»

S I L U R I A N FOSSILS in S T R A T I G R A P H Y

20. Acritarchsb y FR A N C IN E M A RTIN

T he purpose o f this chapter is to give readers with no specialised knowledge of acritarchs an overview of Silu­rian palynofloras, to list references leading to addi­tional information, and to gauge the possibilities for worldwide correlation based on this group.

Acritarchs are often common and highly varied in marine Silurian deposits. Tappan (1980) and Downie (1984) give general comments on these organic-walled microfossils o f disputed origin, some o f which are considered as cysted stages o f phytoplankton and all of which are treated taxonomically under the International Code of Botanical Nomenclature. Systematic study of acritarchs began during the 1930s. Following the pioneer studies of Eisenack, from 1931 onwards and covering, inter alia, the Silurian o f the Baltic region, it was only towards the end of the 1960s and particularly following the example o f Loeblich (1970) that the indis­pensable detailed descriptions were provided, supported by observations using the scanning electron microscope. The present state of taxonomy is extremely chaotic, the result on the one hand o f the accumulation o f too brief diagnoses, leading to the production o f often long rang­ing ‘balloon’ taxa, and on the other o f a lack of unanimity in hierarchial choice of morphological criteria (see Loeblich 1970, pp. 708-710; Cramer and Diez 1972b, pp. 139-146: Tappan 1980, pp. 205-206). Moreover, relatively few detailed monographs have been published on type sections and/or stratigraphically continuous deposits dated by means o f macrofossils. These general comments apply particularly to the Silurian System.

Fig. 148 shows principal Silurian acritarch localities, excluding regions for which suitable data are lacking. The numbers (see list in explanation of Fig. 148) indicate bibliographic references corresponding generally to the most recent publications that clearly include previously published information. Localities that have furnished only poorly characteristic or badly identifiable taxa (e.g., in Austria; Bachman and Schmid 1964), or those without adequate precision of provenance or list of determinations (e.g., northern Canada and Saudi Arabia; Cramer 1970, text-fig. 1A) are omitted; these localities may be checked in Cramer and Diez (1979, fig. 6.3). Publications on acritarchs from the eastern part of North America (Refs. 1 to 8) concern essentially the

Llandovery, from the end o f the Rhuddanian onwards, and the Wenlock, particularly in southern Ontario and western New York State. The oldest samples from the lowest Llandovery at Anticosti Island, Quebec, Canada, are only partly published (Ref. 1). Palynological data for the Ludlow and Pridoli Series in North America refer to boreholes in Florida and lack adequate chrono- stratigraphical control (Ref. 4, p. 122).

Data from South America (Argentina, Bolivia, Brazil; Refs. 9 to 14) and from Asia (Siberia and Tuva; Refs. 65, 66) are very dispersed and usually have little independent age control. The most abundant data are from Europe, particularly the western part, where numerous localities, the age control of which is variable, give a glimpse o f the whole Silurian System. In particular, partially published palynological study of the British stratotypes (Refs. 20 to 25) has permitted the establishment of a regional scale of four assemblage biozones in the Llandovery, from the end o f the Rhudd­anian onwards, and o f seven range zones in the com­bined Wenlock and Ludlow (Ref. 23). In addition seven biozones were recognised in the Llandovery Series of the type Llandovery area (Ref. 22). The basal Rhuddan­ian contains indeterminable acritarchs (personal observation) at the type locality o f Dob’s Linn, in southern Scotland, and long ranging forms in the Llan­dovery area o f Wales (Refs. 21, 22). The base o f the Downton Group, at the type locality in the Welsh Borderland, is very poor in acritarchs and no new appearance o f any taxon has been formally established (Ref. 24). In the Baltic region (Refs. 28 to 32), as in Belgium (Refs. 38 to 40), where acritarchs trom the acuminatus Biozone are partially known (Ref. 39), analyses refer especially to the Llandovery and Wenlock Series. In Norway, Austria, Romania, and Sardinia (Refs. 26, 36, 37, 53) the data are very preliminary and often based on isolated samples. In Spain (Refs. 3, 48 to 52) published monographs are based on samples ‘with little accurate age control’ (Cramer and Diez 1977, p. 290) from the Wenlock onwards. In Brittany and northern France (Refs. 41 to 45) strata have been attri­buted generally to the Ludlow or the Pridoli on the basis o f palynological criteria; at Klonk, Czechoslovakia (Ref. 35), the Pridoli is very poor in acritarchs. In Podolia (Refs. 33, 34), authors’ taxonomic concepts

