2}5

勿E. A. Yolkin', A. L KiM2 , K. Weddige-了, J. A. Talent4 and M. R. House-'

Definition of the Pragian/Emsian Stage boundary/ Department ql'Palaeontology & StratigraphY, histaine‘，厂Geology and GeophYsics, Novosibirsk (A 030090, Russia2 Departn7CIII以Strotigrapiri. at the Tashkent 6eological Siirve.v, Tashkent Area, Zongiolo Di.stri( t, 702050, Ul-bekhi.mm3 ForschIffl,"'SillStitilt Senckenberg, Senckenbet}q-Aldoge 25. Frankfiirr W-00325, German N4 School ol'Earth Scien〔二．、，Macquorie Universirv, Noah R)而 N.S.W.2109, AUNIRIH415 Department o/'Geologv, Southampton 0( conographic Centre, Etiopean Wav, }outhampton, Eiighm(IS014 3211（lated Kingdom

The boundtiry介)r the Pragian-Enisian Stage 61obal Strati-raphy OCS) on the basal Enisian GSSP, ratified by RI丁GSIn

StratotYPe Section and Point (GSSP) in the Lower

Devonian has beet，ratified by the ICS and the 1UGS andis placed in a section at the Zilizil'ban Gorge in the

Kitab State Geological Reserve, 170 kin SSE of'

Samarkand, Uzbekistan, near the base（）／’the ZinzilbanBeds. The position丫the boundary ivas． selected bY theSubcommission on Devonian StratigraphY in 1989 tocoincide with the level tit which the ph刃ogeneticsucce-sor to the conodont Polygnathus pireneae appeared,that is the species then named Polygnathus dehiscens

but in this report, because可uncertain ties regarding theholot}ype可Polygnathus dehiscens, the name PolYg-nathus kitabicus is used because the type material．加，

the latter camefirom the GSSP, although it is thought b.}sonie to be“junior sYnonyrn可Po. dehiscens. The evo-lutionar), seri . es associated with these changes hasalreadY been published. The GSSP is located ver-N, soon

after a global sea level，ise and the onset of changedconditions. Rich．斤tunas丫other户ssil groups occur inthe Zin-ilban Formation. Several species of monograp-

tids and several gene二‘0厂brachiopods occur above theGSSP and new subspecies (}f docryoconarid genera and

0厂brachiopods occur above the GSSP Also appearingabove the GSSP level is the tabulate coral Favosites

regularissimus which is the name-giver for the Regu-larissimus Zone widely traced in Asia. This account

documents the record. Since the acceptance才‘thisGSSP has concluded decisions on all the Devonian svs-

tem, series and stage boundaries, comments are made

on the problems that remain, especially those resulting

加)m the fact that most of the GSSPs have been definedin pelagic户cies, leaving outstanding their correlationinto neritic and terrestrialfiacies where auxillary strato-

types are required to provide a better internationalchronostratigraphic firamework户r加ture internationalscient沂c work on the Devonian Svstem.

Introduction

This report describes the recommendations of the Subcommissionon Devonian Stratigraphy (SDS) and International Commission oil

AUgUSt 1996. 1 his reconinicridation brings to a conclusion decisionson all the systcm, series and stage hOUndarv GSSP's for the Devon-ian Systern: the problems that rernain, partiCUlarly the establishmentofauxilliary sections in ncritic and tcri-estrial facies are diSCUSSCd illa final section. The pl-CViOLls decisions on Systern, Series and Stageboundaries have been rcportcd carlicr as foll~ : base of De\ollialland of the Lochkovian Stage (Martinsson (ed) 1977): base of thePragian Stage (Chlup6} and Oliver 1989)} base of Ernsian }tagc(described herein)} base of Middle Dc\onian and the Eifelian Stage(Ziegler and Klapper 1985} Ziegler and Werner (eds) 1985): base ofthe Givetian Staoc (Walliser and others 1995)} base of the UpperDevonian and base ofthe Frasnian Sla}!e (Klapper and othei-, 1987):base ofthe Fainennian StaoeI（Klappei and othcrs 1993): base、们lieCarboni lel-OL1.1; (Paproth and othei、1991）．There have been surnjnar}reviews by House（1988) and by Chlupi(} and Oliver（1991）ancLwith the complclion of、 DeNorilan boundary definition with thisreport, a角11 and Updated report on all Dc\ onian boundaries and theiicharactensation by most fossil groLIPS is ill preparation for pUbliCa-tion in the Courier For.vhtmgsin.}Iilut Senckenberg. Since theseboundaries were defincd in pelagic facies, some discussion is givenat the close of this contribution on the problem ofstandards and rec-orninendations Of aLiXilliary stratotypes for neritic and terrestrialfacies.

