Post on 07-May-2023
Journal of the Geological Society, London, Vol. 163, 2006, pp. 1–14. Printed in Great Britain.
1
Testing thrust tectonic models at mountain fronts: where has the displacement
gone?
R. S. J. TOZER 1,2, R . W. H. BUTLER 1, M. CHIAPPINI 3, S . CORRADO 4,
S . MAZZOLI 5 & F. SPERANZA 3
1School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK2Present address: BP Exploration, Chertsey Road, Sunbury-on-Thames TW16 7LN, UK
(e-mail: Richard.Tozer@uk.bp.com)3Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy
4Dipartimento di Scienze Geologiche, Universita degli Studi di Roma Tre, Largo San Leonardo Murialdo 1,
00146 Rome, Italy5Dipartimento di Scienze della Terra, Universita di Napoli ‘Federico II’, Largo San Marcellino 10, 80138 Naples, Italy
Abstract: The alternative relationships that can exist between a mountain front and the adjacent foreland
basin have been recognized for many years. However, seismic reflection data from such areas are commonly
of poor quality and therefore structural models may contain large uncertainties. In view of scientific and
commercial interest in mountain belts, we have reviewed the methods for discriminating between alternative
interpretations using a case study from the Montagna dei Fiori in the central Apennines, Italy. In this area
Mesozoic and Tertiary carbonate sediments are juxtaposed with a foredeep basin containing up to 7 km of
Messinian and Plio-Pleistocene siliciclastic sediments. A new structural model for this area demonstrates how
the structures in this area form a kinematically closed system in which displacement is transferred from the
thrust belt to blind structures beneath the present-day foreland. Growth strata show that Pliocene shortening
was initially rapid (15 mm a�1) followed by slower rates during the final stages of deformation. Variations in
structural elevation indicate a component of basement involvement during thrusting, and this is further
supported by magnetic modelling. The results illustrate the interaction of thin- and thick-skinned structures in
the central Apennines, and the methods for discriminating between alternative structural models.
The outer parts of mountain belts are commonly defined by a
thrust carrying a frontal anticline that is evident as a topographic
high. In active orogens such as the Himalayas these structures
have proved useful for determining rates of tectonic processes by
linking dated landscape features or sediments to kinematic
descriptions of the deformation (e.g. Mugnier et al. 1992).
Anticlines at mountain fronts also trap important accumulations
of hydrocarbons (see Needham et al. 2004, and papers in the
same volume). For both of these and many other issues, it is
critical to resolve the relationship between the frontal anticline
and the adjacent foreland basin. In simple terms this ‘mountain
front problem’ (Vann et al. 1986) can be paraphrased as follows:
how is orogenic shortening that created the mountain front
anticline accommodated in younger strata and at the surface of
the Earth (Fig. 1)? In continental fold and thrust belts the
problem generally arises because although the anticline crest
may be exposed the critical lower parts of the forelimb are
commonly masked by young deposits. The solution lies in
integrating outcrop with seismic reflection data, but because the
forelimbs of folds are difficult to image, structural interpretations
have been model-driven rather than data-led. In the absence of
an emergent thrust (Fig. 1a), Vann et al. (1986) suggested four
general solutions to the problem (see also Morley 1986). One
solution is that a major backthrust is present at the mountain
front (creating the ‘triangle zone’ of Jones 1982; Fig. 1b).
Another explanation is that the thrust beneath the anticline was
formerly emergent but is now inactive, so that the younger
foredeep sediments onlap and bury the structure (Fig. 1c). A
geometric option is that the thrust carrying the anticline loses
displacement rapidly towards the foreland, with the displacement
gradient expressed as layer-parallel shortening in the overlying
sediments (e.g. Williams & Chapman 1983; Morley 1986; Fig.
1d). Alternatively, the anticline may not be the true mountain
front at all and the displacement beneath the frontal anticline
could be transferred out into the foreland basin (Fig. 1e).
In many active orogens the most obvious solution to the
mountain front problem, and the simplest geometry interpreted
from outcrop data alone, is to suggest that the thrust that is
inferred to carry the anticline simply emerges onto the synoro-
genic landscape (Fig. 1a). However, seismic reflection and well
data acquired from frontal anticlines commonly show that this
option is inappropriate. Our aim here is to describe how the
integration of seismic and well data together with outcrop
structural and stratigraphic data can limit the number of
geologically viable solutions to the mountain front problem. This
is illustrated with a case study from the Montagna dei Fiori in
the central Apennines of Italy. We review existing interpretations
of the structure, testing each against field and subsurface data
using the criteria of Vann et al. (1986). We then propose a new
kinematic model for this part of the thrust belt and examine its
implications.
Background
The Montagna dei Fiori area lies on the eastern side of the
central Apennines of Italy (Fig. 2). The region is a fold and
thrust belt that developed in the Neogene; during this time
compressional deformation migrated eastward so that the young-
est folds and thrusts are located on the eastern margin of the
Italian peninsula. The thrust belt has received much attention
over the past 20 years as it has become evident that the crustal
shortening it represents balances with crustal extension in the
orogenic interior (Malinverno & Ryan 1986; Lavecchia 1988;
Faccenna et al. 1996). A variety of tectonic models for the thrust
belt have been proposed, including very thin-skinned, high-
displacement versions (e.g. Bally et al. 1986). Orogen-wide
tectonic models lie outside the scope of this contribution, except
to say that they rely on appropriate choices of structural
geometry at the scale of the Montagna dei Fiori study area (see
Tavarnelli et al. 2004).
Stratigraphy
The stratigraphy of the Montagna dei Fiori and surrounding area
(Fig. 3) is well described and understood. Two distinct deposi-
tional cycles can be distinguished; the first is a broadly layer-
cake succession of Triassic to Miocene carbonate sediments.
Overlying and onlapping these are siliciclastic foredeep sedi-
ments of Messinian and Plio-Pleistocene age, as described below.
Pre-Messinian stratigraphy
The pre-Messinian stratigraphy of the Montagna dei Fiori is a
record of the evolution of the southern margin of the Tethys
Ocean during the Mesozoic and Tertiary (Parotto & Praturlon
1975). By analogy with the exposed stratigraphy in Tuscany (e.g.
Bortolotti et al. 1970), the succession is thought to begin with
Permo-Triassic continental siliciclastic sediments (the Verrucano
Group), followed by a thick succession of Triassic evaporites
(Burano Anhydrites), which record the evolution to marine
conditions (Fig. 4a). These are followed by platform carbon-
ates (Castelmanfrino Formation or Calcare Massiccio) of late
Triassic–Liassic age, the oldest formations known to be present
in this area both from outcrop and well data.
Rifting of the passive margin led to the establishment of a
pelagic basin during the Jurassic, within which both ‘complete’
(Corniola, Rosso Ammonitico, Salinello and Aptici Formations)
and ‘condensed’ (nodular limestones) pelagic successions are
present as a result of important normal faults of Liassic age
(Giannini 1960; Paradisi et al. 1969; Parotto & Praturlon 1975;
Mattei 1987). Thermal subsidence of the pelagic basin is
recorded by the deposition of fine-grained limestones and marls
from the Late Jurassic to the Mid-Miocene (Maiolica, Fucoidi
Marls, Scaglia Bianca, Scaglia Rosata, Scaglia Cinerea, Bisciaro
and Cerrogna Marls Formations). To the north (southern Marche)
and east (Adriatic Sea) at more marginal positions in the basin,
the sediments coeval to the Cerrogna Marls are neritic marls of
the Schlier Formation.
Messinian and Plio-Pleistocene stratigraphy
During the Late Miocene a NNW–SSE-trending foredeep basin
(the Laga Basin; Centamore et al. 1991) developed ahead of the
Fig. 1. Schematic illustrations of possible
explanations for the mountain front
displacement problem, after Vann et al.
