SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES • NUMBER 20

Catalonian, Eastern Betic, and

Balearic Margins: Structural Types

and Geologically Recent Foundering

of the Western Mediterranean Basin

Daniel Jean Stanley, Henri Got,

Neil H. Kenyon, Andre Monaco,

and Tehezkiel Weiler

SEP SO 1378

SMITHSONIAN INSTITUTION PRESS

City of Washington

1976
ABSTRAC T

Stanley, Daniel Jean, Henri Got, Neil H. Kenyon, Andre Monaco, and Yehezkiel

Weiler. Catalonian, Eastern Betic, and Balearic Margins: Structural Types and

Geologically Recent Foundering of the Western Mediterranean Basin. Smithsonian Contributions to the Earth Sciences, number 20, 67 pages, 33

figures, 1976.—A high-resolution seismic study of the Catalonian, eastern Betic,

and Balearic regions in the western Mediterranean emphasizes the importance of

large-scale post-Miocene vertical displacement of upper Miocene and overlying

unconsolidated sediment sequences. The structural configuration of the Pliocene

and Quaternary series observed on subbottom profiles indicates that the geologically recent margins in these sectors have subsided along preexisting (Oligocene

or older) as well as more recent (post-Miocene) tectonic trends. The post-Miocene

movements are not necessarily synchronous and marked differences of structural

styles are identified. The origin of the three major types of margins—abrupt,

intermediate (or steplike), and progressive—is closely related to tectonic trends

on land. Subsidence of the sub-Pliocene seafloor on the order of 1500 m is

estimated on the basis of seismic profiles presented here.

The abrupt margin type, exemplified by the Emile Baudot and Mazzaron

escarpments, occurs in areas where the edge of the basin parallels the major

structures on land and where vertical displacement has developed in a relatively restricted structural zone. Intermediate margins, such as the sector southeast of the Betic chain, are localized in areas where two major structural trends

converge (NE-SW and NW-SE fractures predominate), and show a steplike

(growth fault) displacement landward. Progressive margins, such as off Catalonia,

display a flexing of the Pliocene and Quaternary cover and are related to

Pliocene foundering followed by more gentle subsidence from the upper Pliocene to the present. This type of margin occurs seaward of Tertiary basins

where older (Hercynian to Miocene) tectonic trends have been reactivated.

Seismic evidence indicates that submarine canyon development on these different

margins is associated with the post-Miocene tectonics as well as with Quaternary

eustatic events.

The Balearic Rise, a large continental block detached from the southern

part of the Balearic Platform, foundered largely in post-Miocene time, but this

feature has not yet completely subsided to the level of the Algero-Balearic Basin

plain. It is possible that large continental blocks beyond the base of slopes that

are presently buried by a thick Pliocene-Quaternary cover may have a structural

origin analogous to that of the Rise. Margin formation and the evolution of the

western Mediterranean Basin bear some similarities to the structural development of rift zones.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: Aerial view of Ulawun

Volcano, New Britain.

Library of Congress Cataloging in Publication Data

Main entry under title:

Catalonian, eastern Betic, and Balearic margins.

(Smithsonian contributions to the earth sciences ; no. 20)

Bibliography: p.

Supt. of Docs, no.: SI 1.26:20

1. Geology-Mediterranean region. 2. Seismic reflection method. I. Stanley, Daniel J. II. Series: Smithsonian Institution. Smithsonian contributions to the earth sciences ; no. 20.

QE1.S227 no. 20 [QE260] 550'.8s [551.4'62'1] 76-608011
Contents

Page

Introduction 1

Acknowledgments 3

Methodology 3

The Catalonian Margin 5

Geological Framework 5

Physiography 5

Stratigraphic Interpretation 7

Structural Configuration 11

Outer Margin Evolution during the Neogene and Quaternary 15

Submarine Canyons 21

Discussion 27

Eastern Betic Margin 29

Geological Framework 29

Physiography 30

Stratigraphic Interpretation 31

Structural Configuration 32

Discussion 34

Balearic Margins 35

Physiography . . 35

Stratigraphic Interpretation 36

Structural Configuration 37

Balearic Platform 37

Balearic Rise 42

Menorca Valley 43

Discussion 47

Regional Continuity of Neogene Sequences 53

Structural Configuration of Margins in Study Area 55

Age of Margin Formation 56

Margin Formation and Western Mediterranean Basin Evolution 57

Conclusions 59

Summary 60

Literature Cited 62

i n
Catalonian, Eastern Betic, and

Balearic Margins: Structural Types

and Geologically Recent Foundering

of the Western Mediterranean Basin

Daniel Jean Stanley, Henri Got,

Neil H. Kenyon, Andre Monaco,

and Yehezkiel Weiler

Introduction

The origin of the western Mediterranean Basin

is a complex and extremely challenging subject.

The rapidly growing number of studies concerned

with the Tertiary evolution of this deep enclosed

sea are based mainly on analyses of deep penetration seismic profile, gravity, and magnetic data

coupled with interpretations of the results of the

Deep Sea Drilling Project D/V Glomar Challenger

(1970 cruise, leg 13) and of the geology of adjacent

land regions. Considerable discussion has revolved

around the age of the basin and the mechanisms

responsible for its formation, including oceanization (de Roever, 1969), and sea floor spreading

(Le Pichon et al., 1971). Some workers, for instance,

have proposed that the Mediterranean already had

its extensive deep basin configuration at the end

Daniel Jean Stanley, Division of Sedimentology, National

Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. Henri Got and Andre Monaco, Centre de

Recherches de Sedimentologie Marine, Centre Universitaire

de Perpignan, Perpignan, France. Neil H. Kenyon, Institute

of Oceanographic Sciences, Wormley, Godalming, England.

Yehezkiel Weiler, The Israel Institute of Petroleum, Ramat

Aviv, Tel Aviv, Israel.

of the Miocene and was essentially a desert environment at that time (Benson, 1972; Hsu, 1972; Cita,

1973; Ryan et al., 1973b). However, most geologists

and oceanographers, including us (Got et al., 1973;

Stanley et al., 1974a), favor the more classic view

expressed by Bourcart (1950, 1963), Glangeaud

(1962, 1968, 1970), Storetvedt (1973), and earlier

workers, i.e., that the configuration of the Mediterranean as presently observed and the nature of

the sediments which fill it are related to geologically recent foundering. This sea-floor subsidence,

initiated in the Oligocene and perhaps earlier, is

thought to have accelerated in post-Miocene time.

The geological and geophysical arguments pertaining to the origin and time of formation of the

present western Mediterranean Basin are presented

elsewhere (Hersey, 1965; van Bemmelen, 1969;

Pannekoek, 1969; McKenzie, 1970; Hsu, 1971; Vogt

et al., 1971; Dewey et al., 1973; Drooger, 1973;

Mauffret et al., 1973; Auzende and Olivet, 1974;

Biju-Duval et al., 1974; Sonnenfeld, 1975; and

others).

Although bearing on these problems, this investigation has a somewhat different and more specific

purpose, i.e., to define selected margins bounding

1
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FRANC E

ALGERI A

Xrv

42

•41

40° I I studied areas

200m isobath

—~ 2600m isohath

h39°

-38

-37

36°

FIGURE 1.—Chart of the western Mediterranean showing the three study areas: A, Catalonian

margin; B, eastern Betic margin; c, Balearic Platform and adjacent margins. (Topographic

details shown in Figures 3 and 22.)

the western part of the Balearic Basin. Particular

attention is paid to the late Miocene to recent

evolution of structure, stratigraphy, and physiography in three regions: the Catalonian margin east

of the Pyrenees, the eastern Betic margin southeast of Spain, and the Balearic Platform and its

contiguous margins (Figure 1). An attempt is made

to relate these margins to the structural framework of the adjacent land.

In these respects, the three continental margins

have received little attention to date. Among the

points considered here are the regional distribution

and thickness variations of Pliocene and Quaternary

sequences, and the modification of these young

series by post-Miocene tectonic events. The origin

of submarine canyons as related to margin evolution and the role of these features in sediment

transport in the study areas are also evaluated. The

configuration of the Pliocene and Quaternary units

is detailed with low- to moderate-penetration

seismic profiling systems which provide higherresolution subbottom detail than that obtained

with more powerful systems used to study the

deeper (late Miocene salt and infrasalt) sequences

underlying the basin (cf. Mauffret et al., 1973).

Our subbottom investigations are supplemented

by coring and deep drilling surveys in several

sectors of the study area.
NUMBER 20

The three areas were initially examined independently by the different authors who used

roughly comparable subbottom profiling methods.*

Although these areas are topographically and geologically quite distinct, a joint investigation was

subsequently conducted with the expectation that

a comparison of the Catalonian, eastern Betic, and

Balearic margins would shed light on the related

problems of margin origin and basin evolution.

We also believe that a comparison of our results

with those compiled by others in the other parts

of the western Mediterranean Basin would provide

insight into post-Miocene history of the Mediterranean.

ACKNOWLEDGMENTS

We are indebted to a number of organizations

for their generous backing including financial aid,

ship-time, equipment and materials, and facilities

provided which made this investigation possible:

Centre National pour l'Exploitation des Oceans

(CNEXO), Centre National de la Recherche Scientifique (CNRS), Institut fur Geophysik (University

of Kiel), Institute of Oceanographic Sciences

(Wormley, U. K.), Lamont-Doherty Geological

Observatory (Columbia University), Musee Oceanographique de Monaco, National Geographic

Society (Research Committee), New York State

Maritime College, Smithsonian Research Foundation, and the U. S. Naval Oceanographic Office

(NAVOCEANO). Bottom and subbottom surveying

was conducted on the N/O Catherine Laurence,

R/V Conrad, RRS Discovery, T/S Empire State IV,

N/O Frangois Blanc, USNS Lynch, N/O Professeur Lacaze-Duthiers, D/S Terebel, and N/O

Winnaretta-Singer. The captains, officers, and men

of these ships are thanked for support so efficiently

given in the work at sea.

We acknowledge with gratitude the many persons with whom we have had an opportunity to

discuss the various problems raised in this study.

We thank, in particular, Dr. O. Leenhardt, Institut

fur Geophysik (Kiel); Dr. A. H. Stride, Institute of

• The initial investigations of the Catalonian margin were

made by Monaco (1971) and Got (1973); the eastern Betic

by Kenyon (unpublished); and the Balearic Platform and

adjacent areas by Weiler and Stanley (1973) and Kenyon

(unpublished).

Oceanographic Sciences (Wormley); and Commandant J. Alinat, Musee Oceanographique de

Monaco, who made special contributions to this

undertaking. We also shared pleasant and productive hours at sea and in the laboratory with Dr.

J.-C. Aloisi, University of Perpignan; Mr. R.

Belderson and Mr. B. S. McCartney, Institute of

Oceanographic Sciences, Wormley; Dr. A. Blackman (deceased) and Mr. R. S. Anderson, U. S.

Naval Oceanographic Office; Professeur M. Gottis,

University of Bordeaux; Mr. G. Serra-Raventos,

University of Barcelona; and Dr. F. Theilen, Institut fur Geophysik (Kiel.)

We thank Messrs. L. Isham and H. Sheng

(Smithsonian Institution) and S. Pierrot (Muse"e

Oceanographique de Monaco) for their help with

drafting and processing of data.

Drs. B. Biju-Duval, Institut Francais du Petrole,

and G. Kelling, University of Wales at Swansea,

read the manuscript and provided helpful suggestions improving the text. We also thank Dr. W. B.

F. Ryan, Lamont-Doherty Geological Observatory,

for his thought-provoking review of the manuscript.

Although we clearly stand on opposite sides of

an important scientific argument discussed in this

monograph, we welcomed the opportunity to consider his comments. The data interpretation and

conclusions presented here, however, reflect the

views of the authors.

Support for continued coordination of the Mediterranean Basin (MEDIBA) Project, including

travel and preparation of the manuscript, has been

provided by the Smithsonian Research Foundation

grants (numbers 460132, 430035, and 450137) to

Stanley. Support by these SRF grants has also been

given to Got and Weiler. Travel funds to participate in this MEDIBA Project also have been

provided to Weiler by the Smithsonian Foreign

Currency Program, and to Got by the French

Government (Ministere des Affaires Etrangeres,

Direction Generate des Relations Culturelles,

Scientifiques et Techniques).

Methodology

The data presented in this study were collected

on numerous cruises conducted independently by

the authors and their colleagues during the past

decade. Reasonably dense bathymetric and sub-
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

bottom seismic coverage is available in the three

study areas as a result of these surveys. Numerous

profiles are supplemented locally by other data

including cores, grab samples, and observations

made during submersible dives and bottom

camera and side-scan sonar surveys.

Bottom and subbottom data on the Catalonian

margin east of the Pyrenees and the French-Spanish

border were collected between 1965 and 1974 on

the N/O Catherine Laurence,, N/O Frangois Blanc,

N/O Winnaretta-Singer and N/O Professeur

Lacaze-Duthiers. Positioning was made by radar

and RANA navigation (precision of within 500 to

1500 m) and the following systems were used:

1. 12 kHz transducer for bathymetry

2. EG&G Boomer (300 and 500 J), with a HP-60B hydrophone and EG&G 254 recorder (ship's speed of 4 knots, a

total of about 1000 km)

3. EG&G Sparker (3000 J), with a HP-60B hydrophone and

EG&G 254 recorder (speed of 8 knots, a total of about

500 km)

4. EG&G Sparker (9000 J), with a Chesapeake M-16 hydrophone and EG&G 254 recorder (speed of 6 knots, a total

of about 1500 km)

Other seismic data in this area have been published by Alia (1970), and Got et al. (1971). The

methods used and results obtained during these

surveys are detailed in Monaco (1971) and Got

(1973). Also available were data from piston cores,

grab samples, and submersible dives (Reyss, 1964;

Reyss and Soyer, 1965; Got and Stanley, 1974).

Stratigraphic interpretations of seismic profiles in

this region are based on correlation with exploratory petroleum drilling on land (Gottis, 1958)

and on the adjacent Gulf of Lion continental

shelf (Cravatte et al., 1974).

Bathymetric and seismic coverage on the margin

east of the Betic range off southeastern Spain is

less dense than on the Catalonian margin. Among

the profiles used are 9000 J sparker lines obtained

on the 1969 cruise of the D/S Terebel (EG&G

Sparker 9000 J; Chesapeake M-16 hydrophone;

EG&G 254 recorder; ship's speed 5 knots) and airgun profiles from the R/V Conrad 9 (August 1965)

courtesy of W. B. F. Ryan (Lamont-Doherty Geological Observatory). These were complemented

by seismic data collected on cruises 27 and 28 of

the RRS Discovery (June-July 1969) of the Institute of Oceanographic Sciences, Wormley, where

the following equipment was used:

1. Precision Echo Sounder for bathymetry

2. A free-running type air gun (28 cu. in), with a 200-ftlong hydrophone, trailed at ship's speed of about 6

knots

3. 36 kHz short-range, side-scan sonar on the shelf and

upper slope

The largest of the three areas studied, the

Balearic Platform and adjacent margins, has been

surveyed during several cruises:

2. RRS Discovery (cruises 27 and 28, 1969) using equipment

described above, and in addition GLORIA (6.5 kHz geological long-range inclined ASDIC)

2. RRS Discovery cruise 35 (11 July to 19 August 1970),

where positioning was made by satellite and radar; seismic gear similar to that of 1969 cruise, but ship's speed

8 knots and length of hydrophone 300 ft

3. USNS Lynch-I (cruise January-February 1972) used satellite, Loran-C, and radar for positioning; 3.5 kHz and 12

kHz transducers used for bathymetric profiling (G. Kelling, A. Maldonado, and D. J. Stanley, in preparation),

and 30,000 J Teledyne Sparker with Precision Electrographic Recorder (Raytheon) used for subbottom profiling at ship's speed of 10 knots; additional material

collected includes piston and gravity cores that provide

sediment sound velocity data (NAVOCEANO velocimeter

equipment); bottom photographs obtained at 8 stations

on the Balearic Rise

4. T/S Empire State IV cruise (June 1972) provided additional coverage of Balearic region south of islands of

Menorca and Mallorca using EG&G 8000 J sparker

5. Conrad-9 (1965) air gun transect provided information on

area east and southeast of Menorca (cf. Ryan et al., 1970);

ship's speed 10 knots

Stratigraphic interpretations are based on correlation of seismic profiles with those that traversed

JOIDES 13 site 124 (Ryan et al., 1973a) immediately east of the Balearic Rise. The thickness of

the upper (Quaternary) acoustic layers takes into

account the sediment velocity measurements made

on cores collected on the Lynch-I cruise, i.e., about

1.7 km per second. Recent sound velocity estimates

for the entire Pliocene and Quaternary sequence

range from 1.7 to 2.8 km per second and from 3.5

km per second (Hinz, 1972) for the underlying

salt ("couche fluante") (including M or K reflectors); velocities to as high as 4.3 km per second

are attributed to some older consolidated infrasalt

layers above acoustic basement (Mauffret et al.,

1973). Considerably lower values (3.0 km/sec.) have

been recorded in some cases, thus resulting in a

velocity inversion below the salt layer (Ryan, pers.

comm.). In this study we assume a 2.0 km per

second value in our calculations of the Pliocene

and Quaternary thickness.
NUMBER 20

The Catalonian Margin

GEOLOGICAL FRAMEWORK

The Catalonian margin extends between the

southwestern part of the Gulf of Lion and the

northern extremity of the Catalonian Chain (Gavarres Massif, Spain) off the eastern Pyrenees

(Figure 1A, 41°50' to 42°50'N lat.). The Gulf of

Lion shelf and slope form the broadest and most

extensive margin in the western Mediterranean,

and this crescent-shaped borderland extends from

the eastern Pyrenees near the French-Spanish

border to the Provence region east of Marseille in

southern France. The shelfbreak between PortVendres and Marseille is approximately 200 km

long, and the widest sector of the Gulf of Lion

shelf (65 km) occurs along a transect extending

SSE from the Gulf of Aigues-Mortes west of the

Rhone delta.

