Geologic evolution and geodynamic controls of the Tertiary

Transcription

Bull. Soc. géol. Fr., 2004, t. 175, no 4, pp. 361-381
Geologic evolution and geodynamic controls of the Tertiary intramontane
piggyback Meso-Hellenic basin, Greece
JACKY FERRIÈRE1, JEAN-YVES REYNAUD2, ANDREAS PAVLOPOULOS3, MICHEL BONNEAU4,
GEORGES MIGIROS3, FRANK CHANIER1, JEAN-NOËL PROUST5 and SILVIA GARDIN6
Key words. – Sedimentary basin, Greece, Cenozoic, Piggyback, Gravity deposits
Abstract. – The Meso-Hellenic Basin (MHB) is a large, narrow and elongated basin containing up to c. 5 km of Cenozoic sediments, which partially covers the tectonic boundary between the external, western zones (Pindos) and the internal, eastern zones (Pelagonian) of the Hellenide fold-and-thrust belt. New results, based on micropaleontologic,
sedimentologic and tectonic field data from the southern half of the MHB, suggest that the MHB originated as a forearc
basin during the first stages of a subduction (Pindos basin), and evolved into a true piggyback basin as a result of the
collision of thicker crustal units (Gavrovo-Tripolitsa). The late Eocene forearc stage is marked by sharply transgressive,
deep sea turbiditic deposition on the subsiding active margin. At this stage, large scale structures of the Pelagonian basement (i.e. the newly defined “Pelagonian Indentor”) control deposition and location of two main subsiding sub-basins
located on both sides of the MHB. The Eocene-Oligocene boundary corresponds to a brief tectonic inversion of the basin, at the onset of collision (main compressive event). The true piggyback stage (Oligo-Miocene) is recorded by slope
deposition and dominated by gravity processes (from slumped, fine grained turbidites to conglomeratic fan- or Gilbertdeltas). The new elongated geometry of the MHB is controlled by the underthrusted, NNW-SSE trending, thick external
zones. During this stage, the locus of subsidence migrates in the same direction (eastward) as underthrusting. This subsidence, favoured by thick dense ophiolitic basement, is attributed to basal tectonic erosion of the upper Pelagonian unit
while the tectonic structures of this upper unit control the stepped migration of subsidence. Growing duplexes in the Gavrovo underthrusted unit, which formed local uplifts, were mainly situated on the eastern side of the subsiding areas and
associated with normal faulting (late Oligocene–early Miocene). They constituted new loads that could also have been
responsible for minor but widespread lithospheric subsidence. The development of the local and regional uplifts explains the basin evolution toward shallow, dominantly conglomeratic deposits and its final emergence at the end of the
middle Miocene. This trend toward emersion is emphasized by the late Miocene global sea-level fall. The MHB was
subsequently overprinted by neotectonic deformation associated with the development of a continental basin (Ptolemais) and uplift attributed to the evolution of the Olympos structure that developed further east as the underthrusting
moved in this direction. These results demonstrate that the Meso-Hellenic Basin evolves as a large scale piggyback Basin and that its sedimentary infill is largely controled by tectonic activity rather than only eustatic sea-level variations.
Evolution géologique et contrôles géodynamiques d’un bassin intramontagneux cénozoïque :
le bassin méso-hellénique, Grèce
Mots-clés. – Bassin sédimentaire, Grèce, Cénozoïque, Piggyback, Dépôts gravitaires
Résumé. – Le bassin mésohellénique (MHB) est un sillon intramontagneux présentant près de 5 km de séries cénozoïques en son dépôt-centre. Les dépôts post-éocènes scellent partiellement la suture entre les zones externes (Pinde) et les
zones internes (Pélagonien) des Hellénides continentales. De nouvelles études sédimentologiques, micropaléontologiques et tectoniques de la partie méridionale du bassin suggèrent que le MHB s'est mis en place en position d'avant-arc
lors des premiers stades de la subduction du Pinde (Eocène supérieur), et qu'il a évolué en véritable piggyback lors de la
collision des unités du Gavrovo-Tripolitsa (essentiellement à partir de l'Oligocène). Le stade avant-arc du bassin est
marqué par une sédimentation turbiditique profonde contrôlée par la subsidence rapide de la marge active et localisée
dans des sous-bassins liés à l'héritage structural de la marge pélagonienne (i.e. le « poinçon pélagonien », structure
transverse majeure). La limite Eocène-Oligocène est un épisode bref d'inversion tectonique du bassin (phase compressive majeure) correspondant à l'entrée en collision de la marge pélagonienne avec la plate-forme externe. L'Oligocène
enregistre ensuite une sédimentation marine relativement peu profonde, dominée par les processus gravitaires (slumps,
turbidites fines), et alimentée par l'ouest (la chaîne du Pinde qui commence à émerger). A ce stade, le bassin est contrôlé
par les zones externes en sous-charriage, qu'il s'agisse de sa géométrie, désormais allongée NNW-SSE et parallèle au
front tectonique ou de sa subsidence qui se met à migrer par à-coups dans la même direction que le sous-charriage de
ces zones externes (vers l'est). Cette subsidence, favorisée par la présence d'un substratum ophiolitique dense, est attribuée à de l'érosion tectonique sous l'unité pélagonienne. Elle s'atténue progressivement au Miocène, probablement par
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Université de Lille 1, UFR Sciences de la Terre, UMR Pbds 59655 Villeneuve d’Ascq cedex, France. [email protected]
Museum National d’Histoire Naturelle, Laboratoire de Géologie, 43 Rue Buffon, 75005 Paris, France.
Mineralogy-Geology, Agricultural University of Athens, Iera odos 75, 11855 Athens, Greece.
Département de Géotectonique, Université Pierre et Marie Curie, 4 Place Jussieu, BP 129, 75252 Paris cedex 05, France.
Géosciences Rennes, Bat. 15, Université de Rennes 1, 35014 Rennes cedex, France
Lab. Micropaléontologie, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris cedex 05, France.
Manuscrit déposé le 10 octobre 2003 ; accepté après révision le 19 janvier 2004.
Bull. Soc. géol. Fr., 2004, no 4
362
J. FERRIÈRE et al.
la croissance de duplex dans les unités sous-charriées, qui seraient bloquées sur la faille égéenne (début de la surrection
du massif de l'Olympe). Cet épisode s'enregistre dans le bassin par des failles normales et par le dépôt d'éventails conglomératiques marins de type Gilbert-deltas alimentés par l'est. L'émersion est accélérée par la chute eustatique du Miocène terminal. Au Plio-Quaternaire, le MHB enregistre une néotectonique correspondant à la structuration du relief
pélagonien plus loin vers l'est (bassin de Ptolémais, montée de l'Olympe qui se poursuit). Cette étude suggère que l'évolution du MHB est essentiellement imputable à la géodynamique des Hellénides continentales et que les fluctuations
eustatiques n'y ont qu'un rôle secondaire.
INTRODUCTION
The Meso-Hellenic Basin (MHB), located in northern
Greece and Albania (fig. 1), was formerly called “Albanothessalian” by Bourcart [1925], before being named MHB
by Brunn [1956] and Aubouin [1959]. It has been said to be
“molassic” by these authors as it is filled with detrital sediments unconformably overlying the deformed MesozoicPaleocene basement and some early Tertiary thrusts.
The MHB is of importance because of (i) its large size
(about 300 km long, 30 km wide), pointing to a relationship
with major orogenic processes, (ii) its lower Cenozoic age,
which is a poorly known period of the Internal Hellenic
chain; (iii) its nature, as the basin develops as a thrust sheet
top or piggyback basin on the main upper tectonic unit of
the converging system, by contrast to most basins of that
size that form on the lower one [ca. foreland systems: Allen
et al., 1986; Sinclair, 1997a, 1997b].
This paper aims to present relevant field observations at
various scales from selected areas of the MHB in order to
discuss some of the possible mechanisms at the origin of
subsidence of this peculiar piggyback basin system. Struc-
FIG. 1. – Simplified geological map of the Meso-Hellenic basin (MHB) in northern continental Greece. 1 to 4: main formations of the MHB, 1: Krania and
Rizoma (late Eocene), 2: Eptachorion (latest Eocene?-early Oligocene), 3: Taliaros-Pentalofos (late Oligocene-early Miocene), 4: Tsotyli-Ondrias-Orlias
(early to middle Miocene), 5: Ptolemais basin (late Miocene-Pliocene, mp), 6: recent deposits. Abr. Pz: Paleozoic, TJ: Triassic and Jurassic, Ng : Neogen, V: Vourinos massif, S: synclines, A: anticlines (Af: Filippi anticline, At: Theopetra-Theotokos anticline; Fe, Fk, Ft, cf. Fig. 2. AA’: cross-section
(fig. 2). Bold lines: major tectonic contacts, with rectangular boxes: late Jurassic thrusts, with white triangles: main Tertiary thrusts. Lines with black
triangles: Tertiary back-thrusts or main reverse series. Dashed lines: normal faults.