(1986). For the purposes of the Montagna
dei Fiori case study, the pre-thrusting
stratigraphy equates to the pre-Messinian
carbonate succession and the foredeep basin
fill equates to the Messinian and Pliocene
siliciclastic stratigraphy.
Fig. 2. Simplified geological map of the Apennines showing the location
of the Montagna dei Fiori study area. After Funiciello et al. (1981).
R. S . J. TOZER ET AL .2
active thrust belt to the west. The inception of this basin is
recorded by a few tens of metres of hemipelagic marls (Orbulina
Marls; Fig. 4a). In the Messinian the basin was fed axially from
the north by siliciclastic turbidite flows that built up the Laga
Formation (Mutti et al. 1978; Chiocchini & Cipriani 1992). The
eastward-tapering geometry of the Laga Basin is clearly defined
by low-angle onlap (c. 38) of the formation onto the pre-
Messinian carbonate succession exposed in the Montagnone
Anticline to the south (Centamore et al. 1991; Vezzani &
Ghisetti 1998) and in seismic reflection profiles of the area to the
north (e.g. Bally et al. 1986). The Laga Basin never underwent
desiccation during the Messinian salinity crisis, an event re-
corded only by a 15–30 m thick horizon of resedimented gypsum
arenites, which is used to divide the formation into pre- and
post-evaporite members (Fig. 4a; Cantalamessa et al. 1986;
Roveri et al. 2001). To the east of the Montagna dei Fiori the
total thickness of the Laga Formation is almost 3000 m (Vezzani
& Ghisetti 1998), whereas coeval shales and gypsum deposited
on the foredeep margin (Gessoso-solfifera Formation) are
,100 m thick. These are penetrated by wells beneath the
Adriatic Sea to the east, and in the Marche region to the north
(Fig. 4b).
The foreland to the east of Montagna dei Fiori contains a thick
succession of Plio-Pleistocene sediments that record the final
episodes of the development of the central Apennine fold and
thrust belt (Fig. 4b). In keeping with previous studies of the area
(e.g. Crescenti et al. 1980; Paltrinieri et al. 1982; Cantalamessa
et al. 1986; Calamita et al. 1994), the informal subdivision of
the Pliocene into lower, middle and upper intervals is retained.
The succession begins with the lower Pliocene Teramo and
Cellino Formations (Sphaeroidinellopsis, Globorotalia (G.) mar-
garitae and G. puncticulata biozones), both of which comprise
siliciclastic turbidite deposits interbedded with clays and marls
deposited under several hundred metres of water (Artoni &
Casero 1997; Vezzani & Ghisetti 1998). These are followed by
the middle and upper Pliocene Castilenti Formation (G. crassa-
Fig. 3. Simplified geological map of the Montagna dei Fiori (MF), Acquasanta (AQ) and Montagnone (MO) Anticlines; ST denotes the Salinello Thrust.
Map compiled from Paradisi et al. (1969), Centamore et al. (1991) and Vezzani & Ghisetti (1998); it should be noted that the trace of the thrust fault to
the west of Teramo is interpretation-driven.
TESTING THRUST TECTONIC MODELS 3
formis and G. inflata biozones), which comprises similar turbi-
dite deposits intercalated with conglomerates and calcareous
sandstones derived from the emergent thrust belt. The sequence
is capped by Pleistocene sandstones and clays (Hyalinea (H.)
balthica and younger biozones) deposited in shallow marine
and continental environments, which complete the general
shallowing-upward pattern (Vezzani & Ghisetti 1998). The
thickness of the Plio-Pleistocene sediments varies greatly as a
result of syndepositional growth of the underlying structures, but
the maximum thickness, beneath the Adriatic coastline, is over
7000 m.
Structure
The Montagna dei Fiori area is limited to the west by the north–
south-trending Sibillini front, a major line of thrust faulting
along which sediments of the Umbria–Marche pelagic basin are
thrust over the Laga Formation to the east. The southern limit of
the area is defined by the east–west-trending Gran Sasso thrust
belt, along which sediments deposited on the margin of the
Latium–Abruzzi Carbonate platform override north–south-
trending structures in the Laga Basin. This basin has been
deformed into two major anticlines, from west to east the
Acquasanta and Montagna dei Fiori Anticlines (Fig. 3). Seismic
reflection profiles show that two major structures are also present
beneath the foreland to the east of these anticlines.
Surface structures
The surface geology of the area is dominated by the Acquasanta
and Montagna dei Fiori Anticlines, which have a wavelength of
15 km. The Acquasanta Anticline is an asymmetric, east-vergent
structure with a gently west-dipping western limb and a sub-
vertical eastern limb. The oldest sediments exposed in the core
of this structure are the Scaglia Rosata and Scaglia Cinerea
Formations. To the east of this structure lies a west-dipping
minor thrust (the Acquasanta Thrust; Fig. 3); at the surface, the
hanging wall and footwall of this fault are both composed of the
pre-evaporites member of the Laga Formation, which is dis-
placed by a maximum of a few hundred metres. This thrust dies
out to the south and north and has a maximum length of
,40 km.
In contrast to the Acquasanta Anticline, the greater structural
elevation in the centre of the Montagna dei Fiori Anticline has
resulted in the exposure of limestone formations, which are
resistant to erosion (Fig. 3). Therefore, the zone of maximum
structural elevation is also the area of maximum topographic
elevation. The Montagna dei Fiori Anticline plunges in both
directions along its axis; to the south the equivalent structure is
known as the Montagnone Anticline and has a similar asym-
metric geometry to the Acquasanta Anticline.
Within the core of the Montagna dei Fiori Anticline an
important minor thrust, the Salinello Thrust, is exposed (Giannini
1960; Mattei 1987; Calamita et al. 1998; Fig. 3). This has an
antiformal geometry and separates the east-dipping upper limb of
the Montagna dei Fiori Anticline from the overturned lower limb.
The horizontal shortening accommodated by this fault is only
750 m, as shown by the separation between the hanging wall and
footwall cutoff of the top Fucoidi Marls (Mattei 1987). Although
this thrust has been interpreted to emerge on the eastern side of
the anticline by Paradisi et al. (1969) and Vezzani & Ghisetti
(1998), these maps do not agree on its location further to the
south where field relationships are less clear. To avoid this
problem, seismic reflection data have instead been used in this
study to constrain the structure in this area.
The western side of the Montagna dei Fiori Anticline is cut by
a major normal fault (Fig. 3); this dips steeply to the WSW, is
c. 15 km in length and has a maximum displacement of at least
1400 m (Paradisi et al. 1969; Centamore et al. 1991; Vezzani &
Ghisetti 1998). There is evidence that this fault was active in the
Early and Mid-Miocene (Calamita et al. 1998; Mazzoli et al.
2002; Scisciani et al. 2002; Fig. 4a) and during the Pleistocene
(Ghisetti & Vezzani 2000); that is, both before and after
compressional deformation. In the southwestern part of the study
area lies a second major fault with a similar orientation, the
Monte Gorzano normal fault (Ghisetti & Vezzani 2000; Fig. 3).
Fig. 4. Simplified stratigraphic columns: (a) the pre-Messinian carbonate
succession and Messinian Laga Formation, based on exposure in and
around the Montagna dei Fiori Anticline; (b) the Plio-Pleistocene
sediments beneath the present-day foreland, based on wells drilled on the
crest of the Costiera Structure. Ash bed fission-track dating of outcrop
samples is from Bigazzi et al. (2000).
R. S . J. TOZER ET AL .4
This is a Pleistocene structure, which has a maximum displace-
ment in excess of 1000 m and juxtaposes the Laga Formation in
the hanging wall against the Cerrogna Marls in the footwall.
