basin research (2001) 13, 199–216 chronostratigraphic …forth/publications/garces01.pdf ·...
Post on 01-Jun-2020
3 Views
Preview:
TRANSCRIPT
Chronostratigraphic framework and evolution of theFortuna basin (Eastern Betics) since the Late MioceneM. GarceÂs,* W. Krijgsman² and J. Agusti³
*Institute of Earth Sciences Jaume Almera, CSIC, Sole i SabarõÂs
s/n, 08028-Barcelona, Spain
²Paleomagnetic Laboratory Fort Hoofddijk, Budapestlaan 17,
3584 CD Utrecht, The Netherlands
³Institut de Paleontologia Miquel Crusafont, Escola Industrial 23,
08201 Sabadell, Spain
ABSTRACT
A Tortonian to Pliocene magnetostratigraphy of the Fortuna basin supports a new
chronostratigraphic framework, which is signi®cant for the palaeogeographical and geodynamic
evolution of the Eastern Betics in SE Spain.
The Neogene Fortuna basin is an elongated trough which formed over a left-lateral strike-slip zone
in the Eastern Betics in the context of the convergence between the African and Iberian plates.
Coeval with other basins in the Alicante±Cartagena area (Eastern Betics), rapid initial
subsidence in the Fortuna basin started in the Tortonian as a result of WNW±ESE stretching.
This led to transgression and deposition of marine sediments over extensive areas in open
connection with the neighbouring basins. Since the late Tortonian, N±S to NW±SE
compression led to inversion of older extensional structures. The transpressional tectonics along
the NE±SW-trending Alhama de Murcia Fault is related to the rising of a structural high
which isolated the Fortuna basin from the open Mediterranean basin. The progression of basin
con®nement is indicated by the development of restricted marine environments and deposition
of evaporites (7.8±7.6 Ma). The new basin con®guration favoured rapid sediment accumulation
and marine regression. The basin subsided rapidly during the Messinian, leading to the
accumulation of thick continental sequences. During the Pliocene, left-lateral shear along the
Alhama de Murcia Fault caused synsedimentary folding, vertical axis block rotations and uplift
of both the basin and its margins. The overall sedimentary evolution of the Fortuna basin can
be regarded as a developing pull-apart basin controlled by NE±SW strike-slip faults. This
resembles the evolution that has taken place in some areas of the Eastern Alboran basin since
the late Tortonian.
INTRODUCTION
The Neogene tectonic evolution of the Betic, Rif and
Alboran region, at the western end of the Alpine±
Mediterranean collisional system, continues to puzzle
geoscientists (Sanz de Galdeano, 1990; Maldonado &
Comas, 1992; Lonergan & White, 1997; Comas et al.,1999; Torne et al. 2000). Controversy surrounds the
origin of the Alboran basin, the geodynamic evolution of
the Betic and Rif cordilleras, and the timing of closure and
palaeogeography of the late Messinian marine passages
across the Gibraltar Arc. To achieve a complete picture of
the tectonic and sedimentary processes acting in the area
since the early Miocene, onshore and offshore strati-
graphic records must be integrated. Moreover, correlation
between the intramontane basins of the Betic Cordillera is
crucial in understanding the vertical crustal movements
that controlled the post-collisional evolution of the overall
region. A high-resolution chronostratigraphic frame is
therefore required before onshore and offshore basin
stratigraphy can be combined with the results of deeper
crustal geophysical studies to produce satisfying forward
models of the basin-forming mechanisms.
The predominance of restricted marine and continental
facies, with poor biostratigraphic resolution, found in the
Neogene intramontane basins provides a weak chronos-
tratigraphic framework (Sanz de Galdeano & Vera, 1992).
As a result, interbasinal correlations have been made
without a well constrained time frame. Recent studies
(GarceÂs et al., 1998; Krijgsman et al., 2000) have
Basin Research (2001) 13, 199±216
# 2001 Blackwell Science Ltd 199
challenged earlier correlations of the stratigraphic record
of the Fortuna and Lorca basins. In particular, the
interpretation of the evaporitic and diatomitic formations
in these basins as related to the Messinian Salinity Crisis
(Santisteban, 1981; MuÈller & HsuÈ, 1987) was shown to be
clearly untenable. In this paper, we present fuller and
more extended magnetostratigraphic and biostratigraphic
dataset that support these results. A new Tortonian to
Pliocene chronology places the stratigraphic record of the
Fortuna basin in a more consistent palaeogeographical
and geodynamic context, with wider implications for the
evolution of the eastern Betics.
GEODYNAMIC ANDPALAEOGEOGRAPHICAL SETTING
The Betic±Rif mountain belt constitutes the western edge
of the Mediterranean Alpine thrust-belt, which formed
during the Cenozoic in response to the convergence
between the African and European plates. The palaeo-
geographical reconstruction of the belt is complicated by
large-scale tectonic transport oblique to the belt axis,
coupled with very important extension in the central parts
of the chain (Andrieux et al., 1971; Durand Delga &
FontboteÂ, 1980; Sanz de Galdeano, 1990). Lower to
middle Miocene collision led to thrusting and westward-
directed migration of the Alboran domain units (Internal
zones) over the relative autochthonous units of the Iberian
and African continental margins (External zones) (Fig. 1).
One striking feature of the Betic and Rif Cordilleras is the
substantial subsidence accommodated in the Internal
Zones, leading to the generation of the Alboran basin
since the early Miocene. Subsidence of the Alboran basin
re¯ects important crustal thinning, largely accomplished
by means of subcrustal detachments and low-angle
extensional faults as identi®ed along the uplifted ¯anks
of the Alboran basin (GarcõÂa-DuenÄas et al., 1992). A
number of models that involve the removal of subcrustal
continental lithosphere, such as convective removal (Platt
& Vissers, 1989) or delamination (Docherty & Banda,
1995; Platt et al., 1998), have been invoked as a possible
extension driving mechanism. Other authors (Doglioni
et al., 1997; Lonergan & White, 1997) suggest alternative
scenarios in which the Alboran basin, together with
the South Balearic basin, is regarded as a consequence
of the back-arc extension related to a rapidly retreating
subduction of the old Tethyan oceanic crust.
Following continental collision and the emplacement of
the thrust sheet units, the oblique convergence between
Africa and Iberia during the late Miocene caused
deformation along NE±SW and NW±SE strike-slip
faults and the generation of intramontane basins (Sanz
de Galdeano & Vera, 1992). During the Tortonian, the
Alboran basin occupied a wider area than its present-day
Fig. 1. Sketch showing the principal tectonic elements of the Gibraltar arc and Alboran basin region. WAB: West Alboran
basin; EAB: East Alboran basin; SBB: South Balearic basin; AR: Alboran Ridge.
M. GarceÂs et al.
200 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
con®guration, extending towards the north and south to
encompass the Betic and Rif regions. The intramontane
Betic basins are therefore regarded as an uplifted ¯ank of
the Alboran basin (Comas et al., 1992). Among these, the
Fortuna basin is an elongated (15±20 km wide and 60 km
long) trough, sealing the contact between the Internal
and the External zones in the Eastern Betics (Figs 1
and 2). Two major NE±SW-trending shear zones, the
Crevillente Fault and the Alhama de Murcia Fault, limit
its north-western and south-eastern margins, respectively
(Montenat et al., 1990a). The main terrigenous sediment
sources were the External Betics massifs, mainly consist-
ing of Mesozoic and Cenozoic carbonates. Detrital input
from the Internal Betics was less signi®cant and mostly
restricted to the alluvial sequences north of Murcia
(Fig. 2), where an emerged domain known as the SeguraMassif (Montenat, 1973) was present since the Tortonian.
