Sea cliffs resulting from late Miocene extensional tectonics: the Serra Gelada case study (Betic Cordillera, Spain)

Sea cliffs resulting from late Miocene extensional tectonics: the

Serra Gelada case study (Betic Cordillera, Spain)

Alfonso Yebenes *, Pedro Alfaro, Jose Delgado, Antonio Estevez, Jesus M. Soria

Dpto. Ciencias de la Tierra, Universidad de Alicante. Ap. Correos 99, 03080 Alicante, Spain

Received 27 September 2000; received in revised form 17 March 2001; accepted 20 March 2001

Abstract

The Serra Gelada sea cliffs are carved in Mesozoic carbonate rocks belonging to the External Zones of the eastern Betic

Cordillera (Alicante, SE Spain). Several normal faults with vertical slips of more than a hundred metres have played an

important role in the origin of this coastline. Some previous studies propose that the present cliff morphology was mainly

originated by Quaternary fault activity. However, the integration of geomorphological features, stratigraphical and

sedimentological data, together with the results of the tectonic analysis of fractures occurring in Serra Gelada, and a detailed

study of seismic reflection profiles carried out in the adjacent continental shelf, indicate that these normal faults were active

mainly during the late Miocene. Therefore, the Serra Gelada sea cliffs represent a tectonically controlled long-term landscape.

Thus, normal faults have not significantly modified the Serra Gelada relief since then. Furthermore, the northern part of the

Serra Gelada cliff may be considered as an inherited pre-Quaternary relict palaeocliff since it has only undergone very little

erosive recession. D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Palaeocliff; Extension; Tectonic geomorphology; Betic Cordillera; Spain; Mediterranean Sea

1. Introduction

In spite of the significant extent of sea cliffs along

the Mediterranean coastline in southeast Spain, very

few geomorphological studies have addressed the

origin of these coastal cliffs. The northern part of

the coast of the province of Alicante is characterized

by a predominance of these stretches of cliff, includ-

ing the Serra Gelada, the object of the present study.

The Serra Gelada is a small mountain chain, aligned

in a NE–SW orientation, composed of calcareous and

marly Lower Cretaceous materials. It gives rise to

cliffs more than 400-m high that extend along 6 km

of coast between the bays of Benidorm and Altea

(Fig. 1).

Previous authors (Navarro et al., 1959; Gaibar-

Puertas, 1974; Dumas, 1977; Sanjaume, 1985) pro-

pose a tectonic origin for this cliff-dominated coast-

line. However, both the timing of its formation as

well as its more recent development have been sub-

jects of controversy. Thus, some authors attribute the

formation of these cliffs to recent tectonic activity

that was responsible for the elevation of the Serra

Gelada during the Quaternary. Dıaz del Rıo et al.

(1986) related the geomorphology of this area with

the neotectonic activity of normal faults, which af-

fected Mesozoic and Neogene materials. Rey et al.

(1993), Rey and Fumanal (1996) and Rosello and

Fumanal (1999) also highlighted the importance of

0169-555X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0169-555X(01 )00086 -1

* Corresponding author. Fax: +34-965-903-552.

E-mail address: [email protected] (A. Yebenes).

www.elsevier.com/locate/geomorph

Geomorphology 42 (2002) 197–211

neotectonic processes on the geomorphology and

sedimentology of the continental and marine areas

of the Serra Gelada, pointing out that the activity of

the normal faults affected very recent Quaternary ma-

rine materials, significantly altering this sector of the

coast during the Pleistocene and Holocene. On the

other hand, Yebenes (1996), although also defending

a tectonic origin, suggested a pre-Quaternary origin

for the principal cliff of the Serra Gelada and linked it

to a process of extension, which would have taken

Fig. 1. Geological map of Serra Gelada. Location of geological cross-section and seismic profiles, respectively shown in Figs. 3 and 6, is

also drawn.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211198

place close to the Miocene–Pliocene transition. This

extension would be, in his opinion, responsible for

the subsidence of a block situated to the SE of the

present-day relief of the Serra Gelada giving rise to

the main cliff running NE–SW.

This paper is a multidisciplinary study, which aims

to establish a long-term landscape development of a

coastal area. We define the type and timing of the

events responsible for the genesis of the Serra Gelada

sea cliffs. The geomorphological analysis of the study

area and its integration with tectonic, stratigraphic

and sedimentological data obtained both from the

emergent parts of the mountain range as well as from

the adjacent marine continental shelf (by means of

seismic reflection profiles, deeper than those used by

previous authors), have enabled us to set out a pro-

posal concerning the timing of the formation of this

cliff. In addition, its recent development has been

examined, the relevance of tectonic activity during

the Quaternary is discussed and its possible repercus-

sion on the present-day morphology of the Serra

Gelada is assessed.