As a result ol、 discussion Over a number of' years, the SDS by

1989 had agreed that the most use丘il level for defining the base ofthe Finsian Would be the appearance of the conodoin Polvgnathusi1chiscens Philip and Jackson in the lineage Po. pircneae Boersina toPo. &,hiscens (or Po. kitabicus as used here), the eVOIL]Iionar} entryof definitive characters being held to be time specific. Since the typearea for the name Emsian, around Ems in Germany, is in neriticfacies, a serviceable boundary could not be proposed there becauseof the absence of pelagic faunas which the SDS regarded as the mostuseful for international correlation. Although a globally useful GSSP

had been proposed for the base of the Pragian in the vicinity ofPrague in Bohen-iia, sequences in that area about the Pragian-Ernsianboundary had proved unsatisfactory for proposal ofa GSSP based onpelagic faunas. Though data and proposals for potential candidatesections foi a GSSP ]or the base of the Ernsian were considered froin

several parts of the world, only one formal submission was finallyforthcoming: the Zinzil'ban Gorge section in the Kitab GeologicalState Reserve, Uzbekistan. This clearly demonstrates the superjoinature of the Zinzil'ban sections. The type section was visited by theSDS in 1978 and subsequently by a special SDS party. It wasincluded in field trips of the International Geological CongressMoscow 1984, as Excursion 100. "The Middle Palaeozoic of theSouthern Tien Shan" (Kim and others］984).

The SDS has previously remarked in submissions that. for theDevonian, faunas of pelagic sequences offer the best means lot- intcinationally precise correlation. Such groups are represented in theproposed sequence. Widespread international correlation seems bestfacilitated hv the recommended horizon an(] }cction.

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Figure I Maps showing the position of the Kitab State Geological Reserve in Uzbekistan (southernTien Shan) and the position of the GSSP proposedfor the base of the Entsian. Geological mapmo晰 edfrom Kim and others, 1978.

correlation into other facies.

Although noticeably thinner-beddedthan the underlying Madmon Forma-tion (Figure 2), there is no evidenceof diasterns within the sequencesthrough the proposed GSSP，‘ Thesuggested Global Stratotype Horizonat the base of Bed 9/5 is located 35

cm above the top of the MadmonFormation. The boundary betweenthe Khukar and Zinzil'ban Beds at

the GSSP level should not be con-

fused with the li th ostrati graphicboundary between the Madmon andKhodzha Khurgan Formationsbetween Units 8 and 9 (Figure 3).

Beds through the boundaryinterval yield a mixture o,f benthicand pelagic organisms, thus provid-ing potential for correlations to bemade into exclusively benthic as wellas exclusively pelagic faunas. Con-odont data relative to the GSSP have

already been published (Yolkin andothers 1989, 1994); conodonts occurin relative abundance in almost all

beds. Data on distribution of benthic

fauna have been published (Kim andothers 1984) and are summarised on

Recommended stratotype

The approved recommendation level for the GSSP to define the baseof the Emsian stage is at the base of Bed 9/5 in the Zinzil'ban See-tion in Uzbekistan about 170 km south-southeast of Samarkand at

67018'20" east and 39012' north. The Zinzil'ban Gorge is withinthe 52 km2 Kitab State Geological Reserve (Zapovednik) in Uzbek-istan. The location of the section is shown on Figure 1. Exposuresthrough the proposed GSSP occur in the continuous face on thewestern wall of the Zinzil'ban Gorge (Figures 1-4). The successionforms part of a virtually continuous outcrop extending through mostof the Lower Devonian into the early Middle Devonian.