Some present-day relicts of an Internal Betics palaeo-
margin to the east of the Alhama de Murcia Fault are
the Orihuela and Callosa massifs (Fig. 1). The prolonga-
tion of this uplifted block to the SW is detected below
the Quaternary sediments of the Guadalentin corridor
(Fig. 3) by means of a gravimetric anomaly (Gauyau et al.,1977). On the SW edge of the basin, the Sierra EspunÄa
mountain range was an uplifted block of the Internal
Zones between the Fortuna and Lorca basins. Proximal
basin-margin sediments on the sides of the Sierra
EspunÄa indicate the presence of this emergent domain
since the Tortonian (Montenat et al., 1990b; Lonergan &
Schreiber, 1993). On the NE edge of the Fortuna basin,
the Crevillente strait (Montenat, 1973) allowed a marine
connection with the Mediterranean basin in the
Tortonian. The uplift of the eastern margin of the
Fortuna basin, resulting from the transpressional left-
lateral strike-slip tectonics along the Alhama de Murcia
Fault, played an important role in the closure of marine
gateways and in the subsequent isolation of the Fortuna
basin from the Mediterranean Sea, as discussed below.
THE FORTUNA BASIN SEDIMENTARYRECORD
The sedimentary in®ll of the Fortuna basin can be simply
grouped into three basinwide units: (1) a lower trans-
gressive marine unit; (2) a regressive marine to transi-
tional evaporitic unit; (3) a very thick continental alluvial
and lacustrine unit.
Lower Marine unit
An approximately 500-m-thick lower marine succession is
represented by turbidites and pelagic marls, ®rst referred
to as Fortuna marls by Montenat (1973), and later
informally termed the Los BanÄos Fm (MuÈller & HsuÈ,
1987). These marls grade laterally into deltaic facies as
well as reef complexes towards the western and southern
margins of the basin (Santisteban, 1981; Lonergan &
Schreiber, 1993). Pelagic facies yielded lower to upper
Tortonian planktonic assemblages (Montenat, 1973).
Other studies have suggested a Messinian age for the
upper part of the Fortuna marls (Lukowski et al., 1988),
but solid biostratigraphic evidence for this has not been
demonstrated. Magnetostratigraphic data from the Lorca
and Fortuna basins (Krijgsman et al., 2000), however,
con®rmed a late Tortonian age for this unit, as had been
suggested by Montenat (1973).
Evaporitic unit
Overlying the Fortuna marls, an almost 200-m-thick
regressive sequence, with gypsiferous marls, diatomites,
massive gypsum and terrigenous deposits, is referred to as
the RõÂo Chicamo Formation (MuÈller & HsuÈ, 1987). In the
Chicamo section, this unit is grouped into two members: a
lower gypsum unit (Tale Gypsum) and an overlying
cyclic diatomitic±evaporitic sequence (Chicamo diato-
mites). These two members have been lithostratigraphi-
cally traced to the SW edge of the Fortuna basin, in the
Librilla area, where a similar evaporitic sequence has been
described (OrtõÂ et al., 1993; PlayaÁ et al., 1999). Because of
the extreme restriction of the depositional environment,
no reliable marine biostratigraphic markers have been
reported in this unit. Nevertheless, the evaporites of the
Fortuna basin have generally been correlated with the late
Messinian Mediterranean Salinity Crisis (MuÈller &
HsuÈ, 1987; Lukowski et al., 1988; DinareÁs-Turell et al.,1999). Yet, GarceÂs et al. (1998) provided contradictory
data suggesting an older age, and recently has it been
demonstrated that they correspond to a local Tortonian
phase of basin restriction, affecting both the Fortuna and
the Lorca basins (Krijgsman et al., 2000).
Continental unit
The Rio Chicamo Fm. grades upwards into a very thick
continental succession. At the Chicamo section only the
lower part (150 m) of this sequence is exposed, where it
consists of a thinly bedded alternation of evaporites, clays
and sandstones informally known as the Rambla Salada
Fm. (MuÈller & HsuÈ, 1987). More complete exposures
of this upper continental unit occur around Molina de
Segura and in the Librilla area, where it reaches a thick-
ness of about 1000 m. The continental deposits mainly
consist of lacustrine marls and limestones alternating
with alluvial red clays and conglomerates, arranged in an
overall coarsening-upward sequence.
The lower levels of this continental unit have yielded
fossil rodents of middle Turolian age (MN12 Mammal
Neogene Unit, late Tortonian to early Messinian) at the
classical site of Casa del Acero (Mein & AgustõÂ, 1990),
7 km to the south of Fortuna, as well as in some other new
sites in the sections of this study (Figs 4 and 6). The
overlying alluvial±lacustrine sequences are rich in fossil
mammals of late Turolian (MN13, Messinian) to early
Ruscinian (MN14, early Pliocene) age (AgustõÂ et al., 1985).
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 201
Fig. 2. Geological map of the Fortuna basin and neighbouring areas of the eastern Betics (south-east Spain). m: transgressive marine beds recording the Pliocene ¯ooding in the Librilla
area. Redrawn and modi®ed from Montenat et al. (1990a).
M.
Garc
e Âset
al.
202
#2001
Blackw
ellS
cience
Ltd
,B
asinR
esearch,13,
199±216
Fig. 3. Cross-section of the southern sector of the Fortuna basin and the Guadalentin corridor.
The
Neogene
Fortu
na
basin
,B
etic
Cord
illera
#2001
Blackw
ellS
cience
Ltd
,B
asinR
esearch,13,
199±216
203
STUDIED SECTIONS
Earlier magnetostratigraphic studies in the Fortuna basin
focused on the late Turolian (Messinian) continental units
of the Librilla and Molina de Segura areas (GarceÂs et al.,1998) and, more recently, on the evaporitic sequences
of the Chicamo section (DinareÁs-Turell et al., 1999;
Krijgsman et al., 2000) (Fig. 2). In this study, we have
extended the magnetostratigraphic and biostratigraphic
analysis to the complete outcropping sequences in the
Librilla and Molina de Segura areas, where tectonic
deformation has favoured the exposure of thick contin-
uous sequences spanning from the Tortonian marine
marls up to the Pliocene continental units.
The Librilla area
In the area to the north of Librilla, at the southern edge of
the Fortuna basin, the upper Fortuna marls, the Rio
Chicamo Fm and the overlying continental units were
sampled in the Barranco de la Salada and the SifoÂn de
Librilla sections (Figs 2 and 3).
The Barranco de la Salada section
The Barranco de la Salada (BS) section represents a
500-m-thick regressive sequence, consisting of marine
marls and sandstones (uppermost Fortuna marls),
evaporites and terrigenous deltaic deposits towards the
top (Fig. 4). The presence of desiccation cracks, raindrop
impressions and bird footprints indicates that the entire
succession was deposited in a shallow water environment
with periods of subaerial exposure. The lower marls
alternate with thinly bedded sandstones and, rarely, with
conglomerates containing debris from Tortonian basin
fringing reefs. The evaporitic sequence starts with a thick
laminated gypsum unit (Librilla gypsum). A second gypsi-
ferous and marly unit followed by laminated diato-
mitic clays has been lithostratigraphically correlated
with the evaporitic±diatomitic cycles of the Chicamo
section (OrtõÂ et al., 1993), at the NE edge of the basin
(Fig. 2). The upper part of the BS section consists of
terrigenous fan delta sediments corresponding with the
marine±continental transition in the basin. Conglomer-
ates contain clasts of Cretaceous and Palaeocene lime-
stones, suggesting a western source in the External Betics
and in the exhumed North-Betic Foreland basin to the
Fig. 4. Magnetostratigraphy of the Barranco de la Salada section and correlation with the Chicamo section (see location in
Fig. 2). Closed circles indicate reliable palaeomagnetic directions; open circles represent low intensity samples with uncertain
palaeomagnetic directions. Lithostratigraphic units: 1: Lower Marine Unit (Fortuna marls); 2: Evaporitic units; 3: Upper
Continental Unit (see Fig. 2 for location). LG: Librilla Gypsum; TG: Tale Gypsum.
