ArticlePDF Available

Radiolarian biostratigraphic constraints for latest Jurassic-earliest Cretaceous submarine volcanic activity in the Tethyan oceanic realm of the Sevan ophiolite (Armenia)

Authors:

Abstract and Figures

Biostratigraphic constraints for the sedimentary cover of the ophiolites preserved in Armenia are of key importance for the palaeogeographic and geodynamic reconstruction of the greater area between Eurasia and the South-Armenian block, which is a micro-continent of Gondwanian origin. We present here radiolarian data obtained from radiolarites that are intercalated in a sequence of mafic volcanic rocks on the northern flank of the Dali valley (east of Lake Sevan), which is considered to be part of the Sevan ophiolite. Mafic sills and dykes with well-preserved igneous textures are probably part of the same sequence. The pseudomorphosis of primary phases indicates that the igneous rocks are strongly affected by alteration in the greenschist facies condition. The plagiogranites that are present in this locality appear to be intrusive into the mafic sequence. The radiolarian assemblages extracted from radiolarian cherts intercalated in the mafic volcanic rocks are dated as latest Tithonian-Late Valanginian; they contain metric rounded blocks of oolitic limestones with crinoid fragments, suggesting that these shallow water limestones slid during the Jurassic/Cretaceous transition into a rugged oceanic floor in which radiolarian ooze accumulated.
Content may be subject to copyright.
Radiolarian biostratigraphic constraints for latest Jurassic-earliest Cretaceous
submarine volcanic activity in the Tethyan oceanic realm of the Sevan
ophiolite (Armenia)
GAYANÉ ASATRYAN1,2,TANIEL DANELIAN3,LILIT SAHAKYAN1,GHAZAR GALOYAN1,MONIQUE SEYLER3,
MARC SOSSON4,ARA AVAGYAN1,BENOIT L.M. HUBERT5and SANDRA VENTALON 3
Key-words. – Radiolaria, Radiolarites, Submarine volcanism, Late Jurassic, Early Cretaceous, Ophiolites, Armenia, Lesser Caucasus
Abstract. – Biostratigraphic constraints for the sedimentary cover of the ophiolites preserved in Armenia are of key im-
portance for the palaeogeographic and geodynamic reconstruction of the greater area between Eurasia and the
South-Armenian block, which is a micro-continent of Gondwanian origin. We present here radiolarian data obtained
from radiolarites that are intercalated in a sequence of mafic volcanic rocks on the northern flank of the Dali valley (east
of Lake Sevan), which is considered to be part of the Sevan ophiolite. Mafic sills and dykes with well-preserved igneous
textures are probably part of the same sequence. The pseudomorphosis of primary phases indicates that the igneous
rocks are strongly affected by alteration in the greenschist facies condition. The plagiogranites that are present in this
locality appear to be intrusive into the mafic sequence. The radiolarian assemblages extracted from radiolarian cherts
intercalated in the mafic volcanic rocks are dated as latest Tithonian-Late Valanginian; they contain metric rounded
blocks of oolitic limestones with crinoid fragments, suggesting that these shallow water limestones slid during the Ju-
rassic/Cretaceous transition into a rugged oceanic floor in which radiolarian ooze accumulated.
Contraintes biostratigraphiques apportées par les radiolaires pour une activité volcanique
sous-marine d’âge jurassique terminal-crétacé basal préservée au sein de l’ophiolite de Sevan
(Arménie)
Mots-clés. – Radiolaires, Radiolarites, Volcanisme sous-marin, Jurassique supérieur, Crétacé inférieur, Ophiolites, Arménie,
Petit Caucase
Résumé. – Les contraintes biostratigraphiques sur la couverture sédimentaire des ophiolites préservées en Arménie sont
d’une grande importance pour la reconstitution paléogéographique et géodynamique des terrains situés entre l’Eurasie
et le bloc sud-Arménien, un microcontinent détaché du Gondwana. On présente ici des microfaunes de radiolaires ex-
traits des radiolarites qui sont intercalées dans une série de roches volcaniques basiques qui affleurent sur le flanc nord
de la vallée de Dali (à l’est du lac Sevan), considérées comme faisant partie de l’ophiolite de Sevan. Des sills et des fi-
lons de roches basiques dont les textures sont bien préservées malgré la pseudomorphose des phases primaires par une
paragenèse schiste vert font probablement partie de la même série. Les plagiogranites situés sous cet ensemble semblent
être intrusifs dans une série de roches basiques. Les radiolaires extraits des radiolarites intercalées dans les roches basi-
ques sont datées du Tithonien terminal à Valanginien supérieur ; celles-ci contiennent des blocs métriques de calcaires
oolithiques à fragments de crinoïdes, ce qui suggère que ces calcaires peu profonds ont glissé au cours de la transition
Jurassique/Crétacé sur le fond océanique accidenté où s’accumulaient des boues radiolaritiques.
INTRODUCTION
The sedimentary cover of most Mesozoic ophiolites along
the Tethyan belt is made essentially of radiolarian-rich sili-
ceous sediments. Radiolarian biochronology is an important
tool to unravel the geodynamic and palaeoenvironmental
evolution of Tethyan oceanic basins and their margins
[Al-Riyami et al., 2000, 2002; Baumgartner, 1984, 1985;
Bill et al., 2001; Caridroit and Ferrière, 1988; Chiari et al.,
1997, 2000; Cordey and Bailly, 2007; Danelian et al., 1997,
2008a; De Wever and Dercourt, 1985; De Wever et al.,
1987; Danelian and Robertson, 1997, 2001; Smuc and
Gorian, 2005; Ziabrev et al., 2003]. This is especially true
for the Dinarides-Hellenides system [i.e. Baumgartner,
1985; Bortolotti et al., 2004, 2006, 2008; Caridroit et al.,
2000; Chiari et al., 2003, 2004; Danelian et al., 2000;
Bull. Soc. géol. France, 2012, t. 183, no4, pp. 319-330
Bull. Soc. géol. Fr., 2012, no4
1. Institute of Geological Sciences, National Academy of Sciences of Armenia, 24a Baghramian avenue, Yerevan, 0019, Armenia. asatryan@geology.am
2. University Pierre & Marie Curie (Paris VI), CNRS-UMR 7207 Centre de Recherches sur la Paléobiodiversité et les Paléoenvironnements (CR2P),
C. 104, 4 place Jussieu. 75005 Paris, France
3. University Lille 1, Department of Earth Sciences, CNRS-UMR 8217 “Géosystèmes”, SN5, 59655 Villeneuve d’Ascq, France
4. University of Nice – Sophia Antipolis, CNRS-UMR Géoazur, OCA, 250 rue A. Einstein. 6560 Valbonne 2, France
5. Catholic University of Lille, CNRS-FRE 3298 “Géosystèmes”, SN5, 59655 Villeneuve d’Ascq, France
Manuscript received on May 12, 2011; accepted on March 22, 2012
Gorian 1994; Karakitsios et al., 1988; Stais et al., 1990],
as well as for the Alpine chains of Turkey [Bragin and
Tekin 1996; Danelian et al., 2006; Moix et al., 2009; Tekin
and Göncüoglu, 2007; Tekin et al., 2002; Vrielynck et al.,
2003]. Reliable ages for ophiolitic lavas are still fairly rare
further to the east, such as in the Lesser Caucasus area, in
spite of some recent radiolarian data generated through a
French-Armenian collaborative project [Danelian et al.,
2007, 2008b, 2010; Asatryan, 2009; Asatryan et al., 2010,
2011].
The Sevan ophiolite [Aslanyan and Satian, 1977;
Galoyan, 2008; Galoyan et al., 2009; Knipper, 1975;
Knipper and Khain, 1980] crops out essentially at the NE
part of Lake Sevan (fig. 1; for a geological map of the area
see Danelian et al. [2012]). It belongs to a NW-SE oriented
zone extending for ca. 400 km from the Amasia-Stepanavan
ophiolite in the NW part of Armenia to the Hagari (Akera)
ophiolite in Karabagh [Galoyan et al., 2007; Rolland et al.,
2009; Sokolov, 1977; Sosson et al., 2010]. It represents the
main Tethyan suture zone between Eurasia and the
South-Armenian block (SAB), a micro-continent that was
detached from Gondwana during the Late Palaeozoic – Early
Mesozoic time interval [Barrier and Vrielynck, 2008].
Few palaeontological ages exist for the sedimentary
cover of the Sevan ophiolite. Early radiolarian reports
pointed to a poorly constrained Late Jurassic-Neocomian
time interval for radiolarites intercalated or overlying
ophiolitic lavas from the Sevan zone [Zhamoida et al.,
1976; Zakariadze et al., 1983], but more precise ages were
reported in the 1990s [Middle Jurassic, Vishnevskaya,
1995; Late Triassic, Knipper et al., 1997] and more recently
following a French-Armenian collaboration [Middle Juras-
sic, Middle Cretaceous, Asatryan et al., 2010, 2011].
In this paper, we present a new palaeontological age ev-
idence from a radiolarite sequence overlying volcanic for-
mations of the Sevan ophiolite in Armenia; our results
establish that submarine volcanic activity was taking place
during the Jurassic-Cretaceous transition in the Tethyan
oceanic realm.
GEOLOGICAL SETTING
The studied outcrop is situated on the northern side of the
Dali valley, at about 5 km to the northwest of the village Jil
(fig. 1; Alt. 2,125 m, N40o29.11’, E 45o25.31’).
A large intrusion of plagiogranites within isotropic gab-
bros of the Sevan ophiolite crops out along this valley
[Galoyan, 2008]. These plagiogranites are locally covered
unconformably by flows of pillow lavas that include lenses
or horizons of radiolarian cherts [Galoyan et al., 2009]. In
the southern part of the Dali valley (at the opposite side of
our studied section), radiolarites can be observed interca-
lated with volcanic rocks above the plagiogranites.
In the northern part of the same valley, where the Dali
section was studied and is described here, we recognized
Bull. Soc. géol. Fr., 2012, no4
320 ASATRYAN G. et al.
FIG. 1. – Simplified geological map of the ophiolitic outcrops in the east of Lake Sevan, including the location of the studied Dali section [modified after
Galoyan et al., 2009].
