the reefs at Lengwu - Springer Link

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Guadalupian Algae-Sponge Reefs in Siliciclastic Environments the Reefs at Lengwu (South China) Compared with the Reef at Iwaizaki (Japan)

Jian-wei Shen, Brisbane and Toshio Kawamura, Sendai KEYWORDS: ALGAE-SPONGE REEF - SILICICLASTICENVIR()NMENT GUADALUP1AN

Summary Guadalupian reefs occur locally in Guangxi, Guizhou, Yunnan and Western Zhejiang, South China. Two types of Guadalupian reefs can be recognized, one is developed in carbonate platforms, e.g. those in the juncture areas of Guangxi, Yunnan and Guizhou; the other occurs in a littoral elastic shelf. The Lengwu reef in Western Zhejiang is a representative of the latter type, which is a major topic of this paper. Lcngwu algae-sponge reef, more than one hundred meters in thickness, are composed mainly of sponges, hydrozoans, algae, bryozoans, microbes and lime mud. Reef limestones sit on the mudstone interbcddcd with fine sandstone of the proximal prodelta facies and are overlain by coarse clasts of the delta front sediments. Lengwu reef displays a lens-shaped relief, dipping and thinning from the reef core, which is remarkably different from the surrounding sediments, showing a protruding relief. Sponges and microbe/algae form bafflcstone, bindstone and framestone of the reef core facies. Fore-reef facies is characterized by lithoclaslic rudslonc and bioelastic packstone. Reef limestone sequence is composed of three cycles and controlled by sea level changes and sediment influx. Such reef is unique among the Guadalupian reefs in South China, but seems similar in some aspects to Iwaizaki reef limestones of south Kitakami in Japan. Algae and microbes growing around sponges to form rigid structure in Lcngwu reef are a typical feature, which is distinctly different to Guadalupian reefs in a stable platform facies of Guizhou, Yunnan and Guangxi, South China. 1 INTRODUCTION Guadalupian reefs have been reported world widely from tropical to cool temperate zones in Permian time such as those in Texas and New Mexico (Pray and Estcban, 1977, Weidlich and Fagerstrom, 1998, 1999, Eagerstrom and Weidlich, 1999), Oman (Weidlich and Fli.igel, 1995), Thailand (Fontaine et al., 1982, Baird. 1990, Tabakh and Utha-Aroon, 1998), Slovenia (Fliigel ct al., 1984), Western Sicily (Fliigel and Reinhardt, 1989, Fl0gcl ctal..

Lt!NGWU(SOUTH CHIN,\) - IWAIZAKI (JAPAN) -

1991), Tunisia (Razgallah and Vachard, 1991; Toomey, 1991), Urals (Chuvashov, 1983, 1995), Japan (Sano ctal.. 1990; Kawamura and Machiyama, 1995; Sano et aI., 1996) and southwest of China (Fan ct al., 1990: Zhang et al., 1992). However, in the most part of South China. Guadalupian reefs arc not so common as Changhsingian reefs even though the South China (Yangtze block) was located in Permian tropical zone during Guadalupian time. Guadalupian reefs in South ('hina arc locally developed in the.iuncturc area of (}uizhou. Guangxi and Yunnan provinces, upper Yangtze region (Fan et al.. 1990; Zhang et ul., 1992), and exceptionally at Lcngwu (Fig.l), Tonglu County, Zhcjiang Province (Wang, 1987; Luo, ct al.. 199 1) in the lower Yangtze region. Guadalupian reefs in the upper Yangtze region are exposed in the carbonate sequences and developed in a stable carbonate platform facies, underlying and overlying beds all are carbonates. To the contrary, kcngwu reef occurs in a elastic sequence, overlying the mudstone-shale intcrbcddcd with sandstone and siltstonc and covered with coal-bearing deposits showing regressive characteristics. I.cngwu reel in Western Zhejiang is built by sponges and algae, whose composition is unique among the Permian reefs in South China, showing major differences fiom Guadalupian reef types in the middle and upper Yangtze region. Comparable reefs have been reporlcd from Palcoththys realm, especially from the south Kitakami of .lapan. Their sedimentary environment, palacogcography and partly reel: organisms are critical for comparisons. The purpose of this paper is to describe Lengwu reef facies, microfacics, vertical shifting, reef organisms, sedimentary environment, to discuss the palaeogeographic pt)sition of rccf and rccf development, and compare with cocwd reels in Palacotethvs reahn. These lines ,,,,'ill enable us to expand our understanding of the overall reef development throughout the Permian not only in stable platlk~rm of South China but also in active margin and ocean ic seamounts of Western Zhcjiang and .lapan.