Blind structures
The area beneath the Acquasanta and Montagna dei Fiori
Anticlines is covered by very few seismic profiles and these are
uncalibrated by wells; because of confidentiality restrictions
these data are not presented. The most important observation is
that beneath the Acquasanta Anticline a repetition of the seismic
stratigraphy can be recognized, indicating that a major thrust
underlies this structure. The footwall ramp to this thrust appears
to lie beneath the western limb of the surface anticline where the
footwall cutoff of the top Calcare Massiccio is located 11 km
west of the outcrop position of the Acquasanta Thrust. Given that
this thrust accommodates a maximum of a few hundred metres
shortening at the surface, most of the displacement must remain
in the subsurface and continue beneath the Montagna dei Fiori
Anticline. Seismic data covering the southern part of this
structure confirm that this thrust is present (T1 in Fig. 5a). In this
area a type example of the seismic stratigraphy of the pre-
Messinian carbonate succession can be recognized beneath the
surface anticline; this is believed to connect to the footwall
beneath the Acquasanta Anticline.
Two major structures are present beneath the foreland to the
east of the Montagna dei Fiori Anticline (Fig. 5b). The more
internal of these, which we indicate as the Bellante Structure, is
characterized by a zone c. 5 km wide of very poor quality
seismic data. However, imbricates can be recognized within the
Messinian and Pliocene sediments, and older on younger tectonic
contacts have been reported for at least two of the wells drilled
on this structure. In contrast, seismic data provide spectacular
images of the most external structure beneath the foreland, the
Costiera Structure. This is an east-vergent thrust-propagation
anticline composed of two or more imbricates of Pliocene
sediments (Artoni & Casero 1997).
The mountain front problem at the Montagna dei Fiori
The seismic reflection data reveal that a major thrust lies beneath
the study area; the separation between the footwall ramp beneath
the Acquasanta Anticline and the hanging wall cutoff beneath the
Montagna dei Fiori Anticline (Fig. 5a) shows that this thrust has
a displacement of at least 25 km. What happens to this displace-
ment at the mountain front on the eastern side of the Montagna
dei Fiori? The purpose of the following analysis is to review the
possible answers to this question using the framework of Vann et
al. (1986; Fig. 1). Several of the alternative explanations have
already been proposed in published cross-sections and are
reviewed where appropriate.
Emergence of a major thrust
This option was explicitly omitted from the original work by
Vann et al. (1986) which instead focused on situations where it
is demonstrably not the case. However, in several previous
models for the area a major thrust has been interpreted to emerge
on the eastern side of the Montagna dei Fiori Anticline (Ghisetti
et al. 1993; Ghisetti & Vezzani 1997, 2000; Alberti et al. 1998).
This fault has c. 12 km of displacement and places the Mesozoic
and Tertiary carbonate sediments over the Messinian Laga
Formation (e.g. Fig. 1a). Along much of the eastern side of the
Montagna dei Fiori Anticline it is unclear if this thrust is
emergent as much of this area is covered by drift (Fig. 3).
However, projecting this fault 10 km along strike to the NNW
into an area of better exposure, geological maps show that the
members of the Laga Formation have little (Paradisi et al. 1969)
or no (Centamore et al. 1991) stratigraphic separation at this
position.
In addition, seismic reflection data from the southern part of
the Montagna dei Fiori Anticline do not support this option (Fig.
5a). In this area the forelimb dips moderately east and is
distinctly resolved; it is very clear that the thrust beneath the
anticline does not cut across this limb to emerge at the surface.
Presence of a major backthrust at the mountain front
The idea that large displacements beneath the Montagna dei Fiori
anticline are accommodated by a major backthrust at the base of
the Laga Formation (e.g. Fig. 1b) has been proposed by several
workers (Bally et al. 1986; Bigi et al. 1995; Barchi et al. 2001).
However, kinematic fabrics at the mountain front close have
unambiguous top to the east shear sense (Fig. 6; see also
Averbuch et al. 1995) related to the presence of an important
pre-existing detachment at the base of the Laga Formation
(Koopman 1983). In addition, backthrusts are not shown on any
of the geological maps of this area (Paradisi et al. 1969; Mattei
1987; Centamore et al. 1991; Vezzani & Ghisetti 1998), no
growth strata related to a major backthrust are evident in seismic
data (e.g. Fig. 5a), and backthrusting of the Laga Formation over
the Montagna dei Fiori and Acquasanta Anticlines raises serious
mechanical questions (Vann et al. 1986). Another possibility is
that a major backthrust is located at the base of the Pliocene as
suggested by Bally et al. (1986), but there is no map, field or
stratigraphic evidence for this structure and those workers
admitted that this is a ‘major problem’.
Burial of a formerly emergent thrust
The pre-Messinian carbonate succession is ubiquitously folded
and faulted and clearly predates contractional deformation. No
westward onlap of the Laga Formation onto the Montagna dei
Fiori Anticline can be observed in seismic data (e.g. Fig. 5a) or
in the field. In addition, in the external central–northern
Apennines, the spread of palaeomagnetic rotations with respect
to the Adriatic–African foreland for both the pre-Messinian
carbonate succession and the Messinian Laga Formation is very
similar (Dela Pierre et al. 1992; Mattei et al. 1995; Speranza et
al. 1997), indicating that rotations occurred after Messinian
times. Therefore there is no evidence for large pre-Pliocene
displacements.
Westward onlaps onto the Montagna dei Fiori Anticline are
present in some Pliocene units, but if this is the blanketing unit
then all of the displacement (.25 km) would have had to have
occurred almost instantaneously. This is because the post-
Messinian rock-record to the east of the Montagna dei Fiori
Anticline is up to 7 km thick and has accumulated almost
continuously. Indeed, the Costiera Structure (Fig. 5b) provides a
spectacular illustration of the depositional geometries that result
from contractional deformation during sediment deposition.
A good example of the problem with burial of an emergent
thrust is provided by the balanced cross-section of Calamita et
al. (1994, plate 1c). In this model, the main thrust beneath the
Montagna dei Fiori Anticline is shown to be buried at the
mountain front beneath middle Pliocene sediments, yet there is
c. 15 km separation of the top of the lower Pliocene along this
TESTING THRUST TECTONIC MODELS 5
Fig.5.
Sei
smic
refl
ecti
on
pro
file
sac
ross
(a)
the
sou
ther
np
art
of
the
Mo
nta
gna
dei
Fio
riA
nti
clin
ean
d(b
)th
efo
rela
nd
and
Ad
riat
icS
eato
the
east
of
this
.N
ote
wo
rthy
feat
ure
sar
eth
ere
pet
itio
no
fth
e
seis
mic
stra
tig
rap
hy
ben
eath
the
Mo
nta
gna
dei
Fio
riA
nti
clin
ein
(a)
and
the
spec
tacu
lar
thru
stpro
pag
atio
nfo
ld(t
he
Cost
iera
Str
uct
ure
)ben
eath
the
coas
tlin
ein
(b).
Tri
ang
les
repre
sen
thy
dro
carb
on
exp
lora
tio
nw
ells
;th
em
ain
thru
sts
are
nu
mb
ered
T1
–T
5.
TW
TT
,tw
o-w
aytr
avel
tim
e.
R . S . J. TOZER ET AL .6
fault. This implies that thrusting was almost instantaneous at the
end of the early Pliocene.
Loss of displacement into a zone of distributed strain
There is no field evidence for major zone(s) of distributed strain
at the mountain front (e.g. Fig. 1d), and none are reported in the
literature (e.g. Mattei 1987). In addition, measurements of the
anisotropy of magnetic susceptibility (AMS) in the Laga Forma-
tion show a magnetic fabric typical for weakly deformed
sediments, with the plane of magnetic foliation always coincident
with bedding (Sagnotti et al. 1998). The magnetic fabric at the
sites just east of the mountain front is similar to that at the other
sites, documenting no local variation related to an increase of
shortening (Averbuch et al. 1995).
