SILURIAN VERTEBRATE BIOZONAI, SCHEME

THE M ~ R S S , DENISE F R E D H O L M , VALF.NTINA TALIMAA, SUSAN TURNER, LENNART J E P P S S O N & GODFREY NOWLAN

MJ~SS T., FREDHOLM D., TALIMAA V., TURNER S., JEPPSSON L. & NOWLAN G. 1995. Silurian vertebrate biozonal scheme. [Biozones de Vertdbrds du Silurien : un schdma d'ensemble]. GEOBIOS, M.S. n ° 19 : 369-372.

ABSTRACT

Improved vertebrate biozonal scheme is presented for the Silurian : boundaries of all zones have been revised, and new zones Valyalepis crista in the Lower Llandovery and Loganellia avonia in the Lower Wenlock part of the succession have been established

KEY-WORDS : VERTEBRATE, BIOZONE, SILURIAN.

RI~SUMI~

Un sch6ma d6j~ publi6 des biozones du Silurien est propos6, mais les limites de toutes les biozones ont dt6 revues. Une nouvelle zone, Valyalepis crista, pour le Llandovery inf6rieur, et une autre, Loganellia avonia, pour le Wen- lock inf6rieur, sont d6fmies.

MOTS-CLI~S : VERTI~BR]~S, BIOZONE, SILURIEN.

Following the decision of the Subcommission on Silurian S t ra t ig raphy accepted in 1990 to detail the s tandard left-hand side of national and inter- national correlation charts, first the internat ional graptolite and conodont zonations were drafted (Cocks & Nowlan 1993). Vertebrates (which, in our sense, do not include conodonts) were also proposed for inclusion in the same correlation chart (the so-called Global Standard). As a result, the ver tebra te zones were shown together with chitinozoans and spores. At the Silurian Subcom- mission meetings in Prague in 1992 and in Aus- tr ia in 1994, biozonal schemes were discussed again and decisions were achieved on graptolite and conodont zonations by the researchers of the corresponding groups (see Nowlan 1994, and Ta- ble herein). These two zonations are not the topic of this contribution, except tha t the ver tebra te column will be correlated with the conodont one.

The revised scheme will serve as a basis for the definition of time-slices by palaeogeographic stu- dies, and for detailing the Silurian chronostrati- graphic s tandard scheme.

Four ver tebrate researchers and two conodontolo- gists, have since worked on the Silurian verte- brate scheme. In December 1994 an improved scheme was presented to the Secretary of the Si- lurian Subcommission (Nowlan 1994).

The succession of index-species and their bounda- ries have been agreed ; we have tried (and par t ly succeeded) to tie the microvertebrate zonation to the s tandard conodont one ; as yet we have no direct correlation with the s tandard graptolite zo- nation. Here we stress the need to continue the studies on the ver tebrate taxonomy and distribu- tion to refine the scheme.

370

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GRAPTOLITES C O N O D O N T S

boucekl - t ransgredlen$

bronlkensls. lochkovensls

parul l lmus-ul t l rnus

VE RTEB PJkT£S

O. ternscheldensls Inlei 'vol zone

formosus .

bohemlou$ tenul$- kozlowskll .,

O. eOltelnhOmensls.O.e, @etorl¢ K. t lrnorl lcus.Ko Iltl'~Janlcu$

P. punc ta tu$ '~T-g-raa~5

le lntwardensl$

$corl lcu$

nllssonl

ludensl$

p rae deub e l l -deub el l

parvus-nassa

O. cr lspa

O. snoJdrl In lerval zone

P. sllurlcus A, ploeckensls

NOT ZONED

K. stauro$

O. bohernlccl

T. sculpt l l l$

A. hedel

R ele~an$

. . . . ~ p. o m o t o / " . . . .

