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Radiolarian Cretaceous age of Soulabest radiolarites

in ophiolite suite of eastern Iran

SEYED AHMAD BABAZADEH1

and PATRICK DE WEVER2

Key words. – Eastern Iran, Lut and Afghan blocks, Sistan suture zone, Gazik Province, Ophiolite Suite, Soulabest Radiolarites,

Cretaceous Radiolaria.

Abstract. – The ophiolite-flysch range (accretionary prism) of the Sistan suture zone from eastern Iran includes several

intensely deformed tectonic units, some of which consist of volcaniclastic rocks, volcanic rocks, siliceous pelagic sedi-

ments (cherts and radiolarites) and calcareous rocks (deep marine, platform), whereas others are represented by terrige-

nous turbidites. The Soulabest radiolarites are located in the Ratuk complex of the Tirrul’s subdivision [Tirrul et al.,

1983], or in the ophiolite suite of the Gazik province.

The local biostratigraphy of this region is based on two faunal assemblages. Faunal assemblage I is dated early

Aptian, faunal assemblage II is attributed to middle-late Albian. The most abundant fauna is found in the middle-late

Albian. The timing of the oceanic opening in eastern Iran remained questionable until now. The study of the radiolarites

of the Soulabest area provides new data for dating the primary opening between two microcontinents : the Lut and

Afghan blocks. It is proposed that the oceanic opening of the two blocks occurred prior to the early Aptian. In previous

reports, the age of opening was attributed to Upper Cretaceous.

All reported Radiolaria are found in red radiolarites and green-red argillaceous cherts. This formation is uncon-

formably overlain by Maastrichtian conglomerates. It indicates that the closure of the basin occurred in Maastrichtian

age.

Age crétacé des radiolarites de Soulabest dans la suite ophiolitique d’Iran oriental

Mots clés. – Iran oriental, Blocs de Lut et Afghan, Zone de la suture de Sistan, Province de Gazik, Suite ophiolitique, Radiolarites de

Soulabest, Radiolaire du Crétacé

Résumé. – La zone à ophiolite et flysch (prisme d’accrétion) de la suture de Sistan (Iran oriental) comprend différentes

unités tectoniques intensément déformées. Certaines se composent de roches volcanoclastiques, de roches volcaniques,

de sédiments pélagiques siliceux (des cherts et des radiolarites) et de roches calcaires, tandis que d’autres sont représen-

tées par des turbidites terrigènes. Les radiolarites de Soulabest sont situées dans le complexe de Ratuk de la subdivision

de Tirrul, ou dans la série ophiolitique de la province de Gazik. Deux assemblages ont été identifiés. L’âge de l’assem-

blage I appartient à l’Aptien inférieur et l’âge de l’assemblage II est Albien moyen-supérieur. La faune la plus abon-

dante est trouvée dans l’Albien moyen-supérieur.

La datation de l’ouverture océanique en Iran oriental restait mal connue. Dans le présent article, cet âge est déter-

miné par des radiolaires pour la première fois. Les nouvelles données acquises dans la région de Soulabest permettent

de dater l’ouverture entre deux microcontinents (blocs de Lut et Afghan). L’ouverture océanique des deux blocs a donc

eu lieu avant l’Aptien inférieur. Jusqu’à présent cette ouverture était attribuée au Crétacé supérieur. Tous les radiolaires

rapportés sont trouvés dans le corps central d’une série ophiolitique et dans des radiolarites rouges, des cherts argileux

rouges et des cherts gris-vert. Cette série ophiolitique est recouverte en discordance de conglomérats du Maastrichtien.

Cela montre que la fermeture du bassin a été réalisée au Maastrichtien.

INTRODUCTION

The Soulabest radiolarites are located in the Sistan su-

ture zone (eastern Iran) which are subdivided into two nor-

thwest-trending belts, termed the Ratuk and Neh complexes

and the Sefidabeh forearc basin (fig. 1). They consist of an

ophiolite mélange including oceanic complexes where ba-

salts are associated with crystallized limestones, red argilla-

ceous cherts, green-red radiolarites and green-black cherts.

These associations characterize the oceanic basin of the

west border of the Afghan platform, pointing to the primary

opening time of the Neo-Tethys in this region.