2. Geological and geomorphological setting

The Alicante region is located in the eastern part of

the Betic Cordillera, which constitutes the western-

most part of the Alpine Mediterranean chain (Fig. 1).

The Betic Cordillera is subdivided into an Internal

Zone in the south, and an External Zone in the north,

corresponding to the foreland fold-and-thrust belts of

the orogeny and composed of Mesozoic and Tertiary

sedimentary rocks. These rocks represent the former

continental margin of southern Iberia (Garcıa Hernan-

dez et al., 1980). The External Zone is subdivided into

the Subbetic Zone in the south, characterized by

pelagic facies, and a Prebetic Zone in the north, where

shallow marine facies prevail. The Serra Gelada is

located in the northeastern part of the Prebetic Zone,

also called the Alicante Prebetic.

According to De Ruig (1992), the Alicante Pre-

betic presents a large-scale structure characterized by

a deformed sedimentary cover overlying a thinned

continental crust. Its basal detachment corresponds to

Upper Triassic, lutitic and evaporitic materials. This

unit plays an important structural role as the level of

detachment, as well as being the material responsible

for the halokinetic activity, as illustrated by the Altea

diapir (Moseley, 1973). The post-Triassic cover is

composed mainly of Jurassic, Cretaceous and Ceno-

zoic limestones and marls. Folds and thrusts with

NNW trend, along with normal and strike-slip faults,

dominate the structure of this cover.

Present-day climate in this region is semi-arid and

characterized by geomorphological processes con-

trolled by the occasional, but very strong, storm

events. These cause widespread erosion and supply

large sediment loads to mainly ephemeral stream

channels.

The coast is characterized by a succession of sea

cliffs (Toix, Serra Gelada, Torre Vigıa, etc.) and

beaches (Altea, Benidorm, etc.) whose distribution is

mainly controlled by tectonic and lithological factors.

The inland region shows a mountainous relief (Serra

Cortina, Serra de Bernia, etc.) resulting from a com-

plex geological structure (Moseley, 1990) concerning

rocks of different competence (predominantly lime-

stone and marl). Lowland areas and valleys are do-

minated by Pleistocene alluvial fans and valley fills.

The evolution of the Pleistocene alluvial fans, issuing

from the surrounding mountains, show complex his-

tories with early phases, predominantly of alluvial

accumulation and formation of calcrete crusts, and

later phases of dissection of the fans (Harvey, 1978).

3. Stratigraphy of Serra Gelada

The Mesozoic frame of the Serra Gelada comprises

a succession more than 800-m thick of predominantly

calcareous materials, whose age extends from the Late

Jurassic to the Late Albian (Granier, 1987; Castro,

1998). Within this succession, it is possible to differ-

entiate a series made up of seven lithological units

(Yebenes, 1996), as illustrated in Fig. 3A.

Overlying this Mesozoic substratum, and specifi-

cally on the taluses of the Serra Gelada waterfront,

three successive units were defined by Fumanal and

Yebenes (1996): ‘‘megabreccia’’, ‘‘red breccia’’ and

‘‘aeolian complexes’’ (Fig. 3B).

The oldest unit corresponds to the ‘‘megabreccia’’,

a deposit 2–6-m thick consisting of large ( > 4-m F),

derived basically from the Cretaceous ‘‘sandstones

and calcarenites’’ unit. The unit is totally cemented

(but without any signal of calcrete development) and

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 199

displays a strong karstification, developing cavities

with stalagmitic crusts and filled by Upper Pleistocene

sandy aeolian deposits. The unit, with a crude trian-

gular elongated morphology, outcrops exclusively in

the Els Illots area and directly overlies a palaeotalus

developed on C1 unit (marls and limestones with

ammonites). Its apex arises from the base of the cliff,

at 200-m elevation, and extends to 20 m above sea

level with a uniform slope of about 34�. Sedimento-

logically, it is characterized by: the large size of its

clasts, consisting of boulders and blocks; a highly

immature texture (poor sorting and angularity of

clasts); a crude trend to clast size increase towards

its lower sector; and a clast-supported nature. All

these features indicate that the ‘‘megabreccia’’ deposit

represents the preserved core of a colluvial fan,

generated by a series of large rock avalanches (Blikra

and Nemec, 1998; Nemec and Kazanci, 1999), devel-

oped at the foot of a palaeocliff. The unit, once

cemented, underwent an important denudation and

the consequent development of a palaeorelief into

which later deposits (‘‘red breccia’’ and ‘‘aeolian

complexes’’) were accumulated. There are no avail-

able data to precisely date the ‘‘megabreccia’’. Indirect

evidence available includes: its position underneath

the ‘‘red breccias’’ attributed to the Middle Pleisto-

cene; its total cementation not comparable to any

other old Quaternary deposit in the region (Dumas,

Fig. 2. Geomorphological map of the Serra Gelada littoral range.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211200

