J ournal of China University o f Geosciences , Vol. 17 , No. 3 , p. 221 - 230 , September 2006 ISS N 1002 - 0705 Printed in China Ordovician Cephalopod Biofacies of South China and Its Provincialization Xiao Chuantao*(肖传桃) Faculty o f Earth Sciences , China University o f Geosciences , Wuhan 430074 , China ; Geosciences College , Y angtze University , J ingz hou 434023 , China Chen Zhiyong (陈志勇) Faculty o f Earth Sciences , China University o f Geosciences , Wuhan 430074 , China ; Qinghai Oil f ield Com pany , Dunhuang 736202 , China Liu Li (刘莉) He Youbin (何幼斌) Geosciences College , Y angtze University , J ingz hou 434023 , China ABSTRACT :The research on biofacies and its provincialization is of important significance not only for the increasing of precision of stratigraphic subdivision and correlation in South China, the reconstruction of ancient environment and paleogeography and even the guiding of oil and gas exploration, but also for the study of paleobiogeogrphy and sea level changes of southern China in Ordovician. On the basis of the studies of the ecological characteristics of Ordovician cephalopods from South China , eighteen cephalopod biofacies are recognized and described :(1)Open platform Proterocameroceras biofacies ;(2) Restricted platform Pseudoectenolites-Xiadongoceras biofacies; ( 3 ) Open platform Retroclitendoceras- Pararetroclitendoceras biofacies;(4)Open platform Prona jaceras-Mamagouceras biofacies;(5) Shelf slope-basin Cyclostomiceras biofacies;(6) Open platform Cameroceras-Cyrtovaginoceras biofacies ; (7) Open platform Coreanoceras-Manchuroceras biofacies;(8) Shelf slope-basin Kaipingoceras- K yminoceras biofacies;(9) Inner shelf Bathmoceras-Protoc ycloceras biofacies;(10) Middle shelf Dideroceras-Ancistroceras biofacies;(11) Deep-water shelf Lituites-Cyclolituites biofacies;(12) Stag- nant basin Lituites-Trilacinoceras biofacies;(13) Deep-water basin Paraendoceras-Sactorthoceras bio- facies;(14) Deep-water shelf Sinoceras-Michelinoceras-Disoceras biofacies;(15) Deep-water shelf Be loitoceras-Jiangshanoceras biofacies;(16) Deep-water shel-f basin Eurasiaticoceras biofacies ;(17) Shelf-slope Jiangxiceras-Yushanoceras biofacies;(18) Deep-water basin Michelinoceras biofacies. The cephalopods of these biofacies, their ecological characteristics, and living conditions are elucidated in this article. The association law of cephalopod biofacies in time and space shows that there were three cepha- lopod biofacies provinces in South China during the Ordovician, i. e. , Yangtze biofacies province , East Guizhou (贵州)-West Hunan (湖南) biofacies province (mixed-type biofacies province), and Central Hunan-West Zhejiang(浙江) biofacies province. It is suggested that differentiation of cephalopod biofa- cies was mainly controlled by sea level changes and tectonic evolution. The differentiation is obvious dur- ing lower sea level and not developed during high sea level. KEY WORDS:cephalopod biofacies, cephalopod biofacies province , sea level changes, Ordovician , South China. INTRODUCTION Bio facies refers to an association of org anism- This paper is suppo rted by the National Natural Science Foundation of eco logy and sedim entary characteristics , w hich can C hina (No. 40272060). reflect a specific ancient environment. Research o n *C orresp on ding author :ctxiao188 @yahoo. com. cn biofacies and its provincialization is significant no t o nly for increasing the precisio n of stratigraphic sub- M anu scrip t received March 10 , 2006. M anu scrip t accepted June 25 , 2006. divisio n and co rrelation , reconstructing ancient envi- 222 Xiao Chuantao , Chen Z hiyo ng , Liu L i and He Yo ubin ronments and paleo geog raphy , and oil and gas ex plo- ance to fo rw ard mov em ent , and a small siphuncle and ration , but also fo r the study of interco ntinental pa- large chambe r are favorable to reg ulate the fluids leobiogeog raphy and sea level chang es. w ithin them . In contrast , cephalo pods w ith a hig h Altho ug h the term biofacies w as established expansion rate , large siphuncle , and sediments w ith- mo re than 30 y ears ago by Bouco t (1981) and Schafer in chambers are po or sw immers and suitable for a (1972), detailed studies have only beg un to em erge shallo w-w ater enviro nment (Fig. 1). in the last few years. There is little research on the paleoecolo gy o f O rdovician cephalopo ds (Zhou , CEPHALOPODS BIOFACIES 2000 ;Xiao and Pan , 1997 ;Xu and Xu , 1986 ). Open Platform Proterocameroceras Biofacies Therefo re , m ore studies on biofacies a re required. It is mainly found in the Xinchang S tage (China This ar ticle presents new research concerning the O r- Stratig raphic Group , 2002) in the Upper Yang tze dovician cephalopo d biofacies o f southern China. area , this biofacies is low in diversity , dominated by O n the basis of the studies on the paleoecological P roterocameroceras and associated with Camero- characteristics o f Ordovician cephalopods