Propagation of the thrust front into the foreland
Almost all published cross-sections for the area show that the
blind structures beneath the foreland are detached within the pre-
Messinian carbonate succession (Paltrinieri et al. 1982; Bally et
al. 1986; Ghisetti et al. 1993; Calamita et al. 1994; Bigi et al.
1995; Ghisetti & Vezzani 1997, 2000; Alberti et al. 1998;
Scisciani et al. 2002). This precludes these structures from
absorbing displacement along the major thrust beneath the
Acquasanta and Montagna dei Fiori Anticlines (Fig. 5a), because
the seismic data show that this thrust runs along the top of the
pre-Messinian carbonate succession.
However, the position of the detachment beneath the most
external blind structure (the Costiera Structure) has been reas-
sessed. Detailed analysis of this structure by Artoni & Casero
(1997) showed that it is detached from the carbonate succession
along the Messinian Gessoso-solfifera Formation. Therefore,
several kilometres of the displacement along the major thrust
beneath the surface anticlines could be accommodated by this
structure (e.g. Fig. 1e). Accounting for the remaining displace-
ment is more difficult. In view of the evidence against any of the
other solutions, the only viable interpretation is that large
amounts of shortening are accommodated by the remaining
structure beneath the foreland, the Bellante Structure (Fig. 5b).
This interpretation is supported by the recognition of imbricates
within the Laga and Teramo Formations in seismic reflection
data (Fig. 5b). These also appear to be detached from the top of
the pre-Messinian carbonate succession. In addition, thrust faults
are reported in several wells drilled on this structure.
A new structural model for the Montagna dei Fiori
Data and methods
The cross-section presented in Figure 7 was constructed at a scale of
1:100 000 using geological maps of the area (Paradisi et al. 1969; Mattei
1987; Centamore et al. 1991; Vezzani & Ghisetti 1998) and additional
structural data collected in the field. Where sufficient outcrop and
topographic relief allows, structure contours have been used to constrain
the precise geometry of geological boundaries.
In the subsurface, the cross-section has been completed using seven
exploration wells and 38 km of commercial seismic reflection profiles
(e.g. Fig. 5); a further 18 wells and 350 km of time-migrated seismic data
in the immediately surrounding area were used to determine the seismic
stratigraphy and calibrate these lines. Wells were projected a maximum
distance of 3.0 km and then tied to the relevant seismic line by converting
the depths of key horizons to two-way travel time using time–depth
curves or interval velocities from the closest common depth point on the
seismic line. In the eastern part of the area the seismic data covering the
Costiera Structure are of sufficient density and quality to allow loop
tying. However, to the west of this correlations based on seismic facies
are required because the data are more sparse and of lower quality.
Throughout the area there is much variation in the seismic signature of
fault planes; these are therefore interpreted both where discordant seismic
reflectors are present and where compound reflector terminations occur.
Following interpretation, key seismic horizons have been depth converted
with interval velocities calculated using the method of Dix (1955) and
assuming vertical raypaths.
The cross-section has been restored using 2DMove software; two
restoration algorithms have been used in particular. The pre-Messinian
carbonate succession that forms the base of the Adriatic monocline has
been restored using vertical shear, a type of deformation that is envisaged
to have been induced by the loading of Plio-Pleistocene sediments.
Further west, the dominant deformation mechanism within the thrust belt
Fig. 6. Photograph, field sketch and kinematic data (lower hemisphere,
equal area projection) illustrating pervasive S–C fabric developed in the
uppermost part of the Cerrogna Marls on the eastern side of the
Montagna dei Fiori Anticline (GR 42847.999N, 13837.229E; refer to Fig.
3 for location). The east-vergent kinematics at this outcrop strongly
suggests that a backthrust previously interpreted in this position cannot
be present. (See also Averbuch et al. (1995) for a similar interpretation.)
TESTING THRUST TECTONIC MODELS 7
is flexural slip, as evidenced by ubiquitous slickenfibres parallel to
bedding and perpendicular to fold axes (e.g. Mattei 1987). These
structures were therefore restored using the flexural-slip algorithm using
pins located along zones of no interbed slip; that is, parallel to axial
surface traces in the plane of cross-section (Dahlstrom 1969). A zone of
distributed strain (undefined imbricates and/or ductile deformation) is
also interpreted where the Bellante Structure is located; this has simply
been area balanced with the corresponding area in the restored cross-
sections.
Assumptions
In our 2D restoration we assume that there is no movement of material in
or out of the section plane. To determine the correct orientation for such
a section of plane strain it was therefore necessary to analyse the
kinematics of minor structures in the field. The results of this are shown
in Figure 3. Using a combination of minor structures (S–C fabrics,
slickensides and duplexes) the mean transport direction at 13 locations
(180 striae) throughout the area has been determined. Although there is
some variation in these directions between individual sites, the mean
displacement vector of 0708N agrees well with previously published
kinematic analyses in this area in which values of 0758N (Mattei 1987;
249 striae) and 0628N (Averbuch et al. 1995; 107 striae) were reported.
The pin lines within the thrust belt are not vertical in the present-day
and partially restored cross-sections and therefore it is necessary to take
all measurements from a single horizon (key bed) that is representative of
the overall structure. The top of the Calcare Massiccio was selected for
this because it is composed of .1 km of platform carbonates, which have
probably controlled the style of deformation to a large extent. In addition,
its position (and therefore length) in the subsurface is commonly clearly
defined by seismic reflection data.
Results
In contrast to published cross-sections, which generally cross the
central part of the Montagna dei Fiori anticline in the area of
greatest structural complexity, the new section (Fig. 7) crosses an
area in which the surface structures are relatively simple. The
advantages of this line of section are that the surface strati-
graphic relationships and subsurface seismic data are much
clearer.
The westernmost structure is the Monte Gorzano Pleistocene
normal fault, along which the Laga Formation in the hanging
wall is juxtaposed against the Cerrogna Marls. The line of
section then runs to the south of the southern tip of the
Acquasanta Thrust; in this area only a broad syncline is present
in the Laga Formation, an arrangement that clearly demonstrates
that the Acquasanta thrust is a low-displacement structure. East
of this, only the uppermost formations in the carbonate succes-
sion (Cerrogna and Orbulina Marls) are exposed in the Montagna
dei Fiori Anticline, which has an open geometry defined by
outcrop and seismic data. The eastward onlap of the Laga
Formation onto the pre-Messinian carbonate succession below is
clearly shown by the cross-section.
In the subsurface at the western end of the cross-section, the
position of the main footwall thrust ramp is located beneath the
Monte Gorzano normal fault. East of this, beneath the Montagna
dei Fiori Anticline, lies a major thrust (T1), which has an
antiformal geometry (note that this is not the equivalent of the
more minor Salinello Thrust described previously); in the hang-
ing wall the pre-Messinian carbonate succession on the eastern
limb of the Montagna dei Fiori Anticline is cut off against this.
At the top of the footwall to this thrust (T1) is a condensed
succession of the Schlier and Bisciaro Formations, thickening
westward. Below this the rest of the carbonate succession has
normal thickness. However, on the eastern side of the subsurface
anticline a pre-existing normal fault is interpreted; this is similar
to those exposed in the Montagna dei Fiori Anticline (e.g.
Giannini 1960; Mattei 1987; Calamita et al. 1998). To the east of
this fault the Jurassic succession is condensed.
The footwall beneath the Montagna dei Fiori Anticline is itself
duplicated along a deeper thrust (T4), which dips moderately
west; there is c. 5.5 km of displacement along this. Thrusts T1
and T4 branch together in the subsurface to the east of the
Montagna dei Fiori Anticline along a major horizontal detach-
ment at the top of the pre-Messinian carbonate succession at
6100 m. Above the detachment, dips in the Laga Formation
immediately east of the Montagna dei Fiori Anticline decrease
from subvertical at the surface to gently east in the subsurface.