FIG. 1. – Carte géologique simplifiée du basin méso-hellénique (MHB) au nord de la Grèce continentale. 1 à 4 : formations principales, 1 : Krania et Rizoma (Eocène terminal), 2 : Eptachorion (Eocène terminal ?- Oligocène), 3 : Taliaros-Pentalofos (Oligocène supérieur-Miocène inférieur), 4 : TsotyliOndrias-Orlias (Miocène inférieur à moyen), 5 : bassin de Ptolemais (Miocène supérieur-Pliocène, mp), 6 : dépôts récents. Abréviations : Pz : Paléozoïque, TJ : Trias-Jurassique, Ng : Néogène, V : massif du Vourinos, S : synclinaux, A : anticlinaux (Af : anticlinal de Filippi, At : anticlinal de Theopetra-Theotokos), Fe, Fk, Ft cf. fig. 2. AA’ : coupe figure 2. Lignes en trait épais : contacts tectoniques majeurs ; avec barbules rectangulaires :
chevauchements du Jurassique supérieur ; avec barbules triangulaires blanches : chevauchements tertiaires majeurs ; avec barbules triangulaires noires : rétro-chevauchements tertiaires ou séries inverses principales. Lignes tiretées : failles normales.
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THE MESO-HELLENIC PIGGYBACK BASIN
tural analysis (stress axes, nature, scale and especially timing of deformation) as well as sedimentological studies
(1D-2D facies logging and correlation) and
biostratigraphical revisions (nannofossils) have been performed to assess or refine the chronostratigraphic pattern
and tectonic evolution of the southern half of the MHB,
where tectonic features are well expressed and stratigraphic
series more complete (i.e. late Eocene is present).
BACKGROUND
The first studies of the MHB were focused on mapping
lithological formations [Brunn, 1956; 1969; Savoyat et al.,
1969, 1971a, 1971b, 1972a, 1972b; Mavridis et al. 1979;
1993; Koumantakis et al., 1980; Vidakis et al., 1998]. Other
publications provided biostratigraphic refinements
[Soliman and Zygojiannis, 1980; Zygojiannis and Muller,
1982], source rock studies from heavy minerals
[Zygojiannis and Sidiropoulos, 1981] or olistoliths
[Papanikolaou et al., 1988; Wilson, 1993], dynamics of
depositional systems [Faugères, 1977a, 1977b; Desprairies,
1979; Ori and Roveri, 1987; Zelilidis et al., 1996, 1997]
and large-scale industrial seismic data [Zelilidis and
Kontopoulos, 1996; Kontopoulos et al., 1999; Zelilidis et
al., 2002]. Tectonic data have also been used to assess the
first basin models [Doutsos et al., 1994; Ferrière et al.,
1998].
The MHB is a Tertiary basin, 30 km wide and more
than 300 km long including its Albanian part (fig. 1). The
basin mostly developed east of the main tectonic boundary
between external and internal zones of the Hellenides,
known as the “Internal Zones Thrust” (fig. 1 and fig. 2),
part of a very large thrust system located beneath the MHB.
In this area, the internal zones are made up of the
Pelagonian continental crust (Triassic to Jurassic metamorphic limestones and Paleozoic gneiss) partly overlapped by
upper Jurassic ophiolites thrusted again towards the west
onto the Pindos area during the Tertiary events [Brunn,
1956; Aubouin, 1959]. The external zones consist of Pindos
flysch nappes just west of the Pelagonian zone below which
the thin [oceanic, Bonneau 1982] Pindos crust was
underthrusted to the east.
The series cropping out in the Olympos tectonic window have been attributed to the external zones [Godfriaux,
1968; fig. 1 and fig. 2], sometimes to the Parnassos zone
[Mercier et al., 1989], but more generally (as in this publication), because of the age of the flysch, to the GavrovoTripolitsa zone [Fleury and Godfriaux 1975]. The MHB is
thus located above the main thrust bounding the internal
and external zones. The Eocene age of the Olympos series
in the window [Fleury and Godfriaux 1975], the ages that
can be used to determine the end of deposition of the Pindos
series [Lutetian on its eastern part, Lecanu 1976] and the
beginning of the tectonic activity along the “Internal zones
thrust” recorded in the early MHB deposits (middle and late
Eocene), show that the thrust was active below the MHB
during its evolution (middle or late Eocene to middle Miocene). Therefore the MHB is a true piggyback basin as defined by Ori and Friend [1984].
However, according to Doutsos et al. [1994], the MHB
behaves as a retroarc foreland basin, developing in front of
Pindos and ophiolitic thrusts moving towards the east, while
the major thrust faults exhibit a clear vergency towards the
west. For these authors, the basin architecture is related to
the development of these eastward moving thrusts (including blind thrusts). The MHB has been more recently interpreted as a “strike-slip half graben”, mainly based on new
interpretations of seismic lines [Zelilidis et al., 2002]. Still,
we could not find any clear evidence neither for major eastverging thrust faults, nor for NNW-SSE main strike-slip
faults (fig. 2). We here present an alternative hypothesis for
the development of the MHB, in which the basin evolves as
a piggyback basin controlled by eastward-directed
underthrusting, corresponding to the Pindos subduction and
the collision of the Gavrovo-Tripolitsa unit since the midlate Eocene .
STRATIGRAPHY AND SEDIMENTOLOGY
Overview of basin formations
The MHB is filled up with about 4500-5000 m of middle
Eocene to middle Miocene deposits (fig. 2 and fig. 3). Strata mostly dip towards the east, from subvertical to slightly
overturned strata at the western basin boundary, down
FIG. 2. – Cross section of the MHB [modified from Ferrière et al., 1998]. See figure 1 for location. 1 to 4: MHB Formations, same captions as in figure 1.
Fk, Fe and Ft: faulted-flexures of Krania (Fk), Eptachorion (Fe) and Theopetra-Theotokos (Ft). F1 and 2: main Tertiary thrusts, Fj: Jurassic obduction. Vertical scale: maximum thickness of the MHB sediments on the cross-section: 4 km.
FIG. 2. – Coupe du MHB [modifié d’après Ferrière et al.., 1998]. Voir figue 1 pour la localisation. 1 à 4 : formations du MHB, mêmes légendes que dans
la figure 1. Fk, Fe et Ft : flexures faillées de Krania (Fk), Eptachorion (Fe) et Theopetra-Theotokos (Ft). F1 et 2 : chevauchements tertiaires principaux ;
Fj : obduction jurassique. Echelle verticale : épaisseur maximum des dépôts sur la coupe : 4 km.
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J. FERRIÈRE et al.
slightly westward dipping at the eastern border (fig. 2 and
fig. 4). Miocene strata are absent in the west and rest onto
the basement in the east. Seismic profiles show a pinch out
of deposits at depth [Kontopoulos et al., 1999; Zelilidis et
al., 2002]. These data show that deposition is controlled by
an overall eastward migration of depocentres and thus of
subsidence (fig. 3). The Oligocene to Miocene siliciclastic
deposits were first described as six main lithostratigraphic
units by Brunn [1956, 1960] from the northern part of the
MHB, where Eocene strata are absent. These are: (i)
Eptachorion Formation (1100 m, mainly early Oligocene)
dominated by silty marls with decimetre thick very fine
sandstone beds often resting on thick conglomerates; (ii)
Taliaros (or Tsarnos) and (iii) Pentalofos Formations
(2500 m, late Oligocene and early Miocene): sandstone
beds coarsening upwards to conglomeratic beds; (iv)
Tsotyli Formation (600 m, early-mid? Miocene): marls
interbedded with sandstones; (v) Ondria and (vi) Orlias For-
mations (350 m or more, early-mid Miocene): sandstones
and marls with fossiliferous limestone beds.
The chronostratigraphy of MHB formations is still not
very precise, mostly because of the scarcity of fossils or due
to their reworking in gravity dominated facies. The only
available ages are from marls (pelagic foraminifera,
nannofossils) or from a few carbonate shelf intervals (benthic foraminifera, invertebrates). Moreover, published ages
are significantly divergent, even for the same faunal associations [ca. Zygojiannis and Müller, 1982, vs Kontopoulos et
al., 1999]. The lack of precise datations led authors to correlate sedimentary successions on the main base of lithology, but the absence of accurate field data on lateral facies
variations induced some mistakes. An attempt of stratigraphic synthesis is given here together with a revision including our additional field and biostratigraphic data in
key-areas located in the southern half of the MHB (fig. 5
and fig. 6).
FIG. 3. – Lithological formations of the MHB in the study area, from the geological maps of Greece at 1:500,000 and Bornovas and Rondogianni-Tsiambaou, 1983], and 1:50,000 (cf. references), and the synthetic map of Doutsos et al. [1994], modified in the southern half of the MHB, from our field study
(see fig.4 for cross sections). Depth contours of the basement below the basin after seismic data of Kontopoulos et al. [1999] completed in the south from
field data. Abr: E: early, M: middle, L: late, Eoc: Eocene, Olig: Oligocene, Mio: Miocene, N: Neogene, H: Holocene.
FIG. 3. – Formations lithologiques du MHB dans le secteur d’étude, d’après la carte géologique de Grèce au 1:500 000 [Bornovas et Rondogianni-Tsiambaou, 1983] et au 1:50 000 (voir bibliographie), ainsi que d’après la carte de synthèse de Doutsos et al. [1994], modifiée dans la partie méridionale du
MHB d’après nos données (voir les coupes fig. 4). Isohypses du toit du substratum d’après les données sismiques de Kontopoulos et al. [1999] complétées
dans le sud par des données de terrain. Abréviations : E : inférieur, M : moyen, L : supérieur, Eoc : Eocène, Olig : Oligocène, Mio : Miocène, N : Néogène, H : Holocène.
