中国科技论文在线 http://www.paper.edu.cn Chinese Science Bulletin © 2007 Science in China Press ARTICLES Springer-Verlag The first discovery of Permian conodont fauna from peri-Gondwana cool water facies in Tibet, China ZHENG YouYe1,2, XU RongKe1,3, WANG ChengYuan4† & MA GuoTao1 1 Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China; 2 Research Institute of Geological Survey of Tibet Autonomous Region, Lhasa 850000, China ; 3 Research Institute of Geological Survey of Gansu Province, Lanzhou 730050, China; 4 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China The Angjie Formation and Xiala Formation, present in the Shiquanhe area of Gar County in the western part of Gangdise, Tibet, belong to the Gangdise stratigraphic subregion. Conodonts have been found in the Angjie Formation, and they permit an age determination of Early to Middle Permian for that formation. The age of the Xiala Formation could be late Middle Permian. Whether the Late Permian marine deposits are present in this area still needs to be determined, but it is possible that the lower part of the Xiala Formation overlaps partly the upper part of the Angjie Formation. More importantly, the study has brought about a finding of typical peri-Gondwana cool water facies conodonts, namely, Vjalovognathus sp. nov. x. This is the first report and brief description of a conodont fauna from peri-Gondowana cool water facies in China. It indicates that the Gangdise stratigraphic subregion can be subdivided; the western part belongs to peri-Gondwana cool water facies, and the eastern part belongs to Tethys. Gondwana, cool water facies, conodont fauna, Vjalovognathus, Gar County, Shiquan River, Tibet Permian conodonts are reported herein from the Angjie it provides important biostratigraphic data for correlat- Formation in the Shiquanhe area, west Gangdise, Tibet. ing strata between Gondwana and Tethys and for inter- It has been debated whether Late Permian marine depos- preting the tectonic evolution of Tethys. its are present in this area. Most authors considered that there are no Late Permian marine deposits there[1―8]. 1 History of lithostratigraphy and chara- They assigned basically the Angjie Formation and Xiala cteristics of this area Formation to Early-Middle Permian. Changhsingian Late Paleozoic strata crop out in the Shiquanhe area, deposits were found at the type locality of the Jian- located within the Zuozuo fault uplift zone (possibly zhanong Formation in Geize County, but those are non- equivalent to the western part of the Longger fault uplift marine deposits[1,9]. There are no Late Permian marine zone) between the Gangdise volcanic-magmatic arc and deposits dated by conodonts in the Shiquanhe area of Shiquanhe-Sainza-Jiali suture zone. Guo et al.[13] divided Gar County. In recent years, some outcrops of the Jian- the strata, in ascending order, into the Naziduopo, Yang- zhanong Formation have been found in the Geize area, weishan, and Zuozuo formations. The Naziduopo and those strata all have been dated back to the Middle [10―12] Permian . Received June 1, 2006; accepted January 25, 2007 GEOLOGY The finding of Permian conodonts in the Shiquanhe doi: 10.1007/s11434-007-0168-2 †Corresponding author (email: [email protected]) area, Tibet is very helpful to dating the age of the Angjie Supported by the Chinese National Key Project for Basic Research (Grant No. Formation. More important is the discovery of Permian 2002CB412610), the National Natural Science Foundation of China (Grant Nos. 40542008 and 40672012) and Chinese Geological Survey Project (Grant No. cool water conodonts of this part of peri-Gondwana, as 200213000009) www.scichina.com www.springerlink.com Chinese Science Bulletin | May 2007 | vol. 52 | no. 9 | 1231-1237 转载 中国科技论文在线 http://www.paper.edu.cn Formation consists of sandstone in the lower part and will be published in another paper). clastic limestone and black slate in the upper part; its base is not exposed, and there is no fossil record from 2 The locations of the sections and de- this formation, but it was dated as Early Permian ac- scription cording to regional correlation.The Yangweishan For- mation consists of bioclastic limestone and micrite, 2.1 The Langjiu Power Station section in Gar yielding corals, brachiopods, foraminifers, bryozoans, County bivalves, fusulinids and some other fossils. It was dated This section is located in the western part of Zuozuo [13,14] as late Chihsian Stage of the Early Permian . The Township, about 20 km east of Shiquanhe Town, in Gar Zuozuo Formation, composed of a suite of dolomites, County, Tibet (section 1 in Figure 1). The section begins contains no reported fossil record. It was considered to from the Langjiu Power Station (80°20′5E, 32°23′58″N), [14] be Late Permian . The Bureau of Geology and Mineral and terminates near Tangnale (80°21′28″E, 32°29′38″N); Resources of Tibet Autonomous Region has abolished it is about 10 km long, in which the succession of the these three formation names mentioned above, and has Permian system is as follows (Figure 2): assigned the lower part of the Naziduopo Formation to the Carboniferous Laga Formation and the upper part to the Late Carboniferous-Early Permian Angjie Formation. The Yangweishan Formation was considered to be equivalent to the Xiala Formation, but maybe a little higher than this Formation; its lower limit could be mid- dle-late Early Permian, but it could extend up to Late Permian (the Permian System was treated as two-fold at that time). The upper limit of the Xiala Formation is not younger than the Maokouan Stage. The Zuozuo Forma- tion was considered to be equivalent to the basal part of the Jipuri’a Formation (with adoption of a three-fold Permian System, its upper limit is not younger than the end of the Middle Permian.)