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
ABSTRACT
Stanley, Daniel Jean, Henri Got, Neil H. Kenyon, Andre Monaco, and YehezkielWeiler. Catalonian, Eastern Betic, and Balearic Margins: Structural Types and
Geologically Recent Foundering of the Western Mediterranean Basin. Smith-sonian 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 overlyingunconsolidated sediment sequences. The structural configuration of the Pliocene
and Quaternary series observed on subbottom profiles indicates that the geolog-ically recent margins in these sectors have subsided along preexisting (Oligocene
or older) as well as more recent (post-Miocene) tectonic trends. The post-Miocenemovements 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 isestimated on the basis of seismic profiles presented here.
The abrupt margin type, exemplified by the Emile Baudot and Mazzaronescarpments, occurs in areas where the edge of the basin parallels the major
structures on land and where vertical displacement has developed in a rela-tively restricted structural zone. Intermediate margins, such as the sector south-
east of the Betic chain, are localized in areas where two major structural trendsconverge (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 toPliocene foundering followed by more gentle subsidence from the upper Plio-
cene to the present. This type of margin occurs seaward of Tertiary basinswhere 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 Quaternaryeustatic events.
The Balearic Rise, a large continental block detached from the southernpart 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 Basinplain. 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 structuralorigin analogous to that of the Rise. Margin formation and the evolution of the
western Mediterranean Basin bear some similarities to the structural develop-
ment of rift zones.
OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recordedin the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: Aerial view of Ulawun
Volcano, New Britain.
Library of Congress Cataloging in Publication DataMain 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. Se-ries: 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
in
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 penetra-
tion 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 oceaniza-
tion (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, Wash-
ington, 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 environ-
ment 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 Medi-
terranean as presently observed and the nature of
the sediments which fill it are related to geologi-
cally 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 pertain-
ing 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 investi-
gation has a somewhat different and more specific
purpose, i.e., to define selected margins bounding
1
SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
FRANCE
ALGERIA
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 physiog-
raphy in three regions: the Catalonian margin east
of the Pyrenees, the eastern Betic margin south-
east of Spain, and the Balearic Platform and its
contiguous margins (Figure 1). An attempt is made
to relate these margins to the structural frame-
work 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 evolu-
tion 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 higher-
resolution 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 inde-
pendently by the different authors who used
roughly comparable subbottom profiling methods.*
Although these areas are topographically and geo-
logically 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 Mediter-
ranean.
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 Scien-
tifique (CNRS), Institut fur Geophysik (University
of Kiel), Institute of Oceanographic Sciences
(Wormley, U. K.), Lamont-Doherty Geological
Observatory (Columbia University), Musee Ocean-
ographique de Monaco, National Geographic
Society (Research Committee), New York State
Maritime College, Smithsonian Research Founda-
tion, 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 Profes-
seur 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 per-
sons 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 Comman-
dant J. Alinat, Musee Oceanographique de
Monaco, who made special contributions to this
undertaking. We also shared pleasant and produc-
tive 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. Black-
man (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, In-
stitut 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 sugges-
tions 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 con-
sider his comments. The data interpretation and
conclusions presented here, however, reflect the
views of the authors.
Support for continued coordination of the Medi-
terranean 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 par-
ticipate 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 hydro-
phone 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 hydro-
phone and EG&G 254 recorder (speed of 6 knots, a total
of about 1500 km)
Other seismic data in this area have been pub-
lished 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 explora-
tory 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 air-
gun profiles from the R/V Conrad 9 (August 1965)
courtesy of W. B. F. Ryan (Lamont-Doherty Geo-
logical Observatory). These were complemented
by seismic data collected on cruises 27 and 28 of
the RRS Discovery (June-July 1969) of the Insti-
tute 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-ft-
long 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 geo-
logical long-range inclined ASDIC)
2. RRS Discovery cruise 35 (11 July to 19 August 1970),
where positioning was made by satellite and radar; seis-
mic 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 satel-
lite, Loran-C, and radar for positioning; 3.5 kHz and 12
kHz transducers used for bathymetric profiling (G. Kell-
ing, A. Maldonado, and D. J. Stanley, in preparation),
and 30,000 J Teledyne Sparker with Precision Electro-
graphic Recorder (Raytheon) used for subbottom pro-
filing 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 addi-
tional 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 corre-
lation of seismic profiles with those that traversed
JOIDES 13 site 124 (Ryan et al., 1973a) immedi-
ately 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 reflec-
tors); 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 (Ga-
varres 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 Port-
Vendres 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 ter-
rains, illustrated in Figure 2, are described below
(from north to south):
1. The Roussillon coastal plain, a low-lying sedi-
mentary 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 Pyre-
nees includes primarily metamorphic units, includ-
ing 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 Cata-
lonian 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 meta-
morphic (largely schist) sequences. This topo-
graphic 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 configura-
tion is discussed in subsequent sections.
