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L. Cernobori et aL /Tectonophysics 264 (1996) 175-189 185

b l o c k r e p r e s e n t P l i o - Q u a t e r n a r y c l a y s , M e s s i n i a n

s a n d s , s h a l e s a n d l i m e s t o n e , T o r t o n i a n m a r l s a n d

s h a l e s a n d a s t a c k o f o t h e r u n i ts , p r o b a b l y c o m p r i s -

i n g M e s o z o i c c a r b o n a t e s , c r o p p i n g o u t i n C a l a b r i a

( C . N . R . , 1 9 8 3 ) a n d t r a n s p o r t e d d o w n s l o p e b y g r a v i ty

s l id i n g . T h e i m a g e o f i n t e r n a l s t r u c tu r e s o f t h e c r y s -

t a l li n e c r u s t d o w n t o t h e b a s e o f t h e c r u s t at 2 1 - 2 2

k m d e p t h ( a b o u t 1 0 s ) a r e s i m i l a r t o t h o s e re c o r d e d

o n l a n d i n t h e S e r r e ( L t i s c h e n e t a l . , 1 9 9 2 ) . T h e d i p

o f t h e s e s t r u c tu r e s ( a p p r o x i m a t e l y 1 0 ° t o w a r d s t h e

s o u t h e a s t ) i s a ls o c o n f i r m e d . A t t h e e a s t e r n t e r m i n a -

t i o n o f t h e I O N - 4 p r o f i l e w e o b s e r v e t h e c o l l i s i o n

s t r u c t u r e s w i t h i n t h e I o n i a n c r u s t . H e r e , w e i n v o k e

t h e a i d o f t h e r e f r a c t i o n d a t a ( F e r r u c c i e t a l. , 1 9 9 1 ) ,

a s t h e p o o r s i g n a l - t o - n o i s e r a t io o f t h e r e f l e c t io n d a t a

p r o v i d e s o n l y s p a r s e i n f o r m a t i o n . A c c o r d i n g t o t h e

w i d e - a n g l e d a t a , t h e I o n i a n M o h o i s a g a i n a t 3 0 k m

d e p t h w i t h a t e r m i n a t i o n ju s t b e n e a t h t h e s e a w a r d

e x t e n s i o n o f t h e C a l a b r i a n c r y s t a l l i n e c r u s t ( t h i c k

b l a c k d o t i n F i g . 6 ) .

T h e s i g n a tu r e o f t h e I o n i a n l o w e r c r u s t is a g a i n

w e l l - i m a g e d o n p r o f i l e I O N - 5 . T h e f l e x u r e o f t h e

I o n i a n M o h o i s o f t h e o r d e r o f 1 5 ° o v e r a d i s t a n c e

o f a b o u t 6 0 k m . T h e C a l a b r i a n a r c s t r u c tu r e s a r e

a l s o w e l l d e s c r i b e d , w i t h l a r g e t h r u s t s t r a n s p o r t i n g

c o n s o l i d a t e d s e d i m e n t s , a s i m p l i e d b y t h e h i g h e r

v e l o c i t i e s , 2 . 7 t o 4 . 0 k m / s , d e r i v e d f r o m t h e s t a c k i n g

v e l o c i t ie s a n d f r o m M a k r i s e t a l . ( 1 9 86 ) .

O n t h e p r o f i l e I O N - 6 ( F i g . 7 ) w e r e t u r n t o a

v e r y t h in c r u s t ( M o h o a t a d e p t h o f a b o u t 1 6 k m ,

0.000

1 . 0 0 0

2 . 0 0 0

2 4 6 8 l0 12 14 16 Krn

I 3 . 0 0 0

4 . 0 0 0

5 . 0 0 0

6 . 0 0 0

7 . 0 0 0

8 . 0 0 0

9 . 0 0 0

I0 .000

1 1 . 0 0 0

Fig. 7. L ine ION -6: the low er crust reflective band is indicated and a depth of abo ut 16 km has been comp uted for the M oho.



186 L. Cernobori et al. / Tectonophysics 264 (1996) 175 -18 9

sea bottom at 3 kin, as on ION-l). On this line

we do not observe any important influence from

the Calabrian arc, but the seismic response does

not reveal significant layering or bedding of the

sedimentary crust. The lower-crust reflective band is

clearly arched with indication of dips both towards

the Calabrian arc (west) and the Hellenic arc (east),

a pattern comparable to that described by Ferrucci et

al. (1991, Fig. 3).