In 1979 the Kitab State Geological Reserve was gazetted by theUzbek Government as a reserve for ＊ ＿

me Dreservation oi its suDerD Lyeoi- 1麟筋餐麦魏牙 } I兹碰挽孤 . -

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Figure 3. Note that Yolkin and others (1994) paper refines the mea-surements and numbers of the type section used in 1978 and 1984. Aconsiderable part of the shelly fauna has been formally documented(Kim and others, 1988).

There are minor dislocations in the massive Madmon Forma-

tion (Figure 2) well below the proposed GSSP, but the section form-ing the basis for the GSSP is remarkably free from structural com-plication. The conodonts, having a conodont alteration index (CAI)of 3.5, indicate incipient metamorphism.

On an accompanying diagram (Figure 3) the occurence of awide range of taxa in beds above and below the GSSP is indicated.These should enable precision to be obtained by the study of othergroups. It may be noted that graptolites continue a short way abovethe boundary; these may represent the last known occurences of the

Khod7aK五urgan儿rmation M树Mon FOm讯t云on

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Samarkand, then by a ca. 45 krnpaved road to the Zapovodnik vil-]age, from whence the section can bereached by road and pack-track, adistance of about 4krn (Figure 1)

The proposed GSSP occurs in arelatively uniform sequence of darkmicritic limestones characterized bylack of significant abrupt fauna]change such as would support theview that major diastems are notpresent (Figures 2, 3). An associa-tion of benthic and pelagic faciesnoted above provides potential for

撇

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Figure 2 Photograph showing the position of the proposed GSSP in the Zinzilban Gorge sectionbetween Beds 9514 and 9515.

December 1997

2-47

STAGE

FORMATION

BEDS

ZONE

PRAGIAN

Madmon

Kliukar

EM STAN

Khodzha Khurgan

kindlei

21314

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｝516！718 9 ｝10｝11

Zinzil'ban

kilabicus

12！13！14｝15116｝17！is I19｝20｝2 1122 123 124｝251 26CONODONTS

八Zndorinella miae

Pedavis mariannae

Eognathodus kindleiPolygnathus pannonicusPot. pireneaePot. Aitabicus

Pot. sokolovi

八〕1. hindei

Pot. tamara

GRAPTOLITES

Monograptus craigensis craigensisMon. cr. mojiangensh

Mon. pacificus aiviliMon. aequabilisMon. ex. gr. yukonensisBRACHIOPODS

Gorgostrophia gorgoPlicanoplia (P.) aff. carlsiDevonochonetes zeravvchanicus

Carinata syrrnaticaTABULATECORALS

Favosites interstinctus

Fav. nitidus

Fav. regulatissunusPachyhelioplasma kettnerovaeOculipora multiplexaRUGOSE CORALS

Lyrielasma petchorenseDendrostella columnatis

Farabophyllum farabicumDACRYOCONARIDS

Viriatellina sp. AVir. sp. BNowakia n.sp. ANow. n. sp. BNow. acuaria ssp. ANow. acuaria ssp. BStyliolinids＆Homoctenids

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f igure 3 Log showing the large scale section of the Zinzil'han Gorge and the record of graptolites, brachiopods, conodonts,corals and dacryoconarids. Note that the bed numbering given in the detailed sequence presented both in the 1978 and 1984 hasbeen revised to the numbering shown here; as a result Bed 9 goes down to the base of the Zinzil'ban Beds.

grouP．Also coiled goniatites aPPear a little above the boundal-y.group. Also coiled goniatites appear a little above the boundaiVery useful dacryoconarids are associated with the critical beds.