208 F. M A R T I N

6 5

T í 24; pU ^ > 2 8 - 3 2

" 3 8 - 4 0 3 3

* ' 3 5 * - 3 4 3 6 - * 3 7

2 6

r 2 51 6 - 1 8 — f ,

6 6 - '4 1 - 4 6

473 , 4 8 - 5 2 - r ' * ’

3 - 7

3 - 4 ' • 5 4

5 5 >

5 65 7 - 6 0

6 26 46 3

, - 1 2

f i g . 148. Generalised geographical map of Silurian acritarch localities. 1, Duffield and Legault (1981, 1983). 2, Achab (1976). 3, Cramer (1970). 4, Cramer and Diez (1972¿>). 5, Thusu (1973a, 1973¿>). 6, M. A. Miller and Eames (1982). 7, Loeblich (1970). 8, Tappan and Loeblich (1971). 9, Lange (1967). 10, Brito (1967). 11, Cramer et al. (1974). 12, Bultynck and Martin (1982). 13, 14, Pöthe de Baldis (1974, 1981). 15, Doming (1982), 16, Clayton etal. (1980). 17, Smith (1981). 18, Holland and Smith (1979). 19, Downie (1963). 20, Lister (1970). 21, P. J. Hill (1974). 22, P. J. Hill and Doming in Cocks etal. (1984). 23, Doming (1981a). 24, J. B. Richardson et al. (1981). 25, Downie (1984). 26, Doming and Aldridge (1982). 27, Schultz (1967). 28, Cramer et al. (1979). 29, Le Hérissé (1984). 30, 31, Eisenack (1970, 1974). 32, H. N. Umnova (1975). 33, Kirjanov (1978). 34, Sheshegova (1974). 35, Deunff (1980). 36, Martin (1978). 37, Kalvacheva (1978). 38, 39, Martin (1969, 1974). 40, Vanguestaine (1979). 41, Deunff and Paris (1972). 42, Deunff et al. (1971). 43, Rauscher and Robardet (1976). 44, Deunff and Chateauneuf (1976). 45, Rauscher(1974). 46, Moreau-Benoit (1974). 47, Deflandre (1944-1945). 48, Cramer (1964), 49, Eisenack etal. (1976). 50, Diez and Cramer (1976). 51, Cramer et al. (1976). 52, Rodriguez (1983). 53, del Rio et al. (1980). 54, Erkmen and Bozdogan (1979). 55, Rahmani(1983). 56, J. B. Richardson and Ioannides (1973). 57, Magloire (1967). 58, Jardiné and Yapaudjian (1968), 59, 60, Jardiné etal. (1972, 1974). 61, Schrank (1984). 62, Cramer and Diez (1972a). 63, Baudelot et al. (1980). 64, Bär and Riegel (1980). 65, 66,

Sheshegova (1984, 1975).

limit the understanding of palynological results relating to the Silurian, from the end o f the Llandovery or the beginning o f the Wenlock. In North Africa the principal works (Refs. 57 to 60) concern the Algerian Sahara, from the Llandovery onwards, estimated as equivalent to the Aeronian or the Telychian; most of the Silurian deposits are assigned to the Ludlow on the basis o f their correlation with other Saharan boreholes dated by means o f graptolites, or by comparison with palynological data, principally from Spain. A synthesis (Ref. 60) o f the combined sections has permitted the establishment o f six informal biozones for the Silurian. In Turkey (Ref. 54), Guinea (Refs. 62, 63), and Ghana (Ref. 64) dating o f beds is based principally on acri­tarchs or chitinozoans, and in one publication (Ref. 63)

the list of the former group suggests that assemblages of different ages, or containing reworked material, have been considered together.

Among several hundred acritarch taxa recorded from the Silurian, 33 with characters sufficiently distinct to avoid ambiguous determination are listed here (Fig. 149). This choice, which is not exhaustive and proposed only by way o f an example, is also influenced by per­sonal rapid examination o f samples from the Llan­dovery of Gaspé, Anticosti Island, and Norway, and from the Llandovery to Downton of Great Britain collected by the author during Silurian Subcommission field meetings in 1979, 1981, and 1982; others were obtained with M. G. Bassett and W. T. Dean in the Llandovery area, Wales, in 1984. The selection of

A C R I T A R C H S 209

acritarchs could have been wider, or different, but it would still show the same deficiencies in knowledge, notably the lack of information on the lowest Llandovery and the unreliability of most datings of Homerian to Pridoli strata outside their type areas. All the genera and species chosen, except for two indicated by an asterisk*, are present in at least two continents.