The Ratuk complex to the east, was built before

Maastrichtian age ; the Neh complex located to the south-

west was dated as Senonian to Eocene. The Sefidabeh

forearc basin (Cenomanian to Eocene) was deposited un-

conformably on both the Neh and Ratuk complexes and the

southwest margin of the Afghan block [Tirrul et al., 1983]

(fig. 1). Therefore, the Soulabest area is located in the

Ratuk complex. The studied area is limited by 60o

17’ to

Bull. Soc. géol. Fr., 2004, t. 175, no

2, pp. 121-129

Bull. Soc. géol. Fr., 2004, no

2

1Faculty of Sciences, Payame noor university of Birjand, Birjand, Iran ; Current address : ISTO, Université d’Orléans, Bâtiment Géosciences, Rue St.

Amand, BP 6759, 45067, Orléans, France2Laboratoire de Géologie, Muséum National d’Histoire Naturelle, 43 Rue Buffon, F-75005 Paris, France

Manuscrit déposé le 20 février 2002 ; accepté après révision le 16 septembre 2003.


2

122 BABAZADEH et al.

FIG. 1. – Geological subdivisions of the Sistan suture zone [from Tirrul et al., 1983, simplified].

FIG. 1. – Subdivisions géologiques de la zone de suture de Sistan.

FIG. 2. – Location of the two studied sections (R & Rs) in the Soulabest area and their cross sections. Geological map of Gazik [from Alavi Naini and

Behruzi, 1981, simplified].

FIG. 2. – Localisation et coupes des sections étudiées (R et Rs) dans la zone de Soulabest.

Fig. 1

Fig. 2

60o

20’ of longitude east and 32o

30’ to 32o

33’ of latitude

north (fig. 2). Rocks containing radiolarians were previ-

ously reported by Stöcklin et al. [1972], Tirrul et al. [1983],

Fauvelet and Eftekhar-Nezhad [1990] in thin sections, with-

out any specific identification and therefore without any

age. In the present study, the identification of Radiolaria

was made with the scanning electron microscopic method.

The goal of this paper is to present a new age determi-

nation of radiolarian assemblages from this region along the

west border of the Afghan platform, in order to test previ-

ous interpretations of the creation of the oceanic crust dur-

ing the divergence (opening) of the Lut and Afghan blocks.

REGIONAL SETTING

Iran is an assemblage of marginal Gondwana fragments that

detached from the Gondwanian-Arabian plate during the

late Paleozoic (Permian), or early Triassic [Stöcklin, 1977].

The age of the disappearance of the Paleo-Tethys is doubt-

ful in northern Iran. It is attributed to Upper Paleozoic due

to Permo-Triassic marine transgression [Volvosky et al.,

1966 ; Seyed-Emami, 1971 ; Stöcklin, 1974] or it was a

consequence of pre-early Jurassic collision of Laurasia with

central Iranian microcontinental fragments [Stöcklin, 1974,

1977 ; Sengör and Kidd, 1979 ; Wensink and Varekamp,

1980 ; Soffel and Förster, 1980 ; Davoudzadeh and

Schmidt, 1982] or it took place in early Cretaceous in the

Sabzevar area [McCall and Eftekhar-Nezhad, 1994].

Central Iran is a continental fragment with the same Pa-

leozoic history as typical Gondwanian areas such as Arabia

or India, in sharp contrast with the coeval history of south

Eurasia [Stöcklin, 1977]. Therefore, central Iran detached

from Gondwana and migrated northwards through the open-

ing of a southern ocean and closure of a northern one before

it collided with Eurasia. The northward migration was rec-

ognized later for blocks that presently are widely distrib-

uted between the Black sea and southeast Asia [Shvolman,

1978 ; Bassoullet et al., 1980 ; Metcalfe, 1988]. The subse-

quent consumption of a younger ocean basin (in the south

of Iran), the Neo-Tethys, beneath the southern margin of

central Iran led to collision with the Arabian plate along the

Main Zagros thrust [Stöcklin, 1977].


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RADIOLARIAN CRETACEOUS AGE OF SOULABEST RADIOLARITES 123

FIG. 3. – Modified sketch map of Iran showing the major tectonic units [Lensch et al., 1984], the inner microcontinental nucleus (Yazd, Tabas and Lut

blocks) [Sengör et al., 1988], the positions of the main ophiolites [Stöcklin, 1977 ; Dilek and Delaloye, 1992].

FIG. 3. – Carte simplifiée d’Iran montrant les unités tectoniques principales, le noyau microcontinental et la position des ophiolites.

