Quantitative subsidence-uplift analysis of the Bajo Segura Basin (eastern Betic Cordillera, Spain): tectonic control on the stratigraphic architecture

Quantitative subsidence-uplift analysis of the Bajo Segura Basin(eastern Betic Cordillera, Spain): tectonic control on the

stratigraphic architecture

J.M. Soriaa, P. Alfaroa, J. FernaÂndezb, C. Viserasb,*

aDepartamento de Ciencias de la Tierra, Universidad de Alicante, Apdo. Correos 99, 03080 Alicante, SpainbDepartamento 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 shallowing-

upward 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

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 intra-

cratonic 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

Sedimentary Geology 140 (2001) 271±289

0037-0738/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved.

PII: S0037-0738(00)00189-5

www.elsevier.nl/locate/sedgeo

* Corresponding author. Fax: 134-58-248528.

E-mail address: [email protected] (C. Viseras).

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 Monte-

nat (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 subsi-

dence 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 strati-

graphic 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 Mediterra-

nean 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 origi-

nated 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 conver-

gence 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 sedi-

mentation 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 Exter-

nal 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 funda-

mentally 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 stack-

ing pattern and the second on the changes in water

J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289272

J.M. Soria et al. / Sedimentary Geology 140 (2001) 271±289 273

SPAIN

BETICCORDILLERA

CAFS

CFZ

TASZ

Alicante

Cádiz

BETIC EXTERNAL ZONES

BETIC INTERNAL ZONES

IBERIAN FORELAND

100 km

RIF

ALBORÁN SEA

MEDITERRANEANSEA

CAFZTASZCFZ

: Cádiz - Alicante fault system: Trans-Alborán shear zone

: Crevillente fault zone

Alicante

Santa Pola

BA

SE

ME

NT

InternalZones

ExternalZones

Miocene toPleistocene

Holocene

5 km

N

1

23

4

studiedsections

1: Albatera2: Crevillente3: Castro4: Colmenar

CFZ

CFZ

BAJO SEGURA BASIN

Guardamar

SegurariverOrihuela

Albatera

Elche

Crevillente

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.

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 recogni-

sable 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 deposi-

tional 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 sedi-

mentary environment. Detailed facies analysis of four

stratigraphic successions (Fig. 3) was carried out for

sedimentary characterisation of the units and deposi-

tional 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, serpu-

lids, 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 shallowing-

upward sequence. On the basis of the planktonic fora-

minifer assemblage, we have been able to establish


I

II

III

IV

V

VI

TO

RT

ON

IAN

ME

SS

INIA

N

VE

NT

IAN

TURO-LIAN

PLIOCENE

PLEISTOCENE

LAT

EM

IOC

EN

E

LAT

E

EARLY

BASEMENT

Albatera Crevillente Castro Colmenar1 2 3 4

E0

E1

E2

E3

E4

E5

UN

ITS

&E

VE

NT

S

SERIE

MARINE &

STAGESCONTINENTAL

DEPOSITIONAL SYSTEMS EW

a

a

a

a

b

b

b

b

c

c d

d

e

Skeletal limestonesRamp type platform

Calcarenites & coralsShallow platform & reefs

Marls with planktonicsSlope and pelagic basin

ConglomeratesTurbidites

Clays and conglomeratesAlluvial s.l.

Marls with vertebratesDelta plain complex

CalcarenitesBeach

ConglomeratesCoarse grained delta

DEPOSITIONAL SYSTEMSLITHOLOGY AND SEDIMENTARY ENVIRONMENTS

LEGEND

AB

SO

LUT

EA

GE

(Ma)

ca. 1.5

ca. 7.5

ca. 8.2

ca. 8.3

1.8

5.3

7.1

910.5

Fig. 2. Stratigraphic architecture of the northern margin of the Bajo Segura Basin.

J.M.

So

riaet

al.

/S

edim

enta

ryG

eolo

gy

140

(2001)

271

±289

275

0

100

200

300

400

500

600

met

res

CON-TINEN-

TAL

CON-TINEN-

TAL

CON-TINEN-

TAL

CON-TINEN-

TAL LITO

R.