No formal scheme based on standard successions and of intercontinental application has yet been proposed. Ideally it should be based on first appearances o f taxa in order to avoid errors resulting from the presence of reworked material; the latter may only be detected with confidence either on the basis o f differences in state of preservation from that o f autochthonous material, or if several cycles o f redeposition sufficiently different in age can be recognised. In the British Isles, for example, reworked Ordovician and Silurian palynomorphs were found by J. B. Richardson and Rasul (1978) in the Lower Devonian o f southern England, and by Clayton et al. (1980) in the Lower Carboniferous o f western Ireland. Late Cambrian and early Ordovician acritarchs are present at least from the late Rhuddanian to early Telychian in the type Llandovery area (personal obser­vation: samples GB-1-3-1, WAL-162-1, WAL-162-3, W-TRE-5).

Cramer (1970) and Diez and Cramer (1974, 1977) pre­sented the first generalised global range charts o f selec­ted Lower Palaeozoic acritarchs. These are useful, but with regard to the Silurian the stratigraphical results are biased by the conviction (see Cramer and Diez 1974a, 1974b for earlier references) that these micro-organisms were distributed in six provinces (or biofacies) arranged concentrically with reference to palaeolatitudes inspired by the palaeogeographical maps o f Bullard et al. (1965); not enough account is taken of possible age differences between the samples, which in many cases are insuffi­ciently numerous, as Tappan (1980, p. 200) has already indicated. There is, as yet, no more than local evidence to support schemes that have been proposed for the broad palaeoecological and biogeographical signifi­cance o f Silurian acritarchs. Fairly numerous observa­tions in Europe (see references in Deunff et al. 1971) and isolated ones in Argentina (see synonymies in Appendix 1; Bultynck and Martin 1982) and on Anti­costi Island (personal observation: sample A7A1) are in disagreement with the distribution of Cramer and Diez’s Deunffia and Domasia provinces.

More recently, Downie (1984) charted the distribution of 114 selected acritarch species in British Silurian strati­graphy and, to some extent, their worldwide strati­graphical ranges.

The synthesis (Fig. 150) in this chapter assembles the most reliable data shown in Fig. 149. It permits the recognition o f six acritarch groupings, the lower limits o f which are correlated approximately with correspond­ing graptolite biozones. Unless indicated otherwise, the acritarchs listed appear to be geographically widespread.

Group 1: Rhuddanian Stage and Aeronian Stage (in part) Certain Ordovician taxa range into the Silurian. Hogklintia visbyensis and Eupoikilofusa rochesterensis appear in the acuminatus Biozone (basal Rhuddanian); Elektoriskos mill­

erae appears in the atavus Biozone. Eupoikilofusa aff. E. ampulliformis at the beginning of the Llandovery is documen­ted only in Anticosti (Duffield and Legault 1981, 1983) and Gaspé (personal observation; sample BC-1-1).

Group 2: Aeronian Stage (in part)Marked by the appearance of Domasia, essentially D. limaci­formis, from the sedgwickii Biozone onwards, and of Dactylo­fusa estillis.

Group 3: Aeronian Stage (in part) and Telychian Stage (in part)Appearances of several new species of Domasia and of Dilati­sphaera willierae a little below the turriculatus Biozone. Appearance and development of species of Deunffia from the crispus Biozone onwards. Appearance of Elektoriskos aurora, Neoveryhachium carminae, Solita, and Geron; the last three extend into the Lower Devonian. The absence of Domasia and Deunffia is noted clearly only in the Algerian Sahara (Jardiné et al. 1974).

Group 4: Telychian Stage (in part), Sheinwoodian Stage, and, questionably, part o f the Elomerian Stage Appearance, approximately from the griestonensis Biozone or the crenulata Biozone, of Gracilisphaeridium encantador, Visbysphaera dilatispinosa, Schismatosphaeridium rugulosum, and Florisphaeridium. Domasia and Deunffia decrease from the end of the Sheinwoodian onwards.

Group 5. Questionably part o f the Elomerian Stage plus part o f the Gorstian StageAppearance, probably at the end of the Homerian taludensis Biozone), of Psenotopus chondrocheus, Cymbosphaeridium pilaris, and C. ? cariniosum, the last two of which extend into the Lower Devonian; C.? cariniosum has not been recorded from the British Isles (Doming 1981a; Downie 1984).

