THE STATE OF SI LURI AN STRATI GRAPHY by C. H . Holl and Thi s short arti cle revi ews recent deci sions t aken bv t he IUGS Subcom mi ssi on on Si l uri an St rati graphy,丈he 11 加ci nq worker s on t八e pr ocedures by which recom mendations are made and some o厂 t he chal l enges sti Sil uri an. i nt roducti on Th e g eo l ogi cal s ci e nc es dema nd cl os e i n t er na t i o nal coop er - at i o n as wel l a s a r i g or ous a nd cl e ar l y u nd er s t o od l ang ua ge of wo r d s . Nowher e i s t hi s mor e ke enl y f el t t ha n i n s t r a t i gr a ph y wh er e , d es pi t e t h e l u xur y of l o ng p hi l os op hi c al di s cu s s i on s on r o ck s v er s u s t i me, man y f e el a s en s e o f u r ge ncy a bout a t t e mp t s t o achi e ve a s t and ar d gl o bal ch r o nos t r a t i g r a phy. For s t a g es wi t h i n t he s e t wo s er i es , t h e S u bc ommi s s i on a gr eed t o us e t he " S he i nwo odi an" a nd " Hor r i er i an " s t ag es f o r t h e We nl o ck. Th es e a ga i n h ad be en d ef i ne d by Ba s s e t t et al . ( 1 9 75 ) . The bo un dar y s t r at ot y pe f or t he b as e of t he f ormer was to be the same as t hat for the Wenl ock Seri es. A bo un dar y s t r a t ot yp e f or t he b as e of t he Homer i a n S t a ge The now wel l - known pi oneer work of t he i nter nati onal com- mi t tee on t he Si l u r i a n- Devoni an Boundar y t ook 12 year s to co mpl et e, t hou gh this was a pioneering exercise. Correl- nti nns about thi slevel were also found to have been in such gr i evous err or thatmu ch r ea dj u s t ment an d ev en t ualco川 pro- mi s e wer e needed b ef ore agr eement coul d be r eached ( Boucek , of al . , 1966; Hol l and, 1965; Marti ns son, 1977) . Now was accept ed wi t hi n t he Wenl ock area. I n t he case of the Ludl ow Seri es, Hol l and et al . (1963) had p r e vi o us l y de f i n ed f o ur s t age s , bu t t h e f i r s t and s e co nd o f thes e wer e di f fi cul t to s eparat e out si de the Wel sh Bor der l and a nd t h e t h i r d ( Lei nt war di n i an ) s t ag e c or r es p on d ed t o onl y on e gr aptol i te bi ozone, wi despr ead though that i s. Accor di ngl y, the Subcommi ssi on deci ded that onl y two s tages were approp- ri ate f or the Ludl ow and, as i n t he case of the Wenl ock, t hes e t h e l UGS Commi s s i on on S t r at i gr aph y, t han ks e s pe ci a l l y t o t h e vi s i o n a nd i ni t i a t i v e of pa s t ChaI r man Aca de mi ci a n V. V. c or r es pon d b r oa dl y t o t wo b r ach i o po d f au n as a s wel l a s b ei n g t i ed mor e p r e ci s el y t o t he gr a p t ol i t e bi oz on al s eq uen ce ( Fi g . 2) . Ma ny o t he r g r ou ps ar e o f co ur s e r ec ogn i z ed as act ual l y o r po t e nt i al l y us e f u l i n c or r el a t i o n. menner of t he Sovi et Uni on, act s as an umbr el l a to a whol e l i s t o f S ub co mmi s s i ons f or t he v ar i o us g eo l o gi c al s ys t ems an d o f wo r k i n g g r o ups c onc er ne d wi t h s et t l i ng t h e b ou nda r i e s . Th e S ub co mmi s s i o n on S i l u r i an S t r at i gr ap hy was co ns t i t u t e d Those concerned most di r ect l y wi t h wor k i n the Ludl ow area fr om an a生垫签 body at a meeti ng hel d i n the Uni versi t y of wer e a s k ed t o s ug ge s t n ames f o r t h es e t wo n ew s t a ge s an d t h e S ub commi s s i o n ap pr ov ed t h ei r c hoi ce o f " Gor s t i a n" an d " Lud f o r di an " ( Hol l and et al . 