Sedimentary Geology 140 (2001) 271±289
www.elsevier.nl/locate/sedgeo
Quantitative subsidence-uplift analysis of the Bajo Segura Basin
(eastern Betic Cordillera, Spain): tectonic control on the
stratigraphic architecture
J.M. Soria a, P. Alfaro a, J. FernaÂndez b, C. Viseras b,*
b
a
Departamento de Ciencias de la Tierra, Universidad de Alicante, Apdo. Correos 99, 03080 Alicante, Spain
Departamento de EstratigrafõÂa y PaleontologõÂa, Facultad de Ciencias, Universidad de Granada, Campus de Fuentenueva s.n.
18071 Granada, Spain
Received 29 June 1999; accepted 8 December 2000
Abstract
The Bajo Segura Basin is located in the eastern Betic Cordillera, at present connected with the Mediterranean Sea to the east.
It has a complete stratigraphic record from the Tortonian to the Quaternary, which has been separated into six units bounded by
unconformities. This paper is concerned with the northern edge of the basin, controlled by a major strike±slip fault (the
Crevillente Fault Zone, CFZ), where the most complete stratigraphic successions are found. The results obtained (summarised
below) are based on an integrated analysis of the sedimentary evolution and the subsidence-uplift movements. Unit I (Early
Tortonian) is transgressive on the basin basement and is represented by ramp-type platform facies, organised in a shallowingupward sequence related to tectonic uplift during the ®rst stages of movement along the CFZ. Unit II (lower Late Tortonian)
consists of shallow platform facies at bottom and pelagic basin facies at top, forming a deepening-upward sequence associated
with tectonic subsidence due to sinistral motion along the CFZ. Unit III (middle Late Tortonian) is made up of exotic turbiditic
facies related to a stage of uplift and erosion of the southern edge of the basin. Unit IV (upper Late Tortonian) consists of pelagic
basin facies at bottom and shallow platform facies at top, de®ning a shallowing-upward sequence related to tectonic uplift
during continued sinistral movement on the basin-bounding fault. Units V (latest Tortonian±Messinian) and VI (Pliocene±
Pleistocene p.p.) consist of shallowing-upward sequences deposited during folding and uplift of the northern margin of the
basin. No de®nitive evidence of any major eustatic sea-level fall, associated with the `Messinian salinity crisis', has been
recorded in the stratigraphic sections studied. q 2001 Elsevier Science B.V. All rights reserved.
Keywords: Stratigraphy; Subsidence-uplift movements; Strike±slip basin margin; Bajo Segura Basin; Betic Cordillera, Spain
1. Introduction
Quantitative subsidence analysis has been widely
treated in sedimentary basins developing on passive
margins (Watts and Ryan, 1976; Royden and Keen,
1980; Royden et al., 1980; Wooler et al., 1992), as
* Corresponding author. Fax: 134-58-248528.
E-mail address: [email protected] (C. Viseras).
well as in foreland (Hagen et al., 1985; Cross, 1986;
King, 1994), forearc and back-arc (Moxon and
Graham, 1987; Legarreta and Uliana, 1991) and intracratonic basins (Gallagher and Lambeck, 1989; Izart
and Vachard, 1994). However, studies on this subject
for the case of basins controlled by strike±slip faults
are very scarce, with a few examples having been
cited by Sawyer et al. (1987), Field and Browne
(1993) and Dorsey and Umhoefer (2000). The present
0037-0738/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.
PII: S 0037-073 8(00)00189-5
272
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
paper therefore deals with the interesting case of the
quantitative analysis of subsidence in a basin margin
controlled by a major strike±slip fault of the Betic
Cordillera (Spain).
At present there is a large amount of information
available on the stratigraphic and tectonic record of
the Neogene±Quaternary basins of the eastern Betic
Cordillera. This record extends from the Tortonian to
the Quaternary and shows the recent geodynamic
evolution of the orogens surrounding the Western
Mediterranean. The hundreds of papers published on
the stratigraphic and tectonic characteristics of these
basins were brought together in a synthesis by Montenat (1990). Nonetheless, there are very few studies on
the quantitative analysis of vertical movements
(subsidence and uplift) in this area, the most signi®cant being those by Kenter et al. (1990), Cloetingh
et al. (1992), De Ruig (1992), Watts et al. (1993),
Jansen et al. (1993) and Geel (1995). The present
paper provides new data on the history of the subsidence and uplift in one of these basins of the eastern
Betic Cordillera, the Bajo Segura Basin. The results
obtained are based on an up-to-date stratigraphic
model of the basin in order to evaluate the relative
role of vertical movements to the different recognised
sedimentary events. The complete outcropping stratigraphic record in the Bajo Segura Basin, together with
its position on the Mediterranean margin, makes the
analysis presented of interest in the reconstruction of
the geodynamic evolution of the Western Mediterranean during the Late Miocene±Quaternary.
2. Geological setting
Together with the Rif (North Africa), the Betic
Cordillera (southern Iberian Peninsula) represents
the westernmost member of the Alpine orogens
surrounding the Mediterranean, which basically originated in the closure of the Tethys due to African±
Eurasian plate convergence (Sanz de Galdeano,
1990). In essence, it consists of two structural
domains: the Internal Zones or AlboraÂn Block to the
south (Andrieux et al., 1971) and the External Zones
or South Iberian Palaeomargin to the north (GarcõÂa
HernaÂndez et al., 1980; Geel et al., 1992; Vera,
2000). Both domains underwent a process of convergence and collision that ceased in the Early Miocene
and caused important crustal thickening. After this
compressive phase an extensional phase dominated
by detachment movements (Platt and Vissers, 1989;
GarcõÂa DuenÄas et al., 1992; Jabaloy et al., 1992)
developed during the Middle Miocene and played a
principal role in the con®guration of the Betic
Neogene basins. From the Late Miocene on, the
Betic Cordillera was subjected to a nearly N±S
compressive stress ®eld (Sanz de Galdeano, 1990;
Galindo ZaldõÂvar et al., 1993), which generated a
complex network of tectonic structures that were
both compressive and extensional in character.
These structures were active at the same time as sedimentation was taking place in the Betic basins and
controlled the placement of the margins, as well as
subsidence within the basins.
