bY, Marlin Brasier, John Cowie and Michael Tavlor D eci si on on the P r ecambr i an- Cambr i an boundar y str atotype

The Global Stratotype Se(,tion and Point j br the Pro- dominate elsewhere. It wits for this reas（川that B Dai ly (unpub- terozoiC- Canibrian botindar v has been agreed upon. li shed) emphasised the potential of' [race fossi l strati graphy as a subsidi ary gVuide. The botindarY is defi ned in a coastal section near the T his wa s l 'oll ow cd i n 1974 by a meeting in Pari s. at which the loviln Of' Fortune in soti theaste，二 Netyfl )undland, fol lowi ng Points Were 1.111anini ousl y agreed (Cowie, 1992). Canada. T he pri mary task of the Working Group was the choice of a stra - Lotype boundary poi nt-, a secondary task was the consideration ot associ ated str atigraphic di visions above and below the bound- a ry . I nt r oducti on Any su ccession selected for the boundary point must be as con- fi nUOUS as possible, mari ne. and as monofacial as possible} the main method of guidance i n selecti on should be biostrati g- T he problem of the Precambrian-Cambrian boundary is part of one raphy al though all possible methods of correl ation shoul d be ol' i he Lreatcst eni gmas of the f ossi l record; i.e. the relatively abrupt enl is ted. appear ance of skeletal fossi ls and complex, deep burrows i n sedi- T he ' Edia ca ra ' ty pe fauna should be considered as Precambri an- inerriary Successions around the world. As wi ll be recounted below, T he 'oleii el lid/t'al lotaspid' tr ilobite faunas shoul d be consi dered its defi nition has i nvol ved the roll i ng back of a maj or frontier in as Cambrian- geology over the last three decades. B etween the ' E d i ac ara' and the tril obite faunas, those f os si 川七r－ U nti l the late 194 0 s. i t was ass um e d th a t the Precambrian was ous successions that Could not be al located with certai nty to largely wi thout fossil s and that the base of the Cambri an was mar ked ei ther the Precambri an or the Cambr ian, should hav e the W ork - by the l owest appearance of tril obi tes, e.g. the ' Olenell us Z one' of' i ng Group’S Cl ose attention. Walcott （1890) and Wheeler 门947). More traditional ly, it was I ncreased SUppor t for wor k o n th e boundary was made possi - drawn a[ a reuional Unconformi ty below them, c-g. i n Rayner （1967). ble i n 1974, when 'T he Precambrian- Carnbr ian Boundary' was T he fi rst steps towards a more precise defi ni ti on of the base were accepted i ts Project 29 by the IGC13 Board. A meeti ng i n Cam- taken i n 1960. at the Norden IGC i n Copenhagen. when M F Glaess- bridae. UK , in 1978. reviewed discoveri es Of SUb-tr i lobitic smal l net- proposed the establ ishment of a Subcommission on Cambrian s keletal fos s i 卜 and [race fos s i ls f rom around the w or ld, as well as StratioCraphy, and i n 1968 when Chair man C I Stubblefi eld and Sec- the potential ：）「unacCynetostrati graphy. T he Cambr idge meeti ng retary J W Cowie chose the problem of' the ' Base of the Cambrian recommended to the Wor ki ng Group that " T he Precambr ian- System' its one of its fi rst tasks. By thi s time, the existence ol' a latest Cambr ian boundar y should be placed as close as is practi cabl e to Precambrian fauna was widel y acknowledged, e.g- i n Glaessner and the base Of the oldest stratigraphic uni t to yield T orninoti an Wade （1966), and work by Russi an gL,eologi sts was begi nni ng to (sensu lato) fossi l assemblages" (Cowie, 1978). Although there demonstrate a pre-tr ilobitic succession of skeletal faunas, which was l ittle suppor t at thi s ti me for it boundary defi ned by trace fos- were referred to the Cambrian System. e.v. i n Rozanov （1967). siJs. their potenti al for the correlati on ot strata bel ow the fi rst Meetings on the boundary were organized for the IGC in Cz echoslo- tr i lobites wits now being explored (see Al per t, 1977; Brasier , vaki a in 1968, and at Montreal i n 1972. Much di scussion ensued at 1979, fi gure I ）． the latter ni celi ng and it ' Worki n.- Group on the Precarribrian- Cam- Candidates fo r t he P recani br ian- Cani brian GS S P w ere dis - brian Boundary' (PC-CBWG) was for med, wi th J W Cowie as its cussed in some detai l at a mectingC. in Br istol, England in 1983. and Chairman. Some of the history of the Working Group has been sum- three were selected for (urther consideration, as fol low s . mari zed elsewhere (Cowie, 1992). Ul akfi an-SLII.UgLir on the Aldan River in castern Si b eri a, ot the In ef fect, thi s Worki ngC Group w a s s etting i tself the chal leng- f or mer USSR (now in Russia)-, here the boundary level (at the i na task of defi ni ng the ' bottom li ne' of the biostr ati g r aphic scal e; base of bed 8) lay in carbonate faci es, withi n a succession of i .e. ［（）di scover, naine and i nterpret f ossi ls where few had been smal l skeletal fossils and al gae that l ay below the earl iest found before. Many of the fossi ls unearthed over the fol lowing archaeocyathans, brachiopods and other markets ot bTommoti an decades were not r eferable to previousl y known groups and their type' : thi s section was well known and well studied. potenti al for strati gr aphic correlation was, therefore, completely T he section at Mei shucun near Kunmi ng, in Yunna n Provi nce untes ted. of souther n Chi na. Here, the boundary level (Marker B) lay T he W or kin gV Gr ou p held i ts fi rst fi eld meeti ngV i n S iberi a in wi thi n a phosphori te facies and was marked by the abrupt 1973, sponsored by the Acaderny of Sciences of the USS R, to con- appearances of phosphati sed inicromol kiscs and pr oblematica. sider possi ble str atotypes For the Precambri an- Cambr ian bound- T his s ection was w ell -studied but l ittle known outsi de of ary al ong the middle reaches of the Al dan and L ena ri vers in China. Y akuLia, eastern Si beria. Here, 29 Forei gMn gCeologi sts were i ntro- S ev eral s ec ti ons on the B uri n Peninsula of southeastern New - duced to the 'T ommoi ian I'auna' and the secti ons of R ozanov and foundland, Canada; here both small skeletal fossils and trace fos- others （1969）一Members di scussed, not for the l ast ti me, the ori gin s i ls w ere know n to occur i n it rnix ed carbonale-s i licicl astic s uc- of' the lowest smal l shel ly fossi l (S SF ) asscrnblagl e i n bed 8 at cessi on. Only outline studies were avai lable from thi s region and Ulakhan Sul ugur, that was refer red to the base Ot the T ommoti an no preci se section was pi npoi nted. Stage (Cowie and Roz anov, 1974). Discussi ons also focused on At this meeti ng, i t was agai n dec i de d tha t the boundary strato- the relationship between li thofaci es and biofacies, notably the type should be pl aced " as close as practi cabl e to the l owest known problem of correlatinCg carbonate shelf facies with archaeocy- appearance of diverse shelly fossils with a good potential for corre- athans (as in Siberia) with clastic shelf to basinal facies that pre- lation" (Cowie, 1985). Such an emphasis upon SS17s provi ded a great