1 980 ) . Th e b ou nd ar y s t r a t o t yp e Bi r mi ng ha m, U. K. , i n 1 9 74. At a f or ma l mee t i n g of t he Subcommi ss i on hel d duri ng the I nt ernati onal Geol ogi cal Con- g r es s i n S yd ney , Aus t r a l i a, i n Au gu s t 1 9 76 , i t wa s a gr eed t o p r o c eed wi t h an ei g ht - ye ar p r o gr a m de s i g n ed t o s o l ve t he ma j or p r o bl e ms o f S i l u r i a n ch r o no s t r at i gr ap hy.Wo r k c ont i n - u ed us i ng q u es t i on nai r es a nd ev e nt u al l y t h er e was al mos t for t he base of the Gor st i an St age i s t he same as that for the base of the Ludl ow Ser i es. For t he bas e of the Ludf or di an St ag e, al s o s i t ed wi t h i n t he Lud l o w a r ea ( Fi g. I ) ,t h e d eci s i o n i s t o u s e t he bou nd ar y pr opo s e d b y Hol l a nd et al .( 1 96 3) f o r unani mous support for a comprehensi ve f i el d meeti ng i n t h e b a s e o f t he i r Lei nt wa r d i ni an St age . Br i t a i n i n 1 97 9. Thi s me et i ng r an ge d f r o r n S out h Wal es , Di s t r i ct , t o Mof f at i n t he S out he r n Up l a nds of Sc ot l and. Th es e d eci s i o ns wer e pr es en t ed t o t he Co mmi s s i on o n S t r a - t i gr aph y at i t s meet i ng i n Par i s i n Au gus t 1 9 80. Pr o f e s s o r Var i ous f ormal meeti ngs of the Subcommi s si on wer e hel d, Anders Mar ti nsson and Dr. M. G. Bass ett , r espect i vel y Chai r - i nc l u di ng s ha r ed meet i ng s wi t h t he Wor ki n g Gr oup on t h e Or d o vi ci a n- S i l u r i a n Bou nda r y s i n ce t h es e t wo gr ou ps had a n umb er o f member s i n common. Th e t ype ar ea s of t he man and Se cr e t a r y o f t he Commi s s i o n, t h en ci r cu l at ed d ocu - thr ough t he Wel s h Bor der l and, Nort h Wal es, and the Lake ment ati on and arr anged a pos tal vote by al l members of the Commi ssi on. The deci si ons al ready outl i ned above were r a t i f i e d wi t h out d i s s ent ( s ee Mar t i n s s on et al . , 1 981 ) . I - l andover y, Wenl ock, and Ludl ow seri es were exami ned, as was Charl es Lapworth' s famous l ocal i ty f or the Or dovi ci an- Cock s , To ghi l l , and Zi eg l er ( 1 97 0) h ad a l r eady di vi de d t h e Ll and ov er y S er i es i nt o f our s t ag es , e qua t e d r e s p ect i v el y wi t h Si l uri an tr ansi t i on at Dobb' s Li nn near Mof fat. The Subcomm i ssi on has 16 Ti t ul ar Members and a con- the much us ed l et tered and number ed di vi si ons Al一A4, BI-B3, s i d er ab l y l a r ge r n umb er of Cor r e s po nd i ng Memb er s . Th os e Cl- C3 . an d C} - C6 . The s e wer e gi v en g eo gr aphi ca l name s based on l ocal i ti es wi thi n t he t ype area near Ll andovery i n pres ent at i ndi vi dual meet i ngs t ook part i n di s cussi ons and S o ut h Wal e s . As t he l owes t Al di vi s i on at Li and o ver y p r o ve d d ec i s i o n maki ng, but f or mal p r op os al s wer e P ut t o