The Bajo Segura Basin is located on the eastern end
of the Betic Cordillera, and is at present connected to
the Mediterranean Sea. This paper deals with the
northern margin of this basin (Fig. 1), where the two
geologically independent domains crop out. The ®rst
is the Mesozoic basement of the basin, consisting of
carbonate and evaporitic rocks from the Betic External Zones (External Subbetic and Internal Prebetic),
and the second the Neogene±Quaternary rocks ®lling
the Bajo Segura Basin, which provide the data for the
present study. From a tectonic point of view, the study
area constitutes a N708E monoclinal structure fundamentally controlled by the strike±slip Crevillente
Fault Zone (CFZ). This fault zone represents the
convergence of two main structures of the Betic
Cordillera (Fig.1): the CaÂdiz±Alicante Fault System
(Sanz de Galdeano, 1990) and the Trans-AlboraÂn
Shear Zone (De LarouzieÁre et al., 1988).
3. Sedimentary record
The most complete stratigraphic successions of the
Bajo Segura Basin crop out on its northern margin and
are made up of sediments ranging from Tortonian to
Quaternary (p.p.) in age. The sedimentary record for
this interval has been divided into six stratigraphic
units bounded by unconformities or their correlative
conformities. The bounding surfaces were established
using two criteria proposed by Catuneanu et al.
(1998), the ®rst of which is based on the stratal stacking pattern and the second on the changes in water
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
273
SPAIN
BETIC
CORDILLERA
ND
LA
E
OR
NF
RIA
IBE
R
CAFZ: Cádiz - Alicante fault system
TASZ: Trans-Alborán shear zone
CFZ: Crevillente fault zone
Alicante
S
NE
ZO
FS
CA
L
NA
S
NE
ZO
TER
C IN
I
BET
MEDITERRANEAN
SEA
TA
S
Z
TE
EX
IC
T
BE
L
NA
CFZ
Cádiz
ALBORÁN SEA
Z
CF
RIF
Alicante
100 km
4
CF
Z
N
Elche
3
2
IN
BAS
URA
Crevillente
1
Albatera
O
BAJ
5 km
SEG
Santa Pola
Holocene
Miocene to
Pleistocene
Guardamar
r
rive
BASEMENT
Orihuela
a
gu r
Se
studied
sections
External
Zones
Internal
Zones
1: Albatera
2: Crevillente
3: Castro
4: Colmenar
Fig. 1. Location of the Bajo Segura Basin in the Betic Cordillera and simpli®ed geological map of the basin with locations of the stratigraphic
sections studied on the northern margin of the basin.
ca. 1.5
1.8
SERIE
MARINE &
CONTINENTAL
STAGES
2
3
4
Crevillente
Castro
Colmenar
1
Albatera
VENTIAN
MESSINIAN
a
c
b
E5
a
V
b
e
d
c
d
E4
LATE
a
IV
III
EARLY
I
b
E3
E2
II
9
10.5
E
DEPOSITIONAL SYSTEMS
VI
TUROLIAN
TORTONIAN
ca. 8.3
LATE
ca. 8.2
MIOCENE
5.3
7.1
W
PLEISTOCENE
PLIOCENE
ca. 7.5
U N ITS
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
& EVENTS
ABSOLUTE
AGE (Ma)
274
b
a
LEGEND
E1
DEPOSITIONAL SYSTEMS
E0
LITHOLOGY AND SEDIMENTARY ENVIRONMENTS
BASEMENT
Skeletal limestones
Ramp type platform
Marls with planktonics
Slope and pelagic basin
Calcarenites & corals
Shallow platform & reefs
Conglomerates
Turbidites
Clays and conglomerates
Alluvial s.l.
Marls with vertebrates
Delta plain complex
Calcarenites
Beach
Conglomerates
Coarse grained delta
Fig. 2. Stratigraphic architecture of the northern margin of the Bajo Segura Basin.
depth and the relative changes in sea level. These
surfaces represent tectonic and/or eustatic events,
here referred to as E0, E1, etc., and are easily recognisable throughout the entire Bajo Segura Basin.
We have followed the chronostratigraphic scales
proposed by Ruiz Bustos (1990), Cande and Kent
(1995) and Krijgsman et al. (1996) for the precise
dating of the six stratigraphic units. Several coeval
depositional systems (sensu Fisher and McGowen,
1967) can be distinguished within each of the units,
whose situation in the new outline of stratigraphic
architecture is summarised in Fig. 2. These depositional systems coincide with the lithostratigraphic
units established in previous studies (Montenat,
1977; Alfaro, 1995), each of them corresponding to
the sediment assemblage deposited in a single sedimentary environment. Detailed facies analysis of four
stratigraphic successions (Fig. 3) was carried out for
sedimentary characterisation of the units and depositional systems. The most signi®cant results of these
analyses are described below.
3.1. Unit I
This unit rests on the basement of the External
Zones. Lithologically, most of it consists of skeletal
limestones made up of red algae, gastropods, serpulids, pectinids and oysters. Thin intercalations of
sandy marls with abundant planktonic organisms
appear in its lower part. The stratal stacking pattern
de®nes a coarsening-upward sequence and the vertical
distribution of the facies corresponds to a shallowingupward sequence. On the basis of the planktonic foraminifer assemblage, we have been able to establish
a
PALAEOBATHYMETRY
a
VI
e
d
b
100
V
c
a
V
V
200
b
a
d
a
IV
IV
b
a
IV
400
alluvial
b
II
b
III
b
II
I
BASEMENT
600
I
BASEMENT
metres
500
a
conglomerates
III
a
IV
I
clays
a
marly
limestones
BASEMENT
300
BASEMENT
V
a
calcarenites
platform
skeletal
limestones
conglomerates slope and
marls
pelagic basin
turbidites
lagoon
marls
conglomerates
calcarenites
200 1000 m
PLATF.
SLOPE
0 5 30
CONTINENTAL
PELAG.
BASIN
LITHOLOGY and
DEPOSITIONAL SYSTEMS
LITOR.
INT.
MED.
OUT.
U N IT
a
200 1000 m
PLATF.
SLOPE
VI
CONTINENTAL
PELAG.
BASIN
0 5 30
LITHOLOGY and
DEPOSITIONAL SYSTEMS
b
c
Colmenar
PALAEOBATHYMETRY
LITOR.
INT.
MED.
OUT.
SLOPE
200 1000 m
PLATF.
PELAG.
BASIN
0 5 30
CONTINENTAL
LITOR.
INT.
MED.
OUT.
U N IT
SLOPE
VI
Crevillente
LITHOLOGY and
DEPOSITIONAL SYSTEMS
4
Castro
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
a
b
200 1000 m
PLATF.
PELAG.
BASIN
0 5 30
CON-
LITHOLOGY and
TINENDEPOSITIONAL SYSTEMS TAL
PALAEOBATHYMETRY
U N IT
VI
3
2
PALAEOBATHYMETRY
LITOR.