This defines a minor hanging-wall syncline in the Laga and
Teramo Formations. Beneath the syncline a gently west-dipping
thrust fault (T2) with c. 3.0 km of displacement branches from
the main detachment and separates this syncline from the
Bellante Structure to the east.
The Bellante Structure has an antiformal geometry and is
limited on its eastern side by a moderately west-dipping thrust
fault (T3), which branches from the main detachment below. The
internal structure is not defined in the cross-section, but com-
prises stacked slices of the Laga and Teramo Formations. The
structure has associated growth strata of early Pliocene age and
is sealed within the lower Pliocene ii unit of the Costiera
Structure.
Beneath the foreland and coastline the geometry of the
Costiera Structure is defined by a pre-kinematic unit of earliest
Pliocene age (lower Pliocene i unit). This has been deformed into
a major east-vergent anticline as a result of movement along an
underlying thrust fault (T5), which branches from the main
detachment. Associated with this structure are growth strata of
early Pliocene to late Pliocene age (LPii to UPQ). This structure
accommodates 4.5 km of shortening. Below the Adriatic Sea to
the east, the pre-Messinian carbonate succession dips gently west
and is penetrated by exploration wells 17 km offshore. Above
this, the Pliocene sediments onlap the top of the carbonates and
thin to the east.
The total shortening determined by restoration of this cross-
section is 32.6 km.
Shortening rates
In the new model almost all of the displacement is transferred to
the blind structures beneath the foreland (i.e. the portion of the
thrust system that has been analysed is kinematically closed).
Therefore the timing of deformation revealed by the blind
structures must equally relate to more internal structures. Seismic
stratigraphic analysis of the blind structures suggests that the
main period of contractional deformation began after deposition
of the Teramo Formation and during deposition of the Cellino
Formation, in the interval containing both G. margaritae and
Fig. 7. Present-day (top) cross-section covering the southern part of the Montagna dei Fiori Anticline and Acquasanta Syncline (refer to Fig. 3 for the line
of section). The restored cross-section shows the onlapping geometry of the Laga foredeep basin at the end of the Messinian; also shown are intermediate
steps in the restoration. Total shortening revealed by restoration is 32.6 km. Triangles represent hydrocarbon exploration wells; dashed arrows are pin
lines. The main thrusts are numbered T1–T5.
TESTING THRUST TECTONIC MODELS 9
G. puncticulata. The youngest structure (the Costiera Structure)
is sealed within sediments of late Pliocene age (G. inflata
biozone) and below Pleistocene sediments (H. balthica biozone).
Many of the first and last occurrences (FO and LO) of the
Pliocene Foraminifera have been calibrated (� 0.01 Ma) using
precession-controlled sedimentary cycles exposed in Sicily (Lou-
rens et al. 1996). It is therefore possible to calibrate this relative
time scale with absolute time (Fig. 8). Although no absolute
dating is available for H. balthica, at the type section for the
Plio-Pleistocene boundary in Calabria it is synchronous with first
occurrence of the calcareous nannofossil Gephyrocapsa spp.
.5.5 �m (Pasini & Colalongo 1997; Rio et al. 1997), which is
dated at 1.61 Ma (Lourens et al. 1996). Using this chronology,
deformation is estimated to have started at 4.3 Ma (� 0.2 Ma)
and ended at 1.7 Ma (� 0.1 Ma), a total period of 2.6 Ma
(� 0.3 Ma). The average shortening rate for the new model is
therefore 12.5 (� 1.5) mm a�1.
It is possible to break down further the deformation chronology
into two main steps corresponding to the periods of growth of the
Bellante and then Costiera Structure (Fig. 8). The start and end
dates discussed above relate to these two structures respectively;
additional seismic stratigraphic analysis shows that the Bellante
Structure was sealed during the later part of the early Pliocene (G.
puncticulata biozone; c. 2.5 (� 0.2) Ma) and that the Costiera
Structure began to develop just before this but within the same
interval (c. 2.7 (� 0.1) Ma). Using this refined chronology, the
initial 27.3 km shortening, accommodated by the Bellante Struc-
ture, occurred at a rate of 15.2 (� 3.5) mm a�1 (27.3 km between
4.3 and 2.5 Ma). This was followed by a period of much less rapid
shortening at a rate of 5.3 (� 1.1) mm a�1 (5.3 km between 2.7
and 1.7 Ma), as recorded by the Costiera Structure.
Discussion
General points
In the new cross-section the displacement beneath the Acqua-
santa and Montagna dei Fiori Anticlines is transferred to the
Bellante and Costiera Structures beneath the foreland. The key
to this interpretation is the presence of a major detachment at
a stratigraphically shallower level than the main detachment
within the Burano evaporites. This second detachment lies at
the base of the Laga and Pliocene Formations and below the
blind structures under the foreland. Thus it is no longer
Fig. 8. Range chart for key Pliocene and
Pleistocene Foraminifera in the Marche–
Abruzzi Apennines and Adriatic Sea; the
biostratigraphic ranges have been calibrated
in absolute time using dating by Lourens et
al. (1996). Using these dates it is possible
to interpret the deformation chronology for
the Bellante and Costiera Structures; this is
shown on the right of the figure. FCO, first
common occurrence; FO, first occurrence;
G., Globorotalia; LCO, last common
occurrence; LO, last occurrence; mP,
middle Pliocene.
R. S . J. TOZER ET AL .10
necessary to have an emergent thrust, backthrust, high-strain
zone or buried thrust to the east of the Montagna dei Fiori
Anticline.
East-vergent folds are present further east beneath the Adriatic
Sea, but these clearly involve the entire pre-Messinian carbonate
succession regardless of whether they are interpreted to have
been generated by thin- (Bally et al. 1986; Ori et al. 1986) or
thick-skinned thrusts (Argnani & Gamberi 1995). Therefore they
cannot accommodate any of the displacement along the main
thrust beneath the Montagna dei Fiori Anticline. For this reason,
the shallow structures in the new cross-section form a kinemati-
cally closed system; that is to say, shortening on one structure is
balanced by shortening on another elsewhere within the cross-
section.
The difference in structural style of the blind structures can be
correlated with a change in detachment composition. In the
Bellante Structure imbrication is the main shortening mechan-
ism; this structure is detached towards the base of the Laga
Formation. In contrast, thrust-propagation folding along one
dominant thrust characterizes the Costiera Structure; this is
detached along the Gessoso-solfifera Formation, an easy slip
horizon composed of marl and gypsum. Specific predictions of
the models are therefore compatible with the geological reality.
The origin of the Laga Formation’s onlap around the Acqua-
santa Syncline along the line of section is debatable. A similar
relationship is well mapped and described on the Montagnone
Anticline adjacent to the south of the Montagna dei Fiori
Anticline (e.g. Centamore et al. 1991; Vezzani & Ghisetti 1998;
Scisciani et al. 2001). It might seem coincidental that the marker
bed exposed along the cross-section pinches out on the crest of
the Montagna dei Fiori Anticline (Fig. 7); was this a pre-existing
structural high at the time of Laga deposition? The lack of
carbonate conglomerates and/or breccias (derived from structural
highs) within this formation suggests not, and if an onlapping
foredeep basin were to be folded, some of the onlaps would
naturally coincide with the crests of anticlines.
It is tempting to interpret that the location of the Monte
Gorzano Normal Fault has been controlled by the T1 thrust ramp
below (Fig. 7). However, if the position of this thrust ramp is
mapped using additional seismic data, serial cross-sections and
palaeomagnetic constraints (Speranza et al. 2003), it strikes
north–south beneath the Laga Mountains, a trend that is oblique
to the strike of the normal fault (Fig. 3). The coincidence of
these two structures is therefore simply a quirk of the section
line.