The emerged terrain bounding the Catalonian

margin can be subdivided into several well-defined

regions on the basis of morphology, stratigraphy,

and structure. These four emergent Catalonian terrains, illustrated in Figure 2, are described below

(from north to south):

1. The Roussillon coastal plain, a low-lying sedimentary basin consisting of Neogene deposits, is

separated from the Languedoc region to the north

by Cape Leucate, a headland comprising Mesozoic

rocks. The continental margin off the Roussillon

coastal plain is the southern extension of the Gulf

of Lion.

2. The zone of the eastern extension of the Pyrenees includes primarily metamorphic units, including schists of the Alberes region and gneissic rocks

of the Canigou Massif; the latter forms the point

of highest elevation (2785 m) on the emerged Catalonian region. This sector is bounded to the north

and to the south by a complex network of faults.

3. The Ampurdan coastal plain, a. sediment-filled

basin, is morphologically similar to the Roussillon

coastal plain. However, a topographic high, the

Montgri Massif, separates this low-lying region into

two zones: the Haut Ampurdan lies north of the

massif, and the Bas Ampurdan to the south. The

Montgri Massif, the remnant of a laterally thrusted

mass of Cretaceous limestone, is presently exposed

along the coast south of the Gulf of Rosas.

4. The Gavarres Massif, forming the northern

part of the Catalonian Massif of northeastern

Spain, comprises primarily crystalline and metamorphic (largely schist) sequences. This topographic high is separated from the Ampurdan

region by a set of E-W trending faults.

The structural orientation southwest of the study

area is NNE-SSW; faults define the Palafrugell

zone ("Couloir de Palafrugell") in the northeastern

Gavarres Massif. The predominant fault trend

(Pyrenean) in the study area, however, is NW-SE

(Figure 2). The evolution of the Catalonian margin

is to a large degree related to the complex fault

network cited above, and this structural configuration is discussed in subsequent sections.

PHYSIOGRAPHY

The physiographic configuration of the Catalonian continental shelf (Figure 3) is directly related to that of the contiguous emerged terrains

described above. The Roussillon shelf (Figure 3),

which forms the southwestern extension of the

Gulf of Lion shelf is, for the most part, a broad,

gently seaward dipping surface; topographic relief is subdued in the zone between 30 m and

110 m. The Pyrenean shelf, farther to the south

(Figure 3, B) is narrower and the topography considerably more irregular. Here, three physiographic

provinces are recognized between the coast and the

shelf break: (1) a relatively steep margin extends

from the coast to about 30 m depth; (2) the shelf

slopes gently and uniformly in the zone between

30 and 90 m; and (3) an undulatory surface occurs

between 90 to about 110 m. The outer shelf is

bounded by the slope with an average gradient of

6 degrees. The lower Catalonian slope merges with

the western part of the Rhone submarine fan (also

called the Rhone Cone, Menard et al., 1965).

The continental margin off the Ampurdan

coastal plain (Figure 3, C) is relatively deep, and

the 100 m isobath is located only about 12 km

from the coast. The gradient increases progressively seaward so that a transect across the margin

in this sector appears as a convex-up profile; both

shelf and shelf break are poorly defined. The degree of convexity of the profile increases to about

midslope depths.

The physiography of the margin seaward of the

Gavarres Massif in the southern portion of our
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

Cape Leucate

I I Neogene-Quaternary

Eocene

Mesozoic

n!jij|:| Metamorph i c rocks

Granite

Faults

Tet R. _^-^ - Canet#

wm ROUSSILLON

XXX

FIGURE 2.—Simplified geologic map showing major structural trends on land bordering the

Catalonian margin.
NUMBER 20

study area (Figure 3, D) is similar to that of the

Pyrenean shelf described above.

The Gulf of Lion submarine canyons have been

mapped by Bourcart (1959, 1960a) and other workers. Several large submarine valleys also occur on

the Gatalonian margin, and include the following,

from north to south (cf. Figure 3):

1. The Lacaze-Duthiers Canyon heads at a depth

of 120 m, trends NNW-SSE, is slightly sinuous and

is dissected by numerous tributary valleys along

both canyon walls. Its general orientation becomes

WNW-ESE at a depth of about 1000 m and the

lower valley can be traced to about 1700 m. Crossvalley profiles are V-shaped and the configuration

is typical of classic canyons described by Shepard

and Dill (1966). Steplike terraces and other topographic irregularities along the canyon walls

reflect, to a large degree, erosion and exposures of

indurated bedrock (Got and Stanley, 1974).

2. The Cap Creus Canyon is oriented WNW-ESE

and it heads, at a depth of 150 m, close (6 km) to

Cape Creus. The trend is less sinuous than that of

the Lacaze-Duthiers Canyon, but the axial gradient

is greater. Cross sections reveal a wider profile and

a flatter canyon floor than that of the preceding

canyon (Reyss, 1964). The lower valley has been

mapped to a depth of about 1700 m.

3. The La Fonera Canyon trends E-W and

differs from submarine valleys lying farther to the

north in possessing a U-shaped profile with a welldefined flat canyon floor. The canyon head is

cirquelike and highly dissected, and the axial slope

is high (to 10°). The lower valley can be followed

to a depth exceeding 2000 m. Submarine canyons

are absent on the margin off the Ampurdan

coastal plain.

STRATIGRAPHIC INTERPRETATION

Certain seismic reflectors in subbottom profiles

on the Catalonian margin (Figures 4A and 4B) can

be correlated with surface and subsurface strata;

the latter have been mapped in petroleum drill

holes on land and in the Gulf of Lion (Cravatte

et al., 1974). The following is a brief analysis of

the major subbottom sequences examined.

PALEOZOIC BASEMENT.—The Gulf of Lion shelf

is formed by Tertiary and Quaternary sedimentary

sequences lying above the Hercynian basement.

Cores of the Paleozoic basement have been recovered in four wells (Sirocco, Mistral, Tramontane,

and Autan) (Cravatte et al., 1974), and these show

that the Pyrenees extend geologically eastward to

the Maures Massif on the Provence coast of southeastern France (Arthaud and Mattauer, 1972;

Burollet and Dufaure, 1972).

The substratum in the Roussillon coastal plain

has been penetrated at two petroleum (Compagnie

Franchise de Petroles) exploratory drill sites (Gottis,

1958), Elne and Canet, at depths of 2140 m and

1785 m, respectively. The basement is shallower in

the Ampurdan coastal plain (1300 to 1600 m).

Seismic profiles obtained on the shelf in the study

area (Figure 5A, B) enable us to follow, in continuous fashion, the basement between the north

Pyrenean margin and the Gavarres Massif. As in

the Gulf of Lion (Alia et al., 1972), this basement

deepens rapidly seaward, and deep seismic work

has enabled this horizon to be followed to the base

of the slope (Delteil et al., 1972).

PRE-PLIOCENE SEDIMENTARY SEQUENCES.—Although the subbottom penetration by various

seismic systems used has been relatively low (500

m), units of probable pre-Pliocene age are occasionally recorded. The oldest Tertiary series crop

out on the edge of the Ampurdan coastal plain

and also have been cored at several drill sites in

this area. Seismic profiles obtained on the Catalonian shelf and slope reveal several units that are

interpreted to be older than Pliocene. The oldest

stratigraphic horizon above the basement, noted

on records collected north of the Gavarres Massif,

appears as a concentrated sequence of reflectors

(Figure 6B) showing distinct stratification and an

unconformable contact with the underlying basement. It is possible that these seismic reflectors are

of equivalent age and composition to calcareous

and marly sandstones of Eocene age that are

exposed above older metamorphic units on adjacent land sequences.

On the shelf south of La Fonera Canyon (off the

Catalonian Massif) there occurs locally a sequence

of subparallel reflectors that are well stratified and

offset by a fault complex. The upper part of this

unit displays a sharp surface (Figure 6c) believed

to be erosional in origin. The penetration by

seismic profiling is considerably more extensive

than in the series described above. These reflectors

are tentatively interpreted as Miocene strata

(Serra-Raventos and Got, 1974).
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 3.—Catalonian margin southwest of the Gulf of Lion: left, chart showing major

topographic features discussed in text (depth in meters), modified after Bourcart (1959, 1960a)

and Alia et al. (1969); right, schematic profiles oriented E-W across (A) Roussillon shelf,

(B) Pyrenean shelf, (C) Ampurdan margin, and (D) Catalonian Massif margin.

The presence of deep cores increases the reliability of correlation in the Gulf of Lion shelf. Here

the basement is buried by a conglomerate unit of

Aquitanian age which, in turn, is covered by hemipelagic sediments of Burdigalian and middle

Miocene (undefined) age. Farther to the south, in

the Balearic Basin plain, this sequence is covered

by evaporites of Messinian (uppermost Miocene)

age (Burollet and Byramjee, 1974). These suprasalt

(?) sequences appear to pinch out toward the base

of the slope; they are replaced laterally on the

slope and shelf by an unconformable erosional surface. This hiatus, dated as Pontian (^ Messinian)

by Glangeaud et al. (1966, 1967), may be equivalent

to what is designated elsewhere in the western

Mediterranean as Reflector H and Reflector K

(Alia et al., 1972); this band of reflectors is also

called Reflector M or M reflectors (Biscaye et al.,

1972 and Ryan et al., 1973b).

PLIOCENE SEDIMENTARY SEQUENCES.—Reflectors

attributed to the Pliocene on the basis of correlation with drill sites on land occur throughout the

study area; they are absent only in the immediate

vicinity of crystalline massifs (i.e., Pyrenees and
NUMBER 20

Sea level

S.L.

S.L. _.

r

-W

U.Q Upper Quaternary j £

M.Q Middle Quaternary

L.Q Lower Quaternary

P Pliocene

C Cretaceous

B Paleozoic and crystalline basement

S. L.

Gavarres massifs) and on topographic highs underlain by Miocene deposits off the Catalonian coast

(Figure 6c). The acoustic characteristics of these

Pliocene units change in a direction away from

the coast, i.e., from oblique, well-stratified reflectors truncated at the top by a near-horizontal

erosional surface, Reflector G (Figure 7A), to horizontal, acoustically less well-defined reflectors

termed the "transparent layer" (Figures 14—16).

Unlike the pre-Pliocene units described earlier, the

Pliocene sequence is characterized by an undulose

folded (but not faulted) structure (Figure 6c).

QUATERNARY SEDIMENTARY SEQUENCES.—Quaternary units are distinguished by a succession of

well-defined subhorizontal reflectors on the shelf

as well as on the slope and in the Balearic Basin

plain. Several key horizons on the shelf are defined

by means of shallow, high-resolution profiles (300

J Boomer) coupled with coring of the uppermost

sedimentary sequences. A basal unit above Reflector G consists of a succession of conformable reflectors of low amplitude (ax and a2, Figure 7A) of

probable lower Quaternary age. This sequence is

followed upward by a series of well-marked reflec-
3000 3°30 4 00 4°30 5°00

FIGURE 4.—Charts showing position of available seismic records on the Catalonian margin: A, coverage on

slope and basin plain (9000 J sparker); B, track lines

on shelf.

10 km

3°00
NUMBER 20 11

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FIGURE 5.—Two roughly parallel sections oriented N-S showing general stratigraphic and

structural configuration: A, transect on land from the Gavarres Massif to Cape Leucate;

B, submarine profile off the same region. (Approximate vertical scale: 1 cm = 1000 m.)

tors (a3) of probable Riss age. This latter sequence

is capped by an undulose, discordant surface

(Reflector J) that cuts units a2 and a,3; these latter

units are eroded by the oldest fluvial channels off

the Roussillon coastal plain (Monaco, 1973).

The upper Quaternary sequence comprises a

series of low amplitude and oblique reflectors (a4)

that fill irregularities and depressions of the J

horizon. The upper part of this horizon has been

cored and consists of muds of early Wurm age

(Wiirm II—III). In turn, these are covered by conformable reflectors of low amplitude (a5) dated

by carbon 14 as upper Wiirm to postglacial. On

the midsector of the shelf, the preceding Quaternary sequence is covered by a discontinuous transparent layer (ae) of Holocene (Flandrian) age

(Figure 7B). These surficial muds thin on the continental slope.

STRUCTURAL CONFIGURATION

GENERAL.—Deep drilling and mapping on land

show that the underlying structure of the Ampurdan and Roussillon coastal plains is controlled, to

a large extent, by the Pyrenean fault complex. A

major E-W fault delineates the Roussillon plain

and a series of NW-SE trending faults controls the

orientation of the Ampurdan coastal plain. Thus,

these coastal plains are interpreted as tectonic

depressions whose maximum downthrow is located

on the margins of the Pyrenean chain. The depth

of the crystalline basement underlying these depressions is irregular, i.e., apparently displayed by a

series of normal faults as a result of vertical tectonics (Figure 8). The basement rises gently northward toward Cape Leucate and southward toward

the Gavarres Massif. A seismic profile (9000 J

Sparker) trending parallel to the coast demonstrates this structural displacement (Figure 6A).

DEFORMATION OF THE PALEOZOIC BASEMENT.—

The seismic surveys on the shelf reveal the irregularities of the uppermost basement surface (Figure

8). As on land, (cf. Fontbote" and Guitard, 1958;

Mattauer, 1968) the position of the basement is

directly controlled by a network of fractures with

a predominant Pyrenean (WNW—ESE) orientation.
12 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

N

FICURE 6.—Seismic profiles selected to show major acoustic reflectors on the Catalonian margin

and their stratigraphic interpretation: A, 9000 J sparker profile (see interpretation on Figure

5B); B, 3000 J sparker; c, 300 J Boomer, (B = acoustic basement.)
NUMBER 20

GAVARRES MASSIF La Fonera Canyon

Seaward, the basement rises locally as a result of

N-S trending faults.

The basement can be followed seaward to the

Basin plain by means of deep penetration (Flexotir,

Flexichoc and other) systems; it deepens rapidly

by a series of stepfaults, and the total tectonic

throw approximates 4000 m (Delteil et al., 1972).

This complex of faults is oriented N—S in the study

area; the fault trend changes suddenly to an E-W

orientation north of 41°30'N latitude.

DEFORMATION OF THE NEOGENE SEQUENCES.—The

structural displacement of pre-Pliocene units offshore in the study area remains poorly denned as

a result of the limited acoustic penetration of the

equipment used. On the other hand, subbottom

data are sufficiently abundant to define the attitude

of Pliocene sequences. These latter units appear

to be depressed rapidly seaward as shown by the

progressive downwarping of deeper acoustic reflectors and the apparent bending (or flexuring) of

these reflectors away from the coast (Figure 9).

This phenomenon, referred to as the "flexure continentale" by Bourcart (1950, 1960b), has been

attributed to subsidence of the Basin plain basement with accompanying depression (and seaward

depositional progradation) of the overlying sedimentary series. Regional mapping of the Reflector

G (Pliocene-Quaternary boundary) (Figure 10)

shows that this surface is cut by the three previously described submarine valleys (LacazeDuthiers, Cape Creus, and La Fonera canyons) and

a presently buried valley (La Escala Canyon) off

the Ampurdan coastal plain. The downwarping

phenomena affecting Reflector G have been particularly intense off Ampurdan, between the Cape

Creus and La Fonera canyons, submarine valleys

that follow major fault trends. Movement along

these faults has apparently resulted in important

vertical displacement of the Reflector G isochrons

between the canyons and pronounced lowering of

the Ampurdan shelf relative to the other sectors

of the Catalonian margin.

The tectonic displacement that offset the basement and overlying series lessened at about the

time of Reflector G; this is demonstrated by the

undulations of the G Reflector in zones where

faults offset the underlying basement, i.e., in the

head of the Cape Creus Canyon and off Puertode-la-Selva, La Escala, Estartit, and Palamos. This

observation suggests that the major movements are

Pliocene in age and occurred along older (preTertiary) tectonic lineaments. Some pre-Pliocene

movement cannot be excluded. Displacement

involving local readjustments along these same

fault trends has occurred during the Quaternary

(i.e., Canet fault and the Canet-Agly anticline in

the Roussillon shelf cited in Monaco, 1971).

The G Reflector can be traced laterally and

appears to correlate with the Pliocene-Quaternary

surface in the Roussillon and Haut-Ampurdan

coastal plains. Elsewhere, this acoustic horizon is

directly transgressive above the basement offshore

and it is absent in near-coast sections. Erosion of

this sedimentary section is related to regressive

phases of sea level in the Quaternary.

DEFORMATION DURING THE QUATERNARY.—The
14 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

\ -

r

; *-/ - r^t':-y :- -?£f/ %*-'•$;-"**?'**'**<fv ^5C^!i ^ Y.:-vT:!*s*-F1

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- B /

FIGURE 7.—Two (A,B) seismic profiles (300 J Boomer) selected to show major acoustic reflectors

above the Pliocene. (G = Pliocene-Quaternary boundary; a2 and a3 = lower Quaternary;

J = lower-upper Quaternary boundary; a4 = Riss; a5 = Wiirm; a6 = Holocene.)

structural map of Reflector J (Riss age) (Figure 11)

differs from that of Reflector G. The position of

the three major Catalonian canyons is noted on

this map, while that of the now-buried La Escala

Canyon is completely absent. The position of the

latter is denoted only by a gentle depression of the

150 to 200 ms isochrons and by the appearance

seaward of large undulations that probably resulted

from structural deformation of the basement. However, the central margin off Ampurdan, displaying

the greatest differential downwarping, is apparent.

The major change observed is the lateral displacement seaward of the "zone de flexure" that

occurred during the time between the G and J

reflectors; the process involved in the downwarping was explained in the preceding section (cf.