1977), and its extremely different intensity and style

of cementation to that observed in the overlying ‘‘red

breccia’’; its strong palaeokarstification (with devel-

opment of metre-scale cavities and stalagmite infill

fossilized by Tyrrhenian aeolianites), in which disso-

lution has affected the fragments and cement alike. Its

separation from overlying Middle Pleistocene ‘‘red

breccia’’ by means of a very important unconformity,

corresponding to a palaeorelief, implies a pronounced

erosive intervening period. Consequently, the age of

the ‘‘megabreccia’’ formation can be placed between

the Late Pliocene and the Early Pleistocene.

Above the Els Illots ‘‘megabreccia’’ or immedi-

ately over the marly Cretaceous substratum of the

remainder of the talus, outcrops the ‘‘red breccia’’. It

is a very extensive deposit forming a continuous

fringe that covers all the taluses developed along the

Serra Gelada waterfront, as a thin veneer (though

locally, in the area of Els Illots, it fills incisions of

more than 10-m deep). In many sectors, it extends

from the base of the upper cliff to below the sea level

(to at least � 25 m.) with a constant inclination of

about 25–30�. The ‘‘red breccia’’ is a deposit slightly

lutitic and with poor cementation, except in its upper

part, where a complex calcrete crust is locally devel-

oped. Sedimentologically, it is characterized by a

smaller size of clasts than the ‘‘megabreccia’’ and is

dominated by pebbles and cobbles. Its highly imma-

Fig. 3. (A) Geological cross-section showing the stratigraphy and structure of Serra Gelada. (B) Scheme showing the geometrical relationship

between the ‘‘megabreccia’’, ‘‘red breccia’’ and ‘‘aeolian complexes’’ in the Els Illots sector.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 201

ture texture (very poor sorting, angularity of the clasts

and reddish lutitic matrix), the irregular alternation of

both clast-supported and matrix-supported fabric, and

the presence of inverse grading and outsized cobbles

in the matrix-rich levels, suggest a deposit of a

colluvial apron resulting from the coalescence of

colluvial fans, where processes of rock fall avalanch-

ing and high viscosity debris flow alternated irregu-

larly (Morris and Hebertson, 1996; Blikra and Nemec,

1998). There are no direct data on the age of the ‘‘red

breccia’’, but it can be correlated with alluvial fan

deposits outcropping in the northwestern sector of

Serra Gelada, with a similar topmost calcrete dated as

late Middle Pleistocene.

Over the ‘‘red breccia’’, sets of large ‘‘aeolian

complexes’’ are developed, along almost all of the

talus. Aeolian deposits are dominated by climbing

dunes that ascended over the palaeotalus reaching the

base of the cliff. Fumanal and Yebenes (1996) iden-

tified four dune-building periods developed during the

Upper Pleistocene, with TL ages ranging between 100

and 38 ka (isotopic stages 5c to 3). Still active dunes

are present in the upper part of the Pleistocene aeolian

complexes in front of Els Illots.

It may be emphasized that Holocene and currently

active gravitational and run-off processes are respon-

sible for the development of erosional gullies and the

accumulation of very thin deposits (small colluvial

fans and slope-foot aprons).

In some sectors, such as the northwestern face of

the Serra Gelada and its NE and SW margins, various

alluvial fan deposits occur, which are made up of

debris-flow deposits (Fig. 2A). In this sector, Rey et

al. (1993) established four alluvial deposits whose

surfaces defined four glacis surface. The oldest one

(G-4) is characterized by the presence of a topmost

well developed calcrete, with a complex composite

profile and several morphological horizons, dated by

Bruckner and Radtke (1985, 1986) as Middle Pleis-

tocene (Th/U, age of 205F 30 ka).

4. Tectonic geomorphology

From a morphostructural point of view, Serra

Gelada shows a characteristic cuesta-type relief, with

its steeper flank facing to the SE (Fig. 3A). Serra

Gelada displays a rectangular morphology elongated

in a NE–SW direction and shows a monoclinal

structure with stratification strike N50 and dip some

20–25� towards the NNW. The general orientation of

this structure coincides with the Betic structural

trends. Its steeper SE flank (6-km long) corresponds

to the coastal cliff-line, studied in this work. In

contrast, its NW flank corresponds to a much gentler

slope (approximately 20�) dissected by a mainly

consequent drainage network.

