by 0 H Walliser, P Bultynck, K Weddige, R T Becker and M R House

Definition of the Eifelian-Givetian Stage boundary

The boundary for the Eifelian-Givetian Stage Global

Stratotype Section and Point (GSSP) in the MiddleDevonian has been ratified勿the ICS and the IUGS andis placed in a section at Jebel Mech Irdane in the Tafilaltof Morocco. The position of the boundary was selected妙the Subcommission on Devonian Stratigrap勿in 1992to coincide with the level at which Polygnathus pseudo-

foliatus changes to Polygnathus hemiansatus asdescribed herein. The boundary corresponds closelywith the base of the goniatite Maenioceras Stufe used asa Middle Devonian division, and with the entry of thedacryoconarid Nowakia otomari. Although spores arenot describedfrom the section owing to thermal modifi-cation, the level is thought to lie below the appearance ofGeminospora lemurata the entry of which has beenwidely used elsewhere in spore-bearing regions as aguide to the Givetian. Comments are made on the rela-

tions of the GSSP level to the associated Kaedk orotomari Event.

Introduction

The Devonian System has been divided into three series, Lower,Middle and Upper, essentially since the Bologna Congress of Geol-ogists in 1888 recommended this pattern for all geologic systems.The Subcommission on Devonian Stratigraphy (SDS) has alreadyrecommended Global Stratigraphic Section and Point (GSSP)boundaries for both the upper and lower limits of the Middle Devon-ian and these have been ratified by the ICS and lUGS (Ziegler andMapper, 1985; Mapper and others, 1987). The chronostratigraphicdivision of the Middle Devonian is into a lower Eifelian stage, andan upper Givetian stage. This paper gives details of the GSSP rec-ornmended by SDS to define the base of the Givetian: it was for-mally ratified by lUGS at a London meeting of the Executive Com-mittee held in January 1994.

The classic area for the Givetian is in the Ardennes of southern

Belgium and northern France where the term Givetien has beenavailable for rather over a century being introduced by Gosselet(1879) for the Calcaire de Givet or Calcaire a Stringocephalus bur-tini. However, even in the type area there has been no consistent def-inition of a base (Errera and others, 1972). Some have placed thelowest 5-6 m of dark bluish limestones in the Eifelian (locally Cou-vinian, Carte g6ologique d6taiII6 de la France, Givet, 1970); and oth-

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Episodes, VoL 18, no. 3

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、 释哪翼Figare2 Photographs illustrating the position of the GSSP Eifelian-Givetian boundary level, Bed 123, at Jebel Mech Irdane, 25kin SSW of Erfoud and 12 km SW of Rissani, Tqfilalt, Morocco (Photos bv 0 H Walliser).

September 1995

109

ers not (Bultyrick, 1970, 1987). Another boundary used has been theentry of Stringocephalus burtini, which appears above the base ofthe Givet Limestone in the type area, and in the Loogh Formation inthe Eifel Mountains of adjacent Germany (Struve, 1982a). With theincreasing dominance of highly discriminating goniatite biostratig-raphy in more pelagic facies, especially developed in Germany eastof the Rhine, other faunal guides have been used such as the Zone ofCabrieroceras crispiforme（＝rouvillei) but that species group isnow known to occur as early as the conodont australis Zone (Beckerand House, 1994a) and well within the Eifelian of the revised defin-ition. Another index, Maeneceras (now Maenioceras) undulatum

was suggested by Schmidt (1958, p.309), and that closely corre-sponds to the boundary now recommended.

However it has been the growth in conodont studies which hascontributed most to the detailed correlation of Eifel ian-Givetian

boundary sections internationally and demonstrated the need forclear definition. The sequence of the classic Ardennes area wasdescribed by Bultynck (1970, 1987) and was clarified by his work inMorocco. The sequence of the Eifel area was described by Weddige(1977, 1988, 1989). This led to proposals that the boundary should

be related to a level in an evolutionary sequence where Polygnaihuspseudofohatus changes to Polygnaihus hemiansatus by a changefrom a steep outer anterior platform margin to an obliquely decliningone. Potential sections had been considered in Germany andMorocco. After much discussion, the SDS received three formal

submissions for the GSSP, all in southern Morocco, at Ou Driss, BouTchrafine and Jebel Mech Irdane. After all three were visited by theSDS in December 1991 all but Jebel Mech Irdane were withdrawn

and this was unanimously accepted at a Business Meeting andaccepted in the subsequent postal vote with 20 votes in favour andone against. The advantages of the Moroccan sections lie in theirassociation with a wide range of other faunal elements likely to be ofvalue for international correlation. Some details relating to the defin-ing characteristics arc given later in this account.

In parallel with the work of the SDS on international correlationat about this level has been the recognition of the importance of awidespread hypoxic sedimentary perturbation near the Eifelian--Givetian boundary which has been named the KaMk Event (House,1985) or, after associated faunal indicators, the otoinari or rouvillei

Event (Walliser, 1984, 1985). At Jebel Mech Irdane it is represented

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Figure3 Table showing the ranges of taxa across the Eifelian-Givetian boundary at Jebel Mech Irdane (Modifiedfioin Walliser, 1991).

