Late Ordovician and Early Silurian Acritarchs
F. Martin
D épartem ent de P aléontologie, Institut Royal des Sciences N aturelles de Belgique, Rue V autier
29, B-1040 Bruxelles, Belgium
Synopsis
T he principal stra tig rap h ic al d a ta for late O rd o v ician a n d early Silurian acritarch s are review ed; at
present they d o n o t justify an y form al z o n atio n on a b ro a d geographic scale. T he system ic basal b o u n d a ry
stra to ty p e at D o b ’s L inn, so u th e rn Scotland, has n o t yielded index acritarchs. A p relim in ary selection of
tax a from correlative stra ta on A nticosti Island, Q uébec, eastern C a n ad a , indicates th a t the a rea has the
m ost co n tin u o u s palynological record from at least the Ashgill to the late L landovery, w ith the best
p o tential for establishing d etailed acritarch system atics an d interregional correlation.
Introduction
In general, the b iostratigraph ical tool provided by the acritarchs is still only partly exploited for
interregional correlation, for the following reasons: (i) sufficiently detailed system atic descrip­
tions have becom e available only during the last fifteen years or so, th ro u g h the use of SEM ,
and a coherent taxonom ic fram ew ork is still lacking; (ii) precisely defined taxa are m ost often
rep o rted only from regions w here their total stratigraphical range is not established; (iii) a large
num ber of d ata relate to dispersed samples, for which there is no m acrofossil age control. In
particular, acritarchs of latest O rdovician an d earliest Silurian age have received little d o cu ­
m entation. This scarcity of d a ta reflects the lack of palynological investigations rath e r th an of
suitable m arine deposits, for these p robably planktonic, organic-w alled microfossils ap p ear to
be relatively w eakly facies-controlled w hen com pared with macrofossils. N evertheless, the
Ashgill extinction th at affected num erous other fossil groups also involved the acritarchs.
Differences in com position of assem blages between the end of the O rdovician and the begin­
ning of the Silurian are indicated in the following areas: A nticosti Island, eastern C a n ad a ;
southern A ppalachians, U.S.A.; Belgium ; and the A lgerian S ahara. These differences are am pli­
fied by the absence of H irn an tian or G am achian strata, except on A nticosti, where, on the basis
of prelim inary d ata (Duffield & Legault 1981, an d a u th o r’s personal observations), the d isap ­
pearance of num erous O rdovician taxa seems to occur in the G am achian. A m ark ed change
between acritarch associations from the late Ashgill and the L landovery is m entioned briefly
(Le H érissé 1984) for the subsurface rocks in southern G otlan d . C o lb ath (1986) has reviewed
different hypothetical causes for these acritarch extinctions, ranging from the effects of sea-level
and clim atic changes associated w ith glaciation to a bolide im pact model.
Review of data
The m ap (Fig. 1) shows the distribution of late O rdovician and early Silurian acritarchs and
indicates detailed references. N um bers (see explanation of Fig. 1) refer generally to the m ost
recent publication that indicates previous d a ta ; exceptions are A nticosti an d G re at B ritain, for
which further references are given. A nticosti an d southern Scotland provided the tw o final
candidate sections for the O rdovician -S ilu rian b o u n d ary strato ty p e considered by the S ubcom ­
m ission on Silurian S tratig rap h y (H olland 1984). Since then the In tern atio n al C om m ission on
S tratigraphy (Bassett 1985) has chosen to fix the base of the L landovery Series, together with
th at of its lowest stage, the R huddanian, at D o b ’s Linn, so u th ern S cotland; the b o u n d ary
stratotypes for the tw o other Llandovery stages, A eronian and Telychian, are located in the
type area of the L landovery in W ales (Cocks 1985).
Areas from w hich no index acritarchs are know n (for exam ple, the Ashgill of southw est
France, R auscher 1974) are om itted. O w ing to the lack of agreem ent on precise correlation
between the N o rth A m erican and British upper O rdovician sta n d ard successions (Barnes et al.