5 . S e a - l a n d c o n n e c t i o n s

Land stations in Calabria, emplaced on outcrops

of the granitic basement, recorded the sea airgun

shots when the ship was approaching the coast from

the south (line ION-3) and when it was steam-

ing away towards the east (lines ION-4 and -5). Asingle station (Reftek jr.) with Mark-L4-3D/2 Hz

geophones and one DFS-V recording system with 48

channels, two tape units and sixteen Mark L4-3D/2

Hz geophones distributed in a large array of 540

x 300 m, were installed. The recording conditions

were extremely severe with repeated interruptions of

the operations at sea, an unfavourable environment

and bad wea ther conditions with a very strong wind.

An example of the data is shown in Fig. 8. The

records were stacked for all the sixteen stations of

the array and summed (weighted mix) for five con-

secutive shots in order to increase the S/N ratio. Thetime section was corrected for the water depth with

the replacement of the water by sediments having a

velocity of 3.0 km/s. The maximum s ource-receiver

offset, for which a coherent signal was recorded, was

about 82 kin, not enough to obtain a refracted first

arrival from the base of the crust. Bright wide-angle

multi-cyclic reflections from the base of the crust

were obtained in the LMO sections (Fig. 8a, with a

reduction velocity of 6 km/s), from the shots along

the line ION-4 and the beginning of the line ION-

5. In the NMO section (Fig. 8b, obtained after the

application of a velocity function with 4350 m/s at

twt = 0 s, 5700 m/s at twt = 12 s) the base of the

crust corresponds to a reflective marker at about 10

s, which correlates to the reflectors seen in the ION-4

multichannel line (about 22 km depth).

6 . Co n c l u d i n g rema rk s

Earlier problems of signal-to-noise ratio and pen-

etration in the crust of the Ionian Sea and its margins

could be overcome by using up-to-date oil explo-

ration reflection seismic techniques. A well tuned

source, with a large airgun array supplying ca. 120

1 per shot and coverage as great as 30- or 45-

fold with a 4.5-km streamer were crucial. Advanced

data processing improved the definition of the seis-

mic stratigraphy within the basin and also of the

structures at the collision margin. A highly reflec-

tive interval within the lower crust has been recog-

nised. This reflective interval terminates against themargins that have been deformed by collision or

where the crust thickens towards a passive continen-

tal margin (i.e., central tract of ME). Its topographic

variations suggest recent mobilisation of the mantle

possibly associated with extensional structures o f the

northern tract of the ME. Alternatively, the topo-

graphic variation may be linked to the tectonically

controlled subsidence of the basin such as transcur-

rent motion along crust-cutting faults in response to

the stresses applied at the active margins (Ceruobori

et al., 1994), and to the loading of materials on a

thin, cold, and brittle crust. We noticed the differ-ences with the images of the deep-crustal data in the

Mesozoic eastern Atlantic Ocean. Comparative data

in the Mediterranean do not confirm the presence of

a reflective band in the 'oceanic' areas (de Voogd

et al., 1991), but landward-dipping reflectors and

crustal thickening by a factor greater than five were

observed across the passive continental margin in the

Gulf of Lions. These features can be compared with

the seismic data on the prolongation of the ION-1

line across the ME (Nicolich et al., 1995).

The rapid subsidence of the Ionian basin still

remains unclear within the framework of the re-

construction of Dercourt et al. (1986): why did the

rotation of Apulia with respect to Africa, during the

Fig. 8. Refraction and wide-angle data from land stations (array of 16 geophones, TS-1 in Fig. 1). In (a) a LMO correction with avelocity reduction of 6 km/s was applied. In (b) a NMO correction was utilised for the correlation and landward extension of the ION-4profile.