Figure 9). Reflector J can be traced laterally and

correlated with equivalent units on land, as in the

case of the Pliocene-Quaternary boundary (Reflector G). The absence of this horizon in the sector

north of Cape Creus is due to the relatively more

intense tectonic displacement and related erosional

phase affecting this region toward the end of the

Quaternary.

STRUCTURAL MODIFICATION OF LATE QUATERNARY

SEQUENCES.—Regional mapping of the Late Quaternary horizons (Figure 12) shows that structural

modification continued during the Late Quaternary and Holocene. Deposition accompanied subsidence in the three offshore Catalonian sectors.
NUMBER 20 15

42°20

42°0O

Basement

Canyon

Isochron (ms)

Faults

10 km

3°00 3020

FIGURE 8.—Isochron map of upper acoustic basement surface

reveals major fault trends (in milliseconds, two-way travel

time).

Coring demonstrates that these movements affected

not only the lateral extension and thickness of

each of the dated (by carbon 14, Monaco, 1971;

Got, 1973) horizons, but also the lithological nature

of the deposits (Got et al., 1975). For example, on

the margin off Ampurdan where subsidence has

been most intense (Figure 13), the deposits are

thick and consist essentially of marine mud

sequences accumulated during the Wiirm III-IV

(a5llb) while on the Roussillon and Pyrenean

shelves, littoral sand and gravel sequences (a5llc)

were deposited during this same period (dated at

about 18,000 years B.P., Got, 1973). Furthermore,

Holocene muds appear lithologically uniform off

Ampurdan. In adjacent regions, subtle textural

variations, including gradual vertical grain-size

changes, are observed. These lateral variations

resulted from differential downwarping of the

Catalonian margin during the late Quaternary.

Subsidence maintained the Ampurdan margin

surface well below sea level during the Quaternary, while sectors undergoing less downwarping

off the Roussillon coastal plain, off the Pyrenees,

and off the Catalonian Massif more clearly reflect

the effects of transgression and regression related

to the eustatic oscillations in late PleistoceneHolocene time. It appears that the vertical displacement of the Catalonian margin has continued

until the present.

OUTER MARGIN EVOLUTION DURING THE

NEOGENE AND QUATERNARY

SLOPE STRUCTURES.—The network of subbottom

seismic lines on the outer Catalonian continental

slope and contiguous Balearic Basin plain is less

dense than on the shelf and uppermost slope

(Figure 4A,B); mapping of individual reflectors in

the outer sector is not feasible. The seismic equipment used (9000 Joules sparker), however, provides deeper penetration of subbottom series and

thus enables us to interpret in a general way the

major depositional and structural events affecting

these more distal environments during the Neogene and Quaternary.

The region extending seaward of the Ampurdan

coastal plain (margin displaying a convex-up profile) shows a marked thickening of the Quaternary

sediment section, and this depositional sequence

is deformed by large-scale undulations (lateral

wavelength amplitude of 2000 m). On the slope

proper, this undulatory structure is replaced by

a series of large, discontinuous, lunate features

interpreted as a sequence of displaced slump

masses that have modified the otherwise well-stratified Quaternary units (Figure 14). Some of these

allochthonous slump tongues (see arrows, Figure

14B) are about 5 km wide and approximately 450 m

thick. The underlying Pliocene and uppermost

Miocene sequences locally are offset by stepfaults
16 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 9.—An E-W profile (3000 J sparker) across the Ampurdan margin showing seawardtilted Pliocene and Quaternary reflectors related to subsidence ("flexure continentale")

mechanism.

(Figure 14c). Growth faults affect the upper Pliocene and Quaternary deposits. Another type of

structural deformation that affects the Quaternary

series is noted locally: subbottom highs in the

form of anticlinal folds and horsts, produced by

early Quaternary displacement. The thickness of

Quaternary sequences is reduced over these highs

(Figure 14c).

We interpret the different types of structures

affecting the surficial sequences as the result either

of downwarping of the "continental flexure" type,

or growth faults that have offset the underlying

Pliocene sequences, or both (Aloisi et al., 1974).

Subsidence has triggered slumps and other mass

movement of younger, less well-indurated Quaternary horizons above the more cohesive underlying

sequences on slopes of 5 degrees. These displacements of Pliocene and Quaternary units are concentrated in zones where older series have been

offset by movement along faults. Uplifted zones

serve as topographic barriers (tectonic dams, T. D.,

Figure 14c) that stop the downslope movement of

slump tongues. After continued sedimentation has

leveled the slope behind a tectonic dam, slump

masses can, once again, bypass such a sector and

be deposited farther downslope.

Thus, each episode leading to failure and displacement of an allochthonous mass modifies the

sea-floor topography. All of the displacement

phenomena described here that modify sediment

thickness and morphology have affected primarily

the Quaternary series. The irregular nature of the

surface topography of the Catalonian outer margin

reflects the importance of continuing mass gravity

movements on the slope. Somewhat analogous

deformation also has occurred in canyons (i.e., on

the walls of the Bourcart Canyon north of the

study area); the resulting modification of the seafloor has been described by Glangeaud et al. (1968)

as "phe'nomenes pelliculaires et e'pidermiques."

Comparable features are observed in the Catalonian canyons (Got and Stanley, 1974, fig. 4).

BASE-OF-SLOPE STRUCTURES.—The marked thickening of the Quaternary section in the base-of-slope

environment results, in part, from the accumulation of downslope-moving slump masses that

accumulate near the break in slope between the

continental slope and the basin plain. In some

instances, seismic profiles show Pliocene and

Quaternary strata which dip toward the slope

(Figure 15). This phenomenon appears to be independent of the structural configuration of the

underlying (M or K) reflector. This particular type

of structure is interpreted as follows: the prePliocene evaporite sequence, including Messinian

salt (Burollet and Byramjee, 1974), pinches out

toward the base of the slope. The movement of

salt by doming and diapirs (salt tectonics) locally

uplifts and laterally displaces (by sliding) the

unconsolidated Pliocene-Quaternary sedimentary
NUMBER 20 17

FIGURE 10.—Isochron map of the G Reflector (PlioceneQuaternary boundary) in milliseconds, two-way travel time.

(Note seaward tilt oft Ampurdan and trend of the buried

La Escala Valley.)

FIGURE 11.—Isochron map of the J Reflector (lower-upper

Quaternary boundary) in milliseconds, two-way travel time.

(Note extensive seaward tilting off Ampurdan between Cape

Creus and La Fonera canyons.)

cover toward the base of the slope. Strata dipping

toward the slope as a result of this salt-withdrawal

phenomenon have been observed on several E-W

seismic traverses across the base-of-slope environment between the Catalonian margin and the

Balearic Basin plain south of the Gulf of Lion.

BALEARIC BASIN PLAIN STRUCTURES.—The structure of the Basin plain seaward of the slope is

considerably less complex as demonstrated by the

near-horizontal and subparallel attitude of the

acoustic reflectors between the sediment-water

interface and the K (or M) Reflector. Reflectors in

these basinward zones are locally deformed into

swells and depressions of low amplitude (Figure

16A), in some cases by salt tectonism (Mauffret,

1969). Structural displacement is more clearly

apparent on Basin plain seismic sections than on

those of the slope due to the relatively thin and
18 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

10 km

3O00

FIGURE 12.—Map showing details of the extent of the late

Quaternary sedimentary sequences at different time intervals: 1, landward limit of sediment at about 27,000 years

before present (B.P.); 2, isopach of the sediments dated between 23,000 and 27,000 years B.P. (contoured at 25 ms (25 m)

interval); 3, landward limit of sediment at about 23,000 years

B.P.; 4, landward limit of sediment at about 20,000 years

B.P.; 5, landward limit of sediment at about 15,000 years B.P.;

6, seaward limit of the Holocene sequences. (The upper

Quaternary sequence is thicker and more complete in the

rapidly subsiding zone off Ampurdan than north of the

Cape Creus Canyon and south of the La Fonera Canyon;

see Figure 13.)

near-horizontal upper sediment section. Particularly visible are faults that displace the Quaternary

reflectors and which thus modify the surface topography (Figure 16B); vertical offset of strata ranges

to 40 to 50 ms (40 to 50 m).

The position of the different structural zones

described above is depicted on the chart in Figure

17. Three major arcuate tectonic zones are apparent and these are oriented roughly parallel to the

Gulf of Lion margin, i.e., oriented NE-SW in the

study area and trending E-W farther to the east.

The boundary between the zone of slope-tilted

strata and the less tectonically deformed Basin

plain sequence coincides rather closely with the

outer edge of the evaporite sequence in the

Balearic Basin. The boundary between the middle

(or slope-tilted strata) zone and the slope proper

corresponds to an area where some large vertical

fault displacement has been recorded on deeppenetration seismic profiles (Delteil et al., 1972;

Burollet and Byramjee, 1974). It would appear

that these faults, some of which can be traced

upslope, are closely related to the subsidence and

foundering of the sea floor to its present depth

(>2400 m).

As is apparent from the above observations,

structural patterns in the region off the Catalonian

margin have been influential in the present distribution pattern of the Pliocene and Quaternary

cover. The thickness of sediment on the shelf and

in the Basin plain provides a means to interpret

both the dispersal pattern and volumes of sediment

deposited. In the former environment, two factors

control the sediment distribution: proximity and

availability of sediment from terrigenous (fluvial)

sources on the adjacent land, and the contemporaneous subsidence of the margin during sedimentation (cf. Ampurdan margin). In the Basin plain,

where sedimentation rates are generally lower, the

geologically recent subsidence of the basin floor

and formation of the slope has accelerated sediment transfer from land seaward by downslope

entrainment, largely slumping. The movement of

these allochthonous masses downslope has resulted

in the irregular sediment thicknesses and increased

relief on the slope, and in considerable thickening

of the Pliocene and Quaternary sequences at the

base of the Catalonian slope. Significant amounts

of terrigenous material also have been transported

by mass-gravity processes to this deeper environment by way of the submarine canyons, which act
NUMBER 20 19

ROUSSILLON CONTINENTAL SHELF

PYRENEAN CONTINENTAL SHELF

AMPURDAN MARGIN

CATALONIAN CONTINENTAL SHELF

FIGURE 13.—Schematic cross-margin profiles along the four major Catalonian sectors showing

variations of thickness, lithology, and distribution of the Wurm to Holocene sediments. (These

profiles detail the surficial sequences shown in the transects in Figure 3.)
20

SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

WNW

; : i*i :

*P^'' " ''!:/>"

!*g*fti»3E.frf; £SE

Cape Creus ,\ .•" • ? f^

Canyon >

WNW

FIGURE 14.—Selected 9000 J sparker profiles on the Catalonian slope showing evidence of

slumping (arrows) of Pliocene-Quaternary sequences related to faulting and growth-faults

of underlying layers (see Figure 17). (On C note fault-bounded tectonic dam (T.D.) behind

which are trapped Quaternary units.)
NUMBER 20 21

W

I BASIN PLAIN ? _

f * —*V E

FIGURE 15.—An example of Pliocene and Quaternary strata dipping landward at the base of

the slope (see also Figure 17). Note fault (f) extending to the sediment-water interface, the

Quaternary-filled Cape Creus Canyon, and an erosional surface defined by the small hyperbolae

characteristic of the K Reflector (= M reflectors, uppermost Miocene) on left of profile.

(9000 J sparker profile.)

as funnels in the transfer of sediment from land

to the basin (Got and Stanley, 1974).

SUBMARINE CANYONS

STRUCTURAL CONSIDERATIONS.—Many of the submarine canyons of the western Mediterranean,

particularly those incised on the northern margin

of the Balearic Basin, have been intensively surveyed (Bourcart, 1959, 1960a, 1963). Among the

more recent studies are those of Reyss (1964, 1969),

Reyss and Soyer (1965), Gennesseaux (1966),

Glangeaud et al. (1968), Bellaiche (1970), Pautot

(1970), and Mascle (1971). Many of these investigations consider both the tectonic origin of canyons and their role in the transportation of

sediments from land to the deep basin plain. The

result of our bathymetric and seismic surveys of

the Catalonian canyons is summarized as follows:

1. Canyon physiography is characterized by steep

canyon walls, a sinuous axial trend, and a network

of tributary canyons that call to mind a subaerial

fluvial system. The relief between canyon axis and

intercanyon ridge exceeds 900 m along most of the

slope off the Gulf of Lion.

2. In spite of the apparent subaerial configuration of the canyon morphology, there does not

appear to be any major visible connection between

the canyon axes and present valleys on the adjacent

coast. The absence of continuity is the result of

erosion that occurred during the recent Wiirm

eustatic lowstand of sea level when a large sector

of the continental shelf became truncated. Nevertheless, a buried channel, extending 1 to 2 km

landward from the canyon heads, is observed on

high-resolution seismic profiles (Figure 18A).

3. The initial downcutting of the canyons occurred in Pliocene or Quaternary time as demonstrated by the erosion of Pliocene sequences. In

some cases pre-Pliocene sections, including the

crystalline Paleozoic basement, are eroded (Figure

18B). In other instances, Pliocene reflectors do not
22 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 16.—TWO profiles (9000 J sparker)

showing examples of tectonic deformation on the Balearic Basin plain east of

the Catalonian margin (see also Figure

17): A, gentle undulatory configuration of

the Pliocene-Quaternary sequences; B,

fault (f) with a throw of 40 ms (40 m).

appear to be truncated below the lowest canyon

axis incision, and no earlier pre-Pliocene (including Miocene) incision appears (Figure 19.) The

major canyon cutting phase in this region appears

to be dated at, or about, the Pliocene-Quaternary

boundary, i.e., recorded by the Reflector G unconformity surface.

4. Submarine valleys originate along the major

fault fracture zones that offset the basement. These

fault systems include the NNW-SSE Cape Creus

faults and the E-W faults in the La Fonera area.

5. Each of the valleys displays several distinct

phases of successive cutting and filling between the

head and the midsector of the canyon to depths of

about 1000 m. The canyon axes migrated laterally

and progressively in a predominant direction during

these Quaternary phases (Figure 20), i.e., away from

the Pyrenean axial zone. An analogous migration

of fluvial systems on land during the Quaternary

is also recorded (Got, 1967).

6. The lateral migration of the canyon axes is

related to the uplift of the Pyrenees during most

of the Quaternary. The role of uplift is recorded

topographically, i.e., the canyon walls on the

Pyrenean side lie at shallower depths than the

opposite canyon walls.

ORIGIN OF SUBMARINE VALLEYS.—Geologists concerned with the evolution of the western Mediterranean Basin, including Bourcart et al. (1961) and

others, in recent years have suggested that an extremely important phase of regression exposed the

shelf and adjacent shallow margin at the end of

the Miocene. In support of this theory, some

workers propose that submarine canyons presently

observed on the Mediterranean margins were

formed in Pontian ( ^ Messinian) time and subsequently have been filled with Pliocene and Quaternary sediments. Thus, if one follows this line of

reasoning the present physiography of the western

Mediterranean is one directly inherited from

"relict" (pre-Pliocene) events, without important

changes in earlier periods.

One such example frequently cited is the LacazeDuthiers Canyon whose structure and origin have
NUMBER 20

FIGURE 17.—Chart showing major structural zones on the outer Catalonian margin west of the

Rhone Cone. (Examples of the Pliocene-Quaternary sequences in the different zones are shown

in Figures 14, 15, and 16.)

been discussed by Bourcart (1959). On the basis of

Miocene and Pliocene sequences recovered in grabs

and cores, Bourcart postulated that this canyon

was cut in Miocene limestone and subsequently

filled with Pliocene sediments. Our observations,

based on numerous seismic traverses across the

canyon, do not support this hypothesis but indicate

instead that the initial and most important erosive

phase in the Catalonian region took place at the

end of the Pliocene. This first phase of canyon

cutting is associated with the G Reflector, which

is an unconformable erosional surface delineating

the boundary between the Pliocene and the Quaternary. This is confirmed by the dense seismic net

and good stratigraphic control in this sector, i.e.,

the Pliocene sedimentary sequences into which the

Lacaze-Duthiers Canyon is cut can be traced laterally in continuous fashion onto the shelf and adjacent land. Continuity of these units is confirmed by

drill sites on the coast. The seismic profiles show

no evidence of pre-Pliocene cutting in the lower

part of the canyon.

The important period of erosion at the end of

the Pliocene was followed by successive episodes of

Quaternary sea level oscillation, which resulted in

repeated migration of the sea across the shelf. On

the Catalonian margin, sedimentation patterns

record these eustatic events as well as the almost
24 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

NE sw

flMgjfcj-r- . 'v.""\

FIGURE 18.—Seismic profiles: A, record (300 J Boomer) reveals the filled

head of the Cape Creus Canyon, which is cut in inclined bedded Pliocene

units and follows a fault (note offset reflectors on opposite canyon walls);

B, record (3000 J sparker) across the head of La Fonera Canyon cut into

basement.

continuous downwarping of the western Mediterranean Basin. Perhaps the most important eustatic

phases occurred in the middle to upper Quaternary

(Mindel and Riss) as recorded by Reflector J. This

is clearly the case in the region off Ampurdan,

where the erosional effects associated with the Riss

horizon are apparent and indicate the final major

erosive event in this sector. After the Riss, the La

Escala Valley no longer was eroded; the platform

on which it was cut was lowered and remained

submerged as a result of tilting and subsidence.

The La Escala Valley was buried by sediment in

post-Riss time.

The above and other considerations serve to
NUMBER 20 25

sw

40ms.