Bull. Br. Mus. nat. Hist. (G eol) 43: 2 99 -3 0 9
Issued 28 April 1988
300
F. M A R TIN
33-37
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30
8
4,37
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24-27
24,25
23
20
22
Fig. 1 G eneralized w orld m ap show ing late O rd o v ician a n d early Silurian a crita rc h localities. T he
follow ing a b b rev iatio n s in dicate the info rm atio n included in pub licatio n s 1-37 listed below : (CA),
un differentiated late C a ra d o c a n d A shgill; A, A shgill; P, P u sgillian; R, R a w th ey a n ; H, H irn a n tia n ;
G , G a m a c h ia n ; L, u n differentiated L landovery, possibly including R h u d d a n ia n ; Rh, R h u d d a n ia n ;
Ae, A ero n ian ; T, T ely ch ian ; p.d., palynological d a tin g only. C h ro n o stra tig ra p h ic units groups
w ithin p arentheses are n o t differentiated from each other.
1, Hill 1974, Rh-T: 2, Aldridge et al. 1979, Rh-T: 3, H ill & D o m in g in C ocks et al. 1984, R h-T : 4, D ow n ie 1984,
R h -T : 5, Eisenack 1968, A: 6, Eisenack 1963, A : 7, U m n ova 1975, A, L: 8, G órka 1969, A: 9, K onzalováM azan ková 1969, (PR ): 10, V avrdová 1974, A: 11, V avrdová 1982, H : 12, M arlin 1969, (CA), R h-T: 13, Martin
1974, (CA), Rh: 14, E laouad-D ebbaj 1981, (CA), A, p.d.: 15, Jardiné et al. 1974, (C ?A), (AeT), p.d. in part: 16,
D eu n ff & M assa 1975, ?C, p.d., ?Rh: 17, M olyneux & Paris 1985, A, p.d.: 18, Hill et al. 1985, (RhAe), p.d.: 19, Bär
& Riegel 1980, (AL), p.d.: 20, Brito 1967, L, p.d.: 21, G ray et al. 1985, L, p.d.: 22, M elendi & V olkheim er 1985, L:
23, C olbath in press, (CA), (PR), (RhAe): 24, L oeblich & T appan 1978, (CA), (PR ): 25, L oeblich & M cA dam 1971,
(CA), (PR): 26, L oeblich 1970, (PR): 27, C olbalh 1979, (CA): 28, John son 1985, L: 29, W right & M eyers 1981,
(CA), p.d.: 30, M iller & Eam es 1982, Rh: 31, M arlin 1980, (PR): 32, Legault 1982, (CA), p.d.: 33, Slaplin et al.
1965, (PR ): 34, C ramer 1970, (AeT): 35, D ufheid & Legault 1981, 1982, G , R h-T: 36, Jacobson & A chab 1985,
(PR): 37, M arlin in press and personal observation, G (at A nticosti only), Rh-T. [Since subm ission o f this paper,
W helan (1986) has com m ented briefly on the acritarchs from D ob's Linn.]
1981; Ross et al. 1982; S haver 1985), palynological references for bo th late E denian and
M aysvillian stra ta in U.S.A. are included. In the L landovery Series, acritarch d a ta given for the
R h u d d an ian som etim es include those for the A eronian an d Telychian. L ocalities w here the
sections begin only with the A eronian or T elychian are om itted here and m ay be found in
M artin (in press).
LATE O R D O V IC IA N A N D EARLY SILU R IA N A C RITA R CH S
301
Europe
In G re at B ritain, no palynological w ork has been published on the Ashgill. T he O rd o v ic ia n Silurian b o u n d ary strato ty p e strata at D o b ’s Linn (Cocks 1985) are com posed of condensed,
deep-w ater, graptolitic shales, the base of the L landovery being coincident w ith the base of the
P. acuminatus Zone. T he w hole succession, from the Climacograptus peltifer Z one (early
C aradoc) upw ards, contains rare, blackish acritarchs, but these are too poorly preserved to
provide useful inform ation. The type H irn an tian (H irnant Lim estone) at Cwm H irn an t quarry,
near Bala, N o rth W ales, yielded rare acritarchs belonging to either poorly-defined or rem nant
A ren ig -L lan virn taxa (personal observation). The C arad o c Series (C ostonian to O n n ian stages)
in the type area of S hropshire contains well preserved assem blages (T urner 1984) of C arad o c
age, associated w ith others derived from T rem adoc and A renig-L lanvirn deposits. R h u d d an ian
m icrofloras from near L landovery are bo th poorly preserved an d of low diversity b u t perm it
(Hill & D o m in g in C ocks et al. 1984) the recognition of three biozones characterized, on the
basis of published lists, by the successive appearance of taxa th at, for the m ost part, are
long-ranging in the Silurian or are left in open nom enclature. T he top of the R h u d d an ian there
also contains rew orked, pre-C arad o c O rdovician m aterial (M artin in press).