L . C e r n o b o ri e t a l . / T e c t o n o p h y s i c s 2 6 4 ( 1 9 9 6 ) 1 7 5 - 1 8 9 18 7

• 0 0 0

5 . 0 0 0

1 8 k m of fse t f rom land s ta tion 8 2

. . . • , . - ..:~.~.~::..~:,:'..~::.~~ . . - z . ' .. : ' ~ - . - .z ~ . ~ ? ~ : S ~ . : ~ . ~ . -

~ ; - . - :. z - __ 2 - - - - " ~ - - _ _ ' ~ _ _ : - - - - " ~ - - _ _ " ~ - = ~ - : , . ~ - ; - . ~ t ; - . . : : : ' .' . ~. : :i ~ ;- ~ '~ . .7 -~ - ~.'. :~.-z.--.---

: T . : : - :x ' : . :. . . . v z . ' - . . - ' : . - :- - ~ - : z - ~ z ~ - - ~ - ' : ' ~ ' : ~ : - : - . ' : " ~ ' ~ - ~ ' , - ' - ~ - : . ~ ~ : : 5 ; : U - ' :: ~ - 7 . - . ': " - : ;'. .~ .z r: -:: ~..

: - - . ' ~ 5 : . ~ " : " - : ' i " - - ' . " ~ : ' ~ - ' ~ - ' : 2 : : : ' : :. < - : : " : " - ~ - ~ : > ~ . ' - - - z - - ~ . . . . - - - . - : . z : - ' . . . ~ _ " - . " . : ~ . " - ~ " : ' - : ' . ~ . - ; " 2 - ~ . "~ _ : L : ~ . : . . ' :

. ' ~ : . . : . . ' ~ . - . -' : I 2 " * " - ' - : - . . ~ . : z . " : .. : . :: . ' . . ~ . . . z . : ' . _ _ ~ . : ~ . _ _ ~ . _ ~ . . , ; . . ~ L . ~ . 7 . : . . . ~ : " : " . : ~ .. _ . : . ~ : . . : . : ~ . : . .

~ ' ~ : . ~ . ~ - :: 5: : . ' ~ - ; ' - . : . r - . . . ~ . ~ : ; : ~. -.s . - : : : : ÷ : . . ' ~ 4 ~ : -> - , . - - ~ : - - _ - - :- - - - : - - ~ ~ : - . ~ -. ' . . ~ -~ : : . - - - ~ . : . - ' _ - - . : . - ~ : . : : _ : , , ~ - ~ - 2 <~ - - _ ' . . ~ = E -

; : a , . : ~ ' . : . : ~ . ~ : ; - : - - - - ;. : 2 : - - ' . ~ : ; ' . - : ' - . - . ~ : C ' . : . - - " . ~ ' ~ ' ~ ' ' : : .- " ~ - . " : " - ; - : - : -" : ~ '- " :~ . "~ . " - ~ - - ' - " - " - " " ~ : - " : : : " -~ : ': ": ~ : . % r

k m

• 0 0 0

5 , 0 0 0

a )

I A | I t .r>

5 . 0 0 00 S 1 0 1 5 2 0 K M

I

i 0 . 0 0 0 1 0 . 0 0 0

t 5 . 0 0 0 1 5 . 0 0 0

tec4914 F ig . 8

b )



188 L. Cernobori et al. / Tectonophysics 264 (1996) 175-189

A p t i a n , r e s u l t in r a p i d s u b s i d e n c e i n t h e a d j a c e n t

b a s i n ? I n t h e c o u r s e o f e x t e n s i o n ( L a t e J u r a s s i c ) a c -

c o m p a n i e d b y t h e t h in n i n g o f t h e l i th o s p h e r e , t h e

r o o f o f t h e u n d e r l y i n g a s t h e n o s p h e r e m o v e d u p -

w a r d . T h e m a n t l e m a t e r i a l u p l i ft e d a t t h e r o o f o f

t h e a s th e n o s p h e r e c o u l d h a v e p a r t i al l y m e l t e d , o w -

i n g t o t h e r e d u c t i o n o f p r e s su r e . P o s s i b l y , a p o r t i o n

o f t h e m a g m a t i c m e l t p e n e t r a t e d t h r o u g h t h e c ru s t

a n d l e d t o t h e v o l c a n i c a c t i v i t y i n th i s a r e a i n th e