[10]. The Chengdu Geology and Mineral Resources Institute (2002) adopted a three-fold Permian and assigned the Laga Formation, Angjie Formation and Xiala Formations to the Late Carboniferous to Early Permian, Early Permian and Middle Permian, respectively (The Southwest Pro- Figure 1 The location of the sections. gramm Office of Geologiccal Survey Bureau of China: Stratigraphic Subdivision and Correlation of the Qing- Overlying strata: Early Triassic Tangnale Formation consists of hai-Xizang Plauteau (unpublished)). sand-and pebble- sized intraclastic dolomite and massive dolo- The definition of the Laga, Angjie, and Xiala forma- mite, yielding conodonts: Pachycladina obliqua Staesche 1964, Pachycladina cf. tridentata Z. H Wang et Cao 1981; tions in present paper adapted the point of views in the Pachycladina spp., Neohindeodella triassica Müller, 1956: Stratigraphy (lithostratigraphic) of the Tibet Auto- Cornudina sp., Hadrodontina sp., Hibbardella sp. etc. monous Region compiled by Bureau of Geology and -------Parallel unconformity------- Mineral Resources of Tibet Autonomous Region, but the Xiala Formation Px) 733.44 m first two authors of the present paper have found that the 14. Gray-black, massive silty micrite 180.48 m Zuozuo Formation is quite different from the Jipuri’a 13. Gray, massive silty siliceous limestone 175.61 m Formation in lithological characters and biota. Also, be- 12. Gray, massive silty siliceous limestone intercalated with purple thick siliceous rocks 134.97 m cause Triassic conodonts have been found from the 11. Dark gray, massive siliceous calcilutite intercalated with gray- Zuozuo Formation, the first two authors of the present white silty sparite 64.12 m paper have named a new unit called the Tangnale For- 10. Dark gray, massive siliceous calcilutite 11.80 m mation instead of previously Zuozuo Formation (This 9. Gray, massive silty calcilutite 88.28 m 1232 ZHENG YouYe et al. Chinese Science Bulletin | May 2007 | vol. 52 | no. 9 | 1231-1237 中国科技论文在线 http://www.paper.edu.cn ARTICLES ARTICLES Figure 2 The Langjiu Power Station Permian section and the positions of samples. Er, Rigongla Formation; Td, Tangnale Formation; Px, Xiala Formation; Pa, Angjie Formation; HS-36, Sample positions and numbers. 8. Dark gray, medium-thin bedded bioclastic siliceous limestone 14. Grayish, medium- to thin-bedded fine-grained- calcirudite in- intercalated with calcareous sandstone, yielding brachiopods, tercalated with yellow brown sandy slate crinoid stems, and bryozoans 23.69 m 59.00 m 7. Dark gray, massive siliceous limestone alternated with thin- 13. Gray, medium- to thin- bedded grain-caorse sparite, yielding bedded siliceous limestone 8.53 m conodonts in sample HS-64: Mesogondolella sp.nov., Meso- 6. Dark gray, purple, medium- to thin-bedded bioclastic siliceous gondolella sp. 22.61 m limestone yielding brachiopods and crinoid stems 45.96 m Underlying strata: Laga Formation: Medium- to thick-bedded -------Conformity------- fine-grained quartz sandstone intercalated with gray-green Angjie Formation (Pa) > 215.77 m thin-bedded shale. 5. Dark gray, medium- to thin -bedded silty calcilutite 36.99 m 4. Gray, medium-bedded bioclastic calcilutite intercalated with thin- bedded silty limestone, yielding foraminifers, brachipods, and crinoid stem fragments 16.77 m 3. Dark gray, medium-bedded micrite intercalated with thick- bedded silty limestone, yielding brachiopods, ostracods, cri- noid stems, and algae fragments. Sample HS-40 (Coordinate: 80°22′1″E, 32°2′31″N) yields conodonts: Mesogondolella cf. stampflii, Pb element of gondolellids, Pa element of gondolellids, 4.78 m 2. Brown-yellow, medium-thin bedded coarse-grained-calcareous Figure 3 Section of the Permian and sampling location at Yangwei sandstone, yielding brachiopods and bryozoans. 4.78 m Mountain. 1. Thick-bedded bioclastic micrite (bottom not exposed). Samples HS―41, 43 yield abundant algae, corals, brachiopods, bryo- 3 Geologic ages of the Angjie Formation zoans, crinoid stems, and foraminifers. and Xiala Formation Sample HS ― 44 (80°20′57″E, 32°23′59″N) yields conodonts: Vjalovognathus new sp. x, Hindeodus sp. Pa The Angjie Formation was named in 1980 by the Ti- element, Pb element of gondolellids, M element of gon- dolellids >152.45 m betan comprehensive geologic team, and it was assigned to the Late Carboniferous.