In the sam e region, an d especially in the the W elsh B orderland (Hill 1974), p artly published
results for the L landovery show, from the A eronian onw ards, a refined palynological zonation
th a t m ay be com pared w ith th a t outlined for Belgium (M artin 1969). O f p articu lar significance
are species of Domasia D ow nie, 1960 em end. Hill, 1974 an d Dilatisphaera williereae (M artin)
Lister, 1970.
In the M assif of B rabant, Belgium (M artin 1974), m oderately well preserved acritarchs,
m ostly long ranging an d including som e know n from the T rem adoc to the A renig-L lanvirn,
are from boreholes. P arts of these rock successions are assigned a late C arad o c a n d /o r Ashgill
age on lithological and stru ctu ral grounds in the absence of diagnostic m acrofossils; those of
the basal R h uddanian are dated by graptolites and include strata of the P. acuminatus Zone.
In the Baltic region (G otland, E stonia, L atvia— Eisenack 1963, 1968; U m n o v a 1975), P oland
(G ó rk a 1969) and C zechoslovakia (K onzalová-M azanková 1969; V avrdová 1974, 1982), as in
P o rtu g al (E laouad-D ebbaj 1981), d a ta are relatively few for the Ashgill an d absent for the
R h uddanian. T he only H irn an tian acritarchs so far illustrated com e from the P rag u e region
(V avrdová 1982).
Africa and South America
M icrofloras from boreholes in n o rth Africa are well preserved. At the G ra n d Erg O ccidental in
the A lgerian S ahara (Jardiné et al. 1974) acritarch zone F corresponds to the C a ra d o c and
perhaps Ashgill; it also contains taxa characteristic of the A ren ig -L lan v irn and is present to o in
deposits of the Illizi Basin attrib u ted doubtfully to the M . sedgwickii Z one of the A eronian. In
Libya (Deunflf & M assa 1975; M olyneux & P aris 1985; H ill et al. 1985) acritarchs from the late
O rdovician and early Silurian, cited and partially figured, are d ated w ith p articu lar reference to
palynological d ata from w estern E urope and central U.S.A. In D eunff & M assa (1975) the list
of tax a alleged to have been found in the early R h uddanian C. vesiculosus Z one indicates a
post-L landovery age and is not considered further here.
A critarch d ata for the relevant interval in G h a n a (Bär & Riegel 1980), Brazil (Brito 1967;
G ray et al. 1985) and A rgentina (M elendi & V olkheim er 1985) are dispersed an d m ainly
w ithout independent age control. T he m ost notew orthy illustrated observation is th a t samples
from G h an a said to occur at the O rdovician/S ilurian bou n d ary share only a single species,
Dactylofusa marahensis B rito & Santos, 1965, w ith strata of the M a ra n h äo Basin attrib u ted to
the Low er Silurian. In b o th cases the age is based on stru ctu ral an d palynological argum ents.
North America
P ublications referring to th e eastern and central U.S.A. deal m ainly w ith num erous new late
O rdovician taxa from O k lah o m a (Loeblich & M cA dam 1971; Loeblich & T ap p a n 1978) and
the C incinnati area (Loeblich 1970; L oeblich & M cA dam 1971; Loeblich & T ap p a n 1978;
C olbath 1979); how ever, th e acritarchs from the R ichm ondian Stage, w hich is correlated with
p art of the Ashgill Series, are from isolated samples. In the so u th ern A ppalachians (southw est
302
F. M ARTIN
Virginia, northw est G eorgia and east Tennessee), a consistent acritarch co rrelatio n , based
largely on new taxa, is docum ented (C olbath, in press) for the passage from O rdovician to
S ilurian; bu t the presence of the G am achian and earliest R h u d d an ian in the region is d eb a t­
able. An acritarch assem blage of u n doubted R h udd an ian age in w estern N ew Y ork State
(M iller & Eam es 1982) enables prelim inary correlatio n s to be m ade w ith assem blages in the
so u th ern A ppalachians, A nglo-W elsh area an d Belgium. A very few L landovery, including
p erhaps R huddanian, acritarchs are know n from central P ennsylvania (Johnson 1985).