po s t al v ot e by t he Ti t ul ar Membe r s . De ci s i o ns a chi ev ed by a s u bs t ant i al to be unf oss i l i f er ous and of uncertai n ext ent, these aut hors chose Dobb' s Li nn f or t he def i ni ti on of t he base of thei r fi r st , ma) ori t y were: The second and t hi rd of the f our seri es i nto whi ch t he Rh ud da ni an St ag e. Th e b as a l b oun da r i es o f t h e r emai ni n g dwi a n, Fr o ni a n, a nd Tel ych i a n s t ag es wer e r ef er r ed t o l o cal - Si l ur i an S ys t em i s t o b e di v i d ed wer e t o be cal l ed”We nl ock I Seri es" and "Ludl ow Ser i es", and boundary st rat ot ypes for i ti es wi t hi n the Ll andovery area. Unf ortunatel y, detai l ed the base of each of t hese were chosen i n the Wel sh f au na l ch ang es t h r ou gh c o nt i n uo us bou nd ar y s t r at ot yp e e ct i on s wi t h ac cu r at el y de f i n e d mar ker p oi nt s wer e not Borderl and, wher e f ul l y des cri bed st andard ar eas pr ovi de a s l abl e and i ndeed there was much di scuss i on by Subcom- s e t t i ng f or t he s e s ec t i o ns . The s e ar e i nd i ca t ed i n Fi g ur e I avai s s i on membe r s o n t he di f f i c ul t i es o f di s cr i mi na t i n g b e- a n d de t ai l s of t he d eci s i o ns wer e r e po r t e d i n 兰et h ai a mi ( Hol l an d 1 9 80 ) . Fu l l d es c r i p t i on s of t he a r ea s a nd s e ct i on s t we e n at l ea s t s ome o f t he s e s t age s el s ewhe r e i n t h e wor l d . ar e t o be f oun d i n Ba s s et t et a l . ( 1 975 ) f or t he Wenl ock, A S ub co mmi s s i on wor k i n g gr ou p i s now l ook i ng c ar ef u l l y at and Hol l and et al . (1 963) f or the Ludl ow. The secti ons ar e the so- cal l ed "nort hern ar ea" of the Li andovery di s tri ct , e more graptol i tes may be avai l abl e. But what ever t he now cared f or by the Nat ure Conser vancy. wher EPI SODES, Vol . 1982, No. 3. 21 N‘.||-t-||||ee| k 5 Dobb' s Li nn and Ant i costi f or thi s purpose. They ar e con- 10 c er ned al s o wi t h t he d i f f i c ul t q u es t i on of t he b i os t r at i gr aph i - cal hori zon best chos en for the boundar y. a The f ou r t h . p os t - Lud l ow p r e - Gedi nn i an s er i es of t he Si l ur i an S ys t em i s t he di vi s i on whi ch wa s r ec og ni zed a s a r e s ul t of t he wor k of t he Si l ur i an - De von i an Bo und ar y Commi t t ee ( Mar - t i n s s o n, 1 97 7) . Er r or s i n pr e vi ou s co r r e l a t i ons h ad be en s u ch t hat t he r oc ks dep os i t ed i n t h i s i n t er val had ac t ua l l y be en "l ost", mai nl y because of the ass umpt i on that grapt ol oi ds mu s t i n s ome ( my s t i cal ) s e ns e b e a b s en t f r om p os t - Si l ur i an 夕’ 健 2 s trata. The t op of the fourt h s eri es i s al r eady defi ned by the n ow a gr eed ba s e of t he Dev oni an at t he b a s e of t h e Mo no- C HU RCH STRETTO N 三 MUCH: ・ gr a pt us un i f or mi s Bi o zon e, a s r ec og ni z ed i n t he bou nd ar y W ENLOCK str at otype secti on at Kl onk i n t he Barrandi an ar ea of Czech- o s l ova k i a. Al t hou gh t her e ha s bee n c on s i der abl e d i s cus s i on and t h r ee s ub mi s s i ons h av e al r e ady b e en ci r cu l a t ed , t he bou nd ar y s t r a t ot y pe f or t he ba s e of t he f our t h s er i es , an d A i ndeed i ts f ormal name, are sti l l to be deci ded by the Subcom m i ssi on. 