There are some inconsistencies about the time of colli-

sion along the Main Zagros Thrust which is interpreted to

be either a late Campanian-Maastrichtian [Ricou, 1971 ;

Berberian and King, 1981] or a Miocene event [Bird et al.,

1975 ; Sengör and Kidd, 1979 ; Stoneley, 1981]. Neverthe-

less, in the late Cretaceous, Iran was colliding with the

Gondwanian Afro-Arabia plate, but the oceanic area was

not completely closed as evidenced by the presence of Cre-

taceous-Tertiary flysch deposits in eastern Iran.

Three major tectonic units (Turanian, Iranian and Ara-

bian plates) recognized by Lensch et al. [1984] in Iran, are

separated from each other by ophiolit ic complexes

[Stöcklin, 1977] (fig. 3). These are subdivided into smaller

elements such as Kopet Dagh, southern Caspian sea, Zagros

thrust, Zagros folded belt, Alborz mountain and Central

Iran. Central Iran comprises the Sanandaj-Sirjan belt, the

Orumiyeh-Dokhtar belt, the Central-East-Iran microplate

[Davoudzadeh and Schmidt, 1981], the latter subdivided

into Yazd, Tabas and Lut blocks (fig. 3).

There are the remnants of oceanic basin that separate

the segments of Alpine belt. The three components of the

inner microcontinental nucleus (formerly termed the Lut

block by Stöcklin [1968], the Yazd, Tabas, and Lut blocks

are separated by fracture zones and have been rearranged

from their original position [Sengör et al., 1988].

In Central Iran, there are two ophiolite belts including

mélanges and deep water marine sedimentary rocks : i) one

of these ophiolite complexes extends from Esfandagheh to

the Nain area and along the Great Kavir Fault to the exten-

sive ophiolitic mélange exposures around Sabzevar ; ii) the

second major belt, the Sistan suture zone (Sistan ocean),

branches from the central Makran ranges northward to the

Birjand area, but does not join the mélange of the Sabzevar

zone [Stöcklin, 1977] (fig. 3).

The ophiolite-flysch range of the second belt is subdi-

vided into two northwest-trending “en echelon” belts

termed the “Ratuk” and “Neh” complexes. These complexes

are characterized by pillow-lava, basaltes, ophiolitic blocks,

or serpentinite-matrix mélange, and large fault slivers of

epidote blueschist tectonite. The Ratuk complex is situated

in the eastern part and was built prior to Maastrichtian time.

The Neh complex is located to the southwest ; its age

ranges from Senonian to Eocene [Tirrul et al., 1983]. The

studied area is situated within the Sistan suture zone, in the

Ratuk complex or in the Gazik province of the ophiolite

unit.

MATERIALS AND METHODS

The faunas analyzed in this paper were obtained from the

red radiolarites, red argillaceous cherts, and green-black

cherts after repeated treatments of the samples with diluted

hydrofluoric acid (10% HF) and were extracted by using

standard techniques in radiolarian research and the methods

elaborated by Dumitrica [1970], Pessagno and Newport

[1972], De Wever [1980], De Wever [1982] and De Wever

et al. [2001]. The scanning electron microscope (SEM) with

much greater magnification was used for study of the wall,

inner structure of the cephalis and exterior morpho-

structural elements.

LOCATION AND LITHOLOGY OF SAMPLES

Two studied outcrops located north and south of the

Soulabest village were examined (respectively R and Rs in

fig. 2). (i) The radiolarites of the northern side of the vil-

lage, so-called northern unit, consist in stratified basalts,

radiolarian cherts, red radiolarian argilaceous cherts,

green-gray to black cherts without Radiolaria, radiolarites

and conglomerates containing fragments of basalt, patched

limestone and dolomites in different colors of red, green

and black, containing moderately preserved radiolarian

skeletons. The true thickness is 60 m. (ii) Radiolarites of

the southern side of the village make up the so-called south-

ern unit. The lower part of the southern unit shows a body

of mélange containing the radiolarites, the pillow-lavas and

the patched limestones with the intercalation of the cherts.

It is covered by the disorganized complex containing red

radiolarites, red radiolarian argilaceous cherts showing

weak metamorphism and bedded gray cherts without

Radiolaria. In contrast with the northern location, these

radiolarians are well preserved. The thickness of this body

reaches 100 m. The contact between these two units is

faulted. On the basis of radiolarian assemblage, the south-

ern unit appears to be younger than the northern one. The

lower part of the section overlies conformably massive and

pillowed basalts, the upper part is unconformably overlain

by Maastrichtian conglomerates containing the cherts, the

basalts and the limestones (fig. 4).