即isodes, Vol. 18, no. 3

110

by a black shale intercalation near the level of the proposed defini-tion. Some comments on this are made later.

Recommended stratotype

The recommended level for the GSSP to define the base of the Givet-

ian is at Jebel Mech Irdane, 25 kni SSW of Erfoud and 12 krn SW of

Rissani, Morocco (Figure 1) (1:100,000 Carte du Maroc, FeuilleNH-30-XX-2, Erfoud, Lambert's coordinates: x＝599 2, y＝4706).Jebel Mech Irdane translates as 'Hill of the Little Mouse'. The local-

ity is about 6 km from the metalled Msissi road west of Rissam (Fig-ure 1) and easily reached by four-wheel -drive vehicles. The ridgethere gives continuous exposure. The proposed level is at the base ofBed 123 in the succession (Figures 2a-c)

The ridge of Jebel Mech Irdane is 4 km long and exposes a fulland fossiliferous succession from the Emsian into the Frasnian.

Exposure is complete and each bed may be examined in numerousplaces along the ridge. The actual proposed stratotype sequence is onthe gently sloping western side of a knoll which gives easy access toall beds. Around the GSSP the section is primarily one of pelagiccalcilutites and micrites with shales at the Ka}Ak Event level. The

detailed faunal record of the section is given in Figure 3 (modifiedfrom Walliser, 1991). The area is extremely isolated and unlikely tobe threatened in any way. Access is available to scientists but autho-risation papers should be sought from the Bureau of Mines, Rabat.

The boundary proposed represents the level at which Polyg-nathus pseudofoliatus changes to Polygnathus hemiansatus by achange from a steep outer anterior platfann margin to an obliquelydeclining one and in particular the new form recognised as Polyg-nathus hemiansatus; this level, of Bed 123 at Jebel Mech Irdane, iswithin the upper Freilingen Formation in the Eifel (Bultynck andothers, 1991). The Stringocephalus entry level in the Eifel lies at theoverlying Ahbach-Loogh boundary, thus the range of the trueStringocephalus is wholly within the Givetian under the proposeddefinition. The main development of black limestones in the Oder-sh5user Formation of the eastern Rhenish Schiefergebirge lies belowthe new boundary (Bultynck and others, 1991；Weddige, 1990), asdoes much of the Ka}jk Member of the Srbsko Formation in the

Prague Basin; these units correspond to the entry of Nowakiaotomari and mark the otomari Event (Walliser, 1985) or Ka}&Event (House, 1985), and hence to the upper part of the classicalcrisp晌rme（＝rouvillei) Zone (MD-1-F2 of Becker and House,1994a), the top part of which represents a marked extinction eventfor goniatites (House, 1985, 1993; Becker and House, 1994a). Thelatter seems to lie within beds 117 and 119 in the Mech Irdane sec-

tion. The proposed boundary level appears to be just above the entryof the genus Maenioceras and hence close to the base of the widelyused Maenioceras Stufe of the goniatite terminology but now to beused excluding the Cabrieroceras crispiforme levels.

Conodont record

The conodont definition of the Eifelian-Givetian boundary is basedon the entry of a definitive form of the conodont species Polygnathushemiansatus Bultynck (1987) which appears in Bed 123 of the GS SPat Mech Irdane. The Po. hemiansatus lineage was derived mostprobably from the Po. pseudofoliatus Group. The critical point in thedevelopment from Po. pseudofoliatus Wittekindt (1966) to Po.henuansatus is the transformation from a steep outer anterior marginto an obliquely declining one (Figure 4).

Within the succeeding development of Po. hemiansatus theouter adcarinal trough in front of the geniculation point flattensincreasingly. Variations in this flattening can be used for morpho-metric differentiation within Po. hemiansatus. Two extremes are

obvious. One is represented, for instance, by the holotype of Pohemiansatus (Bultynck, 1987, pl. 7, fig. 26) which demonstrates a

strongly bowed outwards, thus forming a spoon-like shelf. Thisspoon-like structure can be less pronounced in early varieties (Figure4d) and even more strongly pronounced in late varieties (Figure 4e).A further characteristic feature is a distinct constriction of the outer

platform just posterior to the geniculation point where its upper mar-gin forms a high 'shoulder' which arises above the general platformsurface.

The opposite extreme also shows a flat slope of the anteriorouter platform. The shelf structure, however, is in this case narrower,without a distinct spoon-like expansion, a constriction on the outerplatform, or a prominent 'shoulder' (Figure 4c). This variety occursat the beginning of the range of Po. hemiansatus and, in our samplesfrom pelagic realm facies, is already accompanied by the first speci-mens of the Po. hemiansatus morphotype with a moderately devel-oped spoon-like structure.