2 GE()LOGICAI. SF.TTIN(, The late Guadalupian reel in Western Zhejiang is situated near l.cngwu village about 16-kin northwest of Tonglu County (Fig. 1). Lengwu ree flies in the core of the secondary syncline

Addresses: Dr. Jian-wei Shen, Departmcn! o lEarth Sciences, lJ n ivcrsity of Queensland, Q I,D 4{172.Austral ia, c-mail: shcn(o earth, uq.cdu.auDr. Toshio Kawamura, Geology, Department of Sciences, Miyagi University of Education, Sendal 980, Japan

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Fig.1 Locality of the Lengwu reef and palaeogeographical sketch map of Western Zhejiang in Maokouan age A. Location of Zhejiang province where Lengwu reef occurs B. Location of Lengwu reef in Western Zhejiang C. Sketch map showing the occurrence of Lengwu reef l imeslone D. Palaeogeographical map of Western Zhejiang in Maokouan age in the Zhcxi-Wannan platformal fold belt. It is overlain unconformably by the sandstone and conglomerate (PI. 25/ 7) of the Jurassic. Palaeogeographically, the initial sealevel rise and transgression in the Cisuralian led to a broad littoral plain to be formed in South China, where some littoral and swamp coal deposits accumulated. During the sea level rise, Su (Jiangsu)-Zhe (Zhejiang)-Wan (Anhui) paleoland was drowning, where shallow-water carbonate platform was formed. The platform sediments are rich in organic (pitch mineral) and silica substances, and rare in terrigenous clasts. Subsequent sea level fall led to form the wackestones interbedded with the calcareous mudstone and dolomite yielding abundant brachiopods. With a continuously sea-level fall during the late Guadalupian, Western Zbejiang was situated in a shallow-water bay. The sediments are mainly elastic rocks, siliceous rocks, stone coals and limestone lens. Locally a bay delta was developed. The

algal flat and algal-sponge reef were formed associated with delta deposits at Lengwu, Tonglu County. Permian strata at Lengwu, 956 m in thickness, are divided into the Donghua, Chihsian, Tingchiashan, Lengwu and Lungtan Formations in ascending order (Fig.2). 1. Chihsian Formation: The basal part (about 3 m in thickness) of the formation is characterized by silty shale intercalated with thin-bedded limestones and limestone lens. This part is correlated to the Liangshan Formation. The middle and upper parts are composed of dark-gray bioclastic limestone intercalated with argillaceous limestone, silty mudstone and siliceous rock. Cherts and thinbedded siliceous rocks occur in the limestones and become common upwards. The formation yields fusulinids, brachiopods, algae, foraminifers, echinoderms, corals, sponge spicules, bryozoans and gastropods, and about 369 m in thickness. Known fusulinids include Misellina claudiae (Deprat), Cancellina neoschwagerinoides (Deprat), Verbeekina minor Chert, Yangchienia sp., Parafusulina yabei Hanzawa, Nankinella sp., Sphaerulina sp., Eoparafusulina sp., Pseudofusulina japonica Chen, Pseudodoliolina sp.. 2. Tingchiashan Formation: The lower part is characterized by black mudstone and shale intercalated with carbonaceous siliceous rock, siliceous mudstone and calcareous shale. Mudstones contain phosphatic or calcareous concretions and argillaceous limestone lens. It is about 52 m in thickness. The upper part is composed of gray and black mudstone interbedded with quartz siltstone and sandstone, and intercalated with beds of calcareous shale and bioclastic limestone. Its thickness is about 148 m. Fossils include ammonoids: Tongluceras lengwuense Zhou, Michelinoceras sp., A ltudoceras sp., Paragastrioceras sp.; bivalves: Euchondria? sp., Schizodus sp.; brachiopods: Urushtenia maceus Ching, Dictyodostus sp., Orthotichia sp., Spiriferellina sp., Chonetes chonetoides (Chao), Leptodus sp., Derbyia sp., Retichonotes sp., Squamularia sp.; trilobite: PseudophiUipsia sp.; gastropods: Murchisonia sp.. 3. Lengwo Formation: Light gray massive reef limestones 115 m in thickness, later described in detail. Fossils are calcisponges, algae, bryozoans, echinoderms, brachiopods, corals, and fusulinids. Coral: Tachylasma sp., Asserculinia sp. and Duplophyllum sp.; Brachiopod: Urushtenia macens Ching, Aulosteges sp., Athyris sp., Dielasma sp., Enteletes cf. hemiplicatus Hall, Leptodus sp., Marginifera sp., Spirifer cf. tastubensis, Uncinunellina sp.; Bryozoan: Fistulipora sinensis Yoh; Polypora sp.; Fusulin id: Polydiexodina chekiangensis Sheng, P. tungluensis Sheng; Ammonoid: Michelinoceras sp.. 4. Lnngtan Formation: The formation is about 272 m in thickness. The lower part is characterized by gray-yellow quartz sandstone interbedded with silty mudstone, argillaceous siltstone and thin-bedded stone coal. The upper part is composed of black mudstone and siltstone intercalated with gray-yellow quartz sandstone, alum clay and thinbedded stone coal. Fossils are mainly terrestrial plants including Pecopteris sp., P. cf. lativenosa Halle, Gigantopteris sp., G. nicotianae folia Halle, Neuropteridium sp., N.

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Fig.2 Stratigraphic units and lithology of Permian rocks in Northern and Western Zhejiang

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