BIOSTRATIGRAPHY

Radiolarian assemblages play an important role in the

biostratigraphy of accretionary complexes (ophiolitic

mélange and flysch) in regions with high tectonic intensity,

where other diagnostic fossils, such as ammonoids,

foraminifers, are absent. In these regions, the radiolarian

preservation and abundance are largely controlled by the

process of dissolution [De Wever et al., 1979] which in

some cases, result from a deep burial diagenesis [De Wever

and Caby, 1981]. The stratigraphical succession is incom-

plete due to exclusion or repetition of sedimentary bodies in

subduction zones. In order to know the absence of a certain

species or an interval zone, it is necessary to systematically

analyse the occurrence of the species in all available sec-

tions (e.g. sections of south of Birjand in Neh complex).

Several samples were examined in this study and among

them, only in 10 samples, identifiable radiolarian species

have been found. Among 40 determined radiolarian species,

only 17 specimens are figured (plate I) from the early Creta-

ceous to lowermost late Cretaceous age. The stratigraphic

range as known from literature [De Wever and Thiebault,

1981 ; Gorican, 1994 ; O’Dogherty, 1994 ; Bak, 1999] is

shown in figure 5.

The assemblages are dominated by cryptothoracic

Nassellaria corresponding to Holocryptocanium. multi-

segmented Nassel lar ia are also common : Pseudo-

dictyomitra, Archaeodictyomitra, Dictyomitra, Thanarla, Xitus

and Stichomitra etc.

Radiolaria are more abundant and diversified within the

deposits of the south Soulabest village than in the deposits

of the northern location. The northern Soulabest samples

(R7, R10, R15 and R19) yield the radiolarian association


2


(fig. 4) : Dictyomitra cf. excellens (TAN), Stichomitra

communis SQUINABOL, Stichomitra cf. japonica Nakaseko

& NISHIMURA, Thanarla pacifica NAKASEKO & NISHIMURA

and Parvicingula sp. This association is attributed to the

faunal assemblage I, and allows to assign an early Aptian

age.

The south Soulabest samples (Rs6, Rs7, Rs12, Rs17 and

Rs23) yie ld the radiolar ian associa t ion (fig . 4) :

Archaeodictyomitra aff. A. vulgaris PESSAGNO, Archaeo-

dictyomitra sp., Dictyomitra gracilis (SQUINABOL), D.

montisseri (SQUINABOL), Holocryptocanium barbui

DUMITRICA, Pseudodictyomitra pseudomacrocephala

(SQUINABOL), Rhopalosyringium adriticum (O’DOGHERTY),

R. hispidum (O’DOGHERTY), R. majuroense SCHAAF, R.

perforaculum O’DOGHERTY, R. scissum (O’DOGHERTY),

Stichomitra communis SQUINABOL, S. cf. japonica NAKASEKO

& NISHIMURA, Thanarla pulchra (SQUINABOL), T. aff. veneta

(SQUINABOL), Xitus mclaughlini (PESSAGNO). This association

is attributed to the faunal assemblage II. The age of this as-

semblage is middle-late Albian.


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FIG. 4. – Succession of microfauna of Soula-

best Radiolarite.

FIG. 4. – Microfaune de la radiolarite de

Soulabest.


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RESULTS

Two radiolarian assemblages (I and II) have been identified

in the Soulabest ophiolite suite. The age of faunal assem-

blage I in the north Soulabest village is early Aptian as in-

ferred from the radiolarian in the radiolarian cherts and red

radiolarian argilaceous cherts. The samples of red argilla-

ceous chert, red radiolarites and gray chert in the faunal as-

semblage II at the south Soulabest village assign the

middle-late Albian. During these periods, an oceanic crust

with the deep marine sediments (upper part of ophiolite

suite) were created between two microcontinents. Thus, the

age of primary opening is prior to early Aptian. No rocks

older than the early Aptian are reported in this ophiolite

suite.

DISCUSSION

The study of the suture zone of eastern Iran requires a de-

tailed analysis of foraminiferal limestones, flysch deposits,

radiolarites and radiolarian cherts in order to establish the

timing of setting of each ophiolite mélange in each horizon.