In eastern C an ad a, except for palynologically d ated latest C arad o c o r Ashgill strata in a
borehole in the L ab rad o r Sea (Legault 1982), d a ta relate to the P rovince of Q uébec. O nly
reconnaissance studies are available for the p re-H irn an tian Ashgill of the Percé area (M artin
1980) in the G aspé Peninsula. The W hite H ead F o rm atio n at W hite H ead (Lespérance 1985;
Fig. 2 herein) has n o t yielded index acritarchs in the H irn an tian interval, and the basal L la n d o ­
very p o rtio n (base o f U nit 6; personal observation) co n tain s specim ens deform ed by crystal
gro w th ; som e of the latter, for exam ple Eupoikilofusa aff. E. ampulliformis, sensu D ufheid &
Legault 1981, are very characteristic of the R hud d an ian at A nticosti, from the base upw ards of
the Becscie F o rm a tio n at Ellis Bay.
At A nticosti an O rdovician/S ilurian b o u n d ary strato ty p e w as pro p o sed (Barnes &
M cC racken 1981) in an allegedly co ntinuous lim estone-shale succession in the u p p er p art of the
Ellis Bay F o rm a tio n (sensu P etryk 1981) at Ellis Bay. T he base of the S ilurian is m ark ed by the
app earance of the co n o d o n t Ozarkodina oldhamensis (Rexroad, 1967); O ulodus? nathani M cC ra­
cken & Barnes, 1981 is an auxiliary ind icato r for the b o u ndary. H ow ever, Lespérance (1985)
places the b o u n d ary higher and in the Becscie F orm atio n , on the assu m p tio n th a t the ap p e ar­
ance of the trilobite Acernaspis coincides w ith the base of the P. acuminatus Z one. The shallow
m arine platform deposits there are very rich in m icrofloras an d in m icro- an d m acrofaunas,
except graptolites (see L espérance 1981 for num erous co n trib u tio n s and earlier references). O n
the w hole, the Ashgill and L landovery acritarchs of A nticosti are very well preserved and
relatively ab u n d a n t, but have been described only partially (Staplin et al. 1965; C ram er 1970;
Duffield & Legault 1981, 1982), ap a rt from strata dated as D. complanatus Zone, assigned to the
early or m iddle Ashgill (Jacobson & A chab 1985).
The Anticosti acritarchs
T he q uality of the palynological m aterial at A nticosti an d its age co n tro l based on shelly
m acro faunas an d co n o d o n ts justify a prelim inary synthesis. T he ranges of som e taxa there are
com pared (Fig. 2) w ith those from other regions. T he com pilation is based on the references
given in the general d istribution of d a ta (Fig. 1) and for the post-A eronian of the sam e regions,
follow ing those assem bled by M artin (in press; explan atio n of Fig. 1). T his restricted choice of
taxa is conditioned by personal exam ination of twelve sam ples (see A ppendix) from the upper
p art of M em ber 4 o f the Ellis Bay F o rm atio n , of G am ach ian age, to the up p er p art of the
Ju p iter F o rm atio n , correlated w ith the Telychian (C 5) (Lespérance 1981). T he choice could have
been different, b u t in the present state of know ledge the com m ents w ould p ro b ab ly have been
co m p arable with those below.
T he observations of Duffield & Legault (1981) are confirm ed w ith regard to the change in
com position of acritarch assem blages ju st above the base of the Silurian as defined on the basis
of the ap pearance o f diagnostic con o d o n ts (Barnes & M cC racken 1981) w ithin M em ber 7 of
the Ellis Bay F o rm a tio n . If the correlation proposed by L espérance (1985) is accepted, the
m ajo r change in term s of appearance of new acritarch taxa occurs w ithin the late G am achian,
rath e r th a n in the early L landovery. At its type locality, on the west side of Ellis Bay, the entire
m em ber, 1 to 4 m thick, is very p o o r in acritarchs. In p articular, the locally developed bioherm al bed, 1-5 to 2 m thick, above the system ic b o u n d ary is sterile. Im m ediately above this
bed, from the base of the Becscie F o rm a tio n (sensu Petryk 1981; sam ple A2B7) onw ards, the
m ajority of taxa know n from oth er regions and of O rdovician affinities are absent. Arem orica­
n u m squarrosum Loeblich & M cA dam , 1971 (see synonym y in Jaco b so n & A chab, 1985: 171) is
recognized in the early R ichm ondian, w hich is equated w ith latest Pusgillian to early Raw-
303
Fig. 2
Ranges of selected Anticosti acritarchs in other regions.