Serra Gelada can be considered as a structural

relief limited by faults (Fig. 1). The SE margin of

the block corresponds to the main cliff face of the

Serra Gelada and is limited by a fault zone, which

runs more or less parallel to it. As perpendicular seis-

mic transects cannot approach the coast, seismic pro-

files cannot consequently detect the main fault trace.

Nonetheless, in some high-resolution profiles perpen-

dicular to the coast (Rey and Fumanal, 1996), it is

possible to see this fault plane in the zone closest to

the coastline. The NW edge of the block is defined by

a fault dipping to the NW (Fig. 3A), placing in contact

the Lower Cretaceous of Serra Gelada with the

terminal Cretaceous and Palaeogene of the Beni-

dorm-El Albir trough, mostly covered by Quaternary

alluvial fan deposits (Harvey, 1978; Rey et al. 1993).

The sharp termination of the NE border of Serra

Gelada suggests that it is controlled by a fault respon-

sible for the subsidence of the bay of Altea. The SW

boundary corresponds to a dextral oblique slip fault

(Punta de les Caletes fault).

In addition to the main faults bordering Serra

Gelada, the entire cuesta-type relief is affected by

numerous normal faults, with vertical slips ranging

from a few centimetres to more than 100 m (Fig. 1).

Most of the faults are high angle. Along the cliff

face, various faults can be observed, among which

the Punta de les Caletes and Punta Bombarda faults

(both at the extreme ends of the sierra) show notice-

able vertical displacements of 150 and 170 m,

respectively (Figs. 4 and 5). Other relevant normal

faults are located in Els Illots and Banc de Ribes,

with vertical displacements of 60 and 80 m, respec-

tively.

It is important to note that the two faults with the

largest displacements (Punta de les Caletes and Punta

Bombarda) are sealed by Quaternary alluvial fan

deposits topped by calcrete crusts similar to the

Middle Pleistocene (G-4) alluvial fan of El Albir.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211202

The morphology of the main cliff of the Serra

Gelada is determined, not only by the faulting, but

also by the lithological characteristics of the different

units that it comprises. Thus, the Serra Gelada

waterfront shows three main cliff types: plunging

cliff, talus-cliff, and composite cliff. Plunging mor-

phology (sensu Sunamura, 1992) appears in the

sectors where the Cretaceous ‘‘sandstones and cal-

carenites’’ unit (C2, Fig. 3A) outcrops down to the

sea level. This unit, formed by relatively thick and

erosion-resistant materials, constitutes a large part of

the cliff, favouring the development of such mor-

phology. On the other hand, the petrologic features

also favour the development of processes of halo-

clastic granular disintegration (Goudie and Viles,

1999), as demonstrated by the occurrence of some

tafoni and honeycomb, typical of the most exposed

coastal zones (Sunamura, 1996). A significant por-

tion of the detrital components (quartz and calcare-

ous lithoclasts) of the Pleistocene aeolian deposits

Fig. 4. Sketch cross-sections of the Les Caletes fault. (A) Scheme of its eastern end where Upper Pleistocene aeolianites are not affected by

normal faults. (B) General view of its western outcrop; Middle Pleistocene alluvial fan sediments are not cut by the fault.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 203

might originate through this kind of mechanical

disaggregation process.

On the other hand, where that unit does not outcrop

down to the sea level, talus-cliff morphology appears

with the talus developed on the easily erodible Creta-

ceous underlying unit (marls and limestones with

ammonites) (C1, Fig. 3A). The Plio-Pleistocene col-

luvial and aeolian deposits cover those taluses.

Fig. 5. (A) Detail of the eastern end of Les Caletes fault. (B) Panorama of the cliffs of Serra Gelada with the Quaternary aeolianites leaning

against to the upper cliff. Some recent blocks are scattered over the aeolianites.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211204

In the sector of Morro de Sant Jordi (Fig. 2), the

presence of very erosion-resistant outcrops of the

Jurassic ‘‘white limestones with clypeina’’ (JC, Fig.

3A) at sea level, control the development of a lower

plunging cliff, in some places up to 50-m high. At

these points, the Serra Gelada waterfront displays a

composite configuration as illustrated in Fig. 3A:

lower plunging cliff, talus and upper cliff.

At the plunging cliff toes, a very marked notch is

developed coinciding with the present sea level.

However, on these rocky shores, we have not found

bioconstructive or erosive evidence that would in-

dicate recent tectonic uplift along this part of the

coast.