LITO

R.

LITO

R.

LITO

R.

PLATF.PLATF.PLATF.PLATF.

INT.

INT.

INT.

INT.

ME

D.

ME

D.

ME

D.

ME

D.

OU

T.

OU

T.

OU

T.

OU

T.

SLO

PE

SLO

PE

SL O

PE

SLO

PE

PE

LAG

.B

AS

IN

PE

LAG

.B

AS

IN

PE

LAG

.B

AS

IN

PE

LAG

.B

AS

INLITHOLOGY andDEPOSITIONAL SYSTEMS

LITHOLOGY andDEPOSITIONAL SYSTEMS



VIVI VI VI

Albatera Crevillente Castro Colmenar

V

V

V

V

IV

IV

IV

IV

III

II

III

IBA

SE

-M

EN

T

BA

SE

-M

EN

T

BA

SE

-M

EN

T

BA

SE

-M

EN

T

III

UN

IT

UN

IT

UN

IT

UN

I T

ba

a

a

b

b

a

b

b

a

a

a a a

a

e

d

d

a

a

b b

b

c

c

I

1 2 3 4

conglomeratesdelta

calcarenites - beach

calcarenites

calcarenites

platform

slope andpelagic basin

skeletallimestones

marlsturbidites

conglo-merates

corals - reef

marlylimestones

marls

claysalluvial

lagoon

conglomerates

0000 5555 30303030 200200200200 1000 m1000 m1000 m1000 mPALAEOBATHYMETRYPALAEOBATHYMETRYPALAEOBATHYMETRYPALAEOBATHYMETRY

Fig. 3. Stratigraphic sections chosen for quantitative analysis of subsidence and uplift (see location in Figs. 1 and 2).