INT.
MED.
OUT.
0
U N IT
1
Albatera
delta
corals - reef
calcarenites - beach
Fig. 3. Stratigraphic sections chosen for quantitative analysis of subsidence and uplift (see location in Figs. 1 and 2).
275
276
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
the age as Early Tortonian, Globorotalia acostaensis
zone, equivalent to the calcareous nannoplankton NN
9 zone (following the timescale of Cande and Kent,
1995). Unit I is interpreted as a ramp-type platform
with temperate carbonates and facies similar to other
examples described in the Neogene basins of the Betic
Cordillera (MartõÂn and Braga, 1994). This unit marks
the beginning of marine sedimentation in the study
area. The lower boundary characterises an Early
Tortonian Ð E0 Ð transgressive event on the basement of the Bajo Segura Basin. This event, known as
the `Tortonian transgression' is well documented in
other basins of the Betic Cordillera (FernaÂndez and
RodrõÂguez FernaÂndez, 1989; Montenat, 1990; FernaÂndez et al., 1996; Soria et al., 1999; among others) and
has been associated with the global eustatic rise coinciding with the boundary between the 2nd-order TB2
and TB3 cycles of the Exxon curve (Haq et al., 1987).
3.2. Unit II
Unit II consists of two depositional systems with a
lateral facies change, one mainly calcarenitic (DSIIa), represented in the Crevillente stratigraphic
section, and the other marly (DS-IIb), cropping out
in the Albatera section.
3.2.1. DS-IIa
This system is made up of medium- and coarsegrained calcarenites in which bioclasts (mainly lamellibranchia and red algae) predominate over lithoclasts
(fragments of carbonate rocks from the basement of
the External Zones). These facies constitute a ®ningupward sequence, in the upper part of which marls
rich in planktonic organisms intercalate in increasingly thick layers towards the top. We interpret this
vertical organisation of facies to be a deepeningupward sequence in a shallow-marine platform
environment.
3.2.2. DS-IIb
This system is represented by marls containing
abundant planktonic organisms (foraminifera and
calcareous nannoplankton) and notably lower proportions of benthic foraminifera. In the lower part of the
system, the rocks are intercalated with ¯at to convexup bodies ranging from 0.5 to 2 m thick and 20±40 m
wide. Lithologically, these lobes are similar to the
calcarenites of the previous depositional system, and
represent a ®ning-upward sequence. The abundant
calcareous nannoplankton ¯ora show the age to be
Late Tortonian, zone NN 10 (according to the timescale of Cande and Kent, 1995). We interpret DS-IIb
as being a deepening-upward sequence beginning
with slope facies dominated by Tab carbonate turbidites interbedded with increasing amounts of periplatform ooze and ending with pelagic basin facies.
This facies association is similar to that shown in
modern carbonate slopes (Mullins et al., 1984). In
the upper part of the system, the marls clearly depict
a deep pelagic character, as documented by the
absence of turbiditic sands and a high planktonic/
benthic foraminifera ratio.
Overall, Unit II shows the proximal±distal evolution of shallow platform environments towards slope
(Crevillente series to the east) and pelagic basin
(Albatera series to the west) conditions. The similar
sedimentary polarity detected in both depositional
systems indicates increasing depth towards the top,
consistent with a retrogradational stacking pattern.
The beginning of sedimentation in Unit II coincides
with the E1 event, which is characterised by more
accentuated deepening towards the western sectors
of the basin (i.e. Albatera.).
3.3. Unit III
Lithologically, this unit presents mainly coarsegrained clastic facies. The bioclastic components are
resedimented fragments of pectinids, oysters, Balanus, corals and pebbles with lithophaga borings. The
main lithoclasts are fragments of metamorphic rocks
(marbles, schists and quartzites) from the basement of
the Internal Zones located to the south and southwest
of the Bajo Segura Basin. These facies are organised
in sequences several metres thick with a channelled
base and ®ning-upward grading, made up of conglomerates set in the matrix and pebbles corresponding to
viscous and inertial debris ¯ows. We interpret this
unit as coarse-grained turbiditic deposits transported
by viscous ¯ows and supplied from a shallow-marine
platform on the basement of the Internal Zones.
Unit III represents an important change as regards
Unit II in both depositional conditions and supply
source. Its lower boundary, coinciding with the E2
event, is characterised by the sudden appearance of
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
high-energy turbiditic deposits in parts of the basin
previously dominated by pelagic sedimentation. The
exotic nature of these supplies, from both the basement of the Internal Zones and neighbouring basins,
allows us to relate the E2 event with an episode of
tectonic uplift and erosion of the southern margin of
the Bajo Segura Basin.
3.4. Unit IV
This unit consists of a calcarenitic (DS-IVa) and
another marly (DS-IVb) depositional system. In the
Albatera and Crevillente sections, DS-IVb occupies
the lower part of the unit, gradually developing to
DS-IVa topwards. In these series both depositional
systems de®ne a coarsening-upward sequence. In the
Castro and Colmenar sections Unit IV is only represented by DS-IVa.
3.4.1. DS-IVa
The predominant lithology is calcarenite, in which
lithoclasts (fragments of carbonate rocks from the
basement of the External Zones) dominate over
bioclasts (mostly lamellibranchia, red algae and echinoderms). These facies appear in some cases as
massive strata and in others with horizontal to lowangle hummocky cross-strati®cation. Some beds
show a basal lag of rock fragments and shells on a
erosive base as well as a wave-rippled top surface.
According to Nelson (1982); Snedden and Nummedal
(1991); Hequette and Hill (1993), they were deposited
in a shallow-marine platform environment affected by
storms. These facies are predominant in DS-IVa and
are locally associated with both conglomerates deposited by debris ¯ow in a small coarse-grained delta and
corals (Porites and Tarbellastrea) forming reefal
domes (see Albatera section, Figs. 2 and 3).
3.4.2. DS-IVb
This system consists of irregularly bedded marls
with abundant planktonic organisms (foraminifera
and nannoplankton) showing a gradual increase of
sand towards the top (i.e. towards the transition to
DS-IVa), de®ning a thickening- and coarseningupward sequence. The sandy beds are typically
sharp-based, parallel-sided and occasionally show an
ordered Bouma sequence of internal lamination. The
bottommost marly levels in this system have similar
277
facies to those at the top of DS-IIb, with no sand
fraction and a clear predominance of planktonic
over benthic foraminifera. All this points to the deep
pelagic nature of the sedimentation at the start of
DS-IVb. We therefore interpret the system in accordance with Stow and Shanmugam (1980) as occurring
in a basin dominated by pelagic sedimentation evolving vertically towards a slope environment characterised by the inclusion of turbiditic clastic facies. Age
was established, on the basis of abundant nannoplankton, as Late Tortonian, zone NN 11.