PHYSIOGRAPHY
The physiographic configuration of the Cata-
lonian continental shelf (Figure 3) is directly re-
lated 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 re-
lief 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 con-
siderably 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 progres-
sively 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 de-
gree 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#
ROUSSILLONwm
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 work-
ers. 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. Cross-
valley profiles are V-shaped and the configuration
is typical of classic canyons described by Shepard
and Dill (1966). Steplike terraces and other topo-
graphic 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 well-
defined 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 recov-
ered 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 south-
eastern 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 con-
tinuous 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.?Al-
though the subbottom penetration by various
seismic systems used has been relatively low (500
m), units of probable pre-Pliocene age are occa-
sionally 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 Cata-
lonian 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 base-
ment. 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 adja-
cent 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 relia-
bility 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 hemi-
pelagic 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 sur-
face. 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 correla-
tion 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-WU.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 under-
lain 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 reflec-
tors truncated at the top by a near-horizontal
erosional surface, Reflector G (Figure 7A), to hori-
zontal, 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.?Quater-
nary 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 Reflec-
tor G consists of a succession of conformable reflec-
tors 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 seis-
mic 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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10 km
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 con-
formable reflectors of low amplitude (a5) dated
by carbon 14 as upper Wiirm to postglacial. On
the midsector of the shelf, the preceding Quater-
nary sequence is covered by a discontinuous trans-
parent layer (ae) of Holocene (Flandrian) age
(Figure 7B). These surficial muds thin on the con-
tinental slope.
STRUCTURAL CONFIGURATION
GENERAL.?Deep drilling and mapping on land
show that the underlying structure of the Ampur-
dan 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 depres-
sions is irregular, i.e., apparently displayed by a
series of normal faults as a result of vertical tec-
tonics (Figure 8). The basement rises gently north-
ward toward Cape Leucate and southward toward
the Gavarres Massif. A seismic profile (9000 J
Sparker) trending parallel to the coast demon-
strates this structural displacement (Figure 6A).
DEFORMATION OF THE PALEOZOIC BASEMENT.?
The seismic surveys on the shelf reveal the irregu-
larities 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 off-
shore 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 reflec-
tors and the apparent bending (or flexuring) of
these reflectors away from the coast (Figure 9).
This phenomenon, referred to as the "flexure con-
tinentale" by Bourcart (1950, 1960b), has been
attributed to subsidence of the Basin plain base-
ment with accompanying depression (and seaward
depositional progradation) of the overlying sedi-
mentary series. Regional mapping of the Reflector
G (Pliocene-Quaternary boundary) (Figure 10)
shows that this surface is cut by the three pre-
viously described submarine valleys (Lacaze-
Duthiers, 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 partic-
ularly 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 base-
ment 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 Puerto-
de-la-Selva, La Escala, Estartit, and Palamos. This
observation suggests that the major movements are
Pliocene in age and occurred along older (pre-
Tertiary) 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
u
">?CAPE BEAR
i
CAPc
rV
E CREUS,
L ?">
-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. How-
ever, the central margin off Ampurdan, displaying
the greatest differential downwarping, is apparent.