FIG.1.–Carte géologique simplifiée des principaux affleurements ophiolitiques à l’Est du lac Sevan, y compris la localisation de la coupe étudiée de Dali
[modifié d’après Galoyan et al., 2009].
overall three superimposed units. The uppermost unit (a)
comprises mafic rocks with intercalations of sedimentary
layers (radiolarites, siliceous argilites; fig. 2); the lower
unit (c) is made of granitoids including mafic xenoliths; the
transition or contact zone (b) is a thin faulted level made of
brecciated mafic rocks. Below we describe in more detail
the petrographic and geochemical characteristics of the en-
countered igneous rocks (see chapter “Results”).
The main sedimentary unit crops out along a mountain
track (fig. 2a, 3) and consists of a sequence of radiolarites
Bull. Soc. géol. Fr., 2012, no4
RADIOLARIAN BIOSTRATIGRAPHIC CONSTRAINTS FOR SUBMARINE VOLCANIC ACTIVITY (SEVAN OPHIOLITE, ARMENIA) 321
FIG. 3. – Schematic representation of the studied outcrop situated along the mountain track at Dali.
FIG.3.–Représentation schématique de l’affleurement étudié le long du sentier montagneux de Dali.
FIG. 2. – Photographic view of the studied outcrops at Dali; a) the arrows point to the position of the studied outcrops; right arrow points to the section ob-
served along the mountain track; left arrow points to the section observed on the northern flank of the Dali valley; b) detail of the limestone blocks inclu-
ded in the radiolarian chert sequence studied along the mountain track; c) detail of the eastern part of the studied outcrop along the mountain track.
FIG.2.–Vues photographiques des affleurements étudiés à Dali ; a) les flèches indiquent la position des affleurements étudiés ; la flèche droite pointe la
coupe observée le long du sentier montagneux ; la flèche gauche pointe la coupe observée sur le flanc nord de la vallée de Dali ; b) détail des blocs de
calcaires inclus dans la série radiolaritique étudiée le long du sentier montagneux ; c) détail de la partie orientale de l’affleurement étudié le long du sen-
tier montagneux.
ca. 3 m thick that include towards their top metric and fairly
rounded blocks of oolithic limestones incorporated within
them.
Another sequence of radiolarian cherts was studied on
the northern side of the Dali Valley, about 200 meters from
the Dali section (fig. 2a). These cherts are up to 6 m thick
and colored dark red/pink. The nature (stratigraphic or tec-
tonic) of their contact with both the underlying and overly-
ing igneous rocks is not clearly visible in the field (fig. 4).
The entire sequence of rocks described above is over-
lain unconformably by a thick pile of Campanian pelagic
limestones [Galoyan et al., 2009; Sosson et al., 2010],
which display in places transgressive sandstones and con-
glomerates at their base.
MATERIAL AND METHODS
Radiolarians were extracted in the laboratory by repetitive
leaching of samples with low-concentration hydrofluoric
acid (HF 4%). Three of the processed samples yielded iden-
tifiable Radiolaria. The material was dry picked and
mounted on SEM stubs. In general, the preservation of the
fauna is relatively good. All three samples yielded fairly di-
verse assemblages. Taxonomic concepts applied during this
study follow essentially those in Baumgartner et al.
[1995a], but also those of Steiger [1992], Yang [1993],
Chiari et al. [1997], Dumitrica et al. [1997], Beccaro
[2006] and Dumitrica and Zügel [2008] for some species.
Generic names are updated according to O’Dogherty et al.
[2009]. Microfacies observations were performed under a
polarized microscope. In order to identify the mineralogy of
some crystals we acquired Raman spectra that were recorded
with a LabRam HR800 Jobin-Yvon™ microspectrometer
equipped with 1800 g/mm gratings and using a 532 nm
(green) laser excitation.
RESULTS
Radiolarian biochronology
Biostratigraphic results are summarized below. The main
species identified are given in table I and most of them are
illustrated in plates I-III.
Sample Dali-1 (fig. 3) is characterized by a relatively
well-preserved and diverse radiolarian assemblage, in which
species Parapodocapsa amphitreptera appears to be the
most common. Representatives of genera Dicerosaturnalis,
Archaeodictyomitra, Emiluvia, Pantanellium, Podobursa,
Sethocapsa and Tritrabs are also abundant. Based on the
identified assemblage (table I) the fauna can be assigned to
the U.A.Z. 13-17 of Baumgartner et al. [1995b] and thus it
can be correlated with the latest Tithonian to early Late
Valanginian time interval. The lower boundary of this in-
terval (U.A.Z. 13) is based essentially on the presence of
species/subspecies Angulobracchia (?) portmanni port-
manni,Emiluvia chica decussata,Obesacapsula bullata
and Svinitzium depressum. The upper boundary of the
above mentioned interval (U.A.Z. 17) is based on the pres-
ence of species Cinguloturris cylindra,Emiluvia pessagnoi
s.l.,Obesacapsula cetia and Ristola cretacea.
Sample Dali-2 (fig. 3) yielded a less rich and diverse
radiolarian assemblage than the previous sample. The most
common species are Archaeodictyomitra apiarium and
Pantanellium squinaboli. Representatives of genera
Archaeodictyomitra, Pantanellium, Parapodocapsa and
Tethysetta are also abundant. Based on the co-occurrence of
species Pantanellium squinaboli and Parapodocapsa
amphitreptera the assemblage can be assigned to the U.A.Z.
11-18 of Baumgartner et al. [1995b] and can be correlated
with the Late Kimmeridgian to latest Valanginian/earliest
Hauterivian interval. A specimen that resembles to
Zhamoidellum ovum was yielded from this sample, but its
preservation does not allow a confident identification. If the
presence of this marker species is confirmed in the future,
sample Dali-2 could be assigned to the U.A.Z. 11 only
(Late Kimmeridgian-Early Tithonian).
Sample Jil-3 (fig. 4) yielded a relatively well-preserved
radiolarian assemblage in which representatives of genera
Archaeodictyomitra,Dicerosaturnalis,Hemicryptocapsa,
Bull. Soc. géol. Fr., 2012, no4
322 ASATRYAN G. et al.
PLATE 1. – Scanning electron micrographs of Radiolaria yielded from sample Dali-1.
PL.I.–Photos au microscope électronique à balayage des radiolaires extraits de l’échantillon Dali-1.
1) Angulobracchia (?) portmanni portmanni BAUMGARTNER;2)Archaeodictyomitra mitra DUMITRICA;3)Archaeodictyomitra multicostata (TAN);
4) Archaeodictyomitra sp. cf. A. excellens (TAN); 5) Archaeodictyomitra apiarium (RÜST); 6) Archaeodictyomitra excellens (TAN); 7) Archaeodictyomitra
sp. cf. A. oleadita HULL;8)Cinguloturris cylindra KEMKIN and RUDENKO;9)Dicerosaturnalis trizonalis (RÜST)sensu Dumitrica and Zügel [2008];
10) Ditrabs sp. cf. D. sansalvadorensis (PESSAGNO); 11) Emiluvia chica decussata STEIGER; 12-13) Emiluvia pessagnoi s.l. FOREMAN; 14) Stichomitra
sp. cf. S. doliolum AITA; 15) Loopus yangi DUMITRICA; 16) Obesacapsula cetia (FOREMAN); 17) Obesacapsula bullata STEIGER; 18-19) Parapodocapsa am-
phitreptera (FOREMAN); 20) Praecaneta sp. cf. P. cosmoconica (FOREMAN); 21) Pyramispongia sp. cf. P. barmsteinensis (STEIGER); 22-23) Ristola cretacea
BAUMGARTNER; 24) Pseudodictyomitrella tuscanica (CHIARI,CORTESE and MARCUCCI); 25) Svinitzium depressum (BAUMGARTNER); 26) Favosyringium sp.
cf. F. latum (YANG); 27) Favosyringium sp.; 28) Spinosicapsa (?) sp. cf. Dibolachras chandrika KOCHER; 29) Favosyringium sp. cf. F. affine (RÜST);
30) Triactoma tithonianum RÜST.
FIG. 4. – Stratigraphic column of the radiolarite sequence that crops out on
the northern side of the Dali valley.
FIG.4.–Log de la série radiolaritique qui affleure sur le flanc nord de la
vallée de Dali.
Bull. Soc. géol. Fr., 2012, no4
RADIOLARIAN BIOSTRATIGRAPHIC CONSTRAINTS FOR SUBMARINE VOLCANIC ACTIVITY (SEVAN OPHIOLITE, ARMENIA) 323
Pantanellium,Sethocapsa,Svinitzium and Tethysetta are
fairly abundant. The co-occurrence of the Dicerosaturnalis
trizonalis dicranacanthos (SQUINABOL) morphotype sensu
Baumgartner et al. [1995a] (= Dicerosaturnalis trizonalis
(RÜST)sensu Dumitrica and Zügel [2008]) and of
Hemicryptocapsa capita would suggest assignment of sam-
ple Jil-3 to the U.A.Z. 17 of Baumgartner et al. [1995b].
However, we prefer to correlate it with a wider (and more
confident) age range that covers the Berriasian to latest
Valanginian/earliest Hauterivian interval (U.A.Z. 14-18)
and it is established based on the co-occurrence of species
Emiluvia chica decussata, Hiscocapsa zweilii and
Svinitzium depressum.
Petrography of limestone blocks
Details of the microfacies of the main limestone block
(sample Dali-06 calc-1; fig. 3) are illustrated on plate IV.
The microfacies of this limestone correspond to an oolitic
grainstone with fragments of crinoids (pl. IV, fig. A). Ra-
dial ooids are well-preserved, abundant and of variable size
(pl. IV, fig. B). Oolites, echinoderm bioclasts and
lithoclasts appear to have been redeposited as they are in-
cluded in a clayey matrix, which is composed of a dark
clayey micrite, and surrounds common bioclasts (i.e. algal
fragments, pl. IV, fig. C). Oolites are in general aggregated
[lump stage sensu Tucker and Bathurst, 1990] and limited
by a stylolithic joint displaying evidence of compaction
(black arrow, pl. IV, fig. D). In these microbreccias, the
original cement displays a microspar texture (white arrow,
pl. IV, fig. D). Various cavities, formed after partial dissolu-
tion of bioclasts, are filled with microcrystals of quartz
(black arrow, pl. IV, fig. E). Numerous idiomorphic crystals
of silicate minerals can be observed inside all clasts (both
lithoclasts and bioclasts) or oolites. They do not display a
Bull. Soc. géol. Fr., 2012, no4
324 ASATRYAN G. et al.
TABLE I. – Radiolarian species identified from the three fossiliferous samples.