， 广 ＿1 1 1 气， 污 卜 ， I ， 了

Sti1 111.11L IS ［。、their study. but there was growi ng concern about thei r however- that [lie whole section was remagnetised i n Ordovi cian util ity for con-cl ation. A preli minary mandate For ill e MeishUCUII SCC- times. A Wor king Group visi t to the Burin Peninsul a in 1979 was ti on was del'erred at the Moscow IGC in 1984, when i t was recog- l'ollowed up by i mportant ,round work on SSFs. trace lossi ls and nised that greater international aIgreement oil SSF taxonomy was Ii [ hostr at igraphy (Bengi son and Fletcher, 1981．1983). Further necessary- 'I’h i s led to -,in "SSF Workshop" i n Uppsala in 1986, orga- researches Culmi nated in a series ol' papers which detai led the strati - nized bv S Benatson. It call now be seen that thi s mecting resulted i n gIOraPphic dli、S1h1-ibLUlti（o川n （o）f trace l O SS jl S, SS[7s and l ithostrati -raphy several new thrusts. First, it becalm apparent that the boundary SLIC- (Cri mes and A nderson, 1985: N arbonne and others. 1997: N ar- cess ions in C hina had it dis ti nct character, w hi ch Could be tr aced i nto bonne and Myrow, 1998: L anding, 1988; Landi ng and others, Indi a. Paki stan and Iran (Brasier , 1999a) but correlation beyond 19 89 ). these former terranes of' Gondwana was more probleni atical . Scc- A n u nd er manding emerged that SSF s, which had hitherto pro- ond, it cricoura-ed the view that small skeletal l ossi ls were ]oil ,,- vided the focus of一 Working Group discussi ons, Were very greatl y ranging, hi ghly variable, over-spl it taxonomically, taphonotnicall y affected bV provincial ism and a Virtual restri cti on to shallow car bon- poorly understood. oft en restricted by Iacies and provi nci al i n di stri- ate facies. T his suggested. to some, that clefi nition of the boundary buti on (Landing and others. 1989} Qi an ii nd Bell " Ison, 1989). miaht be better (TUided by [race fossi ls as well its body fossils. The Ai tempts Were Made to draw [lie data oil paridemic lorni s togt-ether, advanl aacs of trace fossi l s were stressed to he as foll ows (c.(, COMParill ", the fi rst appCitrall U S 01一 SLICCCSSIVC. taXa Oil it 10lobal Scale Cr imes. 1987} Narbonne and others. 1997. Narbonne and Myrow (c.- . Brasi er, 1989b) but the results WCI-C not Cil li l-CIV CUIC01-11-all ing 19 88 ). I'm hi gh-resoluti on strati graphy. T he problems of' SS I}s were begi n- 'I’h e y a re es pecial ly common in si licicl astic I'lacies. i n whi ch SS I's ning. to come into l ocus. arc typi cal ly rare and poorly preserved- T his is i mportant since KnowledLg,e about th e C h i ne se sections improved after visits by these deposits compr ise nearl y 70 per cent of' exposed rocks i n Group members i n [li e l ate 1970s -.in([ car ly 1980s, and most espe- the boundary interval. ciall y aft er publ ications i n English (IAIO and others. 1984, Xing and Cambri an trace lossi ls ap pe ar to have been less restri cted in ier nis others, 199 1）and the inter national meetinu oil i fi eT eri ni nal Precam- of habil at range than in later intervals. brian and Cambri an Systems at Yichangt} i n 1987. T he problems of' Several Successi ve trace f ossil zones fr om a ro und the world may cor relatingZ.- the three SUb-tri lobitic niar kers a( Mei shUCLII) (termed A, be reco(mized i n strata below the lowest tr ilobi tes. B and C) were reviewed i n En,ghsh hy Brasier （1989a). Scientists I'li ese zones incl ude ichnogener a wi th it l i mited St ra LiIg raphi c Outsi de C hi na showed consi derable concern about fi ve I'actors relat - ran-e and it broad strati graphic di str ibUti O11. Of these. the P h) - i n,) to the GSSP candidate at Mei shLIC1111- codes pethim Z one assembl alye contai ns typical Cambri an i ch- T he comparati ve age ol' i li e Z one 11 a ss embla-c above Mar ker notaxa i n -it hi,yh-divcrsi ty assemblage with branched mor- B, chosen by (li e Chinese as [lie Candi date boundary [)Oi ll l } phologi es, compl ex feedi ng burrows. escape traces and thi s questi on arose because i t was thought ．‘）contai n l ossil s dwel li nt., burrows. ']'he Underl ying Hai-kiniell a poti ol i ca Z one found above the T ornill oti an i n Si beri a（Bengr.,i son and others, assembl atle i s of l ower diver si ty and compri ses s imple. hori - 19 9 4 )} zontal. sedi rrient-Iceder traces, c.a. Nenm il es, I'al ueopascich- T he pre se nce ol' a possible gap_j UsI below Market- B, shown by 11 1i s . an abr upt changzl}e i n l ithol"acies (c.gI . Brasi ci ，198911: Landin1g. T he ra il o es of Har laniell a pml ofi ca and Ph)-coel es pedum arc 19 94 ). bel ieved not to overlap} one succeeds [he other. providing. it T he l a ck ‘） 门 111.111al C0110 111.1itV between [li e three markers, also rare exampl e oi 加Urial replacement withi n it boundary succes- su-}L,-estive of' breaks in [he sequence (Qian at记 Bengtson. s i o n . 