The shortening value for the Costiera Structure (4.5 km) in
this study is likely to represent only a minimum, as shortening
by distributed strain is not considered and the internal structure
is simplified. More detailed restoration of the structure by Artoni
& Casero (1997) suggests that this structure accommodates
7.4 km shortening. This is because their interpretation contains
five imbricates in contrast to the simplified structure shown in
Figure 7. In addition, a greater amount of shortening was
determined by Artoni & Casero (1997) as a result of their
assumption that deformation commenced during the earliest
Pliocene. In contrast, the analysis in this study shows that the
sediments deposited during this time have a pre-kinematic
geometry and therefore predate compressional deformation.
Comparison with published models
Many existing models fail because of their interpretations of
emergent thrusts, which are incompatible with geological map
patterns for the Acquasanta Anticline (Bally et al. 1986; Ghisetti
et al. 1993 (thin-skinned model); Calamita et al. 1994; Scisciani
et al. 2002) or the Montagna dei Fiori Anticline (Ghisetti et al.
1993 (thick-skinned model); Ghisetti & Vezzani 1997, 2000;
Alberti et al. 1998). There are also problems with the two
alternative explanations that have been presented for the ‘miss-
ing’ displacement on the eastern side of the Montagna dei Fiori
Anticline. Burial of a formerly emergent thrust below the
unconformity at the base of the middle Pliocene introduces the
‘instantaneous thrusting’ problem (Calamita et al. 1994; Sciscia-
ni et al. 2002) and there is no evidence reported for a major
backthrust in this area (Bally et al. 1986; Ghisetti et al. 1993
(thin-skinned model); Barchi et al. 2001). None of these
structures are present in the new models so these do not suffer
from the problems described above.
The key difference between the new model and those
described above is that none of these solutions are required
because all of the displacement has been transferred to the blind
structures below the foreland. The amount of shortening east of
the Sibillini mountains determined by restoration of the cross-
section (32.6 km) is therefore much less than previously esti-
mated (e.g. 52 km, Calamita et al. 1994; c. 60 km, Bigi et al.
1995). This is because the blind structures are kinematically
linked to the more internal structures.
Basement involvement and magnetic modelling
The new cross-section is completed only to the base of the
Calcare Massiccio–top of the Burano evaporites. This horizon
corresponds to the deepest reflector that can be identified with
confidence in the seismic data; its position can also be estimated
with knowledge of the thicknesses of the units above. The
horizon therefore provides the best guide to the depth of the top
of the basement below; in the footwall below the Acquasanta
Syncline it lies .1 km shallower than below the foreland despite
the reduced thickness of the pre-Messinian carbonate succession
below the foreland. Is this difference in elevation due to a pre-
existing structural high or to involvement of the basement in the
thrust belt? Given that the Jurassic and Miocene pelagic
carbonate sediments are more condensed in the region of lower
basement elevation (below the foreland), the currently more
elevated area cannot have been a pre-existing high at the time of
their deposition. Although it is not possible to rule out the
presence of a pre-existing high at the eastern margin of the Laga
Basin, it seems more likely that there is a component of
basement involvement in the thrust belt at this position. This
hypothesis is supported by the most recent magnetic anomaly
map of Italy (Chiappini et al. 2000), which shows that a þ53 nT
magnetic anomaly is centred below the southern part of the
Montagna dei Fiori Anticline (Fig. 9). The line of section runs
across the southern part of this anomaly.
To test the hypothesis of basement involvement a magnetic
model was constructed for the line of section (Fig. 10a).
Assuming a constant geothermal gradient of 25 8C km�1 along
the line of section (della Vedova et al. 2001), the 600 8C
isotherm (corresponding to the Curie temperature of magnetite)
was placed at the base of the model at 24 km; above this, a top
basement horizon was added 1600 m below the base of the
Calcare Massiccio. Although there are no susceptibility measure-
ments available for the Verrucano, it is thought to have moderate
susceptibility by analogy with similar formations (Speranza &
Chiappini 2002); a value of 10 000 �SI was therefore assigned to
the basement (including Verrucano and underlying basement
down to 24 km depth). This value represents a mix between
susceptibility values of the Verrucano and similar low-grade
TESTING THRUST TECTONIC MODELS 11
metamorphic rocks (c. 1000 �SI), and high-grade and lower
crustal rocks, which are known to be very magnetic (up to
100 000 �SI, e.g. Rochette 1994). The Laga–Plio-Pleistocene
below the foreland were also added as a simplified polygon with
a susceptibility of 100 �SI (e.g. Sagnotti et al. 1998). The
Triassic to Miocene carbonate succession is known to be
essentially non-magnetic (Speranza & Chiappini 2002).
The results of this first model are shown in Figure 10a. In the
eastern part of the cross-section the positive anomaly exceeding
50 nT represents the northernmost part of a regional intense
(100–200 nT) positive anomaly characterizing the whole external
central Apennines (Chiappini et al. 2000; Fig. 9) and interpreted
to arise from intrusions at 13–18 km depth within the basement
(Speranza & Chiappini 2002); the target of the modelling was
not this but the more subtle positive anomaly over the Montagna
dei Fiori Anticline. The top basement horizon was therefore
modified to obtain a match with this; the result is shown in
Figure 10b. A good fit is achieved between the observed and
modelled anomaly by adding a major top basement step (from
�8.3 to �15.0 km) below the Montagna dei Fiori Anticline and
deepening the basement to the west of this; there can be
confidence in this solution because a change in only one
parameter is necessary to obtain agreement. The basement step
lies directly below the anticline, a geometry that is similar to
idealized models of reactivated half-grabens (e.g. Williams et al.
1989). However, we do not rule out the possibility that the
displacement on thrust T4 could also be the expression of
thrusting or distributed shortening within the half-graben. In
summary, there is evidence for a component of basement influ-
ence to the surface structure in the Montagna dei Fiori area.
Conclusions
A repetition of the seismic stratigraphy at depth below the
Acquasanta and Montagna dei Fiori Anticlines indicates that a
major thrust lies beneath these structures. A new model has
therefore been constructed to illustrate a possible solution to the
‘missing’ displacement on the eastern side of the Montagna dei
Fiori Anticline. In the absence of data showing a major emergent
thrust, backthrust, buried thrust or high-strain zone, the solution
is to balance the displacement with shortening of the blind
Bellante and Costiera Structures beneath the foreland. These are
detached at the base of the Pliocene, a shallower stratigraphic
level than the Acquasanta and Montagna dei Fiori Anticlines,
and this is therefore a viable solution. The main implication is
that the Bellante Structure accommodates a large amount of the
total shortening, .20 km. The total amount of shortening for the
new model is 32.6 km.
The secular shortening rate for the new model is 12.5 mm a�1.
This can be broken down into two periods corresponding to
growth of the blind Bellante and Costiera Structures; early
shortening took place at c. 15 mm a�1, followed by shortening at
one-third of this rate during the final stages of contractional
deformation in the central Apennines.
The base of the footwall to the Acquasanta and Montagna dei
Fiori Anticlines is shallower than the equivalent horizon beneath
the foreland, indicating a component of basement-involved uplift
of these structures. Modelling of magnetic anomalies along the line
of section indicates that a major top-basement step (lower in the
west) lies directly below the Montagna dei Fiori Anticline, further
supporting a composite thin- and thick-skinned uplift mechanism.
Financial support from the NERC (award reference GT 04/99/ES/118)
and BG is gratefully acknowledged (R.S.J.T.). BG generously provided
seismic and well data, and L. Vezzani kindly supplied geological maps of
the area. Figure 9 was prepared by F. D’Ajello Caracciolo. Cross-section
restoration was carried out using 2DMove provided by Midland Valley
Exploration. Constructive reviews by P. Shiner and E. Tavarnelli helped
to improve the manuscript and figures.