TABL. I. – Liste des espèces de radiolaires déterminés dans les trois échantillons productifs.
Bull. Soc. géol. Fr., 2012, no4
RADIOLARIAN BIOSTRATIGRAPHIC CONSTRAINTS FOR SUBMARINE VOLCANIC ACTIVITY (SEVAN OPHIOLITE, ARMENIA) 325
PLATE II. – Scanning electron micrographs of Radiolaria yielded from sample Dali-2.
PL. II. – Photos au microscope électronique à balayage des radiolaires extraits de l’échantillon Dali-2.
1) Alievium sp.; 2) Parapodocapsa amphitreptera (FOREMAN) ;3)Pantanellium squinaboli (TAN);4)Spinosicapsa sp. cf. S. vannae (BECCARO);5)Pseudo-
dictyomitra sp. cf. P. lilyae (TAN);6)Svinitzium sp. cf. S. mizutanii DUMITRICA ;7)Pseudodictyomitrella tuscanica (CHIARI,CORTESE and MARCUCCI) ;
8) Pseudodictyomitrella sp. ; 9) Tethysetta sp. cf. T. ovoidala DUMITRICA ; 10) Tethysetta sp. cf. T. usotanensis (TUMANDA) ; 11) Triactoma sp. cf. T. m ex i -
cana PESSAGNO and YANG ; 12) Zhamoidellum sp. cf. Z. ovum DUMITRICA.
PLATE III. – Scanning electron micrographs of Radiolaria yielded from sample Jil-03.
PL. III. – Photos au microscope électronique à balayage des radiolaires extraits de l’échantillon Jil-03.
1) Dicerosaturnalis trizonalis dicranacanthos (SQUINABOL) sensu Baumgartner et al. (1995) = Dicerosaturnalis trizonalis (RÜST)sensuDumitricaand
Zügel (2008); 2) Emiluvia chica decussata STEIGER;3)Hemicryptocapsa capita TAN;4)Mirifusus dianae s.l. (KARRER); 5) Pseudoeucyrtis sp. cf. P. acus
JUD;6-7)Hiscocapsa zweilii (JUD); 8) Favosyringium sp.; 9) Svinitzium depressum (BAUMGARTNER); 10) Tethysetta ovoidala DUMITRICA; 11) Svinitzium
sp. cf. S. columnum (RÜST).
preferential orientation which points to a post sedimentary
growth (pl. IV, fig. F). Raman acquisition spectra establish
that they are all idiomorphic crystals of albite.
Petrography of igneous rocks
The igneous rocks consist of two units of mafic volcanic
rocks, overlying the plagiogranite body. Although the pri-
mary phases of the mafic rocks are extensively replaced by
secondary low-temperature minerals, igneous textures are
well-preserved and igneous minerals can still be identified
under the microscope. They are described below from top to
base.
a– Mafic rocks of the upper unit are dark, massive and
fine-grained, forming a homogeneous, banded sequence;
some levels contain amygdules filled with calcite. In thin
section, textures vary from intersertal through intergranular
to subophitic; true ophitic texture is also present locally.
Such fine-grained subophitic to ophitic textures are charac-
teristic of slow-cooling and can be observed in the central
parts of thick lava flows as well as in hypabyssal diabases
filling dikes or sills. As a consequence, distinction between
massive lava flows and hypabyssal rocks is not easy, and an
effusive origin has been considered for two samples of this
preliminary study based on the presence of vesicles and a
higher amount of glass alteration products. Also subophitic
texture is diagnostic of basaltic primitive or only slightly
differentiated compositions, whereas intersertal to intergra-
nular textures are more common in evolved compositions,
although also present in basalts. On the whole, all these
characteristics suggest that this upper unit represents part of
a thick volcanic sequence. Studied samples of lava flows
contain phenocrysts and microphenocrysts of clinopyro-
xene, plagioclase and magmatic brown amphibole; they are
frequently aggregated in glomerules. The intersertal
groundmass is composed of microlites with three distinct
grain sizes. The larger microlites form a loose network of
thin plagioclase laths and clinopyroxene and brown amphi-
bole prisms, often distributed in sheafs. The interstices are
filled with tiny crystals of the same mineral phases with in
addition dendritic titanomagnetite. The spaces between
these tiny crystals are occupied by quenched minerals of
feldspar, clinopyroxene and brown amphibole; chlorite-rich
felty patches or polygonal grains of albite also locally filled
these interstices. Fluorapatite is a common accessory phase.
Plagioclase is commonly replaced by albite and calcite; rel-
ict compositions vary from An56 in the coarser laths to An34
in the smaller-sized laths. Clinopyroxene and brown amphi-
bole are partially replaced by calcite, quartz (for
clinopyroxene), chlorite, titanite and iron oxides. EDS
Bull. Soc. géol. Fr., 2012, no4
326 ASATRYAN G. et al.
PLATE IV. – Microfacies of limestone sample Dali-06 calc-1. A) Oolitic and bioclastic grainstone. Bioclasts are mainly crinoidal stems. The matrix is a dark
and homogeneous fine grained micrite. Scale bar = 1 mm. B) Radial and fibrous ooids. Scale bar = 1 mm. C) Fragments of bioclasts. Scale bar = 0,1 mm.
D) Amalgamated oolitic microbreccia. White arrows indicate the raw microcrystalline calcitic matrix. Black arrow shows a stylolitic suture due to the
compaction. Scale bar = 1 mm. E) Moldic porosity. Scale bar = 1 mm. F) Authigenic quartz and feldspar crystals association. Scale bar = 0,1 mm.
PL.IV.–Microfaciès de l’échantillon de roche calcaire Dali-06 calc-1. A) Grainstone oolithique et bioclastique. Les bioclastes correspondent majoritaire-
ment à des fragments crinoïdiques. La matrice est constituée de fines particules homogènes constituant une texture micritique sombre. Barre d’échelle = 1 mm.
B) Oolithe à structure radiaire et fibreuse. Barre d’échelle = 1 mm. C) Fragments bioclastiques indéterminés. Barre d’échelle = 0, mm. D) Microbrèche
composée d’un amalgame oolithique. Les flèches blanches indiquent la présence de matrice microcristalline calcitique originelle. Les flèches noire s mon -
trent une suture stylolithique liée aux phénomènes de pression-dissolution. Barre d’échelle = 1 mm. E) Porosité résiduelle. Barre d’échelle = 1 mm.
F) Association de cristaux de quartz authigène et de feldspath. Barre d’échelle = 0,1 mm.
analyses indicate that the amphibole is Al-, Na- and
Ti-rich, subjective of an alkaline affinity. Other samples
representing lava flows are extensively altered but appear to
have had similar mineral compositions; rare primary biotite
microcrystals have been observed. The lavas underlying the
radiolarites appear different, since they are characterized by
an intersertal texture with high proportion of glass. Tiny
minerals are quench plagioclases showing characteristic
hollow cores, and quench ferromagnesian minerals olivine
and/or clinopyroxene); small Cr-rich spinel grains are also
present. These features suggest a primitive basaltic compo-
sition that cooled very rapidly. More crystalline samples are
porphyric to glomeroporphyric basaltic rocks with
fine-grained, intergranular- to ophitic-textured matrix
(fig. 5). Some samples show a rough igneous lamination.
Like the vesicular rocks, they show several groups of grain
sizes of phenocrysts and groundmass microlites. But they
differ by the occurrence of olivine commonly associated
with interstitial clinopyroxene. Brown magmatic amphibole
has not been observed as phenocrysts but is present in the
groundmass. The phenocryst assemblage is plagioclase +
clinopyroxene (+ olivine?), and the groundmass assemblage
is plagioclase + clinopyroxene + olivine + brown amphibole
+ dendritic titanomagnetite + fluorapatite. Secondary min-
erals pseudomorphosing the igneous phases are albite,
chlorite, titanite, calcite, quartz and Fe-oxides, characteris-
tic of alteration in the greenschist facies conditions.
b– The base of the mafic unit is represented by
brecciated basalts, crosscut by veins and microfractures
filled with quartz or calcite or quartz-feldspar assemblages
likely related to the neighboring granitoid intrusion. Angu-
lar fragments of basalt are dark, glassy rock with small ves-
icles filled with calcite. Some of the samples are polygenic,
containing at least two types of basalts. All are fine-grained
mineral assemblages composed of chlorite, albite, titanite,
calcite, quartz and iron oxides; clinopyroxene and
plagioclase pseudomorphs define various textures from
intersertal with a high proportion of ancient glass (dark
fragments) to more crystalline (gray fragments). Pheno-
crysts of plagioclase and clinopyroxene are present. A sam-
ple contains a xenolith of microgabbro (diabase).
c– The granitoid is a coarse-grained assemblage of
quartz, plagioclase and a lesser amount of green hornblende
with accessory apatite and zircon grains. Its base is rela-
tively homogeneous and contains oval, decimetric-sized xe-
noliths of oriented diorite. To the top, the granitoid
becomes brecciated, crosscut by dykes of more felsic com-
position and veins of calcite or quartz. In addition, it en-
closes angular fragments resembling the mafic rocks of the
above unit, suggesting that the granitoid is intrusive in the
mafic formation (fig. 6).
DISCUSSION
Previous data on the sedimentary cover of the Sevan ophiolite
suggest a pre-Cretaceous history of submarine volcanic activ-
ity starting since the Late Triassic. Thus Knipper et al. [1997]
found Carnian siliceous pelites overlying breccia with frag-
ments of ophiolitic rocks at Old Sotk (Zod) Pass SE of Lake
Sevan (fig. 1). According to the stratigraphic data of the above
authors, large olistolith blocks of nodular limestones slid in
Bull. Soc. géol. Fr., 2012, no4
RADIOLARIAN BIOSTRATIGRAPHIC CONSTRAINTS FOR SUBMARINE VOLCANIC ACTIVITY (SEVAN OPHIOLITE, ARMENIA) 327
FIG. 5. – Microphotograph of a characteristic texture observed in the stu-
died magmatic rocks from Dali. Twin clinopyroxene interstitial between
feldspar laths include smaller laths of feldspar in subophitic diabase.