Studied series in the southern basin
The southern part of the basin exhibits the most complete
sedimentary succession (starting in the late Eocene) exposed within the MHB and shows clear relationships between tectonics and deposition, as demonstrated further in
this paper. The Oligo-Miocene Formations have the same
characteristics as their stratotypical counterparts in the
north, except that Pentalofos and Tsotyli Formations exhibit
a higher conglomeratic content. Two areas are detailed here,
where upper Eocene deposits are present (fig. 5 and fig. 6).
Krania area (western border)
The Krania Formation, 1500 m thick, is well developed and
preserved only inside a syn-sedimentary syncline (fig. 5B).
Toward the syncline edges, various facies laterally pass to
each other and finally pinch out below the EoceneOligocene unconformity. The Krania Formation exhibits a
set of two sequences of deposits. The deposits rest onto
roughly bedded, polygenic clast-supported conglomerate
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beds, interpreted as alluvial fan deposits, onlapping a sole
of ophiolitic epiclastites (Krania). In the central part of the
basin, the lower sequence is composed of fine-grained fining upwards and homogeneous sandstone beds interpreted
as deep water turbidites (Krania, Microlivadon). On the
northern side of the syncline, this succession passes laterally to highly bioturbated, fine grained marly sandstones
with thin channel bodies of sandstones showing mud pebbles at the base, interpreted as bay-fill deposition
(Trikomo), and to roughly bedded conglomerates interpreted as alluvial fans (Parorio). This facies may be highly
disrupted by slumps and locally makes part of a large scale
olistostrome (Monachiti), set on at the end of deposition of
the lower sequence. This olistostrome, mainly composed of
Cretaceous limestones collapsed from the northern basin
margin, feeds channels and gullies down to the southern basin floor. It is coeval to a paroxysm of slumping in the
turbiditic basin. The upper sequence is made up of the same
turbiditic sands as the lower one, but exhibits at the base a
sharp-based hectometric succession of thicker sandstone
FIG. 4. – Typical cross-sections of the MHB (see fig. 3 for location), compiled from our field work, geological maps of Greece at 1: 50,000 (cf. References) and seismic profiles published by Kontopoulos et al. [1999]. Lithological formations: Kr: Krania Turbidites, Ep: Eptachorion, Ta: Taliaros, Pf: Pentalofos, Ts: Tsotyli . Main faulted-flexures: Fk: Krania, Fe; Eptachorion, Ft: Theopetra-Theotokos. Vertical and horizontal scales are similar (no vertical
exaggeration: v.e. = 1).
FIG. 4. – Coupes significatives du MHB (voir fig. 3 pour positionnement), compilées d’après nos données de terrain, les cartes géologiques de la Grèce
au 1:50 000 (voir bibliographie) et les profils sismiques publiés par Kontopoulos et al. [1999]. Formations lithologiques : Kr : turbidites de Krania, Ep :
Eptachorion, Ta : Taliaros, Pf : Pentalofos, Ts : Tsotyli. Flexures faillées principales : Fk : Krania, Fe : Eptachorion, Ft : Theopetra-Theotokos. Les échelles
verticales et horizontales sont identiques (pas d’exagération verticale).
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J. FERRIÈRE et al.
beds with locally abundant burrows (Skolithos), plant fragments, water escape structures and intraclastic breccias, interpreted as part of a basin floor fan (Monachiti). The
Krania basin deposits are topped by the Eocene-Oligocene
major unconformity made up of reddish conglomerates and
paleosoils truncating the turbidites.
Meteora area and eastern border
In the famous Meteora area, the MHB Tertiary Formations
are thinner, scattered, and show several unconformities.
These unconformities are due to the interplay of the NNWSSE Theopetra-Theotokos structure, composed by a structural high (At) bounded to the east by the TheopetraTheotokos Fault (Ft; fig. 5C, see also fig. 12). On the western side of At-Ft, the series are similar to the northern ones
with the conglomeratic, Pentalofos Formation (Meteora
cliffs) resting on the Eptachorion Formation. By contrast,
on the eastern side of Ft, Pentalofos conglomerates are absent, but the succession is more complete at the base and at
the top (fig. 5).
In the area around Rizoma, the succession starts with a
few metres of late Lutetian benthic macroforaminifera-rich
(abundant Nummulites) limestones, corresponding to a carbonate shelf sedimentation (near Lagada these limestones
are interfingered with and overlain by more than 100 m of
well-rounded conglomerates). The limestones are overlain
by a thick upper Eocene succession (more than 200 m)
made up of marly distal turbiditic sequences, locally with
sandstone beds interpreted as fluvial dominated deltaic
mouth bar systems (wood fragments, floating mud pebbles,
water escape features, current ripples, Skolithos traces and
various burrows). The Eocene succession is covered by
Oligocene basal conglomerates or Miocene conglomeratic
Tsotyli beds. Mid-Miocene Echinid-rich limestones and
marly turbiditic deposits delivering Globigerinidae associations typical of the Ondrias-Orlias Formations, directly deposited on the basement in the southern part of this area,
cap the succession.
Sedimentary record
Depositional setting
Our results agree with the previous sedimentological and
mineralogical studies, assuming that the Miocene conglom-
FIG. 5. – Schematic stratigraphic sections of the MHB in the central (B) and southern (C) areas, compared to the former published (see text) northern one
(A). 1: Pelagonian basement with ophiolites (v), 2: basal conglomerates (unconformity), 3: Conglomerates and sandstones, 4: sandstones (mainly turbiditic), 5: sandstones and shales (mainly turbiditic), 6: shales (partly hemipelagic), 7: major olistoliths, 8: Eocene detrital limestones, 9: Miocene Echinidrich limestones. Nannofossils biozones after: [], Zygojiannis and Müller [1982]; (), Kontopoulos et al. [1994] and Zelilidis et al. [2002]; free thick numbers: this publication. D: major angular unconformities, S: other significant surfaces (main lithological changes), Pz: Paleozoic, TJ: Triassic–Jurassic,
UK: upper Cretaceous, Eo: Eocene, Olig: Oligocene, Mio: Miocene, E: early, M: middle, L: late.
FIG. 5. – Colonnes synthétiques du MHB dans sa partie centrale (B) et méridionale (C), comparées à la colonne synthétique publiée précédemment pour
la partie nord (A, voir le texte). 1 : soubassement pélagonien avec ophiolites (v) ; 2 : conglomérats de base (discordance) ; 3 : conglomérats et grès ; 4 :
grès (principalement turbiditiques) ; 5 : grès et shales (principalement turbiditiques) ; 6 : shales (partiellement hémipélagiques) ; 7 : principaux olistolithes ; 8 : calcaires détritiques éocènes ; 9 : calcaires à oursins miocènes. Biozones de nannofossiles d’après : [] Zygojiannis et Müller [1982], () Kontopoulos et al. [1994] et Zelilidis et al. [2002], nombres libres en gras : cette publication. D : principales discordances angulaires ; S : autres surfaces
importantes (limites lithologiques). Pz : Paléozoïque, TJ : Trias-Jurassique, UK : Crétacé supérieur, Eo : Eocène, Olig : Oligocène, Mio : Miocène, E : inférieur, M : moyen, L : supérieur.
367
FIG. 6. – Compared ages of MHB deposits from foraminifera (D) or nannoflora biozones. A: Brunn [1956], B: geological maps of MHB areas, IGME,
Greece, at 1:50,000 scale (cf References) and Bizon et al. [1968], C: Zygojiannis and Müller [1982], D: Barbieri [1992], E: Doutsos et al. [1994], Zelilidis
et al. [1997, 2002] and Kontopoulos et al. [1999], F: this study. Abr. CN: nummulitic limestones, Kr.: Krania, Riz.: Rizoma, Ep.: Eptachorion, Ta.: Taliaros, Pf.: Pentalofos s.l. (Pf and Ta) or s.s. (Pf), Tso.: Tsotyli, l. and u. Met.: lower (Pf) and upper (Ts) Meteora. Single and double lines: different formations; broken thick lines: uncertainties; nannoflora biozones 16 to 25 = NP 16 to NP 25, 17 + minimum age (biozone 17 or younger), 1 to 5 = NN1 to
NN5; Foraminifera biozones: P20 and P21 (D). Biozones stratigraphic boundaries and ages from Haq et al. [1987]; new stratigraphical ages from Abreu et
al. [1998] on the right.