The ancestors of Po. hemiansatus, which are still present withthe early Po. hemiansatus morphotypes, have a steep outer anteriorplatform margin (Figure 4a, b). They are included in the Po. pseudo-foliatus Group, typical representatives of which are characterised bydeep and narrow anterior adcarinal troughs. Immediate ancestors,however, already demonstrate a slight expansion of the outer ante-rior platform (for example, in Bultynck, 1989, pl. 2, fig. 5). Also theslope of the anterior outer margin of such Po. pseudofohatus speci-mens tends to become shallower, thus indicating the transition to the

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Figure 4 Morphotypes of the conodonts Polygnathuspseudofoliatus-Polygnathus bemiansatus lineage. A, B, Po.pseudofoliatus Wittekind} with steep outer anterior platformmargin; in B, the outer anterior advarinal trough is already lessnarrow than in A. C, D, Po. hemiansatus Bultynck, with obliquelydeclined outer anteriorplatform marginjorming a spoon-likestructure; the latter becomes gradually more evidentfrom C to E;D coincides with the holotype of Po. hemiansatus. Allmagnifications ca. x 60. (From Bultyuck and others, 1991).

September 1995

厂

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selliallves of尸0.（mwnsis, tile alliel iol- pkilfol-ill ol w1lidi is sti-oll"kI Isen-atecl oil both sides, }nv i-atliVCIV ti-eCILIC111 ill 1CVC1S \601 ",Pool)mol-pbotypes, of' Po／，‘mlansajll.}.

FUrtlier in(lic}iloi-s toic‘、1一1一c卜、tl戈，‘飞 }we }-,ivell 11V Com)(ioill's of, 111C

Oenus /criodit,v- particukidy‘们lie ljjle}i,(e 1. regidaricrelccim Bill-mick（1970) to 1. obliqllimar,}iiwms Biscliol I' an(f Zievlej（］9}7),Trnnsitional 1}ol-ljls（）！holli species mW cm-1v morphotNpes ol' 1.‘）乃11仔111 /) I ( I，几钾malits occm- wifli flie cmliei- repi-csentatives of' Ile)heMiWI}eMI.A. RUI the moi-e tvpicA morphotvpes of' 1. Obliquillim.-}!hiemo, which }av c1mractef-i,,ed by ohfiLjLlC I)OS(Cf-iol CIC116C[Cs,}Wccolllpan,v Ole spool) mol-pflot),Pcs‘）｝Po. 11cmialm(die's.

Goniatite record

Figure 6 Sufural diagrams ofMiddle Devonian goniatifesre/C vant阳the E}Ieliai卜Givelian boundary. A-D,Moeiiiot-ei-atid,ie,vlio;i,,iitgprogre.v.vii,e elaboration ofthe ventro-lateral adventitious lobe,- A, Maenjoceras琪 koeneni (Frech)from Bed,T}VVI. Jebel Ainelane (AID II-A), O-Kford UniversityMuseum, House Collection, No. 2476, X 3.5. B, suture ofMaenioceras cf. koenem (Frech) based on Be 1517, BeckerCollection, Institute of Palaeontology, Free University Berlin, atwhorl height of9minjust before the onsel qf ventro-lateraljurrows,firom Bed If 9, Mech Irdane (,WD H-A), X 4.6. C,Maenioceras molarium (Whidborne) reversed sutural diagrain o.faspecimen illustrating an early Givetian zonefimil (AID II-B)加in Wolborough Quarry, south Devon, Geological Survey可6reat Britain Va. GS 7112, X 4.6; D,阿‘，‘，｝，，‘）‘尸j了1、／‘rebrallim (G.

& V Sandberger) suture illustrattag the nzid-6ivelian zonefi)ssil(AID II-C), enlarged. E, F, Tornoceratidae showing thedevelopment ofthe lateral adventitious lobe.凡Parodicerasdiscoidetim (Hall), suture based on the holotypeftom the CherryValley Limestone, New York, New York Vate Aluseuln 405,1, X.3.3. Tornoceras mesopleuron House, the holotype斤0111Thedf6rd, Ontario.from beds rej},red to the early Givetian, A 1.3.

MIC P0.／1〔·］）］；‘1］，人（1111、 type. FO）I-IJICI-ly.山ese transitional fol-Ins havebeen regarded： is early varictics of尸。）．hemiansams (for example.Bultynck, 1987, pl. 7, h,,. 22: Wcddipe} 1988 in ian-c chart of theHeilim-'ell Formation）．

The尸0. henjimls(IlIts evA llioll call be dcm(）门、trated ill two sec-

(1011S OfSOLIthern Morocco. at Jbcl Oil Driss and Jbel Mcch fi-dane, a}}

well as in the Blauer Butch Section in Germany. in the Achel OuDriss section（Bultynck, 1989), a south-western outlier ofthe Ma'IdetBasin, tile two earliest morphotypes (sensu Fi2urc 4c. d) occul- ill,,amplc ODE 7-1 1 and specimens similar to the hololype in "ampleODE 7-13. In the Nlech Iro：me section, specimens of' P0. hemiltIlml-ms are first reco-nised in sample 123, cqLliVaiCntS of tile holotype illsalllplc}',！25} 127 and 129, and [Ile y0l-Ingest morphotypcs, withextremely developcd 'spoons I . in sample 131．Ill tile section ofMauer Bruch, Po. hemiansatus appears },vithin the Uppel-IlloSt part offile Odersh;iLlser Limestone (in sample a ofthe collection of、 Walliseiand smilple D2 ill the collection of、 Wed山},.C). I lie Vi rst 'Spool] Mot--pholypes' occur within the first massive limestone bed ofthe overly-in,, discoidcs Limestone (sample d of Walliser, sample C4 of Wed-Idi(,c).I JlItClISiVC StUdieS Of the different conodont SCqLICIICCS in