Length of field = 1.5 mm.
FIG.5.–Microphotographie d’une texture caractéristique observée au sein
des roches magmatiques de l’affleurement de Dali. Clinopyroxène maclé
incluant de petites lattes de feldspaths dans une diabase à texture ophi-
tique. Largeur du champ = 1,5 mm.
FIG. 6. – Field photograph of the brecciated contact between the plagiogra-
nite (below) and the basic rocks (above), that consists of mafic rocks intru-
ded by felsic rocks. Angular blocks (arrow) of basalts are crosscut by
numerous felsic veinlets, suggesting a hydraulic fracturing in response to
the granite intrusion into a cold mafic unit. A second type of xenoliths oc-
curs as rounded blocks of diorite.
FIG.6.–Photo d’affleurement montrant la structure bréchique du contact
entre le plagiogranite et les roches basiques sus-jacentes. Des blocs angu-
leux de basaltes (flèche) recoupés par de nombreux filons felsiques suggè-
rent une fracturation hydraulique provoquée par l'intrusion du magma
granitique dans un encaissant basique relativement froid. Le plagiogranite
contient un deuxième type d'enclaves sous forme de blocs arrondis de dio-
rite.
the Toarcian part of the section. Jurassic volcanic events are
known in the Sevan-Hagari (Akera) zone. In the Karawul lo-
cality of Karabagh, Vishnevskaya [1995, 2001] established the
presence of Middle Jurassic cherts that overly stratigraphically
basaltic lavas. More recently, at the Sarinar valley of Sevan
area, Asatryan et al. [2010] reported on upper Bajocian-lower
Bathonian cherts overlying ophiolitic lavas. In this locality, the
above authors reported also Middle Jurassic radiolarian cherts
intercalated between tuffites. Finally, much younger Creta-
ceous (upper Barremian-lower Aptian) radiolarian cherts over-
lying stratigraphically pillow lavas were recently dated by
Asatryan et al. [2011] in Karabagh.
Our results from the Dali section establish for the first
time evidence for submarine volcanic activity slightly before
or some time during the Late Tithonian-Late Valanginian in-
terval.
Radiolarian ooze accumulation took place on a bathy-
metrically complex sea floor, fractured probably by impor-
tant normal faults cropping out on the Jurassic sea floor,
which were subject to submarine weathering. The presence
of limestone blocks intercalated within the radiolarites is of
particular importance because it provides, for the first time,
the evidence of shallow-water depositional environments of
carbonate sedimentation in the vicinity of a basin in which
radiolarites were being accumulated. Oolites and crinoid
bioclasts were initially formed (during the Late Jurassic?)
in very shallow and agitated waters of a platform barrier
and they were subsequently redeposited in an upper slope
depositional environment.
CONCLUSION
Radiolarian ages for the sedimentary cover of the Armenian
ophiolites are of great significance for the palaeogeographic
and geodynamic reconstruction of the Tethys in the Lesser
Caucasus. The Sevan ophiolite records both ophiolitic lavas
and pelagic sediments of latest Tithonian to Late Valanginian
age that allow us to constrain the age of submarine volcanic
activity that took place within the Tethyan ocean floor.
Shallow water oolitic platforms presumably existed some
time during the Late Jurassic (?) in the vicinity of this oce-
anic basin, since parts of them slid into the radiolarite basin
close to the Jurassic-Cretaceous transition.
Acknowledgments. – This study was initiated in 2006 with the support of
the French Ministry of Foreign Affairs (ECO-NET grant to T. Danelian);
the French Embassy in Armenia provided a student grant to G. Asatryan for
studying at the University Pierre & Marie Curie (Paris VI). This work was
completed with the financial support of the DARIUS program. Fieldwork
was greatly facilitated by the continuous support of the Institute of Geolo-
gical Sciences (National Academy of Sciences of Armenia). Constructive
remarks by M. Chiari (Florence), S. Zyabrev (Khabarovsk) and Špela
Gorian (Ljubljana) improved the initial manuscript.
References
Bull. Soc. géol. Fr., 2012, no4
328 ASATRYAN G. et al.
AL-RIYAMI K., ROBERTSON A.H.F., XENOPHONTOS C., DANELIAN T. &
DIXON J.E. (2000). – Tectonic evolution of the Mesozoic Ara-
bian passive continental margin and related ophiolite in Baer-
Bassit region (NW Syria). In :I.P
ANAYIDES,C.XENOPHONTOS
and J. MALPAS,Eds.,Third International Conference on the Geo-
logy of the eastern Mediterranean, Proceedings, Nicosia, 1998,
61-81.
AL-RIYAMI K., DANELIAN T. & ROBERTSON A.H.F. (2002). – Radiolarian
biochronology of Mesozoic deep-water successions in NW Syria
and Cyprus : implications for south-Tethyan evolution. – Te r r a
Nova,14, 271-280.
ASATRYAN G. (2009). – New data about the age of ophiolites in the Vedi
zone on the basis of Radiolarian assemblages. – Proc. Nat. Acad
Sci. Armenia, Earth Sciences,62, 16-28.
ASATRYAN G., DANELIAN T., SOSSON M., SAHAKYAN L., PERSON A., AVA -
GYAN A. & GALOYAN G. (2010). – Radiolarian dating of the sedi-
mentary cover of Sevan ophiolite (Armenia, Lesser Caucasus). –
Ofioliti,35, 91-101.
ASATRYAN G., DANELIAN T., SOSSON M., SAHAKYAN L. & GALOYAN G.
(2011). – Radiolarian evidence for Early Cretaceous (late Barre-
mian – early Aptian) submarine volcanic activity in the Tethyan
oceanic realm preserved in Karabagh (Lesser Caucasus). –
Ofioliti,36, 117-123.
ASLANYAN A.T. & SATIA N M.A. (1977). – On the geological features of
Transcaucasian ophiolitic zones. – Izvestia Acad. Sci. Armenian
SSR, Nauki o Zemle 4-5, 13-26 (in Russian).
BARRIER E. & VRIELYNCK B. (2008). – Palaeotectonic map of the Middle
East, Atlas of 14 maps, tectonosedimentary-palinspastic maps
from Late Norian to Pliocene. – Commission for the Geologic
Map of the World (CCMW, CCGM), Paris, France
BAUMGARTNER P.O. (1984). – Middle Jurassic-Early Cretaceous low-lati-
tude radiolarian zonation based on Unitary Associations and age
of Tethyan radiolarites. – Eclogae geol. Helv., 77, 729-837.
BAUMGARTNER P.O. (1985). – Jurassic sedimentary evolution and nappe
emplacement in the Argolis Peninsula (Peloponnesus, Greece). –
Mém. Soc. Helv. Sciences Naturelles, 99, 1-111.
BAUMGARTNER P.O. , O DOGHERTY L., GORIAN Š., DUMITRICA-JUD R.,
DUMITRICA P., P ILLEVUIT,A.,URQUHART E., MATS U O K A A.,
DANELIAN T., B ARTOLINI A., CARTER E.S., DEWEVER P., K ITON.,
MARCUCCI M. & STEIGER T. (1995a). – Radiolarian catalogue
and systematics of Middle Jurassic to Early Cretaceous Tethyan
genera and species. In : BAUMGARTNER et al., Eds., Middle
Jurassic to Lower Cretaceous Radiolaria of Tethys : occurrences,
systematics, biochronology. – Mém. Géol. (Lausanne), 23, 37-685.
BAUMGARTNER P.O. , B ARTOLINI A., CARTER E.S., CONTI M., CORTESE G.,
DANELIAN T., D EWEVER P. , D UMITRICA P. , D UMITRICA-JUD R.,
GORIAN Š., GUEX J., HULL D.M., KITO N., MARCUCCI M., MAT-
SUOKA A., MURCHEY B., ODOGHERTY L., SAVAR Y J., VISHNEVS-
KAYA V., W IDZ D. & YAO A. (1995b). – Middle Jurassic to Early
Cretaceous radiolarians of Tethys based on Unitary Associa-
tions. In:B
AUMGARTNER et al., Eds., Middle Jurassic to Lower
Cretaceous radiolaria of Tethys : occurrences, systematics, bioc-
hronology. – Mém. Géol. (Lausanne), 23, 1013-1048.
BECCARO P. (2006). – Radiolarian biostratigraphy of Middle-Upper Jurassic
pelagic siliceous successions of western Sicily and the southern
Alps (Italy). – Mém. Géol. (Lausanne), 45,86p,12pls.
BILL M., ODOGHERTY L., GUEX J., BAUMGARTNER P. O . & M ASSON H.
(2001). – Radiolarite ages in Alpine-Mediterranean ophiolites :
Constraints on the oceanic spreading and the Tethys-Atlantic
connection. – Geol. Soc. Amer. Bull., 113, 129-143.
BORTOLOTTI V., C HIARI M., MARCUCCI M., MARRONI M., PANDOLFI L., PRIN-
CIPI G. & SACCANI E. (2004). – Comparison among the Albanian
and Greek ophiolites, in search of constraints for the evolution
of the Mesozoic Tethys ocean. – Ofioliti,29, 19-35.
BORTOLOTTI V., C HIARI M., KODRA A., MARCUCCI M., MARRONI M., MUSTAFA
F., P ANDOLFI L., PRINCIPI G. & SACCANI E. (2006). – Triassic
MORB magmatism in the southern Mirdita zone (Albania). –
Ofioliti,31,1-9.
BORTOLOTTI V., C HIARI M., MARCUCCI M., PHOTIADES A., PRINCIPI G. &
SACCANI E. (2008). – New geochemical and age data on the
ophiolites from the Othrys area (Greece) : implication for the
Triassic evolution of the Vardar ocean. – Ofioliti,33, 135-151.