The inland continental face of the Serra Gelada

shows a gentle slope, but highly dissected by a

Fig. 6. Seismic profiles undertaken on the continental shelf next to Serra Gelada. Profiles are located on Fig. 1.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 205

consequent drainage. The first- and second-order

stream channels display the characteristic subparallel

pattern of a cuesta-type relief. Preserved headwaters

show a very characteristic lobed morphology and an

incision up to 30 m, diminishing progressively down-

stream. In distal positions, stream channels disappear

under the system of alluvial fans (G-2) filling this

sector of the Benidorm-El Albir trough (Rey et al.,

1993).

To the north of the Els Illots sector, the headwaters

of most of the stream valleys are situated 200 m from

the edge of the cliff. Nonetheless, in the southern half

Fig. 6. (continued).

A. Yebenes et al. / Geomorphology 42 (2002) 197–211206

of the sea cliff, the old headwaters have been clearly

beheaded by the marine cliff (Fig. 2). This evidences a

greater recession of the SW sector of the cliff in

comparison to its NE sector.

5. Stratigraphy and tectonic features of the

adjacent continental shelf

From the stratigraphic and palaeontological data

obtained from the offshore exploration well ‘‘Alicante

1’’, situated about 8 km to the SE of the Serra Gelada,

and the offshore seismic reflection profiles (Figs. 1

and 6), Catafau et al. (1994) established several

Triassic to Quaternary seismic units. In this paper,

we have grouped them in three main seismic units.

(1) Basement seismic unit, comprising Triassic to

Middle Miocene sedimentary rocks.

(2) Late Miocene seismic unit, with relatively

shallow-water marine clays, anhydrite, argillaceous

dolomite and limestone, which is supported at a

discordant angle over the underlying unit. Its distri-

bution is irregular and it shows significant variations

in thickness, since it appears as a fill within exten-

sional half-grabens. In the Alicante 1 well, this unit

was attributed to the Tortonian, based in micropaleon-

tological data (presence of Heterostegina complanata

and other benthic foraminifera.

(3) Plio-Holocene seismic unit, consisting of deep-

water marine clays with occasional, thin interbeds of

sandstone. Its base clearly erodes the underlying

‘‘Late Miocene’’ or ‘‘basement’’ seismic units. In

the Alicante 1 well, the lower part of the unit con-

tains frequent and diverse planktonic foraminifera

dated as Early–Middle Pliocene. The thickness of

the ‘‘Plio-Holocene’’ unit tends to diminish towards

the coast.

The analysis of the seismic profiles reveals the

existence of faults, related to the ‘‘basement’’, parallel

to the coastline. The ‘‘Late Miocene’’ seismic unit

generally fills troughs. Seismic profiles (Fig. 6) show

clearly that most of them exhibit a half-graben struc-

ture with throws that can exceed 1000 m.

The ‘‘Plio-Holocene’’ seismic unit seals normal

faults affecting ‘‘basement’’ and ‘‘Late Miocene’’

seismic units, and shows no evidence of extension.

Based on the fact that the Upper Miocene top reflec-

tor is, in general, undeformed, a pre-Pliocene age may

be inferred for the main vertical displacements asso-

ciated with the movement of the fault zone in this

sector.

Although the main fault zone is situated some 13

km from the coast, normal faults belonging to the

same system, though less numerous and less impor-

tant in displacement, also occur very close to the

coast.

6. Discussion

Analysis of the seismic profiles obtained from the

continental shelf adjacent to Serra Gelada reveals the

occurrence of important sets of normal faults, approx-

imately parallel to the coast. These faults fundamen-

tally affect the materials of the ‘‘basement’’ and ‘‘Late

Miocene’’ seismic units. The latter unit displays a

characteristic half-graben structure in which the

geometry of the reflectors indicates that the graben-

fill is contemporaneous with the extension process.

The sediments that constitute the ‘‘Plio-Holocene’’

seismic unit lie unconformably over the underlying

units sealing the extensional structures. Thus, in this

sector, a significant extension took place between the

Tortonian and the Early Pliocene.

These results agree with studies undertaken in the

inland sector. As De Ruig (1992) pointed out, there

was a generalized uplift of the eastern Prebetic from

the Early–Late Tortonian, with a simultaneous devel-

opment of transtensional faults.

The normal faults crosscutting Mesozoic materials

of Serra Gelada, including the one bordering its SE

margin, were formed mainly during the Tortonian–

Early Pliocene interval. As a consequence of the

extension, the present Serra Gelada block was uplifted

while the SE sector subsided. Thus, the Serra Gelada

relief may be considered as a faulted block, similar to

those observed in the seismic lines on the continental

shelf (Fig. 6).

By the reasons mentioned previously, most of the

seismic profiles cannot detect the main fault trace.