M. GarceÂs et al.
204 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
north of the Sierra EspunÄa (Fig. 2). Palustrine ¯oodplain
deposits at the top of the section have yielded fossil
rodents of middle Turolian age (MN12), similar to the
Casa del Acero faunal assemblage (Mein & AgustõÂ, 1990).
The SifoÂn de Librilla section
The base of the SifoÂn de Librilla (SL) section is
about 2 km to the north of Librilla (Fig. 2). An earlier
palaeomagnetic study focused on the very rich fossilifer-
ous lower part of the section (GarceÂs et al., 1998). In the
present paper we extended the sampled section to the
complete 800-m-thick outcropping sequence. The SL
section is grouped into four members (Fig. 5), from
bottom to top:
1 An alluvial±palustrine member (400 m) consisting ofcyclic alluvial red beds and palustrine organic-rich greymarls and minor lacustrine limestones. Fossil mammalsindicate an MN13 (late Turolian=Messinian) age.2 A prograding conglomeratic member (30 m) thatrepresents a marked basin-wide spread of the alluvialwedges fed from the western margin (External Betics).3 A shallow marine member (30 m), consisting of greysandstones and marls with bivalves, echinoderms andbenthonic foraminifera indicative of shallow (<30 m)water depths and an early Pliocene age. This probablyrepresents the basal Pliocene marine transgression thatfollowed the re-establishment of marine conditions inthe Mediterranean after the Messinian Salinity Crisis.This is the ®rst report of the presence of marinePliocene sediments in the Fortuna basin.4 An upper alluvial member (350 m), consisting ofred silts and channellized conglomerates. Clast com-position again indicates a sediment supply from theExternal Betics. Incised channels and scours indicateNE±SW palaeocurrents, parallel to the long axis ofthe basin and to the axis of a syndepositional synclineaffecting the sediments of this member. Fossil mammallocalities yield early Ruscinian (MN14, early Pliocene)faunas.
The Molina de Segura area
In the Molina de Segura area the two stratigraphically
overlapping Chorrico (CH) and Salinas de Molina (SM)
sections merge into a 900-m-thick composite section
spanning most of the upper continental unit (Fig. 6). The
SM section is about 2 km to the north-east of Molina
de Segura (Fig. 2), and can be approximately anchored
to the top of the CH section on the basis of the bio-
stratigraphic and lithostratigraphic content (Fig. 6).
The Molina de Segura succession was deposited in a
continental environment. The sediments are organized in
an overall coarsening-upward trend re¯ecting the pro-
gradation of an alluvial conglomeratic fan delta system
derived from a western source and advancing over a pre-
existing evaporitic lacustrine environment. The fan delta
deposits inter®nger over the upper part of the section
with red alluvial deposits fed from the eastern margin
(Orihuela±Callosa massifs, Internal Zones).
Fossil mammal localities in the CH section have
yielded a series of middle to late Turolian (MN12 to
MN13) faunas, similar to those described in the Librilla
area. The SM section yields an MN13 age in its lower
part, while Ruscinian (MN14) faunas are found in its
uppermost beds (AgustõÂ et al., 1985).
Fig. 5. Magnetostratigraphy of the SifoÂn de Librilla (SL)
section (see Fig. 2 for location). Closed circles indicate
reliable primary palaeomagnetic directions; open circles
represent secondary palaeomagnetic directions (remagnetized
samples). Lithostratigraphic members: 3.1: alluvial±palustrine;
3.2: prograding alluvial; 3.3: shallow marine; 3.4: upper
alluvial (see text for explanation). e: erosional surface. The
same legend of Fig. 4.
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 205
PALAEOMAGNETIC ANALYSIS
All the studied sections were sampled at approximately
1±2 m stratigraphic intervals with a portable drill and
orientated in the ®eld with a magnetic compass.
Palaeomagnetic analysis in the laboratory included
standard stepwise (<50 uC steps) thermal demagnetiza-
tion and measurement of the natural remanent magne-
tization decay by means of a three-axis SQUID
magnetometer. The majority of the samples displayed a
two-component magnetization (Fig. 7a±c), consisting of
a subrecent normal polarity overprint and a dual polarity
characteristic remanent magnetization. Successful isola-
tion of the characteristic magnetization was possible
after moderate thermal demagnetization (250±350 uC).
Stepwise demagnetization was continued until complete
removal of the characteristic magnetization. We employed
least squares analysis for the estimation of the direction
of the characteristic remanent magnetization.
An exception to the typical two-component natural
remanent magnetization was observed in a number of sites
sharing the same organic-rich grey clay lithology, in the
lower part of the SL section. In those speci®c sites, the
addition of a prefolding reversed magnetization produces
Fig. 6. Magnetostratigraphy of the Molina de Segura composite section (see Fig. 2 for location). See legend to Fig. 4.
M. GarceÂs et al.
206 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
a triple-component magnetization (Fig. 7d). This has
been explained as a remagnetization event linked to the
fall in the sea level at the end of the Messinian, which
favoured the ¯ow of meteoric ground waters to deeper
levels across the sedimentary basin in®ll (GarceÂs et al.,
1998; GarceÂs & Krijgsman, 2000). Oxidation of meta-
stable iron sulphides to magnetite would have produced a
new chemical remanent magnetization parallel to the
reversed geomagnetic ®eld that occurred at that time.
Palaeomagnetic directions show varying degrees of
rotation depending on the location of the sites studied
(Table 1). The mean palaeomagnetic directions from the
CH and SM sections are rotated anticlockwise 50u and
35u, respectively (Fig. 8). This indicates that the overall
Fig. 7. Representative Zijdervelt demagnetization diagrams and natural remanent magnetization decay plots.
Table 1. Mean palaeomagnetic directions and Fisher statistics (Fisher, 1953) of the studied sections. k: precision parameter; a95:
95% con®dence limit.
Site Polarity N
Bedding coordinates
dec inc k a95
Librilla area
Bco de la Salada Normal 115 353 47 11 4
Reverse 19 177 x13 3 25
All samples 134 353 43 7 5
SifoÂn de Librilla Normal 86 354 43 20 4
Reverse 75 185 x45 11 5
All samples 161 359 44 12 3
Molina de Segura area
Chorrico Normal 69 317 30 12 5
Reverse 52 120 x22 11 6
All samples 121 309 27 10 4
Salinas de Molina Normal 05 334 45 6 33
Reverse 47 148 x37 8 8
All samples 52 329 38 8 7
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 207
Fig. 8. Structural sketch of the Fortuna basin and equal area projection of palaeomagnetic directions of the studied sections. Note signi®cant anticlockwise rotations in the Molina de Segura
area (Chorrico and Salinas de Molina sections). See legend to Fig. 2.
M.
Garc
e Âset
al.