BRAGIN N.Y. & TEKIN U.K. (1996). – Age of radiolarian-chert blocks from
the Senonian Ophiolitic Mélange (Ankara, Turkey). – The Island
Arc, 5, 114-122.
CARIDROIT M. & FERRIÈRE J. (1988). – 1st precised radiolarian age datings
of the Paleozoic from New-Zealand – Geological and paleonto-
logical significances. – C. R. Acad. Sci., Paris, 306, 321-326.
CARIDROIT M., FERRIÈRE J., DEGARDIN J.M., VACHARD D. & CLÉMENT B.
(2000). – First age dating of the Lydian stones in the Inner Hel-
lenides (Mount Parnis, Greece); geological significances. – C. R.
Acad. Sci., Paris, 331, 413-418.
CHIARI M., CORTESE G., MARCUCCI M. & NOZZOLI N. (1997). – Radiolarian
biostratigraphy in the sedimentary cover of ophiolites in south-
western Tuscany, Central Italy. – Eclogae Geol. Helv.,90, 55-77.
CHIARI M., MARCUCCI M. & PRINCIPI G. (2000). – The age of radiolarian
cherts associated with the ophiolites in the Apennines (Italy) and
Corsica (France) : a revision. – Ofioliti, 25, 141-146.
CHIARI M., BORTOLOTTI V., M ARCUCCI M., PHOTIADES A. & PRINCIPI G.
(2003). – The Middle Jurassic siliceous sedimentary cover at the
top of the Vourinos ophiolite (Greece). – Ofioliti,28, 95-103.
CHIARI M., MARCUCCI M. & PRINCIPI G. (2004). – Radiolarian assemblages
from Jurassic cherts of Albania : new data. – Ofioliti,29, 95-105.
CORDEY F. & BAILLY A. (2007). – Alpine ocean seafloor spreading and on-
set of pelagic sedimentation : new radiolarian data from the Che-
naillet-Montgenevre ophiolite (French-Italian Alps). – Geodin.
Acta,20, 131-138.
DANELIAN T. & ROBERTSON A.H.F. (1997). – Radiolarian evidence for the
stratigraphy and palaeo-oceanography of the deep-water northern
passive margin of the Indian plate (Karamba Formation, Indus su-
ture zone, Ladakh Himalaya). – Mar. Micropal., 30, 171-195.
DANELIAN T., D EWEVER P. & A ZÉMA J. (1997). – Palaeoceanographic si-
gnificance of new and revised palaeontological datings for the
onset of Vigla Limestone sedimentation in the Ionian zone of
Greece. – Geol. Mag., 134, 869-872.
DANELIAN T., L EKKAS S. & ALEXOPOULOS A. (2000). – Découverte de ra-
diolarites triasiques dans un complexe ophiolitique à l’extrême
sud du Péloponnèse (Agelona, Lakonie, Grèce). – C. R. Acad.
Sci., Paris, 330, 639-644.
DANELIAN T. & ROBERTSON A.F.R. (2001). – Neotethyan evolution of eas-
tern Greece (Pagondas Mélange, Evia island) inferred from Ra-
diolarian biostratigraphy and the geochemistry of associated
extrusive rocks. – Geol. Mag., 138, 345-363.
DANELIAN T., R OBERTSON A.H.F., COLLINS A. & POISSON A. (2006). – Bioc-
hronology of Jurassic and Early Cretaceous radiolarites from the
Lycian Mélange (SW Turkey) and implications for the evolution
of the northern Neotethyan ocean. In : A.H.F. ROBERTSON and D.
MOUNTRAKIS, Eds., Tectonic development of the eastern Medi-
terranean region. – Geol. Soc., London, Sp. Publ., 260, 229-236.
DANELIAN T., G ALOYAN G., ROLLAND Y. & SOSSON M. (2007). – Palaeonto-
logical (Radiolarian) Late Jurassic age constraint for the Stepa-
navan ophiolite (Lesser Caucasus, Armenia). – Bull. Geol. Soc.
Greece,40, 31-38.
DANELIAN T., D EWEVER P. & D URAND-DELGA M. (2008a). – Revised radio-
larian ages for the sedimentary cover of the Balagne ophiolite
(Corsica, France). Implications for the palaeoenvironmental evo-
lution of the Balano-Ligurian margin. – Bull. Soc. géol. Fr., 179,
169-177.
DANELIAN T., A SATRYAN G., SOSSON M., PERSON A., SAHAKYAN L. &
GALOYAN G. (2008b). – Discovery of Middle Jurassic (Bajocian)
Radiolaria from the sedimentary cover of the Vedi ophiolite
(Lesser Caucasus, Armenia). – C. R. Palevol., 7, 327-334.
DANELIAN T., A SATRYAN G., SAHAKYAN L., GALOYAN G., SOSSON M. & AVA-
GYAN A. (2010). – New and revised radiolarian biochronology
for the sedimentary cover of ophiolites in the Lesser Caucasus
(Armenia). In :M. SOSSON,N.KAYMAKCI,R.STEPHENSON,
F. BERGERAT AND V. STAROSTENKO, Eds., Sedimentary basin tecto-
nics from the Black Sea and Caucasus to the Arabian platform.
Geol. Soc. London, Sp. Vol., 340, 383-391.
DANELIAN T., A SATRYAN G., GALOYAN G., SOSSON M., SAHAKYAN L., CARI-
DROIT M. & AVAGYAN A. (2012). – Geological history of ophioli-
tes in the Lesser Caucasus and correlation with the Izmir-
Ankara-Erzincan suture zone : insights from radiolarian bioc-
hronology. In:T.D
ANELIAN .GORIAN, Eds., Radiolarian
biochronology as key to tectono-stratigraphic reconstructions. –
Bull. Soc. géol. Fr., 183, 4, 331-342.
DEWEVER P. & DERCOURT J. (1985). – Les radiolaires triasico-jurassiques
marqueurs stratigraphiques et paléogéographiques dans les chaî-
nes alpines périméditerranéennes : une revue. – Bull. Soc. géol.
Fr., 8, I, 5, 653-662.
DEWEVER P., DANELIAN T., D URAND-DELGA M., CORDEY F. & K ITO N.
(1987). – New datings of postophiolite radiolarites from Alpine
Corsica by means of radiolarians. – C. R. Acad. Sci., Paris, 305,
893-900.
DUMITRICA P., I MMENHAUSER A. & DUMITRICA-JUD R. (1997). – Mesozoic
radiolarian biostratigraphy from Masirah Ophiolite, Sultanate of
Oman. Part I : Middle Triassic, Uppermost Jurassic and Lower
Cretaceous Spumellarians and multisegmented Nassellarians. –
Bull. Nat. Mus. Natur. Sci., 9, 1-105.
DUMITRICA P. & ZÜGEL P. (2008). – Early Tithonian Saturnalidae (Radiola-
ria) from the Solnhofen area (southern Franconian Alb, southern
Germany). – Paläont. Zeitsch., 82, 55-84.
GALOYAN G. (2008). – Etudes pétrologiques, géochimiques et géochronolo-
giques des ophiolites du Petit Caucase (Arménie). – PhD Thesis,
Univ. de Nice Sophia Antipolis, 287p.
GALOYAN G., ROLLAND Y. , S OSSON M., CORSINI M. & MELKONYAN R.
(2007). – Evidence for superposed MORB, oceanic plateau and
volcanic arc series in the Lesser Caucasus (Stepanavan, Arme-
nia). – C.R. Geoscience,339, 482-492.
GALOYAN G., ROLLAND Y. , S OSSON M., CORSINI M., BILLO S., VERATI C. &
MELKONYAN R. (2009). – Geology, geochemistry and 40Ar/39Ar
dating of Sevan ophiolites (Lesser Caucasus, Armenia) : Evi-
dence for Jurassic back-arc opening and hot spot event between
the South Armenian block and Eurasia. – J. Asian Earth Sci., 34,
135-153.
GORIAN Š. (1994). – Jurassic and Cretaceous radiolarian biostratigraphy
and sedimentary evolution of the Budva Zone (Dinarides, Mon-
tenegro). – Mém. Géol., Lausanne,118, 120 pp.
KARAKITSIOS V., D ANELIAN T. & DEWEVER P. (1988). – Datations par les
radiolaires des Calcaires à Filaments, Schistes à Posidonies su-
périeurs et Calcaires de Vigla (zone ionienne, Epire, Grèce) du
Callovien au Tithonique terminal. – C. R. Acad. Sci., Paris, 306,
367-372.
KNIPPER A.L. (1975). – The oceanic crust in the Alpine belt. – Tr. GIN
NAS USSR, Edition 267, 207 p. (in Russian).
KNIPPER A.L. & KHAIN E.V. (1980). – The structural position of ophiolites
of the Caucasus. – Ofioliti, Sp. Issue,2, 297-314.
KNIPPER A.L., SATI A N M.A. & BRAGIN N.Y. (1997). – Upper Triassic-Lower
Jurassic volcanogenic and sedimentary deposits of the Old Zod
Pass (Transcaucasia). – Stratigraphy, geological correlation, 3,
58-65, (in Russian).
MOIX P., GORIAN Š. & MARCOUX J. (2009). – First evidence of Campanian
radiolarians in Turkey and implications for the tectonic setting
of the Upper Antalya Nappes. – Cret. Res., 30, 952-960.
ODOGHERTY L., CARTER E.S., DUMITRICA P., G ORIAN Š., DEWEVER P. ,
BANDINI A.N., BAUMGARTNER P.O. & M ATSUOKA A. (2009). –
Catalogue of Mesozoic radiolarian genera. Part 2 : Jurassic-Cre-
taceous. – Geodiversitas,31, 271-356.
ROLLAND Y., G ALOYAN GH., BOSCH D., SOSSON M., CORSINI M., FORNARI
M. & VERATI C. (2009). – Jurassic back-arc and Cretaceous
hot-spot series in the Armenian ophiolites – Implications for the
obduction process. – Lithos,112, 163-187.
SMUC A. & GORIAN Š. (2005). – Jurassic sedimentary evolution of a car-
bonate platform into a deep-water basin, Mt. Mangart (Slove-
nian-Italian border). – Riv. Ital., 111, 45-70.
SOKOLOV S.D. (1977). – The olistostroms and ophiolitic nappes of the Les-
ser Caucasus. – Izdatelstvo Nauka, Moscow, 92 p. (in Russian).