19 99 ). At F o r tu ne H ead. B uri n Peninsula, these tw o Iraces are s een T he int er pretation ol' carbon isotopic proj iles repor ted by Brasier withi n it strati- raphic succession that shows littl e evi dence ol' and others （1990). For example. K ii-schvi nk and others （1991） envi ronmental change. Correl ations of the boundary level are sm- ested that Z one If ii i i-l it correlate with the basal Aidabani an also possible between Fortune Head and other local ities on the CXCLI I-Si o n s i n S i be r i a . Burin Peni nsula. Si milar faunal changes Were Purported to take ’I ’h e interprelation of' Rb /Si- clay mi neral isochrons W,g. 596.91 place at other local ities around the world. 4.6 Ma, X ing and others, 1991）：recent data 1'rom LJ-Pb i sochrons T hese i deas were di scussed !It a rnecti qg at S t John’s . New- I'rorn ash hands near Market- 13 indicate it much younoer age of f 0tindland i n August 1997. and fol lowed by f’ield excursions 5251 7 Ma (Coni pslon and others, 1992). throuoh the ' T ermi nal Proterozoic' and lower Cambri an (Nar- Further documentation al so became av ail ab le o n the S iberi an bonne, 19K ). By this time. the WorkingC (!]-Out) was under sorne secti ons ( Sokolov an(] Z huravleva, 1% 3} R ozanov and Sokolov, pressure to reach a deci si on, because i t had examined the probl em 1984) and some member s ol' the Worki ng Group were able to exam- si nce 1972. It was also cl ear that whi lst i t mi 'l l-it he possi ble to ine the GSSP at Ul akhan-SUIL1,21I.Ir dUri nO山e Second International reach a deci sion on the boundary poi nt, i ts gl obal correlati on wits SVII1pOSiUIII Oil the Cambr ian Systern in 1990 (Astas hki n and others. going to be open to wide di spute. Non-biostrati graphic methods 1990). Its potenti al 1"or carbon i sotope- and magnelostrati graphy of con-clai i on. Such its carbon一，strontium一，even1 -st ralj ar aphy appeared good W.g. Ki rschvi nk and others. 199 1）．Discussi on, how- ,a nd oVe oc hr onol oCgy- W ou l d be needed to i mprove str atiLo-raphic res- ever, centred on the ori gi n ol' hcd 8: Was it 11 StratIfi CLI layer. or was i t ol uti on at this level . A proposal was put forward. ther efore, by M piped down along karstic li SSLII-CS fi -0111 about ;I inetre above" Support ［）Brasi er and K J Hsu to the IGCP Board in 1989. to e11COL1ra(1c l"or the fatter view was oi ven bv li eld data (Khoni cniovsky and oth- 5S：LIcCl1l1 lr℃esce：a11rche、s thlr，：o川ugah a proJect on ' Pi-ec：iiil bi-i iiii -(' ainbi-jaii ers, 1990) but isotopic data has proved more equivocal (Brasier and E vent Strati gr aphy' . Pr oj ect 303 was accepted and its first inect- other s, 1993）一A view i s emerging ol' it widespread unconf'orni i Ly i n-(-, took place i n Si heri a in July- AuIMSI 1990. T he findi ngs of near the base of' the T oni ni otian across inuch of' the S i ber ian Plat- thi s proJect have an impor tant heari ng on cor rel ation of the Pro- l'or ni . represcmi ng -.I hia[LIS 01' 1111CCIl ai n duration (C.g. L anding carri br ian- Carnbr ian boundar y. which wi l l be di SCLIssed el se- 19 94 ). w here. U nti l 1 98 1 the potential Ol' SOL11heasiern NeWlOfl idland Im it T h e ch o se n GS S P candi date at I -ortune H cad. B uri n Peni ns ula. inixed. carbonale/SSF -siI ici cl astic/1 race, I"ossi I strati graphy was li t- Newfoundland wits fir st put forward by Canadian and US members li e tested. Hutchinson （1962) and Greene and W il li ams （1974) had of thc Worki ng Group i n 1987. T he resul ts of a straw pol l held in St reported SS F assernblaves below [he earliest Iril obi les. T P Fletcher John 's W that ti me seerned favourable (Cowie and B rasier, 1989 ). （1978) had presented an Outli ne Stratigraphy （们li e Buri n Peni nsula Wr itten proposals were then reCILICsted by Chairman J W Cowie at Cambridge. T his work was l'ol lowed ti p by Furthcr fi th(）一and bio- From each of the three GS S P candidates . to outli ne their uti li tv for strati graphy CF P Fl etcher, 1.111111-il-i fi shed), accompanied by inaaneto- cor rel ation by biostrati graphi c and non-bi osiratioraphic (e.,, strali graphy 0 K irschvi nk, unpubli shed)- T he littler discovered. 1,1.eocli roii olo.L,i c. pal aeornagnetic and stable i sotopic) techniques,