Group 6: Gorstian Stage (in part) plus Ludfordian Stage and, questionably, Pridoli SeriesAppearance, probably at the beginning of the Gorstian (nils­soni Biozone or scanicus Biozone), of Leioniella carminae and Onondagaella, both of which extend into the Lower Devonian. Appearance of Percultisphaera stiphrospinata at the beginning of the Gorstian in Shropshire (Lister 1970) and in the upper Silurian of the Cantabrian Cordillera (Rodriguez 1983). No significant new appearances have yet been reported in the Pridoli.

It is obvious that these biostratigraphical groupings within the Silurian are only provisional. Stratigraphical results obtained from local studies, although much more detailed, can be used in international correlation only after numerous complementary analyses have been carried out on samples for which there is reliable in­dependent age control, and after the taxonomic criteria for genera and species have been stabilised and stan­dardised. Neverthless, there are clear indications that acritarch palynofloras have the potential to play an increasingly important role in Silurian biostratigraphical zonations.

Acknowledgements. I am indebted to Geoffrey Playford (University of Queensland) for critically reviewing the original manuscript.

210 F. M A R T I N

SE L E C T E D SILURIAN

A C R IT A R C H S

C A N A D A

EA

ST

ER

N

U.S

.A.

AR

GE

NT

INA

BO

LIV

IA

IRE

LA

ND

EN

GL

AN

D

a W

AL

ES

NO

RW

AY

AN

TIC

OS

TI

GA

SP

É

C a r m i n e l l a m a p l e w o o d e n s i s C R A M E R 1 9 6 8 T p T 2 ( A T ) 4 S 4 ( T Sh ) 1 2 T - L 2 5

C y m b o s p h a e r i d ¡ u m ? c a r i n i o s u m ( C R A M E R )J A R D I N É e t a l . 1 9 7 2 S 4 ( WLu ) 1 1

C y m b o s p h a e r i d i u m p i l a r i s ( C R A M E R )L I S T E R 1 9 7 0 S 4 r 1 6 L ? 2 3

D a c t y l o f u s a e s t i 11 i s C R A M E R & DI E Z 1 9 7 2 T 2 T 4 T 2 5

D e u n f f i a f u r c a t a D O WN I E 1 9 6 0 ( A T ) 4 W 5 S h 2 5

D e u n f f i a f u r c a t a n i a g a r e n s i s T H U S U 1 9 7 3 W 5 ? ? L u 1 4

D e u n f f i a m o n o s p i n o s a D O WN I E 1 9 6 0 T 4 W 5 T S h 2 5

D e u n f f i a r a m u s c u l o s a D O W N I E 1 9 6 0 T 4 W 5 S h 2 5

D e u n f f i a r a m u s c u l o s a r o c h e s t e r e n s i sT H U S U 1 9 8 3 W 5 ? ? L u 1 3

D i l a t i s p h a e r a w i l l i e r e a e ( MA R T I N )L I S T E R 1 9 7 0 T p T 2 r 1 6 T 2 1 G ? 2 3

D o m a s i a a l g e r e n s i s ( C R A M E R ) HI LL 1 9 7 4 ( A T ) W 4 A - S h 2 1 T ? 2 6

D o m a s i a a m p h o r a MAR T I N 1 9 6 9 ( A T ) 4 W 5 S h 2 5

D o m a s i a l i m a c i f o r m i s ( S T O C K M A N S &WI L L I È R E ) C R A M E R 1 9 7 0 T p T 2 ( A T ) 4 W 5 ( T Sh ) 1 2 T 1 7 A - S h 2 5

D o m a s i a t r i s p i n o s a D O W N I E 1 9 6 0 T p T 2 ( A T ) 4 W 5 T 1 7 A - S h 2 3 T 2 6

E l e k t o r i s k o s a u r o r a L O E B L I C H 1 9 7 0 T p ( A T ) 7 ( T Sh ) 12 T S h 2 3 Tp

E l e k t o r i s k o s w i l l i e r e a e ( D E F L A N D R E &D E F L A N D R E - R I G A U D ) V A N G U E S T A I N E 1 9 7 9 R - T p R 6 ( A T ) 7 A T p

E u p o i k i l o f u s a a f f . E. a m p u l l i f o r m i s * ! M A R T I N )C R A M E R 1 9 7 0 R 1 ( R T ) p

