PROGRESS IN NATURAL SCIENCE Vo l .13 , No .11 , November 2003 Early Cambrian eodiscoid trilobites of the Yangtze Platform and their stratigraphic implications＊ YANG Aihua , ZH U Maoy an＊＊ , ZHANG Junming and LI Guoxiang (Nanjing Institute of Geology and Palaeontology , Chinese Academy of S ciences, Nanjing 210008 , China) Received June 6 , 2003 ;revised June 16 , 2003 Abstract Analysis of the taxonomy and stratigraphic distribution of the Early Cambrian eodiscoid trilobites of the Yangtze Plat- form indicates that species of Tsunyid iscus and Hupeidiscus can be used for biostratigraphic correlation .T .aclis occurs only in the lower Qiongzhusian, T .armatus occurs in the low er and middle Qiongzhusian , w hile T .niu titangensis and T .tingi occu r mainly in the middle and upper Qiongzhusian , w ith only T .tingi extending upw ard into the low er Canglangpuian .H .orienta lis first appears in the upper Qiongzhusian , reaching peak abundance in the lower Canglangpuian and becoming extinct above the Drepanuroides Zone .Biostrati- graphic and lithostratigraphic correlations indicate that the limestone in the low er part of the Mingxinsi Formation , the Upper M ember of Jiumenchong Formation , and the upper part of the Middle Member of the Huangbailing Formation , can be correlated with each other as Huped iscus, an index fossil of the low er Canglangpuian, is abundant in all these units.The low er part of the Niutitang and Jiumenchong formations in eastern Guizhou , w hich mainly represent Qiongzhusian strata, can be correlated with the Low er Member of the Huangbail- ing Formation .The basal part of the Niutitang Formation , w hich may be equivalent to the Upper Meishucunian Shiyantou Formation in eastern Yunnan , is very condensed .Well-preserved sponge faunas and non-mineralized fossils in the lower part of the Niutitang and Het- ang formations are not older than Qiongzhusian in age. Keywords: eodiscoids, trilobites, black shale, stratigraphy, Early Cambrian, Yangtze Platform, South China . Lower Cambrian black shales are w ell developed 1 Synopsis of stratigraphic sections in the transitional region of the Yang tze Platform . How ever , because of the rarity of index fossils, sub- 1 .1 Eastern Guizhou Province division and stratigraphic correlation of these shales Longshancun section:This section is located at remain controversial[ 1 ～ 6] .Eodiscoid trilobites are Yonghe , Weng' an County , Guizhou Province (Fig .1 abundant in certain parts of the black shales , but ④).Here the Neoproterozoic-Low er Cambrian se- trilobite specialists are in disagreement over the tax- quence is well exposed .The Lower Cambrian succession onomy and stratigraphic distribution of these fossils . Consequently , the usefulness of these trilobites to the correlation of the Lower Cambrian black shales of the Yang tze Platform and beyond has been limited . Based on the results of recent investigations on the Niutitang and Jiumenchong fo rmations of eastern Guizhou Province and the Huangboling Formation of southern Anhui Province , we here revise the taxono- my and clarify the stratig raphic distribution of the Lower Cambrian eodiscoids of the Yangtze Platform . In addition , w e use these fossils to develop a new set of stratig raphic correlations of the Lower Cambrian black shales . Fig .1 . Geographic maps show ing the locations of investigated sections, note the section numbers are the same as in Fig .2 . ＊ Supported by the National Natu ral Science Foundation of China (Grant Nos.40232020 and 40172002), the Chinese Ministry of Science and Technology (Grant No .GT 2000077700) ＊＊ To w hom correspondence should be addressed .E-mail:myzhu @nigpas.ac .cn 862 Progress in Natu ral Science Vol.13 No .11 2003 consists (in ascending o rder ) of the Niutitang , the Niutitang Form ation (the lowest occurrence of M ingx insi and Jinding shan formations .The Niuti- this trilobite is 16 .8 m above the Dengying tang Formation is composed of black shales and dis- dolomite).The Ming xinsi Formation , w hich consists conformably overlies the upper dolomite member of mainly of limestone with trilobites and archaeocy- the Dengy ing Formation .Tsunyidiscus niutitangen- athids , conform ably overlies the Niutitang Formation sis has been found in the lower and middle parts of (Fig .2(4)). Fig.2 . Stratig raphic correlations of the Low er Cambrian black shales of South C hina (fossil occu rrences in each section are based on our own new data).1 , dolomite ;2 , limestone w ith intercalations of black shale ;3 , silicastone;4 , carbonaceous mudstone;5 , siltstone and mudstone;6 , siliceous m udstone ;7 , limestone ;8 , carbonaceous shale;9, black shale ;10 , carbonaceous silty mudstone ;11 , siltstone; 12 , phosphatic dolomite;13 , interbeds of siliceous siltstone