／凡} bY C. E. M itchell', Chen X[12, S . M . BergstrbM 3, Zhang Yuan-dong2, Wang ZhI-ha02, B. D . Web勿4 and S. C. Finne-y5 D efinition of a global boundary stratotype for the D arriw ilian Stage of the O rdovician System

I I)epartm ent qf'G eologv, dic State U iiiversit) ‘，／N ew York at B yf}do, Buflato, N Y 14200-3050, USA 2 Van.jing Institute of'G eolog ) and Paleontolog}，3 9 B e}png E ast Road, N anjing 2 /0008, C hina 3 I)epartm ent (?f*G eologi‘二／S( io lc}、O hio ,State U niversitv, C oluttibus, O H 43210-1,397,U SA 4 C entre ／‘，，Ecostratigraph.N and Palaeobiology, M acquarie U niversiA-, N SW 2109, A ustralia, 5 D epartm ent‘，／G eological Sciences (itG diftm aa State U niversitv, Lo，ng Beach, C ahfi)rnia 90840, U SA

The International C onunission on Stratigrap hic N om en- provincially based, regional subdivisions are still actively used. T he c la ture a nd th e lU G S E xec utive C o m m ittee ha ve O rdovician System w as first established in the British IsIcs and con- sequently the B ritish series, although also based on local and often recenth , approved selection 。，／‘，global stratot}vpe sec- endem ic biotas, have been w idely em ployed as a lingua ft anca for tion and point defining the base of． the second stage of international correlation w ithin the O rdovician. G iven these facts, the M iddle O rdovician Series. This stage is nained the adoption ofthe new global subdivisions and nom enclature w ill be a -raclual process. N evertheless, several im portant first steps have D arriw ilian Stage “力er the A ustralian regional stage o／ been accom plished, including the first. form ally ratified proposal for thesaine name, with which itshares identical definition a global O rdovician stage. and scope. The base o0 he D arriw ilian Stage is．fi xed at Early in 1996. by a 9 0 % m ajority, the T itular m em bers of the O rdovician Subcom m ission voted in favor of a division of the sys- the base 可the U ndulogC}raptus austrodentatus B iozone in tern into three series nam ed the Low er, M iddle. and U pper O rdovi- o section through the N ingkuo Shale exp osed at H uang- cian. This provides the basis for the next step} that is, to adopt a sim - niiang, Changshan C ountY, Zhejiang P rovince, south- ple six-fold global stage level d ivision in w hich each series is eo.s t China. This boundarY is defined bY the.万rst appear- divided into tw o stages. M ost of the stages and series have yet to be form ally defined or nam ed, but potential levels for their bases have ance datum (Y 'the U . }iustrodentatus w ithin a densel-v been identified w ith particular conodont or graptolite biozones w ith sam p led su〔工cession 可．graptolite 万rst occurrences that potential for long range correlation. I he general fram ew ork of these facilitate p recise global correlation of' this boundarv. global stages and series ofthe O rdovician System has now em erged (Figure I）．It is w ithin this context that the D arriw ilian G SSP has C onodont species (ire also present w ithin this section been proposed. and indicate that the base 可. th e D arriw ilion is likelv to T he task of id e ntifying suitable levels for series and syste，二sub- lie w ithin the low er part ol'the M icrozarkodina parva division has been conducted by m eans ofa series ofintra-0 rclovician w orking groups. W ithin the interval（们 he M iddle O rdovician (Fig- Bio71,one 可．the N orth A tlantic ‘onodout 7,onal succes- ure I），the O rdovician Subcom m ission w orkim , ,roups identified SiOn. C orrelation ol'this boundarY w ith w ell studied suc- tw o biozonal levels that appeared to have potential for subdivision of (T ASIO ns elsew h ere ind ica tes tha t it is co eval w ith a level the series: the base of the I)id.vinograptiis arnis (=L). b功dus of Elles), and the U ndidograptus austrodentalus biozones. I he form er ；，，the m id W h iterockian in N orth A m erica. an d in the leve l is co incid en t w ith th e b ase o f the B ritish I.lanv irn S eries, an d low et- T ennian Stage ‘，／the upp e，一A 二，iig of W ales. The the second w ith the base ofthe D arriw ilian Stage ofA ustralia. 'the base ‘）／the D at-rA vilian is ahout 40 7.5州 材“ scope. rank, and correlation oft he Llanvirn Series have been the sub- ject of m uch discussion and disagreem ent (am ong recent papers see, for exam ple, Fortey and others. 1990: C ooper and Lindholin, 1990} In tro d u c tio n M aletz.］992: Berry, 1995). Fortey and others门995). in an effort to address the need for it better unit in this interval, recently revised the ［lanvirn Series. A lthough they identified a possible stratotype sec- A dvances in our know lcd},e of the Earil-i's history, including devel- tion for the hase of' the Llanvirn in W ales (see Fortey and others, opincrit ol'an increasingly refined geological tim e scale, have led to 199 1, p. 13 ), no W elsh candidate sections for a Ldobal stratotype at the posing of' questions in inany areas of' geological research that th is leve l h ave b een SUb m itted to the S ubco m m issio n lo t- O rd ov ic ian reCjUirc yet further increase,, in the precision and reliability of this Stratigraphy fo）r consideration. M em bers of the A rtits W orking tim e sca le. T o add ress th is need in the O rd o vic ian , th e IU G SA C S G roup discussed several additional sections from other regions of Subcom m ission on O rdovician Stratigraphy since 1989 has been the w orld as a potential stratotype for a stadia] boundary at the base engaged in an active prograin anned at identify ing those biological of the D . artas B iozone, but none appear ideal and again none have c\cru horizon,, that exhibit the greatest potential for chronostrati- been subm itted forinally to the Subcom m ission for consideration. graphic subdivision of the O rdo\ ician Systern for w orld-w ide use. T he O rdovician succession in A ustralia has ：、long history o f In particular, this effort has focused on especially w idely recogniz- biostlr飞altig"lr}I ip hic study. T he D arriw i han StaaIe w as erected by H alI able biozones w ithin the pelagic graptolite and conodont faunas. T he （1899). redefined by H ari-is （1916, 1935). H ari-is and K eble （1932), hi-li dc-ree of biogeographic differentiation w hich characterizes and m ost recently by V andenB er- and C ooper 门991 P. 53) for the O rdovician biotas has m ade developm ent of a precise. unified global interval betw een the base ofthe Uiidu1ogr(ipm s austrodetitattis B io- standard a slow and difi cult process. In m ost regions 。们he w orld, zone and the N em agraptus gra(ilis B iozone. S ince the I 930's, the

Septem ber 1997 5 9

芝 二│ ＿一（ │ │ 一 │ │ 口日 │ Cc │ 一│ G S LT OA BG AE LS │ 一│ K ： 丫 G R A P T O L IT E / │ T R A D IT IO N A L R E G IO N A L S U B D IV IS IO N S │ (SO M E UN ITS LIKELY T O BE USED IN G LO BAL STA GE N│OM ENCLA IURE) │ 卜 │ │ │ ｝ C O N O D O N T (C ) │ │ V ) │ │ │ 一 B IO H O R IZ O N S │ │ ＞－ │ │ ├─────────────┤ │ B R ！丁A IN │ B A L T O S C A N D IA │N O R T H A │U S T R A L A S IA │C H IN A │ │ (A │ │ │ │ 一 ： ＿ ＿P - d c u m in a t u s 、 │ A M ER IC A │ │ │ │ │ │ 4 4 3 2 Q !│! 一 │二 二 ？二 二 ｛ 一 ‘│lap e tog na th u s n .s│p . I │ A shgill │ Harju C i n c in│nati│an │ Bolindian C│hientang-│ M a E asto n ia n │k ia nqian ││ │ │ │