E u p o i k i l o f u s a r o c h e s t e r e n s i s C R A M E R 1 9 7 0 ( A T ) 4 W 5 Ll ?2 1

F l o r i s p h a e r i d i u m s p . S h G 2 3

G e r o n s p . T 4 W 5 G L 2 3 Tp

G o n i o s p h a e r i d i u m o l i g o s p i n o s u m( E I S E N A C K ) E I S E N A C K 1 9 6 9 R - T 1 ( R T ) p

G r a c i l i s p h a e r i d i u m e n c a n t a d o r ( C R A M E R )E I S E N A C K & C R A M E R 1 9 7 3 T 3 T S h 2 5 Tp

H o g k l i n t l a v l s b y e n s i s ( E I S E NACK)DO R N I N G 1 9 8 1 R - T 1 ( R T ) p T 2 ( A T ) 3 W 4

L e i o n i e l l a c a r m i n a e C R A M E R 1 9 6 4 G L ? 2 5

M o y e r i a c a b o t t i i ( C R A M E R ) MI LLER &E A M E S 1 9 8 2 T 4 R 6 ? W 1 8 T S h 2 5

N e o v e r y h a c h i u m c a r m i n a e ( C R A M E R )C R A M E R 1 9 7 0 ( A T ) 7 ( WLu) 1 1 G 2 3

O n o n d a g a e l l a s p . L 2 3 P 2 4

P e r c u l t i s p h a e r a s t i p h r o s p i n a t a L I S T E R 1 9 7 0 G P 2 0

P s e n o t o p u s c h o n d r o c h e u s TAP PAN &LOEBLI CH 1 9 7 1 H 8 H G 2 5

S c h i s m a t o s p h a e r i d i u m r u g u l o s u mDO R N I N G 1 9 8 1 Tp T S h 2 3 Tp

S o l i t a s p . ( A T ) 3 S 4 G L 7 2 3

T y l o t o p a l l a s p . Tp ( R T ) p R 6 ( A T ) 7 T - L 2 3 T 2 6

V i s b y s p h a e r a d i l a t i s p i n o s a ( D O WN I E )L I S T E R 1 9 7 0 W 5 T 2 5 - L 2 0 T 2 6

A C R I T A R C H S 211B

AL

TIC

<_iOQO0.

CZ

EC

HO

SL

OV

AK

IA

AU

ST

RIA

BE

LG

IUM

NO

RTH

&

NO

RT

H­

WE

ST

FR

AN

CE

SP

AIN

EA

ST

ER

N

TU

RK

EY

NO

RTH

A

FR

ICA

WE

ST

AF

RIC

A

SIB

ER

IA

TUVA

A

.S.S

.R.