The major change observed is the lateral displace-
ment seaward of the "zone de flexure" that
occurred during the time between the G and J
reflectors; the process involved in the downwarp-
ing 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 (Reflec-
tor 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 Quater-
nary horizons (Figure 12) shows that structural
modification continued during the Late Quater-
nary and Holocene. Deposition accompanied sub-
sidence 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 Quater-
nary, 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 Pleistocene-
Holocene time. It appears that the vertical dis-
placement 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 equip-
ment used (9000 Joules sparker), however, pro-
vides 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 Neo-
gene and Quaternary.
The region extending seaward of the Ampurdan
coastal plain (margin displaying a convex-up pro-
file) 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-strati-
fied 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 seaward-
tilted Pliocene and Quaternary reflectors related to subsidence ("flexure continentale")
mechanism.
(Figure 14c). Growth faults affect the upper Plio-
cene 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 Quater-
nary horizons above the more cohesive underlying
sequences on slopes of 5 degrees. These displace-
ments of Pliocene and Quaternary units are con-
centrated 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 dis-
placement 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 sea-
floor has been described by Glangeaud et al. (1968)
as "phe'nomenes pelliculaires et e'pidermiques."
Comparable features are observed in the Catalo-
nian canyons (Got and Stanley, 1974, fig. 4).
BASE-OF-SLOPE STRUCTURES.?The marked thick-
ening of the Quaternary section in the base-of-slope
environment results, in part, from the accumula-
tion 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 inde-
pendent of the structural configuration of the
underlying (M or K) reflector. This particular type
of structure is interpreted as follows: the pre-
Pliocene 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 (Pliocene-
Quaternary 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 environ-
ment between the Catalonian margin and the
Balearic Basin plain south of the Gulf of Lion.
BALEARIC BASIN PLAIN STRUCTURES.?The struc-
ture 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 inter-
vals: 1, landward limit of sediment at about 27,000 years
before present (B.P.); 2, isopach of the sediments dated be-
tween 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. Particu-
larly visible are faults that displace the Quaternary
reflectors and which thus modify the surface topog-
raphy (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 appar-
ent 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 deep-
penetration 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 distri-
bution 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 contempo-
raneous subsidence of the margin during sedimen-
tation (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 sedi-
ment 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 environ-
ment 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 sub-
marine canyons of the western Mediterranean,
particularly those incised on the northern margin
of the Balearic Basin, have been intensively sur-
veyed (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 investi-
gations consider both the tectonic origin of can-
yons 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 configura-
tion 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. Never-
theless, 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 oc-
curred in Pliocene or Quaternary time as demon-
strated 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 deforma-
tion 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 (includ-
ing 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 uncon-
formity 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 con-
cerned with the evolution of the western Mediter-
ranean Basin, including Bourcart et al. (1961) and
others, in recent years have suggested that an ex-
tremely 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 subse-
quently have been filled with Pliocene and Quater-
nary 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 Lacaze-
Duthiers 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 Quater-
nary. 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 later-
ally in continuous fashion onto the shelf and adjac-
ent 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 Mediter-
ranean 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
I200 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 tec-
tonic tilting have resulted in the progressive sub-
sidence 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 con-
tinued, 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 mar-
gin, are oriented perpendicular to the major N?S
faults.
5. The relief between the valley axes and adja-
cent intervalley highs became accentuated during
submergence as a result of enhanced deposition in
the intervalley sectors; this buildup of the inter-
valley 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 tectonic-
paleogeographic canyon evolution is not applicable
to all sectors of the northwestern Mediterranean
margin. There is evidence, for instance, of pre-
Pliocene erosion on the Provencal margin to the
northeast, and in the sector south of the Cata-
lonian margin. In this latter region, late Miocene
erosion appears to have occurred primarily on
structural highs, and the best evidence of pre-
Pliocene 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 Plio-
cene; (3) the Pyrenean high formed by the Paleo-
zoic 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 Plio-
cene 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 mid-
Ampurdan 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 asso-
ciated 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 growth-
faults and associated slump movements; the import-
ance of these phenomena has diminished somewhat
during the Quaternary.