LATE O R D O V IC IA N A N D EARLY SILU R IA N A C RITA R CH S
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NVI1NVNHIH
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(IJBd) N V IN3Q3
NVmiOSfld
304
F. M A R TIN
theyan by B arnes et aí. (1981). T he disappearance of Orthosphaeridium rectangulare (Eisenack)
Eisenack, 1968 (Figs 4a, b ; see synonym y in E laouad -D eb b aj 1981: 48) an d of O. insculptum
Loeblich, 1970 (Figs 3a, b) occurs w ithin an unobserved interval in the G am ach ian , betw een the
u p p er parts of M em ber 5 (about 5 m below its to p ; sam ple A2B3) and M em ber 6 (0-3 m below
its to p ; sam ple A2B4) of the Ellis Bay F orm atio n . Baltisphaeridium plicatispinae G ó rk a , 1969
(Fig. 9) extends, according to Duffield & Legault (1981), in to M em ber 7, below the bioherm al
bed. T he appearan ce of taxa of Silurian affinities, w hich occurs m ainly and progressively from
the base of the Becscie F o rm a tio n onw ards, begins in the G am ach ian , no later th a n the upper
p art of M em ber 5 (sam ple A2B3), source of the present exam ple of M ultiplicisphaeridium sp. 1,
sensu Duffield & L egault 1981 (Fig. 16). T he latter recalls the ‘Aí. fo rq u iferu m -M . forquillum ’
g ro u p found by C ram er & Diez (1972) in the late L landovery of K entucky. Eupoikilofusa aff. E.
ampulliformis (Figs 14a, b), w hich appears a t the base of the Becscie F o rm a tio n (sam ple A2B7),
earliest L landovery, is close to a L landovery species know n from the early R h u d d an ian in
Belgium (M artin 1974). T he entry of Domasia D ow nie, 1960, em end. Hill 1974 (Fig. 6) and
T ylotopalla Loeblich, 1970 (Fig. 10) on the one hand, an d of Dilatisphaera williereae (M artin)
L ister 1970 (Fig. 5) on the other, occurs in the Ju p iter F o rm a tio n at levels th a t are correlated
(Barnes & M cC racken 1981) respectively w ith the late A eronian ( C j- C 2 ; sam ple A6A, ab o u t
3 m above base of M em ber 3) and w ith the Telychian (C 5; sam ple A7A1, 4 m below to p of the
Ju p iter Form ation). As yet no diacro d ian has been identified from the up p er p art of the
G am achian, and no form suspected of being rew orked from the O rdovician h as been found in
the L landovery of Anticosti.
T he richness and variety of the m icrofloras in the G am a ch ian an d L landovery at A nticosti
will lead inevitably to the intro d u ctio n of new taxa, som e of w hich will be index fossils. As an
exam ple, tw o form s from the Ellis Bay F o rm a tio n (sam ple A2B3) are illu strated for the first
tim e here an d left in open n o m enclature: Pheoclosterium sp. nov. (Figs 7a, b) and G en. et sp.
nov. cf. Rhopaliophora (Fig. 8). T he only species form ally assigned to the form er genus, Pheo­
closterium fuscinulaegerum T ap p a n & Loeblich, 1971, is characteristic of the late O rdovician. Its
range (see Jacobson & A chab 1985 for all references) is from the E denian of In d ian a (K ope
F o rm a tio n ; T ap p a n & Loeblich 1971 ; C o lb ath 1979) an d from the O n n ian , highest C arad o c, in
Shropshire, E ngland (upper p a rt of O nny Shales; T u rn er 1984) to the H irn an tian in C zechoslo­
vakia (K osov F o rm a tio n , V avrdová 1982). T he second acritarch, cf. Rhopaliophora, differs from
th a t exclusively O rdovician genus in its opening and resem bles '’Hystrichosphaeridium' wimani
F igs 3 -1 6 A critarchs from A nticosti. All figured specim ens are in the type fossil collection of the
G eological Survey o f C a n a d a , O tta w a , an d have nu m b ers w ith the prefix G SC.