P. rnart lnssonl

lundgren l O. sagllta sagllla L. grossl

NOT ZONED r lg ldus-perner l

[ Iccar lonensis. be lophorus

centrEugus-murchlsonl

lapwor lh l . lnsectu$

splralls [n le lva l zone

gr lestonensls.crenulata

turr loulatus-crlspus

guer lch l

sedgwlckl l

oonvolutus

argenteus

f r langulotus-pect lnatus

O. sag l l la r h e n a n a . K, pa fu la

K. ranulfformls' Inlerval zone

R amorphogna tho lde$

R ce l lon l

R tenu l s . D, s taurognatholdes

Z < cyph us z < D. kentuckyensls o veslculosus 0

ooumlno lus I I '

L, avonla

L, $co t l ca ° L° $1blrlca

V, cr ls ta

GSN 29 DEC. 94

Table 1 - S i lu r i an b iozones be- tween Graptol i tes , Conodon t s a n d Ver t eb ra t e s . Biozones & Graptolites, Conodontes et Ver- tdbrgs du Silurien.

The idea of using the East Baltic Silurian-Devo- nian ver tebra te succession as a reference succes- sion was put forward by Blieck et al. (1988). The Silurian par t of it has been proved in several dif- ferent regions as Scandinavia, British Isles, Ti- man-Pechora Region, the Central Urals, Novaya and Severnaya Zemlya Archipelagos (Turner 1973 ; Karatajute-Tal imaa 1978 ; M~irss 1986 ; Fredholm 1988, 1990). The studied succession/zo- nation of the Silurian ver tebrates is still the most advanced among other ver tebrate zonations. That was the reason for the proposal made in 1993, and from that foundation we have carried on the present work.

In the scheme the lower boundary of each zone is defined by the earliest occurrence of its index- species, thus making our biozones interval biozo- nes. The index-species can extend into the suc- ceeding upper zone. A dash in the ver tebra te co- lumn indicates that two species occurred at the same time in different regions.

Within the lower Llandovery, Rhuddanian, we es- tablish the Valyalepis crista biozone (Table 1) which generally corresponds to the D. ken- tuckyensis conodont zone (V. crista TURNER in Turner & Nowlan in press). The index-species oc- curs in the Upper Clemville Formation of eastern Canada.

371

The Aeronian, except its lowermost part, and the whole Telychian, are characterized by the Loga- nellia scotica - L. sibirica biozone. Differently from the scheme proposed in 1993, we add here Loganellia sibirica to cover a wider geographical a r e a .

In the Lower Wenlock, Sheinwoodian, another new zone is erected, the L. avonia biozone. It starts on the lower boundary of the Sheinwoo- dian. The index-species comes from the Brinkmarsh Beds of Tortworth Inlier (Turner in prep.).

The L. avonia biozone is followed by the Loganel- lia grossi and Paralogania martinssoni biozones. Two name changes have been taken into conside- ration : the Baltic '%. taiti" has been revised (Fredholm 1990) and L. grossi distinguished instead of it, and Loganellia rnartinssoni has been placed in a new genus Paralogania KARATA- JUTE-TALIMAA (in press).

The lower boundaries of Loganellia grossi, Para- logania rnartinssoni, Phlebolepis ornata, Phlebole- pis elegans and Andreolepis hedei zones have been lowered if compared with the scheme in 1993. This is based on the conodont fauna found on Gotland and southern East Baltic (see Fredholm 1988, Jeppsson et al. 1994, Karatajute- Talimaa & Brazauskas (in press).

The L. grossi biozone occurs in the upper Shein- woodian and lower Homerian, the lower bound- ary of the zone being in the uppermost part of the O. sagitta rhenana-K, patula conodont zone.

The lower boundary of the P. martinssoni biozone is at the level or close to the lower boundary of the O. bohemica conodont zone (correlative with the lower boundary of the parvus-nassa graptolite zone).

The P. ornata biozone was defined in Estonia in the upper Sauvere Beds of the Paadla Stage (it corresponds to the upper part of the scanicus graptolite zone). The P. ornata biozone is very short and its lower boundary is only slightly be- low tha t of the A. ploeckensis s. str. conodont zone on Gotland, and si tuated high within the "not zoned" conodont interval of the scheme.

The P. elegans biozone, with its lower boundary, starts at or very close to the lower boundary of the A. ploeckensis zone. The lower boundaries of the A. hedei vertebrate zone and P. siluricus co- nodont zone more or less coincide (A. hedei possi-

bly appearing a little later). The Thelodus sculp- tilis biozone starts in the upper Ludlow, in the O. snajdri interval zone. The exact level of its lower boundary is not quite clear. In Gotland the lo- west level with T. sculptilis is in the uppermost Eke Beds, in the Central Urals there are data on the co-occurrence of T. sculptilis and A. hedei in the lower Tabuska Beds. In the northern East Baltic the lower boundary of the T. sculptilis bio- zone is in a hiatus.