March & J ime / 9 V4 for accessi bi li ty. and potenti al for conserv ati on . T hese were submit- In this rcgCi on, Cambrian depos ition (Figure 2) was accornni o- ted in October 1990 as fol lows: A Yu Rozanov (Ulakhan-Sul ufL_f ): dated by local , long-term extensi on of the basement, compr ising Xi no Y, L uo. H, Jiang, Z and Z hang, S (MeiShUcun): and E Landi ng Late Precambr ian vol canics and clastics affected by the -Aval onian and G N Narbonne (Fortune Head, Newfoundland). A postal ball ot Orogen' - T he Fortune Bay Basin began wi th the deposi tion ol ot the 23 Voti na Members was ar ranged by J W Cowie in the Spri ng 2750 ti t ol' upwardl y fi ninLg_ red b eds that gL_rade i nto peril idal sand- of 1991．T hi s bal lot recei ved a 100 per cent response, Yi vi nC- an stones tit the top (Beng(son an(] I 1cicher. 19H3. Landing and others, overall majority ol' 52 per cent to the BUrin candi date. 35 per cent to 1988). T hese were succeeded by ca- 1000 tit of' si liciclasti c shelf' Chi na and 13 per cent to Si ber ia. Fol lowing the guidcl ines o1ACS . a l'acies, pl aced in the Chapel Island I-ormation, and deposi ted dur- second postal bal lot was held on the Burin .,}Lction alone, in the SUrn- in ,L_y ：：maj o，二、ca level ' cycle its foll ows: peritidal sandstone and ni er of' 199 1, which led to a 61 per cent majori ty for the section at shales (Member I ）：S1.01-111-i nfILIC11CCd Muddy deltaic and shel f Fortune Head. T hi s maj ori ty wits l arge enough to allow rati fi cation sandstones and IIIUdstoncs (Member 2A)} thinly larni nated sil t- by the ICS and the IUGS (at the IGC i n Kyoto. August 1992), when stones of the di stal shelf', deposited below wave base (Member 213 Chair manship of' the Cambr ian Subcommission passed to M D ti nd Member 3): UnUdstoncs with thin li mestones. deposited under Brasier . Responsi bi l ity for the basal boundary of the Cambrian also low energy, inner shelf' to penti dal con山tions (Member 4): and passed from the Wor kinCg Gr oup to the Cambr ian Subcommission at sandstones and s il ts tones of all offs hore to s horel'ace s torni-domi- t h i s ti me . nated shel f (Myrow and Hiscol t, 1994). T hese were then capped by the macrol idal sandstones all (] si ll s tones of the Random Formati on, which call be traced across the Avalonjan regi on (Hutchi nson, T he F or tune H ead GS S P 1962, L andi ng, 1992)- Member I ol一 th e C ha pel Isl and For mation (ca. 180 111) T he Fortune [lead GSSP section IS Situated near the tip of the Burin includes upper most Precambrian se山ments. It yi elds biostrati- Peninsula. Southeastern Newfoundl and (fi gure I ），in low cl if f's that gL,raphicall y important trace lossi ls （们he Har taniel la podolica i ch- extended beyond ' Fortune Dump’. E asy access is possible frorn the nol'ossi l Biozone (Benatson and Fl etcher, 1993二（.rinies and town of' Fortune; there are no pol itical or geographical problems ol Anderson, 1985）一I l arl ani el la podoli ca and Palaeopasci chims del - access. T he stral otype was Pi ctured in E-pisodes of’ December 1987 icams ranCa.e into Member 2, wli cre山ey are l ast seen 0.2 ill below (Narbonne, 1987, figure I ）． the GS S I1. O rLanic-wal led tubes of" Subefi ehles cambfi ens ts l'il-SL Coastal cl iff' cxposures at Fo rt une Head di splay some 440 m of' appear near the top ol' Mernber I and range at least its high as Mcm- the Chapel Island Formation. wi th beds dipping a[ 15 to 46 degrees her 4 . T he Subefi di les candwiens ts s kel etal los si l B ioz one i s to the west (steeper dips are towar d the top（们li e section). Several def ined between the First occurrence ol' this taxon, and the hi- her SnIal l faUl ls are present wel l above the stratotype level , but market- first appearance of calcareous lube ’L adatheca’c.1-fi lldr ica i ll hori zons al low easy correlati on across them (Landing and others. Member 2 B . 198K p.35). Breaks in deposition are minor and restricted to the T he Pre ca mb r i an -Cambrian boundary point (Figure .1) lies bases ol' thi n. wave-deposi ted sand units. 2.4 in above the base ol' Member 2 in the Chapel Isl and Formati on.

FA C IE S A S S O C IAT IO N S ｛二］黯 貂egsreen sandstones 场 }}Y 了 卜 口 Gsarenyd sttoo nbela cakn din steiltrsbteodndee/dshale 配／ 4L 内 Il ly/ - 0 丫 ；，7 ，犯 － 口 氦愁器饥esrabneddsstone and I I 叮 学 B O N AV IS T A ，， 夕 ， NI N S U L A ｝石刃 R}cl.and green 个 ／ L 一一- i s ms t o ne 勺 份，书‘厂少日 ．一 ，～～～～曰 勺尸 了 5 0 k m 丫 ： 军分 ME M B E R I 、 、 甲 不／ 妙 ／ 7:4L . 飞 ’ 2 ， M E MB E R 2 勺 j ｛｛

， ／ 毋 、

4 ＼ 沪 冲 ，、 ． 声 向

叮， 哪 J o h n 's 八甘A L O N 乙3 峭．卜 P E N IN S U L A ． 一一」 厂 沪 l o o m N 了 甘 篡 q 、 FORT UNE HEAD GS SP SECT ION, 多 S O U T HE A S T E R N N E W F O U N D L A N D S O U T H E A S T E R N N E W F OU N D L A N D

F i gur e I Generali zed l ocali ty map of N ewf oundland (inset) showing l ocati on of t he F or tune H ead str atotype and detai l map of t he 440 m-thick section at F or tune Head. Diagonal r uli ng i ndi cal es .wr i ke direction. FA =f acies associations. Based on l anding and others (1988,fi gures 4and19).