Nonetheless, it has been located very near of the

Morro de Sant Jordi and near the seawards face of

the Mitjana Island (Fig. 1). The resulting pre-Pliocene

original palaeocliff would be much more extensive

than the preserved one, probably extending as far as

the Benidorm Island.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 207

Therefore, the present lower sea cliff of the Morro

de Sant Jordi sector and the seawards face of the

Mitjana Island (both formed by the very erosion-

resistant Jurassic limestones) represent the relicts of

the original palaeocliff resulting from the Upper

Miocene faulting.

Later evolution of the original palaeocliff was not

significantly affected by tectonics, but was mainly

controlled by lithology and, to a lesser grade, by

eustatic and climatic factors. Thus, the early develop-

ment of a palaeotalus on ‘‘marls and limestones with

ammonites’’ unit was clearly related to its easily

erodible lithology. Similarly, the development of the

upper main cliff also was controlled by the erosion-

resistant nature of the ‘‘sandstones and calcarenites’’

unit.

The presence of the ‘‘megabreccia’’, a colluvial fan

deposit developed on the palaeotalus and joined to the

main sea-cliff face, is fundamental to understand the

Plio-Pleistocene evolution of the original palaeocliff.

In fact, the occurrence of these materials indicates

that: (a) the upper cliff was already perfectly devel-

oped when the ‘‘megabreccia’’ was deposited (Late

Pliocene–Early Pleistocene); (b) the ‘‘megabreccia’’

overlies an equilibrium slope of a well developed

cliff – talus palaeomorphology, and therefore, an

appreciable time lag between the formation of the

original palaeocliff and the deposition of the ‘‘mega-

breccia’’ could be considered; and (c) the slope of the

‘‘megabreccia’’ deposit indicates that, since its depo-

sition, the sierra has undergone no tilting around a

NE–SW axis.

The intense denudation undergone by the ‘‘mega-

breccia’’ makes it impossible to evaluate the original

distribution of these old colluvial fans. However, it is

clear that, at least in the sector of the cliff situated to

the north of Els Illots, recession of the upper cliff

face has been imperceptible. Therefore, the upper

cliff can be also considered as a pre-Quaternary

palaeocliff.

Since their deposition and complete cementation,

the colluvial sediments of the ‘‘megabreccia’’ under-

went intense karstification and significant denudation

that eventually led to their almost total disappearance,

with the exception of the outcrop preserved in the Els

Illots sector. After a noticeable sedimentary gap, with

respect to the deposition of the ‘‘megabreccia’’, a

Middle Pleistocene colluvial apron, the ‘‘red breccia’’,

developed all along the palaeotaluses of the main

Serra Gelada cliff-face. This deposit extends from

the upper cliff-toe, implying that, after its deposition

and up to present day, the cliff has not receded.

An analysis of the Plio-Pleistocene deposits and

the geomorphology of the mountain range highlight

the fact that the cliff has evolved differently in the NW

and SE sectors (Fig. 7). Throughout the majority of

the southern sector of the sierra, the cliff was subject

to erosive recession of a few hundred metres. The

geomorphological study indicates that in the northern

sector, the streams draining the NW flank of Serra

Gelada preserved their original headwaters. However,

in the rest of the range, the current sea cliff beheads

the stream valleys (Fig. 2), implying a few hundred

metres (ca. 200 m) recession of the palaeocliff. The

distance between Mitjana Island (representing the

remains of the original sea cliff) and the coastline

confirms that value as an acceptable estimation of the

recession for the southern sector.

While the northern sector of the upper cliff has

remained stable since the deposition of the ‘‘mega-

breccia’’, the rest of the palaeocliff underwent a

recession starting between the moment of its forma-

tion and the age of the ‘‘red breccia’’ (Middle Pleis-

tocene). The resultant abrasion platform is not visible

today because it is probably buried by the recent

marine sediments (Upper Pleistocene and Holocene),

which cover the littoral zone and the internal shelf

opposite the Serra Gelada (Rey and Fumanal, 1996),

The reason for the different recession between the

northern and southern sectors of Serra Gelada may be

explained in terms of differences of lithology (lime-

stones or marls). Numerous Upper Miocene normal

faults affect the Serra Gelada waterfront so that

hanging wall blocks drop to the south placing the

more erodible rocks (Cretaceous ‘‘marls and lime-

stones with ammonites’’) near the present sea level.

Probably, in the southern sectors, periods of maximum

cliff recession coincided with Early Pleistocene

eustatic highstands where sea level was similar to

present. As Pliocene and Quaternary marine and

continental deposits show, the Serra Gelada block

has not undergone since any tilting southwards around

a NW–SE axis.