References
Alberti, M., Decandia, F.A. & Tavarnelli, E. 1998. Kinematic evolution of the
outer zones of the northern Apennines, Italy: the contribution of sequential
cross-section balancing techniques. Memorie della Societa Geologica Itali-
ana, 52, 607–616.
Argnani, A. & Gamberi, F. 1995. Stili strutturali al fronte della Catena
Appenninica nell’Adriatico centro-settentrionale. Studi Geologici Camerti,
Volume Speciale, 1995/1, 19–28.
Artoni, A. & Casero, P. 1997. Sequential balancing of growth structures, the late
Fig. 9. Magnetic anomaly map (total
intensity at sea level) of the study area from
Chiappini et al. (2000); contours are spaced
at 2 nT intervals. Also shown are the main
faults and the boundary between the Laga
Formation and the underlying pre-
Messinian carbonate succession. The
þ53 nT anomaly centred over the southern
part of the Montagna dei Fiori (MF)
Anticline should be noted. Symbols are as
in Figure 3.
R. S . J. TOZER ET AL .12
Tertiary example from the central Apennine. Bulletin de la Societe
Geologique de France, 168, 35–49.
Averbuch, O., Mattei, M., Kissel, C., Frizon de Lamotte, D. & Speranza, F.
1995. Cinematique des deformations au sein d’un systeme chevauchant
aveugle: l’exemple de la Montagna dei Fiori (front des Apennins centraux,
Italie). Bulletin de la Societe Geologique de France, 166, 451–461.
Bally, A.W., Burbi, L., Cooper, C. & Ghelardoni, R. 1986. Balanced sections
and seismic reflection profiles across the Central Apennines. Memorie della
Societa Geologica Italiana, 35, 257–310.
Barchi, M., Landuzzi, A., Minelli, G. & Pialli, G. 2001. Outer Northern
Apennines. In: Vai, G.B. & Martini, I.P. (eds) Anatomy of an Orogen: the
Apennines and Adjacent Mediterranean Basins. Kluwer Academic, Dordrecht,
215–254.
Bigazzi, G., Bonadonna, F.P., Centamore, E., Leone, G., Mozzi, M., Nisio, S.
& Zanchetta, G. 2000. New radiometric dating of volcanic ash layers in
Periadriatic foredeep basin system, Italy. Palaeogeography, Palaeoclimatol-
ogy, Palaeoecology, 155, 327–340.
Bigi, S., Calamita, F., Cello, G., Centamore, E., Deiana, G., Paltrinieri, W.
& Ridolfi, M. 1995. Evoluzione Messiniano–Pliocenica del sistema
catena–avanfossa nell’area Marchigiano–Abruzzese esterna. Studi Geologici
Camerti, Volume Speciale, 1995/1, 29–35.
Bortolotti, V., Passerini, P., Sagri, M. & Sestini, G. 1970. The miogeosyncl-
inal sequences. Sedimentary Geology, 4, 341–444.
Calamita, F., Cello, G., Deiana, G. & Paltrinieri, W. 1994. Structural styles,
chronology rates of deformation and time–space relationships in the
Umbria–Marche thrust system (central Apennines, Italy). Tectonics, 13,
873–881.
Calamita, F., Pizzi, A., Ridolfi, M., Rusciadelli, G. & Scisciani, V. 1998. Il
Butressing delle faglie sinsedimentarie pre-thrusting sulla strutturazione
Neogenica della catena Appenninica: l’esempio della M.gna dei Fiori
Fig. 10. Magnetic models for the cross-
section (Fig. 7; see Fig. 9 for location). (a)
Original cross-section and magnetic model;
the top of the basement has been
constructed 1600 m below the base of the
Calcare Massiccio. (b) Modified cross-
section and magnetic model; a major top-
basement step has been added to obtain a fit
with the positive anomaly over the
Montagna dei Fiori Anticline.
TESTING THRUST TECTONIC MODELS 13
(Appennino Centrale esterno). Bollettino della Societa Geologica Italiana,
117, 725–745.
Cantalamessa, G., Centamore, E., Chiocchini, E., Micarelli, A. & Potetti,
M. 1986. Il Miocene delle Marche. Studi Geologici Camerti, Volume Speciale,
35–55.
Centamore, E., Adamoli, L. & Berti, D. et al. 1991. Carta geologica dei bacini
della Laga e del Cellino e dei rilievi carbonatici circostanti, scale 1:100 000.
Studi Geologici Camerti, Volume Speciale, 1991/2.
Chiappini, M., Meloni, A., Boschi, E., Faggioni, O., Beverini, N., Carmis-
ciano, C. & Marson, I. 2000. Shaded relief magnetic anomaly map of Italy
and surrounding marine areas. Annali di Geofisica, 43, 983–989.
Chiocchini, U. & Cipriani, N. 1992. Provenance and evolution of Miocene
turbidite sedimentation in the central Apennines, Italy. Sedimentary Geology,
77, 185–195.
Crescenti, U., D’Amato, C., Balduzzi, A. & Tonna, M. 1980. Il Plio-
Pleistocene del sottosuolo Abruzzese–Marchigiano tra Ascoli Piceno e
Pescara. Geologica Romana, 19, 63–84.
Dahlstrom, C.D.A. 1969. Balanced cross sections. Canadian Journal of Earth
Sciences, 6, 743–757.
Dela Pierre, F., Ghisetti, F., Lanza, R. & Vezzani, L. 1992. Paleomagnetic
and structural evidence of Neogene tectonic rotation of the Gran Sasso range
(central Apennines, Italy). Tectonophysics, 215, 335–348.
della Vedova, B., Bellani, S., Pellis, G. & Squarci, P. 2001. Deep
temperatures and surface heat flow distribution. In: Vai, G.B. & Martini,
I.P. (eds) Anatomy of an Orogen: the Apennines and Adjacent Mediterranean
Basins. Kluwer Academic, Dordrecht, 65–76.
Dix, C.H. 1955. Seismic velocities from surface measurements. Geophysics, 20,
68–86.
Faccenna, C., Davy, P., Brun, J.-P., Funiciello, R., Giardini, D., Mattei, M.
& Nalpas, T. 1996. The dynamics of back-arc extension: an experimental
approach to the opening of the Tyrrhenian Sea. Geophysical Journal
International, 126, 781–795.
Funiciello, R., Parotto, M. & Praturlon, A. 1981. Carta tettonica d’Italia.
CNR 1:1 500 000.
Ghisetti, F. & Vezzani, L. 1997. Interfering paths of deformation and develop-
ment of arcs in the fold-and-thrust belt of the central Apennines (Italy).
Tectonics, 16, 523–536.
Ghisetti, F. & Vezzani, L. 2000. Detachments and normal faulting in the Marche
fold-and-thrust belt (central Apennines, Italy): inferences on fluid migration
paths. Journal of Geodynamics, 29, 345–369.
Ghisetti, F., Barchi, M., Bally, A.W., Moretti, I. & Vezzani, L. 1993.
Conflicting balanced structural sections across the Central Apennines (Italy):
problems and implications. In: Spencer, A.M. (ed.) Generation, Accumula-
tion and Production of Europe’ Hydrocarbons III. Special Publication of the
European Association of Petroleum Geoscientists, 3, 219–231.
Giannini, E. 1960. Osservazioni geologiche sulla Montagna dei Fiori (Ascoli
Piceno–Teramo). (Includes 1:25 000 geological map.). Bollettino della
Societa Geologica Italiana, 79, 183–206.