208
#2001
Blackw
ellS
cience
Ltd
,B
asinR
esearch,13,
199±216
Molina de Segura area was signi®cantly affected by
sinistral block rotations associated with the left-lateral
shear along the Alhama de Murcia fault. Vertical axis
rotations as a result of the strike-slip deformation,
however, did not occur homogeneously along the
Alhama de Murcia shear zone. Sites in the Librilla area
do not record any signi®cant rotation despite being close
to the shear zone. It is noticeable that block rotations in
the Molina de Segura area appear to be associated with a
bend of the Alhama de Murcia Fault (Fig. 2), where the
sinistral shear displacement probably resulted in local
E±W extension. It is suggested that the extensional
component oblique to the direction of strike-slip trans-
port played a role in favouring vertical axis rotations
in such a transpressive context.
MAGNETOCHRONOLOGY OF THE BASININFILL
In each section we have inferred a local magnetic strati-
graphy by calculating the virtual geomagnetic pole
latitude from each single palaeomagnetic direction
(Figs 4±6). Palaeomagnetic directions from the CH and
SM sections were unrotated 50u and 35u, respectively,
before VGP calculation in order to align them with
the axial geomagnetic mean dipole. In addition to the
magnetostratigraphic results of this study we incorpo-
rated the magnetostratigraphy of the Chicamo section in
the NE edge of the basin (Fig. 4) (Krijgsman et al., 2000).
Basinal correlations
Magnetostratigraphic correlation between the Librilla and
the Molina de Segura areas is determined on the basis of
the coincident reversal patterns and the biostratigraphic
records in the SL and CH sections (Fig. 9). Particularly
signi®cant is the faunal datum provided by the entry
of the fossil rodent Paraethomys, an African genus of
Asian origin that entered the Iberian peninsula at 6.2 Ma
(chron C3An.1n) through the Gibraltar passageway
(GarceÂs et al., 1998). In addition to its chronostratigraphic
signi®cance, this bioevent represents further evidence
for the progression of the land-locking in the Gibraltar
area during the pre-evaporitic late Messinian.
Magnetostratigraphic results from the lower marine
units cannot be independently tied to the upper con-
tinental sections because of insuf®cient stratigraphic
overlap. Their integration into a single magnetostrati-
graphic framework requires the incorporation of the
geomagnetic polarity time scale to the correlation chart
(Fig. 9).
The BS section cannot be stratigraphically tied to its
neighbouring SL section because of a fault contact
(Fig. 2). However, on the basis of the mammal biostrati-
graphic content and the basinal lithostratigraphic frame-
work we know that BS is older than the SL section. A
middle Turolian (MN12) age is determined for the
evaporitic units in all the studied areas (Fig. 9).
Furthermore, there is good agreement between the
magnetic stratigraphy of the BS and Chicamo sections
(Fig. 4), as well as with the previously suggested
lithostratigraphic correlation of the evaporitic units
between the Librilla and the Abanilla areas (OrtõÂ et al.,1993).
Correlation with the time scale
In this paper we take as numerical ages of geomagnetic
reversals those provided by the astronomically calibrated
geomagnetic polarity time scale (Hilgen et al., 1995;
Krijgsman et al., 1999). Earlier results (GarceÂs et al.,1998) con®rmed a Messinian age for the late Turolian
continental units of the Fortuna basin in agreement with
the marine±continental relationships described in the
locality of La Alberca (Fig. 2) (Mein et al., 1973), on the
north-western slopes of the Carrascoy massifs, and in the
Crevillente area (Fig. 2) (Bruijn et al., 1975). The long
and distinctive record of magnetic reversals in the SL
section results in a perfect match with the expected
magnetic polarity sequence of the Miocene±Pliocene
time transition (Fig. 9). The resulting correlation with the
time scale is further supported by the identi®cation of
transgressive marine sediments corresponding to the basal
Pliocene within chron C3r as detected in the SL section,
in the Librilla area (Fig. 2).
The magnetostratigraphy of the marine and evaporitic
units shows a characteristic pattern that perfectly cor-
relates with the late Tortonian chrons C4n.2n, C4n.1n
and C3Br.2n. Correlation with older ages can be ruled
out since MN12 terrestrial faunas are necessarily
younger than 8 Ma (Krijgsman et al., 1996; Opdyke
et al., 1997).
Our correlation challenges the conclusions of an earlier
magnetostratigraphic study (DinareÁs-Turell et al., 1999;
PlayaÁ et al., 1999) which suggested a Messinian age for the
Rio Chicamo Fm. Their proposed correlation is appar-
ently supported by radiometric ages of volcanic rocks
inter®ngered with the sediments of the transitional
evaporitic units (Bellon et al., 1983). However, it
should be noted that whole-rock K/Ar dates are prone
to yield younger ages as a result of rock alteration and/or
Ar loss from the glass fraction. Moreover, their suggested
correlation is in con¯ict with the integrated mammal
biostratigraphic, lithostratigraphic and magnetostrati-
graphic frame as shown in this study (Figs 9 and 10).
Chronology of the basin in®ll
This new chronology indicates that marine sedimentation
in the Fortuna basin ®nished in the late Tortonian at
about 7.6 Ma, after a period of progressive basin
restriction and deposition of evaporitic and diatomitic
formations (7.8±7.6 Ma) (Fig. 9). The development of
diatomitic facies was largely isochronous, not only at basin
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 209
Fig. 9. Magnetostratigraphic correlations between the studied sections and absolute ages based on the astronomically calibrated
Polarity Time Scale (Hilgen et al., 1995; Krijgsman et al., 1999).
M. GarceÂs et al.
210 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
scale, but also between the Fortuna and Lorca basins
(Krijgsman et al., 2000), suggesting the existence of
a marine connection between the two basins at this
stage. In contrast, their associated gypsiferous units
show a time-transgressive character: the youngest marine
evaporitic deposits of the Fortuna basin are about
200 kyr older than the main gypsiferous member of
the La Serrata Fm in Lorca (Krijgsman et al., 2000).
This facies distribution agrees with the overall marine
regression towards the south-west in a palaeogeographical
scenario which is regarded as a restricted elongated gulf
with a connection to the Mediterranean in the south
(Montenat, 1973).
After deposition of the evaporitic units, continental
environments developed all over the basin since the late
Tortonian. Ongoing subsidence led to the accumulation
of thick alluvial sequences throughout the Messinian.
Only at the base of the Pliocene a rapid and brief marine
transgression affected the south and eastern areas of the
basin. These results depict an evolution of the Fortuna
basin which challenges earlier studies based on erroneous
age interpretations (Santisteban, 1981; MuÈller & HsuÈ,
1987; Lukowski et al., 1988; PlayaÁ et al., 2000).
BASIN EVOLUTION
Based on the new chronostratigraphic framework for the
Fortuna basin we have carried out a geohistory analysis of
the basin in®ll (Fig. 11). High-resolution magnetochro-
nology, however, has only been available since the late
Tortonian as provided by the present study. For older
units we rely on previous regional stratigraphic studies
which constrain the onset of marine sedimentation to
the early Tortonian (Montenat et al., 1990a). Another
Fig. 10. Plot of stratigraphic thickness with absolute time. TSC: Tortonian Salinity Crisis; MSC: Messinian Salinity Crisis.
Fig. 11. Geohistory analysis of the Fortuna basin
stratigraphic composite sequence. Age of onset of rifting as
well as palaeobathymetry of the older pelagic sediments is not
precisely constrained. Therefore, the slope of the ®rst
segment of the subsidence curve has a signi®cant uncertainty
(see text for explanation). The two curves in the subsidence
graphs refer to the maximum and minimum bounds of
palaeowater depth.