＜ 口│习 │ │ ｝， }C ) │ │ 乙 氏 │ │ │ │ │ ＞ a│- │ │ │ │ ├─────┤N e ich ia n- │ │ │ │ O 习 ││ │ │ │ C a rad o c ├─────────┤│ M o h a w k i│ a n │ │ s h a n i│a n ││ I X X X │ │ │ │ │ │ vVir。u xx xxBB├──────┤M 日│ │ │ │ G is b o │ r n │ia n ├─────┤ │ │ │ │ │ │ │

匕 │ │口习 】 │D A R R IW IL IA N ！ │ │ Lian v irn │ │ ├───────┼─────┤│ │ 1 口 │ K u├──┬──────┤n d a │ │ │ D a r r │i│w ilia n │Z hep a ng ian ├─────┤│ 0 _ _j│ ├────────┤ │ │ W ├─────┤h ite ro ck ian │ │ │ │ O │ 【 ││ 一 │ │ O │ │ │ │ │ Cu │ │ │ │ │ Y a p e e n ia n │ Y u s h a n ia n │ 网门． ． │ │ │ │ 门 │ │ V o l│k h o v │ ├───────┼─────┤ 乏 │ │ │ │ │ O ├────┼────────┤│ │ 0 │ │ │ C a s t le m a in ia n │ │ │ │

比 │ 一 │ │ 一 │ │ A renig │〔 ├──────┤│ │ │ │ L ato rp │lb ex ian │C h ew to n ia n │ ├─────┤ │ │

Bendigonian├─────┤ │Ichangian │ │ │ │ 日J 一 ├────────┤ │ │ │ 弓 一│ │ │ 一 │ │ 0 │ │ 一 │ “ ’ │ a p p r o x im a│lu's ├───┼────┼────────┤ │ － │ │ │ │ │ T rem ad o c │ ├──────┤ │ La nc efi e ld ia n │ ││ T re nnad o c │ ├───────┤ │ │ │ │

4 9 5

F igure I C hart illustrating stratig raphic relationships betw een global O rdovician Series, Stages, key fi 7unal m arkers (two of w hich ，，。、 ha ve rat访ed G SSP s) and som e regional subdivisions (after W ebby, 1997). Volcanic ash event m arker (the B ig (=Kinnekulle) B entonite, B B , and correlative M illbrig B entonae, M B ), as w ell as approxim ate radiom etric dates (after Tucker & M cKerrow 1995), also show n.

"raptOlile Zonation Upon w hich the D arriAilian is bascd h j ,; b e en T he n am e D arriw ilian (H all, 189 9 ). b ased on the A ustralian w idely used as a ba.,,is 1or internalional correlation. particularly in re2ional stage. w as chosen by the JC Y w orkin" group because of its the Pacific Pro＼一ince, and ，、reaclil} recognizable in graptolite facies priority for the interval extendinIg upw ards from the base of一 U. ou}- around the -lobe. The D arriw ilian Sta},e sl)ans a strati-raphic inter- trodentants Biozone. FUl山erniore, it has been agreed by a vote of val w hich is sim ilar to but slightly larger than that of、 the revised the T itular m em bers of the SUbCOM M ISSiOll (8214 in favoi）川Febi Ll- Llanvirn Scrics ot'Fortey and 、）山ers （1995). ary 1996 that the overlyin2 global stage (and series) w ill be defined ISSLICS raised by 山e need to choose on e o r the other of' the D . by the base of the 刀e｝1，‘191了、1）了1，、又1丫，（、111＼ B i ozone. Thus, the concell- arm s or I人‘m y,rodelfi lluv lc}cls w ere dk eusscd at length clUring tion ofthe global D arriw ilian Stage intcr\ it], from its base to its top, w orkshoj)s held at the Sixth International S}rnposiuni on the O rdo- conform s exactly w ith prior A ustralian re.010nal LlSa(-1C vician Systern in Sydney, A LISII-aha. In 199 1．and at a subcom m ission In July Ot 1996 the D arriw ilian G SSP propos a l w as ovci- field niecting in N anjin- in 1993. and apain at the Seventh Intei-nj- w helm ingly approved by the T itular m em bers o f' the O rdovician fional Sym posium on the O rdovician System at Las V e-as. U SA . in Subcom m ission （17 votes in favor, I against, 2 abstentions. and I no 1995, all m inuted ill issues of' O rdovician N ews, nos. 9 （1992), 11 response, for a 94(/t m ajority). Subsequently, the D arriw ilian G S SP （1994 ), ai记 13 （1996 ). In 1992-93, in response to discussions at the w as also approved by the IC S, and finally. ratitied by a unaninIOLIN Sydney F11CCtiu,' Of the S ubcom m ission, C hen X U or,,anized an intei- vo te of the JU G S E xecu tive C o m m ittee at its Janu arv. 199 7 nicetii),-,. national w orkinL, oroup to investigate sections spanning the Y apeen- ian-D arriw ilian interval in llic Jl：1：19、11：、，1一C l：：lllgsh：，1卜Y ush：In a r ea (JC Y area) alono the border betw een Z hejiang and Jiangxi province,;, C hina, and an open in\itation w as m ade for participants R ecom m ended global stratotype section to join the w orking -LrOLIP (O rdoviciati News. no. 9. p. 20, 1992) and point J he rcstilting, JC Y w orking }'FOUJ) included specialists trom C hina the I ISA , France, G erm any. and A ustralia. B ased on this joint inves- OL'ation, as v clI：、、the pre\ ions w ork Ot'OUl- C hinese COlICal"Hes, the T he recom m ended G SSP is located along, an unpaved road on the base ot the U ndulograptus ati.m odew am s B iozone of the H uan-ni- riverside near H uan-nitan- }illaoe, 3.-} kin southw est of the (’f iam 2 tant-1 section in this arca has been identified its：、suitable G SSP for the shan C ounty Tow n of Z hejian, Province (1-i,,urcs 2. 3). T he section D arriv, ilian （（hen and others 1995b: C hcn and 13crostrorn, 1995} is accessible by, vehicle (in fair w eathct）front the tow n oj'E rduqi}io. M itc he ll 是i n(] N lalc tz 199 5 ). T his sectio n w as cho sen as the G S S P 500rn east of H uanonitaiw,. A state lii-h\}aN connects the C ham -, I)CCZIU}C it represents the best a\ailable section thl-OLI,I,h the interval shan C ounty T ow n w ith H angzhou and Shanghai （onscrvation ,ilid includim , the hase of the U . in istrodenlan o B iozone. F ive othcr sec- protection ofthe section has been a',SL1FC,-I by the C hangshan （01,1111\ tions in the Y Y reI,,ion w ere included in the Study, and several of G overnm ent and the Z liciian9 Provincial G o、厂ernm ent to,-,clhci- \A, ith these com e near to rivaling the H uangnitan" section ill their expo- the N anjin2 Institute of' G eology and Palacontology, A cadenii}i Sinica sure, fossil content, and (2011611161V Of Succession. W ith this w ork in inind. R. D . W ebby. C han （们 lie O rdovician Subcom m ission. sent T h e s ection exposed at FlUangnitamI, provides the thickest }tnd an advisory questionnaire to T itular m em bers of’t he O rdovician Sub- m ost fassififerous succession across the base of the U nelulograpitt} com m ission in early 1995 (O ido viciw i N ews, no. 13. 1). 30-3 1）．The austrodeniatits B iozone of any that w e hjvc cxaniined (Fi}-'Llie 4) results of this survc} provided further guidance for clecision-ru aking T he H uangnitang section com pri,;es m ainly the N inA uo Form ation in I'- or Of usi'llu the hasc ofille U . ousirodcm ants B io/onc w hich at this locality spans the interval froin Bendigonian confi n［卜