Jones, P.B. 1982. Oil and gas beneath east-dipping underthrust faults in the Alberta
Foothills, Canada. In: Powers, R.B. (ed.) Geologic Studies of the Cordilleran
Thrust Belt. Publications of Rocky Mountain Association of Geologists, 1,
61–74.
Koopman, A. 1983. Detachment tectonics in the central Apennines, Italy.
Geologica Ultraiectina, 30, 1–55.
Lavecchia, G. 1988. The Tyrrhenian–Apennines system: structural setting and
seismotectogenesis. Tectonophysics, 147, 263–296.
Lourens, L.J., Antonarakou, A., Hilgen, F.J., Van Hoof, A.A.M., Vergnaud-
Grazzini, C. & Zachariasse, W.J. 1996. Evaluation of the Plio-Pleistocene
astronomical timescale. Paleoceanography, 11, 391–413.
Malinverno, A. & Ryan, W.B.F. 1986. Extension in the Tyrrhenian Sea and
shortening in the Apennines as result of arc migration driven by sinking of
the lithosphere. Tectonics, 5, 227–245.
Mattei, M. 1987. Analisi geologico-strutturale della Montagna dei Fiori (Ascoli
Piceno, Italia Centrale). (Including Carta Geologica della Montagna dei Fiori
(Apennino Centrale), scale 1:25 000.). Geologica Romana, 26, 327–347.
Mattei, M., Funiciello, R. & Kissel, C. 1995. Paleomagnetic and structural
evidence for Neogene block rotations in the Central Apennines, Italy. Journal
of Geophysical Research, 100, 17863–17883.
Mazzoli, S., Deiana, G., Galdenzi, S. & Cello, G. 2002. Miocene fault-
controlled sedimentation and thrust propagation in the previously faulted
external zones of the Umbria–Marche Apennines, Italy. In: Bertotti, G.,
Schulman, K. & Cloetingh, S.A.P.L. (eds) Continental Collision and the
tectono-sedimentary evolution of forelands. EGU Stephan Mueller Special
Publication Series, 1, 195–209.
Morley, C.K. 1986. A classification of thrust fronts. AAPG Bulletin, 70, 12–25.
Mugnier, J.-L., Mascle, G. & Faucher, T. 1992. La structure des Siwaliks de
l’Ouest Nepal: un prisme d’accretion intracontinental. Bulletin de la Societe
Geologique de France, 163, 585–595. (For a version in English see:
International Geology Review, 35, 1–16.)
Mutti, E., Nilsen, T.H. & Ricci Lucchi, R. 1978. Outer fan depositional lobes of
the Laga Formation (Upper Miocene and Lower Pliocene), East–Central Italy.
In: Stanley, D.J. & Kelling, G. (eds) Sedimentation in Submarine
Canyons, Fans, and Trenches. Dowden, Hutchinson and Ross, Stroudsburg,
PA, 210–223.
Needham, D.T., Matthews, S.J. & Butler, R.W.H. 2004. Introduction to ‘Oil
& Gas in Compressional Belts’. Marine and Petroleum Geology, 21,
783–784.
Ori, G.G., Roveri, M. & Vannoni, F. 1986. Plio-Pleistocene sedimentation in the
Apenninic–Adriatic foredeep (Central Adriatic Sea, Italy). In: Allen, P.A.
& Homewood, P. (eds) Foreland Basins. International Association of
Sedimentologists, Special Publications, 8, 183–198.
Paltrinieri, W., Zanchini, G., Martini, N. & Roccia, L. 1982. Evoluzione del
bacino torbiditico Marchigiano–Abruzzese a partire dal Messiniano in base a
lineazioni profonde. Memorie della Societa Geologica Italiana, 24, 233–242.
Paradisi, A., Girotti, O., Guerricchio, A. & Colacicchi, R. 1969. Carta
Geologica D’Italia, Foglio 133–134, Ascoli Piceno–Giulianova, Scale
1:100 000.
Parotto, M. & Praturlon, A. 1975. Geological summary of the Central
Apennines. Quaderni de ‘La Ricerca Scientifica’, 90, 258–311.
Pasini, G. & Colalongo, M.L. 1997. The Pliocene–Pleistocene boundary-
stratotype at Vrica, Italy. In: Van Couvering, J.A. (ed.) The Pleistocene
Boundary and the Beginning of the Quaternary. World and Regional Geology,
9, 15–45.
Rio, D., Raffi, I. & Backman, J. 1997. Calcareous nannofossil biochronology and
the Pliocene–Pleistocene boundary. In: Van Couvering, J.A. (ed.) The
Pleistocene Boundary and the Beginning of the Quaternary. World and
Regional Geology, 9, 63–78.
Rochette, P. 1994. Comment on ‘Anisotropic magnetic susceptibility in the
continental lower crust and its implication for the shape of magnetic
anomalies’ by G. Florio et al. Geophysical Research Letters, 21, 2773–2774.
Roveri, M., Bassetti, M.A. & Ricci Lucchi, F. 2001. The Mediterranean
Messinian salinity crisis: an Apennine foredeep perspective. Sedimentary
Geology, 140, 201–214.
Sagnotti, L., Speranza, F., Winkler, A., Mattei, M. & Funiciello, R. 1998.
Magnetic fabric of clay sediments from the external northern Apennines
(Italy). Physics of the Earth and Planetary Interiors, 105, 73–93.
Scisciani, V., Calamita, F., Tavarnelli, E., Rusciadelli, G., Ori, G.G. &
Paltrinieri, W. 2001. Foreland-dipping normal faults in the inner edges of
syn-orogenic basins: a case from the Central Apennines, Italy. Tectonophysics,
330, 211–224.
Scisciani, V., Tavarnelli, E. & Calamita, F. 2002. The interaction of extension
and contractional deformations in the outer zones of the Central Apennines,
Italy. Journal of Structural Geology, 24, 1647–1658.
Speranza, F. & Chiappini, M. 2002. Thick-skinned tectonics in the external
Apennines, Italy: new evidence from magnetic anomaly analysis. Journal of
Geophysical Research, 107(B11), 2290.
Speranza, F., Sagnotti, L. & Mattei, M. 1997. Tectonics of the Umbria–
Marche–Romagna Arc (central northern Apennines, Italy): new paleomag-
netic constraints. Journal of Geophysical Research, 102, 3153–3166.
Speranza, F., Adamoli, L., Maniscalco, R. & Florindo, F. 2003. Genesis and
evolution of a curved mountain front: paleomagnetic and geological evidence
from the Gran Sasso range (central Apennines, Italy). Tectonophysics, 362,
183–197.
Tavarnelli, E., Butler, R.W.H., Decandia, F.A., Calamita, F., Grasso, M.,
Alvarez, W. & Renda, P. 2004. Implications of fault reactivation and
structural inheritance in the Cenozoic tectonic evolution of Italy. In:
Crescenti, U., D’Offizi, S., Merlini, S. & Sacchi, R. (eds) The Geology
of Italy. Societa Geologica Italiana Special Volume, 201–214.
Vann, I.R., Graham, R.H. & Hayward, A.B. 1986. The structure of mountain
fronts. Journal of Structural Geology, 8, 215–227.
Vezzani, L. & Ghisetti, F. 1998. Carta Geologica Dell’Abruzzo. Scale 1:100 000.
Williams, G. & Chapman, T. 1983. Strains developed in the hangingwalls of
thrusts due to their slip/propagation rate: a dislocation model. Journal of
Structural Geology, 5, 563–571.
Williams, G.D., Powell, C.M. & Cooper, M.A. 1989. Geometry and
kinematics of inversion tectonics. In: Cooper, M.A. & Williams, G.D.
(eds) Inversion Tectonics. Geological Society, London, Special Publications,
44, 3–15.
Received 5 November 2004; revised typescript accepted 30 May 2005.
Scientific editing by Ian Alsop
R. S . J. TOZER ET AL .14