The succession is included in the folded and thrust sequences otthe Tien Shan ranges. The beds are steeply inclined. Nevertheless theactual successions are readily demonstrable not only in theZinzil'ban Gorge section, but also in the adjacent Khodzha KhurganGorge and there are other sections in the area. Metamorphism isslight and not untypical of that to be expected of Mid-Palaeozoicsequences.

It seems likely, however, that for magnetostratigraphy andgoeochronometry, most advances will come from other successionswhich can be correlated with the GSSP using the precise biostrati-graphic tools provided by the work on the type section.

Conodont record

The critical incoming fauna for the boundary level is represented inBed 9/5 of the Zinzil'ban section corresponding to the entry otPolygnathus dehiscens as determined. illustrated and published by

Yolkin and others（1989, p.237-246). Following lengthy discussionat a meeting held in Washington in July 1989, the Zinzil'ban sectionreceived a majority vote; this was subsequently confirmed by anSDS postal ballot and by the ratification of the International Com-mission on Stratigraphy (ICS) and the IUGS.

Subsequently, because it was argued that there was some ambi-guity in the definition of Po. dehiscens, a new specific name was pro-posed for a specimen from the GSSP section, Po. kitobicus. This wasproposed to avoid any ambiguity in the defining characteristics of thecritical form (Philip and Jackson, 1967, Mapper and Johnson, 1975).Although some conodont workers regard this new taxon as a subjec-tive junior synonym of Po. dehiscens. Po. kitobicus is used in thisreport since it forms the basis of the only detailed published work onthe GSSP section (Yolkin,Weddige and others 1994, Yolkin, lzokhand others 1994). Also. during the course of subsequent work on thesection, some slight modification to the original bed numbering wasadopted; attention is drawn to this is on Figure 4.

Because of the ensemble of distinctive characters, and rapidevolution, the Po. pireneae to Po. kitabicus lineage can be traced

助isodes, Vol. 20, no. 4

2子入

polygnathids (Fil-HU-c 5）MLIN PI-0Ve useful iniecognition of the earliest 1-111sian.

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Brachiopod record

The brachiopods in the CjSSP section enter abovethe boundarv (Fi2ure 3) so that a sequence is notdemonstrated there. From c\ idcnce in Spain andGermany (Cails and Valen/tiela-Rios 1993) itseems clear that the ne}k level will move well-

known Siegenian brachiopod faunas into theErnsian. Such incon2ruities bemeen old neritical记ne", pelagic hOUndarjes have been usual inthe process of boundary definition for the Devon-ian mer the years: this has emphasised the impor-tance of establishino auxilliary stratotypes inIfacies other than pelagic as a next stage in the" ork of the S DS

17

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Figure 4 Lithological colitinn of the tipper part of the Madnion Formation (units 1-8)and the lower part of the Khodzha-Kni-gan Formation (units 9-25). Here are indicatedthe conodont sampling levels (Yolkin and others 1989, 1994) and the alignment withearlier bed numbering (Kini and others 1982, 1984).

Dacryoconarid record

In Current terminology the GSSP boundary lieswithin the Zone of Nowakia acuaria (Chlupd}｝995). Note that Alberti（1993) refers th is speciesto the -emis Turkestonella. But it is clear thatthere are several subspecies within the acitariagroup which should enable a inore precise chron-olo,,N to he established. Ran,-,es of new sub-specie,1℃c（） Illlsc〔1 111 tlle GSSP scctiol飞a］ -e given,, recognised in the GSSP section aton Figure 3. Alberti（1996) has listed a SUCces-sion of named Subspecies of acuari(i but theirrelation to the GSSP level is not clear. In Cicchia,Guenchina stran,,,ulata and Noitakia muciriacross the hOUndary (011LIPaO 1995) and are docu-mented in the Stydle vody and Mrainorka see-tions (Weddige 1989).