均fi s odeN, Vol . 17 , nos - I & 2 6

Interpretation Me mb er Palaeobathymetry A 1

10 0 0 丁 内 UJ 卜 S 厂 5 隔 ＜ 墓 H 子 ｜ 卜 几 厂 q 0 0 1 夕 万 标袭 十 石 叹 二 L。’二1 才 了气广沙 扮争e" 0' }N' j 入 8 0 0 4 魏 一 山 S L V 一 工 产 L 中 几 1 lwe 7 0 0 一 ｜ 3 一

6 0 0 一

5 0 0 嚣。 。 1 吕 5 翔一。 卜 。 4 0 0 2 户 一 山 S 二 下 V 3 0 0 、 H 架 d 二 S B I 一 尸 全I - 沐 玉 CA MB R I A N 2 0 0 ／1 ＊一 一 F S 一 ／－ P R E C A M 13 R I A N 耸 泛 J、 es川 10 0 es es 口 9 咚 一 1 叹 巨 厂 霎墓，二｝｝f li 1111 } 一Mn.j}dfi Col-,t, 厂 越 门 0 一 一 十 一 U U 1 S S 山 ①＾ 亡 S 的 S 山 ﹂ 。 5一 一 匕 巴 庄 巴 山 IS W 日 U一 一 分 鼠一STah,.d/W1 ,h," ,'I-,.at T Shd-,} SdO b,N}td.Id ---d - SdW- SdGh,a,I Sl}tcO,, G -as1l1, G} ,- C. F igur e 2 6 ener al ized stratigraphi c section ．f i n- th e Chapel ／ I sl and F ormati on, showi ng inl }r red pal tohathlyni etry, thr ee- F igure3 Faunal successi on and l ithol ogy throngh the phase deposi ti onal InstorY, and sequence-str atigr aphic Pr ecanibr ian- Cani br ian boundary stratot ype se cti on at F orl une i nterpr etation. The Pr ecanibr ian- Cani brian boundary stralotype Head. Based on Nar bonne and other s; (1987,fi gur e 5) and poi nt is shown. F S = fl oodi ng su}14ce; AI F S ＝i nax tinuinfl oodi ng l andi ng and other s (1988,fi gur e 20). F or fi )ssil distr ibuti on and surj } ce. SB ＝sequence boundar y. TST ＝tr ansgr essi ve sYsteni s li thologi cal datafi roin the overlying 420 in oj 'continuousl-v tract. HS T ＝highstand systems tract. S WB ＝sl or in wave base. Sh exposed strato at F or tune Head, see Nar bonne and other s} (1987, ＝shalel- Sltst ＝sil istone; S's ＝sandstone; L S ＝l itnestone. T he fi gur e 4), L anding and others (1988, f igures 21- 23); A}Yr ow and

scal e is i n inetres ft oin the b egi nni ng of 1he exposur e. Based on fl iscott (1993, 万gur e 8少．

M Yr O W and H iscott ( 1993, 欣 tir e 3)

i.e. j ust above the transi ti on to ston-n-infl Uenced facies and 18.2 in above the base of the Succes s ion at F or tune H ead. T his GS S P is it Non一biostratigraphic means of point in rock that defi nes it moment in ti me and was selected with cor r el ation Ouidance from the level mar ked by the lowest Occurrence of Plj＿%?- codes pe(han (a trace flossi l ), at the base of the Cambri an PhYcodes peduin Biozone (F igure 2; see Narbonne and others, 1987, li gure T he hmil](Lfy IC\rel lack,, carbowltCS 141itable for carhon or stron- 8B ，．T he inarker fossil is preser ved as it series ol' branched, hypich- tiLIIII isotope anal ysis. StUdICS 011 IIOCILIICS and bedded l imestones nial ridges on the lower sur face of a sandstone- Its appearance at this hi, her in the Burm sLICCCSSiOII sho）v, the CITects of, widespread thel level is not directly traceable to a change i n faci es, which takes pl ace mal alteration clLf i ll g deep hL11-ial and 21-all i tiC i IItI-LISiOII （Brasier and l ower in [he sequence (Member I to Member 2A boundary). In addi - other s. 1992). Si mi lar problems have af ected sui tabi li ty of' the s(I-a- ti on. both peril idal and subtidal facies in Member I contain Har - to）tYPC i ()'- Pal acomaIgn et ic coi rcl ati on (see above). RcI, rcttahly, this lani ella podol ica, and facies identical to those i n Member I are m can s th at t he A si at i c s cct i on s o f S i be i i a and 〔h i na can no t be co r inlerbedded wi thin Member 2A, but do not show Lipper Precambr ian related wi th the ncw GSSP by mcans of carbon isotope- and maIg- trace fossi l s. T hese features SLJ}IgCSt that environmental factors, netostratigraphy, althOLILIh they pro\idc a valLiahle tool for con-cla- tion CI SCw herc （K ii-sch%i nk and others. 199 1二B I aI,iCI and others whil e sioni fi cant, were only of second- order i nfl uence upon the dis- tri buti on of trace fossi ls thougC.h thi s secti on. T he boundary point also ！9 94 ). defi nes the base （）！一the L ow er Cambrian 'Placentian S eries ' ol"L and-

ing and others （1989). T he fi rs t occurre n ce of c alcareous shel led s ke l etal fos si ls Geochronology of the boundary