During the Upper Pleistocene (from the isotope

stage 5c) the accumulation of climbing dunes began,

ascending over the ‘‘red breccia’’ of the talus. The

A. Yebenes et al. / Geomorphology 42 (2002) 197–211208

more voluminous aeolian complex (‘‘white eolianite’’)

formed during the first regressive phases, as shown by

its richness in bioclasts (mainly warm-water benthic

foraminifera, some of relatively deep-water, remobi-

lised by the wind when the continental shelf was

being exposed).

Finally, during the Holocene, the aeolian deposits

located at the lowest parts of the taluses of the Serra

Gelada cliff were subject to significant marine ero-

sion that culminated during the last transgressive

episode, with the removal of large volumes of Pleis-

tocene aeolianites.

Fig. 7. Interpretative scheme of cliff retreat in SE Serra Gelada. (A) Plan view. (B) Three-dimensional sketches showing lateral variation of cliff

recession.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 209

None of the Quaternary deposits of Serra Gelada

seem to have been affected by appreciable tectonic

deformation. In fact, the two large faults that occur in

the extremes of the Serra Gelada (the Punta Bombarda

and Les Caletes faults) are fossilized by Middle

Pleistocene alluvial fan deposits (Fig. 4B).

As mentioned in Introduction, most of previous

authors attribute the formation of the cliff to the recent

tectonic activity responsible for the uplift of the block

of the sierra. Although the weak seismicity in the zone

suggests the occurrence of certain recent activity

(Yebenes, 1996), no evidence has been found that

demonstrates the role of this activity in the morpho-

logical configuration of the Serra Gelada cliff. Rey

and Fumanal (1996) report normal faults affecting

Upper Pleistocene and Holocene on the inner con-

tinental shelf in front of Serra Gelada. We think,

though (as it may be inferred in the figures of that

paper), that these faults do not propagate downwards

and not affect deeper deposits. So, they are likely

synsedimentary faults caused by gravitational pro-

cesses.

The fact that we have not found any evidence of

Quaternary compression in the Serra Gelada block is

consistent with the possibility that elsewhere, such

structures could exist due to active compressional

regional tectonics.

7. Conclusions

Through a multidisciplinary approach, we have

developed a model for the long-term landscape evo-

lution of Serra Gelada sea cliffs.

Data obtained from the seismic profiling of the

continental shelf leads us to consider that during the

late Miocene, important normal faults developed in

this sector, which were related to tensional processes.

The original cliff of the Serra Gelada formed as a

consequence of the activity of these faults. The main

alignments that define the morphology of the moun-

tain range and determined the Pleistocene sedimenta-

tion are, therefore, clearly pre-Quaternary.

In the sector to the north of Els Illots, the original

palaeocliff is preserved, having been subject to nei-

ther tectonics nor erosive recession since the Late

Pliocene. However, in the southern sector, the palae-

ocliff has recessed several hundred metres, though

this recession was not a consequence of tectonic

activity but of erosional processes, which occurred

between its formation and the Middle Pleistocene.

From that time, there has been no appreciable reces-

sion of the cliff.

The Quaternary deposits outcroping in Serra

Gelada are not influenced by tectonic deformation.

This fact rules out any significant geomorphological

consequence of tectonic activity during the Quater-

nary.

Acknowledgements

The authors wish to warmly thank the reviewers,

P. Silva and M. Stokes, for their careful and con-

structive comments and suggestions on the original

manuscript. We are also grateful to the Direccion

General de Hidrocarburos del Ministerio de Econo-

mıa of Spain for providing the offshore seismic lines

and Alicante-1 well data. This investigation was

financed by the research projects of the Spanish

Direccion General de Ensenanza Superior e Inves-

tigacion Cientıfica (DGESIC) Project PB96-0327 and

Direccion General Investigacion (DGI) Project

BTE2000-0339.

References

Blikra, L.H., Nemec, W., 1998. Postglacial colluvium in western

Norway: depositional processes, facies and palaeoclimatic re-

cord. Sedimentology 45, 909–959.

Bruckner, H., Radtke, H., 1985. Neue Erkenntnisse zum marinen

Quartar an Spaniens Mittelmeerkuste. Kiel. Geogr. Schr. 62,

49–71.

Bruckner, H., Radtke, H., 1986. Paleoclimatic implications de-

rived from profiles along the Spanish Mediterranean coast.

In: Lopez-Vera, F. (Ed.), Quaternary Climate in Western Med-

iterranean. Universidad Autonoma de Madrid, Madrid, pp.

467–486.

Castro, J.M., 1998. Las plataformas del Valanginiense superior–

Albiense superior en el Prebetico de Alicante. Tesis Doctoral.

Universidad de Jaen, 464 pp.