Moroccoand Central Luropc led to the preferred use. "hich has beenaccepted, of the lineage (it’ Po. henjim),swits rather than that of Po.Iciisensis Zie-ler and Klappei（1976) which fornlcrlv bad been takeninto consideration as, a houndary index (for cxample, Weddi(-,e1989). Ill tile svctiolls studied. 11o, cnSellsi's、、distinctly less frequentthan P0. hemiolvVwu、一This explains why Understandino of' the evo-lution of 111). ellsellsis is les's well Known that] that of Po. hemitifl.m-

Ito. Up to the present it has been recol-Inised that the typical repre-

Ill tile last CCIMIIA FlollapIcl（1895) 1-ccol-nised tile importance of agolliatite lic I'Ctci.].C(l lo tile LCIILI', MeICIIC( （1884)(rcilamcd Alaeniewvtw.} hy Schindc"olt ill 19-)3), for defillill" tilelate middIc Devolliall. 'I一 his has led lo the widely reco},,uiscd AM。一IliOCCI-ON SlfliC 01 FCCCIII 111CMILH-C ICI)LICHIL tile OIJCF一StIlle、｝。、macill（cla.} lerchraIIIIII, of Frech（1902). Fornicrk *,lie Macnio-

CeRIA StUte k\ al, aj1j)roXilllatCI\ C(jUi\ alCllt to tile Gi\ctiail but theSDS/IUGS (feci"ioll oil the mi(ICIIC/t一ppcr F)e\onian ,cric,; houlldal-Vtrans)'erred file tormcf- Fraalien Via ,\s,,i,,c cic I } rollic fell ne,,,（）（Bel-

Oluill, alld tile八山nhan lu of' Gcrman} to (lieMiddle Dc%onian（Klapper and otIlcr,,. 1987）：HoLi.,,c（1985) therefore wpalalcd tile/ollal equivaicilt：、、tile Pharui( eras SIL11C：、、'111 uppcr山、1111011、）！tileGivoian,

The piect,,,c debuition ol the lo,,\ct houndavy ha"', kultil vceellfl}.beell：。maticrof tjnccrutint} (HOLISC, 1978). The (fcfilmw chalacletII ;t I c（们he I-10IMS，、lhe phN （）‘all dds'CillitiOU', sC1111-0-late：一川lobe (I·i"!LIIC }A, 13), 1IMS Chaill-"HW" Jfl JMCS11-al d1ldl-CCStidpatient, in xhich tile laicral Jobe of, the adult lilk-'rate" ktlcr}dlv dur-1111-1 ollto(,}C[JV, bUt tile VC110-0-latCl-al、Odie i, Ll 11 (h,7iCIC(j． r rhe icheiMuch fi-clane slratot}pc, togethcr with the adjacent、 Ichel八lildalleSection Mcc}cv all(( I follsv, (99（，I IJ94a), pro\ide、 tile fir}t detaileddoclimentation of, tile exact IcvcI（）｝clifrv of山。gell。，、认1〔1］；‘）（、）丫1、and Calilils/ MaCIIIO）CCI-atidaC dhONC taLfflaS vs一 iih Agoii.‘ wvtdcm(,} and

Cubricro( cj a,v 0 hat i,,, around heck 1 12 to 1 14). The -m-cen and111,11 IN, LIPPCY IN11-t Of hCd I I〔）of the Johel Mech h-dane ,ection \ icideda rich }-'Orlialk 1"ItIlla \A1111 IIHMUOLI') PU，一‘uli( cra S, lJol, (tj?1(,10( C)Yl %,滩9‘）11“1111（L“(.()SI11／。1111丫 (cf'Archiac alld VCHICLIH) With fal-C-C\Cdphacopid trilobitc.,,. A,,,,ociaied kvith thi,,, I'auna} htit liol nu-C, i" tilecal-lic'o of tile Macniocc，一：lljdac. mm｝］，‘）‘cra's cj-. koeweni (Flech): it

ha,; a diell shape similar to山at in Mucnio(‘1 V y ICI一‘j）I丫1 I I III I ( G d I ILI I-Sandber-cr) (TIL'Ure 51-)) bill with：、%Cl-}' SIMIlOkk }td\elltiliOll̀, loheoil tile VCIIII-O-LuCl-ill Shoulders. 'I’ lie type o(Macnio. koem,ni (Frech)was from tileM0111;T111CN() I 1-C赫wilio. 1110111alltm Molzaplel) llojuGcrinally is Somcwha卜nill lilf- but‘、,,}Iid (0 Po）sse,, Founded I-',It[ICIthau angulai laterni lobes.！；，，、：、｝dOleFnnWfli0n MUNt： 11A'dn：、rex 11110nand illt]Slr}16011 of the older species of Xlaeiiioccros. Adetermination of specimens from Jehel Aniclane (Figure 5A）byBecker and House（1994a) lias heen as Macnio. aft. imelidamm bill