FIG. 6. – Âges comparés des formations du MHB d’après les foraminifères (D) ou la nannoflore calcaire. A : Brunn [1956] ; B : carte géologique de la
Grèce au 1:50 000 (voir bibliographie) et Bizon et al. [1968] ; C : Zygojiannis et Müller [1982] ; D : Barbieri [1992] ; E : Doutsos et al. [1994], Zelilidis
et al. [1997, 2002] et Kontopoulos et al. [1999] ; F : cette publication. Abréviations : CN : calcaires nummulitiques, KR : Krania, Riz : Rizoma, Ep :
Eptachorion, Ta : Taliaros, Pf : Pentalofos s.l. (Pf et Ta) ou s.s. (Pf), Tso : Tsotyli, l. et u. Met : Météores inférieur (Pf) et supérieur (Ts). Lignes simples
et doubles : formations ; lignes brisées : indéterminations. Biozones de la nannoflore calcaire 16 à 25 : NP16 à NP25 ; 17+ : âge minimum (biozone 17
ou plus jeune) ; 1 à 5 : NN1 à NN5. Biozones de foraminifères : P20 et P21 (D). Limites stratigraphiques de biozones et âges chronostratigraphiques
d’après Haq et al. [1987]. Nouveaux âges d’Abreu et al. [1998] sur la droite.
erate-rich formations (Pentalofos, Tsotyli) correspond to
remnants of deltaic bodies [Desprairies, 1979] and, especially in the Meteora area, to Gilbert-type, piedmont fan
deltas [Ori and Roveri,1987]. Some other conglomerates
have been attributed by Zelilidis et al. [1997] and
Kontopoulos et al. [1999], to alluvial fans (as those locally
observed at the base of Eptachorion Formation) or shelf
delta deposits (southern parts of the Pentalofos and Tsotyli
Formations). The finest-grained deposits can be related to
prodeltaic domains, gradually passing to the sandstones
(Eptachorion to Taliaros) or interfingered with them (Rizoma).
Even in the most marly, hemipelagic deposits (i.e. upper
Eptachorion near Alatopetra), graded or rippled sandy
laminae still occur, pointing to the permanence of turbiditic
flows at the basin floor. Most of the non-conglomeratic formations have also been interpreted by Kontopoulos et al.
[1999] as inner or outer fans (Krania, Eptachorion, northern
Pentalofos and Tsotyli Formations) but this is partly confusing as fans may occur either on a shelfal epicontinental setting, or at the floor of a deep basin.
Our observations show that most of the southern MHB
deposits are related to deposition along a steep basin profile
characterised by many slope instabilities (slumps, olistolites,
debris flows, mass flows, turbiditic flows) in most of reported lithologies. The maximum impact of slope failure is
recorded in Eocene sandstones of Krania, one of the deepest
– or the deepest – settings (common occurrence of
Zoophycos traces) recorded in the MHB evolution. However, because depositional systems cannot be traced from
tributaries to basin, doubt remains about the permanence of
a true shelf-devoid, steep basin margin profile throughout
the whole MHB evolution. For instance, Eocene Rizoma
sandstones exhibit rather features of very rapid deposition
(floating wood clasts, flames etc..) but no typical sliding.
Sediment sources
The clast petrography and mineralogy of the MHB deposits
designate the proximal borders of the basin as the sources
for sediment supply. The Eocene Krania deposits have a
high ophiolitic content. Ophiolites constitute the bulk of the
basin basement and also most of the mountains that bordered the former Krania basin to the west. To the east, by
contrast, upper Eocene Rizoma deposits are not resting on
ophiolites but on Mesozoic marbles and Paleozoic gneisses
(due to the interplay of the basement “Pelagonian indentor”,
368
J. FERRIÈRE et al.
see below). This lithological contrast is reflected in the
clast composition of the deposits above. Paleocurrent analysis based on clay mineralogy and clasts imbrication, show
that most of the basin fill was sourced in the west before the
late Oligocene and in the east after that time [i.e. Pentalofos
and Tsotyli; Desprairies, 1979]. However, Miocene transport paths may locally be much more complex, especially
because of the northward deepening of the MHB (see
fig. 3).
Syntectonic deposition
Some unconformities at the formation boundaries are the result of major basin deformation, as for example between deposition of Krania and Eptachorion Formations (fig. 5 and
fig. 10). This deformation brings about emersion, as evidenced by the occurrence of reddish conglomerates and
paleosoils above the unconformity in the west of Krania.
Other unconformities only express the depocentre migration
to the east, as evidenced by the contact of Tsotyli Formation onto the pelagonian basement (fig. 5, see also fig. 11).
At the boundary between the lower and the upper part of
Krania Formation, the tectonic imprint is marked by the
presence of olistolithic events associated with paroxysmal
slope failures (fig. 5 and fig. 10). This Eocene tectonic activity is also underlined by the unconformity between these
two parts at the northern border of the Krania basin
(fig. 10).
The first analysis of the large scale formation geometries pointed to synsedimentary polyphased deformation
along folded and/or faulted structures, described as
“faulted-flexures” [Ferrière et al., 1998]. This is the case
for: (i) the northern Krania basin border in the late Eocene,
which controls the development of a large turbiditic
synsedimentary fan and is the source of olistolithic deposition in the basin (fig. 5B and fig. 10); (ii) the TheopetraTheotokos structure bounding the late Eocene Rizoma Formation; this axis was a topographic high in the Oligocene
(conglomerates only on the eastern side), still active and
controlling the fan delta conglomerates of MeteoraPentalofos and Tsotyli in the Miocene (Ft; fig. 5, see also
fig. 11); (iii) the western side of the MHB (locally faulted
Fe flexure; fig. 4, see also fig. 9) at the beginning of
Oligocene, where Eptachorion Formation also exhibits a
rapid decrease of the angle of dip of turbiditic strata, locally
sharply based by scattered reefal limestone build-ups, that
suggests a very sudden sink of depositional areas [Ferrière
et al., 1998].
Subsidence
The subsidence evolution pattern is particularly well expressed in the southern MHB. As described above, subsidence overall migrates to the east. However, this is not a
continuous evolution. In the late Eocene, sedimentation
(Krania and Rizoma sub-basins) takes place on both sides
of the MHB. During the Oligocene and early Miocene, deposition is mainly restricted to the west of the TheopetraTheotokos axis, infilling the basin in an overall west to east
accretion trend but without significant subsidence migration. In the early Miocene, subsidence abruptly shifts to the
east of the MHB (from Pentalofos to Tsotyli Formations;
fig. 5C and fig.8).
Concerning the amount of subsidence and its behaviour
in 3D, the lack of available boreholes, drillholes, and seismic profiles, as well as local erosion within the series and
the fact that turbiditic slope depositional systems are poor
bathymetric indicators, bring about uncertainties. Despite
these uncertainties, some curves based on extrapolated vertical sedimentary records, from outcrops, map-derived
cross-sections and published seismic profiles [Kontopoulos
et al., 1999] are proposed (fig. 7). Because of the overall
eastward migration of the depocentres, the onset of subsidence differs from one area to another. However, some geometrical changes, as at the Eocene-Oligocene boundary
(Krania, fig. 7), or, even, main facies changes, as between
Eptachorion marls and Taliaros-Pentalofos conglomerates
(Alatopetra, fig.7), can be observed on the corresponding
curves. The two subsidence curves proposed by
Kontopoulos et al. [1999] evidence an uplift stage during
Pentalofos sedimentation, from 21 to 16 Ma, but they are
FIG. 7. – Subsidence curves concerning the central part of the MHB (1:
Alatopetra, 2: Grevena and 3: Krania series), from our field and seismic
published data. Abbreviations: Ep: Eptachorion Formation, P: Pentalofon
Formation, Ts: Tsotyli Formation. Approximations on the subsidence calculations are related to some age (see fig. 6) or formation thicknesses uncertainties, and mainly to paleobathymetric data, particularly for deep
water facies (i.e. turbidites). Backstripping has been computed with
SUBSILOG [Dubois et al.., 2000], using the standard parameters defined
by Sclater and Christie [1980]. Grey area (c.35-33 Ma) corresponds to the
main compressional episode.
FIG. 7. – Courbes de subsidence pour la partie centrale du MHB (1 : Alatopetra, 2 : Grevena, 3 : Krania), d’après nos données et les profils sismiques publiés. Abréviations : Ep : formation d’Eptachorion, P : formation
de Pentalofon, Ts : formation de Tsotyli. Des approximations sur le calcul
de la subsidence sont liées aux incertitudes sur les âges (voir fig. 6), sur
l’épaisseur des séries ou sur les estimations paléobathymétriques, particulièrement pour les faciès profonds. La restauration verticale des séries a
été réalisée à l’aide du logiciel SUBSILOG [Dubois et al., 2000], utilisant
les paramètres standards de Sclater et Christie [1980]. Les zones en grisé
(35-33 Ma) correspondent à l’épisode compressif principal.
369
match areas of drastic facies changes and follow tectonic
structures (as at the Krania sub-basin northern limit,
fig. 5B). For instance, the major geographic gap between
Pentalofos and Tsotyli Formations (fig. 3 and fig. 5, see
also fig. 11), follows the Theopetra-Theotokos structure, although no major facies change occurs at the boundary between these two conglomeratic formations in this area. By
contrast, the main lithologic changes from Eptachorion
marls to Pentalofos conglomerates are not associated to major changes in basin limits. Thus, an eustatic sea-level fall
[Haq et al., 1987; Abreu and Haddad 1998] could be partly
responsible for this evolution. However, tectonic movements also exist, notably uplifts evidenced by the development of Gilbert-deltas, as in the Meteora area. Zelilidis et
al., [2002] argues that all 'the stratigraphic occurrence of
lowstand facies compares closely with published eustatic
sea-level curves’.. We consider that this apparent correlation remains more than questionnable, because (i) there is
no accurate biostratigraphic control and (ii) the required
tectonic calendar is not considered, although the authors admit the existence of syntectonic sedimentation and major
tectonic contacts.