Taking into account both of the systems described
above, we interpret Unit IV as a shallowing-upward
sequence, resulting from the progradation of a shallow
platform (DS-IVa) on a slope and a pelagic basin (DSIVb). E±W progradation can be inferred from the area
distribution of both systems (see Fig. 2). The beginning of the sedimentation of DS-IV coincides with the
E3 event, which marks a change in sedimentary polarity as regards Unit II, from a ®ning- and deepeningupward (retrogradational) to a coarsening- and
shallowing-upward (progradational) stacking pattern.
3.5. Unit V
This unit consists of four, laterally equivalent
depositional systems which are, from west to east
and as de®ned by their predominant lithology, as
follows: red lutites and conglomerates (DS-Va),
marls with vertebrates (DS-Vb), sandstones and
coral limestones (DS-Vc) and marls with planktonic
organisms (DS-Vd).
3.5.1. DS-Va
This system is represented by the Albatera and
Crevillente sections (Fig. 2). It is characterised by
alternating ®ne and coarse facies. The ®ne facies are
sands and mudstones with horizontal lamination or
small-scale ripples with subaqueous bioturbations in
the lower part of the system and root casts and laminar
calcretes in the upper part. The coarse facies are
conglomerates and coarse sands developing three
main morphologies (according to Friend, 1983):
ribbon-, sheet- and lens-like. The ribbon-like bodies
are 2±5 m wide by 1±3 m deep and have a conglomerate ®ll that extends out over the mudstones. The
sheets are multistorey bodies made of gravel with
a lateral extent of up to 250 m and thicknesses of
278
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
2±6 m. Occasionally, intercalations occur in the
mudstones of small lenses of coarsening-upward
granules and pebbles with a ¯at base and upwardconvex top not more than 2±3 m wide and
20±50 cm in maximum thickness.
According to other examples, the coarse facies can
be interpreted as vertically aggrading alluvial channels (ribbon-like bodies), laterally migrating channels
(sheets) and crevasse-splays (lenses) (FernaÂndez et al.,
1993; Viseras and FernaÂndez, 1994, 1995). Moreover,
the occurrence in the ®ne facies of the carbonate
laminae interbedded with detrital sediments re¯ects
¯ood plain sub-environments where sedimentation
was relatively low and episodic (Wright et al., 1996;
Alonso-Zarza, 1999).
3.5.2. DS-Vb
Represented in the middle and upper parts of the
Castro section, where the predominant facies are
marls with vertebrate remains (macro- and micromammals). These marls include layers of limestone
with oysters, gastropods, benthic foraminifera, ostracods and charophytes, forming an assemblage typical
of coastal lagoons (SaÂnchez Ferris et al., 1995). They
are also occasionally intercalated with seawardinclined, parallel-laminated sandstone characteristic
of a shoreface (swash zone) coastal sub-environment
(Roep et al., 1998), as well as sandy bars showing
development of small reefal domes (Porites and
Tarbellastrea) interpreted as distributary mouth-bar
facies (Postma, 1990). DS-Vb was dated by the vertebrate assemblages in the marls. The lower part was
determined as Early Turolian, equivalent to the upper
part of the MN 11 zone. The respective ages of the
middle and upper parts are Late Turolian and Ventian,
equivalent to the MN 12 and MN 13 zones (Alfaro,
1995). Altogether, the facies making up DS-Vb are
taken to be sub-environments of a predominantly
sub-aerial and episodically submerged delta plain
complex (Postma, 1990).
3.5.3. DS-Vc
This system crops out in the intermediate- and
upper-parts of the Colmenar section. A gradation of
three facies groups can be seen from bottom to top.
The ®rst consists of alternating calcarenites and marls
and de®nes a thickening- and coarsening-upward
sequence. The calcarenites are composed of skeletal
fragments of shallow-marine organisms (pectinids
and oysters) and show intense bioturbation (Thalassinoides). The marls are characterised by a high sandy
content and few planktonic organisms. The second
group is made up of coral limestones (Porites) in
coarsening-upward cycles consisting of mudstone,
grainstone and rudstone from bottom to top. The
third and last group of facies, which represents the
top of DS-Vc, consists of marls with oysters and
microvertebrates, associated with ®ne-grained calcarenite layers with wave ripples and algal limestone
(stromatolites). The vertical evolution of the three
facies groups described de®nes a shallowing-upward
sequence, beginning with shallow-marine platform
facies, followed by reefal facies and ending with
lagoon-beach facies similar to those described by
Roep et al. (1998) in the neighbouring Sorbas Basin.
3.5.4. DS-Vd
This system is represented in the lower part of the
Colmenar succession, where a gradual vertical transition from DS-Vc can be observed. The facies are mainly
marls rich in planktonic organisms (foraminifera and
nannoplankton), with an increase in the sandy fraction
towards the top (coarsening upwards). The abundance
of plankton in this depositional system allows it to be
dated as Late Tortonian, Globorotalia humerosa zone
and Messinian, Globorotalia mediterranea and Amarolithus primus zones, all of which are included in the NN
11 zone. According to the model proposed by Mullins et
al. (1984), DS-Vd represents the predominantly pelagic
sedimentation of a marine basin close to a carbonate
platform. At the bottom of this system, where the
marls contain no sandy sediment, planktonic foraminifera predominate over the very scarce benthic foraminifera, thus indicating the deep pelagic nature of the
sedimentation at the start of DS-Vd. Together, systems
Vd (at bottom) and Vc (at top) de®ne a shallowingupward sequence caused by the progradation of
shallow-marine facies (platform, reefs and lagoonbeach) on open-marine facies (pelagic basin).
In summary, Unit V records a continuous
proximal±distal evolution (i.e. east to west) of
alluvial s.l. (DS-Va), delta (DS-Vb) and marine
environments (DS-Vc and DS-Vd). The new palaeogeographic arrangement characterising Unit V is
related to event E4, which marks an episode of abrupt
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
shallowing in the Albatera, Crevillente and Castro
sectors, and deepening in the Colmenar sector.
3.6. Unit VI
This unit consists of ®ve laterally equivalent
depositional systems which are, from west to east
and as de®ned by their predominant lithology, as
follows: red mudstones and conglomerates
(DS-VIa), coastal calcarenites (DS-VIb), platform
calcarenites (DS-VIc), grey marls with planktonic
organisms (DS-VId) and conglomerates (DS-VIe).