they may he better retered to Macni(，一cl几koenem. Related forins（）！abou曰lie same a,,c are ako known in theI ：甲per parl of一 tile Ka}JkShale ofBohenna Mol/apfeJ in halu), 1903: ChlupaL 1960) hut thc\have not been filprcd. The oldest level \v i山Macnim cra,} in 111C I：，）］－kilt does not co）fflain Lilly typical Eifelian ammonoid (-11-OUJ：、，1 'J：、，101example Werneroceratinac (Mt1?tmatcco(、、Cabi ic，一。）‘erav) olPinacitidac, but only genera known to bloss(）川：ind ranLc InLflici inthe Givetian. A si-nificarit flaunal cliaiwc in ammonoid fial-111',11; UlMorocco secills to lie Within tile KaOk Event jnlcv}al, at (lie hound-

ary between pyl-itic "Imics（Bed 117, " ith the last ohmicimni Cahrh－roccrim) and suhsequent dacryoconal-id-rich c:11-bollates. Thus thebase of' tile Maenim cras Stule lies only fractionally helo" flic cho-sell level for tile base OfthC GiVeli是ln} Mid SUCh a small山Vel Leticc 11"

acceptable.

Episodes, Vol. 18,，，。，＿矛

j／2

In the Tahlalt. lorms which appear to hccome extinct before theentry Of M是ICIIiO）CCF}ts HICILKIC thel，11了‘1‘71亡万一五犷了）1）ljl‘1〔了1“、 Group,slfballarcesl(、，Fidehte,s, and the last Ancioccratinae (Kokeiiia)

I tic Tornoccratidac appear with Mtrodi(cras in (he Eifclian,at记Parodiceray is common helmv the GSSP level at Mech Irdane in

the ko(kehamo /one. In New York, Porodiceras occurs川 the

CherryValley Limestone (Figure 51）where Tornoceao iS alsoreported Mouse, 1965) bill the typical biconvex growth line patternIS not InC( until山c（）vCrl}lll , C 11c m Vill" C itteMI11120 SIMIC. SO it Would SCeIll山'it file true I , ornoceras enters in the earliest Givetian, but this is 1101

ClOCLIFFICIlted in Mech lt-clanc. 156cidertz（1987) has shown that in

八IL,cria, lorilm‘ra.s cntci,,, to(-,cthcr with /c riodits obliql1clijell-gi,111-tio. an altermitiN e Vuicle torthe earliest Givetian.

L'arly Gi\ctiall linleStolics ahme山C hOUndarv ;it Jebel Mcchli-danc have typical a(,oniatitids and subsequently there is an impor-lant regioual marker levc] with Small WedekimIcNit alT. psillm imi(Becker and HOLISC, 1 994}0.

lure lot- future Ll,C althOLI,I}h the level lo：一：malysis is likely to depend()It hiostratioraphic evidence.I

Dacryoconarid record

Det川ell SILICIV 01' this 21IOLIJ) ill the arc}i ol'thc GSS11 is still needed.NowaAiet ololliari BOU}ck and Prand occurs ill Jebel Mech 11-dalle

and in the Tatilalt lc\一 cl but the Nith olalolomari /one hOUI)dZH-}'： lsused h\ BOUCck（1964) ItIl。曰“6tke（1979) pohabiv lic, i1clo, t h,Cssf) level and at the hase of山e KaLlk ]'\cut interval. Alheni

(1993) indicates that theCSSP level is "i山ill the otomari Zone

interval. The hase of'山。Succeeding pamllomari Zone isINVilhill the I'M ( HA /OlIL-

Spore record

For Spores, it is tile entry of the GemillOSI)M"I／‘murala Balme〔·）），‘，，‘／．Playlord "vilich is：，ver} important tic into tcri-estrial I'aciesalthough SUI)SCCIUCIIIIN (lie species is very 10112 ianLin,}. No sporesha\e }ct been obt：日lie([ from [lie JchcI I'vlech irdline section, but(1CMiW)S/)M(1 1('M111Y11(1 OCCUF、川八1('CFI}l (BlUu1eHLlJC1 and others,1988). In the Filel this spore enters in tile mullerl di} ision of, theAhhach Formation.：，little ahme the GSSP 1c%cl (Lohoziak and oth-

ers, 1990} WcddiLc, 1990). The entry has been widdy LISCCI else-\}hcrc in spore-hearin,, rc,,ionsI ：，、}t 111.1i(IC to tile GjketiMl (Richard-、（），：and McGrcLoi，1986} Streel and others,］987)： in(] this US}1,('C islittle altered hy tile (Ichnilion ploposed.

Magnetostratigraphy

Because of 1-CLional ren1}1'(11C11s：itio）n, P0kJri(V curves IhIVC 1101 beenlV0dUCCd tor the Talikill. Nevcrthclcss. new methods ol, 1-na'-mictic

Susceptibility｛NIS) lo.-Lirw have been undcr(Acii h\ Crick and oth-CYS（1995). YhC.SC studies Sho\A tile Most CX11-Clue level,., of' low sus-

ccptibility associated "ith the Kacak Event in the Tatilalt with：，C(）川parable extreme recorded also ai the same level in the MaiderBasin. Such studies }11-C CoutinLIHILI.