TECTONICS
General view
FIG. 8. – Paleogeographic synthesis of possible basin and sub-basins extension at different stages of MHB evolution. The limits here minimise the
depositional areas (e.g. we could not exclude a possible connection of the
sea between Krania and Rizoma in the upper Eocene, especially along the
tectonic structures bounding the Pelagonian Indentor). Abbreviations: see
figure 3.
FIG. 8. – Reconstitution paléogéographique des bassins et sous-bassins et
de leur extension aux différentes étapes de l’évolution du MHB. Les limites
minimisent les aires de dépôt (par exemple on ne peut exclure une
connexion possible entre les sous-bassins de Krania et Rizoma à l’Eocène
supérieur, particulièrement le long des structures tectoniques du poinçon
pélagonien). Abréviations : voir figure 3.
only representative of the axis of the present MHB (areas of
maximum residual thicknesses). The general pattern of the
migration of MHB depocentres and associated subsidence is
synthesized by the map in figure 8 (see also schematic
curves fig. 13).
Paleogeography
The paleogeographical sketch (fig. 8) is based on subsidence but also lateral and vertical facies variations. The frequent absence of shoreline deposits and possible erosion
brings about uncertainties concerning the true extension of
the basin limits through time. Therefore, the proposed limits minimise the marine depositional area extension: i.e., the
Rizoma and Krania sub-basins probably respectively extended to the north and to the east along the tectonic structures of the Pelagonian Indentor, but they were partly
eroded at the Eocene-Oligocene boundary. These limits
In cross-section, the MHB is an asymmetrical syncline, the
western flank of which is steeper than the eastern one. A
few vertical or nearly overturned strata are even observed at
its western boundary (Fk on D or Fe on E fig. 4, fig. 9 and
fig. 10) or at the eastern border of the Theopetra-Theotokos
structure (TTS, see below) (B on fig. 4 and fig. 11). To the
south, the main syncline splits into two narrow synclines
separated by this structural high (TTS), expressed as an
anticline (At) faulted (Ft) on its eastern border (fig. 9 and
fig. 11). Relationships observed between sedimentary and
tectonic features (olistoliths; progressive variations of strata
dips, as shown inside Eptachorion Formation near
Alatopetra; angular unconformities) show that the syncline
folding is mostly coeval to basin infilling, lasting even well
after marine retreat, as demonstrated by the folding of the
last middle Miocene deposits south of Rizoma (fig. 11 and
fig. 12).
Normal faults of metric to hectometric offset, mostly directed sub-parallel to the basin axis, are common in all formations (fig.4), and important ones follow the basin borders
(Vourinos and Koziakas, fig. 3 and 4). Some large scale normal faults were identified from seismic lines within the basin
[Kontopoulos et al.., 1999]. Some of these normal faults are
certainly of Plio-Quaternary ages [Aubouin, 1956]. Most of
large scale complex fault zones have experienced several
motions, including normal faulting prior to some compressional deformation. They appear now as subvertical or
even slightly reversed faults (e.g. Ft at the eastern border of
the TTS, fig. 4, fig. 11 and fig. 12). Large faults transverse to
the basin axis, as reported on the 1: 500,000 maps [Bornovas
and Rondogianni-Tsiambaou, 1983] are also common. Some
of them linked to deep transverse structures of the MHB basement appear to have had a control on the Eocene sub-basins
organisation (i.e. southern and northern borders of Krania
sub-basin).
370
J. FERRIÈRE et al.
FIG. 9. – Synthetic structural map of the Greek part of the MHB and internal zones of Hellenides. Note the coincidence between the Pelagonian Indentor
(double thin lines bounded by double dashed lines for the northern flexure), the Theopetra-Theotokos structure (TTS=At+Ft) and the Rizoma elongated
subbasin (1B) on the west; and the structural saddle of Kozani (S.4) and Krania sub-basin on the north-west. Abbreviations: S.1 to S.4: synclines; Af: Filippi anticline, At: Theopetra-Theotokos anticline or structural high ; Fk, Fe and Ft: faulted-flexures of Krania, Eptachorion and Theopetra. Enclosed map:
1 to 7: sites of tectonic data reported from stereograms. a (1 to 3): compression observed in late Eocene formations (1: Monachiti, 2: Krania and 3: Rizoma
areas); b (4 to 7): extension observed in the different formations (4: Eptachorion, 5: Krania-Grevena, 6: West Vourinos and 7: Meteora-Theotokos areas);
aD (compression) and bD (extension) from Doutsos et al. [1994].
FIG. 9. – Carte structurale synthétique de la partie grecque du MHB et des zones internes des Hellénides. Noter la coincidence entre, d’une part, le poinçon pélagonien (ligne double limitée par ligne pointillée double pour la flexure nord), la structure de Theopetra-Theotokos (TTS=At+Ft) et le sous-bassin
allongé de Rizoma (1B) à l’ouest, et, d’autre part, l’ensellement de Kozani (S4) et le sous-bassin de Krania au nord-ouest. Abréviations : S1 à S4 : synclinaux, Af : anticlinal de Filippi, At : anticlinal de Theopetra-Theotokos (ou haut structural), Fk, Fe et Ft : flexures faillées de Krania, Eptachorion et
Theopetra. Carte en insert : 1 à 7 : sites de mesure des données reportées dans les stéréogrammes. a (1 à 3) : compression observée dans les formations
de l’Eocène supérieur (1 : Monachiti, 2 : Krania et 3 : Rizoma) ; b : (4 à 7) : extension observée dans différentes formations (4 : Eptachorion, 5 : KraniaGrevena, 6 : Vourinos-ouest et 7 : Météores-Theotokos) ; aD (compression) et bD (extension) d’après Doutsos et al. [1994].
While a lot of microtectonic data concerning the MHB
have been published by Doutsos et al. [1994], the chronology and causality of these deformations are still not well established. Our results show that micro- and meso-structures
are different within late Eocene and Oligo-Miocene formations (fig. 9).
Oligo-Miocene formations
Metric to decametric mostly longitudinal conjugate normal
faults dominate, part of them being post-depositional. A
few are coeval to deposition (as in the north of Theotokos in
the Oligocene). The main direction of σ3 axis is overall perpendicular to the main basin direction (fig. 9). Hectometric
open folds are also present in the vicinity of major
polyphased tectonic structures, mainly affecting Miocene
strata, such as for example between Theotokos and
Asproklissia in Tsotyli Formation (fig. 4C) or to the south
of Rizoma in Ondria Formation (FF’; fig. 12).
Upper Eocene formations
In addition to the features described above, well-expressed
compressional structures are present, thus, related to an
Eocene-Oligocene boundary folding episode. These
compressional structures are mainly metric to decametric
reverse faults and small folds associated or not with slight
cleavage. In Krania and Mylia (SW of Krania) series, these
deformations are pervasive, coupled with decametric thrusts
towards the east (fig. 4D). The main stress axis (σ1) deduced from field data (fig. 9) is generally about NE-SW,
subperpendicular to the MHB elongation. The Monachiti
371
FIG. 10. – Geologic map and cross-section of the northern border of Krania sub-basin (Monachiti transverse structure); see figure 3 for location. 1: ophiolitic basement (v: peridotites, dots: lavas), 2: upper Cretaceous limestones, 3: upper Eocene, lower series within (3a) and beyond (3b-3c) the northern subbasin limits, 3a: turbiditic shales and sandstones (flysch) on basal breccias and conglomerates, 3b: fine grained sandy bay deposits, 3c: well rounded conglomerates; 4: large olistostromes with a breccia matrix (main blocks: black triangles), 5: pluridecametric, massive or little brecciated olistoliths; 6: upper
series (late Eocene); turbidites (flysch) above thick sandstones (dashed lines); 7: early Oligocene (latest Eocene?) conglomerates and sandstones. S (S1,
S1b, S2): surfaces indicating major tectonic events; D: angular unconformities (see also fig. 5). Vertical and horizontal scales are similar (no vertical
exaggeration, v.e.=1).
FIG. 10. – Carte géologique et coupe de la bordure nord du sous-bassin de Krania (structure transverse de Monachiti) ; voir figure 3 pour localisation.