D

FIGURE 19.—Selected seismic profiles across the heads of canyons. Lacaze-Duthiers Canyon: A, 300 J

Boomer. Cape Creus Canyon: B, 300 J Boomer; C,D, 9000 J sparker. (All sections show canyons

incised in Pliocene sequences; offset of reflectors by a fault is noted on C; sediment fill is

reduced in canyon heads (A-C); a thick Quaternary fill is noted in the midslope sector of

Cape Creus Canyon (D).)
26 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

!2kHzMUD-PENETRATOR

N

15 ms |

3000 J . SPARKER

ms

9000 J . SPARKER

-J

N

I

200 ms

0 1 4 km

FIGURE 20.—Comparison of profiles across the same section of the buried La Escala Valley

made with different seismic systems. These profiles show the axes of successive canyons cut

during the lower Quaternary. The configuration of strata reflects differential movements of the

Pyrenean Massif (B, on right side of profiles) and the Catalonian Massif (B, on left side). This

differential movement has produced a migration of the canyon axes toward the south during

the lower Quaternary (axis positions 1 to 4) and subsequent thickening toward the north of

the upper Quaternary strata (5 and 6) after the canyon-cutting phase. The thickening of strata

to the north (upper profile) results from the continued subsidence of the margin from the upper

Quaternary to present.
NUMBER 20 27

interpret the sequence of events which led to the

formation of Catalonian submarine canyons:

1. At least some relief was needed for the initial

cutting of the canyons at the end of Pliocene time.

A relief of at least 200 to 300 m would have been

sufficient to incise a significantly marked feature

such as a subaerial valley.

2. The ongoing "continental flexure" and tectonic tilting have resulted in the progressive subsidence of the platform on which the subaerial

valleys were cut; this progressive subsidence would

have initially submerged the lower sections of the

valleys.

3. As the general subsidence of the basin continued, the accompanying seaward tilt would result

in the progressive drowning of the valleys in a

landward direction.

4. Submergence of the valleys was accentuated

locally by faulting related to the lowering of the

basin floor; these local fault trends, responsible for

the location of the canyons on the Catalonian margin, are oriented perpendicular to the major N—S

faults.

5. The relief between the valley axes and adjacent intervalley highs became accentuated during

submergence as a result of enhanced deposition in

the intervalley sectors; this buildup of the intervalley highs accounts for the present-day canyon

relief of at least 900 m.

6. Subsequent eustatic oscillations superimposed

on the progressive submergence of the margin have

resulted in periodic reincision of the upper to

midsectors of the canyons.

7. The last low stand of sea level (Wiirm IV)

resulted in erosion of the shelf and truncation of

connections between the canyon heads and the

adjacent subaerial valley systems; an exception is

the preservation of a channel cut in the a2 horizon

between the Lacaze-Duthiers Canyon and the Agly

River.

8. Since the last rise in sea level, erosion of the

canyon heads has prevailed as a result of slumping

and other mass-gravity processes, while deposition

has occurred primarily in the lower canyon sectors.

This generalized Pyrenean-Catalonian tectonicpaleogeographic canyon evolution is not applicable

to all sectors of the northwestern Mediterranean

margin. There is evidence, for instance, of prePliocene erosion on the Provencal margin to the

northeast, and in the sector south of the Catalonian margin. In this latter region, late Miocene

erosion appears to have occurred primarily on

structural highs, and the best evidence of prePliocene truncation is recorded on the continental

shelf proper. Pre-Pliocene reflectors (such as the

M reflectors, Messinian) have not been eroded on

the slope, although there is ample evidence of

Pliocene and Quaternary truncation in some sectors

at depths between 100 and 1700 m.

Thus canyon formation, physiography, eustatic

oscillations, and structural configuration are closely

related. In this respect, it is useful to recall the

irregular "touches de piano" configuration of the

northwest Mediterranean margin, i.e., structural

highs with reduced sedimentary cover alternate

with tectonically depressed sectors with a thick

sedimentary cover (Got et al., 1975). In the study

area, the following configuration is mapped, from

south to north: (1) a Miocene high off the Gavarres

Massif, which extends southward; this zone is cut

by the Canyon de Blanes initially incised prior to

the Pliocene (G. Serra-Raventos, pers. comm. and

thesis, in prep.); (2) the foundered Ampurdan

sector with the La Escala Canyon cut in the Pliocene; (3) the Pyrenean high formed by the Paleozoic crystalline units; (4) the depressed Roussillon

margin that extends northward toward the Gulf

of Lion; the Lacaze-Duthiers Canyon in this sector

is a good example of a valley formed in the Pliocene and Quaternary. In summary, late Pliocene

events predominate while late Miocene erosive

phases affected those sectors that were structurally

high. The importance of these and Quaternary

events are closely related to the geologically recent

evolution of the northwest Mediterranean margin.

DISCUSSION

The sedimentary sequences on the Catalonian

margin, as revealed at several drill sites on land

and offshore, includes Neogene and Quaternary

units that lie upon a Paleozoic basement of granitic

and metamorphic rocks. The available network of

shallow to intermediate penetration seismic lines

in this region serves to detail the distribution and

configuration of Pliocene and Quaternary series

whose combined thickness ranges from 100 to 1500

ms (100 to 1500 m). In general, sediment thickness

increases > away from the shelf, where a maximum

of 500 ms (500 m) is recorded, seaward to the base
28 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

of the slope (1.5 seconds, or 1500 m); thicknesses

on the slope are highly variable due to growth

faults affecting the Pliocene units and an irregular

distribution of slump blocks of Pliocene and

Quaternary sediment.

A remarkable variation in sediment thickness is

also observed laterally on the different parts of the

shelf proper. These differences reflect local fluvial

input and also the marked regional differences in

rates of vertical subsidence. The margin surface

has served as an efficient sediment trap in those

regions where subsidence rates are greatest. As an

example, the Quaternary sequence on the midAmpurdan shelf is about 400 ms (400 m), or about

twice as thick as on the adjacent Pyrenean shelf.

The evolution and subdivision of the different

parts of the Catalonian shelf are the result of

differential movements along a network of E—W

trending Hercynian faults; this reactivation of old

fault trends occurred in Miocene and post-Miocene

time, particularly during the Pliocene. Seismic

profiles and cores show that some movement has

occurred as recently as the late Quaternary.

The local readjustment along the E—W trending

faults, which has given rise to the irregular

morphology of the Catalonian shelf, is closely associated with much larger displacements along the

major N—S trending faults in the Pliocene and

Quaternary. The geologically recent formation of

the Catalonian slope and the major subsidence of

the Balearic Basin are closely related to movement

along these N-S faults. The displacement along

these major fault trends has given rise to growthfaults and associated slump movements; the importance of these phenomena has diminished somewhat

during the Quaternary.

The continued deposition of terrigenous sediments has (1) resulted in the accumulation of a

I | Pliocene-Quaternary

&j&il Miocene

Allochthonous c.

Mesozoic

Pre-Mesozoic

Tertiary volcanism

. Faults

V Pre-Betic zone

IV Sub-Betic Zone

Malaguides

II Alpujarrides

I Nevado-Filabrides

ALGERO-BALEARIC BASIN

FIGURE 21.—Simplified geological map of southeastern Spain and the Balearic region showing

major tectono-stratigraphic series and structural trends. (Modified after maps compiled by

Biju-Duval and co-authors, 1974, Julivert et al., 1972, and Bousquet and Montenat, 1974.)
NUMBER 20 29

considerable thickness of Quaternary sequences

that have partially buried the irregular underlying

Pliocene and older structures and (2) has produced

the smooth, convex-up configuration of the seafloor.

We term this configuration of the Catalonian shelf

and slope a progressive structural margin. It represents one type of margin associated with continental flexuring and regular subsidence of the

western Mediterranean Basin.

Eastern Betic Margin

GEOLOGICAL FRAMEWORK

The easternmost extremity of the Betic range

in southeastern Spain and the Balearic islands,

discussed in the following chapter, form a geological entity as demonstrated by the overall stratigraphic similarities and consistent structural style

in the two regions. The major NE—SW trend of

tectonic-stratigraphic units is apparent on the

simplified map in Figure 21 compiled from several

sources (primarily Biju-Duval, 1974, and Julivert

et al., 1972). Studies that treat the relationship

between the Betic chain and the Balearic islands

have been published by Fallot (1923), Hollister

(1934), Stille (1942), Carey (1958), Freeman and

Simancas (1971), and Vogt et al. (1971). Among

the many field studies conducted in the eastern

Betics during the past decade are those by Azema

(1966), Paquet (1969), Bourgeois et al. (1970), Egeler

and Simon (1970), Bizon et al. (1973), and

Montenat (1973). The geology of the Balearic

islands has been summarized recently by Colom

(1957, 1967), Bourrouilh and Magne (1963), Bourrouilh and Colom (1967), Cuerda et al. (1969),

Rangheard (1969, 1970), Colom et al. (1970),

Obrador (1970), Obrador et al. (1971), and Bourrouilh (1972, 1973).

The principal units depicted on Figure 21

include (1) the older (pre-Miocene) tectonically

emplaced series, depicted as "autochthonous,"

which comprise pre-Mesozoic (including NevadoFilabrides, Alpujarides, and Malaguides) and

Mesozoic units; (2) the "allochthonous" series

emplaced during the Neogene (including the subBetic and pre-Betic zones); and (3) the "post-tectonic" or "post-orogenic" units, primarily Neogene

formations, which have been subjected to structural

deformation from the Miocene to the present.

The major fold and fault trends in the eastern

Betics are oriented NE-SW, including the important Murcia fault mapped by Bousquet and Montenat (1974, figs. 1, 2) and an E-W Cartagena-Cape

Palos trend. Smaller N-S transverse fractures have

offset the major NE-SW faults. Detailed studies

(Montenat, 1970; Bousquet and Montenat, 1974)

indicate that significant lateral displacement occurred along older (pre-Miocene) structures during

the Pliocene and Quaternary, and that some faults

in this region are still active.

The stratigraphic and structural configuration of

units forming the islands of Ibiza-Formentera

(Rangheard, 1970), Mallorca (Bourrouilh, 1972)

and Menorca (Hollister, 1934; Obrador et al., 1971)

are comparable in many respects to those of the

NE Betic chain. Here the predominant structural

trend is NE-SW of post-Langhian and older age

(also in Menorca according to Freeman and

Obrador, 1971), as well as NW-SE; these are in

general accordance with the major Betic trend.

The importance of reactivation and offset of

NW-SE Hercynian faults during the Tertiary has

been emphasized by Bourrouilh (1972); this movement may have contributed to the dislocation of

the Balearic Platform into separate blocks. Important vertical displacements of Miocene age are recognized on the Balearic islands by Rangheard

(1970) and Obrador et al. (1971); these movements

continued until the end of the Miocene (Messinian)

according to Bizon et al. (1973). More recent displacement of geologic units on the islands are cited

by Mauffret et al. (1972).

Offshore surveys suggest that the predominant

submarine trends east of the Betics in the vicinity

of the Balearic Block are also oriented NW-SE

(possibly related to major Oligocene-Miocene rotational movements associated with the origin of the

western Mediterranean Basin) and NE-SW. This

latter trend is interpreted as a more recent (Miocene to Quaternary) pattern related to major movements of the African plate relative to the European

plate (Mauffret et al., 1972; Auzende et al., 1973).

These geophysicists have attributed the present

physiography and subbottom configuration of the

margins to these geologically recent, largely postMiocene, movements.
30 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

PHYSIOGRAPHY

The eastern Betic (or Cape San Antonio-Cape

Palos) margin off southeastern Spain includes the

region extending from the Rio Jiicar south of the

Gulf of Valencia to the town of Vera (Figure 22).

The shelf in this region is relatively wide by

Mediterranean standards. Its width off Villajoyosa

is 44 km; it is 37 km off Gandia and 26 km off

Cape San Antonio, the major promontory trending

ENE toward the Balearic islands. The shelf is

reduced to 9 km south of Cape Palos and the Mar

Menor lagoon. The sharply denned E-W trending

outer shelf and slope in this region delineates the

Mazzaron Escarpment.

North of Cape San Antonio, the gentle submarine slope trends toward the northeast, i.e.,

parallel to the axis of the Valencia Trough, the

major depression between NE Spain and the

Balearic Platform. The margin between Gandia

and Cape Palos extends eastward toward the

Balearic Platform. Bathymetric profiles between

Cape San Antonio and Ibiza show the margin

sloping gently (2° to 3°) eastward to a depth of

about 900 m. It is separated from the westward

sloping Ibiza-Formentera margin by a narrow,

N-S trending depression. The slope southeast of

Cape San Antonio is cut by three large SE trending

canyons that apparently do not head onto the shelf.

Fans developed at the mouth of these canyons

merge with the flat Algero-Balearic Basin plain

lying at a depth exceeding 2700 m.

The steep (>12°), narrow E-W trending slope,

south and southeast of Cape Palos, called the

Mazzaron Escarpment (Ryan et al., 1970), is about

90 km long and less than 20 km wide. The slope

and rise becomes progressively wider (40 km) and

more gentle west of Cartagena.

40°

37°

FIGURE 22.—Physiographic chart of the southeastern Spain-eastern Betic margin and Balearic

region. (Based on Defense Mapping Agency Hydrographic Center Chart N.O. 310 (in Stanley,

1972); contours in region of Balearic Rise based on LYNCH-I cruise data; depth in meters.)
NUMBER 20 31

STRATIGRAPHIC INTERPRETATION

The stratigraphic sequence defined in seismic

profiles (Figure 23) can be traced in the various

sectors of the study area. The following acoustic

units are recognized between the base and the seafloor surface:

1. A discontinuous acoustic zone, locally forming

domes and piercement structures, is denned as

basement; it represents consolidated sequences of

variable age and lithology. Ultramafic rocks (peridotite and olivinic pyroxenite) have been dredged

off Alicante; the overlying sequence may include

lower Miocene calcarenites (Borsetti et al., 1974).

2. This is followed locally by a zone of poor to

moderately denned acoustic reflectors, which may

include Reflector N of upper Miocene age (Ryan

et al., 1973b). The total thickness of this sequence

above the basement is unknown, and appears to

vary regionally.

3. The acoustically transparent layer ("couche

fluante"), representing evaporite of Miocene age

(Ryan et al., 1973b), was not identified with certainty except in the region of the Balearic Basin

plain.

4. A bundle of well-defined reflectors, termed M

reflectors (also K reflector by French geophysicists),

has been dated as uppermost Miocene (Messinian)

and consists of evaporite sequences (Ryan et al.,

1973b); it also includes discontinuity surfaces. Its

thickness is about 50 ms (90 m). This sequence,

prominent on all profiles in this region, appears

on sparker records (Figure 24A) as a series of

subparallel reflectors that lie above hyperbolae

(Leenhardt et al., 1969, 1970). On air gun profiles,

at least six phases appear to make up the sequence.

5. The sequence immediately above the sharply

defined M reflectors is poorly defined acoustically

and appears as a transparent layer. This is attributed a Pliocene age (Alia et al., 1972; Ryan et al.,

..... . TEREBEL 1969

.......... . EMPIRE STATE IV 1972

LYNCH 1972

CONRAD 9 1965

DISCOVERY 1969-1970 -

37°

1° 0° 1° 2° 3°

FIGURE 23.—Chart showing position of seismic track lines used in this survey. (Systems used

on each cruise detailed in Methodology section; D/V Glorjaar Challenger leg 13 drill site 124

is shown east of the Balearic Rise.)
32 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

1973b). Along selected profiles, this acoustically

transparent zone laterally becomes well stratified

on the upper slope and shelf, as also was observed

on the Catalonian margin (cf. Figure 24 with

Figure 14). Throughout the study area, the transparent sequence becomes progressively layered

toward the top. This upper unit consisting of

parallel and subparallel reflectors is assigned a

Quaternary age. It is not possible, however, to

define the Pliocene-Quaternary boundary on the

basis of our seismic profiles, nor is the PlioceneQuaternary boundary observed on the shelf where

it probably is represented by an unconformity, as

in the Catalonian region (cf., Figure 7A). The thickness of the Pliocene-Quaternary unit varies considerably. The maximum thicknesses (in two-way

travel time) are 800 ms (800 m) near the base of

the slope in the Valencia Trough, 700 ms (700 m)

on the shelf off Cape Antonio, 600 ms (600 m) on

the slope west of the Mazzaron Escarpment, 400 ms

(400 m) on the slope southeast of Cape San Antonio, and 500 ms (500 m) between Cape San

Antonio and Ibiza. A 300 ms (300 m) sequence of

flat, stratified sediment is observed in the narrow,

deep depression between Cape San Antonio and

Ibiza (Figure 24B).

STRUCTURAL CONFIGURATION

The structural configuration of the eastern Betic

margin is discussed from north to south. The stratigraphy and tectonics of this region have received

little attention to date.

The seismic section extending NNE from Cape

San Antonio (Figure 24A) shows a gentle, nondeformed, convex-up profile underlain by Pliocene

and Quaternary sediments. These subparallel layers

lie above a faulted sequence that includes the M

reflectors (shown as K on some profiles) at the base

of the slope and other displaced layers farther

upslope and on the outer platform. These vertical

offsets have affected the transparent layer but

deformation becomes attenuated in the upper layered (Quaternary) sequence. It thus appears that

the age of deformation occurred between the late

Miocene and early Quaternary. The K (or M)

reflectors and overlying sequences are near-horizontal and undeformed at the base of the Cape San

Antonio slope in the Valencia Trough (Figure

24A).

The region east of Cape San Antonio is traversed

by two parallel ENE-WSW profiles, 35 km apart,

both of which show a relatively thick M reflectorsPliocene-Quaternary series sloping eastward. The

M reflectors are folded and offset by small faults

(Figure 24B); these fractures also have affected the

lower Pliocene transparent layer (see arrow). Deformation decreases in the upper layered sequence

(Quaternary). Thus the displacement is dated as

post-M, i.e., largely Pliocene. On the margin west

of the Ibiza-Formentera shelf the thickness of the

Pliocene-Quaternary cover is reduced and faulting

considerably more extensive. Here, some major

vertical offset and piercement of the M reflectors

and younger sequences by basement (B) materials,

possibly volcanic in origin (Figure 24c), are observed.