["pisolle、，认）／}0. Ile). 3 j 6 0

beds, the lim estone constituents are w ell一、Orled, tine-Irained 卜 〔少 认惬 inicritic intraclasts. superficial ooliths. and skeletal 1'ra-m en卜set In j calcite spin- m atrix. A nalysis by graphic correlation based oil 1'al-inal 刁sha n C o unty Tow n ）／ data fi-oin H uangnitang, and tile fi\e Supplem entary sections Studied in the JC Y area indicates that the Fluam m itanoI section has a consis- tcntly high scdim entation rate and no detectable stratigraphic hreaks. G raptolites are com m on to abundant in the tipper N ingki-10 Form a- tion. A bove Bed A E P 178 m any graptolites are pyritized and pre- served in th ree d im en sion s, a nd I、一（)m A E P 17 9 to abo ut A E P 19 9 the rocks are essentially continuously tossilifcrOLIS. T he base of the U . ouv rodentants B iozonc i n t he H uan-nitan- section is selected as the base ol'D arriw ilian Stage, and is defined as the lc}el of the first appearance datu川（FA D ) of the nam e bearer: U lldlllograptit} austrodentatio (Figure 0 ). This levcl is coincident w ith the base of B ed A EP 184 ot'thc Fluangnitang section, w hich is ． 一 221n below the top of、 the N ingkuo Form ation (FiLlUres 4, 5). G raphic correlation aniong the six sections exam ined in the JC Y area indicates that this appearance in the Fluangnitang section corre- sponds to the oldest know n first appearance of' the species (Z hang,

． 1995). T hus, it is probable that the hase of' the U . au,m -odentatus ｜ ｜ B iozone in this section represents the tim e of'evolutionary origIin of ！ 1 1 this key species. ！ ｜ T he base of th e D arriw ilian is form ally defined its the base of 卜 比 the U . austrodentam s B iozone, how ever, it is im portant to note that 队 厂 口 ,因 identification of this boundary is a distinct process 1'rom its dchni- ： tio n . T h e h ase of the D arriw ilian sh o uld no t he ide ntifi ed o il the ﹂ ，，日, 凡 1 1 日 3 0 basis of the first appearance of' U . aum -odentam s alone, apart from higtirre 2 M ap showing location of the H uangnitang-G SSP its faunal context, but only on the basis of the species' hi-st appear- section relative to the nearby C hangshan County Tow n. ance w ithin a w ell controlled succession of other first-appearariccs, otrdy to D arriw ilian. T he N inA uci Form ation yields abundant grap- A second hi1gh l y distinctive species, A rienigralm iV 71.h e／I't'angensis （＝ to litcs fro m the sh ale s and co no do nts fro m interbed ded lim e ston es. Pseudisograj)tus angel Jenkins), first occurs in bed A EP 182, 0.5 m R anges ofinain graptolite and conodont species in the Fluarignitang below th e F A D o f U . a ustrod entatus. III the other JC Y sectio n s, the scclion are show n in Figure 5. A . zhe.ji(I1I,qe17sis FA D occupies a sim ilar position at or just below the T he N in,,kLIo Form ation is dom inantly a w ell-sorted, line- U . au.strodentatits FA D . W ithin the precision of strjtigraphic corre- }_,rained. thinly and evenly lam inatcd black shale (Figure 4). The base lations in the region, the A rieniqj-(j1)tjjS 7/1(1jiialnl‘gcelt，i、s1i、s f- A D is svn- Of U . austrodem atits B io）zone in the FIuan2nitan2 section. as w ell as chro no us w ith the b ase of th e 口 a u stro den ta tio B io zo ne. T h u s, the the supplem entary sections in the JC Y area. lies w ithin a black shale appearance of A . 1-hefiangensis serves as im portant collateral evi- seClUence that is entirely consistent in its sedim ent character and denc e o f th e lo catio n o f the b ase o f the D arriw ilian. F or th is reaso n . rellects apparently uniform depositional conditions throughout the w e em ploy this species as the nam e-bearer of the low er subzone (it Y apeenian and early D arrixvilian. T abular beds of dark gray lim e- the U . austrodentatus B iozone (see below ). stone interleave w ith the shale. I hin sections reveal that in m any I 0 .:两ngkuo Form ation & ,- H ulo Fo rm ation O Y: Yenw ashan Fo rm ation O i,g: Huangnigang Form ation Huangnitang V illage 活妞 毅一 48' 匆anm en N 飞解 价 八﹄ 谗 S tream 礴 严 扒 引 叉 甲 几 注 肠 ！ e 门 e n 日 L U U ﹂ 户 GsP I,/, 工 三 1 一 ； ‘J 三 三 协产钦 黔 L 三 七 三 三 S ha le l 姗撇黔瓢 /X O Y 尸 r 名 1 ， O h 卜 墓 ， roa,df to rduq,5,5, 5 0 , 企 己 ．L 习 ，J 卜 丁 闷 N o d u la r lim e sto n e O hg ‘ 目︻ － J

r 兀 工 三 ， ‘ H工 J 卜 1 － J 卜r 亡 一 二 I 二 H ～ J嘴 C h ert 气50 m ‘ 1 PM=}":q Limestone 睡 〕Mudstone O R Cover 0 翻 1 1 ． 1 」

Figure 3 6 eological sketch m ap q/ the H uang nitang section, Changshan, C hina. R ocks dip m oderately to the east-sou t it- east, and voting in M at direction.