Radiometric and OFT dating

No Stlid} pro%idcs radionictric dates close to山C GSSp for the haseof' the Giketian. I’ lie review of' Fordhain（1992) SU.(-1,11CStS }t (kite ofabout 388 Ma lor the boundary. very山ft,creill front the estimate ol,380 Ma by Harland and others（1989). AllhOM111 MI eStuMnte lorGivctian time of 6-5 Ma has been given by [louse（1995) LISi 11 11} IM-C-CCSS10）11,11 'JI-MiltUres for dii Orbital Forcin- I inicscalc (01-T). midestimates li}oc been oken for the (JUNItiOn、）！一conodont /ones tor the

stage, SUCh Work has not vet been carried dmvii into the Eijelian}

Event stratigraphy

It is no\,\ appreciated山}it }1 Sediu)CHIM-y hyl)OXiC PCIU11-11,1tion Occursimmediately preceding the proposed definition 1or the hase of' theIGivetian. This otomari Event was rcco-nisat by Wallisci in 1980mid lie oa}c the nam。川！983} lie (Ictines the terin as the hori/on ofI'acics chan',,c to black sediments. The term KaeLik Event MOLISC,1985) has heen applied to the w,hole hypoxic inler% al. The otomori orKacJik E'vent has been increasingly regarded as important ill the lastI IfckN }cars and it is now recognised in Germany (Walliser, 1984}Weddioc, 1988. 1990} Wcddi,,e and StIUVC, 1988）一Sp}till ('I'I-Lly0lS-Massonj and others, 19W BUI-2isCh： 111(1 Others, 1982) C'/CCIIRepublic（House, 1985} Chlupac and Kukal, 1986), North Mrica(\7v allisel，1 9W Becker and HOUSe I 994a) and in SOL1111一west Asia in

the JAHj i112 section of' GLKIll"Xi (KLK11111 and others, 1989). It) shelfJ , I Iarczis there is c\ idencc that the Kac,,'lk or womori Event it) pelaoicsediments is morc or less coc\al with an intcrv川of "aps \AllichIS11-M C（1982h) described as：、Great Gap' Itorn the neritic MiddIcI)CVOlMUl Ol'SOUlh-WCS( Fngland, Aidcnnes, Eifel andcvell Viet日：Hn

(Weddi-c' 1988} Wccldi},,c and Stl-LIVC, 1988). In continental facies,Ione of Lls (,%/]Rfl）has SLl,1gC̀,lCC1 tIMt (he CAT111 may he repiesented inthe Old Red Sandstone h\ the Sandwich： in(]八cll：lrl：11‘：1、、Fish bedsof Scotland. Neither conodont nor goniatitc c\ ideticc places it pre-ciscly in castern North America. bUt the acine of' the event mav hcthe cleepenin- and enn-v of' Mack shales associated with the Chittc-nanL,o Shale of the early Hamilton Group in New }ork 0 louse,1983} Becker and HOU.',C, 1994a} p. I I（））．

I'ru}ol、一Massoni and others（1990) drew attention 10 110Wloosely the c}en曰crins at this level have heen applied in rccern liter-ature. This is partIN, dLIC to file SUCCeSSiVC sta-es in then- rccoLmilionhUt I)c%olli}m hypoxic events arc dernonstrahly polyphase (House.1985: Schindler, 19()(）二Becker and HOLISC, 1994h) and the chronol-

（）(,} of、 clcj}jiled environmental history is only ,lowk heino el Llc i-o 1} ' I ]cdate〔土．So） fiar as the GSSP section is concerned, the 之 lC111C WOUld

appear to he kkhere the pyritic levels are hest developed around heds｝｝71o 1】9

Correlation of the proposed boundarylevel

Chemostratigraphy

Dctailed ,cochemical StUdiCs 1111-01-MIll theI Ibeen atteiflptCd. ISOtOI)iC JILICtUatiOlP, aCI-OSSCLH-rentl%, beim, in,}esti-ated in the Broken

stratotVI)c have not yet 山C hO）LH)daI-V IeVel arc

River area, QUCCIISlandALL'41-alia (TaIC11taildothel-S 1903)andthesame 'I'l-OUI)isworking inthe Mont;igne Noire but results m-e not aNailahle. Only preliminaryresults lot- the Bairandium arc、。）Im- published (Illadilova and oth-ei-,,, 1994). llowcvc，一With SLICh an OhViOUS If山ological Paroxysin atthe Kacac IC\el it SCCIIIS UnlikCIV that山is will [lot provide a signa-I

川1W, bCCII file \ iC" Of the SUI)COHIIIIiSSion山at sections if) pelagicrealm facies are likelv to he more Complete than thos。川IICI'Iticlacies and it has SOUL111t potential stratotype sections Ahich are fitpelaoic fl,icies with good conodont records and with as many othelI --lat-Inal and floral (,roups represented as possible. Followino woi火byBultynck and Hollard门980) it was clear that sections in the Tafilaltarea of Morocco were IIILICII SUperiOF to those known elsewheic.Three proposals wei-e i-eceived for potential stnatotNfics there. atJebel On Driss (Bultynck. 1989: Walliser, 1990. pp.17-23）、BOUTchraline (Bultvnck and Walliser in Walliser, 1991, pp.49-5-7}