3.6.1. DS-VIa
Represented in the upper part of the four successions examined. Root-burrowed, red mudstones,
similar to those described for DS-Va, which seem to
be characteristic of ¯uvial ¯ood plains (Alonso-Zarza,
1999), are predominant. These ®ne facies are intercalated by conglomerate bodies with ribbon-, sheet- and
lens-like geometries, corresponding to the in®ll of
channels and subsequent crevasse-splays (see DSVa, FernaÂndez et al., 1993; Viseras and FernaÂndez,
1995). The magnetostratigraphic analyses carried
out by DinareÂs et al. (1995) on the Crevillente succession show that the Pliocene±Pleistocene boundary is
located in its upper part.
3.6.2. DS-VIb
This system is related to the above one by a surface
of changing facies gently dipping towards the west.
Therefore, DS-VIb appears at the base of DS-VIa in
the Albatera, Crevillente and Castro sections (Fig. 2).
The most complete facies assemblage is found in the
Crevillente section, with three types of vertically
superposed facies. At the base, we ®nd calcarenites
with wave-generated, trough-shaped megacrossbedding, in the intermediate part calcarenites with
seaward-inclined planar cross-bedding and at top
burrowed limestone with gastropods. These three
types of facies can be interpreted, according to Roep
et al. (1998), as corresponding to the shoreface, foreshore and backshore sub-environments, respectively.
Taken as a whole, system VIb represents the shallowing-upward sequence of a sandy beach.
3.6.3. DS-VIc
Located in the lower part of the Crevillente section,
279
directly below the beach sequence described above. It
is represented by calcarenites with lamellibranchia
organised in ®ning- and thinning-upward cycles
bounded by erosion surfaces and onlapping on the
terminal deposits of Unit V. We interpret this depositional system as a shallow transgressive marine platform on Unit V.
3.6.4. DS-VId
The sediments belonging to this system are found at
the base of the Colmenar section, although the thickest outcrops are located between the latter and the
Castro section (Fig. 2). The predominant facies are
grey marls with indistinct bedding rich in planktonic
foraminifera and calcareous nannoplankton, which
indicate the Early Pliocene, zone NN 13. The aforementioned features lead us to interpret this depositional system as per Stow et al. (1996) as a marine
basin dominated by pelagic sedimentation and corresponding to the distalmost and deepest part of Unit VI.
3.6.5. DS-VIe
This system occupies the intermediate part of the
Colmenar section lying directly on the previous
system. Two groups of facies can be distinguished
with gradual vertical evolution. The ®rst, thickest
group located at the base consists of conglomerates
with large-scale sigmoidal strati®cation typical of
delta-front lobes (Galloway and Hobday, 1996). The
second group, located at top, is made up of conglomerates and sand with intercalating red mudstones. The
coarse deposits show mainly ribbon-type channel
geometries containing vertical stacks of several
®ning-upward sequences that we interpret as the in®ll
of distributary channels, according to the model
proposed by Galloway and Hobday (1996). The ®ne
deposits correspond to root-burrowed mudstones
similar to those described above and interpreted as
¯oodplain facies. We therefore interpret the second
group of facies as belonging to a sub-aerial deltaplain context. DS-VIe represents a coarse-grained
prograding delta lying on the pelagic basin facies of
DS-VId.
In summary, Unit VI records a continuous distal±
proximal evolution (west to east) of ¯uvial (DS-VIa),
coastal (DS-VIb) shallow-marine platform (DS-VIc)
and pelagic basin (DS-VId) depositional systems, with
a progradational geometry. The new palaeogeographic
280
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
arrangement characterising Unit VI in contrast to the
previous unit is related to event E5, caused by rapid
transgression in the earliest Pliocene. This event,
known as the `Pliocene transgression', has been documented in other Betic basins, such as the MaÂlaga Basin
(Sanz de Galdeano and LoÂpez Garrido, 1991) and the
basins in the eastern Betic Cordillera (Montenat, 1990;
Fortuin et al., 1995; Montenat and Ott D'Estevou, 1996;
among others). The regional nature of transgressive
event E5 is proof of its relation with the eustatic rise
recorded in the 3rd-order TB3.4 cycle of the Exxon
curve (Haq et al., 1987).
4. Subsidence-uplift history
4.1. Analytical method
In order to illustrate the history of subsidence and
uplift of the northern margin of the Bajo Segura Basin,
we analysed the four stratigraphic sections described
in the preceding heading. The location in the basin
and the stratigraphic features of these successions
are shown in Figs. 1 and 3, respectively. We applied
to each of the series a Fortran version of the `Backstripping' computer program (Allen and Allen, 1990)
based on algorithms proposed by Sclater and Christie
(1980) and Bond and Kominz (1984). The program
calculates total subsidence by decompaction of the
stratigraphic units and tectonic subsidence by eliminating the effects of the sedimentary load. In the latter
case a local, Airy-type isostatic compensation model
is assumed. The data on the porosity, the decrease in
the porosity coef®cient with depth and the density of
the sediments, necessary for running the program,
were adopted from the standard values proposed for
different lithological types by Gallagher and Lambeck
(1989). We added corrections for palaeobathymetry,
palaeoelevation and eustatic changes to the results for
total and tectonic subsidence produced by the
program, thus obtaining values for total and tectonic
subsidence as regards a ®xed datum (sea level). These
values were plotted as geohistoric diagrams (Fig. 4)
following the models described by Van Hinte (1978)
and Angevine et al. (1990). Rates of subsidence and
uplift (Fig. 5) were calculated on the basis of these
geohistory diagrams.
The ®nal results for total and tectonic subsidence
are heavily dependent on the corrections for palaeobathymetry, palaeoelevation and eustatic changes.
Concerning the ®rst two types of correction, we
have adopted the criteria applied by Soria et al.
(1998) in other Neogene±Quaternary basins of the
Betic Cordillera with a similar stratigraphic record
to that of the Bajo Segura Basin. According to these
authors, a detailed analysis of the lithofacies and
biofacies of each stratigraphic unit is required in
order to determine the sedimentary environments
characterising the different depositional systems.
The section of this paper dealing with the sedimentary
record includes an interpretation of the vertical evolution of the sedimentary environments in the four stratigraphic sections analysed (illustrated in Fig. 3). The
quantitative bathymetric estimate is based on the
scales proposed by Heckel (1972), Van Hinte (1978)
and Gradstein and Srivastava (1980). Below we
provide the deduced palaeobathymetry and palaeouplift values for each of the depositional systems
represented.
