Permian and Triassic Radiolarians from the Western Guangxi Area, China
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Journal of Geosciences, Osaka City University Vol. 48, Art. 5, p. 81-93, March, 2005 Permian and Triassic radiolarians from the western Guangxi area, China , '~' /' YAO Akira*, KUWAHARA Kiyoko*, ,.. z:h. YOichi*, Lru Jianbo**, HAG Weicheng**, LUG Yunyi*** and KUANG Guodon*** * Department of Geosciences, Graduate School of Science, Osaka City University, Osaka 558-8585, Japan ** Department of Geology, School of Earth and Space Sciences, Peking University, Beijing 100871, P. R. China *** Guangxi Institute of Geology and Resources, Nanning, P. R. China Abstract Five sections, namely the Shipao section of Xilin, the Wuzhuan section of Donglan, the Shanglao section of Napo, the Lingma section of Wuming and the Longtang section of Pingxiang, of the Permian-Triassic sequence were microbiostratigraphically examined in the western Guangxi, China. These sections are composed mainly of shallow marine sediments in the Jiangnan Terrane which are almost the same lithofacies as those on the Yangzi Platform. Pennian radiolarians were found from siliceous mudstones, cherts and tuffs of the Dalong Formation in the Shanglao section. The horizons that yielded the Permian radiolarians are con-elated with the Neoalbaillella ornithoformis zone of Wujiapingian time. The Lingma section, which had been regarded as the Lower Triassic, contains the Permian-type radiolarians. The Shipao, Wuzhuan and Longtang sections yield the late Early Triassic radiolarians, and these horizons are con-elated with the Parentactinia nakatsugawaensis zone of late Spathian time. No radiolarian fossils were found from the lower - middle Lower Triassic in the western Guangxi area. Key-words: Permian, Triassic, radiolaria, Guangxi, Jiangnan Terrane, South China Paleozoic - Mesozoic of South China since 1991. From Introduction these works, firstly Yao et aJ. (1993) reported Late Paleozoic radiolarians from the Guizhou area on the The greatest mass extinction between Permian and Yangzi Platform and the Guangxi area in the Jiangnan Triassic times is one of the important events of the Ten-ane. Secondly Yao and Kuwahara (l999a) reported Phanerozoic history. It is considered that the faunal Middle - Late Permian radiolarians from the north Sichuan analysis of radiolarian assemblages through the Permian to area where is the northwestern margin of the Yangzi the Triassic indicates the actual conditions of the mass Platform, and Yao and Kuwahara (1999b, 2000) reported extinction in the marine plankton faunas. From this point Permian and Triassic radiolarian assemblages from the of view, the Permian - Triassic continuous sequences of Yangzi Platform. Thirdly Kuwahara et aJ. (2003, 2004) South China are required for radiolarian research. reported Late Permian radiolarians from the Laibin area, The senior author (YAO Akira) has continued the Guangxi in the Jiangnan Tenane. From these results, the Japanese-Chinese cooperative work by microbiostrati Permian and Triassic radiolarian faunal features in South graphical and micropaleontological methods on the China have been cleared, and the radiolarian zones have 82 Permian and Triassic radiolarians from the western Guangxi ar'ea, China been correlated with those of Southwest Japan. the Maokou Formation (the Middle Permian), the We did field survey as a part of cooperative work on Wujiaping Formation (the lower Upper Permian), and the November 2003 in the western Guangxi area (Fig. 1). We Changxing Formation (the upper Upper Permian). Except examined the sections of Permian - Triassic sequence and for the standard units, there are many lithostratigraphic collected rock samples for radiolarian biostratigraphical units because they have different lithofacies from the and faunal analyses. Here we report the result of standard units. The geologic age of these units is radiolarian occurrence and discuss its geological determined by many kinds of index fossils as fusulinaceans significance. and conodonts from limestones, ammonites from mudstones, etc. Geologic Setting The standard lithostratigraphy of the Lower to Middle Triassic in the terrane are as follows in ascending order The Upper Paleozoic to Triassic marine strata (Bureau of Geology and Mineral Resources of Guangxi extensively distribute in the Guangxi area (Bureau of Region, 1985): the Luolou Group (the Lower Triassic) and Geology and Mineral Resources of Guangxi Region, the Baifeng Formation (the lower Middle Triassic). The 1985), where is situated on the western part of the Jiangnan geologic age of these units is determined by index fossils Terrane (Fig. 1). The Jiangnan Terrane is regarded as the as bivalves, anunonites, etc. Caledonian Orogenic Belt which was formed to the south The stratigraphic relationship between the Permian of the Yangzi Platform and amalgamated to the Yangzi and Triassic is conformable except for some sections in Platform at Early Paleozoic time. Since Late Paleozoic which the unconformity is recognized. time the Jingnan Terrane has the similar geohistory with the Yangzi