These studies provide the paleogeographic data for drawing

the primary ancient boundaries of the two microcontinents

(Lut and Afghan blocks).

The Iranian ophiolites were divided into three groups

by Takin [1972] and Stöcklin [1968, 1974, 1977] : (1)

ophiolites of the Alborz range (northern Iran), located in the

Mashhad, Sabzevar and Rasht ; (2) ophiolites of the

High-Zagros-Oman including the Khoy, Kermanshah,

Neyriz and Esphandagheh ; (3) ophiolites that mark the

boundaries of the central Iranian plateau, located at Nain,

Birjand and Iranshahr (fig. 3).

On the other hand, the ophiolites of Iran can be exam-

ined on the basis of two parameters : the age of oceanic

opening and the age of ophiolitic emplacement.

In northern Iran, the age of oceanic opening is not clear.

The ophiolitic emplacement age in Talesh montains and

Kopet Dagh, is attributed to Upper Paleozoic due to the

presence of metamorphic rocks and the Permo-Triassic

transgression of conglomerate, tuff and green tuffaceous

limestone [Volvosky et al., 1966 ; Seyed-Emami, 1971 ;

Stöcklin, 1974] but in Sabzevar area the emplacement took

place in early Cretaceous [McCall and Eftekhar-Nezhad,

1994].

In the High-Zagros-Oman, the first oceanic opening of

the High-Zagros Alpine sea along the High-Zagros belt pre-

sumably started in the Upper Paleozoic (Permian) but the

emplacement age corresponds to la te Campanian-

Maastrichtian time because the High-Zagros Ophiolite-

Radiolarite Thrust (in the Neyriz area) is unconformably

covered by post-emplacement shallow water reef limestone

[Ricou, 1971].

Central Iran is surrounded by ophiolitic belts that have

different histories. In the western part, the age of the pri-

mary detachment of continental fragments is not clear and

also the age of the ophiolite emplacement is doubtful. Sev-

eral authors suggested that it took place prior to the late Pa-

leozoic [Majidi, 1978 ; Davies et al., 1972 ; Stöcklin, 1974,

1977 ; Clark et al., 1975]. In contrast, the others extended

this phenomenon until the late Maastrichtian for the follow-

ing regions, “Khoy, Nain-Baft, northern-eastern Zagros line

belt, Great Kavir fault, Iranshahr and Makran” [Gansser,

1960 ; Sabzehei and Berberian, 1972 ; Stöcklin, 1974,

1977 ; Stoneley 1974, 1975 ; Sabzehei, 1974]. Thus the

ophiolite-mélanges are unconformably covered by the

Paleocene-Eocene shallow water sediments [Berberian and

King, 1981].

In the eastern part, the studied area (Sistan suture zone in

the Gazik province), Tirrul et al. [1983] stated that the oldest

rocks separating the Lut block [Stöcklin, 1968] from the

Afghan block [east Iran-central Afghan of Schreiber et al.,

1972] are attributed to Upper Cretaceous. However, the


2


PLATE 1. – For each sample are necessarily provided : species name, author, sample number in which this specimen was found, stratigraphic range, bar

scale and magnification.

PL. 1. – Pour chaque individu sont notés : nom d’espèce, auteur, nod’échantillon, étage stratigraphique, échelle, agrandissement.

FIG. 1. – Thanarla pulchra (SQUINABOL), Rs23, Middle Albian-Cenomanian, 25µm, X 175.

FIG. 2: Thanarla pacifica NAKASEKO & NISHIMURA, R15, late Barremian-early Aptian, 25µm, X 225.

FIG. 3. – Thanarla aff. veneta (SQUINABOL), Rs17, Middle Albian-Cenomanian, 25µm, X 200.

Figs. 4 & 5. – Xitus mclaughlini (PESSAGNO), Rs23, early Albian-Cenomanian, 30µm, X75.

Figs. 6 & 7. – Rhopalosyringium majuroense SCHAAF, Rs6, early Albian-early Cenomanian, 15µm, X 180; Fig. 7, X150

Fig. 8. – Rhopalosyringium perforaculum O’DOGHERTY, Rs17, middle-late Albian, 15µm, X 180.

Fig. 9. – Pseudodictyomitra pseudomacrocephala (SQUINABOL), Rs17, early Albien-Turonian, 25µm, X 200.