Scptem ber 1997 /6 1

A B

；蓦桌鬓 鬓蘸蕊藻魏、 蠢瘾 巍 戮琪 澡署裂 装然撇 滋端券 粼熬滋 汀 启 权 三 农 塑 镶巍滋盘夔 裘

蘸一璧譬囊誉

群八 片 丫一例 下 泛 分 柑 巍忿 拓 黔擎熬掣攀黔警留譬 厂郊J 汀洛布 ，主 刁嘟珍君次访‘ 班下笼甭奄子澎辞 茎火农奎赓别良分 ： “扮浴娜州田准级经哆理努吸映

豁套鬓爹一

濒 ， 01 蓦夔从

F ig ure 4 A . View of t he H uangnitang section (looking w est), and the surrounding cou ntry side. G SSP is near star along south batik of the N atim en Stream . B . C lose-up of s ection show ing beds in the boundary interval. B ase of the U . austrodentatus B iozone and D arriw ilian Stage lies at base of b ed A E P 184 (indicated 勿 double line), just above lim estone bed A E P 183. Scale m arked in decim eters.

lo w er U . a ustrod en ta tus B iozo ne o ccurs n ear th e b ase o f th e U . sin i- T he graptolite record cus Subzone. These species include Pseudisograp tus m anitbriatus, Isog rap lus victoriae divergens, and O ncograp tus upsilon. O verlap T he presence of several short-ranging species and the pattern of of these species w ith U . sinicus provides a very precise control of the base of the subzone. graptolite species succession through the interval of the D arriw ilian boundary are critical to reliable recognition of the base oft he D arri- The Undidogra p tu s austrodentatus B iozone is overlain in the w ilian as w ell as to its precise international chronostratig raphic cor- JC Y region by the A crograp tus ellesae B iozone (X iao and C hen, relation. Several of the critical species are illustrated in Figure 6. 1990). Prelim inary data (Z hang Y uan-dong, unpublished) indicate T he graptolite fauna present in the 3 in interval just below the base that species of Tylograptus, Sinograp tus and other graptolites char- of the D arriw ilian at H uangnitang is a typical Y apeenian assem blage acteristic of A . ellesae B iozone appear in the upperm ost 5.2 m of the that includes P seudisograptus m anubriatus harnsi, P. m anubriatus N ingkuo Form ation and continue into the low er part oft he H ulo For- koi, E xigrap tus uniform is, and E. clavus (w hich is closely allied to m ation at the H uangnitang section (Figure 5). Ap iograp tus crudus). T he com posite standard constructed for the A ccurate identification -of the index sp e c ie s Undulograptus JC Y region (Z hang, 1995) indicates that strata in this interval in the austrodentatus and A rienigraptus zhejiangensis (see Figure 6) is JC Y area also contain O ncograp tus m agnus, A rtentgrap tus dum o- essential to recognition of the base of this biozone. In the past, con- sus, Isograp tus victortae m axim odivergens, and L victoriae diver- siderable controversy has surrounded the issue of w hether or not the gens (see also M ao and C hen, 1990). W e refer the interval from A E P appearance of "biserial graptolites" w as actually synchronous 180 to 183 to the E xigraptus clavus B iozone, the base of w hich is around the globe (e.g., Skevington, 1963; Berry, 1968; C ooper and covered in this section. Shales of the m id to upperm ost E . clavus Lindholm , 1990; Fortey and others, 1990; M aletz, 1992). M uch of B iozone (A E P 181 at H uangnitang) contain the first appearance of the confusion arose as a consequence of application oft he term "his- Cardiograptus obesus follow ed in bed A E P 182 by C am plus, erial" to a w ide variety of species (including glossograptids) and U ndulograp tus sinodentatus, and A rienigraptus zhejiangensis (Fig- confusion about the identification of particular species such as D idy- ure 5). m og rap tus bifi dus and U . austrodentatus. T his problem has been B a s e d on the H uangnitang stratotype section, as w ell as other solved by recent system atic w ork based on especially w ell preserved supplem entary sections in the JC Y area, w e recognize tw o subzones, m aterial (e.g., C ooper and Fortey, 1982; Fortey and C ooper, 1986; the A rienigraptus zhejiangensis (low er) and Undulograptus sinicus M itchell, 1992, 1994 ; M itchell and M aletz, 1995), although contrary (upper) subzones, w ithin the U . austrodentatus B iozone (C hen and interpretations continue to have advocates (e.g., Berry, 1995). C hen others, 1995b; M itchell and M aletz, 1995). T he base of the A . zhe- and others (1995a) have redescribed U ndulograp tus austrodentatus liangensis Subzone, like that of the zone itself, is defined by the first (H arris ＆ K eble) and A rienigraptus zhejiangensis Y u and Fang in appearance of U . austrodentatus. T he fauna of the A . zhejiangensis detail. Subzone is very diverse and includes a rapid succession of first appearances of species of U ndulograp tus, C ardiograptus, and E xi- graptus (Figure 5), including Undulograptus form osus, and U. T h e co n o d o n t reco rd prim us. T he base of the U ndulograptus sinicus Subzone, is m arked by the first appearance of U . sinicus. This level is very nearly coin- C onadonts from lim estone interbeds w ithin the H uangnitang section cident w ith the first appearance of C ryptograptus antennarius and (com m encing w ith sam ple A E P 167) are referable to the P aroisto- P araglossograp tus tentaculatus, as w ell. T he base of the upper sub- this originalis B iozone (W ang and B ergstr6m , 1995). A lthough the zone defines the top of the low er subzone. The last appearance of fauna is of low diversity, elem ents are num erous and w ell preserved several ofc haracteristically Y apeenian species that continue into the (Figure 4). T hey are typical of the low diversity N orth A tlantic

如 isodes, VoL 2叹no. 3 ／6 2

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万亡1，tel矛了ber l夕97 16 3

F igure ‘ Scanning electron m icrographs of three-dim ensionally preserved, pyritized sp ecim ens of s om e critical graptolite sp ecies. A . E xigraptus clavus (x功．B . U ndulograptus austrodentatus (,0 0). C U ndulograptus sinicus (note that all of the th ecae of t his species bearp rom inent sp ines located at thep oint of m axim um curvaturejust below their ap ertures, how ever, these spines are not preserved i n this internal m old; X 30). D . A rienigraptus zhejiangensis ()0 0).

Province faunas usually obtained in off-shore settings, and contain JC Y area, D . ancoriform e has been previously reported w idely from none of the shallow w ater endem ics found in rocks of the Y angtze the L lanvirn and younger strata in E urope and northern A frica. T his Platform . B ased on these faunas as w ell as occurrences of conodonts species is also present in late A renig rocks w ithin the Sdrka Form a- and graptolites together in the D aw an Form ation of the Y ichang tion in B ohem ia together w ith a D . bulla B iozone chitinozoan fauna region, Y angtze P latform (about 700 km W N N of the JC Y region; (V avrdov6, 1993). seeW ang and B ergstr6m , 1995), and in the V inini Form ation of cen- C learly, addit io n a l w ork is required on these fossils and their tral N evada (Finney and E thington, 1992; M itchell, 1992), the base distrib utio n . F urth er re search into th eir o ccurren ce in th e JC Y and of the U austrodentatus B iozone lies just above the base of the Yangtze Platform regions is underw ay currently. H owever, the M icrozarkodina parva B iozone in the N orth A tlantic conodont zona- availab le data are su fi c ien t to ind ica te that clu tin ozo ans and acri- tion and w ithin the upper part of the H istiodella altifrons B iozone in the N orth A m erican m idcontinent conodont zonation . tarchs m ay offer the opportunity to m ake an accurate correlation of C onodonts from bed A E P 250 in the H uangn i t an g section the base of the D arriw ifian w ith late A renig successions of the pen- include E op lacognathus crassus. In term s of graptolite zones, this G ondw anan realm , w here U . austrodentatus and its associates are bed lies w ithin the A crograptus ellesae B iozone. The A E P 250 con- a b se n t odont fauna indicates that these strata belong to the low er, but not low erm ost, part of the A m orp hognathus variabilis B iozone of the N orth A tlantic conodont zonation, consistent w ith an M . parva B io- zone age suggested for the base of the U . austrodentatus B iozone P rospects for paleom agnetic reversal stratigraphy and radiom etric age d eterm in a tio n s C h itin o zo a n a n d a c rita rch reco rd s