Graptolite record

Monographic treatment of the graptolites fromthe GSSP sequence is still not availablc but thepresent records are shown on Figure 3. In thestandard Barrandian section of Czechia, forms

identified as Monot}raptus Yukonen.}i.s range upinto levels with probable Po. dehiscens. andqueried Monogr. atopus and Monogr.／）‘，。·；万CUSare recorded with last members ot Monogr. yuko-nensis at a level taken to be above the GSSP level

(Chlupi(} 1995). Chlup}(} regards the tie"' bound-ary as "basically unfortunate" and has outlinedthe problems ot "first occurences" of Po. kitabi-cus (=dehiscens) which might not be coeval butthis ignores the fact that definitive recognition ofthe boundary depends on the evolutionary

internationally with ease and the incoming of forms referable to thedefining species can be readily determined. Both species are quasi-}Iobal in distribution, occuring in sequences in Spain (Boersma,1974), Australia (Mawson, 1987; 1995} Mawson and Talent, 1994,Mawson and others, 1992), North America (Mapper and Johnson,1975, Lane and Ormiston, 1979) and China (Hou and others, 1978)as well as central Asia in Tajikistan (Bardashev and Ziegler, 1992)and Uzbekhistan, The GSSP has a broad spectrum of other faunalelements in the Succession giving the potential for documentation otother groups across the boundary although further work is needed toreline this potential.

Though there is globally a dearth ot instructive or well docu-mented sequences for the definition ot the base ot the pireneae Zone.this is (it no moment for the GSSP. Po. pireneae occurs continuouslythrouL,h the critical interval. Beds 8 and 9. within which Po.kitabicusmakes its appearance at Bed 9/5. A remarkable diversihcation in

sequence of Po. pii-eneae to Po. kitabicus (=delnscens) rather thanthe isolated first occurence of the latter; such a sequence has not yetbeen demonstrated in Czechia.

Goniatite record

Goniatites are not relevant to the definition of the boundary. How-ever, it should be noted that the entry of the first coiled ammonoidsoccurs with the early Emsian transgression and rather higher in thedehiscens Zone} the relay like replacement of the last graptoliteswith the entry of the first coiled ammonoids is remarkable as is theirsudden international distribution (House 1996)

December 1997

2＿39

serotirJus

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notho -

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excavatas

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aspects of the Devonian System. The recommended boundarieshowever. have all been in pelagic or near-pelagic facies. In order totrstabifise international nomenclature, it is urgent that auxilhary see-tions are established in neritic and terrestrial facies. For some bound-

aries a correlation with neritic facies was well advanced at the time

of decision making. but clarification ot decisions by internationalagreement is required. The SDS has worked closely with IGCP 328in furthering such correlations using microvertebrates (Turner andBlieck 1996), an approach which seems particularly promising, andthe SDS has always encouraged palynological work. It is in theseareas that progress is most likely to be made. Finally, there is the factthat, as now defined, the Famennian and Emsian stages representsubstantial time divisions in the Devonian which may usefully haveinternationally agreed formal subdivisions.

References

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。r己召、了泞八炸 公泉

人ita6ICUS

Pireneae

篓狱李交妊粉燕 宁，0六。沁、

Figure 5 Diagram illustratuig the evolution of polygnathidconodont taxa, and particularly the entry qf Po4gnathuskitabicus at the GSSP level at the boundary oj the pireneae andkitabicus Conodont Zones (inodifiedfrom Yolkin and others,1994)

Geochronology

Due to the absence of volcanic or ash bands, possibilities forg(leochronometry are not good at the 6SSR but refined placing of theboundary level in other areas using the proposed conodont boundarygive ample opportunity for this in other areas.

Magnetostratigraphy

Work on magnetostratioraphy of the section has been undertakenand is due to be published shortly.

Sequence stratigraphy

As has been already remarked, the boundary between the Madmonand Khodzha-Kur-an Formations shows a change in bedding withthe entry of thin-bedded units: this is thought to correspond to aglobal sea-level rise which will be important when seismo-strati-graphic terminology is established in the Devonian. This level isassumed to correspond to the global eListatic rise at the base ofDepophase lb in the terminology ot Johnson and others（］985). 1 hisshould provide a tool for seismic stratigraphical work in other areas.