（E adatheca' c0 indr ica) here li es some 400 in above the Precam- bri an-Carribr ian boundary. As mentioned above. their appearance is R ecent U一Pb radiometric (Ictcrininations on VOlCaIIiC Zil-COlls aFC related to faci es and laphonoinic condi tions and is unl ikely to mark a\ 7川able 1'rom Ne,,k BI-LIIIS\ViCk- i n stral a possibl y con-clated wi th the the true ori gin ol' biorninerali zation. T ri lobi tes appear some 1400 in LIPPCI- part of Member 5 (Bowr in- and othcrs, 1993). T hese vicid a above the boundary point, and mark the star t of the Lower Cambr ian date of' 530.7+0.7 Ma (Isachsen and other s, 1994): previously ' B ranchian Series' （们 andinla 〔1992 ). reported its 53 ］士I Ma bv B owi一川9 and others （1993) and L andin9

M (i r ch & .1i m e 19 94 7

(1994) and provides a inaxi lnUin a,t,}e fo r the base ol' the over lyinCg Cowic- I W. 197M. It l(;S/]( ;(' 13 Project 29 I3rcCiLiii bi-iaii - ('LLiiibi-iiLn Boundary quartzi te l onnati on. T he boundary point l ies some 800 ni below its Working Group I n CambriLILC. 1979: Geological Magazine, v. 115. pp. possible correlati ve, the Random Formation. in the B1.11-in Peninsul a. 15 1一15 2. A further (,uide to the radiornei ric aae of" the Precambri an- C owic, J W. 1985, ( '0111ifi lin" x%ork On the PI-CC.1111hrian一（'ambrian hOLInd- ary: Upisodes, v. S. pp. 93 -97. Cambri an boundary comes From recent U-Pb dates I、一（)m Si ber ia COWiC, J W. 1991 T WO decades Of l-C-search on the Proteroz oic- Phancroz oic (Bowrino and others, 1993). In the Olenck re,,ion. volcani c hreccias transi tion: 1972- 199 1, Occur wi thin the Neinakit- Daldynian StaCge, above the fi r st smal l Cowie, J W . and Roz anoN．A Y u. 1974 , l UGS Precarnbrian-k arnbrian B ound- shelly fossi l (Canibr ol ubul ti.v sp.) but below the fi rst skeletal assem- ary Working GrOLIp [it Siheria: UICOIOLiCal Ma"aZine. 、。．I l l . pp.237- 25-1. bl age with Antibar tles Irlsil icants. These breccias have recently been Crimes, T 11, 1997. ']"race Fossils and correlation of L ate Precanihrian and dated at 543.610.1-4 Ma (Bowr ing and others, 1993). which gives an I} M-IV Call"Ibrian Strala: GCO]OUiCal Mal-laZille. 、，．124, pp. 97- 119. estimated a- e tor the base（们 he Nemakit -Daldyni an ol' about 544 Crimes. T P. all([ Anderson, M M, 1995, '1’r ace Foss ils I"rom Late Precam- M a. T his lev el has been correlated w ith the bas e ol' the Cambri an i n hrian-carly Cambrian straia 01' SOLIthcasl ern Newl'oundland (Canada): temporal and environnicnial impli cat ions: Journal ol' Palconlology, 、一59. Newfoundland (Nar bonne and other s, 1997), oil the 1,01lowill " 3 1( ）一34 3. ',' rounds: Occurrence of PhYcodes sp. at all Unspeci fi ed l evel withi n Fletcher, T 11. 1979. i n United K ill, ([(）川〔'01111-ibUtion lo [he International the Ncinaki t Daldynian (Fedonkin, 1987} actual ly thi s taxon may Geological Cort-chilion Progran'1111C. 1976- 79 Report: 'I li e Royal Socicly. 110L appeal- unti I the middle ol' the stage: M A Fedonkin, pers. comin.. London. pp. 26- 27. 1993)} occurrence ol' Sabell i(l ites canibri ensis. which ranaL,es 1roni Gl aessner, M F} and W adc. M, 1 966. T he late Pi℃一（'ambrian lossils 1'rom E di- the base of the stagCe (Sokol ov and Fedonkin, 1985). A provisional acara, South Ausi ralia: Palaconlology, v.（）． pli . 599- 628. estimate l or the aue of’ the Precambri an Cambri an boundary is. Greene, B . and W illi ams, I L 1974. Ncw IONSi l 10C1111LICS and the base ol' thc theref'ore- cit. 5 44 M a. C am br i an i n so utli casi er n Ne%k FOLAIW ILHILL C anadi an J our nal of' E ar th S ci - crices, v. 11, pp. 3 19- 323. I IULchinson, R D} 1962, CaInhFiall SLI-atiIoraphy and trilobile fi tunas ol"south- eastern NewFOUndland: 111111CH11 01' Lhe G eo log ical Survey ol' Canada. Mg. Acknowledgements 156 p- Khomentovsky, V V. and K arlova, G A} 1993. Biosiratigraphy ‘们 he Ven- T he I'ollowing are thanked ior comments and C0111-i buti ons：。、this di all- Cambrian beds aild IOWCj- Cambrian boundary in Siberia: Gcologi- report: T P Cr imes, T P F letcher, E Landi ng. and A R Palmer. Cal magazine. 、，．130} pp. 29- 45. Ki rschvink. .L .Magariiz. M二Ripperdan. R I ，Z hUravlev, A Y u. and Rozanov, A Yu, 199 1, T he 1' recaill bl-i!Lll/( 'il ll ibFiilii boundary: magrel osiral igraphy 1111d Carbon isotopes resolve co）rl-ClatiOll problems bLi ween Siberi a R ef er en ces Morocco and South Chill a: GSA T oday. v- 1, li p. 69- 7 1, 97. 9 1 I-arl ding, E. 1988, L owcr Cambrian ol' castern Massachusetts: stratigraphy 八[pert. S 1'. 1977. T race Fossil s and [lie basal Can-lbrian boundary, in Crillics, ：11记S1111111 Shelly I'OSNi]N: .10111-11al （们lillacontology. ＼．62, pp.661--695. 'T P. and Harper. J C eds- T race Fossils 2: Geological JOLU-nal SPCCi!ll Landirl,' , 1-1. 1992. L ower Cambr ian ol' Noutheasi el-ii Newl'oundland: Issue. 1). Seel HOLISC Press, I JVCrPOo1. 1)1). 1 -M. epcirogcny and Lazaru} Fami as. Iii holacies-biol'acies l inkaoc}, and the Aslashkin. V A iind seven others. 1990 , Guidebook [01- CXCUrsion ‘川 Il ie myth ol a 'fl obal chronostratigrapli v, in L ipps, J H} and Signo）r, P W, eds Aldan and L ena R ivers. Sihel'i !Lll Plall'orin. Novosibirsk. 