A seismic profile trending southeast of Cape San

Antonio (Figure 24E) shows the margin to be

broken by a series of large tilted block faults, which

produce the highly irregular steplike physiography

of the slope. The relief of each vertical offset,

which affects the M reflectors and upper sequences,

is of the order of 300 m (resulting in a total of

about 1800 m vertical offset over a distance of 66

km). The geologically young age (post-Miocene) of

these displacements is demonstrated by the faults

that cut the uppermost stratified layers (see arrow).

The M reflectors can be traced from block to block

between the base and the uppermost slope. The

acoustic basement, possibly consisting of volcanic

material, forms domelike highs, which rise to the

sediment-water interface in two areas.

A NE-SW air gun profile east of Cape Palos

(Figure 24D) cuts across the heads of two large

canyons (possibly tilted blocks as in Figure 24E)

partially filled by sediment respectively 300 ms

(300 m) and 500 ms (500 m) in thickness. The walls

of one canyon, formed of basement material, are

free of sediment; the sediment distribution in the

second canyon is asymmetric, i.e., sediment covers

the northeastern wall but is reduced on the southwest wall. This profile traverses the E-W trending

Mazzaron Escarpment revealing its marked relief

(approximately 2300 m) and steepness and the

reduced sediment cover. The contact between the

near-horizontal basin plain surface, locally pierced

by salt domes, and the base of the escarpment is

abrupt.

The southernmost seismic profile, west of the
NUMBER 20 33

I: ir

FIGURE 24.—Selected seismic profiles in area off southeastern Spain and the eastern Betic showing

different types of margins: A, progressive margin (9000 J sparker); B, progressive margin (air

gun); c, E, F, intermediate, or steplike margin (air gun); D, abrupt margin (air gun). (Symbols

for this and following figures: B = basement, C. F. = "couche fluante" (salt), M = M reflectors

(also K Reflector), P = Pliocene, Q = Quaternary; arrows denote selected faults.)
34 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

Mazzaron Escarpment, trends southeast from the

town of Vera to the base of the slope (Figure 24F).

The slope is topographically irregular and displays

one prominent steep escarpment of 220 m relief (see

arrow). The steplike slope physiography reflects a

sequence of vertical offsets that have affected the

M (or K) reflectors and younger sequences. Particularly noteworthy are the well-stratified (mostly

Quaternary) units that are truncated at the escarpment, indicating a post-Pliocene vertical displacement. The bundle of M reflectors, offset by a series

of young faults, can be traced at least to midslope

depths in this profile.

DISCUSSION

The available seismic coverage shows the general

consistency in the stratigraphic sequence and its

lateral extent over much of the submerged area

off the eastern Betic Chain. The acoustic basement

(age unknown), covered in many areas by a moderately stratified sequence of probable Miocene

age, is in turn capped by the M reflectors (Messinian) and thick series of Pliocene and Quaternary

unconsolidated sediment. The latter two units are

ubiquitous, but vary in thicknesses from zero (on

the Mazzaron Escarpment for example) to about

400 to 800 ms (400 to 800 m). The particularly

thick Pliocene-Quaternary cover on the shelf

between the Cape San Antonio and the Cape Palos

area is due, on the other hand, to large sediment

input (Rio Segura fluvial system) and also to the

continued subsidence of this margin (Montenat,

1970), which enabled it to serve as an efficient sediment trap.

The regional variation of the Pliocene-Quaternary thickness in most instances reflects displacement during and after sedimentation as shown by

profiles E and F (Figure 24). The bundle of M

reflectors beneath these sediments can be traced

between upper and midslope depths (^ < 1000 m)

and the Algero-Balearic Basin plain. This horizon

is almost always offset by faults, and a total vertical

relief of at least 1800 m (profile E, Figure 24) is

measured in this region.

The vertical displacement which accompanied

the foundering of the Algero-Balearic Basin and

Valencia Trough in this region differs markedly

from place to place. We observe three major styles

of margin tectonics that can be distinguished on

the configuration of the M reflectors and younger

Pliocene-Quaternary sequences and on the related

seafloor morphology:

1. The first is a gentle seaward-sloping, convex-up

bundle of M reflectors, which is only slightly tectonically offset, covered by a sequence of laterally

continuous, subparallel Pliocene and Quaternary

sediments (Figure 24A,B). Only the basal (Pliocene)

sequence appears broken by the same faults affecting the underlying M reflectors; this deformation

decreases in the upper (Quaternary) units; the

smooth, convex-up physiography of the seafloor

reflects this type of structure. We term this shelfslope configuration, generally associated with the

"flexure continentale" (Bourcart, 1960a, b, 1963)

and basin subsidence a progressive structural

margin.

2. A margin characterized by small to large steps

of as much as 300 to 400 m of relief is generally

associated with important vertical offsets of the

M reflectors and underlying series. Unlike the

above, the Pliocene-Quaternary units are discontinuous seaward, and the amount of offset affecting

these units is similar to that affecting the bundle

of M reflectors. Tilting often accompanies the

vertical displacement of blocks and is reflected in

the sea-floor topography; the M reflectors and

Pliocene-Quaternary units display equal amounts

of tilting. The series of downthrown blocks can be

traced in steplike fashion between the shelf margin

and upper slope to the base of the slope. This

structural configuration is herein termed an

intermediate (or step) structural margin.

3. A steep margin (slope to 12°) showing high

relief within a very narrow range (10 km wide)

without marked steplike configuration and discontinuity of strata is attributed to major faulting.

The best example in this region is the Mazzaron

Escarpment (Figure 24D) whose trend appears to

parallel an E—W fault system. Although seismic

records suggest that the surface topography of such

an escarpment defines a fault plane, it is more

probable that the escarpment surface is actually

a tight series of vertically displaced units. The

Pliocene and Quaternary sequences on this type

of margin appear reduced in thickness and may

be locally absent, unlike the intermediate margin.

This configuration defines an abrupt structural

margin (cf. Mauffret et al., 1973).

Regardless of the particular structural style
NUMBER 20 35

involved, profiles across the different margins show

that both M reflectors and overlying sequences have

been tectonically displaced in post-M time, i.e.,

since the end of the Miocene. The presence of

faults that displace even the uppermost reflectors

indicates the very recent and large-scale nature of

some of these movements offshore. These important

vertical displacements in Pliocene and Quaternary

time, which have shaped the slopes, escarpments,

and canyons in this eastern Betic region, can be

related to major phases of Pliocene-Quaternary

movement on land (cf. specific examples of recent

tectonics of the eastern Betic chain described by

Montenat, 1970; Bousquet and Montenat, 1974;

and other workers). The major fault trends, including a large fracture near Cape San Antonio, are

parallel or subparallel to the Betic and sub-Betic

chain (Bousquet and Montenat, 1974, figs. 1, 2).

Another important E—W trending fault in the

vicinity of Cartagena and south of Cape Palos-Mar

Menor parallels the Mazzaron Escarpment; recent

movement of significant magnitude has been

measured on land adjacent to this area.

It is noteworthy that the margin, when parallel

or near-parallel to major Pliocene and Quaternary

fault trends, is of the abrupt type; the Mazzaron

Escarpment is an excellent example. In contrast,

where oriented normal to major fault trends the

margin is of the progressive type (e.g., the region

north and east of Cape San Antonio).

Balearic Margins

PHYSIOGRAPHY

The Balearic Platform is a shallow topographic

feature, elongate NE-SW and approximately 440

km long, which extends from Cape San Antonio

and the southeastern Spanish Betic margin to the

region east of the island of Menorca. It consists

of two shallow (< 100 m) near-horizontal shelves:

a smaller (55 by 80 km) western shelf on which

rest the islands of Ibiza and Formentera and a

larger one (80 by 185 km) to the east on which lie

the islands of Mallorca and Menorca (Figure 22).

The shallow Ibiza-Formentera shelf is separated

from the Spanish mainland by a deep (900 m)

narrow depression, and from the Mallorca-Menorca

shelf by a broader N-S depression. The northern

margin of the Balearic Platform, forming the

southern limit of the Valencia Trough, becomes

steeper in a northeasterly direction (2° north of

Ibiza; 8° north of Mallorca). The margin east of

Menorca is oriented NW-SE with a slope of 10°

toward the Balearic Basin plain. A remarkably

steep and straight slope extends from the shelf

edge south of Mallorca-Menorca in a southwesterly

direction to the region southeast of the FormenteraIbiza shelf. This feature is called the Emile Baudot

Escarpment and has a gradient of 15° or more

between the abrupt shelf platform and the base of

slope (about 1500 m) south of Menorca. The

escarpment between 4°E, 39°45'N and 2°E,

37°55'N is about 275 km long, dying out westward

at a point about 220 km east of the Spanish coast

at the latitude of Murcia. To the east (southeast

of Menorca) the Emile Baudot Escarpment is truncated by a linear morphologic feature, the Menorca

Ridge, which trends N-S and extends southward

from the Mallorca-Menorca shelf.

The Balearic Rise is a large semicircular feature

located between the slope south of Menorca and

Mallorca, and the near-flat Algero-Balearic Basin

plain (this feature has also been termed the "seuil

sud-minorquais"). The Rise covers an area of about

15,000 km2 and ranges in depth between 1600 and

2600 m. On small-scale charts the Rise resembles

a large fan at the base of the eastern Balearic

Block; however, the relief and surface configuration

distinguish it from most typical subsea cones. The

Rise surface is very irregular and comprises a

group of small seamounts and depressions; in one

area, a mean relief of about 400 m is encountered

along a distance of 3 km (i.e., a gradient of about

7° 30').

One of the main features encountered on the

Balearic Rise is a submarine valley extending

southward from a point near the Menorca Ridge

between Menorca and Mallorca (at about 4°E,

39°45/N). Near the center of the Rise (4°10'E,

38°55/N) this depression trends toward the southwest. This Menorca submarine valley is about 150

km long between its head at the Mallorca-Menorca

shelf platform and its mouth on the lower Rise,

where it meets the Algero-Balearic Basin plain

at a depth of 2600 m.

The Menorca Valley is V-shaped and 3 to 4 km

wide at its head; it has a flat floor (U-shaped) and

widens to 25 km at its lower extremity on the Rise.

The valley walls (the eastern side is generally
36 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

higher in the upper reaches, and the western side

is higher on the Rise proper) have slopes to about

5° (Figure 32), whereas the average overall downslope axis gradient is 1:60 (or about 55'). Gradients

of axial sections vary between 1:30 (or about 2°04')

in the upper valley section and 1:150 (or about

23') in the lower section near the Basin Plain.

Three groups of Balearic Rise seamounts comprising one to three separate topographic highs

are prominently displayed on both sides of the

Menorca Valley. Seamount slopes vary in gradient

between 5° and 15° and their rounded crests are

generally quite narrow (area 3 to 5 km2, cf. Figure

22).

The margin south of Ibiza-Formentera trends

E-W with a more gentle slope of 3°. The westernmost sector of this margin is cut by three large

submarine canyons trending NW-SE off the Spanish coast (see discussion of the eastern Betic margin

southeast of Cape San Antonio, p. 30).

Bathymetric and seismic transects were available

for all sectors although coverage north of the

Balearic Block bounding the Valencia Trough is

less extensive (Figure 23).

STRATIGRAPHIC INTERPRETATION

Interpretation of the stratigraphic sequences

recorded on seismic profiles in the Balearic region

is based mainly on correlation with drilling logs

and description of cores and seismic profiles

retrieved by the D/V Glomar Challenger at site

124 of leg 13 (Ryan et al., 1973a). Site 124 is

located east of the Balearic Rise (38°52.38'N,

04°59.69'E) at a depth of 2726 m; some of our

seismic lines (Figure 23) traverse this area, thus

allowing regional correlation.

Five distinct units can be identified on the

sparker and air gun profiles. Locally, where there

is particularly good resolution of the reflectors, one

or two of these five sequences can be allocated to

subunits. These are as follows, from older to

younger:

1. The acoustic basement (B) is most frequently

recorded on traverses across the Balearic Platform,

particularly in the region between the shallow

island shelves (Figure 25) and also on steep escarpments forming the Platform margin. On the

Balearic Rise, the basement pierces the overlying

series and may represent volcanic (V?) extrusives

(Gonnard et al., 1975) or older rock units (Figure

28C,D).

2. A series of moderately defined reflectors,

usually 3 to 5 in number, locally lies adjacent to

the basement (Figures 25, 26); this series may

include the N Reflector. The lithology and age of

this unit are unknown, but it probably comprises

consolidated or semiconsolidated sequences of

Tertiary (probably post-Oligocene) age (Hsu et al.,

1975). It is observed at the base of the slope and

on the Basin plain, on the Balearic Rise, and on

the Balearic Platform. It is particularly prominent

in the depression between Mallorca and Ibiza

(Figure 25B,C).

3. An almost acoustically transparent series is

commonly observed on the seismic profiles, sometimes displaying a faint, very narrow bundle of

reflectors. The contact between the transparent

layer and overlying unit is usually nonconformable;

this probably results from postdepositional displacement of the overlying sediment above the

series forming the transparent layer.

A group of medium-strength reflectors occurs

near the base of this sequence. These reflectors

(N Reflector of Ryan et al., 1973b) commonly

occur below the limit of penetration of the seismic

systems we have used, but in a few places they can

be identified at depths of 600 to 800 m below the

sea floor (Figure 28). The transparent layer,

termed "couche fluante" by French workers, is

present in the Basin plain and in the western

sector of the Balearic Rise. Workers during the

last decade interpreted this sequence (Ryan et al.,

1970; Montadert et al., 1970; and others) as a salt

series in light of the diapirs and other "plastic

tectonics" observed. This hypothesis was confirmed

by the Glomar Challenger leg 13 drilling in 1970,

although halite was not cored at site 124. The

thickness in those areas where no structural or

diapiric disturbances are apparent varies between

100 and 400 m. At some localities this unit is

missing altogether and elsewhere it is completely

contorted into chaotic masses, where the original

thickness is difficult to assess (Figure 28E, F).

4. A sequence consisting of a prominent bundle

of reflectors, usually six to nine in number, is

laterally extensive; it is interpreted as the M reflectors sequence (Ryan et al., 1973a). The thickness of this unit usually ranges from 100 to 300 m,

and it is affected in places by intense tectonics
NUMBER 20

of diapiric origin (Figure 27F). There seems

to be no correlation between thickness and presentday topography. In some locations, it crops out at

the sea floor due to absence of the overlying sequences but elsewhere it is missing altogether either

because of later erosion or because the unit has

been incorporated in the diapiric, plastic material

which has forced its way through it from below.

Drilling at JOIDES site 124 indicates that this

unit is composed mainly of gypsum and anhydrite

alternating with some carbonates (dolomites) and

marls of Messinian age (Ryan et al., 1973a). The

contact of this formation with the overlying Pliocene sediment is probably an unconformable one;

a sharp change in lithology and compaction, and

hence in reflecting properties, gives rise to a very

prominent seismic signal, which makes it a most

useful stratigraphic marker. This seismic reflector,

however, is not necessarily of the exact same age

throughout the study area (Messinian to lowermost

Pliocene, Biscaye et al., 1972).

5. The uppermost sediment unit is characterized

by 10 to 20 reflectors of moderate intensity, which

fade out downward to an underlying transparent

layer. This section, commonly about 200 m in

thickness, attains a maximum thickness of 700 m;

locally it is missing altogether. The thickness of

this sequence varies with morphology, i.e., the

thickest sections tend to occur in depressions. Noteworthy is the tongue of sediment in the lower section of the Menorca Valley, from about 2195 to

2375 m (Figure 22). In most of the area of the

lower Menorca Valley on the Rise, the sediment

thickness ranges to 700 ms (700 m), while at the

head of the Menorca Valley and on the slope near

the Emile Baudot Escarpment the thickness of

this unit decreases to less than 100 ms (100 m).

Measured core sections at JOIDES leg 13, site 124,

provide additional information on the thickness

and lithology of this unit (Ryan et al., 1973a).

The formation consists mainly of lutites of both

turbiditic and hemipelagic origin, with variable

amounts of turbiditic arenites. The cores penetrating the surficial sediment section are discussed

elsewhere (Kelling, Maldonado, and Stanley, in

preparation). The relative proportion of arenitic

turbidites ranges from about one fifth of the recovered section in the upper part of the Balearic

Rise to about one hundredth of the lithologic

column at the margins of the Rise and in the

Algero-Balearic Basin plain.

The contemporaneous and genetically related

sediment bodies of the Rise and the deeper Basin

plain to the east and south display differences both

in thickness and lithofacies. It is probable that the

rate of sedimentation in the Algero-Balearic Basin

(Leclaire, 1972a,b; Rupke and Stanley, 1974) is

higher than that on the Balearic Rise; coring also

suggests that much of the sub-Recent and Pleistocene sand transported from the Balearic Platform

is presently resting on the Rise surface and has not

yet reached the Basin plain (Horn et al., 1972;

Rupke and Stanley, 1974; Stanley et al., 1974b;

Kelling, Maldonado, and Stanley, in preparation).

Within this sequence, a few reflectors are better

developed than others. These may be related to the

Pa and Pp markers of Ryan et al. (1973a) but such

a correlation is speculative at present.

The age of the transparent and overlying

reflector-rich zone is Pliocene and Quaternary

(Ryan et al., 1973b). It should be noted that the

lower layer of Pliocene age is transparent in the

basin plain and on the Balearic Rise but displays

reflectors on the Balearic Platform. As in the

region off southeastern Spain, it is not possible to

distinguish the boundary between the Pliocene and

Quaternary sequences on the available seismic

profiles.

STRUCTURAL CONFIGURATION

In the following discussion we treat successively

the predominant structural characteristics of the

Pliocene-Quaternary and underlying series on the

Balearic Platform, its margins north and south

(including the Emile Baudot Escarpment), the

Balearic Rise, and the Menorca Valley. Selected

subbottom profiles from the various regions illustrate specific points discussed here. The profiles

used are oriented, wherever possible, either parallel

or normal to each other (Figures 23, 25) and, in

some instances, perpendicular to major structural

trends of the region (Figure 21).