Platform. The Permian to Middle Triassic Study Sections strata in the Jiangnan Terrane are mainly characterized by carbonate rocks and clastic rocks deposited in the shallow The five sections (Fig. 2) in this study are described as sea environment. follows: The standard lithostratigraphy of the Permian units in the terrane are as follows in ascending order (Bureau of (1) Shipao section of Xilin Geology and Mineral Resources of Guangxi Region, Xilin is the capital town of Xilin County. It is located 1985): the Chuanshan Formation (the lower Lower in the northwestern marginal part of Guangxi Province and Permian), the Qixia Formation (the upper Lower Permian), is about 390 km northwest of Nanning (Fig. 2). The z o C') z o C\J ~ Post-Jurassic terranes • Massif • Jurassic terranes • Indo-China orogenic belt TLF: Tanlu fault ~ Pre-Jurassic terranes YZF: Yarlung Zangbo fault Fig. 1 Index map of the study area in South China. YAO Akira, KUWAHARA Kiyoko, EZAKI Yoichi, LIU Jianbo, HAO Weicheng, Luo Yunyi and KUANG Guodon 83 x Location of section Yangzi Massif •~ Jiangnan Terrane • Qinfang Terrane Fig. 2 Location of sections in the Jiangnan Terrane, the western Guangxi. R262 5 R271 5----t------'" R2 71 4----t----e R2 71 3---.---e R262 4 R2712 R262 3 R262 R2711 "- R2710 ci. ci. ci. ci. <J) R2709 <J) <J) <J) c- E O) <J) 0 :; ~ ig -!)1 u 0> -s ~ -0. sslms c: ... Q.l r---·---·:---1...... _. u -u <J) '"E 0 -;:: Q. -e: '" 0) 0 ... '" 0) Cl Emudstone J::'" Jg '"c: ~ J:: C ~ 0 c- 1: <J) o Q.l c- ~ 0 <J) L':':'J" , tuff o <J) .g chert ::J IIIIIIIIII Q.l ~ mlimestone m~m~ sandstone and ;~;~;~;~ conglomerate PIT boundary R2708 =- mudstone R2706 e limestone R2704 Shipao section R2702 R2700 R2698 Fig.3 Columnar section showing the horizons of R2696 radiolarian occurrence in the Shipao section. ~,li:::::::R2694R2692 Shipao section is in the north of Xilin and at the road cutting (Fig. 8a) which connects Xilin with Longlin. The E o location coordinates of this section is 24°30.683'N, 105° 05.781 'E. This section is composed of the Permian R2691 Sidazhai and Shaiwa Formations and the Triassic Shipao R2690 Formation. The strata of these formations strike generally Wuzhuan section 0 N60° Wand dip 40 S. Fig.4 Columnar section showing the horizons of The Sidazhai and Shaiwa Formations consist mainly radiolarian OCCUlTence in the Wuzhuan section. 84 Permian and Triassic radiolarians from th western Guangxi area, China of clastic rocks and volcaniclastic rock. The heet-like northea t and dip west gently. and dome-like ba altic rocks are observed as the intruded The Heshan Formation consist of cla tic , tuff and rock in the lower part of the Shaiwa Formation. The limestone which contains thinly bedded chert layers. The blocks of limestone conglomerate are included in the limestone of the uppermost part of He han Formation uppermo t horizon of the Shaiwa Formation. Rock contain fu ulinacean fossils. Chert samples were samples for radiolarian research were collected from 5 collected from the uppermost horizons (R2690 and R2691) horizons (R2617 to R2621) of the Shaiwa Formation. of this formation. The lowermost part of the Shipao Formation is The Luolou Fonnation is composed of lime tone, tuff compo ed of sandstone and conglomerate which directly and mud tone. The lime tone (microbialite) of the lowest cover the Shaiwa Formation. The andstone and Luolou Formation covers directly the lime ton of the conglomerate of the Shipao Formation grade upward into uppermo t He han Formation. The middle and upper part lnudstone which contains interbedded tuff layers. of the Luolou Formation consi t mainly of mud tone which Siliceou lnudstone samples were collected from 4 contain interbedded tuff layers. This formation i covered horizons (R2622 to R2625: Fig. 3) of the Shipao Formation. confonnably by the alternating bed of and tone and mud tone of the Baifeng Formation (Fig. 8b). Tuff samples (2) Wuzhuan section of Donglan (R2692, R2693 and R2713 to R2715) and lnud tone The Wuzhuan section is about 20 km outhwest of sample (R2694 to R2712) were collected from the middl Donglan which is the capital town of Donglan County, and and upper parts of the Luolou Formation (Fig. 4). about 205 kIn northwest of Nanning (Fig. 2). The ection i at the road cutting. The road connect Barna with (3) Shanglao section of Napo Donglan. The location coordinate of thi ection is 24° Napo i the capital town of Napo County. It i located 21.799/N,107°19.974/E. The ection i compo ed of the in the we tern marginal part of Guangxi Province and i Upper Permian Heshan Formation, the Lower Triassic about 270 km west of Nanning (Fig. 2). The Shangla Luolou Formation and the Middle Tria sic Baifeng section is to the south of Napo and at the road cutting. The Formation. The strata of these formations trend north- location coordinates of this section is 23° 19.246/N, 105° R2 669--t---t-~-+--t--t--t--+--t---i.-+--+--e R2667=-~t=~~=!=:!~=t=~f=:;~-~"~=~;-t:--::;'''~=~;-l=-=+l-=~~ R2665 R2 663--+--+----t-+---+----t--+--+-----if---------f-----l R2661 R2659 I!!!mudstone ~t=:::t==t~I=:::t==t~ R2657 ~silic.ms R2655 R2652 ~tuff.ms E R2649 o IITIIIIIIJ chert Fig.