W 4 9? P 5 2

(WLu)? 5 6

P ? 2 4 P 3 3 P 3 5 ( H G ) 3 8 ? L u4 2? P 4 3 LuP3 L u 5 9

W 3 3 P 3 5 r 4 0? L u4 2

? P 4 3Lu3

? P 5 2 S 5 4 L u 5 9

A 3 8

S h 2 8 L I 3 4 W 3 3

W 3 3

S h ? 2 8 L I 3 4 W 3 3 ( W L u ) 5 6 7 L I - W 6 6

S h 2 8 W 3 3

? L u 3 3 A T 3 8

T S h 2 8

T S h 2 8 T W 3 8

S h 2 8 W 3 3 A - W 3 8 ? ( L I W ) 4 5 S 5 2 ( W L u ) 5 6 L I 65 7 L I - W 6 6

T S h 2 8 L I 3 4 W 3 3 L I 36 A - W 3 8 S 5 2 ?? Lu 63 7 L I - W 6 6

R 3 9 - W 3 8 W 6 5

R 3 9

?Lu? P5 2

Ap ? P 4 3 W - P 4 9 S 5 4 ( W L u ) 5 6

S h 2 9

T S h 2 8

S h 2 8 R 3 9

L U - P 3 3 ? L u 4 2L u 4 8? P 5 2 L u 6 0 ? W 6 2

R 3 9 ? L ? P 5 2 ? L u 6 5

P 2 4 R 3 9 - W 3 8 ? ( L I W ) 4 5 W P 4 9 S 5 4 L l - L u 6 0 ? L u 6 3

P 2 4 ? ? L I - P 3 3 ? L u 4 1 ? P 5 2 S 5 4 ( W L u ) 5 6 ? L u 6 3

? L ? P 5 2

T 3 8 L P 4 9

W 3 8 L I 3 6 R 3 9

T - W 3 8 ( W L u ) 5 6

212 F. M A R T I N

f i g . 149 (overleaf). Stratigraphical ranges and geographical distribution o f selected Silurian acritarchs. Chronostratigraphical subdivisions are those employed by Holland (1984, fig. 2). Numbers in the columns are as for Fig. 148 and indicate references for each area.Abbreviations are as follows: S -Silurian; LÍ - Llandovery; R - Rhuddanian; A-A eronian; T-Telychian; W -W enlock; Sh - Sheinwoodian; H-Hom erian; L u -Ludlow; G -Gorstian; L - Ludfordian; P - Pridoli; r-rew orked material; p-personal observation. Chronostratigraphical units in parentheses are not distinguished from each other; ? before chronostratigraphical symbol = age attribution based on palynological data only or on questionable non-palynological data; ?? before chronostratigraphical symbol = age attribution based on highly questionable palynological interpretation; ? before bibliographic reference number = taxon not illustrated adequately for that area, or never figured adequately for another area by the author reporting its presence, or not observed personally for that area by the present author. The following are omitted from the table: identifications considered here to be erroneous; dubious identifications of poorly localised material; and areas where only one of the selected taxa is present. For new synonymies, see Appendix 1; no new generic combinations are proposed here. For new locality data, see Appendix 2. Since data for this chapter were first prepared Mabillard and Aldridge (1985) have indicated the appearance of Deunffia ramusculosa and Domasia amphora in the uppermost Llandovery, 15 cm below the base of

the Buildwas Formation (basal Wenlock) at Leasows, the Llandovery-Wenlock boundary stratotype section.

a p p e n d i x 1

Synonymies

Dactylofusa esiillis Cramer and Diez, 1972 = (in part) Poikilo­fusa spinata Martin, 1969. Deunffia furcata niagarensis Thusu, 1973 = Downiea argentina Pöthe de Baldis, 1974 = Domasia intermedia Kirjanov, 1978. Deunffia ramuscuculosa rochesterensis Thusu, 1973 = Downiea copoana Pöthe de Baldis, 1974. Domasia amphora Martin, 1969 = D. hermosa Cramer, 1970 = D. canadensis Thusu, 1973. D. limaciformis (Stockmans and Willière) Cramer, 1970 = D. symmetrica Cramer, 1970 = D. cf. trispinosa in J. B. Richardson and

loannides, 1973. D. trispinosa Downie, 1960 = D. elongata Downie, 1960 = Leiofusa sp. in Rodriguez, 1983. Elekto­riskos williereae (Deflandre and Deflandre-Rigaud) Vangue- staine, 1979 = Elektoriskos pogonius Loeblich, 1970. Eupoi­kilofusa rochesterensis Cramer, 1970 = Leiofusa aff. spinata in Martin, 1974. Moyeria cabottii (Cramer) M. A. Miller and Eames, 1982 = Moyeria sp. in Holland and Smith, 1979. Neo­veryhachium carminae (Cramer) Cramer, 1970 = N. mayhill- ensis Doming, 1981.

a p p e n d i x 2

New locality data

Only palynologically productive samples are included; terminology of Series and Stages follows usage of Holland (1984).

c a n a d a : Province of Quebec; all locality numbers in Lespé- rance (1981a).

Anticosti Island

Loe. A2 B: west side of Ellis Bay; section proposed as Ordo- vician-Silurian boundary stratotype by Barnes and McCracken(1981). Sample A2 B7, 2.80 m above oncolitic bed, base of Becsie Formation (sensu Petryk 1981a); Oulodus? nathani Biozone, correlated with Llandovery A24 (Barnes and McCracken 1981); lower Rhuddanian Stage.

Loc. and sample A6 A: Cap Jupiter, north of mouth of Rivière Jupiter; about 3 m above base of Member 3 of Jupiter Formation; Distomodus staurognathoides Biozone; correlated with Llandovery C| 2 (Barnes and McCracken 1981); upper Aeronian Stage.

Loc. 7 A: 4 km south-east of Pointe du Sud-Ouest. Sample A7A1, 4 m below top of Jupiter Formation; Icriodella inconstans Biozone; correlated with Llandovery C5 (Uyeno and Barnes 1981); upper Telychian Stage.