Balearic Platform

The platform east of the Spanish margin and

west of the shallow Ibiza-Formentera shelf, unlike
38 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 25.—Selected seismic profiles on the Balearic Platform: A-C, sections (air gun) between Ibiza-Formentera and Mallorca; D, detail of Mallorca shelf (8000 J sparker) showing

erosional surface (arrows) filled by Pliocene-Quaternary sediments; E, section (air gun) between

Ibiza-Formentera and Mallorca-Cabrera shelves; F, section (air gun) extending NW from the

Mallorca shelf to the Valencia Trough; c, profile (air gun) across Balearic Platform between

Valencia Trough and Emile Baudot Escarpment; H, section (air gun) extending from Valencia

Trough, between Mallorca and Menorca and across Menorca Valley and Menorca Ridge.

(N = N Reflector; symbols explained in Figure 24.)
NUMBER 20

the Cape San Antonio margin bounding the eastern

Betics (see previous chapter and Figure 24c), displays an irregular topography and a much reduced

Pliocene-Quaternary cover (about 100 to 250 ms,

or 100 to 250 m). Thicknesses are reduced on topographic highs; these highs commonly denote the

presence of the acoustic basement, which locally

has pierced the M reflectors and underlying sequences (Figure 25E). A number of faults are observed, which have divided the entire region into

a series of large tilted blocks 5 to 10 kms in

length. Vertical displacement of the M reflectors

approximates 200 ms (^ 200 m), and movement

along these faults appears to have affected the

Pliocene and in some instances Quaternary sequences. The bundle of M reflectors can be traced

upslope onto this sector of the platform to depths

of about 800 ms (a* 800 m). The thickness of Pliocene and Quaternary sequences is even more reduced on the Ibiza-Formentera shelf (< 100 m).

A broad depression characterized by more subdued topography occupies the sector between the
40 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

shallow Ibiza-Formentera and Mallorca shelves.

The Pliocene-Quaternary sequence ranges from <

100 to 400 ms (100 to 400 m) in thickness; it is

thinnest (< 100 ms, or < 100 m) on a NE-SW

trending basement high (see arrow, Figure 25G). The

M reflectors and younger units can be followed almost continuously across the broad depressions

although these sequences are locally displaced by

small faults (Figure 25). Regional mapping shows

that there is a buried depression of thickened

Pliocene-Quaternary sediment outlined to the east

and west by the Ibiza and Mallorca shelves respectively (Figure 25B, C), to the northwest by the

NE-SW basement high, and to the southeast by

the Isla Cabrera Ridge (Figure 25G). A southtrending submarine valley, the Cabrera Canyon

(Figure 25c), cuts this basinal sequence and appears

to be directly related to faults that have displaced

the M reflectors and overlying units. The margins

of this sediment-filled depression are delineated by

large faults that vertically displace the basement

and overlying units by as much as 400 ms (400 m).

Smaller faults also offset units on the eastern

Ibiza shelf. The bundle of M reflectors can be

traced upslope to depths of 600 ms, and it may

well be present at even shallower depths. The Pliocene and Quaternary sequence is attenuated on the

shallow Mallorca shelf. One transect, west of the

island and south of Palma de Mallorca, shows probable upper Miocene sedimentary units covered by

only a very thin veneer of unconsolidated sediments;

the rock unit presents an erosional surface reflecting

truncations of probable Quaternary age (Figure

25D) when presumably the shelf was subaerially

exposed and dissected by fluvial drainage.

The shallow, near-horizontal shelf between the

islands of Mallorca and Menorca also lacks any

significant Quaternary cover (Figure 25H). The

bundle of M reflectors is observed at a depth of

about 600 m. The seismic systems used to profile

across the shallow Mallorca-Menorca shelf do not

enable us to distinguish fault patterns within the

consolidated and upper sedimentary sequences

forming the shelf.

NORTHERN AND EASTERN MARGINS OF THE BALEARIC BLOCK.—The limited number of subbottom

traverses northwest and north of the Balearic Platform, which forms the southern limit of Valencia

Trough, do not enable us to detail this margin.

They nevertheless provide further indication of the

general tectonic styles of this sector, which has

previously been surveyed by Mauffret and Sancho

(1970), Auzende et al. (19726), Montadert et al.

(1970), and Mauffret et al. (1972, 1973). Our profiles

oriented NW-SE show a progressive reduction in

the thickness of the Pliocene-Quaternary sequence

on this margin between the Valencia Trough and

the Balearic Platform (Figure 25F-H). The thickness of these younger sequences on the slope ranges

from 400 to 500 ms (400 to 500 m) in the sector

north of Ibiza to north of Menorca. The bundle

of M reflectors can be traced continuously to at

least upper slope depth (^ 800 m) in all profiles.

This and overlying sequences are tectonically disturbed by a series of small step faults in the uppermost slope regions (Figure 25H). The profile

between Ibiza and Mallorca (Figure 25G) shows

continuity with only minor displacements near

the upper platform margin (i.e., near the NE-SW

trending Ibiza-Mallorca Ridge). The slope topography closely reflects the underlying structural

style: where gentle and smooth, little subbottom

tectonic deformation is observed; a steeper and

more irregular slope indicates the presence of

faults that have broken the margin into a series

of steplike blocks.

East and southeast of Menorca, the slope becomes much steeper (> 10°), locally forming escarpments (Figure 26A). Steep escarpment surfaces

appear free, at least locally, of sediment cover and

the basement crops out in some sectors. Where

present, the Pliocene-Quaternary cover is of the

order of 200 ms (200 m) in thickness (Figure 26B).

The M reflectors are offset by faults; they are

truncated at the base of the slope and cannot be

followed upslope with certainty (Figure 26A). The

physiography of this sector has been interpreted as

a series of faults by Belderson et al. (1970) and

Biju-Divual (1974).

The Menorca Escarpment facing the Balearic

Basin plain forms the eastern edge of the Balearic

Platform. Toward the south the relief of this

feature is progressively reduced, its slope is less steep

(4°), and the Pliocene-Quaternary cover reappears

(Figure 26B). The topographic high extending

south of the Menorca shelf is herein termed the

Menorca Ridge; its crest, with a reduced sedimentary cover, appears to be underlain by acoustic

basement. The western side of the Ridge also

shows considerable relief (1600 ms, 2200 m), re-
NUMBER 20 41

Menorca Ridge

FIGURE 26.—Seismic profiles traversing the Menorca Escarpment: A, 8000 J sparker; B, Conrad-9

air gun. (Note vertical displacement of M reflectors and Pliocene-Quaternary sequences on

Balearic Rise, and the sharp contact between the Rise and Algero-Balearic Basin plain.)
42 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

suiting from probable vertical fault offset (Figure

25H).

SOUTHERN MARGIN OF THE BALEARIC BLOCK.—The

southern margin of the Mallorca-Menorca shelf

edge forms a V-shaped aperture (angle of about

120°) opening southward. This configuration results from the meeting of two steep margins: the

NNW-SSE slope parallel to the crest of the Menorca Ridge, and the SW-NE trending Emile Baudot

Escarpment. A submarine canyon, the Menorca

Valley, lies at the junction of these two trends

and extends southward toward the Balearic Rise.

This region is covered by the Pliocene and Quaternary units ranging from 250 to 300 ms (250 to

300 m) in thickness. The bundle of M reflectors

can be traced reasonably well upslope to a depth

of about 500 m south of Menorca. The combined thickness of the M reflectors and overlying

units remains fairly constant along the slope. The

topography within the narrow V-shaped depression

on the upper slope is very irregular; it is influenced

to some degree by small fault offsets as noted by

displacement of the M reflectors (Figure 33A, B).

The topography and underlying structure are more

gentle on the mid to lower slopes.

The Balearic Block south of Mallorca and Formentera is bounded by the prominent southwesttrending Emile Baudot Escarpment. The

escarpment is limited to the east by the Menorca

Valley (Figure 27A) and its slope (5° to 10°) is toward the southeast (Figure 27B-E). At its eastern

end, the base of the escarpment merges with the

Balearic Rise. In this sector the escarpment presents an irregular, steplike surface including some

small V-shaped irregularities (some of which may

represent submarine valleys, while others may be

tilted and vertically offset blocks, Figure 27c, D).

The M reflectors and overlying PlioceneQuaternary units encountered on the upper

Balearic Rise thin out at the base of the escarpment. Nevertheless, these sequences appear locally

on the slope proper, where they are tilted.

The escarpment is steepest and has greatest relief south and southwest of the island of Cabrera

along a 100-km-long sector (Figures 25G, 27F). The

upper sequences forming the irregular Balearic

Rise topography and, to the west, near-horizonal

Alge"ro-Balearic plain sequences abut sharply against

the base of the escarpment (relief of about 2500 m)

south of this small island (Figure 27F). Deformation

of the acoustically transparent layer, including salt

domes and other forms of salt tectonics, is evident

on the basin plain just beyond the base of the

escarpment (Figure 27F,G). Our profile systems did

not reveal any notable sedimentary cover on the

escarpment in this steepest region. Studies by others

in this area (Mauffret et al., 1972) also show this

reduced Pliocene-Quaternary cover associated with

the NE-SW trending faults which form this feature.

The physiography of the escarpment changes

toward the west. Southeast and south of the

Formentera-Ibiza shelf the slope becomes steplike

and considerably less steep, except locally where

small escarpments are observed (Figure 27H). This

topography reflects a series of vertically displaced

blocks that have offset the sedimentary sequences

(900 ms, or 900 m), including M reflectors; these

latter reflectors can be traced between the AlgeroBalearic Basin plain and the Balearic Platform.

The acoustic basement locally pierces the overlying units on the slope, and even the uppermost

Quaternary sequences have been offset by faults.

Some faults can be traced laterally, as demonstrated by an analysis of two parallel profiles 80

km apart (Figure 27H,I). The Emile Baudot Escarpment, which diminishes in relief toward the

west (see a), disappears as a topographic feature

south of Formentera but is still recognizable as a

fault on seismic profiles (see a'). On the other hand,

an important escarpment (see b) on this latter

profile appears less well developed on the parallel

profile to the east (see b').

The thickness of the sediment cover increases

toward the southwest and the margin is progressively more block faulted and presents a marked

steplike topography in the direction of the Cape

San Antonio margin (Figure 24E).

Balearic Rise

This large feature lying south of the Emile Baudot Escarpment and Menorca Ridge is subdivided

into several tectonic zones on the basis of the

dense network of sparker and air-gun profiles available in this region. By far the largest zone is the

one broken into a series of large (^1 0 km wide)

horsts and grabens. The offset sedimentary sequence includes the Pliocene-Quaternary cover, the

M reflectors, the underlying transparent layer

("couche fluante"), and in some instances the N

reflector (Figure 28). This series appears similar
NUMBER 20 43

to that mapped on the adjacent basin plain. The

Pliocene-Quaternary units vary in thickness, but

they are not necessarily thinner on topographic

highs. The overall structural configuration of this

region appears to be of recent origin. This is particularly well illustrated by displacement of the

M reflectors and both overlying and underlying

horizons (see arrow, Figure 28H).

Seismic transects across the somewhat deeper

and topographically subdued southwest sector of

the Rise (at a depth of 2300 to 2600 m), south of

Mallorca, cross a zone of salt domes, many of which

reach the surface (Figure 28E). These domes are

similar to those observed in the adjacent Alge'roBalearic Basin plain (Watson and Johnson, 1969;

Wong et al., 1970; Alinat et al., 1970; Leenhardt,

1970; Stanley et al., 1974b). Salt dome structures

are absent from the region immediately east of the

Rise and just west of Glomar Challenger site 124

(Figure 28F).

The contact between the southern margin of the

Balearic Rise and the Alge'ro-Balearic Basin plain

is a sharp one as observed on several profiles

(Figures 28G, I, j). Step faults generally separate the

Rise from the Basin plain.

The density of seismic profiles enables us to

determine variations in regional stratigraphy and

to correlate these sequences with those mapped at

the JOIDES leg 13, drill site 124 (Ryan et al.,

1973a). Isopach maps show the following:

1. The Pliocene-Quaternary cover above the M

reflectors (Figure 29) varies irregularly in thickness,

from 100 to 700 ms (100 to 700 m). Isolated wedges

of Pliocene-Quaternary units trend in two predominant directions: NW-SE and NE-SW; these

thickened wedges are sometimes bounded by faults

of similar trend.

2. The thickness of the Messinian M reflectors

unit (Figure 30) is generally reduced about 100 to

150 ms (150 to 220 m) in comparison with that

on the Basin plain immediately south of the Rise

and of the Emile Baudot Escarpment (at least

200 ms). The thickness of the M reflectors is quite

variable across the Rise, and there does not seem

to be a close correlation with the thickness of the

overlying Pliocene-Quaternary units.

3. The transparent layer ("couche fluante") underlying the M reflectors has not been contoured

due to the structural complexities (Figure 31). Profiles show that this unit is present across much of

the Rise and its thickness varies from about 0 to

400 ms (0 to 700 m). This unit tends to thicken

slightly southward toward the Basin plain, and

pinches out at the base of the Emile Baudot Escarpment. W. B. F. Ryan (pers. comm.), who has

examined these records, ascribes the transparent

layer to infrasalt deposits. The thickness of the

transparent layer on the southernmost Rise, however, is comparable with that on the adjacent Basin

plain, where salt tectonics are observed (see Figure

28IJ).

The sum of observations indicates that the

Balearic Rise is an area broken by a complex network of faults. Vertical displacements have affected

the upper unconsolidated sedimentary sequences

as well as underlying basement, indicating the postMiocene to late Quaternary origin of these features.

The highly irregular topography of the Rise attests to this recent structural evolution.

Menorca Valley

A series of seismic profiles was made across the

Menorca Valley between its upper reaches and its

mouth on the lower Balearic Rise. The valley first

trends to the south, and upon reaching the Rise

veers to the southwest. Its cross-sectional character

changes downslope from a narrow V-shaped profile

to a broad, flat-floored U-shaped valley (Figure 32).

The thickness of the unconsolidated fill is negligible at its head and tends to increase downslope to

about 400 ms (400 m). On several cross-canyon

profiles on the upper slope (Figure 33B) the M reflectors appear offset, suggesting that the head of

canyon was cut along a fault. This is not unexpected inasmuch as the valley lies at the sharp

juncture of the Emile Baudot Escarpment and the

Menorca Ridge. Somewhat smaller valleys, adjacent

to the Menorca Valley and observed on the upper

slopes also display similar NNW-SSE trends; some

of these are canyon tributaries. In the two shallowest profiles made just south of the Menorca Shelf,

the V-shaped canyon cuts into the PlioceneQuaternary as well as the underlying bundle of

M reflectors. In all cross-canyon profiles obtained

farther to the south, the valley is cut well into the

Pliocene-Quaternary sequences, but the M reflectors can be traced beneath the valley (Figure 33C-F)

and do not show evidence of earlier (pre-Pliocene)

erosion or truncation by canyon cutting.
44 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 27.—Series of seismic profiles across the Emile Baudot Escarpment from southwest of

Menorca to southwest of Formentera; A-D, 8000 J sparker; E, G, 30,000 J sparker; F, H, I, air gun.

(Profiles A-E extend from the Mallorca shelf to the Balearic Rise; F-I extend to the AlgdroBalearic Basin plain. Note lateral changes of structure and physiography between profiles

G, H, I. The Large escarpment becomes a series of steps (a, on H) which subsequently die out

toward the southwest (a', on I).)
NUMBER 20 45

sla Cabr&ra

Ridge

EMI LE BAUDOT

ESCARPMENT

Algero-Balearic

in pla'n

These observations indicate (1) that the origin

and orientation of the upper reaches of the Menorca Valley were technically controlled, (2) that

the phase of canyon cutting is probably younger

than the M reflectors (i.e., post-Messinian) and in

part may even be Quaternary in age; and (3) that

the character and trend of the lower reaches of the

Menorca Valley are to a large degree sedimentologically controlled: its migratory pattern on the lower

Balearic Rise, well-developed natural levees (N.L.,

Figure 33C-F), and near-flat valley axis attest to its

importance as a byway for sediment between the
46 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

W T N

^ . • . FV "'/ T :7V-\i ,i .-.*[.. " r -•]' . & >

E TN

sw

JOIDESXIII

Site 124

f Balearic pl o ; n V

FIGURE 28.—Seismic profiles across the Balearic Rise showing the horst and graben structure

of this feature: A, B, profiles show the vertical displacement of sedimentary sequences, including

the Quaternary, which gives rise to the irregular topography; c, D, the acoustic basement

(possibly volcanic, V?) locally pierces sedimentary sequences and forms seamounts (also in

profiles A, B and J); F, profile across southern sector of the Rise from the Balearic Basin

(near Glomar Challenger site 124) to the Algero-Balearic plain; salt domes are noted on the

southwestern part of Rise (also on profile E); c, i, j , profiles show fault contact between the

Rise and basin plain; H, profile indicates marked vertical offset of the M reflectors and overlying series (arrow). (All profiles are 30,000 J sparker except F and H, which are air gun).
NUMBER 20 47

Balearic Platform and deep base-of-slope environments (Kelling, Maldonado and Stanley, in preparation).

DISCUSSION

The seismic survey demonstrated that the present

physiography of the Balearic Platform and adjacent regions is a result of extensive structural

displacement that has occurred, for the most part,

since the end of Miocene (i.e., post-M reflectors)

time, or a period of at least five million years

(Drooger, 1973). Not all of the movements need

have occurred simultaneously nor have all the displacements been of equal importance during this

period. For instance, it would appear that the steep

sediment-free escarpments are younger than some

of the more gentle progressive margins where faults

that displaced the M reflectors and transparent

Pliocene series became attenuated within the

Quaternary series.