几 The t h r e e ca nd i d at e s f or t h e s e ri es ( Fi g. 2) ar e t he " Downt o n S er i e s " , " Pr i d ol i S er i e s " an d " Sk al a Se r i es " , or pe r ha ps an al t er nat i v e na me. Th es e woul d be r ep r e s en t e d b y b as a l bo un dar y s t r at ot ype s i n, r es pe ct i v el y, t he We l s h B or d er l and, the Bar randi an area, or Podol i a ( U. S. S. R. ) . The Downton 飞 Ser i e s oc cur s i n cl as s i c cou nt r y wh er e t wo of t h e Si l ur i an s er i e s ar e a l r e ad y de f i n ed an d i t s b as al d i vi s i on, t h e Lu dl o w Bone Bed , i s f a mi l i ar t o ge ol ogi s t s . Her e, howe ver , t h e f a ci e s i s of mar i ne- br a ck i s h char a ct e r . Bas s et t et a] . ( 1 9 80 ) ha ve r ev i e wed t h e co ns i de r a bl e bi o s t r at i gr ap hi cal d at a a vai l - abl e, t o get her wi t h t h e cor r e l at i o n of t he s er i es ac r os s Eu r o pe an d el s ewhe r e, t hr ou gh t he u s e o f a cha i n o f evi d enc e i n vol vi ng os t r ac ode s , s por es , ver t e br a t e s , and gr ap t ol i t e s . Ka l j o ( 1 9 78) has al s o det ai l ed t h i s web of co r r e l a t i ve ev i - 生三兰三 乞J 全 3兰争 于 二 ;干 石石 吕 冲们 I t二二〔 拜 - 一一火 dence. The Pri dol i rocks of Czechos l ovaki a have been cl assi c si nce the work of Bar rande. The base of t he Devoni an i s al ready LUDLOW LLA N D O VERY Dnestr Ri ver and i ts tri butari es i n Podol i a wher e r i ver cl i ffs AND YO UNGER [ 口 < B 月霆吕 K E Y DOW NTO NI AN W EN LO C K 巨 de f i ne d he r e. Th e s t r a t a ar e we l l kn own and wel l r e pr es e nt e d i n mu s e um co l l e ct i ons . Th er e ar e b ot h g r ap t o ) i t i c and S hel l y f aun as . Th e t h i r d p ot e nt i al s t r a t o t y pe i s i n t he a r ea o f t he an d ot h er e xp os u r es cl ear l y di s pl a y a s e qu en ce o f hi gh l y RO CKS W ENL OCK LUD LO W fossili ferous Silurian to lowest Devoni an rocks i n m ari ne TYPE A REA f ac i es an d wi t h s t r u ct ur e of ext r eme si mpl i ci t y. Br ac hi o po ds and os tr acodes are es peci al l y wel l repr es ent ed i n the Skal a. TYPE A REA The S ub co mmi s s i o n i s gr a t e f ul t o Aca de mi ci an B. S. So k ol ov and h i s co l l e agu es wh o ar e ar r a ngi ng det ai l ed ex ami n at i on of t he Sk al a S er i e s i n 1 983 , wh en i t s h ou l d b e p os s i bl e t o as s es s BOUNDARY STRATOTYPES (I一A ) Fi gu r e 1 ; Geol ogi cal map o厂t he Wel s h Bo r de r l an d s howi ng t he rel ati ve meri t s of al l three ar eas under consi der ati on. Si l uri an s ubdi vi si ons and standar d areas厂or t he Wenl ock and Ludl ow seri es. Boundar y str atotype sect i ons as shown i n Many members have al ready seen t he Downton and Barr an- Fi g ur e 2 ar e n umbe r e d as f o l l ows : 1 . Hu ghZ e y Br oo k; 2. por tuni t i es ar e avai l abl e for any necess ar y vi si ts to t he two for mer ar eas . As yet t here i s no demand for the defi ni ti on of t h a n ar e as , t ho ugh f ew h ave p r ev i ou s