L a t e J u r a ss i c . T h i s m a y h a v e p e r v a s i v e l y a f f ec t e d

t h e l o w e r p o r t i o n o f t h e c ru s t c h a n g i n g i ts p e t ro -

l o g i c a n d p h y s i c a l c h a r a c t e r i s t i c s , a s w e l l as t h o s e

o f t h e l o w e r l i t h o s p h e r e - u p p e r a s t h e n o s p h e r e , e s -

p e c i a l l y w h e n t h e t e m p e r a t u r e - p r e s s u r e c o n d i t i o n s

c h a n g e d . T e c t o n i c s u b s i d e n c e o f th e b a si n h a s d e v e l -

o p e d s u b s e q u e n t l y . T h i s f i n a l t e c t o n i c s t a g e o f b a s i n

f o r m a t i o n d o e s n o t c o n t r a d ic t t h e m o d e l o f D e r c o u r te t a l. ( 19 8 6 ) b u t ra t h e r c o m p l e m e n t s t h e m o d e l b y

e x p l a i n i n g v e r t i c a l m o v e m e n t s w i t h i n t h e c r u s t o f t h e

E a s t e r n M e d i t e r r a n e a n .

Acknowl edgement s

W e a r e i n d e b t e d t o M . L o u k o y a n n a k i s a n d D e p -

E k y f o r t h e d a t a p r o c e s s i n g . T h a n k s a r e d u e t o

t h e G e c o - P r a k l a s t a f f a n d c r e w o f th e v e s s e l Bin-

Hai 511. W e a r e g r a te f u l t o H .B . H i r s c h l e b e r a n d

t o a n a n o n y m o u s r e v i e w e r fo r th e i r h e l p f u l c o m -

m e n t s a n d s u g g e s t i o n s t h a t i m p r o v e d t h e m a n u s c r i p t .

F u n d s f o r t h e d a ta a c q u i s i t i o n h a v e b e e n m a i n l y p r o -

v i d e d by E C c o nt ra c t S T R E A M E R S , J O U 2 9 0 - C T -

0 0 1 3 2 ( c o n t r a ct o r s : A . H i m , I P G d e P a ri s ; E . B a n d a ,

C . S . I . C . B a r c e l o n a ; D . B l u n d e l l , R H B N U n i v . o f

L o n d o n ; L . A . M e n d e s V i c to r , U n i v . o f L i s b o n ; R .

N i c o l i c h , D I N M A U n i v . o f T r i e s te ; J. D r a k o p o u -

l o s, U n i v . o f A t h e n s ; N . L a l e c h o s , P P C A t h e n s )

a n d f o r t h e d a ta p r o c e s s i n g b y E C c o n t r a c t P R O -

F I L E S , J O U 2 - C T 9 3 - 0 3 1 3 ( C o n tr a c t o rs : A . H i m ,

I P G d e P a r is ; R . N i c o l i c h , D I N M A U n i v . o f T r i e s te ;

A . L y m b e r o p o u l o s , P P C A t h e n s ) . A d d i t i o n a l f u n d s

w e r e a l s o p r o v i d e d b y t h e a u t h o r s ' i n s t i t u ti o n s a n d

n a t i o n a l r e s e a r c h p r o g r a m m e s .

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ELSEVIER Earth and Planetary Science Letters 168 (1999) 243–254

Foredeep geometries at the front of the Apennines in the Ionian Sea(central Mediterranean)

Carlo Doglioni a,Ł, Saverio Merlini b, Giuseppe Cantarella b

a Dipartimento di Scienze della Terra, Universita La Sapienza, P. le A. Moro 5,

00185, Rome, Italyb ENI–AGIP, V. Emilia 1, 20097, San Donato Milanese, Italy

Received 29 January 1999; revised version received 1 March 1999; accepted 3 March 1999

Abstract

A new regional seismic section in the Ionian Sea across the Apennines belt and related foreland shows how the present

foredeep geometry may be an example for interpreting discontinuous, tilted and deformed earlier basins now incorporated

in the internal parts of the accretionary wedge. Onlap stratal terminations of the foredeep sediments on the foreland

monocline may simulate downlap geometries once involved and tilted by back-thrusting. The geometry of the Ionian

foredeep is controlled by the dip of the regional monocline, and internally by the variable dip and length of the limb of the

external fold, which may be either foreland-verging or hinterland-verging. The generation of a new fold within the foredeep

splits the basin into a new foredeep toward the foreland and a thrust-top basin toward the hinterland. The thrust-top basin

dimension is primarily controlled by the distance between the two folds and related thrusts at its margins. The foredeep, inits overall history, is composed by a series of concave heterogeneous lenses, progressively displaced and piled up toward

the foreland to the east. The formation of each sedimentary lens is controlled by the development of a new fold and the

contemporaneous retreat of the regional monocline which creates new accommodation space. The complex 3D geometry

of the Apennines foredeep mainly results from lateral variations of the latter parameters, as well as variations in sediment

supply and eustasy. © 1999 Elsevier Science B.V. All rights reserved.