In the deep pelagic depositional systems (DSs IIb,
IVb and Vd), the criterion used was the ratio between
planktonic and benthic foraminifera. Our calculations
indicate that the ration is over 10:1, both at the bottom
of systems IVb and Vd and at the top of system Iib.
Taking as a reference the studies on this subject by
Berggren and Haq (1976) and Soria et al. (1998) in
sediments of similar facies and age in other Betic
basins, the estimated palaeobathymetry in this case
is approximately 1000 m (assuming a margin of
error of ^200 m).
In the case of the shallow-marine depositional
systems (platform, reef, beach and lagoon), the palaeobathymetry was estimated from both the biofacies (red
algae, oysters, hermatypic corals and stromatolites,
among others) and from sedimentary structures
(hummocky and foreshore cross-strati®cation and
wave ripple cross-lamination). The average values
deduced, according to each case, are given in Fig. 3.
For the alluvial depositional systems (DSs, Va and
VIa), we have assumed a palaeoheight of 0 m at their
base, since they mark the onset of terrestrial sedimentation in the basin. The palaeoheight of the top of
these systems is dif®cult to estimate precisely,
although in the case of system VIa the value approximately coincides with the current topographic height
(100 m above sea level).
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
Regarding eustatic correction, the only event that
can be reliably dated is a sea-level rise in the earliest
Pliocene. This rise is apparent on a regional scale
(e.g. Sanz de Galdeano and LoÂpez Garrido, 1991)
and was responsible for the deepening detected at
the boundary between Units V and VI. No eustatic
correction has been made for the Messinian record
(especially related with the so-called `salinity crisis')
due to the dif®culty of establishing a speci®c value for
the sea-level fall in the peri-Mediterranean area. This
aspect is discussed in more detail in the chapters
below.
4.2. Subsidence-uplift movements
The geohistory diagrams (Fig. 4) and the graphs of
subsidence and uplift rates (Fig. 5) illustrate the
history of the vertical movements during the evolution
of the northern margin of the Bajo Segura Basin.
There now follows a summary of the most signi®cant
aspects of these movements.
One feature common to all the studied stratigraphic
series is the fact that the boundaries between the stratigraphic units coincide with changes in both the character (subsidence or uplift) and magnitude (rates) of
the vertical movements. Hereafter, in order to
compare the different stages of vertical movement,
we shall only refer to tectonic subsidence and uplift,
thus eliminating the effect of the sedimentary load.
Unit I (10.5±9 Ma) is characteristic of a period of
relatively weak uplift, whose total rate varies from
0.03 (Albatera section) to 0.02 mm/a (Crevillente
section). The extremely low subsidence values
detected in the Castro section (0.002 mm/a) can be
discounted in comparison with the previous values,
as it falls within the margin of error for palaeobathymetric correction. Unit II (9±8.3 Ma), which is only
represented in the western sector of the study area
(Albatera and Crevillente), has a record of high subsidence (1.5 mm/a) that continues with much lower
values throughout Unit III (8.3±8.2 Ma, rates between
0.1 and 0.02 mm/a). Unit IV (8.2±7.5 Ma) is characterised by different behaviour in the western sector
(Albatera and Crevillente) to that of the eastern sector
(Castro and Colmenar). The former has a record of a
stage of high uplift (1.3±1.25 mm/a), whereas the
latter corresponds to a stage of slight subsidence
(0.02±0.03 mm/a). Unit V (7.5±5.3 Ma) records a
281
stage of slight subsidence (0.02±0.06 mm/a) in the
Albatera, Crevillente and Castro successions, whereas
uplift (0.4 mm/a) is detected in the Colmenar succession. Finally, during Unit VI (5.3±1.5 Ma) the whole
study area underwent slight uplift, with rates varying
from 0.01 to 0.001 mm/a.
5. Integration of the results of the subsidence-uplift
history in the sedimentary evolution of the basin
The results obtained from analysis of the sedimentary record and the subsidence-uplift history can be
integrated in a combined graph (Fig. 6), showing both
the different evolutionary phases recorded on the
northern margin of the Bajo Segura Basin and the
signi®cance of the events characterising the boundaries between the stratigraphic units.
At the beginning of the Early Tortonian, a transgressive event (E0) related to a eustatic rise (boundary
of the 2nd-order TB2 and TB3 cycles of the Exxon
curve, Haq et al., 1987) marks the start of sedimentation on the basement of the northern margin of the
Bajo Segura Basin. As a result of this transgression
Unit I formed, represented by a ramp-type platform.
The shallowing-upward nature of Unit I is the result of
a stage of tectonic uplift, related to vertical movement
of the two main blocks bounded by the CFZ (Fig. 6).
Deposition of Unit II began in the Early Tortonian±
Late Tortonian boundary, coinciding with event E1.
This unit only occurs in the western sector of the
study area (Albatera and Crevillente), where it is characterised by a very thick deepening-upward sequence
related to a stage of high subsidence. The fact that
Unit II is absent from the eastern sector of the area
(Castro and Colmenar) is probably due to a period of
emergence (non-deposition) caused by tectonic uplift.
Both of these processes (subsidence and uplift) are
associated with the formation of a step-block structure
south of the CFZ, related to the sinistral strike±slip
movement of this fault zone (Fig. 6). In summary,
Unit II marks an important change in sedimentary
evolution. The ramp-type platform characteristic of
Unit I underwent heavy subsidence in the western
sector, changing to pelagic basin and slope sedimentation (DS-IIb) and locally to shallow platform sedimentation on marginal areas (DS-IIa).
In the lower part of the Late Tortonian, event E2 is
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J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
de®ned by the start of the sedimentation of Unit III,
which is typi®ed by the incorporation of exotic turbiditic deposits (from the southern margin of the Bajo
Segura Basin) onto the deepest facies of Unit II. Sedimentation of Unit III occurred in a context of reduced
subsidence in the western sector of the study area
(Albatera and Crevillente), while the eastern sector
remained emerged and unsedimented. On the basis
of the origin of supplies, event E2 is related to an
episode of tectonic uplift and erosion of the southern
margin of the basin.