l y v i s i t ed Po do l i a. Op- Whi twel l Coppi ce; 3. Pi tch Coppi ce; 4. Sunnyhi l l Quarr y. s t a ge s wi t hi n t h e f ou r t h S i l u r i an s er i e s, t ho ugh t h es e wi l l doubt l ess become the concern of the Subcom mi s si on i n future f i n al d ec i s i on, t he or i gi nal土 y匹 ( as di s t i nc t f r om s t a nd ar d) ar ea mu st co nt i nue t o b e r e gar d ed as pr ovi di ng s i gn i f i ca nt pa r a s t r al ot yp es i n Ll a nd ov er y s t r a t i g r a ph y. years. On ce de ci s i o ns h ave be en mad e t hr o ug h t h e p r op er us e o f t h e i nt er na t i o na l mac hi ner y pr ovi d ed b y t h e Commi s s i on on S t r a - t i gr a ph y a nd i t s s ubs i di ar y bo di e s , i t i s ex ce edi ngl y i mpor t an t t h at t he s e s ho ul d be i mpl eme nt ed na t i ona l l y a nd i n t er na t i on - al l y. Pu bl i ci t y f or t he dec i s i on s i s ne ce s s a r y: he nc e t he pr e s en t a t i o n of t h i s i nt er i m r e po r t on t he a ct i v i t i es of t h e Su b commi s s i on o n S i l ur i an S t r at i g r ap hy a nd t h e p ub l i c at i on of v ar i ou s s hor t s t at emen t s o f dec i s i ons al r e ady r e ac he d as I n the meanti me, i n t he summer of 1981 t he Subcommi ssi on h a d t h e o pp or t u n i t y t o e xa mi ne a n exc eed i ngl y f os s i l i f er ou s an d b eau t i f ul l y ex pos ed Ll a nd ov er y s eq ue nce on Ant i co s t i I sl and, Quebec, Canada, where the st ruct ure i s ext remel y s i mpl e ( Bar nes , 1 982 ) . I n Au gu s t 1 98 2, i t ex ami n ed an ot h er p r omi s i n g s e que nc e i n t h e Os l o di s t r i ct o f Nor way an d, ho pef ul l y i n 1 983 i t wi l l be p os s i bl e t o make d eci s i ons on bo un da r y s t r at o t y pe s f or t h e ch r o no s t r at i g r ap hy of t he f i r s t vari ousl y r ef err ed to above. of t he Si l uri an ser i es. The base of t he fi rst of t he two or t h r ee s t a g es i nt o wh i ch t he " Ll a ndo ve r y ( or Ant i c os t i ) Se r i e s " i s l i k el y t o b e d i vi ded mu s t be t ha t of t h e S i l ur i an S ys t em, an d h er e t h e Wor ki n g Gr ou p on t h e Or do vi ci an- Si l u r i an Bou n- da r y i s i n t he p r oce s s of di s cu s s i ng t h e r el at i v e mer i t s of EPI SODES, Vol . 1982, No. 3. References Bar nes , C. R. , 1982, Ordovi ci an- Si l uri an Boundary Studi ed: EPI S ODES , t 982 /t , p . 33 . 22 CHRO NO STRATI G RAPHY │ │ LO CATI ON OF │ BO UNDARY STRATOT│ YPES │ │ uni form i s │ tr ans gr edi │ns │ e S!LURI AN │ Do wn t on Ser i es ? │ ( di v i s i o n i n t o │ We l s h B o r d e r l a n d ? │ │ SYSTEM │ o r │ s t a g e s t o c .a i t │ B a r r a n d i a n a r e a ? │ │ Ph' dol l Ser i es ? │ ne ces s i t y) │ Po do l i a ? │ │ or │ │ │ │ │ Skal a S│ │ er i es ? │ │ 2 │ │ 2 │ │ Ludl ow Seri es │ │ │ Ludf ordi an St age │L udl o w di s t r i c t {Su n ny b i l l Qu ar r y} │ l ei nt ward │i nensi s│ tum escens, │ │ ( =i n c加i ens │ ) │ Gor st i an St age │ L u dl ow d i s t r i c t ( Pi t c h Co pp i c e} │ │ │ ni l ssoni s . l . │ │ ludensi s │ │ Wenl ock Seri es │ Homeri an St age │ Wen l o c k d i s t r i ct ( Wh i t we l l C o pp i c │ │ e) │ lundgreni │ │ el l esae │ │ She i n wo odi an St a ge│ We n l o c k d i s t r i c t ( H u g h l e y Br o o k ) │ │ │ ce nt r i f u │ gus │ crenul at a │ │ Anti cost i Seri es? │ s t ages ( pr obabl y │ An t i co s ti ? │ │ │ or │ three) to 一be │ Liandowery di │ │ strict ? │ Li an do ver y Ser i es? │ d e f i n e d │ O s l o d i s t r i c t? │ │ │ 户 │ │ , │ │ F4 W e 2; St at e of Si l ur i an ch r o no st r at i gr a phy . Cr i t i c al qr a pt ol i t e bi o zon es ar e al s o i ndi cat e d. Bas set t, M. G. , Cocks, L. R. M. , Hol l and, C. H. , Ri ckards, R. B. nat i on al Un i on of Geol ogi ca l S ci en ces Se r i es A, No.,) , Bas set t, M. G. , Laws on, J. D. and Whi t e, D. E. , 1982, The i f i c a t i o n o f S t a n d a r d C h r o n o s t r a t i g r a p h i c a l D i v i s i o n s 1 , a n d 345 p. and Wa r r e n, P. T. , 1 975 , Th e t ype Wenl oc k S er i es : Re p. I ns t . Geol . S ci . , No. 75 八3 , 1 9 p. Mar t i n s s o n, A. , Bas s et t , M. G. a nd Hol l and , C. H. , 1 981 , Rat - Downton Seri es as the Four th Ser i es of the Si l uri an 3TraToTypes ior Ihe M uri an 3YSleM : r -t -1JU L) r -3q 17OLILIF. Sy s t e m: Let hai a, 1 5, 1 - 74. , 36 Bou ce k, B. , Hor ny, R. a nd Ch l up ac , 1 . , 1 966 , Si l ur i an Ve r s us De von i a n: Act a Nu s . n at I . Pr a ga e, 2 2B, 4 9- 66. Co cks , L. R. M. , To ghi l l , P. an d Zi e gl e r , A. M. , 1 970 , St ag e name s wi t hi n t h e Ll and ov er y S er i es : Geol . Mag. 1 07 , 79 - 87. Hol l an d, C. H. , 1 965 , The Si l ur o- De vo ni an Bo und ar y: Geo l . Ma g. 1 02, 21 3 - 2 21 . Hol l an d, C. H. , 1 98 0, Si l ur i a n s er i e s an d s t a ges : de ci s i on s co nc er ni ng c hr ono- s t r at i g r ap hy : Let hai a, 1 3, 23 8. Hol l and, C. H. , Lawson, J. D. and Wal msl ey, V. G. , 1963, The Si l ur i an r o cks of t he Ludl ow di s t r i ct , S hr op s h i r e: Bul l . Br . 八BOUT THE AUTHOR: Mu s . Na t . Hi s t . , S er . Geol . 8 , p. 93- 1 71 . Pr o f . Ch ar l es Hep wor t h Hol l an d i s Pr of es s o r of Geo l o gy an d Hol l an d, C. H. , Laws on , J. D. , Wal ms l ey, V. G. a nd Whi t e, D. E. , Mi n er a l o gy at t h e Dep t . of Ge ol o gy , Tr i ni t y Co l l eg e, Du bl i n 1 98 0, Ludl ow s t age s : Let hai a 1 3, 26 8. 2 , I r e l a nd. He i s a pas t Pr es i de nt of t he Pa l a eon t o l o gi c al As s oci at i on a nd pa s t Chai r man of t h e S t r at i gr aph y Com- Kal j o, D. , 1 978 , Th e Do wnt o ni a n or Pr i do l i an f r o m t he p oi n t mi t t ee of t he Geo l og i ca l S o ci et y o f Lon do n. Hi s r e s e ar ch of vi ew of the Bal t i c Si l ur i an: Eest i NSV Tead. Akad. i n t e r e s t s ce nt er mai nl y o n Lower Pal a eoz oi c s t r at i gr a ph y a nd Toi m. 27, Geol . Ser i es No. 1, 5-10. pa l a eo nt ol o gy. S i n ce h i s ea r l i er r es ea r c h on S i l u r i an r oc ks of t he Wel s h Bor derl and and Central Wal es, he has exami ned Mar t i n s s o n, A. ( ed. ) , 1 97 7 , The Si l ur i an - D ev oni an Bou nd ar y: S c hwe i z er bar t ' s che Ver l ags b uc hh and l un g, S t ut t g ar d ( I n t er - t h ei r cou nt er p ar t s i n man y pa r t s of t he wor l d. EPI SODES, Vol . 1982, No. 3. 23