Keywords: fore-arc basins; thrust faults; seismic profiles; Apennines; Ionian Sea

1. Introduction

Foredeeps are those basins located at the mar-gin of orogens or accretionary wedges, and they arecharacterized by lens shaped clastic sedimentary se-quences which are controlled by a number of wellknown factors, i.e., subsidence, sediment supply, eu-stasy and climate [1]. The internal geometry of these

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active margin basins is well differentiated from that

of passive margin basins, both in terms of lithologyand geometry of the basin. Foredeeps are locatedand propagate on top of a regional monocline [2]usually dipping toward the interior of the belt withangles ranging between 1º and more than 10º [3].The internal geometries of foredeep basins are no-toriously controlled by growth folds (e.g., [4,5]).

The Apennines accretionary wedge presents a Plio–Pleistocene somewhere 8 km deep basin which un-derwent subsidence rates higher than 1 mm=yr. This

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P I I : S 0 0 1 2 - 8 2 1 X ( 9 9 ) 0 0 0 5 9 - X



244 C. Doglioni et al. / Earth and Planetary Science Letters 168 (1999) 243–254

Fig. 1. Location of the seismic section M5 (Fig. 2) in the frame of the Apennines Arc. The arc migrated ‘eastward’ since the early

Neogene. In grey is the frontal compressive part of the Apennines accretionary wedge which is followed to the west by an extensional

tectonic wave.

foredeep provides excellent examples of geometries[6] which may occur in similar basins.

During the last decade, a large effort for studyingthe crust of Italy and the surrounding seas (ProjectCROP) has been performed by a pool composedby the Consiglio Nazionale delle Ricerche of Italy,

CNR, the national oil company, Agip, and the na-

tional electric company, Enel. The several seismiclines provided new insights on the structure of theItalian crust. Offshore sections are the most read-able seismic lines, and in this paper we present inparticular section M5 (Fig. 1) at the front of the off-shore Apennines in the Ionian Sea. This paper aimsto present in particular a few details of this section

which highlights original geometries and kinematicsof the foredeep evolution (Fig. 2).

2. The Apennines accretionary wedge

The Apennines belt is an arc shaping the Ital-ian Peninsula, from Piemonte-Monferrato in north-ern Italy, down to the northern Africa-Maghrebides(Fig. 1). The arc formed on top of a west-directedsubduction zone which retreated ‘eastward’ during

the last 30 Ma [7–12]. The convex part of the arc isthe area where the roll-back of the subduction hingehas been maximum. The most arcuate part of theApennines Arc is Calabria. The arc migrated ‘east-ward’ about 775 km during the Late Oligocene ina section crossing northern Calabria, the TyrrhenianSea, Sardinia, and the Provencal basin [12]. Thisvalue decreases moving either toward the northernApennines or to the south, toward Sicily and theMaghrebides. The southern Apennines and Calabria,



Fig. 2. Regional seismic section Crop M5 of the Ionian Sea across the Apennines accretionary wedge and its Apulian foreland. See location

wedge is lower than the foreland.



246 C. Doglioni et al. / Earth and Planetary Science Letters 168 (1999) 243–254

being located in the most arcuate part of the belt,travelled eastward at the fastest rates (3–4 cm=yr;[11,13,14]. The earlier foredeep stages were locatedmore internally and to the west they are now aban-

doned due to the high speed of the roll-back. Withinthe southern Apennines and Calabrian Arc there areremnants of the earlier foredeep since the EarlyMiocene (‘pre-Irpinian’) [15], as it was observedin the central-northern Apennines [16]. The fasteastward advancement of the southern Apenninesforedeep is clearly evidenced by highly shortenedPlio–Pleistocene deposits, originally located in theinternal side of the foredeep, or discovered in wellswhere the Pliocene sediments have been overriddenby Mesozoic thrust sheets.