In the middle Late Tortonian, a transgressive event
(E3) related to a sea-level rise caused expansion of the
basin towards the eastern sector (Castro and Colmenar), which had previously been emerged during the
deposition of Units II and III. Transgressive event E3
is recorded in other Betic basins such as the Guadix
Basin, where it coincides with a stage of maximum
marine ¯ooding (Soria et al., 1998), as well as in the
eastern Betic basins (Montenat and Ott D'Estevou,
1996), where it is marked by a stage of sea-level
rise. This event is interpreted as being associated
with the eustatic rise recorded in the 3rd-order TB
3.2 cycle of the Exxon curve (Haq et al., 1987). The
deposition of Unit IV started after this event, this
being the ®rst unit to occupy the entire extent of the
northern margin of the Bajo Segura Basin. In the
western sector, Unit IV is represented by shallowing-upward sequences made up of pelagic basin facies
at bottom (DS-IVa) and by shallow-marine facies at
top (DS-IVb), produced in a context of high tectonic
uplift. In the eastern sector the facies are shallowmarine platform type (DS-IVb), lying unconformably
on the basement or on Unit I and formed in a context
of slight subsidence. To summarise, Unit IV is characterised by subsidence in the eastern sector and uplift
in the western sector of the northern margin of the
basin; the process responsible for these vertical movements is similar to that described for Unit II, where the
sinistral strike±slip displacement of the CFZ generated a step-block structure south of this fault zone
(Fig. 6).
In the latest Tortonian, event E4 is de®ned by a
sudden uplift of the western sector where, as the result
of a fall in sea level and rapid regression eastwards,
the deposition of Unit V began with alluvial facies
(DS-Va). Simultaneously, the eastern sector underwent sudden subsidence and deepening and Unit V
began here with pelagic basin facies (DS-Vd) (Fig.
6). After E4, Unit V (latest Tortonian±Messinian or
Turolian±Ventian, depending on whether we use
marine or continental chronostratigraphy) is characterised by the development of regressive or shallowing-upward sequences all along the northern margin
of the Bajo Segura Basin. In the Albatera, Crevillente
and Castro sections, Unit V is represented by coastal
alluvial (DS-Va) and delta plain (DS-Vb) sequences
produced in a context of moderate subsidence. In the
Colmenar section, this unit forms a shallowingupward sequence beginning with pelagic basin facies
(DS-Vd) and ending with shallow platform facies
(DS-Vc) produced in a context of tectonic uplift.
The subsidence and uplift of this unit are related to
the onset of development of the antiform structure
characterising the northern margin of the Bajo Segura
Basin (Fig. 6).
There is no evidence of a signi®cant, fast sealevel
fall during the Messinian. The salinity crisis event
(HsuÈ et al., 1973, 1977), widely documented throughout the Mediterranean, is dif®cult to locate in our
stratigraphic sections. Tentatively, it could correspond to the surface separating the reefal facies
from the beach and lagoonal facies recognised in
DS-Vc of the Colmenar section (Fig. 4). Nevertheless,
we believe that this superposition of facies can be
explained in the context of a gradual shallowing of
the entire unit V. Therefore, although these data
contradict the much-accepted model of a considerable
sea-level fall and dessication in the Mediterranean
associated with the salinity crisis (Clauzon et al.,
1996; Butler et al., 1995, 1999; Riding et al., 1999;
among others), our evidence indicates that the relative
sea-level fall was not signi®cant in the Bajo Segura
Basin and, as in many other western peri-Mediterranean basins, did not result in generalised sub-aerial
exposure (Reinhold, 1995; MartõÂnez del Olmo,
1996; Michalzik, 1996, among others).
In the Messinian±Pliocene boundary and coinciding with event E5, a eustatic rise (recorded in the 3rdorder TB 3.4 cycle of the Exxon curve; Haq et al.,
1987) caused a transgression recorded all along the
northern margin of the Bajo Segura Basin. As a result
of this transgression, in the Albatera, Crevillente and
Castro sections, the alluvial and delta plain facies of
the top of Unit V are replaced by shallow platform
(DS-VIc) and coastal (DS-VIb) facies from the base
CASTRO
ALBATERA
ELEVATION
ELEVATION
sea level
(metres) 0
sea level
(metres) 0
DEPTH
DEPTH
500
500
I
IV
V
VI
COLMENAR
ELEVATION
sea level
(metres) 0
1500
DEPTH
I
II
IV
V
VI
CREVILLENTE
500
ELEVATION
sea level
(metres) 0
DEPTH
1000
500
1500
I
II
Early
IV
Late
TORTONIAN
1000
10.5 10
9
8
V
VI
MESSINIAN
7
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
1000
II
6
5
Age (Ma)
PLIOCENE
4
3
PLEISTOCENE
2
1
0
CORRECTED TECTONIC SUBSIDENCE
1500
HIATUS
I
II
Early
IV
Late
TORTONIAN
10.5 10
9
8
V
VI
MESSINIAN
7
6
5
Age (Ma)
PLIOCENE
4
3
PLEISTOCENE
2
1
0
283
Fig. 4. Geohistory diagrams for the four stratigraphic sections studied.
284
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
UPLIFT
1
0.4
(mm/a) 0
SUBSIDENCE
COLMENAR
2
0.004 0.007
0.05 0.03
1
2
UPLIFT
1
(mm/a) 0
SUBSIDENCE
CASTRO
2
0.002 0.001
0.004 0.002
0.04
0.02
0.1
0.06
1
2
UPLIFT
1.15 1.25
1
(mm/a) 0
SUBSIDENCE
CREVILLENTE
2
0.02
0.01
0.02
0.05 0.02
0.01
0.07 0.02
1
1.5
2
UPLIFT
1.2
1.3
1
0.015 0.03
0.01
(mm/a) 0
SUBSIDENCE
ALBATERA
2
0.05 0.02
0.1
0.2
1
1.6
2
U n it
I
1.5
II
III
TOTAL SUBSIDENCE
or UPLIFT
IV
V
VI
TECTONIC SUBSIDENCE
or UPLIFT
Fig. 5. Bar chart showing rates of subsidence and uplift.
of Unit VI. Similarly, in the Colmenar section, pelagic
basin facies (DS-VIe) from the base of Unit VI are
superposed on the lagoonal facies of the top of Unit V.
After the transgression characterising event E5, Unit
VI (Pliocene±Pleistocene p.p.) is made up of regressive or shallowing-upward sequences ending at top
with alluvial facies (DS-VIa) produced in a context
of general tectonic uplift due to the folding of the
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
northern margin of the Bajo Segura Basin. This uplift
caused the displacement of the Mediterranean coastline to its present position.