N o paleom agnetic w ork has yet been carried out in the M iddle O rdo- C o rrelatio n b etw een the L ow er O rd ov ician low latitud e fau na s of t he vician sections of the JC Y area. H ow ever, in view oft he fact that the Pacific Province and the dom inantly cool to cold w ater faunas of G ondw ana has been a persistently difi cult problem . C orrelation via C onodont C olor A lteration Index (C A I) is only 3-4 , indicating heat- the trilobite faunas in W ales represents one possibility, albeit largely ing of the rocks to a m axim um of about 100'C-300*C (W ang and untested at present. R ecent attem pts to obtain chitinozoans from the B ergstr6m , 1995), there is clearly potential for successful establish- U . austrodentatus boundary interval suggest another potential solu- m ent of m agnetic reversal stratigraphy across the base of the D arri- tion. Paris and C hen (1995, 1996) report discovery of chitinozoans w ilian. T he only rocks in the N ingkuo Form ation in the study region from H uangnitang and three other sections in the JC Y area. T axa that are potentially useful for radiom etric age determ inations are tw o present include species of the genera C onochitina, C yathochitina, thin K -bentonite beds in the A zygograp tus suecicus B iozone R habdochitina, Tanuchitina, La ufeldochitina, B elonechitina, described by H uf and B ergstr6m (1995) in a section at H engtang. D esm ochitina and Sagenachitina. Specim ens of the first three gen- N o radiom etric age data are yet available from these beds, but in a era are the m ost com m on in their collections. Several of these gen- com panion paper to the present contribution, H uf and others (1997) era are know n from G ondw anan locales and Sagenochitina in partic- report a U -Pb age of 464t2 M a from a K -bentonite located w ithin ular is、 a characteristic elem ent of upper A renig (W hitlandian) to th e lo w er D arriw ilian U . a ustro den ta tu s B iozo ne in th e P re- low er Llanvirn strata in northern G ondw ana (e.g., France, Portugal, A lgeria, and Libya; see P aris, 1990). cordilleran T errane of A rgentina. Servais and others (1995), in an th o rough revision of the dis- finctive acritarch D icrodiacrodium ancoriform e, report that its first appearance lies w ithin the latest Y apeenian U . sinodentatus B iozone in the D aw an Form ation, C hina. A lthough not yet know n from the

Episodes, Vol. 20, no. 3 2(54

A u s tra la s ia I S ．E ．C h in a N o rth A m e ric a B a lto s c a n d ia W a le s

M id - Victorian Grap- Texas Grap- C o no- Trilo- Grap- Trilo- continent shelly Stages graptolite S e ries to lite S eries graptolite Stages to lite do nt b ite S e ries tolite 匕ite co nod o nt z o n e s z o n es z o n e s z on e s z o n e s z o n e s zo n e s z o n eS z o n e s 卜组 zo n e s ． 言·舌 三 。﹄川一 二 的 的 。OJ 泣已 ︸， 泣 一 的 吞O o 。J ． 。 知 二 0 山 山 ︸J ︵ 望 V 一。 毖 J一 习 门 Q－5 O 口 。． － 亡 ︵。 的 月 一 0一 J门 巳． 一幻 0． 理 ︸ － 山一 5 三 七 ﹂ 1 0． U ： 三 忍 彗 里 男 C＝ 巴 心纽二 里 ．召 的 一︼ ，－ n 工 公 V 二 n．巴 口 另 。 仍 － 目 － V． C 4 6 5 .5 + 3 已 一 巴 器 B U︸ 。 门 u 琴 三 丝 O －C＝ 瑟以 ． 。 盆一 ︼ O 凸 一 一 。舅 二之 德 ﹄ 一 Q d． 门 ＝ 口 ， ﹄ 雪 。 。舒 。 一 门 荡 。．勺 O C 二 芍 。 J 丁 二 ：J 吕 ︼ 一 仁 ： 0 男 。︸﹂ 山 0 门 兰 C 。．当 口 ， 劝 ， 忍 伪 ‘ 二 a 一 。 召 C ， 浏 器 J 一 ． 叫一 二：〕 习 一 ， 。 ． 二 J 门 二 一 仁工3 二 二 一习 一 Q uJ 巴． 口 〕 匕 口 J 二 一 竺二」 考 一 。 ‘‘， 的 A. 仁二 芝 ， ︵ 乏． － ， 月 C 〕 山． 芝． ﹄ 0 」二七 且 丫 V zhejiang ． “ 口 阶 467 .51 3 闷，闷 己 己 甲． 勺 ．勺山 s 二 叨 名 仍 u Cardiogr 苗 Exigraptus 吵 I I － o 井 一 。 望 乞 一二 ︸J 二 Clavu5 知 司1 任 Jn 言 一 N oy. 目 u 一 。 弋 德 6 巴的 二 白we 的 口 ，任 。 J一 ． 卫 ． ．一 J卜 男 ｝、CadUCeUS o 芝 口 的 －、瑟 ，。 0 三 勺一 卜 i[ r itatu s 兰 ｝｝、 ｝ 氏， －．

F}qure 7 C orrelation chart showing chronostratigraphic relations betw een the base qj．t he recently ratifi ed global D am wilian Stage oj the M iddle O rdovician Series and several well-known regional series and stages based on data and interpretations cited in M achelland Chen (1995) and M itchell and M aletz. (1995), with radiom etric ages interpolated based on data fi -om Tacker et al. (1995) and H qf et A (1997), and relative stage durations./roin C ooper (1992).