115 pp. Ori- in and Farly EVOIL11ion ()I-ilic Mcla/oa: New Y ork, Plenum Press. pp . Bengison. } , and Flelche门 ’P. 198 1, T he SLICCCSSiOn Ol'SkCIC1,L] Fossils i n the 28 3- 30 9. basal I .0%VC1- CILinbrian ol' southeastern Newl'oundland, in T aylor. M F, L anding., F". 1994. Pi-ec；iiiibi-iiiii- ( 'iiiiihi-iLkii hoUlldal-V global SLI'atotype rati- ed.. Short Pali crs Jbr the Secon（曰nlernalional Symposium on the Cam- tied alld it 11CIA pCrSpCC`1i VC OJ' Cifl ihrian lime: Geology, v. 22, 179- 1142. bri an Syslein: U1111CLI States Geological SLll`VCV Open-F ile Report, L andill_ 1". MV1-0\A．P M. BC11LIS. A 1), alld Narbonne, G W 1989. T he Pill- h 1- 743. 1 X pli . CCll tiW1 Scries: appearance ol' lhe OILICSI A clelal izcd ]'aunas in SoUlli cast- Bengtson, S, and Fletcher. T 11, 19M3, 'Til e oldest SCCl1lCllCe Ol' Sk-elClid FOSNill ern NeWl'OllIl Lillill (l: ,10111-11;11 01’ I'llI a C0111 01O gy. ＼63. 1)1). 739-769. i n the h m el- C ani bri an ol ' soui l i casl er n Ne\% l OUndl an止 Canad i an .10 1.i rnal LandinL. E, Narbonne, （；M. Mvrow, P, 13CIRIS, A 11, and Anderson, M M, oF F.arlh Sciences, v. 20, pli . 523- 526- 19148, Fallil aN and (ICI)OSillOnal cnvironniclils （们 li e uppcr Precambrian Bengtson. S. Missarzhevsky. V V. and Rozanox, A YLI. 1994, 'r i-te n -cciiiii- 0WOU'lli L ower Cambr ian, southeastern Newfoundland: New Y ork State brian- Canibrian boundary a plea lor Cift ilion: ICCP ProJect 29 Ch-CUlar Mtiscuill Bulletin, 、463. li p. I S一52. Ne%sleller. JLMC 1994. li p. I 丰15. L LIO H} Ji angZ ，WLI X . Son, X . V il l" Y. I AU G. Z ang S. and T ao Y. 1984, Bom-ing. S A, GrotzinIger, J P. Isachsen. （一E. Knoll. A H, Pelechaty. S M. 5S1i1l1l1i之a11l1l一-（C、之a1lillhblrji., 111 bo ）un dary candidate ill McishUcun. Jinning. Y Linnan. and K olosov, 11. 1993, Calibrating rates ol一 early Cambrian evol ulion: Sci- China: T he Peo ple 's Pu bli shing I louse, Yunnan. 16 PI). encc} v. 1- 6 1, pl，一］293 1298 M yrow. 11, all ‘川iscoll . R N} 1993, Dellosilional hislory and sequence sn-al ig- B rasi cr , N1 D, 1979 . T he C ambr i an radi ati on even[. i n H OLIS C. M R . CLI., ' r he raphy （们 lie Pi-eciiiiibi-iiiii- C'iiiiiii i-i之iii bOLllldW'V SlraLotype Section. Chapel OriOn of MaJor Invertebrate groups. Academic Prcss. ［ondon. pp. Island I}orlll atioll , somh easi ern Newl'OUndland: Palacogeography, 川 3- 160 . Palacochillatology. Palacoccology. 、104, pp- 13 --35. Brasier. M 1) , 1989a, Chi na and [Il e Palacotel l-tyan Belt (India. Pakistan, [ran, Narbonne, G M. 1987. T race fossi ls, small shelly fossils und the Precam- Kazakhslan, and Mongolia). in Cowic, .1 W. and Brasier, M 1) , eds.. T he brian- Cambrian Boundary: ErIiSOLICS, N. 10, 33，一340. Precarnbriai卜（'ainbrian B(）川I dary: OXfoFd University Press. pp. 40---74. N arbonne. （；M, and Myrow, 1'. 1988, T race fossil biostrangraphy in the Pre- B raNicr. M 1). 1989h. T owards a hioSH-aLigraphy ol"di e earl iest skeletal biwas cambr i an - IC，a mbi-jan houl i dal-V i nter val : New Y ork S l ate M useu m B i l l - i n C ow i e. J W , and B r as i er, \14 D . eds., T he P i-eci i i i i br j ,.i il - ( .ai i i bi -i aii letin, 463, pp. 72--76. Boundary: Oxford University Press. pp. 40- 74, N arbonne, (3, M, Myrow, 11, L anding, F , and Anderson, M M, 1997. A candi- Brasier, M 1) , Anderson, M M, and Corlield, R M, 19921, Oxygen and carbon date sLratotype for the Precambrian- Cambrian boundary, Portunc Head, isotope stral igraphy of carly Cambrian carbonates in SOLItheasLu n New- B ur i n Peni ns ul a. SOU Ill eaSICI-11 New f oundl and : Canadi an Jour nal of E ar th foundland and England: Geological Magazine, 、1219, pp. 265- 279. Sciences, v. 1-4, p. 156. B rasier. M 1) , K homentovsky, V V7 and Corli eld, R M, 1993, Stable isolopic Qian Y . and Il englNon. S. 1989. Palaconlology and boostral igraphy or ihe calibration of the earliest skeletal assemblages in eastern Si beria (Pre- MCiShLICUIliall Stage ill Y unnan Province, south China-. Fossils and Strata, Canibrian- Cambrian bOLIndary): T erra Nova, v. 5, pp. 225- 232. v. 24, 156 pp. Brasier, M D. Corli eld, R M, Derry, L A, Rozanov. A Y u, and Z hURIVIev, A Rayner, D, 1967, T he Stratigraphy of the Bri tish Isles: Cambridge Universi ty Yu, 1994, Multiple S 13C excursions spannin},, the Cambrian explosion to Press, L ondon. the Bol oni ian crisis i n Sibcria: Geology, v- 2121, pp. 455- 459. R ozanov, A Y U, 1967. 1’l i e Cambrian lower boundary problem Geological B rasier, M 1), and ni ne others 1990. T he carbon- alid oxygen-isotope record Magazi ne. v. 104, pi）一4 15-434. o f the Preca川br i an- C ani br i an boundar v i nterval i n Ch i na ；川cl Ir an and Rozanov, A Y U, and Sokolov, B S. 1984, L ower Cambrian stage subdivisio，n: their correlation: Geological Malgazine. v. 127, pp. 3 19-332. sLraligraphy: Akademii NaLik SSSR. Moscow. l zdalelsIvo 'NULIka'. (i n Coni psion. W, Wi lliams, I S. Kirschvink. J I ．Z hang Z . and Ma, G. 1992. Z i r- R uss i an ). con U-13b ages Iroin the Farly CaMbrian tinle-scale: Journal 0 1" LlIe Geo- Rozanov, A Y U, and nine others. 1969. 'File T ommolian Stage and the Cam- logical Socicl) , v. 149. 171一184. br i an L ONW r 1301111dal -V Pr Ohl em: A k adcni i a N aUk S S S R , Or dena T r u-