1 : soubassement ophiolitique (v : péridotites, pointillés : laves) ; 2 : calcaires du Crétacé supérieur ; 3 : Eocène supérieur, séries inférieures au sein du
sous-bassin (3a) et à l’extérieur de celui-ci (3b-3c) : 3a : shales et grès turbiditiques (flysch) reposant sur brèches et conglomérats de base, 3b : dépôts
fins de baie, 3c : poudingues ; 4 : grands olistostromes à matrice bréchique (blocs principaux : triangles) ; 5 : olistolites décamétriques, massifs ou faiblement bréchifiés ; 6 : conglomérats et grès des séries supérieures (Eocène terminal ?). S (S1, S1b, S2) : surfaces indiquant des événements tectoniques
majeurs ; D : discordances angulaires (voir également fig. 5). Les échelles verticales et horizontales sont identiques (pas d’exagération verticale).
structure, as well as other transverse structures (E-W to NESW) might have had some strike-slip activity, especially at
the Eocene-Oligocene boundary, but no clear evidence of
such significant strike-slip motion could be evidenced from
field analysis. Longitudinal basin-scale strike-slip faults
(NNW-SSE) have been proposed by Zelilidis et al. [2002],
based on some microtectonic data [Doutsos et al, 1994] and
interpretations of a few seismic lines. Still, these authors do
not provide any precision about the importance of the displacements implied nor about their chronology. Moreover,
such large longitudinal strike-slip faults could not be observed from field analysis: for example, the contact between
372
J. FERRIÈRE et al.
FIG. 11. – Geologic map of the southern area of the MHB (Meteora). 1: Paleozoic gneisses and schists (Pz), 2: Triassic-Jurassic marbles (TJ, on the east)
and upper Cretaceous(UK) limestones of the Theopetra anticline (At), 3: ophiolites, 4: Middle Eocene clastic limestones overlain by upper Eocene finegrained turbidites (unifites) or deltaic sandstones (Rizoma sub-basin), 5: Oligocene conglomerates, sandstones and marls (Eptachorion Formation), 6: Lower Meteora conglomerates (Pentalofos Formation), 7: Upper Meteora conglomerates (Tsotyli Formation). 8 and 9: Miocene Ondria Formation: Echinidrich limestones (8), sandstones and Globigerinidae marls (9), 10: Quaternary and recent deposits. See figure 12 for cross-sections F to H.
FIG. 11. – Carte géologique de la partie méridionale du MHB (Météores). 1 : gneiss et schistes paléozoïques (Pz) ; 2 : marbres du Trias-Jurassique (TJ,
à l’Est) et calcaires du Crétacé supérieur (UK) de l’anticlinal de Theopetra (At) ; 3 : ophiolites ; 4 : calcaires clastiques de l’Eocène moyen, surmontés
par des turbidites fines ou des grès deltaïques de l’Eocène supérieur (sous-bassin de Rizoma) ; 5 : conglomérats, grès et marnes de l’Oligocène (formation d’Eptachorion) ; 6 : conglomérats inférieurs des Météores (formation de Pentalofos) ; 7 : conglomérats supérieurs des Météores (formation de Tsotyli) ; 8 et 9 : formation miocène d’Ondria : calcaires à oursins (8), grès et marnes à globigérines (9) ; 10 : dépôts quaternaires. Voir figure 12 pour les
coupes F à H.
Eptachorion and Pentalofos Formations supposed to be a
major strike-slip fault [Zelilidis et al., 2002], is clearly
stratigraphic at all localities where it could be observed.
Tectonic structures of the western basin border
The western border of the elongated MHB is basically an
Oligocene flexure, the eastern flank of which is collapsed,
and may locally be defined by reverse faults (Fe, fig. 4 and
fig. 9). North of the Krania sub-basin, the basal Oligocene
deposits onlap the Filippi anticline, an elongated window of
Pindos Eocene flysch below the overthrusted ophiolites
(fig. 4E and Af fig. 9). Because of the characteristics of the
Oligocene strata on the eastern side of the Filippi anticline
(quick deepening of the facies, progressive changes of the
dippings), the growth of this fold is thought to have lasted
during Oligocene. South of Krania, Oligocene strata dip
less, but still rest either onto ophiolites, Pindos flysch or
Koziakas series (bringing about a pre-Oligocene and postLutetian age for the Internal thrust zone and the E-W
Kastaniotikos transverse flexure; fig. 9).
The upper Eocene Krania sediments form a complex
perisyncline termination, which was mainly active during
the late Eocene (see above and fig. 10). It is bounded to the
south by transverse (approximately E-W) faults, and to the
west by a subvertical flexure, locally reverse and faulted
(Fk, fig. 10). East-verging tectonic structures, mostly
decametric reverse faults, are numerous in the Krania subBull. Soc. géol. Fr., 2004, no 4
basin fill, especially near Mylia (SW of Krania) or
Microlivadon (fig. 4D and fig. 10). They are related to the
main compressive phase (at the end of Eocene). To the
north, the Krania sub-basin is bounded by a large WSWENE flexure, the Monachiti-Trikomo structure (MTS), active at least during the late Eocene because: (i) sediments of
this age are different on both sides of the MTS; (ii) the middle Krania sandstones (S1b, fig. 5B and fig. 10) rest unconformably on the northern side of the MTS, source of the
hectometric olistoliths and olistolithic channel-fills of the
Krania sub-basin; (iii) Oligocene strata of the MHB truncate the uppermost, subvertical upper Eocene turbiditic
sandstone strata of the Krania sub-basin onto the southern
flank of the MTS. As the Oligocene transgression proceeded, the northern side of the MTS was probably still
high, as indicated by the presence, exclusively on its southern side, of Oligocene conglomeratic alluvial fans, pointing
to southward paleoflows (fig. 10).
The geometry of the northern boundary of the Krania
sub-basin suggests that the MTS could have developed as a
WSW-ENE dextral strike-slip fault, as already suggested by
Papanikolaou et al. [1988] and admitted by Zelilidis et al.,
[2002]. This remains to be demonstrated as there are no
equivalent structural patterns on both sides of this structure
(fig. 10) and if horizontal slickensides exist, they are rare.
The compressive stresses observed in the Krania sub-basin
(σ1 approximately SW-NE, fig. 9) are able to trigger a
373
FIG. 12. – Cross-sections of the MHB southern area (see fig. 11 for location). 1: Paleozoic gneisses and schists (Pz), 2: Triassic-Jurassic marbles (TJ), 3:
ophiolites, 4: Cretaceous limestones, 5: Upper Lutetian-Bartonian p.p. clastic limestones (above Theopetra Cretaceous rocks and at the base of Rizoma
sub-basin), 6: Upper Eocene fine-grained turbidites (unifites) and deltaic sandstones (Rizoma sub-basin), 7: Oligocene conglomerates, sandstones and
marls (Eptachorion Formation), 8: Lower Meteora conglomerates (Pentalofos Formation), 9: Upper Meteora conglomerates (Tsotyli Formation). 10 and
11: Miocene Ondria Formation with Echinid-rich limestones (10), sandstones and Globigerinidae marls (11). TTS: Theopetra-Theotokos structure. Vertical and horizontal scales are similar (no vertical exaggeration: v.e.=1).
FIG. 12. – Coupes de la partie méridionale du MHB (voir fig. 11 pour la localisation). 1 : gneiss et schistes paléozoïques (Pz) ; 2 : marbres du Trias-Jurassique (TJ) ; 3 : ophiolites ; 4 : calcaires du Crétacé ; 5 : calcaires clastiques du Lutétien supérieur-Bartonien p.p. (surmontant le Crétacé de Théopetra et à la base des séries du sous-bassin de Rizoma) ; 6 : turbidites fines et grès deltaïques de l’Eocène supérieur (sous-bassin de Rizoma) ; 7 :
conglomérats, grès et marnes de l’Oligocène (formation d’Eptachorion) ; 8 : conglomérats inférieurs des Météores (formation de Pentalofos) ; 9 : conglomérats supérieurs des Météores (formation de Tsotyli) ; 10 et 11 : formation miocène d’Ondria avec calcaires à oursins (10), grès et marnes à globigérines (11). TTS : structure de Theopetra-Theotokos. Les échelles verticales et horizontales sont identiques (pas d’exagération verticale).
strike-slip displacement along this WSW-ENE structure.
However, the direction of the main observed decametric
fold (near Trikomo), subparallel to the MTS, argue in favour of a large WSW-ENE directed flexure (fig. 10) responsible for the N-S steep depositional profile (from bay-fill to
more southern basin floor-fan, via canyon-fills and large
slumps).
The Theopetra-Theotokos tectonic structure (median
MHB)
Deposits on both sides of this newly defined TheopetraTheotokos tectonic structure (TTS fig. 9, fig. 11 and
fig. 12) are mostly of different ages (fig. 1, fig. 5 and
fig. 9). The TTS, well expressed in the southern MHB area,
corresponds to a NNW-SSE anticline (At), the eastern flank
of which is bounded by a main fault (Ft). This fault is a major basement boundary as ophiolites appear mainly west of
the fault.
The TTS has controlled deposition in the southern basin
from Eocene to Miocene times (fig. 5C and fig. 12). (i) De-
position of the upper Eocene Rizoma deltaic and prodeltaic
systems was restricted to the east of this structure. If they
ever existed to the west, their total erosion suggests they
had to be very thin compared to the 200-300 m thick deposits in the Rizoma sub-basin (fig. 11 and fig. 12). (ii) During
the Oligocene (Eptachorion Formation), the structure still
existed as a morphological step, as demonstrated by the
presence of conglomeratic alluvial-fans along the footwall
of its eastern side and correlative fine-grained turbidites deposits onlaping the western flank of the structure (see H in
fig. 12). (iii) In the Miocene, the lower Meteora conglomerates (Pentalofos Formation) developed only on the western
side of this structure. The tilting towards the west of the
substrate of Pentalofos Formation is responsible for the sudden reversal of sediment sources from west to east and, for
the internal architecture of these conglomerate fan deltas
(fig. 12). In the same way, due to the interplay of the TTS,
Tsotyli series are restricted to the east of this structure
(fig. 11).