The bundle of M reflectors which are present

almost everywhere in this region can be correlated

with that of the JOIDES drill site 124 a few

kilometers east of the Balearic Rise proper, where

it was recovered as dolomitic marl with interbedded diatomites beneath nodular anhydrite of

an upper Miocene (Messinian) evaporite series;

here it contains brackish to marine shallow-water

faunas (Ryan et al., 1973a). The M reflectors can

be traced across both the gently sloping and the

step-faulted portions of the Balearic Rise and also
48 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

20 30 40 50

THE BALEARIC RISE

0 5 10

0 10 20

ISOPACH MAP

Depth to "Reflector M"

Contour Interval 01 sec (two-way travel time)

20 30 40 50 20 30 40 SO JO 20 30 4O SO

FIGURE. 29.—Isopach map showing the combined Pliocene and Quaternary sediment thickness

and predominant fault patterns affecting these units on the Balearic Rise.

across the Balearic Platform proper, where it is observed at a depth of about 500 m. It probably occurs at shallower depths, but the seismic systems

we used do not permit definition of this unit

on the Ibiza-Formentera and Mallorca-Menorca

shelves. Although the M reflectors are not necessarily synchronous throughout the area, it appears

that some marine sequences of uppermost Miocene

age occur discontinuously between the islands and

the Balearic Basin plain some 2800 m below.

The Pliocene-Quaternary section is well developed in a tectonic depression on the Balearic
NUMBER 20 49

THICKNESS EXPRESSED BY TWO-WAY TRAVEL TIME (IN SEC)

FIGURE 30.—Simplified isopach map showing the approximate thickness of the bundle of M

reflectors (= Messinian age) on the Balearic Rise and adjacent Alg^ro-Balearic Basin plain.

Platform between Ibiza and Mallorca; it thins considerably on the shallow island shelves and adjacent steep margins and is possibly absent on

some steeper escarpments. It is well developed on

the Balearic Rise and Alge"ro-Balearic Basin plain,

where piston cores show that the uppermost sequences consist of alternating hemipelagic mud

and turbidite sand and mud; rates of sedimentation

exceed 20 cm per 1000 years (Rupke and Stanley,

1974).

All of the units mapped, from acoustic basement

to upper Quaternary, are almost everywhere struc-
50 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

THE BALEARIC RISE

SCAL E

9,5 . 10 2On. miles

0 10 20

-39

-38'

-1200-' Isobath (in fathoms)

penetrated

.23 thickness

"COUCHE FLUANTE"

Isopach map

Thickness expressed by two-way travel time (in sec.)

38°

FIGURE 31.—Simplified isopach map depicting distribution and approximate thickness of the

transparent "couche fluante" (upper Miocene salt) layer on the Balearic Rise.

turally deformed by folds and faults. However, the

nature of this deformation and related sea-floor

topography vary considerably regionally:

1. The slope north and west of the Ibiza Shelf

is gentle, relatively undeformed, and physiographically presents a concave-up profile. Seismic profiles

show that the Pliocene and Quaternary sequences

that dip gently toward the Valencia Trough lie

above slightly displaced M reflectors. This configuration is not unlike that observed north and east

of Cape San Antonio and defined as a progressive

margin.
NUMBER 20 51

THE MENORCA VALLEY

Morphological cross-sections

•122Ofm

FIGURE 32.—Menorca Valley cross sections showing the transition from V- to the U-shaped

configuration of the axis (see also Figure 33).
52 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

FIGURE 33.—Seismic profiles across the Menorca Valley: A-C, profiles on slope, 8000 J sparker;

D-C, profiles on Balearic Rise, 30,000 J sparker. (Note possible structural displacement in

sequences below canyon (arrow on B) and continuation of the M reflectors beneath the canyon

on all profiles. See also Figures 25H and 27A. N.L. = natural levee.)
NUMBER 20 53

2. The slope north and northeast of the

Mallorca-Menorca shelf is steeper and considerably

more irregular than (1); it presents a steplike configuration. T,his margin is deformed by large-scale

faulting, which has resulted in the vertical displacement of a series of large blocks between the

shelf and the Valencia Trough. Pliocene-Quaternary

thicknesses here are less important than those on

the margin described in (1). A similar configuration also occurs on the margin south and southwest

of Formentera. The Balearic Rise, lying between

about 1600 m and the Alge"ro-Balearic plain at

about 2700 m, is also broken into a series of large

horsts and grabens. All margins described here are

denned as the intermediate (or step) type.

3. The Menorca Escarpment east of Menorca

and the Emile Baudot Escarpment south and southwest of Mallorca represent an abrupt structural

margin. This type is characterized by a large relief

(about 2000 m) formed by a series of tight faults

with large vertical throw within a narrow (13-15

km wide) zone. In the two regions cited, this type

of margin separates near-horizontal sequences of

two quite different structural zones (i.e., shelf and

basin plain). Furthermore, these abrupt margins

appear devoid of any significant sedimentary cover.

Two other observations should be noted: (a) nearhorizontal basin plain strata abut directly against

the steep escarpment base, and (b) there is an absence of allochthonous slump masses at the base of

the slope. These observations indicate that the

escarpments have not been covered by a PlioceneQuaternary sediment cover of a thickness comparable to that on the Platform and Basin plain.

Nondeposition may be due to erosion by contour

currents (cf. Mauffret, 1969). More likely, the

absence of sediment, including pelagic and hemipelagic cover, indicates a geologically recent formation of this type of margin.

4. The series of parallel transects across the

Emile Baudot Escarpment and its western extension reveal a decrease in surface relief and slope

toward the southwest. The faults producing the

escarpment no longer have a significant surface

expression, although one can trace the Emile Baudot structure westward as an important subsurface

fault (see a', Figure 27i). Moreover, faults that are

poorly denned topographically southeast of IbizaFormentera form pronounced escarpments south

of Formentera (see b, Figure 27i). These observations demonstrate a transition from an abrupt type

margin to an intermediate (or step) structural type

over a relatively short distance (less than 80 km).

In those sectors where two major fault trends merge

or are superimposed, one encounters an intermediate structural margin (i.e., the margin north and

east of the Mallorca-Menorca shelf and the slope

south and southwest of Formentera). Of particular

interest in this respect is the Balearic Rise, which

is interpreted as a large margin block presently

undergoing subsidence by vertical displacement.

This foundering is the result of displacement along

two major fault trends, NNW-SSE (Menorca Ridge)

and NE-SW (Emile Baudot Escarpment); the former may represent displacement along an older

(POligocene) fault trend (Mauffret et al., 1972,

1973). The geologically rapid lowering of the Rise

block is reflected by the broken horst and graben

configuration of this feature, where even upper

Quaternary sequences have been displaced. The

Menorca Valley extending onto the Balearic Rise

has a structural origin that probably postdates the

Miocene, and its incision into Pliocene sediments

suggests that it may be as young as Pleistocene.

Thus both the canyon configuration and the particular tectonic style of the slope into which it is

cut reflect this geologically recent foundering of the

Balearic Rise, whose origin is closely related to

the subsidence of the Alge"ro-Balearic Basin.

Regional Continuity of Neogene Sequences

A synthesis of the seismic surveys of the Catalonian, Betic, and Bealearic margins reveals some

rather significant points common to the three areas,

particularly with regard to the nature and distribution of the uppermost Miocene to Recent sediment sequences. Our observations of the underlying

series, including the upper Miocene salt layer

(transparent "couche fluante"), N Reflector, and

acoustic basement, also supplement the data collected by geophysicists using deeper penetration

systems in the western Mediterranean Basin [cf.,

Mauffret (1969), Alia (1970), Montadert et al (1970),

Mauffret et al. (1972, 1973), Alia et al. (1972), Ryan

et al. (1973b), and others].

The dense subbottom profile coverage provides

good definition of the M reflectors and their regional extent. This is of considerable importance inasmuch as this stratigraphic sequence
54 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

clearly is one of the keys to understanding the

recent evolution of the margins and contiguous

western Mediterranean Basin. This acoustically

well-defined unit and the underlying upper Miocene salt can be traced across much of the Balearic

Basin plain (Hsu, Cita and Ryan, 1973, fig. 3; BijuDuval, 1974). The salt layer generally pinches out

near the base of the margins, although it does

extend marginward somewhat in areas such as

the Gulf of Lion and the eastern part of the Valencia Trough (Mauffret et al., 1973, fig. 1), the

Alboran Sea (Auzende et al., 1975), the Sardinian

margin (Auzende et al., 1972a, 1974) and the Ligurian margin (Rehault et al., 1974). The data we

present here show that the salt does in fact extend

from the Balearic Basin plain to the base of the

slope and occurs on some sectors of the Balearic

Rise; the bundle of M reflectors, on the other hand,

has a broader distribution and can be traced in

all sectors from the basin plain well upslope to

depths as shallow as 450 m. For instance, this unit

is present almost everywhere on the Balearic Platform and southeastern Spanish margin. Furthermore, the M reflectors probably are continuous

between the Catalonian margin and the Balearic

region some 260 km to the south (cf., profiles extending across the Valencia Trough illustrated in

Leenhardt et al., 1970, and in Mauffret and

Sancho, 1970).

The M reflectors are traced with some reliability to shallower depths in the eastern Betic-Balearic

region than in the Catalonian margin. This unit

(or equivalent sequence), however, actually may be

present at shallower depths on the Catalonian

upper slope and shelf, although in different form

than that observed on profiles at the base of the

Catalonian slope. In this respect it is noteworthy

that the M reflectors as such are not recorded in

the Gulf of Lion region northeast of our study

area; here they appear replaced by an unconformable surface interpreted as a Pontian (^ Messinian)

erosional horizon by Bourcart (1963) and Glangeaud et al. (1966). Some authors (Burollet and

Byramjee, 1974) have recently questioned the age

of this unconformity and propose that it is not

equivalent in age to the M reflectors but actually is

older, i.e., upper Miocene, but of presalt age; others

attribute to it a post-Messinian (lower Pliocene)

age (Auzende et al., 1974).

In some areas there is evidence for the presence

of Messinian sediments of this age at shallow

depths. For example, on the islands of Mallorca

and Menorca, Bizon and others (1973) have dated

as Messinian calcarenites containing faunas indicative of open marine conditions (these same units,

however, are dated as Tortonian and pre-Messinian

by W. B. F. Ryan, pers. comra.). Thick evaporite

sequences, possibly of equivalent age, are cited in

the Almeria area of the eastern Betic range (Auzende

et al., 1971, 1972b). Elsewhere, cores on the Provencal slope off southeastern France have recovered

Messinian marine microfaunas at depths of 1750 m

(Glacon and Rehault, 1973). Thus in some sectors

of our study area there is probable continuity of

the M reflectors between the basin plain and shallow environments, while in other regions erosion

of the Messinian unit has prevailed. Additional

coring and drilling programs on the slope and

outer margin sectors are needed to resolve this

problem of lateral continuity of the M reflectors.

The seismic character of the Pliocene and

Quaternary series is similar in the different areas

examined. An upward transition from the lower

transparent layer (Pliocene) to an upper acoustically stratified (Quaternary) unit is noted both on

slopes and in the basin. The acoustically transparent Pliocene unit lying above the bundle of

M reflectors can be traced upslope and onto the

shelf, where it displays a stratified appearance.

Some geophysicists attribute the transparent character of the sediment above the M reflectors to a

purely acoustic phenomenon. The cores retrieved

at the Glomar Challenger JOIDES leg 13, drill site

124 do, in fact, reveal relatively similar textural

sequences (sand and mud) in both the transparent

and reflector-rich horizons (Ryan et al., 1973a).

However, other sediment properties (strength, water

content, etc.) which might account for these acoustic variations cannot be ruled out.

The Pliocene-Quaternary boundary cannot be

clearly defined in the basin plain and lower slope

inasmuch as (1) the passage between the two units

is gradual and (2) there is apparent conformity

between them. Furthermore, as stated above,

JOIDES drilling has shown that the lithology is

not as markedly different as would be suggested

by the differences recorded on seismic profiles.

On the shelf, however, the distribution between

the two units is marked by an unconformable surface (see Reflector G, Figures 7, 9).
NUMBER 20 55

The thickness of these Pliocene and Quaternary

units is generally greater in the basin plain than

on the slope and shelf. The lateral variations measured on the shelf and slope can be explained in

terms of sediment input (i.e., proximity to major

rivers and importance of fluvial supply), and of

relative importance of structural mobility and

vertical displacement of the platform receiving

sediments. For instance, thick Pliocene-Quaternary

units tend to occur in zones offset by active faults

such as on the Balearic Rise (Figure 29) and on

those sectors of shelves that subside rapidly. Examples of subsiding surfaces which act as efficient

sediment traps include the Ampurdan margin

(Figure 3), the eastern Betic margin near Cape

San Antonio (Figure 24), and the large depression

between Ibiza and Mallorca on the Balearic Platform (Figure 25). On those margins that display

greater subsidence rates there has been relatively

little modification of the shelf sediments by the

repeated Pleistocene regressions and transgressions.

This lack of modification is ascribed to the maintenance of such platforms below sea level even during eustatic low stands (Figure 13).

Structural Configuration of Margins in Study Area

Previous geophysical investigations, using deep

penetration (particularly Flexotir and Flexichoc)

systems, have shown that the margins of the western Mediterranean are not uniform in character.

Two contrasting margin types have been defined

(cf., Mauffret et al., 1973, fig. 17): (1) an abrupt

structural margin where the continental slope is

steep and localized within a very restricted area

and where strata of the deep basin plain pinch

out against a rise of the basement; the margin off

the Provence region of France is one example; (2)

a wide intermediate margin zone characterized by a

shallower depth than the basin plain, a sedimentary basement of continental origin, discontinuous infrasalt strata on an irregular basement

surface, absence of salt, and extensive erosion at

the base of the Pliocene-Quaternary sequence; the

margins north of the Balearic islands and north of

Corsica are cited as type examples.

Our investigation confirms the presence of such

tectonically controlled margins but, on the basis

of higher resolution subbottom surveys, we find

that the structural configuration of the western

Mediterranean margins is more complex than envisioned above. A detailed evaluation of the postsalt layers (uppermost Miocene M reflectors and

overlying Pliocene and Quaternary series) reveals

three types of margin: progressive, intermediate (or

steplike), and abrupt.

The first is characterized by a smooth, gently

dipping, convex-up physiography of the sea floor,

reflecting the regular lateral continuity of the Pliocene and Quaternary sediments and M reflectors.

This latter unit is slightly offset by faults that are

attenuated in the Pliocene series above it. Growth

faults and slumping have modified the upper Pliocene and Quaternary sequences. Most of the

Catalonian margin is of this type, as are the eastern

Betic regions north and east of Cape San Antonio

and the margin north of Ibiza.

The intermediate type presents a marked steplike physiography between the outer shelf and the

base of the slope. The relief of each of the steps or

escarpments may be as high as 300 to 400 m or

more, and these reflect a series of important vertical offsets of the Pliocene-Quaternary series, M

reflectors, and underlying series, all of which are

discontinuous between the shelf edge and the base

of the slope. The downthrown blocks are frequently tilted. This structural type defines the

margins southeast of Cape San Antonio, north and

northeast of the Mallorca-Menorca shelf, southeast

and south of the Menorca shelf (including the

Balearic Rise), and southwest of the IbizaFormentera shelf.

The third, or abrupt, type is the steepest and

presents the greatest relief within a restricted zone;

it defines the sharpest and most distinct boundary

between the shelf platform sequences and those

of the basin plain. The near-horizontal basin plain

strata abut sharply against the base of the steep

escarpment and the M reflectors cannot be traced

upslope; the Pliocene-Quaternary sequences are reduced or absent. This type of margin defines three

major sectors in the study areas: the Menorca,

Emile Baudot, and Mazzaron escarpments.

Furthermore, our observations show the interrelation of these three types of structural margins.

We have recorded the transition from abrupt to

intermediate types in the region extending south

of Mallorca to south of Formentera (Figure 27).

The investigation of margins of the eastern BeticBalearic Block reveals the lateral variation from
56 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

progressive to intermediate types (in a northeastern

direction between the Cape San Antonio-IbizaMallorca margins north of the Balearic Platform)

and a succession of intermediate to abrupt margins

in the regions east and south of Menorca and extending toward the Cape Palos-Vera margin.

The canyons detailed in the study area are

present on all three types of margins but are best

developed on the progressive and intermediate

types. On abrupt margins canyons are "perched,"

due to faulting subsequent to their formation. An

example is the Cabrera Canyon, draining the

Mallorca-Formentera basin on the Balearic Platform, which has a steep gradient on the Emile

Baudot Escarpment. All canyons examined in detail reveal complex tectonic as well as sedimentary

origins, i.e., they follow fault trends, and their

subsequent development is largely structurally controlled, although canyon cutting and migration

were modified to some extent by the Quaternary

eustatic events that affected the shallow platforms

and influenced sediment transport across the margins toward the basin plain.

Age of Margin Formation

The present configuration of the Mediterranean

Basin has been attributed to the superposition of

Mesozoic (Hsu, 1971), and Tertiary and postMiocene structural events (Auzende et al., 1973).

Our data in the three study areas provide further

insight on the significance of geologically recent

tectonic phases. Particularly significant in this respect is the regional configuration of the Messinian

and younger series and the structural style of the

margins bounding the deep Balearic Basin.

Compelling evidence for the recent origin of

these margins is provided by the following observations:

1. The M reflectors and their lateral equivalents

(including erosional surfaces), dated as uppermost

Miocene, have a wide-ranging distribution and occur at highly variable depths in different physiographic and structural provinces. These series have

been mapped at depths of 2220 m at the base of

the Catalonian, Gulf of Lion, and other margins

and can be traced upslope from the basin plain

to the shallow margins (i.e., to depths of 450 m on

the Balearic Platform for example) by means of

seismic records and cores (Glacon and Rehault,

1973). In addition, marine Messinian sediments

have recently been recorded on Mallorca and Menorca, and evaporites occur on land in adjoining

areas (Almeria basin, Murcia, Vera, Sorbas, etc.

in the eastern Betics).