Figs 3, 4, 7 -9, 12, 15, 16: sam ple A2B3, Ellis B ay; Ellis Bay F o rm a tio n , up p er p a rt of M em ber 5,
G a m ac h ia n . Figs 11, 13, 14: sam ple A2B7, Ellis B ay; low erm ost Becscie F o rm a tio n , L landovery,
c o rre late d w ith R h u d d a n ia n , A 2_4. Figs 5, 6, 10: sam ple A7A1, 4 k m so u th e ast o f P o in te SudO u e st; u p p er p a rt o f Ju p ite r F o rm a tio n , L landovery, c o rre late d w ith T elychian, C 5. Age assign­
m ents a cco rd in g to L espérance (1981).
Fig. 3 Orthosphaeridium insculptum L oeblich 1970. G S C 82877. Fig. 3a, x 400; Fig. 3b, enlargem ent,
X 3000. o f base o f left process. Fig. 4 O rthosphaeridium rectangulare (E isenack) E isenack 1968.
G S C 82878. Fig. 4a, enlargem ent, x 2000, of base of left low er process. Fig. 4b, x 200. Fig. 5
D ilatisphaera williereae (M artin ) L ister 1970. G S C 82879, x 1000. Fig. 6 Domasia limaciformis
(S tockm ans & W illière) C ra m e r 1970. G S C 82880, x 500. Fig. 7 Pheoclosterium sp. nov. G S C
82881. Fig. 7a, en largem ent, x 3000, o f up p er m edian processes. Fig. 7b, x 750. Fig. 8 G en. et sp.
nov. cf. Rhopaliophora sp. G S C 82882, x 300. Fig. 9 Baltisphaeridium plicatispinae G ó rk a 1969.
G S C 82883, x 300. Fig. 10 T ylotopalla sp. G S C 82884, x 750. Figs 11, 12 ‘H ogklintia d igitata-H .
visbyensis'. Fig. 11, G S C 82885, x 250. Fig. 12, G S C 82886, x 100. Fig. 13 Goniosphaeridium
oligospinosum (E isenack) E isenack 1969. G S C 82887, x 250. Fig. 14 Eupoikilofusa aff. E. ampulli­
form is, sensu D uffield & L egault, 1981. G S C 82888. Fig. 14a, x 1000; Fig. 14b, enlargem ent,
x 5000, of low er right p a rt o f vesicle. Fig. 15 Diexallophasis rem ota (Deunff) P layford 1977. G S C
82889, x 500. Fig. 16 M ultiplicisphaeridium sp. I, sensu D uffield & L egault 1981. G S C 82890,
x 500.
LATE O R D O V IC IA N A N D EARLY SILU R IA N A C RITA R CH S
305
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F. M AR TIN
Eisenack, 1968, determ ined by its au th o r from the latest Ashgill of G o tla n d (B ornholm er Stufe
F2 from an erratic b oulder at O il Myr).
O n A nticosti, in both the Ashgill an d the Llandovery, there are geographically w idespread
form s w ith long stratigraphical ranges th a t are difficult to define because of their wide, co n tin ­
uous m orphological variability w ithin a single sam ple; exam ples are Diexallophasis remota
(Deunff) Playford 1977 (Fig. 15) an d the ‘H ogklintia d igitata-H . visbyensis’ com plex (Figs 11,
12). The recurrent ab undance in certain O rdovician an d Silurian strata, n o tab ly on A nticosti
and in the Baltic region, of the latter com plex and of, for instance, Goniosphaeridium oligospinosum (Eisenack) E isenack 1969 (Fig. 13) p robably results from p articu lar p alaeoenvironm ental
co n d itions; the la tte r led C ram er & Diez (see 1974 for earlier references) to p o stu late a certain
degree of provincialism linked to palaeolatitudes for Silurian acritarchs.