in N orth W ales neat （acinail-on and BangIor (Forte} and others C o rrela tio n o f th e b a se o f th e I9 9（））． D arriw ilian Stage In S w eden, ,A, J ie.fi(m gensi.} Occurs in tile Illiddle part、）！tile 1), hirm ido B io/.onc looctlicr w ith Pscildisograp ilts m onlibliallo jam o and 、or. U. sinic ms and U . C11/H/))VIISi.S Occur 1 h c d istinctive fau na of the I一‘m strod en ia lirs B itm o nc h as been in the LIPI)el' 1). hirundo hio/one (M itchell and M alet／一1995). T he reported f’rom A ustralia. N ew Zealand, N orth A m erica. Europe, base of the H anvirn m ost likcl} coincides w ith a level slight]" abm e South A m erica,（hina- M on},olia, and K a/akhstan perm itting confi- th e b ase o f the A．一夕（Ilesm , B io /one o f SO LIth east C hina. }k hich i,, clcni correlation w ith these re,_,ions (Fil-ItHe 7). A . zheiiim ,,ensis Sub- closely com parable to the U m lidogi,apno intei几、1111's B lozouc （D alr i- lone faunas occur in the M arathon rc(_,ion. 'fe xas, and sim ila：一laUnas w ilian 2 ) in A u stralia and N ew Z eala nd . C o no do w C\'iL[C.IICC Il-0 111 arc also present clseM icic alon.,_, Oic ,kestern N oi-ih A rneiican th e JC Y area ind icalcs that the ba.,,c o f 1he A.'少 ellcsa c B io /olle co l C oidillera (M itchell and C hen X u 1995 ). A n U . Silli(11N SUb/one responds to ：、le}cl near tile base of' the A m orphogiatilm s variabli}s fauna has been recorded froul Q uebec and N ew foundland (M itchell B iozone, w hich is in aorcem ent \AiIh the conodont aLc ofilic ，一（)cks in and M aletz 19 9 } ). (o rre latio ns w ith f,au nas fro m N o rth A m erica the A reni--H anvirn boundary interval in the B altic region ind icate that the base 、）｝、the V . S111h 11A S U hzo ne is n carlv co in cid ent A s m entioned preViOLISII,, COIIO(]Oflt CVi(]CIICC fr(）川 t il e JC Y vJth the base of the w idely reco-ni/'ed a re a in d ic a te s th a t th e b a se o f 创．a lls /m d e n to Ill's B io z o n e is in s tra ta lality B io},orie. Sim ilar relationships are present in the A rgentine that prohabk correspond to either the Upper part of tile Bakoscan- Precordillera (O rte-a and others 1993} A lbanesi and others, 1995 clian 八iroi.slodivs ori-bia lis B iozone or lokker part of the Ed,,el B russa and C .E . M itchell, unpublished data). 盯；‘ro,-.arkodina parva B iozone.〔ornparison w ith the Y anum/.c Plat- T he oldest diplograptacean know n from W ale s is U ndulograp- form conodoill Succession favors the latter interpretafioll (13cl- str6ru tu.} cum brensi.v from the B er}om ia ruslitoni Biozone (Figure 7). Its al记W an-. 1995). T he conodont /onal assignm ent o f rocks from FA D is certainly w ithin the U . sinh us Subzone (M itchell and both Sw eden and N evada that. hased oil their graplolite faLluaS, are M aletz. 1995). 1 he base of the U . em ,w rodentano B iozone, therefore, corre lative s o f th e low er 11. a ustrod en t a lt i.% B io zo ne a lso fa ll w ithin should lie below the oldest occurrence ot'diplograptaccans }e( dis- the 解．parva B iozonc. Strata ofthe A . ellestie B iozone 川the JC Y co%cred in W ales, w ithin the low er part of the Fennian Stage. The area (e.g., A EP 250 ) as w ell as rocks from just ahove the U . m isit'o- inicrval of the low er U. austrodentatus B iozone is represented in dentottis B io/one 川Q uebec an(] Sw eden belong to tile A . varioblis N orth W ales (as at N ant y G adw en) and in the Skiddaw G roup of the B iozone （Bergstr6in and W ang,, 1995: M itchell and M aletz, 1995). Luke D istrict, based on the presence there of- A . 711eiiangensts T he A . variablis B iozone fauna at H uan-nitarn, includes the distinc- (reported as P . an,}el）川the L甲per lso}raptus caduccus }ihberuhf.s tive (albeit new ly recognized) conodont,万oplw ognalhu.s （R I .S.SU S B io/.one (Fortey and others- 1990). 1 he U. sinicus Subzone is pre- C hen and Z hang, w hich is also present in this saine interval in the sent in vounLcr rocks （们 fie L ake D istrict, \,\,here it is equivalent to Y angtze platform region, as w ell as at localities in Sw eden, Estonia, 山L: D idvm o,}raptus hirm ido Bio/.one as used by Jackson ‘1962) and and Poland (see Z hang, 1997). E . iTO.SSUS appeal、to he ：、short ran-