The TTS area is also affected by a NE-SW compression
at the Eocene/Oligocene boundary, characterised by reverse
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J. FERRIÈRE et al.
faulting towards the NE or ENE in the upper Eocene
Rizoma sediments, unconformably covered by nearly horizontal Oligocene strata (fig. 12). Many reverse faults (dipping 60° to the west) recorded in the Cretaceous limestones
are probably linked to the same compressive event, as these
faults are mainly located near the main fault (Ft).
sin remnant on an active marine margin. The pattern of subsidence, in that case, should be constrainable by mechanical
parameters of the subducting crust (thickness, temperature,
angle of subducting slab). However, the boundaries of
Krania and Rizoma basins are still controlled by structures
of the upper unit at this time (flexures at the edges of the
Pelagonian Indentor) (stages A, B fig. 14A and fig. 14B).
The Pelagonian Indentor (eastern MHB)
The Pelagonian Indentor (PI), displaying a main control on
the MHB evolution, is here described for the first time
(fig. 9). It corresponds to an elongated Pelagonian block
transverse to the MHB. It is bounded to the east by the
Aegean fault (between Olympos and Thermaikos Gulf), to
the west by the TTS and late Eocene Rizoma outcrops, to the
south by Larissa and Trikkala subsiding areas, and to the
north by the NE-SW saddle of Kozani-Krania [Kozani
straight of Brunn, 1956; Kozani saddle of Aubouin, 1959],
where some remnants of the Vermion nappe and Vourinos
ophiolites are preserved (fig. 1 and fig. 9). The narrowest
section of the MHB occurs in front of the PI, in the Meteora
sector. The upper Eocene sub-basins of Krania and Rizoma
develop and/or are preserved at its margins (Krania sub-basin
in the axis of the Kozani saddle, Rizoma sub-basin along the
TTS and the PI; fig. 9). The deformation around the PI extends far into the external zones, as series preserved in
Pindos and Gavrovo zones right to the west of the saddle of
Kozani-Krania are younger (Eocene flysch) than external series (mainly Mesozoic sediments) preserved to the south of
the Kastaniotikos transverse structure in front of the PI
(fig. 9). Several hypothesis may explain the high elevation of
the PI regarding to surrounding areas: i) the location beneath
the PI of a thick crustal body subducted from the west of the
Pelagonian margin, before (or during) the Lutetian; ii) a coeval tectonic phase that would have been purely transverse,
as the Cenozoic ones (before Lutetian p.p.) described in
these parts of the internal zones [Ferrière, 1982].
BASIN INTERPRETATION
Our new data show that the piggyback MHB evolution is
mainly controlled by geodynamic processes and that
eustatic controls are of relatively minor importance. The
main trends (depth variations, existence and nature of tectonic episodes, amount of subsidence) are interpreted to result from the behaviour of the underthrusted unit (i.e:
thickness of the crust) while the detailed sedimentological
organisation and architecture depend on the tectonic structures of the upper unit. The eustatic sea-level changes have
a weaker control than tectonics on the basin evolution
(fig. 13, fig. 14 and fig. 15).
Opening: from subduction to collision
Late Lutetian-late Eocene: Pindos subduction
Sedimentation in Krania and Rizoma sub-basins takes place
during the onset of convergence and related Pindos
subduction, responsible for the development of an
accretionary prism below the ophiolitic-pelagonian upper
unit (A, B, fig. 15). Because it originated at the back of a
rising accretionary prism, the deep sub-basin of Krania, and
the sub-basin of Rizoma, may be considered as a forearc baBull. Soc. géol. Fr., 2004, no 4
Eocene-Oligocene transition: Gavrovo-Tripolitsa collision
The Eocene-Oligocene transition corresponds to a major angular unconformity, especially near large tectonic structures
(e.g. Monachiti, fig. 10 and Theopetra, Ft in fig. 11). This is
the period of maximum compressional deformation (eastward verging reverse faults in Krania-Mylia and TheopetraAvra areas, folding and slight cleavage). These features are
consistent with the continuing rise of the Pindos
accretionary prism, opening the main flysch windows below the ophiolitic nappes (fig. 4 E), and leading to the
emersion of the Krania sub-basin (stage C fig. 14A), as evidenced by reddish conglomerates at the unconformity. We
consider that these events are the results of the arrival in the
subduction zone of the Gavrovo-Tripolitsa platform unit (C
fig. 15). The collision seems obvious, even though the
Gavrovo-Tripolitsa crust may have been slightly thinner
than a normal continental crust, as suggested by its continuous subsidence during the Mesozoic and early Paleogene
[Aubouin, 1959]. From this hypothesis it appears that the
time required for the subduction of the whole Pindos basin
is about 10 Ma (45-43 Ma to 35-33 Ma). The width of the
Pindos zone, 300 to 600 km in the northern Hellenides, is
deduced from i) mapping of the isopic zones (fig. 1), ii) the
amount of tectonic shortening estimated from outcrops and
reconstructed cross-sections, and iii) the estimated extension rate of this continental [Thiebault, 1982] or oceanic basin crust [Bonneau, 1982]. These approximate values give
an average Pindos subduction rate of about 3 to 6 cm/year,
that is consistent for such basins.
Eptachorion stage (Oligocene p.p.): underthrusting of the
Gavrovo-Tripolitsa unit
The fine-grained Eptachorion Formation is characterized by
a very strong tectonic subsidence, marked by
synsedimentary normal faults and the onlap of relatively
deep turbiditic facies against sub-aerial to shallow marine
basal conglomerates or reef limestones due to a sharp steepening of depositional profiles. At the same time, the former
Pindos accretionary prism and anticlines keep rising, as
demonstrated by the syntectonic fans recorded in the lower
part of turbiditic deposits. Such a strong subsidence in the
course of the major underthrusting of a thick crust has to be
explained. As the MHB evolves into a major NNW-SSE
marine trough, the process is necessarily at the scale of the
whole margin. The presence of thick dense ophiolitic bodies
west of the Pelagonian unit, forming the basement of the
MHB, as in Albania [Robertson and Shallo, 2000] could
partly control the location of the main subsiding areas.
However, the NNW-SSE direction of the new Oligo-Miocene elongated MHB trough, parallel to the Hellenic front
thrust and to the external zones, argue for a main control by
the external underthrusted units. Delamination at the base
(basal tectonic erosion) of the Pelagonian upper unit beneath the basin (fig. 15D) due to the passing through of the
375
FIG. 13. – Synthesis of MHB stages of evolution. Left: tectonic context, right: eustatic curves [from Haq et al., 1987 and Abreu and Haddad, 1998], bottom: subsidence through time from 1a as early Lutetian. Tp and Tt: local transpression or transtension. See text for discussion.
FIG. 13. – Schéma synthétique résumant l’évolution du MHB. A gauche : contexte tectonique ; à droite : courbes eustatiques [d’après Haq et al., 1987 et
Abreu et Haddad, 1998] ; en bas : évolution de la subsidence au cours du temps depuis le stade 1a : début du Lutétien. Tp et Tt : transpression ou transtension locale. Voir le texte pour discussion.
Gavrovo-Tripolitsa thick platform is here proposed to explain some subsidence processes (C, D fig. 15).
the most recent charts edited for the European basins
[Abreu and Haddad, 1998] (fig. 13).
Closure: from collision to underplating
This basin stage, starting with Pentalofos Formation, is
mainly controlled by uplift of the domain east of the MHB
which becomes the main drainage area (E fig. 15). The high
sedimentation rate (maybe the first time in the basin evolution that sedimentation may take subsidence over) associated with conglomeratic deposition of Pentalofos leads to
rapid overfilling of the basin west of the TTS (stage E
fig. 14B). The subsidence jump to the east (Tsotyli Formation) across this Theopetra-Theotokos structure is interpreted as the eastward progression of the process of
delamination beneath the basin, coupled with an increasing
uplift rate (because of underplating) in the hinterland.
These eastward migration of subsidence and uplifted areas
give probably rise to major normal faults well-expressed in
the MHB. The basin closure is linked to the general uplift
of the MHB area possibly emphasized by the sea-level fall
known in the mid-late Miocene [Abreu and Haddad, 1998].
Flexuration (south-east of Rizoma) and folding (east of
Theotokos) last during and/or after basin closure, due to a
renewed tectonic activity at the eastern side of the basin before the Plio-Quaternary normal faulting well-known in this
part of the Hellenides [Aubouin, 1959; Mercier et al.,
1989].
Taliaros-Pentalofos-Tsotyli stage (latest Oligocene-middle
Miocene)
The transition between the Eptachorion (turbidites and
marls) and Taliaros (deltas) Formations locally gradational
(as observed near Alatopetra), reflects an overall
progradation trend during the Oligo-Miocene times.
Whereas conglomerates of Pentalofos overlie Taliaros deltas in the northern MHB, they directly truncate Eptachorion
turbidites in the south. The onset of conglomeratic fan-deltas, that dominate deposition during the late Oligoceneearly Miocene times is partly due to the tectonic activity.
This is demonstrated by the reactivation of existing tectonic
structures at the time of Pentalofos Formation deposition
(movements along the Theopetra-Theotokos Structure) and
deposition of Gilbert-deltas (as the Pentalofos conglomerates in the Meteora area), that implies progradation on a
steep basin slope (stage E fig. 14A, B). The additional imprint of the Rupelian-Chattian eustatic sea-level fall [Haq et
al., 1987] could explain this sharp Eptachorion-Pentalofos
boundary, but this event seems less prominent on some of
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J. FERRIÈRE et al.