Fig. 10. – Dictyomitra montisserei (SQUINABOL), Rs12, early Albian-early Turonian, 50µm, X 150.



Fig. 13. – Dictyomitra cf. D. gracilis (SQUINABOL), Rs17, early Albian-early Cenomanian, 25µm, X 225.

Fig. 14. – Dictyomitra gracilis (SQUINABOL) Rs23, early Albian-early Cenomanian, 25µm, X 225.

Fig. 15. – Dictyomitra cf. D. excellens (TAN), R7, late Barremian-early Aptian, 50µm, X 150.

Fig. 16. – Archaeodictyomitra sp. , Rs12, Albian, 25µm, X 250.

Fig. 17. – Archaeodictyomitra sp. , Rs23, Albian, 25µm, X 225.

Fig. 18. – Archaeodictyomitra aff. A. vulgaris PESSAGNO, Rs17, Barremian-Albian, 25µm, X 175.

Fig. 19. – Archaeodictyomitra aff. A. vulgaris PESSAGNO, Rs23, Barremian-Albian, 25µm, X 225.

Fig. 20. – Holocryptocanium barbui DUMITRICA, Rs23, Albian-Turonian, 15µm, X105.

Fig. 21. – Stichomitra communis SQUINABOL, Rs17, Aptian-Turonian , 25µm, X 200.

Fig. 22. – Stichomitra communis SQUINABOL, R7, Aptian-Turonian, 25µm, X 225.

Fig. 23. – Stichomitra cf. japonica (NAKASEKO & NISHIMURA), R10, late Barremian-Aptian, 10µm, X 325.

Fig. 24. – Stichomitra cf. japonica (NAKASEKO & NISHIMURA), R7, late Barremian-Aptian, 15µm, X 180.

Fig. 25. – Exitus elegans (SQUINABOL), R7, late Barremian-Aptian, 50µm, X 150.

Fig. 26. – Exitus elegans (SQUINABOL), R15, late Barremian-Aptian, 25µm, X 200.

Fig. 27. – Parvicingula sp., R7, late Barremian-early Aptian, 25µm, X 225.

above results on the radiolarites within the ophiolite suite, in-

dicate that the oldest rocks in the ophiolite belong to an early

Cretaceous (early Aptian and middle-late Albian) oceanic

crust, and the oceanic opening took place in pre-early

Aptian. Moreover, the middle-late Albian radiolarites with

the faunal assemblage II in this region (Gazik province)

could be correlated with the Samail radiolarites containing

Pseudodictyomitra pseudomacrocephala (SQUINABOL),

Thanarla veneta (SQUINABOL) etc. The oceanic crust was

later disrupted and incorporated in the mélange and tectoni-

cally emplaced before the presence of unconformable

Maastrichtian conglomerates in which we found Orbitoides

media, Siderolites calcitrapoides and Omphalocyclus

macroporus. It shows that the age of ophiolite emplacement

is pre-Maastrichtian. Therefore, on the basis of the faunal as-

semblage and the age of ophiolite emplacement, it seems that

the paleogeographic history of this ophiolite branch (Gazik

province) can be similar to that of the High-Zagros-Oman in

the south of Iran during early-late Cretaceous.

Acknowledgements. – We are indebted to Mr. F. Hassani, chairman of

Payame noor University of Birjand for field work facilities. We are grateful

to Dr M. D. Courme for her generous help during the field and to Dr. D.

Cluzel for helpful comments on structural geology. The writers wish to

thank to Dr. L. Jolivet for critically reading of the manuscript. The first au-

thor also indebted to Dr. S. Gorican and Dr. T. Juteau who acted as refe-

rees, for criticism and advice that considerably improved the manuscript.


2


FIG. 5. – Stratigraphic range and faunal assemblage of selected radiolarian taxa in the Soulabest area [Age, after Robaszynski and Caron, 1995]. Stratigra-

phic range for numbers : 1 to 7, 9, 12, 14, 15, 17 [after O’Dogherty, 1994] ; numbers 8 and 16 [after Gorican, 1994] ; number 13 [after Bak, 1999] ; num-

ber 19 [after De Wever and Thiébault, 1981] ; numbers 10 and 11 [after O’Dogherty, 1994 and in this study] ; numbers 18 and 20 [in this study].

FIG. 5. – Échelle stratigraphique et répartition des radiolaires choisis dans la zone de Soulabest.

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