The Apennines foredeep has been interpreted asgenerated by the ‘eastward’ roll-back of the hingeof the subduction induced by the slab pull or by therelative eastward mantle flow [14,17]. There the sub-sidence is among the fastest on the Earth’s surfaceand it exceeds 1 mm=yr [3]. The foredeep eastwardmigration in the Apennines should reflect the ve-locity of the roll-back of the Adriatic slab, whichretreated faster in its southern part where the Ionianoceanic lithosphere was undergoing subduction, incontrast with the slower northern continental part.This appears to be true both for the early Neogene

history of the foredeep but also for the later-to-pre-sent stages of the subduction [18].

3. Seismic section M5 in the Ionian Sea

This seismic section is one of the most completelines across the Apennines front and its foreland.The line runs from offshore eastern Calabria (south-ern Italy) to the northeast, offshore southern Puglia.In the Calabrian part the section crosses extensional

faults which are well known inland to the northin Campania and Basilicata to form grabens (e.g.,the Vallo di Diano, Val d’Agri) and be responsiblefor the high seismicity of the southern Apennines[19]. Moving northeastward, the section exhibits anirregular seafloor, indicating active or very recenttectonic activity. Below the Messinian unconformity(Fig. 2) back-thrusts deform the Miocene sequencesand they determine the formation of triangle zonesin the central part of the section. The front of the ac-

cretionary wedge is marked by an eastward-vergingthrust overriding the narrow foredeep deposits of theTaranto trench. (Fig. 3). The foreland is character-ized by a steep westward dipping monocline made of

continental crust with an about 6 km thick MesozoicApulian carbonate platform and a thin sequence of Tertiary calcarenites and limestone. A few normalfaults also disrupt the seafloor of the foreland whichis even more elevated than the accretionary wedge tothe west (Fig. 2).

From the main section, two details have beenextracted in order to have clearer views of the frontof the accretionary wedge and the present foredeep(Fig. 3) and a more internal part of the wedge whichwas formerly the front of the belt, probably duringthe Late Miocene (Fig. 4). These data allow us togive a look into the complicated geometries of theaccretionary wedge. Dating of sediments is based onprojected unpublished Agip wells.

The frontal section (Fig. 3) shows a 8.5 km wideforedeep, with a seafloor about 2350 m deep, andsediments onlapping the westward-dipping mono-cline. The onlap shows a progressive eastward dis-placement. The accretionary wedge is composed of Plio–Pleistocene sediments. The internal detail of the section (Fig. 4) has been migrated and depth-con-verted. It is characterized by two main back-thrusts

verging toward the southwest, generating two trian-gle zones. Between the two hinterland-verging rampsthere is a basin which is made of two wedges, thelower pointing toward the foreland, the upper point-ing toward the hinterland. The lower wedge appearsas an earlier external foredeep now involved by theaccretionary wedge, and it is limited at the base byapparent downlap stratal terminations at about 5 kmdepth. The overlying upper wedge is a later thrust-top basin onlapping the lower wedge with stratalterminations shifting in the opposite direction toward

the southwest.

4. Discussion on the M5 section

Fig. 5 is an interpretation of the main featuresvisible on Fig. 4. This spectacular section indicatesthat the two-stage basin shape is controlled by thedistance between the two back-thrusts in the up-per wedge, that this upper basin formed during the



C. Doglioni et al. / Earth and Planetary Science Letters 168 (1999) 243–254 247

Fig. 3. The frontal thrust and related fold of the Apennines accretionary wedge in the Ionian Sea with the related foredeep. Deep facies

sediments onlap the foreland monocline. See location in Fig. 2.

growth of the two anticlines (in particular it pinches-out on the back-limb of the internal anticline tothe southwest), and that the lower foreland pinch-ing-out wedge has an apparent downlap of sedi-ments toward the right. The Messinian unconformity

eroded the two folds and post-dates the underly-ing sediments. The Miocene sequences are laterallydisplaced, with the younger one more to the right,

toward the foreland, and laterally overlying the mar-gin of the previous internal section. Therefore, therelative depocentres are progressively displaced to-ward the east. Fig. 6 proposes an interpretation of thekinematics of the geometries occurring in Fig. 4: the

original foredeep sedimentary wedge (first stage) isincorporated and tilted by a back-thrust with syntec-tonic sedimentation (second stage). Original onlap

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