FIG. 14A. – Main stages of MHB evolution from Pindos subduction (upper Eocene) to collision (from Oligocene), Krania-Vourinos section (central
MHB). See text for explanations.
FIG. 14A. – Etapes principales de l’évolution du MHB depuis la subduction du Pinde (Eocène supérieur) jusqu’à la collision (depuis l’Oligocène), coupe
dans la partie centrale du bassin (Krania-Vourinos). Voir explications dans le texte.
377
FIG. 14B. – Main stages of MHB evolution from Pindos subduction (upper Eocene) to collision (from Oligocene), Koziakas-Meteora-Rizoma section
(southern MHB). Vertical and horizontal scales are similar. See text for explanations.
FIG. 14B. – Etapes principales de l’évolution du MHB depuis la subduction du Pinde (Eocène supérieur) jusqu’à la collision (depuis l’Oligocène), coupe
méridionale (Koziakas-Météores-Rizoma). Les échelles verticales et horizontales sont identiques (pas d’exagération verticale). Voir explications dans le
texte.
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J. FERRIÈRE et al.
FIG. 15. – Tertiary geodynamic evolution from Gavrovo-Pindos external zones to eastern Olympos – Vardar/Thermaikos areas and MHB evolution. See
text for detailed discussion on mechanisms. Note that basal tectonic erosion could be partly responsible for subsidence from stages C to D.
FIG. 15. – Evolution géodynamique des Hellénides au Cénozoïque, depuis les zones externes du Gavrovo-Pinde à l’ouest jusqu’aux zones internes du Vardar-Thermaïque à l’est, en relation avec l’évolution du MHB. Noter que l’érosion tectonique pourrait être responsable de la subsidence dans les étapes C
à D.
Olympos rise (after Miocene times)
The uplift of the domain east of the MHB is thought to be
linked to the underplating of basal Pelagonian material and
deep tectonic ramps and duplex caused by locking to the
east of the underthrusted units, probably against the Aegean
fault and block (F fig. 15). The rise of the Olympos area
(50 km east of the MHB) would reflect the piling up of such
duplexes. Metamorphic rocks cropping out in the Olympos
windows have been analysed, mainly from fission tracks.
The results about the Olympos units, excluding the
Ambelakia series (they are not demonstrated to belong either to the internal or external zones), published by
Schermer et al. [1989], Kilias et al. [1991] and Schermer
[1993], do not disagree with the general trend of the tectonic calendar proposed from our MHB study (fig. 15) : i)
42-36 Ma: blueschists; ii) 36-25 Ma: open folds; iii) 23-16
Ma: low-angle normal faults; iv) open folds and high-angle
normal faults.
Our model states the progression of underthrusting as
far as a backstop exists (for instance the Aegean faultblock). It is thus expected that this migration may have a
similar impact on basin generation further east from the
MHB. The development of the Ptolemaïs basin, by its shape
(elongated NNW-SSE trough), age (mainly upper MiocenePliocene), depositional environments (continental) and location on the western side of a main (Olympos) uplift, supports this idea.
SUMMARY AND CONCLUSIONS
Numerous large-scale complex, polyphased structures affect the southern MHB. These features show that deposition
is largely syntectonic, as expected for a piggyback basin.
This is supported by the basin fill nature and stratigraphic
organisation. The following results may be highlighted.
1) Important tectonic structures influenced the basin
evolution. These are either transverse structures, which control upper Eocene depositional areas (i.e. the northern border of the Krania sub-basin), or major structures parallel to
the NNW-SSE basin axis (here named faulted-flexures), active during the main tectonic phases, especially at the
Eocene-Oligocene boundary. These latter structures, as the
Theopetra-Theotokos structure, reactivated during the Miocene, controls the Meteora system. These different structures are mainly linked to major heterogeneities within the
Pelagonian basement, the main one is described here as the
Pelagonian Indentor.
2) Several phases of basin evolution are distinguished.
During the late Eocene (lasting ca. 10 Ma), scattered, possibly deep depocentres evolve as Pindos (thin, probably oceanic, crust) subduction proceeds. A brief episode of major
compression follows (lasting 2-3 Ma), as the GavrovoTripolitsa (thicker crust) collides the Pelagonian basement
of the MHB. This brings about reverse faulting and
emersion of the western Pelagonian margin. During the
underthrusting of Gavrovo zone beneath the Pelagonian
unit, from Oligocene to mid-Miocene (ca. 20 Ma), the MHB
evolves, parallel (NNW-SSE) to the main thrusts and external zones, which are thus considered as the main control
factor on the basin shape. Tectonic erosion at the base of
the Pelagonian unit, migrating in the same direction as
underthrusting, may control subsidence at that time. The
379
overall coarsening of deposits from Oligocene (Eptachorion
Formation) to Miocene (Pentalofos Formation) is related to
the continuing uplift of the basin borders, mainly on the
eastern side, due to the formation of tectonic ramps in the
underthrusted complex. Numerous normal faults appear as
subsidence and adjacent uplifts work and migrate to the
east.
3) Our results are consistent with those expected from a
piggyback basin (this latter point being demonstrated by the
presence of external Hellenides in the Olympos window).
They do not support the hypothesis of a retroarc type basin
[Doutsos et al., 1993], because the observed reverse faults
towards the east at the western basin boundary are nearly
vertical or of limited extension, and mainly active during a
very short period of time (Eocene/Oligocene boundary). In
the same way, our observations do not support the hypothesis that the MHB could be a “strike-slip half graben”
[Zelilidis et al.] as no any major NNW-SSE strike-slip
faults have been recognised, especially in the areas where
such faults are drawn by these authors.
Some of our results may have a general significance for
large-scale piggyback basins.
a) Multi-scale facies and stratal architecture are
mainly controlled by tectonics. – Many observed sedimentary features (as olistoliths and slumps) within the MHB are
the consequence of tectonic events (from elementary seisms
to main uplifts inducing gravity slides). Because tectonics
is active, depositional systems are not graded to their equilibrium profiles. For instance, there is a general lack of
shelfal deposits but presence of Gilbert deltas. This does
not rule out the possible impact of eustatic changes on local
stratal patterns. A sea-level rise could have emphasized the
Oligocene transgression within the MHB area, and a sea-level
fall during mid-Oligocene times could partly explain the transition from Eptachorion marls to Pentalofos conglomerates.
However, main tectonic controls (compressional or
extensional events, vertical motions, folding) are clearly demonstrated for each main change within the MHB; thus eustatic
controls are considered to have weaker effects than tectonic
ones.
b) Both units, above and below the main thrust, successively control subsidence within the piggyback basin. – Before collision, dense ophiolitic basement and large structural
heterogeneities of the Pelagonian crust (upper unit) controlled the basin subsidence (location of Krania and Rizoma
sub-basins linked to the presence of a major Pelagonian uplifted structure, here named the “Pelagonian Indentor”). The
development of subsidence during the collision process, is
more difficult to explain. Because the Oligo-Miocene MHB
becomes a large basin parallel to the thrust front and to the
external zones, it seems to be mainly controlled by the
NNW-SSE elongated units underthrusted below the
Pelagonian crust. Basal tectonic erosion of the upper unit
and tectonic load (duplexes) on the lower one have been
considered to explain the development and migration of this
Oligo-Miocene subsidence.
c) Subsidence migrates. – As in foreland basins, subsidence migrates as thrusting progresses. Foreland basins are
developing in front of the main thrusts and subsidence migrates in the same direction as thrusting. On the contrary,
large piggyback basins, as the MHB, develop on top of the
main thrusting unit and subsidence migrates in the opposite
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J. FERRIÈRE et al.
direction of the thrusting motion. This emphasizes the major role of the underthrusting unit (“subducting” slab) on
the development of this type of basin. However, this general
behaviour is still to be demonstrated for piggyback basins
from other case studies.
d) Basin closure is mainly related to underplating. –
Just before the final basin closure (calcareous, marly
Ondrias-Orlias Formations), coarse grained deposition
(Pentalofos and pro parte Tsotyli formations) is related to
the development of tectonic ramps beneath and beside the
basin (mainly on the eastern side of the MHB) which leads
to the steepening of proximal depositional profiles. The basin remained below sea-level most of the time, due to the
interplay of a strong subsidence, but the overall regressive
trend linked to underplating, maybe emphasized by a sealevel fall, leads to the final emersion before or during late
Miocene.
Finally, the MHB seems a good example for reevaluating the relative importance of piggyback basins in convergent settings. The Hellenic chain records a continuum of
tectonics versus sedimentation processes from an early
subduction to an established collision, and only two well
expressed basin systems are recorded: the first one is equivalent to a deep forearc, and the second one to a true piggyback (the latter being more important in its volume and
stratigraphic record). Other piggyback basins of very large
extent could have been mistaken for foreland basins, especially in areas where blind thrust may have developed.
Acknowledgements. – This work has been supported by EC Projects
(PLATON) and by CNRS (UMR Pbds 8110) and Agricultural University
of Athens fundings. The authors would like to thank the different reviewers, especially P. Vergely, for their helpful remarks.
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Geologic evolution and geodynamic controls of the Tertiary

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