation and the Late Jurassic to Early Cretaceous Formations for the Tuchengzi Formation (Zheng et al., 2001; Swisher et al., 2002; Wang et al., 2004; Zhang et al., 2008; Zhang et al., 2009) In the Tiaojishan Formation the fossil wood specimens are well preserved with distinct growth rings and xylem structures. Plenty of wood taxa have been reported in the Tiaojishan Formation, which are ascribed to Cycadales and Coniferales, including 12 genera, such as Araucarioxylon, Taxodioxylon, Proto- podo-carpoxylon, Phylocladoxylon, Xenoxylon, Sciado-pityoxylon, Protosciadopityoxylon, Podocar- poxylon, Lioxylon, Pinoxylon, Sahnioxylon and Haplomyeloxylon (Wang et al., 2008). The investigations of our recent collection reveal more new wood taxa in this flora assemblage. Besides the fossil wood, impression and compression plant foliage specimens suggest that the flora in this formation is characterized by the dominance of cycads and ferns (which are systematically ascribed to the families of Marattiaceae, Osmundaceae, Dipteridaceae, Dicksoniaceae and Fili- cales Insertae Sedis), followed by ginkgophytes; conifers and sphenopsids are less frequent. Lots of permineralized rhizome materials have been reported in this formation showing anatomically preserved and diverse taxa belonging to fern families such as Osmun- daceae and Cyatheaceae. In the Tuchengzi Formation, the plant fossils are rare, except for few fossil wood, megafossils and dinosaur footprints. The fossil wood taxa include Protophyllocladoxylon franconium Vogellehner and Xenoxylon ellipticum Schultze-Motel; and some fossil plants associated with them, such as: fruit cluster of Czekanowskia: Leptostrobus marginaths Samylyna; reproductive organs of Pinaceae: Pityolepis sphenoides Zheng, P. pachyrachis Zheng, P. laxiformis Wang, P. pinquanensis Wang, Elatides leptolepsis Zheng, Schizolepis beipiaoensis Zheng, S. shangyuan- ensis Zheng, the seed of gymnosperm: Carpolithus fabiformis Zheng et Zhang.; and plant foliage, e.g. Podozamites sp., Brachyphyllum sp., Pagiophyllum sp. Sporo-pollen assemblage mainly consists of Classo- pollis, as up to 86.2%, other type such as fern spores are less than 5%, which indicate arid or semiarid climate (Zheng et al., 2001). Flora aspects of the Tiaojishan Formation indicate that the subtropical to temperate warm and humid climate prevailed during the late Middle Jurassic in Beipiao area (Wang et al., 2006). Growth ring pattern analysis of the fossil conifer wood demonstrates wood growing in a temperate climatic condition with distinct seasonal variation. In addition, the mean sensitivity (MS) index of growth rings shows the variation condition of the environment and the climate tolerance. In the Tuchengzi Formation, the floral assemblage is totally different from that of the Tiaojishan Formation, i.e. fossil plants are rare in the former formation. In the Tuchengzi floral assemblage, the cycads, ferns and ginkgophytes which show warm and humid environment almost disappeared, reflects a dry climate with small desert forests in it. The growth ring of the Tuchengzi Formation has a very wide early wood and very narrow late wood, which indicate a hot long summer and a cold shot winter with seasonal climatic variation. The present floral assemblages in the Middle to Late Jurassic Tiaojishan and Tuchengzi Formations provide palaeobotanical evidences for further exploring the palaeoclimate change and the evolutionary process of the terrestrial ecosystem across the Middle to Upper Jurassic in NE China. Acknowledgements: This study was jointly sup- ported by the National Key Basic Research Program of China (2006CB701401), the Innovation Project of CAS (KZCX-2-YW-154), and National Natural Sciences Foundation of China (NSFC 40972008). This is a contribution to UNESCO-IUGS project IGCP 506.
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Key words: Middle to Late Jurassic; The Tiaojishan Formation; The Tuchengzi formation; Flora assemblage; Palaeoclimate References: Swisher C.C., Wang X.L., Zhou Z.H. Further support for a Cretaceous age for the feathered-dinosaur beds of Liaoning, China: New 40 Ar/ 39 Ar dating of Yixian and Tuchengzi Formation. Chinese Sci- ence Bulletin, 2002, 47(2): 135-138. Wang W.L., Zhang H., Zhang L.J. Standard Sections of Tuchengzi Stage and Yixian Stage and Their Stratigraphy, Palaeontology and Tectonic- Volcanic Actions. Beijing: Geological Publishing House, 2004: 1-451. Wang Y.D., Li N., Yang X.J., et al. Jurassic Fossil woods. In: Zhang W., Li Y., Zheng S.L.,et al. (ed). Fossil wood of China. Beijing: China Forestry Publishing House, 2008: 120-174. Wang Y.D., Saiki K., Zhang W.,et al. Biodiversity and palaeoclimate of the Middle Jurassic floras from the Tiaojishan Formation in western Liaoning, China. Progress in Natural Science, 2006, 26 (Special issue): 222-230. Zhang H., Wang M.X., Liu X.M. Constraints on the upper boundary age of the Tiaojishan Formation volcanic rocks in West Liaoning-North Hebei by LA-ICP-MS dating. Chinese Science Bulletin, 2008, 53(22): 3574-3584 Zhang H., Wei Z.L., Liu X.M.et al. Constraints on the age of the Tuchengzi Formation by LA-ICP-MS dating in northern Hebei-western Liaoning, China. Science in China Series D: Earth Sciences, 2009, 52(4): 461-470. Zheng S.L., Zhang W., Ding Q.H. Discovery of fossil plants from Middle-Upper Jurassic Tuchengzi Formation in Western Liaoning, China. Acta Palaeontologica Sinica, 2001, 40(1): 67-85 (in Chinese with English abstract). 349
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