Framework for the solution of

international problems in the theDevonian

The definition of GSSP's for all the system,series and stage divisionshas provided a precise frannework for modern geological work on all

Alberti, G.K.B. 1993. Dacryoconaride und homectinide Tentactiliten des Unter- und Mittel-Devons. lei] 1. Courier Forsch Ling sin stitut Sencken- berg. v. 15& 229pp.

Alberti. G.K.B. 1996. Reports by the Membership: G.K.B. Alberti. Subcom- mission on Devonian Stratigraphy, Newsletter No. 12. p. 43.

Bardashev. I.A. and Ziegler. W. 1992. Conodont biostrati-raphy of Lower Devonian deposits of the Shishkat section (southern Tien-Shan, Middle Asia). Courier Forschungsinstitut Setickenberg, v. 154. 1-29.

Boersina. K.T. 1974. Description of certain Lower Devonian platform cono- donts of the Spanish central Pyrenees. Leidse geologische Mededelingen. }.49}283-301．

Carls. P. and VaICnZLIela-Rios. JI 1993. Materials near the redefined base of

the Ejusian Stage. Subcommission on Devonian Stratigraphy Newsletter, No. 10, p. 30.

Chlupj}. 1. 1995. Evaluation of some Devonian standard boundaries. No\ a Acta Leopoldina, NF. v. 71(291）．pp. 41-52.

ChlupA(f. 1. and Oliver, Jr.. W.A. 1989. Decision on the Loclikovian-Pragian Stratotype (Lower Devonian). Episodes, v. 12. pp. 109-112.

Chlup,W, 1. and Oliver. Jr., W.A. 1991. Defining the Devonian. Lethaia. v. 24. pp. 119-122.

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Dr A. L Kim is Head of the Depart-ment of Stratigraphy Tashkent Geo-logical Survey. He is currentlyChairman of the Commision of Pal-aeontology and Stratigraphy of theNational Committee of Geologists ofUzbekistan. His researches have con-

centrated on tabulate corals, Dacry-oconarida＆biostratigraphy of theMiddle Palaeozoic of South Tien-Shan. He is a Corresponding Mem-ber of the Subcommission on Devon-ian Stratigraphy.

Dr. Karsten Wedd仓e took hisdegrees from the University of Mar-burg. He taught as Wis-sentschaftlicher Assistent at the Uni-versity of Munich and, since 1987,has worked at the Research Institute

of the Senckenberg Museum. He isengaged in Lower and Middle Devon-ian conodont studies. Currently, he isa Titular Member of the Subcommis-sion on Devonian Stratigrap勿．

Professor John A. Talent is Professorof Geology at Macquarie University.His principal research interests con-cern Silurian and Devonian brachio-

pod and conodont biostratigraphy,global events, and biogeography inrelation to crustal dynamics. He iscurrently President of the Interna-tional Palaeontological Association,is a Titular Member of the Subcom-mission on Devonian Stratigraphyand is co-leader qf IGCP 421.

Dr Eugeny A. Yolkin is Head of theUpper Palaeozoic Laboratory of theUnited Institute of Geology, Geo-physics and Mineralogy, SiberianBranch of the Russian Academy ofSciences. His researches concentrate

on Siberian Ordovician to Devonian

regional stratigraphy, biofacies,global events and palaeogeographicreconstructions specifically for办namic synthesis, and Silurian-Devonian trilobites and conodonts.

He is Titular Member of the Devon-ian Subcommission on Devonian

Stratigraphy.

Professor Michael R. House isEmeritus Professor of Geology at theUniversity of Southampton. He hasbeen a member of all (he committeesconsidering Devonian system, seriesand stage boundaries since 1960. Hehas taught at the Universities ofDurham, Oxfo rd, Hull andSouthampton.. His researches havemostly concentrated on mid-Palaeo-zoic international correlation and

regional and event synthesis, mainlyusing'ammonoids. He is the immedi-ate past Chairman of the Subcommis-sion on Devonian-Stratigrap勺 andhas acted as coordinator for this八port.

December 1997