Bull. Soc. géol. Fr., 2012, no4
RADIOLARIAN BIOSTRATIGRAPHIC CONSTRAINTS FOR SUBMARINE VOLCANIC ACTIVITY (SEVAN OPHIOLITE, ARMENIA) 329
SOSSON M., ROLLAND Y., M ULLER C., DANELIAN T., MELKONYAN R., KEKE-
LIA S., ADAMIA S., BABAZADEH V., K ANGARLI T., AVAGYAN A.,
GALOYAN G. & MOSAR J. (2010). – Subductions, obduction and
collision in the Lesser Caucasus (Armenia, Azerbaijan, Geor-
gia), new insights. In :M.S
OSSON,N.KAYMAKCI,R.STEPHEN-
SON,F.BERGERAT AND V. S TAROSTENKO, Eds., Sedimentary basin
tectonics from the Black Sea and Caucasus to the Arabian Plat-
form. – Geol. Soc., London, Sp. Publ., 340, 329-352.
STAI S A., FERRIÈRE J., CARIDROIT M., DEWEVER P., CLÉMENT B. & BER-
TRAND J. (1990). – New data on the preobduction history (Trias-
sic-Jurassic) of the Almopias domain (Macedonia. Greece). –
C.R. Acad., Sci.,Paris,310, 1475-1480.
STEIGER T. (1992). – Systematik, Stratigraphie und Palökologie der Radio-
larien des Oberjura-Unterkreide-Grenzbereiches im Osterhorn-
Tirolikum (N0rdliche Kalkalpen, Salzburg und Bayern). – Zitte-
liana,19, 1-188.
TEKIN U.K., GÖNCÜOGLU M.C. & TURHAN N. (2002). – First evidence of
Late Carnian radiolarians from the Izmir-Ankara suture com-
plex, central Sakarya, Turkey : Implications for the opening age
of the Izmir-Ankara branch of Neo-Tethys. – Geobios,35, 127-135.
TEKIN U.K. & GÖNCÜOGLU M.C. (2007). – Discovery of the oldest (Upper
Ladinian to Middle Carnian) radiolarian assemblages from the
Bornova flysch zone in western Turkey : implications for the
evolution of the Neotethyan Izmir-Ankara ocean. – Ofioliti,32,
131-150.
TUCKER M.E. & BATHURST R.G.C., Eds. (1990). – Carbonate diagenesis. –
Int. Ass. Sedimentol. Reprint Ser., 1, Cambridge/Mass. (Black-
well), 312 p.
VISHNEVSKAYA V. (1995). – Jurassic and Cretaceous radiolarians from the
Lesser Caucasus (Zod Pass, Mount Karawul and site 22 in the
Koshuni River Basin). In :P.O.B
AUMGARTNER,L.ODOGHERTY,
Š. GORIAN,E.URQUHART,A.PILLEVUIT &P.DEWEVER,Eds,
Middle Jurassic to Lower Cretaceous Radiolaria of Tethys :
Occurences, systematics, biochronology. – Mém. Géol. (Lau-
sanne),23, 701-708.
VISHNEVSKAYA V.S. (2001). – Jurassic to Cretaceous radiolarian biostrati-
graphy of Russia. – GEOS, Moscow, 376 pp., 140 pls.
VRIELYNCK B., BONNEAU M., DANELIAN T., CADET J.-P. & POISSON A. (2003). –
New insights on the Antalya Nappes in the apex of the Isparta
angle : The Isparta Cay unit revisited. – Geol. J.,38, 283-293.
YANG Q. (1993). – Taxonomic studies of Upper Jurassic (Tithonian) Radio-
laria from the Taman Formation, east-central Mexico. – Pa l a eo-
world 3, Sp. Issue, i-iv, 1-164.
ZAKARIADZE G.S., KNIPPER A.L., SOBOLEV A.V., TSAMERIAN O.P.,
DMITRIEV L.V., VISHNEVSKAYA V. S . & KOLESOV G.M. (1983). –
The ophiolite volcanic series of the Lesser Caucasus. – Ofioliti,
8, 439-466.
ZHAMOIDA A.I., KAZINTSOVA L.I. & TIKHOMIROVA L.B. (1976). – Radiola-
rian complexes of the Lesser Caucasus. – Izvestia AS USSR,
Geol. Ser., 2, 156-160 (in Russian).
ZIABREV S.V., AITCHISON J.C., ABRAJEVITCH A.V., BADENGZHU,DAVI S A.M.
&L
UO H. (2003). – Precise radiolarian age constraints on the ti-
ming of ophiolite generation and sedimentation in the Dazhuqu
terrane, Yarlung-Tsangpo suture zone, Tibet. – J. Geol. Soc.,
London, 160, 591-599.
Bull. Soc. géol. Fr., 2012, no4
330 ASATRYAN G. et al.
... In Armenia and Eastern Anatolia, ophiolites are composed of, from bottom to, serpentinized peridotites intruded by gabbros, scattered cross-cutting plagiogranites in extensional shear zones, lava flows of basalt with intercalations of Middle-Late Jurassic radiolarites (ca. 180e150 Ma on gabbros and lavas, Galoyan et al., 2009;Rolland et al., 2010;Hässig et al., 2013a;Topuz et al., 2013a, b, c; 170e145 Ma on radiolarians, Danelian et al., 2007Danelian et al., , 2008Danelian et al., , 2010Danelian et al., , 2012Asatryan et al., 2010Asatryan et al., , 2012Figs. 4 and 5). ...
... Direct dating was undertaken by Ar-Ar analyses on amphiboles from gabbros and by U-Pb analyses on zircons from plagiogranites (Zakariadze et al., 1990(Zakariadze et al., , 2005Galoyan et al., 2009;Rolland et al., 2010;Çelik et al., 2011;Hässig et al., 2013a;Robertson et al., 2013;Topuz et al., 2013a, b). Indirect dating on radiolarians provided similar ages (Danelian et al., 2007(Danelian et al., , 2008Asatryan et al., 2010Asatryan et al., , 2012. For the Anatolian ophiolites, a compilation of ages can be found in Sarıfakıo glu et al. (2017). ...
Article
Full-text available
Full text (free access): https://www.sciencedirect.com/science/article/pii/S1674987119300295 We present new, geological, metamorphic, geochemical and geochronological data on the East Anatolian – Lesser Caucasus ophiolites. These data are used in combination with a synthesis of previous data and numerical modelling to unravel the tectonic emplacement of ophiolites in this region. All these data allow the reconstruction of a large obducted ophiolite nappe, thrusted for > 100 km and up to 250 km on the Anatolian-Armenian block. The ophiolite petrology shows three distinct magmatic series, highlighted by new isotopic and trace element data: (1) The main Early Jurassic Tholeiites (ophiolite s.s.) bear LILE-enriched, subduction-modified, MORB chemical composition. Geology and petrology of the Tholeiite series substantiates a slow-spreading oceanic environment in a time spanning from the Late Triassic to the Middle-Late Jurassic. Serpentinites, gabbros and plagiogranites were exhumed by normal faults, and covered by radiolarites, while minor volumes of pillow-lava flows infilled the rift grabens. Tendency towards a subduction-modified geochemical signature suggests emplacement in a marginal basin above a subduction zone. (2) Late Early Cretaceous alkaline lavas conformably emplaced on top of the ophiolite. They have an OIB affinity. These lavas are featured by large pillow lavas interbedded a carbonate matrix. They show evidence for a large-scale OIB plume activity, which occurred prior to ophiolite obduction. (3) Early Late Cretaceous calc-alkaline lavas and dykes. These magmatic rocks are found on top of the obducted nappe, above the post-obduction erosion level. This series shows similar Sr-Nd isotopic features as the Alkaline series, though having a clear supra-subduction affinity. They are thus interpreted to be the remelting product of a mantle previously contaminated by the OIB plume. Correlation of data from the Lesser Caucasus to western Anatolia shows a progression from back-arc to arc and fore-arc, which highlight a dissymmetry in the obducted oceanic lithosphere from East to West. The metamorphic PT-t paths of the obduction sole lithologies define a southward propagation of the ophiolite: (1) PT-t data from the northern Sevan-Akera suture zone (Armenia) highlight the presence and exhumation of eclogites (1.85 ± 0.02 GPa - 590 ± 5 °C) and blueschists below the ophiolite, which are dated at ca. 94 Ma by Ar-Ar on phengite. (2) Neighbouring Amasia (Armenia) garnet amphibolites indicate metamorphic peak conditions of 0.65 ± 0.05 GPa and 600 ± 20 °C with a U-Pb on rutile age of 90.2 ± 5.2 Ma and Ar-Ar on amphibole and phengite ages of 90.8 ± 3.0 Ma and 90.8 ± 1.2 Ma, respectively. These data are consistent with palaeontological dating of sediment deposits directly under (Cenomanian, i.e. ≥ 93.9 Ma) or sealing (Coniacian-Santonian, i.e., ≤ 89.8 Ma), the obduction. (3) At Hınıs (NE Turkey) PT-t conditions on amphibolites (0.66 ± 0.06 GPa and 660 ± 20°C, with a U-Pb titanite age of 80.0 ± 3.2 Ma) agree with previous P-T-t data on granulites, and highlight a rapid exhumation below a top-to-the-North detachment sealed by the Early Maastrichtian unconformity (ca. 70.6 Ma). Amphibolites are cross-cut by monzonites dated by U-Pb on titanite at 78.3 ± 3.7 Ma. We propose that the HT-MP metamorphism was coeval with the monzonites, about 10 Ma after the obduction, and was triggered by the onset of subduction South of the Anatolides and by reactivation or acceleration of the subduction below the Pontides-Eurasian margin. Numerical modelling accounts for the obduction of an “old” ~80 Myr oceanic lithosphere due to a significant heating of oceanic lithosphere through mantle upwelling, which increased the oceanic lithosphere buoyancy. The long-distance transport of a currently thin section of ophiolites (<1 km) onto the Anatolian continental margin is ascribed to a combination of northward mantle extensional thinning of the obducted oceanic lithosphere by the Hınıs detachment at c. 80 Ma, and southward gravitational propagation of the ophiolite nappe onto its foreland basin.