Seplember 199一5

Becker and House, 1994a) and Jebel Mech Irdane (Walliser, 1991,

pp,25-29). Jebel Ou Driss, although a thicker section, and contain-ing more neritic elements than Jebel Mech Irdane, was poorer ingoniatites. Bou Tchrafine raised problems because there are no lime-stone beds intercalated in the corresponding upper part ot theotomari blackshales and the clift exposures are less accessible. JebelMech Irdane, in the event, was preferred because of the greater abuti-dance ot pelagic and hemipelagic faunas and excellence of the sec-tiODs above and below the boundary. Whilst a spore record is notavailable, it seems probable that this will be forthcoming in readilycorrelatable localities in view of the records in southern Algeria(Blumendjel and others, 1988). In addition the section at MechIrdane provides high potential for other fossil groups, especiallytrilobites and ostracods. but also pelecypods, gastropods, thin-shelled brachiopods and even corals.

Because of the wide range of faunal and floral changes at theproposed level, it is considered that the international correlation pos-sible at the entry of Polygnothus hemiansatus is superior to any otherlevel considered by the Subcommission for this GSSP. 'the mainadvantage of Po. hemiansatus as an index for the Givetian-Eifelianboundary in comparison with other conodont taxa, is its world-widegeographic distribution. Occur-rences are known from the Tafilaltand Ma}ider of Morocco (Bultynck, 1987, 1989; Walliser, 1988);from the Cantabrian Mountains of Spain (Garcia-Lopez, 1987); fromPic de Bissous in the Montague Noire ot France (Walfiser, 1990);from Couvin in the Ardennes of Belgium (Bultynck, 1970, pl.15fi,,.5, identified as P. xyla);的m Blauer Bruch in the eastern Rhen-ish Mountains and the Eifel Mountains of Germany (Weddige,1989)} from Guangxi Province of China (Silhongshan section inZiegler and Wang, 1985, see Bultyrick, 1987, pl. 8, fig. 5)} and fromthe Broken River District of Queensland, Australia (Mawson and

Talent, 1989). The proposed boundary coincides closely with the upper

boundary of the classical goniatite crisfi}forme Zone but is below theentry ot Strinyocephalus and the base of the Calcaire de Giver whichhas been the most common Belgian and French standard. In this areathe earliest occurence of Po. hemiansatus is 42 m below the base of

the Calcaire de Givet. However, it should be stressed that as a con-sequence of the shallow-water facies, Po. hemiansatus is rare andIcriodus obliquiniarginatus is the most valuable boundary index forregional correlation (Bultynck, 1993).

Little work has been done on the precise documentation ofgroups other than conodonts, goniatites and dacryoconarids acrossthe boundary in other areas, especially when compared with theinterest generated by the Frasnian-Famennian extinction event.Nevertheless it does appear to be an extinction event of some impor-tance and, as has been shown, it falls within the range of the variousdefinitions used in Belgium and Germany hitherto. However it is tobe expected that the precision of the new conodont data will enableit to be placed with accuracy in many areas of the globe. The Sub-commission on Devonian Stratigraphy considers that the new GSSPcorresponds closely with classical usages of the basal Givetian andthat the more precise definition will do much to stabilise terminologyand encourage further study.

References

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Becker, R T, and House, M R, 1994a, International Devonian goniatite zona- tion, Emsian to Givefian, with new records from Morocco: Courier Forschungsinstitut Senckenberg, v. 169, pp. 79-135.

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Chlupd}.！．1960. Stratigraphical investigation ol'thc Srbsko Beds iGi}ctian) in the Devonian ol' Central Bohemia: Sbornik Ustfedmho tJSta\L1

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Chlup}}, 1, and Kukal,2，1986, Reflection of possible global De}onian events in the Barrandian area, in Walliser. 0 It. ed，Global bio-events

Lecture Notes in Earth Science, no. 8, pp. 169-179Chlup}ie, 1, and Kukal, Z, 1988, Possible global events and the strati}raphv of'

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slovjkia): Sbornik Geologickcho Wdeck6ho. Geologie, }. 42. pp 83-148

Crick, R E, Ellwood, B, F1 Hassani, M, 1994, Integration of biostratigraph} . magnefic susceptibib飞yand relative sea-level change几a"e,,v took at high resolution correlation: Subcommission on Devonian Stratigraph,N， Newsletter no.｝1, pp. 59-66.

Errera, M, Mamet, B, and Sartenaer, P, 1972, Le Calcaire de Givet et le Gj\e_ tien a Givet: Bulletin de I Institut Royal des Sciences Naturelles de Bel- gique, Sciences de la Terre, v. 48门），pp} 1-59.

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Gbddertz, B, 1987, Devonische Gornatnen aus SW-Algerien und ihre stiati- graphische Eniorchlung in dic Conodonten-Abfolge: Palacontographica. Abteilung A, v. 197(4-6), pp. 127-220.