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 211
limitation for the geohistory analysis is the lack of precise
palaeobathymetric estimates for the lower marine unit,
which makes estimates of tectonic subsidence for the
earliest rifting stages inaccurate. The lower members
of the Fortuna marls contain a rich pelagic planktonic
assemblage which is characteristic of a deep basin
environment. In contrast, micropalaeontological studies
in the upper part of the Fortuna marls point to a relatively
shallow basin environment (Sierro et al., 1992). This
indicates that maximum palaeodepths were reached in
the early stages of the basin in®ll. For younger units
palaeobathymetry is well constrained as being very
shallow to emergent. Palaeoaltitudes for the continental
units are assumed to be relatively low since the basin
maintained feasible connection with the marine environ-
ments towards the south. The fact that the basal Pliocene
marine ¯ooding was recorded in the Fortuna basin
suggests that sedimentation in the basin was close to
sea level.
Tectonic subsidence was calculated by means of back-
stripping techniques, adopting a local isostasy model
under the assumption of no ¯exural lithospheric response.
Such simpli®cation can be assumed given the prime
control of the crustal-scale bounding faults (de LarouzieÁre
et al., 1988) in the evolution of the region, and the very
low lithospheric strength as a result of older stretching
events and the elevated thermal gradient of the region
(Cloetingh et al., 1992; Torne et al., 2000).
The geohistory analysis indicates that the Fortuna
basin accommodated 1 km of tectonic subsidence from
the Tortonian to the early Pliocene. This amount of
subsidence is comparable with other basins such as the
Sorbas and Atalaya basins in the same area (Cloetingh
et al., 1992). A signi®cant feature of the Fortuna basin is
that half of the tectonic subsidence (500 m) occurred
during the Messinian, clearly post-dating the main period
of extension that affected many of the eastern Betics
Neogene basins (Cloetingh et al., 1992).
During the early stages of basin evolution, subsidence
largely exceeded sedimentation, causing deepening of the
basin ¯oor and the accumulation of pelagic sediments
(Fortuna Marls). The Librilla area accumulated nearly
1000 m of marine marls. The Fortuna basin was in open
connection to the north (Crevillente strait) and south
(Guadalentin corridor) with neighbouring troughs of the
eastern Betics, where Tortonian marine sedimentation
shows a large thickness variability (Montenat et al.,1990a), revealing a complicated horst and graben struc-
ture and prime tectonic control by vertical faults on the
distribution of sediment depocentres.
After this initial open marine evolution, the onset
of evaporitic sedimentation at about 7.8±7.9 Ma marks
a drastic change in basin con®guration. Restriction of
marine water circulation and the initiation of hypersaline
conditions in the Fortuna basin must have been related to
the presence of an eastern ridge, controlled by the tectonic
deformation along the Alhama de Murcia Fault. Several
lines of evidence challenge sea level lowering as a prime
controlling factor on basin restriction as previously sug-
gested (Santisteban & Taberner, 1983; MuÈller & HsuÈ,
1987). First, a coeval regression is not observed in
neighbouring basins. On the contrary, the late Tortonian
is generally characterized by transgressive marine deposits
in the eastern Betics (Montenat et al., 1990a). Second, the
shallowing-upward sedimentary sequence in the Fortuna
basin does not provide evidence of a sea-level lowering.
No basin-scale seaward progradation of marginal clastic
wedges is observed. No low sedimentation rates are
recorded as a result of a decreasing accommodation
space in the basin. On the contrary, restriction and
evaporite precipitation in the Fortuna basin is coeval
with increasing sedimentation rates (up to 1.0 m kyrx1)
(Fig. 10). This suggests a large accommodation space
which does not easily match a scenario of lowering base
level. The observed sedimentation pattern is more con-
sistent with a scenario of increasing accommodation
space as a result of the tectonic uplift of the basin margins.
In this context, the shallowing sequence in the Fortuna
basin represents a rapid sediment ®lling favoured by the
rising of an eastern margin and the transformation of the
Fortuna basin into an effective sediment trap. A tectonic
control on the presence of an eastern ridge is favoured
by the existence of stratigraphic angular unconformities
related to a late Tortonian intensi®cation of tectonic
deformation along the NE±SW-trending shear zones in
the Eastern Betics domain (Montenat & Ott d'Estevou,
1990).
Sediment input outpacing subsidence led to rapid basin
®lling and marine regression. Once the basin reached an
over®lled stage, sedimentation decreased to average rates
of 30±40 cm kyrx1 (Fig. 10), matching the generation of
new accommodation space due to the on-going subsidence
(Fig. 11). Complete isolation of the Fortuna basin from
the Mediterranean margin probably did not occur, and
sediment excess was probably transported towards the
marine platforms to the south-east. In contrast to other
eastern Betic basins, Messinian sedimentation was
characterized by high subsidence and sedimentation
rates (Fig. 11).
The scenario during the Messinian was that of a poorly
drained, con®ned, continental basin, with the develop-
ment of shallow lacustrine and palustrine environments in
the distal and marginal areas of the prevailing alluvial fan
systems. Connection to the marine environments was still
feasible towards the south-eastern margin, as can be seen
on the NW slopes of the Carrascoy massif: Messinian
marine sediments inter®nger with late Turolian con-
tinental units in La Alberca (Mein et al., 1973). The
recognition of a basal Pliocene marine transgression on
top of a thick Messinian shallow-marine to continental
sequence in the Librilla area indicates that continuous
tectonic subsidence occurred throughout the Messinian
(Fig. 10).
The Mediterranean sea-level ¯uctuations in¯uenced
the sedimentation in the Fortuna basin. The sea level
drop accompanying the Messinian Salinity Crisis at
M. GarceÂs et al.
212 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
5.55 Ma (Krijgsman et al., 1999) led to a marked decrease
in the basin accommodation space, fast basinward advance
of the alluvial fringing wedges, sediment bypassing
towards outer deeper troughs, and local erosion (Figs 9
and 10). The incision of the drainage network caused
shallow lakes and ponded areas to dry out. A basin outlet
was probably located in the area near Librilla, where a
sediment hiatus of 0.5 Myr indicates that this was an
area exposed to sediment bypassing and erosion at the
end of the Messinian. The late Messinian environmental
changes apparently did not in¯uence the sedimenta-
tion in the Molina de Segura area. There, sedimentation
is apparently continuous across the Miocene±Pliocene
transition (Fig. 10), indicating that erosion at that time
was probably restricted to the areas of valley incision near
the basin outlet.
Linked to the Messinian Salinity Crisis, a remagnetiza-
tion event is detected in the Librilla area. It is expected
that the late Messinian sea level drop caused a deepening
in phreatic levels near the coast. This probably resulted in
an increased ¯owing of oxidizing groundwater through
the buried sediments, a feasible mechanism causing
remagnetization as discussed above (see Palaeomagnetic
analysis). The thickness of the remagnetized stratigraphic
interval in the Librilla section suggests a deepening of the
ground-water table of at least 300 m.
The re-establishment of normal marine conditions in
the Mediterranean is recorded in the Fortuna basin by
means of a brief and areally restricted basal Pliocene
transgression. This marine in¯ux was probably con®ned
to a narrow depressed area following the axis of a growing
syncline parallel to the NW±SE-striking Alhama de
Murcia Fault (Fig. 2).
The last stage of basin evolution was determined by a
phase of transpressional left-lateral shear along the
Alhama de Murcia Fault that caused the basin uplift in
the Pliocene. The contractional nature and age of this
event is recorded by the syndepositional folding of the
Pliocene sediments in the Librilla area. In addition, its
left-lateral strike-slip component is indicated by the
anticlockwise rotations of the Messinian to Pliocene
sediments in the Molina de Segura area (Fig. 8).
THE FORTUNA BASIN IN THE CONTEXTOF THE EASTERN BETICS AND THEALBORAN BASIN EVOLUTION
The overall regressive sequence from open marine to
restricted evaporitic±diatomitic and continental deposits
in the Fortuna basin is also recognized in the Lorca basin.