Catafau, E., Gaytan, M., Pereda, I., Vazquez, J.T., Wandossell, J.,

1994. Mapa Geologico de la Plataforma Continental Espanola y

Zonas Adyacentes, Escala 1:200.000, Elche-Alicante. Instituto

Tecnologico Geominero de Espana, Madrid, 73 pp.

De Ruig, M., 1992. Tectono–Sedimentary Evolution of the Prebetic

Fold Belt of Alicante (SE Spain). Doctoral Thesis. Vrije Uni-

versiteit, Amsterdam, 207 pp.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211210

Dıaz del Rıo, V., Rey, J., Vegas, R., 1986. The Gulf of Valencia

continental shelf: extensional tectonics in Neogene and Quater-

nary sediments. Mar. Geol. 73, 169–179.

Dumas, B., 1977. Le Levant Espagnol: La Genese du Relief. These

Doctorat, Universite Paris-Sorbonne, 520 pp.

Fumanal, M.P., Yebenes, A., 1996. Los depositos cuaternarios de les

Penyes de l’Albir en el contexto sedimentario litoral valenciano.

Cuad. Geogr. Univ. Valencia 60, 259–294.

Gaibar-Puertas, C., 1974. Los movimientos recientes del litoral

alicantino: II. El segmento extendido entre la Punta de Ifach

y el Cabo de las Huertas. Rev. Inst. Estud. Alicantinos 11,

43–106.

Garcıa-Hernandez, M., Lopez-Garrido, A.C., Rivas, P., Sanz de

Galdeano, C.y, Vera, J.A., 1980. Mesozoic paleogeographic

evolution of the External Zones of the Betic Cordillera. Geol.

Mijinbow 59, 155–168.

Granier, B. 1987. Le Cretace inferieur de la Costa Blanca entre

Busot et Altea (Alicante, Espagne): Biostratigraphie, Sedimen-

tologie, Evolution Tectono-Sedimentaire. These Doctorat d’Etat,

Univ. Paris VI, 281 pp.

Goudie, A.S., Viles, H.A., 1999. The frequency and magnitude

concept in relation to rock weathering. Z. Geomorphol. N.F.

Suppl. Bd. 115, 175–189.

Harvey, A.M., 1978. Dissected alluvial fans in southeast Spain.

Catena 5, 177–211.

Morris, T.H., Hebertson, G.F., 1996. Large-rock avalanche deposits,

eastern Basin and Range: emplacement, diagenesis, and eco-

nomic potential. Am. Assoc. Pet. Geol. Bull. 80, 1135–1149.

Moseley, F., 1973. Diapiric and gravity tectonics in the pre-Betic

(Sierra Bernia) of south-east Spain. Bol. Geol. Min. Esp. 84,

114–126.

Moseley, F., 1990. A Geological Field Guide to the Costa Blanca,

Spain. The Geologists’ Association, London, 79 pp.

Navarro, A., Villalon, C., Trigueros, E., 1959. El Cuaternario mar-

ino de la Serra Gelada (Alicante) y la tectonica reciente. Notas

Comun. I.G.M.E. 56, 25–32.

Nemec, W., Kazanci, N., 1999. Quaternary colluvium in west-cen-

tral Anatolia: sedimentary facies and palaeoclimatic signifi-

cance. Sedimentology 46, 139–170.

Rey, J., Fumanal, M.P., 1996. Cuaternario submarino frente a la

Serra Gelada (Alicante) y sus implicaciones eustatico-paleo-

geograficas. Cuad. Geogr. Univ. Valencia 60, 243–258.

Rey, J., Fumanal, M.P., Ferrer, C., Vinals, M.J., Yebenes, A., 1993.

Correlacion de las unidades morfologicas cuaternarias (domi-

nio continental y plataforma submarina) del sector Altea-Villa

Joiosa, Paıs Valenciano, (Espana). Cuad. Geogr. Univ. Valencia

54, 249–267.

Rosello, VM., Fumanal, M.P., 1999. Climbing dunes and interbed-

ded rubble fans. Quaaternary patterns of Serra Gelada (Spanish

Mediterranean littoral). Z. Geomorphol. N.F. 43, 235–254.

Sanjaume, E., 1985. Las Costas Valencianas. Sedimentologıa y

Morfologıa. Tesis Doctoral, Universidad de Valencia, 505 pp.

Sunamura, T., 1992. Geomorphology of Rocky Coasts. Wiley, New

York, 302 pp.

Sunamura, T., 1996. A physical model for the rate of coastal tafoni

development. J. Geol. 104, 741–748.

Yebenes, A., 1996. Estratigrafıa y estructura de la Serra Gelada.

Cuad. Geogr. Univ. Valencia 60, 201–222.

A. Yebenes et al. / Geomorphology 42 (2002) 197–211 211