... Contemporaneously, the oceanic crust of the Sevan-Akera ophiolite formed in a back-arc environment between the SAB and Transcaucasus (Galoyan et al., 2009;Rolland et al., 2009b). Oceanic crust formation is dated to the Middle to Late Jurassic (178-155 Ma), based on gabbro amphibole Ar/Ar ages (Galoyan et al., 2009;Rolland et al., 2010;Hässig et al., 2013a) and radiolarian ages (Danelian et al., 2007;Danelian et al., 2008Danelian et al., , 2010Danelian et al., , 2012Danelian et al., , 2014Asatryan et al., 2010Asatryan et al., , 2012. The Middle to Late Jurassic ages are similar to those obtained by Çelik et al. (2011) and Topuz et al. (2013aTopuz et al. ( , 2013b along the western continuation of the Sevan-Akera suture (i.e. the Izmir-Ankara-Erzincan suture), which suggests that the ophiolites of Sevan-Akera and Izmir-Ankara-Erzincan suture form part of the same ophiolitic belt. ...
Article
This article summarizes the geodynamic evolution of the Caucasus mountain belt from the Paleozoic to Present based on a review of works from Eastern Anatolia, Greater and Lesser Caucasus and Western Iran. The geological history of crystalline basements provides evidence for their derivation from Gondwana, for their drift at 450–350 Ma by roll-back of the South-dipping Rheic slab. Accretion to Eurasia of the Pontides-Transcaucasus block (PTB) occurred in the Carboniferous, and later an active continental margin was formed above a North-dipping subduction zone since at least the Early Jurassic. In the Mesozoic, the Neotethys ocean is separated into two domains, to the North and South of an E-W elongated block, the Taurides–Anatolides-South Armenian (ATA) Block. Two major subduction jumps are accounted for closure of the Tethys domain in Mesozoic to Cenozoic times: (i) jump at 90–80 Ma from the Northern to the Southern branch of Tethys after the closure of the northern branch of Neotethys along the Southern Eurasian margin in the Lesser Caucasus following the accretion of the ATA block to the PTB, (ii) jump at c. 40 Ma from the Southern branch of Neotethys to the Greater Caucasus back-arc basin (GCB), following the accretion of the ATA-Bitlis to the Arabian margin. The GCB will close completely during the Late Eocene to Pliocene and will give rise to the Greater Caucasus mountains. The Pliocene times mark an abrupt transition from a phase of convergence accommodated by subduction of marginal basins into a ‘hard’ collisional phase dominated by the reactivation of sutures and leading to a generalized uplift and diffuse deformation in the whole region.
... Radiolarians are commonly used to date deep-water sediments and to reconstruct the history of their sedimentation (Asatryan et al., 2012, Chiari et al., 2012, Sandoval et al., 2015 ). Such deep-water sediments, represented determined as Pseudodictyomitra pseudomacrocephala (Squinabol ) (Urquhart and Robertson, 2000). ...
Article
Well-preserved Cretaceous (Albian-Turonian) radiolarians were extracted from radiolarian-bearing chert olistoliths of the Monagroulli Member within the Moni Mélange (Campanian-Maastrichtian, Southern Cyprus). Four assemblages were distinguished: Middle Albian-Lower Cenomanian (Thanarla spoletoensis Zone), Upper Albian-Lower Cenomanian (Thanarla spoletoensis Zone, Dorypyle? anisa Subzone), lowermost Turonian (base of Alievium superbum Zone) and Lower Turonian (Alievium superbum Zone). The radiolarian assemblages are diverse and have taxonomic composition similar to coeval assemblages of Italy and Spain. The sediments of the Monagroulli Member differ from coeval rocks of the Mamonia Complex (western Cyprus) by the more common presence of radiolarian cherts and may have been formed in the distal part of a continental margin with less input of clastic material. A new spicular radiolarian genus Cyprothamnus with 2 new species (C. multifurcatus and C. moniensis) is described from the Lower Turonian strata.
... Contemporaneously, the Sevan-Akera ophiolite formed in a back-arc environment between the SAB and Transcaucasus (Galoyan et al., 2009;Rolland et al., 2009b). Ophiolite formation occurred in the Middle to Late Jurassic, which is based on 178-155 Ma Ar/Ar ages (on amphibole) for gabbros within the ophiolite (Galoyan et al., 2009;Rolland et al., 2010;Hässig et al., 2013a) and biostratigraphic ages from radiolaria (Danelian et al., 2007(Danelian et al., , 2008(Danelian et al., , 2014Asatryan et al., 2010Asatryan et al., , 2012. The Middle to Late Jurassic ages are similar to those obtained by Ç elik et al. (2011) and Topuz et al. (2013a,b) along the western continuation of the Sevan-Akera suture (i.e. the Izmir-Ankara-Erzincan suture), which suggests that the ophiolites that are exposed along the Sevan-Akera and Izmir-Ankara-Erzincan suture form part of the same ophiolitic belt. ...
Article
This article summarizes the geodynamic evolution of the Variscan to Mesozoic Tethyan subduction history, based on a review of geochronological data from Eastern Anatolia and the Lesser Caucasus, and new isotopic ages for the Georgian crystalline basements. The geological history of the basements of Georgia (Transcaucasus) and NE Turkey (eastern Pontides) appears to be similar and provides evidence for a continuously active continental margin above a north-dipping subduction since at least the Lower Jurassic. New La-ICPMS U-Pb ages from the Georgian basement provide further evidence for the derivation of the Transcaucasus and its western continuation (the eastern Pontides) from Gondwana. A migmatized granodiorite provides preserved magmatic zircon cores with an age of 474 ± 3 Ma, while the age of migmatization is constrained by its 343 ± 2 Ma metamorphic rims. Metamorphism is synchronous with widespread I-type granites that were emplaced at 335 ± 8 Ma in the neighbouring Dzirula massif, and in the eastern Pontides. These U-Pb ages are in close agreement with recently obtained Ar/Ar ages from biotites and muscovites from metamorphic schists and U-Pb ages ranging from 340 to 330 Ma in the Georgian basement. The narrow range of ages suggests that the Variscan LP-HT metamorphic event in the eastern Pontides and Georgia was of short duration and likely related to mantle-derived intrusives. Furthermore, we suggest that (1) rifting of the Pontides-Transcaucasus block (PTB) from Gondwana at 450–350 Ma could have been driven by roll-back of the south-dipping Rheic slab, (2) that the main metamorphic and coeval magmatic events are related to the accretion of the PTB to the Eurasian margin at c. 350 Ma, while the source of magmatism is ascribed to slab detachment of the south-dipping slab at 340 Ma and that (3) three subduction zones may have been contemporaneously active in the Tethyan domain during the Jurassic: (i) the Lesser Caucasus South Armenian Block (SAB) shares a similar Gondwana affinity, but bears younger ages for its MP-MT metamorphic evolution and calc-alkaline magmatism bracketed from 160 to 123 Ma; (ii) north-dipping subduction below the PTB from c. 210 Ma to 150 Ma; (iii) northward intra-oceanic subduction bracketed from 180 to 90 Ma between the SAB and the PTB.
Article
Офиолиты Базумского горста обладают отчетливой спецификой строения и состава, что отличает их от офиолитов Севан-Акеринского пояса. Офиолиты Базумского горста представлены только олистостромовой толщей сводного разреза офиолитов, где отсутствует толща офиолитового меланжа, которая залегает выше олистостромовой толщи, хотя присутствует почти во всех разрезах офиолитов Севан-Акеринского пояса. Это обусловлено редуцированным объе-мом офиолитов Базумского горста в виду меньшего количества обдуцированного аллохтонного материала океанической коры по сравнению с объемом офиолитов Севан-Акеринского пояса. Проведенные петрографические и петрохимические исследования позволили доказать терригенный осадочный характер матрикса офиолитовой олистостромы, тем самым опровергнув мнение предыдущих исследователей о принадлежности офиолитов Базумского горста к офиолитовому меланжу. На Базумском горсте мной выделен один уникальный геологический памятник, который демонстрирует вид мегаолистостромы. Բազումի հորստի օֆիոլիթները օժտված են կազմի և կառուցվածքի յուրահատուկ առանձնահատկություններով, որով նրանք տարբերվում են Սևան-Աքերայի գոտու օֆիոլիթներից: Բազումի հորստի օֆիոլիթային համալիրը ներկայացված է օլիստոստրոմային հաստվածքով։ Այստեղ բացակայում է օֆիոլիթային մելանժը, որը Սևան-Աքերայի գոտու համարյա բոլոր օֆիոլիթների կտրվածքներում տեղադրված է օլիստոստրոմային հաստվածքից վերև։ Օֆիոլիթային մելանժի բացակայությունը պայմանավորված է Բազումի հորստի օֆիոլիթների ծավալի կրճատված ծավալով, ի տարբերություն Սևան-Աքերայի գոտու օֆիոլիթների մեծ ծավալին: Ըստ պետրոգրաֆիական և պետրոքի-միական հետազոտությունների ապացուցվել է օֆիոլիթային օլիս-տոստրոմի մատրիքսի տերիգեն նստվածքային բնույթը, դրանով հերքելով նախորդ ուսումնասիրողների կողմից առաջ քաշված Բազումի հորստի օֆիոլիթների օֆիոլիթային մելանժին պատկանելիությունը: Բազումի հորստի սահմաններում հեղինակի կողմից անջատվել է եզակի երկրաբանական հուշարձան, որը պատկերում է մեգաօլիստոստրոմի արտաքին տեսքը: The ophiolites of the Bazum horst have a distinct specific structure and composition which distinguishes them from the ophiolites of the Sevan-Akera belt. The ophiolites of the Bazum horst are represented only by the olistostrome sequence of the combined ophiolite section. In the ophiolites of the Bazum horst there is no thickness of ophiolite melange, which lies above the olistostrome sequence, although it is present in almost all ophiolite sections of the Sevan-Akera belt. This is due to the reduced volume of ophiolites of the Bazum horst because of the smaller amount of obduced allochthonous material of the oceanic crust compared to the volume of ophiolites of the Sevan-Akera belt. The petrographic and petrochemical studies made it possible to prove the terrigenous sedimentary nature of the matrix of the ophiolite olistostrome, thereby refuting the opinion of previous researchers that the ophiolites of the Bazum horst belong to the ophiolitic melange. On the Bazum horst, the author has identified one unique geological monument which demonstrates the appearance of a megaolistostrome.