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 base-

ment 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; FernaÂn-

dez et al., 1996; Soria et al., 1999; among others) and

has been associated with the global eustatic rise coin-

ciding 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 (DS-

IIa), 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 coarse-

grained calcarenites in which bioclasts (mainly lamel-

libranchia and red algae) predominate over lithoclasts

(fragments of carbonate rocks from the basement of

the External Zones). These facies constitute a ®ning-

upward sequence, in the upper part of which marls

rich in planktonic organisms intercalate in increas-

ingly thick layers towards the top. We interpret this

vertical organisation of facies to be a deepening-

upward 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 propor-

tions of benthic foraminifera. In the lower part of the

system, the rocks are intercalated with ¯at to convex-

up 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 time-

scale of Cande and Kent, 1995). We interpret DS-IIb

as being a deepening-upward sequence beginning

with slope facies dominated by Tab carbonate turbi-

dites interbedded with increasing amounts of peri-

platform 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 evolu-

tion 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 coarse-

grained clastic facies. The bioclastic components are

resedimented fragments of pectinids, oysters, Bala-

nus, 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 conglom-

erates 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


high-energy turbiditic deposits in parts of the basin

previously dominated by pelagic sedimentation. The

exotic nature of these supplies, from both the base-

ment 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 repre-

sented 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 echi-

noderms). These facies appear in some cases as

massive strata and in others with horizontal to low-

angle 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 depos-

ited 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 coarsening-

upward 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

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 accor-

dance with Stow and Shanmugam (1980) as occurring

in a basin dominated by pelagic sedimentation evol-

ving vertically towards a slope environment charac-

terised by the inclusion of turbiditic clastic facies. Age

was established, on the basis of abundant nannoplank-

ton, 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 (DS-

IVb). E±W progradation can be inferred from the area

distribution of both systems (see Fig. 2). The begin-

ning of the sedimentation of DS-IV coincides with the

E3 event, which marks a change in sedimentary polar-

ity as regards Unit II, from a ®ning- and deepening-

upward (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 conglom-

erate ®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


2±6 m. Occasionally, intercalations occur in the

mudstones of small lenses of coarsening-upward

granules and pebbles with a ¯at base and upward-

convex 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 chan-

nels (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 micro-

mammals). These marls include layers of limestone

with oysters, gastropods, benthic foraminifera, ostra-

cods and charophytes, forming an assemblage typical

of coastal lagoons (SaÂnchez Ferris et al., 1995). They

are also occasionally intercalated with seaward-

inclined, 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 verte-

brate 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 (Thalassi-

noides). 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 calcar-

enite 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 transi-

tion 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 Amaro-

lithus 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 foramini-

fera predominate over the very scarce benthic foramini-

fera, 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 shallowing-

upward sequence caused by the progradation of

shallow-marine facies (platform, reefs and lagoon-

beach) 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 palaeo-

geographic arrangement characterising Unit V is

related to event E4, which marks an episode of abrupt


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 succes-

sions 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 interca-

lated by conglomerate bodies with ribbon-, sheet- and

lens-like geometries, corresponding to the in®ll of

channels and subsequent crevasse-splays (see DS-

Va, FernaÂndez et al., 1993; Viseras and FernaÂndez,

1995). The magnetostratigraphic analyses carried

out by DinareÂs et al. (1995) on the Crevillente succes-

sion 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 megacross-

bedding, 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, fore-

shore and backshore sub-environments, respectively.

Taken as a whole, system VIb represents the shallow-

ing-upward sequence of a sandy beach.

3.6.3. DS-VIc

Located in the lower part of the Crevillente section,

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 deposi-

tional system as a shallow transgressive marine plat-

form 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 thick-

est 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 afore-

mentioned features lead us to interpret this deposi-

tional system as per Stow et al. (1996) as a marine

basin dominated by pelagic sedimentation and corre-

sponding 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 conglom-

erates 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 delta-

plain 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


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 docu-

mented 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 `Back-

stripping' 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 elimi-

nating 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 palaeo-

bathymetry, 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 evolu-

tion of the sedimentary environments in the four stra-

tigraphic 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 palaeo-

uplift 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 palaeo-

bathymetry 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 sedimen-

tation 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 approxi-

mately coincides with the current topographic height

(100 m above sea level).


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 stra-

tigraphic units coincide with changes in both the char-

acter (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 palaeobathy-

metric 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 subsi-

dence (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 charac-

terised 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

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 succes-

sion. 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-uplifthistory in the sedimentary evolution of the basin

The results obtained from analysis of the sedimen-

tary 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 bound-

aries between the stratigraphic units.

At the beginning of the Early Tortonian, a trans-

gressive 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 sedimenta-

tion 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 char-

acterised 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 sedimen-

tation (DS-IIb) and locally to shallow platform sedi-

mentation on marginal areas (DS-IIa).

In the lower part of the Late Tortonian, event E2 is


de®ned by the start of the sedimentation of Unit III,

which is typi®ed by the incorporation of exotic turbi-

ditic deposits (from the southern margin of the Bajo

Segura Basin) onto the deepest facies of Unit II. Sedi-

mentation 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 Colme-

nar), 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 shallow-

ing-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 shallow-

marine 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 char-

acterised 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 move-

ments is similar to that described for Unit II, where the

sinistral strike±slip displacement of the CFZ gener-

ated 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 under-

went 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 charac-

terised by the development of regressive or shallow-

ing-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 shallowing-

upward 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 through-

out the Mediterranean, is dif®cult to locate in our

stratigraphic sections. Tentatively, it could corre-

spond 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-Mediterra-

nean 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 coincid-

ing with event E5, a eustatic rise (recorded in the 3rd-

order 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


J.M.

So

riaet

al.

/S

edim

enta

ryG

eolo

gy

140

(2001)

271

±289

283

I II IV V VI

0

500

1000

1500

DEPTH

ELEVATION

(metres)sea level

ALBATERA

01234567891010.5

Age (Ma)

TORTONIAN MESSINIAN PLIOCENE PLEISTOCENELateEarly

I II IV V VI

0

500

1000

1500

DEPTH

ELEVATION

(metres)sea level

CREVILLENTE

I II IV V VI

0

500

DEPTH

ELEVATION

(metres)sea level

CASTRO

01234567891010.5

Age (Ma)

TORTONIAN MESSINIAN PLIOCENE PLEISTOCENELateEarly

I II IV V VI

0

500

1000

1500

DEPTH

ELEVATION

(metres)sea level

COLMENAR

CORRECTED TECTONIC SUBSIDENCE

HIATUS

Fig. 4. Geohistory diagrams for the four stratigraphic sections studied.