and muddy siltstone ;14 , muddy limestone ;15 , mudstone;16 , carbonaceous siltstone;17 , Middle Devonian ;18 , fault;19 , barite ;20 , siliceous siltstone;21 , phosphatic dolomitic concretions;22 , phosphatic con- cretions;23 , stone coal;24 , limestone concretions;25 , spicule;26 , rhabdopleurids;27 , complete sponges;28 , bivalved arthropods. (1)Meishucun section , Jinning County , Yunnan ;(2)Gezhongw u section , Zhijin County , Guizhou ;(3)Songlin section , Zunyi County , Guizhou ;(4)Longshancun section , W eng' an County , Guizhou ;(5)Huanglian section , Songtao County , Guizhou ;(6)Wuhe section , Taijiang County , Guizhou ;(7)Pangw angcun section , Dongzhi County , Anhui;(8)Lantian section , Xiuning Coun ty , Anhui;(9)Wu- jialing section , Jiangshan County , Zhejiang . Huanglian section:This section is located on the (Sphenothallus)15 m above the base of the forma- eastern limb of the dissected Songtao Anticline (Fig .1 tion .The upper member consists of dark gray argilla- ⑤).Here the Lower Cambrian successions are well ceous limestone w ith trilobites , including Hupeidis- exposed and consist of the (uppermost Proterozoic) cus sp ., Sinodiscus changyangensis and Metared- Liuchapo and the basal Cambrian Jiumenchong , Bian- lichia sp .[ 7] (Fig .2(5)). machong , Balang and Qingshudong formations[ 7] . The Jiumenchong Formation conformably overlies the Wuhe section:This section is exposed along the Liuchapo Fo rmation , w hich consists of black silicol- Qingshui River from Wuhe to Gedong , Taijiang County , ites (cherts)and phosphatic siliceous shales .The Jiu- Guizhou Province (Fig .1 ⑥).The Lower Cambrian suc- menchong Fo rmation is subdivided into tw o mem- cession consists of the Liuchapo , Jiumenchong , Bianma- bers .The low er member consists of black shale yield- chong , Balang and Tsinghsutung formations.The litholo- ing bivalved arthropods (Sunella)and tubular fossils gy of the Jiumenchong Formation is similar to that of the Progress in Natural Science Vol.13 No .11 2003 863 same formation in the section at Huanglian .Hupeidiscus occur in the limestone at the topmost part of the Jiumen- orientalis (Fig .3(a), (b))and Hsǜaspis guizhougensis chong Formation (Fig .2(6)). Fig.3 . (a)～ (c)Hupeidiscus orientalis (Chang , 1953).(a), (b)from the upper part of the Jiumenchong Formation in the Wuhe sec- tion near Taijiang County , Guizhou , (c)from the base of Bianmachong Formation in Bageng section near Taijiang County , Guizhou ;(a) cranidium , GT VI-14 ;b .pygidium , GT VI-15 .(c)cranidium , GTV-1b .(d), (e) Tsu nyidiscus niu titangensis (Chang , 1966)from the Niutitang Formation in the Longshancun section near Weng' an County , Guizhou ;(d)cranidium , WDc-6 ;(e)pygidium , W Dc-5 . (f), (g), (h)Tsunyid iscus armatus (Zhang et Zhu , 1980), from the Niutitang Formation in the Longshancun section near Weng' an County , Guizhou ;(f) cranidium WDc-13 ;(g)pygidium W Dc-15 ;(h)exoskeleton , W Dc-16 , ×15 .(i) Tsunyidiscus aclis Zhou , 1975 , from the base of the “ black shale unit” of Yu' anshan Formation, pygidium (by Steiner et al., 2001). 1 .2 Southern Anhui Province Lantian section :This section is located in north- eastern Xiuning County (Fig .1 ⑧).The Piyuancun Pangwangcun section:This section is located in Formation is similar lithologically to rocks in the southeastern Jianxin , Do ngzhi County , w here it is Pangw angcun section .The Hetang Form ation con- exposed along the road from Pangw ang Village to formably overlies the upper member of the Piyuancun Do ngzhi County Town (Fig .1 ⑦).The section starts Formation , the lower part of w hich consists of about in the Piy uancun Fo rmation .Succeeding strata con- 20 m of “ algal stone coals” containing complete sist of the Huang boling Formation and the lower part sponges (Fig .2(8)). of the Yang liugang Formation .The upper member of the Piy uancun Formation is composed of about 23 m 2 Taxonomic revision and stratigraphic dis- of siliceous sandstone w ith intercalations of carbona- tribution of Early Cambrian eodiscoids ceous shale .In addition , lenticular limestone beds oc- cur in the basal part of this member .The Huangbol- To date , 12 genera and 51 species of eodiscoids ing Formation consists of three members .The low er have been reported and described from the Early member is composed of about 32 m of “alg al stone Cambrian of the Yang tze Platform .Again , how ever , coal” and black carbonaceous shale containing sponge the taxonomy of these fossils is controversial[ 8～ 11] . spicules .The middle member , about 40 m thick , The most recent investigation , based on published contains limestones w ith H upeidiscus orientalis .The type specimens and new material, revealed that only lower part of the upper member is composed of about seven eodiscoid