Article
New field and petrographic observations, combined with whole rock and mineral geochemical analyses are applied on volcanic rocks present in the Dali sector, east of Lake Sevan (Armenia). A small-scale sampling of the volcanic sequence allows us to identify, for the first time in Armenian ophiolites, two groups of lavas (groups B and C1) stratigraphically and geochemically intermediate between previously recognized arc tholeiite (group A) and OIB-like (group C2) basalts. Their age is constrained by two distinct intercalated radiolarite sequences, which were dated as Tithonian – Valanginian. Group B lavas are low-K tholeiitic basalts and basaltic andesites derived from an enriched mantle source (LaN/YbN 1.8–6.1; SmN/YbN 1.3–2.4; Nb/Yb 2.0–6.7). The composition of their clinopyroxenes ranges from Ti-poor augite to Ti-rich diopside augite in correlation with higher La/Yb and Nb/Yb ratios in bulk rocks. Group C1 lavas are basaltic andesites containing Ti and Na-rich amphiboles (kaersutites, hastingsites) as major mineral phases. Three analyzed diopside-amphibole-porphyritic samples are alkaline trachybasalts (LaN/YbN 20–21; Nb/Yb 16–18). Both the group B and C1 lavas exhibit variable, although moderate, enrichments in Th/Yb for given Nb/Yb ratios and Nb negative anomalies in normalized multi-elements patterns (Nb/La 0.53–1.02), which are not correlated with the degree of enrichment of their mantle sources. Our results suggest that transitional and OIB-like volcanic lavas were generated by low- (group B) and very low- (groups C1–C2) melting of a heterogeneous mantle source in an oceanic arc–back-arc system in extension, possibly in relation with slab break-off.
Article
Full-text available
The study tends to clarify the chronostratigraphy scale of the emplacement of igneous formations localized in the central part of the Dali River valley of the Sevan ophiolite complex, observing the formation of rock under various geodynamic settings. Presented new facts indicate the diversity of types and ages of pillow lavas. Based on the new U-Pb age of plagiogranite (~ 172 Ma), a new boundary is "drawn" between the pre-intrusive and post-intrusive basalts. Accordingly, the lower lavas may have an older age, at least, the beginning of the Middle Jurassic, while the upper lavas belong to the age of the Upper Jurassic-Lower Cretaceous. The genetic link of numerous rhyolitic bodies (cross-cutting the lower series) is assumed to be with the main plagiogranite intrusion. It turns out that the magmatic formations consist of both mid-oceanic and island-arc units having complex relationships.
Article
Full-text available
The magmatic arcs of the Eastern Pontides and Lesser Caucasus lie in continuation from one another. A comparison of the subduction related magmatic rocks outcropping throughout this segment of the Northern Tethyan belt exhibits chronological disparities, questioning the common subduction history of the Eastern Pontides and the Lesser Caucasus regions. New data and observations including geochronological and geochemical data, relative to subduction to collision related magmatic rocks argues a novel paleogeographic reconstruction illustrating Mesozoic and Cenozoic evolution of this region. Jurassic to Early Cretaceous arc magmatism runs mainly from the Sochi-Ritsa/Bechasyn regions (Greater Caucasus) towards the south-east to the Alaverdi region and further into the Lesser Caucasus. Late Cretaceous and Cenozoic arc magmatism is evidenced throughout the Eastern Pontides extending through the Bolnisi region to the Lesser Caucasus arc. East to west, Jurassic to Early Cretaceous and Late Cretaceous to Cenozoic portions of arc split to the north and south of the Eastern Black Sea, respectively. Throughout Cretaceous subduction, this segment of the magmatic arc of the Southern Eurasian margin was torn in two due to the oblique opening of the Eastern Black Sea as a back- to intra-arc basin, from west to east. This reconstitution implies that the Jurassic-Early Cretaceous subduction related magmatic rocks of the Greater Caucasus are remnant potions of the Eastern Pontides and Lesser Caucasus arcs. This infers the emplacement of subduction to collision related magmatic rocks throughout the Mesozoic and Cenozoic along the entire Southern Eurasian margin is solely due to a single long-lasting north-dipping subduction.
Article
Full-text available
The magmatic arcs of the Eastern Pontides and Lesser Caucasus lie in continuation from one another. A comparison of the subduction‐related magmatic rocks outcropping throughout this segment of the Northern Tethyan belt exhibits chronological disparities, questioning the common subduction history of the Eastern Pontides and the Lesser Caucasus regions. New data and observations including geochronological and geochemical data, relative to subduction‐ to collision‐related magmatic rocks, argue a novel paleogeographic reconstruction illustrating Mesozoic and Cenozoic evolution of this region. Jurassic to Early Cretaceous arc magmatism runs mainly from the Sochi‐Ritsa/Bechasyn regions (Greater Caucasus) toward the southeast to the Alaverdi region and further into the Lesser Caucasus. Late Cretaceous and Cenozoic arc magmatism is evidenced throughout the Eastern Pontides extending through the Bolnisi region to the Lesser Caucasus arc. East to west, Jurassic to Early Cretaceous and Late Cretaceous to Cenozoic portions of arc split to the north and south of the Eastern Black Sea, respectively. Throughout Cretaceous subduction, this segment of the magmatic arc of the Southern Eurasian margin was torn in two due to the oblique opening of the Eastern Black Sea as a back‐arc to intra‐arc basin, from west to east. This reconstitution implies that the Jurassic‐Early Cretaceous subduction‐related magmatic rocks of the Greater Caucasus are remnant portions of the Eastern Pontides and Lesser Caucasus arcs. This infers the emplacement of subduction‐ to collision‐related magmatic rocks throughout the Mesozoic and Cenozoic along the entire Southern Eurasian margin is solely due to a single long‐lasting north dipping subduction.
Article
Full-text available
The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section.
Conference Paper
Full-text available
The Vourinos ophiolite complex mainly consists of harzburgite-dunite and minor layered crustal cumulates (Moores, 1969; Jackson et al., 1975) covered by an extrusive sequence of IAT type, including pillow lavas, crosscut by transitional to boninitic-type intrusive dykes (Beccaluva et al., 1984). These extrusive rocks in the Zyghosti, Krapa Hills and Mikrokastro areas are covered by thin levels of radiolarian cherts which were never dated before. In the Krapa Hills area, the pillow lavas are overlain by about 3 m of red radiolarian cherts grading upwards to Tithonian thin-bedded cherty limestones with ammonites and belemnites and, finally the succession ends with redeposited shallow-water Jurassic limestones. A sample of radiolarian cherts collected about 2.50 m above the pillow basalts gave a latest Bajocian-early Bathonian to late Bathonian-early Callovian age (UAZ. 5-7) for the presence of Ristola altissima major Baumgartner & De Wever. In the Zyghosti area some tens metres of basalts tectonically cover the harzburgite-dunite. At the top of the basalts thin scattered outcrops of thin radiolarian cherts are present. Two sections were sampled for radiolarians In the first section, a sample collected about 80 cm above the pillow lavas indicates a latest Bajocian-early Bathonian to late Bathonian-early Callovian age (UAZ. 5-7) for the presence of Stichocapsa robusta Matsuoka; in the second section (about 30 m from the first one) a sample collected about 50 cm above the basalts indicates a middle Bathonian age (UAZ. 6) for the coexistence of Stylocapsa oblongula Kocher, Stylocapsa tecta Matsuoka and Unuma sp. A Baumgartner et al.
Chapter
Full-text available
Unitary Associations (U.A.) were calculated with the computer program BIOGRAPH to construct a radiolarian zonation spanning the Middle Jurassic to Early Cretaceous time interval. During test runs, over 60 sections including 800 samples were selected to construct the zonation. Since single runs of the entire dataset revealed too many conflicting superpositional relationships between samples, we had to construct composite sections and to use iterative runs of BIOGRAPH. Regional syntheses were calculated first. Then, regional syntheses from the Mediterranean were combined to make the core of a "snowball" to which successively more data was added. In this way, all data added later were compared to the initially included sections. A synthesis of the Mediterranean Middle and Late Jurassic is calibrated and discussed as a protoreferential. The final zonation spans the Aalenian to early Aptian time interval. It is based on a synthesis including 127 U.A. that were grouped into 22 Unitary Association Zones (UAZones95: 1-22). Each zone is defined by a number of characteristic taxa or pairs of taxa that co-occur in that zone only. Each zone is calibrated to the standard stages by means of ammonites, nannofossils, calpionellids, dinoflagell~tes, as well as paleomagnetic and stable isotope stratigraphy. The UAZones are correlated to the earlier zonations of Baumgartner, Gorican, Jud, Murchey, Matsuoka, and Pessagno et al.
Article
The uppermost part of the Limestones with Filaments and Upper Posidonia Beds of the central Ionian zone yielded radiolarians of Callovian and upper Oxfordian-upper Beriasian ages respectively. The radiolarian fauna extracted from the lowermost part of the Vigla Limestones shows that these strata were deposited after the middle Tithonian. Includes an abridged English version. -English summary
Article
Chert beds from Almopias area have been dated with radiolarian remains: some of them, never described before, are Triassic (Vrissi Unit) while others, chert and volcanic beds from Mavrolakkos Unit are Jurassic-early Neocomian (probably Upper Jurassic). These results give some information on the unknown geological history of this area during Triassic-Jurassic times. They support the hypothesis of the existence of a Jurassic oceanic crust basin east of the Pelagonian zone, initiated during Triassic times. Finally, they modify the data used to discuss the existence of an Upper Cretaceous oceanic crust in the Almopias area. There is an abridged English version. -English summary
Article
Using radiolarian fossils, a Paleozoic suite (Kazanian-Tatarian) of New-Zealand, overlying spilitic rocks, has been precisely dated for the 1st time. The paleontologic characteristics of the collected fauna and the significances of the dated outcrops in their paleogeographic framework are discussed. An abridged English summary is included.-English summary