The continued deposition of terrigenous sedi-
ments 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 repre-
sents one type of margin associated with conti-
nental 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 geolog-
ical entity as demonstrated by the overall strati-
graphic 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), Bour-
rouilh and Colom (1967), Cuerda et al. (1969),
Rangheard (1969, 1970), Colom et al. (1970),
Obrador (1970), Obrador et al. (1971), and Bour-
rouilh (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 Nevado-
Filabrides, Alpujarides, and Malaguides) and
Mesozoic units; (2) the "allochthonous" series
emplaced during the Neogene (including the sub-
Betic and pre-Betic zones); and (3) the "post-tec-
tonic" 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 import-
ant Murcia fault mapped by Bousquet and Mon-
tenat (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 oc-
curred 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 move-
ment may have contributed to the dislocation of
the Balearic Platform into separate blocks. Import-
ant vertical displacements of Miocene age are rec-
ognized 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 dis-
placement 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 rota-
tional movements associated with the origin of the
western Mediterranean Basin) and NE-SW. This
latter trend is interpreted as a more recent (Mio-
cene to Quaternary) pattern related to major move-
ments 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 post-
Miocene, 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 sub-
marine 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 sea-
floor 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 (peri-
dotite 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 cer-
tainty 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 attrib-
uted 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 trans-
parent 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 Pliocene-
Quaternary boundary observed on the shelf where
it probably is represented by an unconformity, as
in the Catalonian region (cf., Figure 7A). The thick-
ness of the Pliocene-Quaternary unit varies con-
siderably. 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 An-
tonio, 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 stra-
tigraphy 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, nonde-
formed, 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 lay-
ered (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-hori-
zontal 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 reflectors-
Pliocene-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). Defor-
mation 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 ob-
served.
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 south-
west 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. Partic-
ularly noteworthy are the well-stratified (mostly
Quaternary) units that are truncated at the escarp-
ment, indicating a post-Pliocene vertical displace-
ment. 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 mod-
erately stratified sequence of probable Miocene
age, is in turn capped by the M reflectors (Messin-
ian) 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 sedi-
ment trap.
The regional variation of the Pliocene-Quater-
nary thickness in most instances reflects displace-
ment 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 tec-
tonically 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 affect-
ing 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 shelf-
slope 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 discon-
tinuous 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 discon-
tinuity 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, includ-
ing 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 Formentera-
Ibiza 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 trun-
cated 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 south-
west. 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 down-
slope 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 com-
prising 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 western-
most sector of this margin is cut by three large
submarine canyons trending NW-SE off the Span-
ish 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 escarp-
ments 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, some-
times 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 dis-
placement 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 re-
flectors sequence (Ryan et al., 1973a). The thick-
ness 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 present-
day topography. In some locations, it crops out at
the sea floor due to absence of the overlying se-
quences 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 Plio-
cene 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. Note-
worthy is the tongue of sediment in the lower sec-
tion 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 pene-
trating 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 re-
covered 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 Pleisto-
cene 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 illus-
trate 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) be-
tween 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), dis-
plays an irregular topography and a much reduced
Pliocene-Quaternary cover (about 100 to 250 ms,
or 100 to 250 m). Thicknesses are reduced on topo-
graphic highs; these highs commonly denote the
presence of the acoustic basement, which locally
has pierced the M reflectors and underlying se-
quences (Figure 25E). A number of faults are ob-
served, 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 se-
quences. 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 Plio-
cene and Quaternary sequences is even more re-
duced on the Ibiza-Formentera shelf (< 100 m).