Gaspésie

Loc. BC-1: Baie des Chaleurs area, in banks of Petite Rivière Port-Daniel. Samples BC-1-1 and BC-1-3, Clemville

Formation; respectively, and approximately, 85 m and 22 m below top of formation and correlated, respectively, with Llandovery Bj-C2 and C.-C2 on basis of conodonts (Nowlan 1981), and with Llandovery A and A ,4 on basis of brachiopods (Boucot and Bourque 1981); Rhuddanian Stage to lower Telychian Stage. Sample BC-1-4, middle part of Anse Gascon Formation; correlated with Llandovery C5 on basis of both conodonts (Nowlan 1981) and brachiopods (Boucot and Bourque 1981); Telychian Stage.

g r e a t Br i t a i n : all locality numbers for England and Wales are in Bassett et al. (1979); names of formations in Cocks et al.(1984).

Southern Llandovery area

Loc. 1-3: south of Pont Pwll-defaid, Grid Ref. SN 757-309; Sample GB-1-3-1, Goleuged Formation; Llandovery top A4; upper Rhuddanian Stage.

A C R I T A R C H S 213

L U D L O WL L A N D O V E R Y W E N L O C K P R I D O L I S E R I E S

L u d f o r -d i a n

G o r s ­t i a n

S T A G EH o m e ­r i an

R h u d d ­a n i a n

S h e i n ­w o o d i a n

A e r o ­n i an

T e l y ­c h i a n A C R I T A R C H S

G o . o l i g o s p i n o s u m

M. c a b o t t i i

T y l o t o p a l l a s p .

Eu. a f f . E. a m p u l l i f o r m i s

H. v i s b y e n s i s

Eu . r o c h e s t e r e n s i s

El . w i l l i e r e a e

Do . l i m a c i f o r m i s

D a . e s t i l l i s

N. c a r m i n a e

? — — — ? C a . m a p l e w o o d e n s i s

Do . a l g e r e n s i s

Do . t r i s p i n o s a

D e . f u r c a t a

? — ? Di . w i l l i e r e a e

D o . a m p h o r a

El . a u r o r a

S o l i t a s p .

D e . m o n o s p i n o s a

De . r a m u s c u l o s a

? G e r o n s p .

Gr . e n c a n t a d o r

S. r u g u l o s u m

V. d i l a t i s p i n o s a

F l o r i s p h a e r i d i u m s p .

Ps . c h o n d r o c h e u s

I N F O R M A L A C R I T A R C H A S S E M B L A G E S

f ig 150. Informal biozonal scheme for the Silurian based on acritarchs.

214 F. M A R T I N

Loc. 1-10: lane section from Brynder Farm to Myddfai, Grid Ref. SN 774-324; Sample GB-1-10, Wormwood Forma­tion; Llandovery top C3; lower Telychian Stage.

Loc 1-11: southern, small disused quarry immediately west of Cefn-cerig road, Grid Ref. SN 7743 3232. Samples WAL- 162-1 and WAL-162-3, Wormwood Formation; respectively 90 cm below and 1.2 m above stratotype base of revised Telychian Stage as proposed by Cocks et al. (1984); the Aeronian-Telychian boundary may probably be correlated approximately with the lower boundary of the turriculatus Biozone.

Loc. 1-12: southernmost exposure in roadcut opposite entrance to Cefn-cerig Farm, Grid Ref. SN 775 323. Sample WAL-163, Cerig Formation; about 49 m above stratotype base of Telychian Stage.

Northern Llandovery area

Locality in transect h, track to Trefawr, 500 m north of Cwm- coed-aeron Farm, Grid Ref. SN 8380 3953. Samples W-TRE-2 and W-TRE-5, Trefawr Formation; respectively 12 m and 10 cm above stratotype base of Aeronian Stage as proposed by Cocks et al. (1984) and defined at base of turriculatus Biozone.

Much Wenlock area, Shropshire

Loc. 2-1: north bank of Hughley Brook, 200 m south-east of Leasows Farm, Grid Ref. SO 5688 9839; stratotype for base of Sheinwoodian Stage (Bassett et al. 1975), which correlates with base of centrifugus Biozone. Sample GB-2-1-1, Purple Shales (uppermost Llandovery), 30 cm below base of Buildwas Formation (basal Wenlock). Sample GB-2-1-3, 50 cm above base of Buildwas Formation; lower Sheinwoodian Stage.