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 regres-

sive 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


I II III IV V VIUnit

2

1

0

1

2

(mm/a)

SU

BS

IDE

NC

EU

PLI

FT

2

1

0

1

2

(mm/a)

SU

BS

IDE

NC

EU

PLI

FT

2

1

0

1

2

(mm/a)

SU

BS

IDE

NC

EU

PLI

FT

2

1

0

1

2

(mm/a)S

UB

SID

EN

CE

UP

LIF

T

ALB

AT

ER

AC

RE

VIL

LEN

TE

CA

ST

RO

CO

LME

NA

R

0.015 0.03

1.6 1.5

0.2 0.1

1.2 1.3

0.05 0.02

0.01

0.01 0.02

1.5

0.05 0.02

1.15 1.25

0.07 0.02

0.02 0.01

0.004 0.040.002 0.02 0.1 0.06

0.002 0.001

0.05 0.03

0.40.004 0.007

TOTAL SUBSIDENCEor UPLIFT

TECTONIC SUBSIDENCEor UPLIFT

Fig. 5. Bar chart showing rates of subsidence and uplift.

northern margin of the Bajo Segura Basin. This uplift

caused the displacement of the Mediterranean coast-

line to its present position.

6. Tectonic control on the subsidence-upliftmovements

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 conver-

gence 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 step-

block structure. Along the length of the CFZ, the stra-

tigraphic 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 chrono-

logical 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 indi-

cation 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 sepa-

rated by the CFZ. The position of the four strati-

graphic 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) charac-

terising 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 conse-

quence, various N1358E faults caused stepping of

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 move-

ment 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) char-

acterises 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 struc-

ture on the northern margin of the Bajo Segura

Basin. This fold was generated by the mixed sinis-

tral-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 (Plio-

cene±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 asso-

ciated 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 uncon-

formities. 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)



Vbplain delta complexalluvial coastal plain

alluvial

Va

VIa

Vc

VIb+ c

Vdbasin

VIdbasin

VIedelta

ramp type platform

TRA N SG RESSI O Nsea level rise

tectonic uplift

tectonic uplift

subsidence

shallowingupwardsequence

deepeningupwardsequence




platform emergedbasin

turbidites

sea level rise

sea level fa ll

sea level rise

TRA N SG RESSI O N

TRA N SG RESSI O N

REG RESSI O N

PLI

OC

EN

E-

PLE

ISTO

CE

NE

TU

RO

LIA

N-V

EN

TIA

NLA

TE

ST

TO

RTO

NIA

N-M

ES

SIN

IAN

LAT

E T

OR

TON

IAN

EA

RLY

TOR

TON

IAN

southern imputs

turbidites

slopeIIaIIb

delta

uplift

uplift

uplift

uplift

uplift

subsidence

subsidence

subsidence

reef

top of DS-II + III

platform

platform

litoral + platform

IVa

IVbbasin

1ALBATERAW E

2CREVILLENTE

3CASTRO

4COLMENAR

sea level

basement

Unit I

E0

E1

E2

E3

E4

E5

Unit II

Unit III

Unit IV

Unit V

Unit VI

Crevillente Fault Zone

C F Z

C F Z

N70ºE N135ºE

C F Z

Fig

.6

.E

vo

luti

on

ary

sch

eme

of

the

no

rther

nm

argin

of

the

Baj

oS

egura

Bas

in:

inte

gra

tion

of

resu

lts

on

sedim

enta

ryev

olu

tion

and

subsi

den

cean

dupli

ftm

ovem

ents

.

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 shallow-

ing-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 Torto-

nian) is characterised by a deepening-upward

sequence associated with a stage of tectonic subsi-

dence 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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