Septem ber 1997 2 6 5

in g sp e c ie s restricted to the lo w e r. b ut not low ei川（)st part of the A . Fortey, R A , H arper, 1) A T, Ingham , J K , O wen, A W and Rushton. A ＼＼A . va r ia b ilis B io/,one (i.e., the upper part of the A va ria b iliv- 1995, A tevi}ion of Oiclo% ician series and states from the hi}torical t\ lie M 1C1-O,-0I-k0diI10 fl Obe/h/111 SUbZO11C). M iscd on these conodow area: G eological M aga/ine. v. 1-32 . pp. 15-30 11raptolite relafions w e aic confident that the a.,2e ot the base of the I/ Fortey, R A . and O x} cris. R, M . I L)ST The Arenig series in south IA ;tlcs:BH卜 a u v ro d c n ta m s B io z o n e is c o n s is te n t a c ro s s b o th fire P a c ifi c a n d letin ol'the British M U',eUrri N atural Histor) (G eology). }. 41，pp. 69一,07 Jacksou, 1) k. 1962. G japtoHtc zones in the Skid(hrw G roup in Cum heiland. A tlantic prov i nccs. En2land: JOL11-11al of PalcontoloVy, \. 36. pp. 300-3 13. H all, T S, 1899, Victorian graptolites: Pt. It. The grapiolites of the Lanccheld beds:Piocec山n's of the Royal SocicIN of Victoria.、．H , pp. 164-178. R e fe r e n c e s H arris.W 川 916. The palacontologicjI sequcnce of the Low er O rdo% ician rocks of the C astlem aine district. Part 1: Proceedings of the Royal Socim Alharresi. G I．H thucken. M A , and O rtega, G . 1995. Revie}} of O rdovician of V ictoria, v. 29, pp. 50-74. conodoin-graptolite hio}tratignaph) of the Argentine Plecordillera一III H arris, W J,］93-}一-f lie gnaptolite succc}sion of Bendigo East, w ith SU,}21'11C(l C ooper, J D , D roser, M I，and Finne}} S C , eds., O rdovician O dyssey: zoning: Proceedings（）｝the Royal SocicIN of V icto6a, v. 47, lip. 3, 14- 11T Short Papeis for the Seventh International Sym posium on the O rdovician H aFri',. W .1一and Kehlc. R A , 1932.'V ictom m grapiolitc /ones. Aith colicia- Sys(ern: Pacific Section. Society Jor Sedirnentar\ Geology (SFPM ) tion,, and description,, of specie}: Proceedm Ls of the Ro}al Sociel\ （、｛ Book 77, pp. 3］35 V ictoria. \. 44. pp. -'}-48. Beigstiom , S M and W ang Z hi-hao, 1995, G lohal correlation of一 C astlennain- H O T, W D and Bergstr6m , S M , 1995} ( astlem ainian K-hentonite beds in the jan to Darrivilian colloclont Lflna} and then relations to the graptolne N in,A 110 Form ation Ol'tll(: lialli-IsIM 11 ('Otlut} 一tl ie tit st Io ver Ordo\ IL K111 Zone SUCCC}}n)u. III (’h en Xu} and Bergstrom , S m . ecis., 'rhe base of the K -b en to n ite s fo u n d in C h in n } in 〔h e n X n , a nd B crL stro in . S M . c d .,,＿I'lle a u v o -o d en ta tu s Z o ne as a le ve l fo r L lo h a l SO d iv isio n o f th e O rd o v ic ia n base （们he aitsliodew am } 7ojic as a lc%cl lot 110hal Subdivision of tile Syqcm : Palaco\vorld. no. 5. pp. 92- 98. O rdovician Systcru: Palacowoild. no. 5. pl) ！川一］（）飞 B c rrv . W B N } 19 6 8 , B ritish an d N o rth A m eric a n L o w c r O rd o \ ic ian c o rre la- H uf , W D , D a\ is, 1), Bergstrom , S M . K rA cler %I P S, Kolala, D R } and C in holl一rcp]N} Bulletin of the G eological Society of A m erica. v. 79} pp. I,,olani,（ 1997. A hiostratigiaphicalIx wcIl-constiained K-bentom ic U - 12 6 }- l 2 7 2 Ph zircon a,I,e o fthe lo}Ncqrro}t Datriwilian SiaL-c (M iddle O rdovi}ian) Bcrrv. 'A' B N} 199}, Plate m otions. oceanooraphic charrLe and ecolotic con- from (he A 1,cntinc Prc}:oidillera: Fpi}odes. v. 20. n o ！，pp.29一33 11-O IS: in flu e nc e O n co rre la tio n （）自 he h a se o f the ［la n v irn S e rie s, O rd o vi- M aletz. 3, 1992. The A renig/H am irn houndar} in the Q Uebec A ppalachians cian Sy}tcni: Ncvv}letters in S(ratigiaphy, }. 32. pp. 45-5s. N c\k,,,Ietter,., in StratigraphN, \. 26. pp. 49-64 C hen X u, and BcrgstrOrn, S M . (eds), 1995. The hase （们he ansirodenialu.s M itchell, C E, 1992. Fvolution of tile D iplograptacca and 山c international Zone W, Lt level 101 91 0hal SUbdi\ ision ‘们 lie O rdovician System : Palac- coriclation oftlic A renig-1.1anxim boundary. ill N\/cbby. B D. and L H-HiC oworld. no. }, I 77p., 8 pl s I R, eds.. G iohal Perspecti\es oil O rdo\ician G eology: B alkenla. Rottel Chen X U. ZIM 11,11 Y Uan-dong. and M itchell, C 1,. 1995a. Castlem ainian to darn, lip ］7卜！8 }. Darrkvilian (Latc Y ushanian to early Zliepangian) graptolite taunas, III M itchelL （’L. 1994. A}toLcnv and rhabdosom e architCCtUre of Lraptolilcs ot C hen X u, and B C]LISIF611). S M . CdS一The ba}e ofthe atrm *odeniatus Zone the Undulogropm .s au,sl，一（0 1'1110110 }PC}res '-'I-C)Llp} ill (’l ien X, Frctm ann 13 as a level for Lflohal subdi\ ision （们he O rdovician Svstem : Palacoworld D . and Ni Y N . eds．G raptolite Research loday: A cadernia Snncj. pp no. 5, pp. 36-66. 4 9 - 6 0 . C h e n X LL a nd M itch e ll, C E , 11)9 5 , In te rna tio n al co rre la tio n o l'th c U n d td o M itchell. C 「．and M aletz. .1, 1995, Proposal ]or adoption of the base of the grapill's tillM ,od(lifi ttil's Zone. ill Chen X u. ;in(] Beqgstr6m , S M . eds.,'Fh e Undulo"relplus anstrodem am s Biozone as a global O rdovician stage ‘i nd h a se o f (lie ello llo d e llia llis Z o n e a s a le } e l fo r Lfl o b a l SU h d iv is io n o f th e .series boundary level: Lcthaia, }. 28} pp. 3 17-33 1． O rdo\ ician System : Palacow orld, no. 5. pp. 7-5-S5. O rtega, G - Toro. 13, and B russa. F, 1993. I-as zonas de Lraptolilos de la 1:or- CIICH X L1. M itchell, C 1,1, /han- Y uan-dong. 13cigstruni, S M . W inston, D m aci6n G ualcam ayo (AreniLnano lardio 一I-Ian\ irniano ternparano) cn el W atiL Zhi-hao. and M alcu , .1. 1995b. G raptolite species succession N orte de la l1recordillm 以Provincias de L.a R ioja y San Juan), Argentina: across the base ‘们lie Undillogroplus 乙1乙了人1）丫）‘人·｝了1‘11乙才丫 Z o ne a( M alr_'Ili- Revista Espatiola cle Palcontologia,、8.pp.207-219 lang. Soulli-cential C hina. and its prospects lot- use as a Ldobal stage stra- P aris, F . 19 9 0 , T h e O rd o \ ic ij n ch ifi n o）z o an b io zo n e s o f th e N o rth ern G o n d - lotype, in Cooper, .1 1). D roscr, M t一and Finney. S C , eds.. O rdovician w ana D ornjin: Reviev, of Paleobotany and Palynology, }. 06, pp O d}ssc}: Short papers I-or the Seventh International SYM POSIUM oil the 18 1- 2 0 9 O rdovician System : Pacific Section, Society for Sedim entary Geology Paris, F. and C hen X u. 1995. Early O rdm iciarl chitinozoans front the H LK111,1 (SEPM ). Book 77. pp. 157-162. nitang section and nearby localitics in the C ooper. R A , 1992. A relative tim escale for the Farly O rdm ician dcrived (X Y ) arca. Ill: Chen X U. and S.M ．Bergst io n n ed％二The base ot the （m }- Irom depositional rate.s ot',(ral)tolite shjIcs. ill W ehb}} B D. and Laurie J trodentatim Zone as a level lor global }uhdi\ ision ofthe Ordovician S\- R, eds.. G lobal Pci-specti\es on O rdovician G colo}y: B alkcina. Rotter- tern. Palaeoworld. no.5. pp. 99- 100 clain一lip. 3-2 1 P aris. F . and C hen X U 19 96. C ontribUtion of一t he chitinozoans to the selectio n C ooper, R 八 and Foilcy, R A. 1982, '1 lie O rdo\ ician graptolites of Spit}- o f a G S S P fo r tire h a sc o t'llic M id d le O iclo v ic ia n in SO LIthe rn C h ina . 9 th hergcn: B ulletin（们he British M USCL1111 (NatUral H istory). G eology, v. 36, International I"llynologic Congress. Houston. Texas, June 23-28. 1996 pp . 15 7 双)2. (A bsu act). C ooper, R A , and Lindholm ,（’‘1990, A precise worldwide correlation of Servais. 1, Brocke. R . and Fatka. 0 . 1995. Variability in the O rdovician acri- early Ordm ician graptolne seclUCtices: Geological M agazine, v. 127, pp. tatch D i( rodio( rotlim n: PalaeontoloL%. }. 39,即 389-405 4 9 7 5 25 Skevington, D . 1963, A correlation （、｝Ordovician graptolite he}ning FlIcs,〔；1925. The characteristic assem blagcs ofthe graptolitc zones of the sequences: G coloLnska Foreningens i Stockholm Foihandhilgal}、8}. British Isles: G colopical M a-a/ine. v. 62, pp. 337-347 pp . 29 8--3 19 . Finncy} S C , and Ethington. R L, 1991 W hiteicickian graptolites and con- Tucker, R D} aud M cKerrow . W S} 1995, Early Paleozoic chronolo,lk: a oclont h-orn the V inini Form ation. N e\a(la: hio.,,traliLraphic im plications. I-C \,ie,A, ill JiL lu o f lI C W t1i- P h z irco n a L c} tiv in N e NO O LUICIL u ld a nd B rilain ill W chhy} B 1). and Latirie ！R. ccls ．G lobal Pci-spective.s oil O rclo\ ician C anadian Journal ol'Farth Sciences. \. 32} pp. 308- 371) G eology: Balkew a, Roltefdam . pp. 1 }3- 1 61) V andcnB cr,. A H M , and Cooper, R 八．1992. The O ido}ician giapw Ille I-ortc\. R A - Bassctt} M G } llaipcr} 1) A T . I'll-Ighes. R A. Ingham . J K} sequence of ALIStralasia: A lcheringa.、1 6} pp. 33 -85 M OI}IICLIX. S 6 , ()well. A ＼ O w cns} R M . R Lishton. A W A } and Shel- V avi-dovJi, M , 1993. A ctuaidi a}scm hla'Lc, ill the八ienw, Series ol'the PI,11-LIC don. 11 R , 199 1. PtoLicss and problem s in the selection of stratotypcs for B asin. Czech Republic: Special Papcr} ill Palaeontolog\, \. 4,}.1) p the N ISC', of the series ofthe O rdovician System of the historical t}pc area 】2 5 - 1 39 日I (lie t ，K ．ill B a rn e s. （’R a nd W illia rn s. S H , ed s ., A d v a n ce s in O rd o v i- W ebbv. B D . 1994. To" ards c}tablishinL -flohally applicab le boundaric, tol ciall（ie吸11。）gy． G e ological Sui\cy of Canada, Paper 90-9} pp. 5-25 the O rdo\ ician System : M ajor intermitiOnal dIN i}ion} and crituria 1ol (Ict 1-ortev. R 八．Bcckl}．A J} and R ushton, A W 八．］（）（）（）．International correla- initions: O rdm ician N cA}- \. I I．pp. 0--1 5 tio n o f th e b a se o f th e L la rn im S e rie s. O rd o \ ic ian S v s(c m : N e w s letters in W eh hv } B 1). 1997. So m e co m m ents oil 0 1-ClO \ ICKIll SLlhdi} isions and Ll'}LLC Stm tigraph} . v. 22, pp. 1 19一1 -11- O rdo\ ician Ncx\ }.、14. (ill prc}s) I-oi-te%- R A . and C ooper. 1980, A pliNlogcrictic cla}sifjcation of the grap- W an- Zhi-hao, and Bergstr6m . S M } 199};一CastIcillainiall (1-ate 、Lr}hajuan) loloids: Palacontolo-Ly. }. 21). pp. 031 054 to D arim ilian (Z hepanp an) collodolu taullas. ill （bell X LL .11111 Bergstrom , S M } eds．The base of the au,fro(h,w atits Zone as }i le} 、｝tol