The value of acanthodians for the subdivision of the Upper Silurian, Pridoli, has repeatedly been under discussion. Because at present it is not possible to give a good alternative, we keep the Nostolepis gracilis and Poracanthodes punctatus zones for the interval which is globally charac- terized namely only by the occurrence of acantho- dians. They both remain in the O. rernsheidensis interval zone.

In the uppermost Pridoli, Katoporodus lithuani- cus is added to the K. timanicus biozone with a dash to characterize different facies. This zone corresponds to the distribution of the Goniporus alatus-Katoporodus spp. -Paralogania kumrnero- wi assemblage, and to the highest conodont zone in the Silurian.

The Devonian starts with the Turinia pagei bio- zone. In Podolia the Silurian-Devonian boundary is marked by the appearance of Monograptus uni- forrnis angustidens and occurrence of the thelo- dont Turinia pagei (Karatajute-Talimaa 1978).

Acknowledgements - We thank A. Blieck (Lille), D. Kaljo (Tallinn), G. Miller (London), R. Thorsteinsson (Calgary), and J. Valiukevicius (Vilnius), for their support and comments in connection of this work, and A. Noor (Tallinn) for linguistic help.

This is a contribution to IGCP 328. Palaeozoic Micro- vertebrates.

R E F E R E N C E S

BLIECK A., MARK-KURIK E. & MARSS T. 1988 - Biostra- tigraphical correlations between Siluro-Devonian invertebrate-dominated and vertebrate-dominated sequences : the East Baltic example. In MCMILLAN J.N., EMBRY A.F. & GLASS D.J. (eds) : Devonian of the World. Vol. III. Canadian Society of Petroleum Geologists, Memoir 14 : 579-587.

COCKS L.M.R. & NOWLAN G.S. 1993 - New left hand side for correlation diagrams. Silurian Times. A newsletter of the Silurian Subcommission, 1 : 6-8.

FREDHOLM D. 1988 - Vertebrate biostratigraphy of the Ludlovian Hemse Beds of Gotland, Sweden. Geolo-

372

giska FSreningens i Stockholm FSrhandlingar, 110 (3) : 237-253.

FREDHOLM D. 1990 - A g n a t h a n ver tebrates in the Lo- wer S i lur ian of Gotland, Sweden. Geologiska F6re- ningens i Stockholm FSrhandlingar, 112 (1) : 61-84.

JEPPSSON L., VIIRA V. • MANNIK P. 1994 - Si lur ian conodont-based correlations between Gotland (Swe- den) and Saa remaa (Estonia). Geological Magazine, 131 (2) : 201-218.

KARATAJLrrE-TALIMAA V. 1978 - Silurian and Devonian thelodonts of the USSR and Spitsbergen. Mokslas, Vilnius : 334 p. (In Russian)

KARATAJLrrE-TALIMAA V. in press - Taxonomy of loga- ni id thelodonts. Modern Geology.

KARATAJUTE-TALIMAA V. & BRAZAUSKAS A. in press - Dis t r ibut ion of ver tebrates in the Si lur ian of Li- thuania . Geologija, 17.

MARSS T. 1986 - S i lur ian ver tebrates of Estonia and West Latvia. Fossilia Baltica 1. Valgus, Ta l l inn : 104 p. (In Russian, with English abstract).

NOWLAN G. (ed) 1994 - S i lur ian times. 3. Subcommis- sion on S i lur ian S t ra t ig raphy news letter, Calgary.

TURNER S. 1973 - Si luro-Devonian thelodonts from the Welsh Borderland. Journal of the Geological Socie- ty, London, 129 : 557-581.

TURNER S. in prep.- Loganellia avonia, a new thelo- dont from the Lower S i lur ian of England.

TURNER S. & NOWLAN G.S. (in press) - Early Si lur ian ver tebrates of eas tern Canada. Miguasha Sympo- s ium Volume.

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