E pi,mde}, V（）／17, i7o.s. I 浅 三 dovogo K rasnogo Z humeni Geologicheskii I nstituta, no. 206, 380 p. (I n Dr J W Cowie has serveda s Secretary Rus si an) of the Cambr ian Subcommissi on Schopf, W J, and Klein, C, 1992, The Proterozoi c Biosphere: Cambridge (1964- 1992), Chai rman and Proj ect University Press. L eader o f t he Precambnan- Cambr ian Sokol ov, B S, and Z huravleva, I T , 1983. L ower Cambrian stage subdivisi on of Siberia. Atlas of fossils: Akade血i Nuak SSSR, Moscow, Trudy Insti- Boundary Working Group (1972- tuta Geol ogi i i Geofyziki , v. 558. (I n Russian). 1992) and as Chai rman of the Inter- Walcott, C D, 1890, The fauna of the L ower Cambri an or Olenel lus Z one: national Commission on Stratigrap砂 T enth A nnual Report of the Director, 1888- 1889, US Geologi cal Survey, (1984- 1992). Ongoing activity in- Par t 1. cludes wor k with the l UGS Geological Wheeler, H E, 1947, Base of the Cambrian System: Journal of Geology, v. Database on Geological Sites (I UGS 55, pp. 153- 159. GE OSI TES) and as Geological X ing Y , L uo, H, Jiang, Z , and Zhang S, 1991 , A candidate gl obal stratotype see- Advisor to World Heri tage. tiona nd函int for the Precarnbrian-Carnbrianb oundary at Meishucun, Yun- nan, China: Journal of C hi na University of Geosciences, v. 2, 47-57口

Dr Martin Brasi er is Chairman of t he Dr Mi chael T ayl or , Secr etary of the Subcommi ssi on on Cambri an Strati - Subcommi ssion on Cambr ian Strati - graphy and Leader of I GCP Proj ect graphy, is a research geologist with 303 on P r ecambrian- Cambr ian E vent the US Geological Sur vey, Denver. Stratigraphy. His r esearch currently H is cur rent res earch interes ts incl ude concentrates on the potential of c arbon early Palaeozoi c tr il obite and moll usc and str ontium isotope stratigraphy f or biostr ati gr ap勺，biof acies analysis improved stratigr aphic resolution of the and carbonate deposi ti onal envi ron- late P recambrian- Cambr ian events, ments. 月‘has developed an ecolog- and on environmental changes assoct- ical model f or explai ni ng the global ated with plate movements (easter n distri buti on of tri l obi te f aunas in Asia to Avalonia少．He lectures in the rel ation to stratifi ed ocean systems E arth Sciences Depar tment at Oxf ord, and is a F ell ow of S t Edmund Hal l.

Sel ected Mi ddl e E ast Paper s fr om G E O ’9 4＿

Presented at the Middle East Geosciences Exhibition and Conf erence, April 1994, Bahrain. Hosted勿 the American Association of P etroleum Geologists, Dhahran Geological Society, Society of E xplorationists of t he Emirates, Society of E xploration Geophysicists.

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