Magnetostratigraphic correlation between the two basins
(Krijgsman et al., 2000) con®rms a parallel sedimentary
evolution, a result which is to be expected since both
basins were tectonically controlled by common major
structures. One striking feature of their sedimentary
record is the `Tortonian Salinity Crisis' (TSC)
(Krijgsman et al., 2000), followed by continentalization
at 7.6 Ma as a result of the regional tectonic uplift of
their eastern margins (Internal Zones) during the late
Tortonian. The installation of continental conditions in
the Lorca and Fortuna basins appears to be roughly coeval
with the uplift and marine regression in the Guadix±Baza
and Granada intramontane basins in the Central and
Western Internal Betics (Soria et al., 1998). However,
signi®cant differences between these basins prevents a
single interpretation of the late Tortonian marine
regression in the Betic zone. In the Guadix±Baza basin,
marine sediments are overlain by a not very thick (about
300 m) late Tortonian to Pleistocene continental succes-
sion, which progressively onlap the relatively passive
fault-bounded basin margins. In the Granada basin, more
active Pliocene±Pleistocene extensional faulting has taken
place, associated with the recent uplift of the Sierra
Nevada mountain range (FernaÂndez et al., 1996). This
led to a marked asymmetric basin in®ll, with migrating
depocentres towards the north, and the accumulation of
variable thickness of lacustrine to alluvial sediments of up
to 1 km (FernaÂndez et al., 1996). The marine regression
in both the Guadix±Baza and the Granada basins resulted
from a regional uplift of the central Betics from late
Tortonian to Present (Soria et al., 1998). This has been
interpreted as a ¯exural rift shoulder uplift, where the
Betic domain represents the uplifted ¯ank of a subsiding
Alboran Sea basin (van der Beek & Cloetingh, 1992).
Alternatively, lithospheric mantle thinning beneath the
topographic highs of the central and eastern Betics has
also been suggested to account for the observed recent
uplift of the chain (Torne et al., 2000).
In the eastern Betics, rift shoulder uplift is not a
plausible mechanism since earlier stretching and the high
thermal gradient would have prevented the lithosphere
from supporting ¯exural stresses, resulting in a local
isostatic compensation (Cloetingh et al., 1992). The size
and geometry of the Miocene sedimentary troughs may
also account for the weakness of the lithosphere in the
eastern Betics. The Fortuna basin has accommodated a
thick (up to 1 km) continental succession in a relatively
narrow trough. In contrast to the intramontane basins of
the central Betics, inter®ngering with marine Pliocene
sediments shows that the rapid sedimentation in the
Fortuna basin was associated with a marked subsidence of
the basin ¯oor. Instead of a long-wavelength regional
uplift, contrasting vertical and lateral motions between
blocks in the eastern Betics agree with a strike-slip
structural setting, with coalescent uplifting blocks and
pull-apart basins. Under a scenario of strike-slip tectonics
only subtle changes of the stress ®eld (Montenat & Ott
d'Estevou, 1990) are required to produce block uplift.
The tectonic activity along the Alhama de Murcia Fault
evolved into a more transpressional component during the
Pliocene as the direction of the local compression shifted
from N±S to NNW±SSE (Montenat & Ott d'Estevou,
1990). This caused the recent uplift of the Fortuna
basin and its eastern margin (Carrascoy massifs) (Sanz de
Galdeano et al., 1998). Early Pliocene syndepositional
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 213
folding in the Librilla area and anticlockwise vertical axis
block rotations in the Molina de Segura area (Fig. 9)
provide evidence for this last stage of basin evolution.
The tectonic and sedimentary evolution of the Fortuna
basin has been appropriately associated with NE±SW
left-lateral strike slip deformation in a context of a late
Tortonian to present N±S to NW±SE compression in the
eastern Betics (Montenat & Ott d'Estevou, 1990;
Montenat et al., 1990a), which resulted from the oblique
NW±SE convergence between the African and Eurasian
plates (Dewey et al., 1989; Srivastava et al., 1990). The
results of the present study are in agreement with this
scenario. On the other hand, we found no evidence
for a general NW±SE shortening and piggyback basin
evolution, as has been suggested (Poisson & Lukowski,
1990), a model which is not substantiated by a reliable
basin chronostratigraphy nor by basin-scale balanced
cross-sections.
As already envisaged by de LarouzieÁre et al. (1988),
such a scenario for the eastern Betics resembles the one
described for the southern and eastern Alboran basins
where NE±SW strike-slip faulting has controlled dis-
tribution of sedimentary troughs since the late Tortonian
(Comas et al., 1992; Alvarez-MarroÂn, 1999). It should
be pointed out that strike-slip tectonics is a feasible
mechanism to explain substantial extension in an overall
convergent setting. This fact should be taken into account
when applying subsidence analysis in order to detect
patterns of migrating depocentres in the Alboran basin
and to constrain models of basin formation. In particular,
limited observations of younger subsidence in the Eastern
Alboran basin might not be a suf®cient evidence for a
south-eastward migration of delaminating continental
lithosphere as proposed by other authors (Docherty &
Banda, 1995; Tandon et al., 1998). The Fortuna basin is
located beyond the limits of the thinned lithosphere of the
Alboran basin, but underwent suf®cient stretching and
subsidence to accumulate 2000 m of sediments in about
5 Myr. Similar structures have been described in the
Eastern Alboran basin, where subsidence has been
associated with a process of tectonic escape within an
area bounded by conjugate strike-slip faults (Alvarez-
MarroÂn, 1999). Therefore, in order to substantiate an
eastward migration of the Alboran basin it is necessary to
show that this extension is not con®ned to pull-apart
structures.
CONCLUSIONS
After an early stage of extension and marine transgression
which affected extensive areas in the eastern Betics, a late
Tortonian marine restriction is detected in the Fortuna
and Lorca basins. A rising eastern ridge prevented the
exchange of marine waters and favoured hypersaline
conditions and precipitation of evaporites. This ridge also
acted as an ef®cient sediment trap, causing increasing
sediment accumulation and marine regression in the
Fortuna and Lorca basins. The shallowing succession
does not represent the initiation of uplift of the basin
itself. On the contrary, continuous subsidence favoured
the accumulation of thick sequences of continental
sediments during the Messinian followed by a brief and
areally restricted marine transgression at the base of the
Pliocene. This evolutionary pattern contrasts with the
general trend in other neighbouring basins to the east
where subsidence was primarily accommodated in the
Tortonian during the main rifting stage which affected
the overall region. It also differs from the evolution of the
intramontane basins of the central Betics, which were
uplifted together with the chain since the late Tortonian.
The Messinian subsidence recorded in the Fortuna basin
as well as the tectonic inversion and uplift from the
Pliocene to the present is consistent with an evolving pull-
apart basin controlled by the strike-slip activity of the
Alhama de Murcia and Crevillente Faults. This is in
agreement with the late Miocene scenario depicted for
both the Alboran and the Betic regions where folding,
strike-slip tectonics and inversion of previous normal
structures developed in a regime of overall convergence
between the African and Eurasian plates.
ACKNOWLEDGMENTS
This research was supported by PB96-0815 MEC project.
Conxita Taberner and Mary Russell are acknowledged
for their assistance in the ®eld. Thanks are also due to
Bert van der Zwaan for analysing the benthic foram-
inifera association at the Pliocene marine beds in the SL
section. Constructive reviews by L. Lonergan, C. Sanz de
Galdeano and P. Haughton improved the manuscript.