A broad depression characterized by more sub-
dued 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 al-
most 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 respec-
tively (Figure 25B, C), to the northwest by the
NE-SW basement high, and to the southeast by
the Isla Cabrera Ridge (Figure 25G). A south-
trending 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 Plio-
cene and Quaternary sequence is attenuated on the
shallow Mallorca shelf. One transect, west of the
island and south of Palma de Mallorca, shows prob-
able 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 BA-
LEARIC BLOCK.?The limited number of subbottom
traverses northwest and north of the Balearic Plat-
form, 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 thick-
ness 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 dis-
turbed by a series of small step faults in the upper-
most 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 topog-
raphy 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 be-
comes much steeper (> 10?), locally forming es-
carpments (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 sedi-
mentary 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 re-
sults from the meeting of two steep margins: the
NNW-SSE slope parallel to the crest of the Men-
orca 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 Quater-
nary 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 com-
bined 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 For-
mentera is bounded by the prominent southwest-
trending Emile Baudot Escarpment. The
escarpment is limited to the east by the Menorca
Valley (Figure 27A) and its slope (5? to 10?) is to-
ward the southeast (Figure 27B-E). At its eastern
end, the base of the escarpment merges with the
Balearic Rise. In this sector the escarpment pre-
sents 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 Pliocene-
Quaternary units encountered on the upper
Balearic Rise thin out at the base of the escarp-
ment. Nevertheless, these sequences appear locally
on the slope proper, where they are tilted.
The escarpment is steepest and has greatest re-
lief 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 Algero-
Balearic Basin plain and the Balearic Platform.
The acoustic basement locally pierces the overly-
ing units on the slope, and even the uppermost
Quaternary sequences have been offset by faults.
Some faults can be traced laterally, as demon-
strated by an analysis of two parallel profiles 80
km apart (Figure 27H,I). The Emile Baudot Es-
carpment, 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 progres-
sively 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 Bau-
dot Escarpment and Menorca Ridge is subdivided
into several tectonic zones on the basis of the
dense network of sparker and air-gun profiles avail-
able in this region. By far the largest zone is the
one broken into a series of large (^10 km wide)
horsts and grabens. The offset sedimentary se-
quence 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 par-
ticularly 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'ro-
Balearic 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 pre-
dominant 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") un-
derlying the M reflectors has not been contoured
due to the structural complexities (Figure 31). Pro-
files 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 Es-
carpment. 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, how-
ever, 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 net-
work of faults. Vertical displacements have affected
the upper unconsolidated sedimentary sequences
as well as underlying basement, indicating the post-
Miocene to late Quaternary origin of these features.
The highly irregular topography of the Rise at-
tests 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 negligi-
ble 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 re-
flectors appear offset, suggesting that the head of
canyon was cut along a fault. This is not un-
expected 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 shallow-
est profiles made just south of the Menorca Shelf,
the V-shaped canyon cuts into the Pliocene-
Quaternary 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 reflec-
tors 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 Algdro-
Balearic 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 Men-
orca 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 sedimentologi-
cally 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
WTN
^. ? . FV "'/T :7V-\i ,i .-.*[.. "r-?]'. & >
ETN
sw
JOIDESXIII
Site 124
f Balearic plo;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 over-
lying 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 environ-
ments (Kelling, Maldonado and Stanley, in prep-
aration).
DISCUSSION
The seismic survey demonstrated that the present
physiography of the Balearic Platform and ad-
jacent 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 dis-
placements 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 inter-
bedded 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 ob-
served at a depth of about 500 m. It probably oc-
curs 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 neces-
sarily 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 de-
veloped 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 con-
siderably on the shallow island shelves and ad-
jacent 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 se-
quences 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
SCALE
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 physiographi-
cally 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 configu-
ration 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 con-
figuration. T,his margin is deformed by large-scale
faulting, which has resulted in the vertical dis-
placement 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 configura-
tion 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 south-
west 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) near-
horizontal basin plain strata abut directly against
the steep escarpment base, and (b) there is an ab-
sence of allochthonous slump masses at the base of
the slope. These observations indicate that the
escarpments have not been covered by a Pliocene-
Quaternary sediment cover of a thickness com-
parable 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 hemi-
pelagic cover, indicates a geologically recent forma-
tion of this type of margin.