6. Tectonic control on the subsidence-uplift
movements
The main tectonic feature in the northern margin of
the Bajo Segura basin is the Crevillente fault zone
(CFZ) (Fig. 1). This is a N708E reverse, sinistral
strike±slip fault zone that is the result of the convergence of two large regional structures, the CaÂdiz±
Alicante fault system (Sanz de Galdeano, 1990) and
the Trans-AlboraÂn shear zone (De LarouzieÁre et al.,
1988). The CFZ is locally cut by a set of dextral faults
with an average direction of N1358E. The sub-surface
data (Montenat et al., 1990) indicate that these faults
cross the entire Bajo Segura basin, producing a stepblock structure. Along the length of the CFZ, the stratigraphic units describe an antiform with an average
axial orientation of N708E. The southern ¯ank of this
antiform is particularly well exposed and is therefore
where the four stratigraphic sections studied in this
paper are located. The antiform is locally affected
by `echelon' folds with N1208E axes.
The in¯uence of all these structures at different
times from the late Miocene to the Quaternary
accounts for the genesis of the subsidence and uplift
deduced from the geohistorical analysis. The chronological succession of tectonic events related to these
vertical movements is given below (Fig. 6).
² A stage of slow tectonic uplift (maximum rate of
0.03 mm/year) recorded during the deposition of
Unit I (10.5±9 Ma) is interpreted as the ®rst indication of the activity of the CFZ after the early
Tortonian transgressive event. This uplift is related
to a small vertical strike shift of the blocks separated by the CFZ. The position of the four stratigraphic sections studied in the southern block of
the fault indicate that this block was raised with
respect to its counterpart.
² A stage of high subsidence (1.5 mm/year) characterising Unit II (9±8.3 Ma) in the western sector of
the study area (Albatera and Crevillente) is related
to the sinistral movement of the CFZ. As a consequence, various N1358E faults caused stepping of
285
the southern block, thus resulting in a sector of high
subsidence westwards and another subjected to
uplift in the east.
² A stage of rapid uplift (1.3 mm/year) during the
deposition of Unit IV (8.2±7.5 Ma) in the western
sector, as well as coeval slow subsidence
(0.03 mm/year) in the eastern sector, can be
explained in the same context of sinistral movement of the CFZ. The southern block, already
stepped by the N1358E faults and subjected to a
gradual eastward drift, underwent a reversal of its
prior vertical movements.
² A stage of slow subsidence (0.06 mm/year) characterises Unit V (7.1±5.3 Ma) in the Albatera,
Crevillente and Castro sections, coinciding with
the uplift (0.4 mm/year) of Colmenar. It is related
to the onset of the formation of the antiform structure on the northern margin of the Bajo Segura
Basin. This fold was generated by the mixed sinistral-reverse movement of the CFZ. The uneveness
of its southern ¯ank, with subsidence in the west
and uplift in the east, can be accounted for by the
drag associated with the lateral movement of the
CFZ.
² Finally, a stage of slow uplift (0.01 mm/year)
recorded during the deposition of Unit VI (Pliocene±Pleistocene p.p.) in the four sections studied
is interpreted in the same context of folding of the
northern margin of the basin that began in the
previous stage. This completed the monoclinal
structure of the southern ¯ank of the antiform associated with the CFZ. The presence of minor,
N1208E echelon folds superposed on this antiform
indicates that the folding was produced in a context
of sinistral lateral movement of the CFZ.
7. Conclusions
The Tortonian±Quaternary stratigraphic record on
the northern margin of the Bajo Segura Basin was
divided into six units bounded by basinwide unconformities. The boundaries between the units represent
eustatic events in some cases and in others tectonic
events.
Events E0 (earliest Tortonian), E3 (middle Late
Tortonian) and E5 (Messinian±Pliocene boundary)
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
VIa
alluvial
VIb+ c
litoral + platform
VId
basin
VIe
delta
U n it VI
shallowing
upward
sequenc e
uplift
E5
TR A N SG R E SSI O N
Va
alluvial c oastal plain
uplift
sea level rise
Vb
plain delta c omplex
Vd
basin
Vc
platform
U n it V
CFZ
shallowing
upward
sequenc e
uplift
subsid enc e
R E G R E SSI O N
E4
sea level fa ll
uplift
subsid enc e
IVa
reef
delta
U n it IV
shallowing
upward
sequenc e
IVb
basin
to p
CFZ
platform
of
-II +
DS
III
subsid enc e
uplift
E3
TR A N SG R E SSI O N
LATE TORTONIAN
sea level rise
U n it III
E2
turbidites
southern imputs
IIb
basin
slo pe
b
tur
e
id it
IIa
platform
emerged
CFZ
s
N70ºE
N1
35
ºE
tec tonic uplift
U n it II
EARLY
TORTONIAN
E1
deepening
upward
sequenc e
subsid enc e
Crevillente Fault Zone
ramp type platform
U n it I
shallowing
upward
sequenc e
tec tonic uplift
sea level
E0
TR A N SG R E
sea level rise
1
2
SSI O N
W ALBATERA CREVILLENTE
basement
3
CASTRO
4
COLMENAR
E
Fig. 6. Evolutionary scheme of the northern margin of the Bajo Segura Basin: integration of results on sedimentary evolution and subsidence and uplift movements.
TUROLIAN-VENTIAN
PLIOCENELATEST TORTONIAN-MESSINIAN PLEISTOCENE
286
J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289
are related to stages of eustatic rise, causing rapid
transgressions recorded all along the northern margin
of the basin. On the other hand, events E1 (Early
Tortonian±Late Tortonian boundary), E2 (lower Late
Tortonian) and E4 (latest Tortonian) were controlled
by phases of tectonic subsidence and uplift that
affected distinct sectors of the basin in different ways.
Subsidence and uplift movements strongly affect
the sequential organisation of the stratigraphic units
contained within the boundaries described above.
Units I (Early Tortonian), IV (upper Late Tortonian),
V (latest Tortonian±Messinian) and VI (Pliocene±
Pleistocene p.p.) show typical examples of shallowing-upward sequences related to stages of tectonic
uplift. The rates of tectonic uplift, obtained from
geohistory diagrams, range from 1.3 mm/a (Unit IV)
to 0.001 mm/a (Unit VI). Unit II (lower Late Tortonian) is characterised by a deepening-upward
sequence associated with a stage of tectonic subsidence at a rate of 1.5 mm/a.
Acknowledgements
The paper has greatly bene®ted by the suggestions
of K.A.W. Crook, D. Leckie and an anonymous
reviewer. This research was ®nanced by DGESIC,
projects PB96-0327 and PB97-0808, and Working
Group RNM-0163 of the Junta de AndalucõÂa. We
are indebted to Christine Laurin and Ian McCandless
for the English version of the paper.
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