REFERENCES
AGUSTI, J., MOYAÁ -SOLAÁ , S., GIBERT, J., GUILLEÂ N, J. & LABRADOR,
M. (1985) Nuevos datos sobre la bioestratigrafõÂa del NeoÂgeno
continental de Murcia. Paleontologia I EvolucioÂ, 18, 83±93.
ALVAREZ-MARROÂ N, J. (1999) Pliocene to Holocene structure of
the Eastern Alboran sea (Western Mediterranean). In:
Proceedings of the Ocean Drilling Program, Scienti®c Results
161 (ed. by R. Zhan, M. C. Comas & A. Klaus), pp. 345±355.
US Govt Printing Of®ce, Washington, DC.
ANDRIEUX, J., FONTBOTEÂ , J.M. & MATTAUER, M. (1971) Sur un
modeÁle explicatif d l'Arc de Gibraltar. Earth Planet. Sci.
Lett., 12, 191±198.
BELLON, H., BORDET, P. & MONTENAT, C. (1983) Chronologie du
magmatisme neÂogeÁne des CordilleÁres beÂtiques (Espagne
meÂridionale). Bull. Soc. GeÂol. France, 7, 205±217.
BRUIJN, H.D., MEIN, P., MONTENAT, C. & VAN DE WEERD, A.
(1975) CorreÂlations entre les gisements de rongeurs et les
formations marines du MioceÁne terminal d'Espagne
meÂridionale. Proc. Koninklijke Nederlandse Akademie Van
Wetenschappen, Series B, 78, 1±32.
CLOETINGH, S., VAN DER BEEK, P.A., VAN REES, D., ROEP, T.B.,
BIERMANN, C. & STEPHENSON, R.A. (1992) Flexural
Interaction and the Dynamics of Neogene Extensional Basin
M. GarceÂs et al.
214 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
Formation in the Alboran-Betic Region. Geo-Mar. Lett., 12,
66±75.
COMAS, M.C., GARCIÂA-DUENÄ AS, V. & JURADO, M.J. (1992)
Neogene Tectonic Evolution of the Alboran Sea from MCS
Data. Geo-Mar. Lett., 12, 157±164.
COMAS, M.J., PLATT, J.P., SOTO, J.I. & WATTS, A.B. (1999) The
origin and tectonic history of the Alboran basin: Insights
from Leg 161 results. Proceedings of the Ocean Drilling
Program, Scienti®c Results 161 (ed. by R. Zhan, M. C. Comas
& A. Klaus), pp. 555±580. US Govt Printing Of®ce,
Washington, DC.
DE LAROUZIEÁ RE, F.D., BOLZE, J., BORDET, P., HERNANDEZ, J.,
MONTENAT, C. & OTT D'ESTEVOU, P. (1988) The Betic
segment of the lithospheric Trans-Alboran shear zone during
the Late Miocene. Tectonophysics, 152, 41±52.
DEWEY, J.F., HELMAN, M.L., TURCO, E., HUTTON, D.H.W. &
KNOTT, S.D. (1989) Kinematic of the Westrn
Mediterranean. In: Alpine Tectonics (ed. by M. P. Coward,
D. Dietrich & D. G. Park), Geol. Soc. Lond. Spec. Publ., 45,
265±283.
DINAREÁ S-TURELL, J., ORTIÂ, F., PLAYAÁ , E. & ROSELL, L. (1999)
Palaeomagnetic chronology of the evaporitic sedimentation
in the Neogene Fortuna Basin (SE Spain): early restriction
preceding the `Messinian Salinity Crisis'. Palaeogeogr.
Palaeoclim. Palaeoecol., 154, 161±178.
DOCHERTY, C. & BANDA, E. (1995) Evidence for the eastward
migration of the Alboran Sea based on regional subsidence
analysis: a case for basin formation by delamination of the
subcrustal lithosphere? Tectonics, 14, 804±818.
DOGLIONI, C., GUEGUEN, E., SAÁ BAT, F. & FERNAÂ NDEZ, M. (1997)
The Western Mediterranean extensional basins and the
Alpine orogen. Terra Nova, 9, 109±112.
DURAND DELGA, M. & FONTBOTEÂ , J.M. (1980) Le cadre
structural de la MeÂditerraneÂe occidentale. Mem. B.R.G.M.,
115, 67±85.
FERNAÂ NDEZ, J., SORIA, J. & VISERAS, C. (1996) Stratigraphic
architecture of the Neogene basins in the central sector of the
Betic Cordillera (Spain): tectonic control and base-level
changes. In: Tertiary Basins of Spain: the Stratigraphic Record
of Crustal Kinematics (ed. by P. Friend & C. Dabrio),
pp. 353±365. Cambridge University Press, Cambridge.
FISHER, R.A. (1953) Dispersion on a sphere. Proc. Roy. Soc.
London, A217, 295±305.
GARCEÂ S, M. & KRIJGSMAN, W. (2000) Remagnetizaciones y
migracioÂn de ¯uidos en la cuenca neoÂgena de Fortuna,
Cordilleras BeÂticas. Geotemas, 1, 105±109.
GARCEÂ S, M., KRIJGSMAN, W. & AGUSTIÂ, J. (1998) Cronology of
the late Turolian deposits of the Fortuna basin (SE Spain):
implications for the Messinian evolution of the eastern
Betics. Earth Planet. Sci. Lett., 163, 69±81.
GARCIÂA-DUENÄ AS, V., BALANYAÁ , J.C. & MARTIÂNEZ-MARTIÂNEZ, J.M.
(1992) Miocene extensional detachments in the outcropping
basement of the northern Alboran Basin (Betics) and their
tectonic implications. Geo-Mar. Lett., 12, 88±95.
GAUYAU, F., BAYER, R., BOUSQUET, J.C., LACHAUD, J.C., LESQUER,
A. & MONTENAT, C. (1977) Le prolongement de l'accident
d'Alhama de Murcia entre Murcia et Alicante (Espagne
meÂridionale). Bull. Soc. GeÂol. France, 7, 623±629.
HILGEN, F.J., KRIJGSMAN, W., LANGEREIS, C.G., LOURENS, L.J.,
SANTARELLI, A. & ZACHARIASSE, W.J. (1995) Extending the
astronomical (polarity) time scale into the Miocene. Earth
Planet. Sci. Lett., 136, 495±510.
KRIJGSMAN, W., GARCEÂ S, M., AGUSTIÂ, J., RAFFI, I., TABERNER, C.
& ZACHARIASSE, W.J. (2000) The `Tortonian Salinity Crisis
of the eastern Betics (Spain). Earth Planet. Sci. Lett., 181,
497±511.
KRIJGSMAN, W., GARCEÂ S, M., LANGEREIS, C.G., DAAMS, R., VAN
DAM, J., VAN DER MEULEN, A.J., AGUSTIÂ, J. & CABRERA, L.
(1996) A new chronology for the middle to late Miocene
continental record in Spain. Earth Planet. Sci. Lett., 142,
367±380.
KRIJGSMAN, W., HILGEN, F.J., RAFFI, I., SIERRO, F. & WILSON,
D.S. (1999) Chronology, causes and progression of the
Messinian salinity crisis. Nature, 400, 652±655.
LONERGAN, L. & SCHREIBER, B.C. (1993) Proximal deposits at
a fault-controlled basin margin, Upper Miocene, SE Spain.
J. Geol. Soc. London, 150, 719±727.
LONERGAN, L. & WHITE, N. (1997) Origin of the Betic-Rif
mountain belt. Tectonics, 16, 504±522.
LUKOWSKI, P., WENLI, R. & POISSON, A. (1988) Mise en eÂvidence
de l'importance des deÂpots messiniens dans le bassin
MioceÁne de Fortuna (Prov. de Murcia, Espagne). C.R.