4. The series of parallel transects across the
Emile Baudot Escarpment and its western exten-
sion 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 Bau-
dot structure westward as an important subsurface
fault (see a', Figure 27i). Moreover, faults that are
poorly denned topographically southeast of Ibiza-
Formentera form pronounced escarpments south
of Formentera (see b, Figure 27i). These observa-
tions 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 intermedi-
ate 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 for-
mer 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 par-
ticular 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 Cata-
lonian, Betic, and Bealearic margins reveals some
rather significant points common to the three areas,
particularly with regard to the nature and distri-
bution of the uppermost Miocene to Recent sedi-
ment 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 col-
lected 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 re-
gional extent. This is of considerable impor-
tance 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 Mio-
cene salt can be traced across much of the Balearic
Basin plain (Hsu, Cita and Ryan, 1973, fig. 3; Biju-
Duval, 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 Valen-
cia Trough (Mauffret et al., 1973, fig. 1), the
Alboran Sea (Auzende et al., 1975), the Sardinian
margin (Auzende et al., 1972a, 1974) and the Li-
gurian 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 Plat-
form and southeastern Spanish margin. Further-
more, the M reflectors probably are continuous
between the Catalonian margin and the Balearic
region some 260 km to the south (cf., profiles ex-
tending across the Valencia Trough illustrated in
Leenhardt et al., 1970, and in Mauffret and
Sancho, 1970).
The M reflectors are traced with some reliabil-
ity 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 unconform-
able surface interpreted as a Pontian (^ Messinian)
erosional horizon by Bourcart (1963) and Glan-
geaud 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 indica-
tive 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 Pro-
vencal 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 shal-
low 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 acousti-
cally stratified (Quaternary) unit is noted both on
slopes and in the basin. The acoustically trans-
parent 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 char-
acter 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 acous-
tic 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 sur-
face (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 mea-
sured 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. Ex-
amples 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 Plat-
form (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 mainte-
nance of such platforms below sea level even dur-
ing 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 west-
ern 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 sedi-
mentary basement of continental origin, discontin-
uous 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 en-
visioned above. A detailed evaluation of the post-
salt 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 Plio-
cene 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 Plio-
cene 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 step-
like 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 verti-
cal 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 fre-
quently 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 Ibiza-
Formentera 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 re-
duced 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 inter-
relation 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 Betic-
Balearic 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-Ibiza-
Mallorca margins north of the Balearic Platform)
and a succession of intermediate to abrupt margins
in the regions east and south of Menorca and ex-
tending 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 Plat-
form, which has a steep gradient on the Emile
Baudot Escarpment. All canyons examined in de-
tail reveal complex tectonic as well as sedimentary
origins, i.e., they follow fault trends, and their
subsequent development is largely structurally con-
trolled, 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 mar-
gins 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 post-
Miocene 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 re-
spect 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 ob-
servations:
1. The M reflectors and their lateral equivalents
(including erosional surfaces), dated as uppermost
Miocene, have a wide-ranging distribution and oc-
cur at highly variable depths in different physio-
graphic 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 Men-
orca, 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 irregu-
lar and obviously displaced configuration on most
margins. One example is the lower Pliocene se-
quence 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 post-
depositional vertical displacement of large ampli-
tudes 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 equiva-
lents, when placed in their original configuration,
outline a late Miocene bathymetry unlike that sug-
gested 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 Pliocene-
Quaternary phases of canyon cutting are well de-
veloped between the upper continental shelf and
the base of slope. Progressive margins do not pro-
vide evidence of pre-Pliocene canyon incision; the
first major phase of canyon incision is dated as
Pliocene.
5. The presence of Pliocene and Quaternary vol-
canism in Catalonia and on the Balearic Rise(?),
including domes which have penetrated thick se-
quences 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 reduc-
tion of sediment cover and are bounded sharply
at their base by the horizontal basin plain Pliocene-
Quaternary sequences; these escarpments probably
record the most recent major vertical movements.