A critarch d ata for the latest O rdovician and earliest Silurian are as yet too d isp arate to
perm it reliable palaeogeographic reconstructions. D ata from A nticosti indicate affinities and
possibilities for correlation as follows. T he G am ach ian m icrofloras contain taxa know n from
the late O rdovician of central U.S.A. a n d /o r the p re-H irn an tian Ashgill of G aspé, and from the
O rdovician of E urope (Baltic region and P ortugal) an d N o rth Africa (Libya). In particular, the
evolutionary schem e proposed by Loeblich & T ap p a n (1971) for the genus Orthosphaeridium
Eisenack 1968, notably in p art of the C incinnatian of central U.S.A. and in the late Ashgill of
the Baltic region, G o tla n d and Estonia, m ay be applied to the G am ach ian of A nticosti and the
late O rdovician of P ortugal. T he possibilities for correlation offered by the L landovery acri­
tarchs of A nticosti concern affinities with, principally and in decreasing order, the G aspé area
of C an ad a, E ngland and W ales, Belgium and the U.S.A. In particu lar, the first occurrences of
Domasia and of Dilatisphaera williereae, the levels of w hich are still inadequately know n on
A nticosti, should perm it correlation with at least the A eronian an d the Telychian of the
A nglo-W elsh area. Palynological d ata for the R hud d an ian of the la tte r area allow only a local
zo n atio n at present.
Conclusions
O w ing to the d ea rth of published data, acritarchs have not been used directly as one of the
criteria for the choice of an O rd o v ician -S ilu rian b o u n d ary d u rin g the activities of the I.U.G.S.
w orking group from 1974 to 1985. T he A nticosti deposits are those likely to provide the m ost
reliable palynological correlations, n o t only in the im m ediate vicinity of the system ic bou n d ary
b ut also at least from the early to m iddle Ashgill to the late L landovery (Telychian, C 5). This
view is supp o rted by the indication bo th of relatively co n tin u o u s d ata and of direct correlations
w ith the G aspé area from the base of the R h uddanian upw ards, an d the A nglo-W elsh area from
the A eronian upw ards.
Acknowledgements
1 am indebted to M . G . B assett (N a tio n a l M useum of W ales, Cardiff), G. K. C o lb ath (Sm ithsonian
In stitu tio n , W ash in g to n , D.C.) a n d J. A. L egault (U niversity of W aterloo, O n ta rio , C a n ad a ) for critically
review ing the m anuscript.
Appendix
Locality d ata for A nticosti Island, P rovince of Q uébec, C anada. All locality num bers in
L espérance (1981: 1).
Loc. A-2A : P o in te L afram boise area. Sam ple A-2A 1: Ellis Bay F o rm a tio n , M em ber 7, 0-40 m above
o ncolithic bed. Sam ple A-2A 2: Becscie F o rm a tio n , 0-60 m above base.
Loc. A -2B: west side of Ellis Bay, section p ro p o sed as O rd o v ic ia n -S ilu ria n b o u n d a ry stra to ty p e by
B arnes & M cC racken (1981). Sam ples A-2B2 to A-2B6: Ellis Bay F o rm a tio n ; A -2B2: m em ber 4, 3 m
below to p of m em b er; A-2B3: m em ber 5, 5 m below to p of m em ber; A-2B4: m em ber 6, 0-30 m below
to p o f m em b er; A-2B5 a n d A-2B6: m em ber 7, respectively ju s t above an d 0-75 m above oncolithic bed.
Sam ples A-2B7 to A-2B9: Becscie F o rm a tio n . A-2B7: im m ediately above the b ioherm al level of
LATE O R D O V ICIA N A N D EARLY SILU R IA N A C RITA R CH S
307
m em ber 7 o f the Ellis Bay F o rm a tio n . A-2B8 and A-2B9: respectively 1-30 m an d 25 m (approxim ately)
above A-2B7.
Loc. A-6A an d sam ple A-6A: C ap Jupiter, n o rth of m o u th o f Rivière Ju p iter, Ju p iter F o rm a tio n , a b o u t
3 m above base o f m em ber 3.
Loc. A -7A : 4 k m so u th e ast o f P ointe du S ud-O uest. Sam ple A-7A1 : Ju p iter F o rm a tio n , 4 m below its top.
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