Acad. Sci. Paris, 307, 941±947.
MALDONADO, A. & COMAS, M.C. (1992) Geology and Geophysics
of the Alboran Sea: an Introduction. Geo-Mar. Lett., 12,
61±65.
MEIN, P. & AGUSTIÂ, J. (1990) Les Gisements de MammifeÁres
neÂogeÁnes de la zone BeÂtique. Doc. Et Trav. Igal., 12±13,
81±84.
MEIN, P., BIZON, G., BIZON, J.J. & MONTENAT, C. (1973) Le
gisement de MammifeÁres de La Alberca (Murcia, Espagne
meÂridionale). CorreÂlations avec les formations marines du
MioceÁne terminal. CR Acad. Sci. Paris, SeÂrie D, 276,
3077±3080.
MONTENAT, C. (1973) Les formations neÂogeÁnes et quaternaires
du Levant espagnol (Provinces d'Alicante et de Murcia).
PhD Thesis, Universite d'Orsay.
MONTENAT, C. & OTT D'ESTEVOU, PH. (1990) Eastern Betic
Neogene Basins ± A Review. Doc. Et Trav. Igal., 12±13, 9±15.
MONTENAT, C., OTT D'ESTEVOU, PH. & COPPIER, G. (1990a) Les
Bassins NeoÂgeÁnes entre Alicante et Cartagena. Doc. Et Trav.
Igal., 12±13, 313±368.
MONTENAT, C., & OTT D'ESTEVOU, PH. & DELORT, T. (1990b)
Le Bassin de Lorca. Doc. Et Trav. Igal., 12±13, 261±280.
MUÈ LLER, D.W., HSUÈ , K. & J. (1987) Event Stratigraphy and
Paleoceanography in the Fortura Basin (Southeast Spain):
a Scenario for the Messinian salinity crisis. Paleoceanography,
2, 679±696.
OPDYKE, N.D., MEIN, P., LINDSAY, E., PEREZ-GONZAÂ LEZ, A.,
MOISSENET, E. & NORTON, V.L. (1997) Continental
deposits, magnetostratigraphy and vertebrate paleontology,
late Neogene of Eastern Spain. Palaeogeogr. Palaeoclim.
Palaeoecol., 133, 129±148.
ORTIÂ, F., GARCIÂA-VEIGAS, J., ROSELL, L., ROUCHY, J.M., INGLEÁ S,
M., GIMENO, D., KASPRYK, A. & PLAYAÁ , E. (1993) CorrelacioÂn
litoestratigra®ca de las evaporitas messinienses en las cuencas
de Lorca y Fortuna (Murcia). Geogaceta, 14, 98±101.
PLATT, J.P., SOTO, J.I., WHITEHOUSE, M.J., HURFORD, A.J. &
KELLEY, S.P. (1998) Themal evolution, rate of exhumation,
and tectonic signi®cance of metamorphic rocks from the ¯oor
of the Alboran extensional basin, western Mediterranean.
Tectonics, 17, 671±689.
PLATT, J.P. & VISSERS, R.L.M. (1989) Extensional collapse of
thickened continental lithosphere: a working hypothesis
The Neogene Fortuna basin, Betic Cordillera
# 2001 Blackwell Science Ltd, Basin Research, 13, 199±216 215
for the Alboran Sea and the Gibraltar Arc. Geology, 17,
540±543.
PLAYAÁ , E., DINAREÂ S-TURELL, J., ORTIÂ, F., GOMIS, E. & ROSELL, L.
(1999) DatacioÂn magnetoestratigra®ca de las evaporitas de la
cuenca neoÂgena de Fortuna (Murcia). Geogaceta, 25, 163±166.
PLAYAÁ , E., ORTIÂ, F. & ROSELL, L. (2000) Marine to non-marine
sedimentation in the upper Miocene evaporites of the
Eastern Betics, SE Spain: sedimentological and geochemical
evidence. Sediment. Geol., 133, 135±166.
POISSON, A. & LUKOWSKI, P. (1990) The Fortuna basin: a
piggyback basin in the Eastern Betic Cordilleras (SE Spain).
Annal. Tectonicae, 4, 52±67.
SANTISTEBAN, C. (1981) PetrologõÂa y SedimentologõÂa de los
Materiales del Mioceno Superior de la Cuenca de Fortuna
(Murcia), a la luz de la ``TeorõÂa de la crisis de la salinidad''.
PhD Thesis, Universidad de Barcelona.
SANTISTEBAN, C. & TABERNER, C. (1983) Shallow marine and
continental conglomerates derived from coral reef com-
plexes after desiccation of a deep marine basin: the
Tortonian-Messinian deposits of the Fortuna Basin, SE
Spain. J. Geol. Soc. London, 140, 401±411.
SANZ DE GALDEANO, C. (1990) Geologic evolution of the Betic
Cordilleras in the Western Mediterranean, Miocene to the
present. Tectonophysics, 172, 107±119.
SANZ DE GALDEANO, C., LOÂ PEZ-GARRIDO, A.C. & GARCIÂA-TORTOSA,
F.J. (1998) Nuevos datos para la estimacioÂn de los valores de
levantamiento desde el Tortoniense Superior a la actualidad en
la parte centro-occidental de la Sierra de Carrascoy (provincia
de Murcia). Geogaceta, 23, 139±142.
SANZ DE GALDEANO, C. & VERA, J.A. (1992) Stratigraphic record
and palaeogeographical context of the Neogene basins in the
Betic Cordillera, Spain. Basin Res., 4, 21±36.
SIERRO, F.J., FLORES, J.A., CIVIS, J., ZAMARRENÄ O, I., VAÂ ZQUEZ, A.,
SANTISTEBAN, C. & PORTA, J. (1992) Las margas de Fortuna.
BioestratigrafõÂa y caracterizacioÂn paleoceanogra®ca. III
Congreso GeoloÂgico EspanÄa Y VIII Congreso Latinoamericano
GeologõÂa, Salamanca, 1, 222±226.
SORIA, J.M., VISERAS, C. & FERNAÂ NDEZ, J. (1998) Late
Miocene-Pleistocene tectono-sedimentary evolution and
subsidence history of the central Betic Cordillera (Spain):
a case study in the Guadix intramontane basin. Geol. Mag.,
135, 565±574.
SRIVASTAVA, S.P., ROEST, W.R., KOVACS, L.C., OAKEY, G.,
LEVESQUE, S., VERHOEF, S. & MACNAB, R. (1990) Motion
of Iberia since mid-Cretaceous: Results of a detailed
aeromagnetic survey in the Newfoundland Basin. Tectono-
physics, 184, 229±260.
TANDON, K., LORENZO, J.M. & DE LA LINDE RUBIO, J. (1998)
Timing of rifting in the Alboran Sea basin -correlation of
borehole (ODP Leg 161 and Andalucia A-1) to seismic
re¯ection data: implications for basin formation. Mar. Geol.,
144, 275±294.
TORNEÂ, M., FERNAÂ NDEZ, M., COMAS, M.C. & SOTO, J.I. (2000)
Lithospheric structure beneath the Alboran Basin: Results
from 3D gravity modeling and tectonic relevance. J. Geophys.
Res., 105, 3209±3228.
vAN DER BEEK, P.A. & CLOETINGH, S. (1992) Lithospheric ¯exure
and the tectonic evolution of the Betic Cordilleras (SE
Spain). Tectonophysics, 203, 325±344.
Received 30 August 2000; revision accepted 5 February 2001
M. GarceÂs et al.
216 # 2001 Blackwell Science Ltd, Basin Research, 13, 199±216
top related