The lack of slump wedges at the base of the es-
carpments provides further evidence of the youth-
ful 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 Quater-
nary 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 mar-
gin. 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 geo-
logically recent vertical displacement of the Bale-
aric Rise, a large continental block dislocated from
the Balearic Platform. Its recent age is demon-
strated 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 dur-
ing 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 rela-
tive displacement of the African and European
plates in the Miocene (Mauffret et al., 1972; Au-
zende 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 im-
portance 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 Maz-
zaron 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 mar-
gins. 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 interme-
diate margins is the postion of the zone undergoing
subsidence, which in time has migrated progres-
sively 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 na-
ture of the displaced configuration of the Pliocene-
Quaternary 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 nord-
tunisienne") 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 NW-
SE 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 sec-
tor 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 frac-
tures 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 se-
quences, and subsidence of continental blocks re-
sult 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 inter-
mediate margins, the M reflectors, which cannot be
traced from the basin upslope to the shelf, are re-
placed 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 un-
consolidated sedimentary cover; displacement re-
sulted in a lowering of the sectors of the margin
progressively closer to the coast relative to the
more seaward position of the older Tertiary mar-
gin, 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 flex-
ing (convex-up folding) of Pliocene and Quaternary
series and in the large-scale slumping of the sedi-
mentary cover on the slopes. Post-Miocene displace-
ment 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 inter-
preted in light of these events. Some canyons were
cut during the Miocene, and the initial valley sys-
tems 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 impor-
tant as well as widespread, but the mechanisms
involved were varied, and the resulting structural
and depositional configuration is by no means uni-
form (Stanley, 1976). Thus, the geologically recent
movements in the western Mediterranean, related
to older Tertiary events, have fashioned a remark-
ably 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 Mediter-
ranean Basin result largely from accelerated foun-
dering 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 sup-
port 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 empha-
sized 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 struc-
tural 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 Med-
iterranean 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 alter-
nating phases of gentle subsidence (associated with
the progressive margin type) and rapid foundering
(abrupt margin type) within any one regional sec-
tor.
The origin of the Mediterranean is frequently
discussed in terms of the formation of the Balearic
Basin plain. Records obtained with deep penetra-
tion seismic systems tend to reveal the plain as a
broad, flat surface extent, suggesting a structurally
quiescent environment, where deposition has pre-
vailed and where the unconsolidated sediment
cover masks the underlying structure of the Mio-
cene 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 sub-
siding continental block detached from the south-
ern part of the Balearic Platform, is significant in
this respect.
It is probable that a similar mode of block foun-
dering 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 hemi-
pelagic 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 (Stan-
ley, 1976).
The large-scale block foundering of the Balearic
Rise cited above, coupled with observations based
on numerous deep penetration seismic profiles ob-
tained 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 lower-
ing 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 aver-
age 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 be-
ginning of the Pliocene. Larger rates of displace-
ment are recorded in the eastern Mediterranean
and other tectonically active ocean basins, as well
as in many sectors of the contiguous land bound-
ing 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 arrange-
ment 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 spread-
ing, or other) that produced large-scale foundering,
we recognize that further detailing of continental
margins is essential for interpreting the geologi-
cally recent evolution of the western Mediterranean
Basin.
Summary
1. Relatively high-resolution, shallow penetra-
tion seismic surveys of the Catalonian, eastern
Betic, and Balearic margins in the western Med-
iterranean detail the regional distribution and con-
figuration 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 Mes-
sinian) 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 Quater-
nary, these deposits have not masked the marked
fault-controlled configuration of the basin margin.
Vertical displacement of Quaternary to Recent de-
posits reflects the geologically recent nature of mar-
gin subsidence.
3. The upper Miocene to Recent movements
have not been synchronous, and significant differ-
ences 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 contin-
ued vertical displacement within a relatively re-
stricted structural zone; this type prevails in areas
where the margin parallels the major tectonic
trend on land (Emile Baudot and Mazzaron Escarp-
ments 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; NE-
SW 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 Plio-
cene to the present. This margin type, which dis-
plays 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 ex-
amples).
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 af-
fected the western Mediterranean Basin during the
Pliocene and Quaternary.
9. The Balearic Rise south of the Balearic Plat-
form is a large, detached continental block which
foundered in the post-Miocene and has not yet com-
pletely 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 for-
10. 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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