from parts ceras, Dayongoceras , and Ellesmeroceras. Cephalo- of South China and the systematic co llectio n and pods of this biofacies a re characterized by a medium- analysis of O rdovician cephalo pods fro m m ore than sized shell , hig h expansion ra te and large siphuncle , ten provinces o f So uth China (Xiao and Pan , 1997 ; therefore , they are no t able to sw im rapidly . Addi- Bureau of Geolog y and M ine ral Resources of H unan tionally , they are mo stly preserved in bioclastic lime- Pro vince , 1997 ;Bureau o f Geo logy and Mineral Re- stone and intraclastic limestone , indicativ e of an sources o f Zhejiang Province , 1997 ;Bureau of Geolo- open-platform enviro nment. g y and Mineral Resources of Jiangxi Province , 1997 ; Bureau of Geolog y and M ineral Resources of Guizhou Restricted Platform Pseudoectenolites-Xiadongoceras Pro vince , 1997 ;Committee o f Chinese Stra tig raphic Biofacies Dictionary , 1996 ;Wang et al. , 1987), the authors This biofacies occurs mainly at the low er par t of have presented the paleoeco logical characteristics the Xinchang Stage (Xiling xia Form ation ) in the pro vided by the da ta and their relationships with sed- Yichang , Songzi , and Tong shan areas of H ubei imentary facies. As a result , 18 cephalopod biofacies Province. It has a high dive rsity of elements do mina- and three cephalopo d biofacies provinces have been ted by Pseudoectenolites and characterized by X ia- recog nized. dongoceras. The co mpo nent members include Changjiangoceras , Dakeoceras , Paraeburoceras , ECOLOGY OF CEPHALOPODS Neoeburoceras, Zhangnanoceras , Anguloceras , Cephalopods are m arine zoo phagous inverte- Clarkoceras , P araconoceras , E llesmeroceroides , and brates , mo st of w hich are nekto nic , w ith so me P arahuaiheceras apart fro m Pseudoectenolites and plankto nic and benthonic org anism s. The lifesty le of X iadongoceras. T hey hav e comm on characteristics , cephalopods depends largely on their shapes and namely , a small-to-medium shell , high expansio n structures. Of the planospiral cephalopods , tho se rate , and a siphuncle lo cated near to the par abdomi- with tig ht spiral , sharp abdo minalis , flattened and nalis , w hich indicates that cephalopods of this bio fa- streamlined shell , sm ooth shell , and complicated su- cies are unable to get used to rapid sw im ming . In ad- ture m ostly adjust to rapid sw imming in deep-w ate r. dition , they are m ostly preserved in dolo rudite. A s a In co ntrast , cephalopods with loose spiral , ventri- result , this biofacies represents a restricted shallow- cous shell , w ell-developed o rnamentation , and simple w ate r enviro nment. suture are unable to become accusto med to rapid sw imming and deep-w ater life , therefore , mo st of Open Platform Retyoclitendoceras-Pararetroclitendo- them are benthonic or saltant sw im in shallow-w ate r. ceras Biofacies H ow ev er , or thomo rphic cephalopo ds are situated dif- This bio facies is mo stly distributed in the m iddle ferently. Cephalopo ds w ith a lo ng shell , low ex pan- part of the Xinchang S tage (N anjing guan Fo rm ation) sion rate , small siphuncle , and no sediments w ithin in East Sichuan , Yichang , Songzi , and Tong shan ar- chambe rs are g ood swim mers and suit a deep-w ater eas of H ubei Province. It is com posed of Retrocliten- enviro nment , because low expansio n rate and no sed- doceras , Pararetroclitendoceras, Sanxiaoceras , Pro- iments in chambers are favo rable fo r reducing resist- terocameroceras , and Escharendoceras. M ost of the O rdo vician Cephalo pod Bio facies o f South China and Its P rov incializa tion 223 genera are w idespread and found in many lo calities a- expansion rate , w hich show s that the cephalopods o f round the w orld. The cephalopods of this biofacies this biofacies are able to become accustomed to mo re are characte rized by a dorsiventrally co mpressed si- rapid sw im ming . M oreover , they are mo stly phuncle and abdominal , curved do rsal part , and low preserved in thick calcsparite intraclastic limesto ne. Figure 1. Environmental distribution of important Ordovician cephalopods in South China. 224 Xiao Chuantao , Chen Z hiyo ng , Liu L i and He Yo ubin Therefo re , this biofacies is indicative of fo rd environ- features indicate that cephalopo ds of this biofacies are m ent , open platfo rm , favo rable to reserving oil and suitable for shallow w ate r and bentho nic sw imming gas. and represent an open platform environment. Open Platform Pronajaceras-Mamagouceras Biofacies Open Platform Coreanoceras-Manchuroceras Biofacies Developed chiefly in the upper par t of the Xin- This bio facies is m ainly distributed in the chang S tage (Fenxiang Formation) in the Middle Daobaow an Stag e of East Sichuan , Yichang and Yang tze a rea such as East Sichuan and the Yichang , Tongshan areas o f H ubei , and the Lo we r Yang tze S ong zi , and To ng shan areas of H ubei Province , this district.