tpi.w dc},＼；（，／-l0 ，）＿矛 16 6

gl obal subdivision of the O rdovician System : Palaeoworld, no. 5, pp M . B ergstrbm is professoro f G eological Sciences at O hio State U ni- 8 6 - 9 1 . versity, U SA w here he has been teaching -since 1968 after having W illiam s, A , Strachan, 1, B assett, D A , Dean, W T , Ingham , J K , W right, A received his graduate training at Lund -U niversity, Sw eden. H e has D , and W hittington, H B, 1972, A correlation of the O rdovician rocks in been a voting m em ber of the Subcom m ission on O rdovician }Stratig- the British Isles: G eological Society ofL ondon Special Report no. 3, 74p. raphy since 1974 and served as subcom m ission secretary in 1976- Xiao Chengxie and C hen H ongye, 1990, Som e graptolite faunas of the Low er 1982. H is principal research interest is global Ordovician geology, and M iddle O rdovician from G ucheng area, Yushan: Geology of Jiangxi especially aspects of t he evolution of the Iapetus, the signif cance of v. 4, no么 244 p. (in Chinese w ith English sum m ary). Low er P aleozoic K -bentonites, and conodonts and graptolite m or- Zhang, Jian-hua, 1997, The Lower O rdovician conodont Eoplacognathus crassus Chen and Zhang, 1993; G FF, v. 119, pp. 61-65. phology and biostratigraphy. Zhang Y uan-dong, 1995, Graptolite com posite standard sequence (G CSS), in Chen X u, and Bergstr6m , S M , eds., The base of the austrodentatus Zone Zhang Yuan-dong, Born in 1967, Graduated 户-om the Changcun as a level for global subdivision oft he O rdovician System : Palaeow orld, C ollege of G eology in 1987, R eceived Ph.D . from the N anjing Insti- no.5,pp.67-74. tute of G eology and P alaeontology, A cadem ia Sinica in 1993 and em ployed 勿 the Institute. A ssociate professor of the Institutefrom Charles E . M itch ell is an associate 1994. W orking on O rdovician and Silurian biostratigrap勿 and professor and A ssistant C hair in the graptolites. D ep artm ent of G eology at the State W ang Z hi-h ao, B orn in 1941, G raduateelfrom the N anjing U niver- University of N ew York at B uf alo sity in 1965, em p loyed 勿 the N anjing Institute of G eology and Pal- (cem @ a csit.b uffalo.e du). R esearch aeontology, A cadem ia Sm ica from 1965 to p resent. R esearch pro- interests include graptolite evolution and b iostratigraphy, as w ell as app li- fessor from 1996. W orking on Ordovician stratigraphy and cono- cation of stratigraphy to understand- do nts. ing basin history and tectonics. H e is a Titular m em ber of t he IC S Subcom - s e n i o r r e se a r c h g e o l ogist at the M acquarie U ni- m ission on O rdovician Stratigrap勺 Bvearrsriyty D C Wenetbrbey f iosr aEcostratigraphy and P alaeobiology, A ustralia, w ith active interests in a num ber of asp ects of O rdovician geology (since 1996), and Secretary and and the palaeontology of c alcifi ed sponges. H e w as Chairm an of t he new sletter editor for the G raptolite ICS Subcom m ission on O rdovician Stratigraphyfrom 1989 to 1996, W orking G roup of the International P alaeontol ogical A ssociation ． and is now one of t he leaders of IG CP project 410focusing on the great O rdovician biodiversification event. Chen X u, B orn in 1936, G raduated Stanley C. Finney is Professor and Chair in the D epartm ent of Geo- from the B eijing C ollege of G eology logical Sciences at Cal扣rm a State University, Long B each. Ilb in 1959, em p loyed by the N anjing research interests include graptolite system atics and biostratig- Institute of G eology and Palaeontol- rap hy, the Late O rdovician extinction, and stratigraphy and paleon- ogy, A cadem ia Sinica from 1959 to tology of O rdovician rocks of the G reat Basin. F inney is C hair o} p resent. R esearch professor from the IC S Subcom m ission on O rdovician Stratigraphy. 1989, Vice-C hairm an of the O rdovi- cian Subcom m ission from 199 1. R esearch fi eld: O rdovician and Sil- urian straligrap勺 and graptolites.

Sep tem ber 199