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Holzapfel, E, 1895, Das Obere Mitteldevon (Schichten mit Stringocephalus Burtini und Maeneceras terebratum) im Rheinischen Gebirge: Abhand- lungen der Kliniglichen Preussischen Geologischen Landesanstalt, Neue Folge, v. 16, 459 pp.

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Weddige, K, 1989, Focusing on 'serrated ensensis': Document submitted to the SDS (ICS, IUGS), Washington, pp. 1, 2.

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Weddige, K, and Struve, W, 1988, Towards a I natural' Givetian Boundary, Voting for a conodont based boundary close to the culmination of the otoinari Event: Document submitted to the SDS (ICS, IUGS), Rennes, pp. I一2.

Wittekindt, H, 1966, Zur Conodonten-Chronologie des Mitteldevons: Fortschritte der Geologic von Rheinland und Westfalen, v. 9, pp. 621-641.

Ziegler, W, and Klapper, G, 1985, Stages of the Devonian System: Episodes, v.8,pp.104-109.

Ziegler, W, Klapper, G, and Johnson, J G, 1976, Redefinition and subdivision of the varcus-Zone (Conodonts, Middle-?Upper Devonian) in Europe and North America: Geologica et Palaeontologica, v. 10, pp. 109-140.

Ziegler, W, and Wang, C-Y, 1985, Sihongshan Section, a regional reference section for the Lower-Middle and Middle-Upper Devonian Boundaries in East Asia: Courier Forschungsinstitut Senckenberg, v. 75, pp. 17-37.

Struve, W, 1982b, The Great Gap in the record of marine Middle Devonian: Courier Forschungsinstitut Senckenberg, v. 55, pp. 433-448.

Talent, J A, Mawson, R, Andrew, A S, Hamilton, P J, and Whitford, D J, 1993, Middle Paleozoic extinction events: faunal and isotope data: Palaeogeograpby, Palaeoclimatology, Palacoecology, v. 104, pp. 139-152.

Truy6ls-Massoni, M, Montesinos, J R, Garcia-Alcalde, J L, and Leyva, F, 1990, The Ka}&-Otomari Event and its characterization in the Palentine

Domain (Cantabrian Zone, NW Spain), in Kauffman, E G,＆Walliser, 0 H, eds., Extinction Events in Earth History, Lecture Notes in Earth His- tory, v. 30, pp. 133-143.

Walliser, 0 H, 1980, The geosynclinal development of the Variscides with special regard to the Rhenohercynian Zone, in Cloos, H, and others eds., Mobile Earth; Research Report Deutsche Forschungsgerneinsch aft 1980, pp.185-195.

Walliser, 0 H, 1983, Statement to the boundaries of the Devonian System, its Series and Stages: Document submitted to the Subcommissionm of Devonian Stratigraphy. Montpellier, 4 pp.

Professor Otto Walliser has retiredas Professor and Director of theInstitute of Geology and Palaeontol-ogy at G(5tungen University. Hisresearch is mainly concentrated onthe geosynclinal development of theVariscides, Silurian to Lower Car-bon沙rous stratigraphy and evolu-tionary processes. He chaired IGCPProject 216, Global BiologicalEvents in Earth History and is aMember of the Subcommissions onSilurian Stratigraphy and on Devon-ian Stratigraphy.

Dr Pierre Bultynck is head of thedepartment of Palaeontology at theRoyal Belgian Institute of NaturalSciences, Brussels and Professor ofPolaeontology at the Geography-Geology Department of theKatholieke Universiteit Leuven (Bel-gium). His research concentrates onDevonian conodont taxonomy andbiostratigraphy. He is currently See-retary of the Subcommission onDevonian Stratigrap脚．

September 1995

115

DrKarsten Weddige, aformerpupilof Professor Willi Ziegler at the Uni-versity of Marburg, has taught at theUniversity of Munich, and is now atthe Research Institute of the Senck-enberg Museum, Frankfurt. He isengaged in Lower and MiddleDevonian conodont studies and was

involved in the GSSP recommenda-tions on several Devonian bound-

aries. Currently he is a Member ofthe Subcommission on Devonian

Stratigraphy and Chairman of theGerman Subcommission for Devon-ian Stratigrap梅·

Pr可essor Michael R House is Pro-jessor of Geology at the Universityof Southampton. He had previouslytaught at the Universities ofDurham, Oxford and Hull. Hisresearches have mainly concen-trated on mid-Palaeozoic interna-

tional correlation and regional andevent synthesis, mainly usingammonoids. He is currently Chair-man of the Subcommission onDevonian Stratigraphy.

刀r R Thomas Becker works at the

Palaeontological Institute of theFree University Berlin.刀￡receivedhis doctorate in 1991,户om theRuhr-University of Bochum, Ger-many, andfroin 1988-90 worked atthe University of Southampton onDevonian extinction events. Cur-

rently he is working on globalfaciesshifts and evolutionary ecology in幼per Devonian outer she扩settings.He is a Corresponding Member ofthe Subcommission on Devonian

Stratigraphy.

Episodes, Vol. 18, no. 3