Loc. 2-2: stream section through Whitwell Coppice, 500 m north of Homer, Grid Ref. SO 6194 0204; standard section for base of the Homerian Stage. Samples GB-2-2-1 and GB-2-2-2, Coalbrookdale Formation; respectively graptolite localities 65

(ellesae Biozone, upper Sheinwoodian Stage) and 66 (lundgreni Biozone, lower Homerian Stage) of Bassett el al.(1975).

Ludlow area, Shropshire

Loc. 3-2: Goggin road (section A of D. E. White and Lawson 1978), Grid Ref. SO 4727 7184; basal Gorstian Stage. Sample GB-3-2-1, 80 cm above base of Lower Elton Formation.

Loc. 3-10: Deer Park Road (section B of D. E. White and Lawson 1978), Grid Ref. SO 4484 7115. Sample GB-3-10-1, 80 cm below boundary between Upper Leintwardine Formation and Lower Whitcliffe Formation; Ludfordian Stage.

Loc. 3-12: Sunny Hill Quarry (Holland et al. 1963), Grid Ref. SO 4484 7115; stratotype for base of Ludfordian Stage, which coincides with base of leintwardinensis Biozone. Sample GB-3-12-2, Lower Leintwardine Formation, 2.3 m above base of Ludfordian Stage.

NORWAY

Ringerike district, north o f Oslo: all localities in Worsley et al.(1982); ages (based mainly on evolutionary lineages of strick- landiid brachiopods) and correlations in M. E. Johnson and Worsley (1982).Loc. 3: Purk0ya. Sample NOR-PUR-1, middle 7c/3 unit of Vik Formation; correlated with Telychian Stage ( = Llandovery upper C4 to C5).Loc. 5: Vintergututangen, northern tip of Stror^ya. Samples NOR-VIN-1 and NOR-VIN-2, unit 8b of Bruflat Formation, respectively in middle of unit and 1.5 m below its top, which is correlated with the Telychian Stage ( = Llandovery C6).

Be l g iu m : additional data from the Lust borehole at Kortrijk. Sample LUS-210 (Martin 1969), sedgwickii Biozone; Aeronian Stage.

E X P L A N A T IO N OF F IG . 151

Figured specimens are in the Institut Royal des Sciences naturelles de Belgique, Brussels (IRScNB). Details of localities are given in Appendix 2.

A, I, J, M, Llandovery Series, Aeronian Stage, LUS - 210, Massif de Brabant, Belgium. B, C, Llandovery Series, Rhuddanian to lower Telychian Stage, BC - 1 - 1 , Gaspésie, Quebec, Canada. D, H, K, Llandovery Series, upper Telychian Stage, N O R - V IN -2 , Ringerike district, Oslo area, Norway. E, Wenlock Series, lower Sheinwoodian Stage, G B - 2 - 1 - 3 , Much Wenlock area, Shropshire, England. F, L, Llandovery Series, Telychian Stage, A7A1, Anticosti Island, Quebec, Canada. G, Ludlow Series, lower Gorstian Stage, G B - 3 —2 - 1, Ludlow area, Shropshire, England.

A. Elektoriskos williereae (Deflandre and Deflandre-Rigaud) Vanguestaine 1979, IRScNB No. bl761, x 1500.B. Poikilofusa aff. P. ampulliformis (Martin) Cramer 1970, IRScNB No. bl762, x 1500.C. Tylotopalla caelamenicutis Loeblich 1970, IRScNB No. bl763, x 2000.D. Schismatosphaeridium rugulosum Doming 1981, IRScNB No. bl764, x 750.E. Moyeria cabottii (Cramer) Miller and Eames 1982, IRScNB no. bl765, x 1000.F. Domasia trispinosa Downie 1960, IRScNB No. bl766, x 1000.G. Psenotopus chondrocheus Tappan and Loeblich 1971, IRScNB No. bl767, x 1000.H. Gracilisphaeridium encantador (Cramer) Eisenack and Cramer 1973, IRScNB No. bl768, x 1000.I. Dactylofusa estillis Cramer and Diez 1972, IRScNB No. bl769, x 1000.J, L. Dilatisphaera williereae (Martin) Lister 1970; J, IRScNB no. bl770; L, IRScNB No. bl771; both x 1000.K. Visbysphaera dilatispinosa (Downie) Lister 1970, IRScNB No. bl772, x 1000.M. Geron guerillerus Cramer 1967 emend. Cramer 1969, IRScNB No. bl773, x 1500.

A C R I T A R C H S 215