2. The Pliocene sequences also present an irregular and obviously displaced configuration on most

margins. One example is the lower Pliocene sequence containing shallow marine microfaunas

recovered at depths of 2000 m (Bellaiche, 1972;

Bellaiche et al., 1974).

3. Seismic records in all areas show that the M

and above units have been subjected to postdepositional vertical displacement of large amplitudes which occurred during the Pliocene and the

Quaternary. Our seismic evidence enables the M

reflectors to be traced from broken block to broken

block and across vertical offsets between the shelf

and basin plain. The M unit and lateral equivalents, when placed in their original configuration,

outline a late Miocene bathymetry unlike that suggested by Hsu (1972), Hsu and Ryan (1972), Benson

(1972), Ryan et al. (1973b), and others.

4. The formation of submarine canyons in the

three areas provides additional support for the

recent date of the major subsidence and locally

accelerated foundering. The age of canyon cutting

is variable along different margin sectors and also

within the same valley. Canyons in areas that were

structural highs in pre-Pliocene time were initially

cut in the upper Miocene; evidence of this early

erosional phase is recorded only on the continental

shelf and upper slope. In contrast, the PlioceneQuaternary phases of canyon cutting are well developed between the upper continental shelf and

the base of slope. Progressive margins do not provide evidence of pre-Pliocene canyon incision; the

first major phase of canyon incision is dated as

Pliocene.

5. The presence of Pliocene and Quaternary volcanism in Catalonia and on the Balearic Rise(?),

including domes which have penetrated thick sequences of the surficial sedimentary cover, may be

related to the post-Miocene tectonics.

6. Further evidence of the youthful origin of

the western Basin margins is indicated by the fact

that the margins are incompletely covered by

Quaternary deposits, although high sedimentation

rates prevail throughout this land-enclosed area

(more than 20 cm per 1000 years are recorded,
NUMBER 20 57

Gennesseaux and Thommeret, 1969; Labeyrie et al.,

1968; Leclaire, 1972a; Rupke and Stanley, 1974).

Although the structural, physiographic, and

sedimentary configuration of margins is generally

youthful, a point of clarification is needed. The

style and scale of recent structural displacement

have varied from region to region, and the age of

the movements was not necessarily synchronous

throughout a particular region. For instance, the

escarpments are characterized by a marked reduction of sediment cover and are bounded sharply

at their base by the horizontal basin plain PlioceneQuaternary sequences; these escarpments probably

record the most recent major vertical movements.

The lack of slump wedges at the base of the escarpments provides further evidence of the youthful nature of these slopes, which apparently are so

young as not to have accumulated a sedimentary

cover of hemipelagic mud. A somewhat older date

for the inception of vertical displacement can be

deduced for some progressive and intermediate

margins, where faults are attenuated in the thick

upper Pliocene and Quaternary sequences. It can

be demonstrated, however, that even those margins

displaying a slightly disturbed and thick Quaternary cover have recently subsided; this is best

exemplified by the evolution of the Ampurdan

sector of the Catalonian margin. Subsidence of the

Ampurdan sector accelerated during the upper

Quaternary and is probably continuing at present,

while shelves immediately to the north and south

have been relatively more stable since the middle

Quaternary (Got et al., 1975). Thus evidence of

both gentle subsidence and foundering are recorded

in the same region.

It should also be noted that in the case of an

abrupt or intermediate margin, there appears to

be a progressive displacement of structural activity

in a landward direction. A case in point is the

Emile Baudot Escarpment south of the Balearic

Platform, where a series of faults parallel the margin. Our seismic profiles in this sector show that

the faults are progressively younger in a direction

away from the basin plain, i.e., up the slope

(cf. Figure 27H,I).

In this same region we find evidence of the geologically recent vertical displacement of the Balearic Rise, a large continental block dislocated from

the Balearic Platform. Its recent age is demonstrated by the close association with the Emile

Baudot Escarpment, the completely broken (horst

and graben) configuration affecting the Quaternary

sedimentary cover, and the fault contact between

the outer Rise and adjacent Balearic Basin.

Margin Formation and Western Mediterranean

Basin Evolution

Although the previous sections have emphasized

the importance of geologically recent movement,

it is recognized that the configuration of the present

western Mediterranean Basin is closely related to

older major structural trends that developed during the Tertiary (cf. structural models of Auzende

et al., 1973 and Mauffret et al., 1973). These trends

are related to large-scale geodynamic events that

included (1) the rotation of the Corsican-Sardinian

block in the Oligocene (Stanley and Mutti, 1968;

Gennesseaux et al., 1974) and/or Miocene (Alvarez,

1972; de Jong et al., 1972) (this resulted in the

formation of NW-SE fractures and foundered

zones in the Gulf of Lion region) and (2) the relative displacement of the African and European

plates in the Miocene (Mauffret et al., 1972; Auzende et al., 1973) (the NE-SW tectonic trends, as

defined by such features as the Emile Baudot

Escarpment, are related to these movements). The

distinct configuration of margins as we know them

today and the marked relief between the shelves

and the Balearic Basin plain are attributed to

continued structural activity in the Pliocene and

the Quaternary. Thus, a Mediterranean margin

formation model should take into account the importance of these recent displacements, for it is

during this most recent geological phase that some

margins became accentuated either by renewed

movement along older trends or by subsidence

along new directions with respect to the earlier

fractures. In both instances, the foundered zones,

in general, are closely related to major structural

trends on land, regardless of age. For instance,

movement has occurred along reactivated Tertiary

faults (NW-SE and NE—SW) as well as along older

Hercynian and Pyrenean (NNW-SSE and E-W)

axes in the region off Catalonia.

The abrupt type margin occurs in sectors where

the Tertiary margins tend to coincide with major

structural trends on land, as in the case of the

Emile Baudot Escarpment, which follows the im-
58 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

portant NE-SW axis cited earlier, and of the Mazzaron Escarpment, which parallels the E-W trend

of the eastern Betic chain. Studies of other parts

of the western Mediterranean such as off Provence

(Glangeaud et al., 1965; Mauffret et al., 1973;

Rehault et al., 1974), off North Africa (Auzende

and Pautot, 1970; Auzende et al., 1973), and off the

Tunisian-Sardinian sector (Auzende et al., 1972a,

1974) also provide good examples of abrupt margins. In these regions, the predominant land and

continental borderland structural trend is parallel,

or subparallel, to the edge of the basin. The major

phases of margin subsidence and accentuation of

basin relief are attributed an upper Pliocene as

well as a Quaternary age.

A significant aspect of progressive and intermediate margins is the postion of the zone undergoing

subsidence, which in time has migrated progressively in a landward direction. These margin types

(the two are ascribed to the intermediate margin

defined by Mauffret et al., 1973) are distinguished

on the basis of sea-floor morphology and of the nature of the displaced configuration of the PlioceneQuaternary cover. These differences reflect distinct

structural and depositional origins of the two types

of margins. The intermediate type as defined in

the present study tends to occur in sectors where

two major tectonic trends converge, such as in the

region south of the Mallorca-Menorca shelf and

southwest of Ibiza and Formentera where NE-SW

and NW-SE fractures intersect (Mauffret et al.,

1972). Intermediate margins in the Alboran Sea

are also related to these same tectonic directions

(Olivet et al., 1972, 1973; Auzende et al., 1975).

The margin southwest of Sardinia is also of the

intermediate type and its origin may be related

to the interplay of the NE-SW ("fracture nordtunisienne") and the NW-SE ("zone de fracture

Bateares-Sardaigne, fracture d'Iglesiente") trends

defined by Auzende et al. (1974). In the Ligurian

Sea farther to the north, an abrupt type margin

parallels the dominant NE-SW trend along the

French and Italian Riviera (Fierro et al., 1973;

Rehault et al., 1974). Here, the presence of NWSE trends is recorded by the orientation of the

major submarine canyons. These NW-SE fracture

patterns are more pronounced on the opposite

margin of the Ligurian Sea in the northwest sector of Corsica; the merging of this and NE-SW

fault trends are associated with an intermediate

type margin (Mauffret et al., 1973, fig. 13; Rehault

et al., 1974, fig. 6). The majority of margins defined

as intermediate in type display a series of fractures along which vertical movement has occurred

during much of the Pliocene and the Quaternary.

The progressive margins tend to occur seaward

of basins on land filled with thick Tertiary sequences, and subsidence of continental blocks result from movement taking place along several

structural lines which may vary in orientation.

Seaward, the Upper Miocene salt pinches out at

the base of the slope; unlike the abrupt and intermediate margins, the M reflectors, which cannot be

traced from the basin upslope to the shelf, are replaced laterally by an erosional surface. These

progressive margin characteristics observed in our

study area also are noted in the Gulf of Lion

(Burollet and Byramjee, 1974) and in the Valencia

Trough (Mauffret and Sancho, 1970).

Evidence of accelerated subsidence during the

Pliocene is recorded by the configuration of the unconsolidated sedimentary cover; displacement resulted in a lowering of the sectors of the margin

progressively closer to the coast relative to the

more seaward position of the older Tertiary margin, which presently lies at greater depths and is

buried by a thick sediment cover (Mauffret et al.,

1973). The foundering phase in the Pliocene was

followed by somewhat more subdued subsidence

during the Quaternary, which resulted in the flexing (convex-up folding) of Pliocene and Quaternary

series and in the large-scale slumping of the sedimentary cover on the slopes. Post-Miocene displacement along preexisting structural trends has, in

some sectors, resulted in subdivision of margins

into individual blocks, some of which have moved

more rapidly than others (an example of this is

the Ampurdan sector of the Catalonian margin).

The origin of submarine canyons can be interpreted in light of these events. Some canyons were

cut during the Miocene, and the initial valley systems are related to the fluvial patterns and to the

structural configuration of the margins then in

existence; incision of the present canyon network

in the study area developed primarily during the

Pliocene and Quaternary. The importance of the

Pliocene erosion is particularly well displayed in

the seismic records collected along the middle and

lower sectors of submarine valleys. The effects of

Quaternary eustatic oscillations, which also have
NUMBER 20 59

played a significant role in canyon formation, are

recorded primarily in the heads and upper reaches

of canyons.

Pliocene-Quaternary foundering has been important as well as widespread, but the mechanisms

involved were varied, and the resulting structural

and depositional configuration is by no means uniform (Stanley, 1976). Thus, the geologically recent

movements in the western Mediterranean, related

to older Tertiary events, have fashioned a remarkably varied but predictable series of margin types.

Conclusions

Evaluation of the data presented here is, in our

view, only compatible with the concept that the

form and depth of the present-day western Mediterranean Basin result largely from accelerated foundering of this area since the upper Miocene

(i.e., the "revolution pliocene" of Bourcart, 1960b).

This in no way minimizes the importance of

Oligocene-Miocene or earlier movement, including

subsidence, although we find no evidence to support a hypothesis of a large, deep (> 2500 m)

Mediterranean basin at the end of Miocene time

as proposed by Hsu (1972), Cita (1973), Hsu et al.

(1973), and Ryan et al. (1973b), or of a very shallow

(< 500 m) basin as proposed by Nesteroff (1972,

1973). On the contrary, the data evaluated by us

suggest a western basin of bathyal depths, locally in

excess of 1000 m.

The post-upper Miocene displacement emphasized here does not imply only one major episode

of foundering, nor does it imply a uniformity in

style or scale. The movement along the margin of

the basin has occurred primarily along major structural trends, some of which are old (pre-Miocene),

and these earlier trends, subsequently reactivated

during the past five million years, are responsible

for the major outline of the modern western Mediterranean Basin. A particular structural style, as

illustrated in the previous sections, is determined

by the orientation of the principal fault trends

relative to land and the degree of interplay along

the major fractures. Almost certainly the vertical

relief of the modern Mediterranean Basin resulted

not from a single structural event but from alternating phases of gentle subsidence (associated with

the progressive margin type) and rapid foundering

(abrupt margin type) within any one regional sector.

The origin of the Mediterranean is frequently

discussed in terms of the formation of the Balearic

Basin plain. Records obtained with deep penetration seismic systems tend to reveal the plain as a

broad, flat surface extent, suggesting a structurally

quiescent environment, where deposition has prevailed and where the unconsolidated sediment

cover masks the underlying structure of the Miocene and older units. However, the more detailed

high-resolution surveys of the different margins

show that basin plain formation did not take place

in uniform fashion and is by no means complete.

The example of the Balearic Rise, the large subsiding continental block detached from the southern part of the Balearic Platform, is significant in

this respect.

It is probable that a similar mode of block foundering has occurred along other sectors of the basin

and that older blocks of this type are now buried

under the thick wedges of turbidite and hemipelagic muds and sands provided by the Rhone,

the Ebro, and by the myriad smaller fluvial systems

bounding the basin, which presently continue to

contribute a considerable volume of sediment (Stanley, 1976).

The large-scale block foundering of the Balearic

Rise cited above, coupled with observations based

on numerous deep penetration seismic profiles obtained across the Balearic Basin, indicate that the

sub-Pliocene sea floor of the plain collapsed and

subsided considerably during the Pliocene and

Quaternary. The displacement of the M reflectors

observed on the margin transects indicates a lowering by perhaps as much as 1500 to 2000 m of the

large blocks presently underlying the basin plain.

This amount of subsidence of the basin plain to

present depths (in excess of 2700 m) is compatible

with the findings of workers in various sectors of

the western Mediterranean (Heezen et al., 1971;

Finetti and Morelli, 1973; Storetvedt, 1973) and of

the most recent JOIDES deep-sea drilling leg 42A,

which suggest that basins possibly as shallow as

500 m, but more likely between 500 and 2500 m,

existed before the deposition of the Messinian

evaporites (Hsu, Montadert et al., 1975). An average rate of subsidence of less than 40 cm per 1000

years is suggested if the larger value of 2000 m of

vertical offset is selected, and if lowering of this
60 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES

amount is assumed to have occurred since the beginning of the Pliocene. Larger rates of displacement are recorded in the eastern Mediterranean

and other tectonically active ocean basins, as well

as in many sectors of the contiguous land bounding the western Mediterranean Basin.

We should be able to see some record of such

marked subsidence of the basin in geologically

recent time and in this respect the disposition of

marginal faults is significant. As emphasized earlier,

some faults paralleling the basin margin appear

younger in a landward direction, and this arrangement of fractures is similar to the fault patterns

in a rift zone. Our observations tend to support

the hypothesis of large-scale regional rifting, which

has been suggested for the origin of the modern

western Mediterranean (Bauer, 1974).

While we do not feel able to comment on the

possible mechanisms (oceanization, sea floor spreading, or other) that produced large-scale foundering,

we recognize that further detailing of continental

margins is essential for interpreting the geologically recent evolution of the western Mediterranean

Basin.

Summary

1. Relatively high-resolution, shallow penetration seismic surveys of the Catalonian, eastern

Betic, and Balearic margins in the western Mediterranean detail the regional distribution and configuration of the upper Miocene units and the

overlying, unconsolidated sedimentary sequences of

Pliocene and Quaternary age. These sedimentary

series, including the M reflectors (dated as Messinian) and lateral equivalents, have been displaced

by post-Miocene vertical movements in all sectors

examined.

2. Although large amounts of sediment, largely

of fluvial origin, have been introduced in this

quasienclosed sea during the Neogene and Quaternary, these deposits have not masked the marked

fault-controlled configuration of the basin margin.

Vertical displacement of Quaternary to Recent deposits reflects the geologically recent nature of margin subsidence.

3. The upper Miocene to Recent movements

have not been synchronous, and significant differences both in terms of structural style and scale

are recorded along the edges of the basin. Three

essentially different types of margin configuration

are defined: abrupt, intermediate (or steplike), and

progressive. There is a direct relation between

margin configuration and tectonic trends on land.

4. The present margin configuration results (1)

from pre-Messinian subsidence along preexisting

(Oligocene or earlier) structural trends and (2)

from geologically recent (post-Miocene) movement

along new as well as older structures.

5. Abrupt margins are characterized by continued vertical displacement within a relatively restricted structural zone; this type prevails in areas

where the margin parallels the major tectonic

trend on land (Emile Baudot and Mazzaron Escarpments are examples of this margin type).

6. Intermediate and progressive margins reflect

a displacement of the margin in time and space.

The former type is identified by subsidence in

which the sedimentary cover has been offset in a

steplike manner. The movements, which occurred

throughout much of the Pliocene and Quaternary,

are found in areas where two major structural

trends merge (the margins southeast of Cape San

Antonio and the Balearic Rise are examples; NESW and NW-SE fractures predominate).

7. Progressive margins are related to phases of

foundering during the Pliocene, followed by more

gentle subsidence occurring from the upper Pliocene to the present. This margin type, which displays a flexing of the Pliocene and Quaternary

cover, occurs seaward of Tertiary basins where

older (Hercynian to Miocene) tectonic trends have

been reactivated (the Catalonian margin and the

sector northeast of Cape San Antonio are examples).

8. It appears that a major phase of submarine

canyon cutting on the different margins examined

occurred in post-Miocene time. Canyon origin and

configuration are closely related to the structural,

paleogeographic, and sedimentary events that affected the western Mediterranean Basin during the

Pliocene and Quaternary.

9. The Balearic Rise south of the Balearic Platform is a large, detached continental block which

foundered in the post-Miocene and has not yet completely merged with the Balearic Basin plain. The

large continental blocks beyond the base of slopes

that are presently buried beneath thick sediment
NUMBER 20 61

sequences of the basin plain may have had an ment of the western Mediterranean Basin, and

origin similar to that of the Balearic Rise. there appears to be a similarity between the for10. Geologically recent foundering of large con- mation of the basin margins and the structural

tinental segments is directly related to the develop- evolution of rift zones.
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