Mud Volcanoes and Dome-Like Structures at the
Eastern Mediterranean Ridge
G. ÇİFÇİ 1, A. LIMONOV 2, L. DIMITROV 3 and V. GAINANOV 2
1
Dokuz Eylül University, Eng. Faculty, Dept. of Geophysics, 35100 Bornova-İzmir, Turkey
Moscow State University, Faculty of Geology, Russian Federation
3
Institute of Oceanography, Bulgarian Academy of Sciences, 9000 Varna, Bulgaria
2
(Received 8 April 1997; accepted 19 November 1997)
Key words: Mediterranean ridge, United Nation rise, mud diapirs,
mud volcanoes, dome-like structures
Abstract. The Mediterranean Ridge is interpreted as a large accretionary complex, which originated due to the northern subduction
of the African lithosphere below the Eurasian one and the partial
collision of those two continents; more precisely, between the
African and Aegean Microplates. The main goals of the UNESCOTTR 5 (Training Through Research) cruise, carried out by several
methods including high resolution seismic profiling, included the
investigations of mud volcanoes, the distribution of the Messinian
evaporites, and mapping the seafloor structures. The high resolution
seismic data were confirmed with other geoacoustic methods as
sidescan sonars (short-ORETECH and long-range OKEAN) and
subbottom sampling. The area of investigation is designed to run
parallel to the Mediterranean Ridge on the eastern end towards the
Florence Rise, and is situated between the northern and southern
deformation fronts of the ridge.
The seismic data were preprocessed onboard (band pass filtering,
horizontal stack and attenuation level) and predictive deconvolution. New mud volcanoes and structures were discovered at the
western part of the target area, named ‘United Nations (UN) Rise’
to celebrate the fiftieth anniversary of the United Nations. With
respect to fluid expulsion, three mud volcanoes were imaged, all of
which show different backscattering characteristics. The investigated
area shows complex structures and the UN area within the inner
deformation front of the Mediterranean Ridge, is much more complicated. Some features are similar to mud volcanoes, but with some
important differences. The typical characteristics of these features
are a positive (up-doming) structure on the seafloor relief, no
acoustically transparent zone, a strong low-frequency reflector
(M-reflector?) down-bent near this object and some of these features
are symmetrical. The Mud volcanism can exhibit itself only where
the evaporitic layer is thin or absent. The mud volcanism on the
Mediterranean Ridge reflects the general tectonic evolution of the
accretionary complex presently progressing.
1. Introduction
Main objectives of the UNESCO scientific and educational program (TREDMAR) later called TrainingMarine Geophysical Researches 19: 421–438, 1997.
Ó 1997 Kluwer Academic Publishers. Printed in the Netherlands.
Through-Research (TTR-5) 1995 cruise, in the eastern
Mediterranean were to investigate the characteristics of
mud volcanoes with high resolution seismic profiling,
the distribution of the Messinian evaporites, and to map
the salient seafloor structures at the eastern part of the
Mediterranean Ridge. It is important to define the Messinian evaporite distribution in the area, because this
layer of plastic evaporites strongly influences the distribution of mud volcanoes and in many respects determines the tectonic style and the seafloor morphology on
the Mediterranean Ridge. The high-resolution seismic
data were combined with long-range sidescan sonar
(OKEAN) and deep-tow high resolution sidescan
sonar/subbottom profiling data. Features which looked
interesting on the long range OKEAN data, were subsequently checked with high-resolution sidescan sonar/
subbotom profiler deep-tow system (ORETECH),
sampled with gravity corer and observed with TV grab.
The seismic lines shot in the target area during the fifth
TTR cruise extend from 150 km southeast of Crete to
50 km south of the Anaximander Mountains (Figure 1).
The area of investigation runs parallel to the Mediterranean Ridge, between its northern and southern deformation fronts, which are related to a set of N and S
verging thrusts. Water depths in the study area vary from
about 1800 to 3000 m.
Two air guns with volumes of 1.5 and 2.1 liters,
respectively were used for high-resolution profiling at
a depth of between 4 and 7 m and were towed at a
distance of 25 m from the stern. Shot was every 10 sec.
The streamer has 2 receiving sections, each having 50 m
active sections with 6 channels. Streamer offsets were
changed for different profiles due to variable noise
level of the seismic data. The data were preprocessed
onboard (band pass filtering: 30–150 Hz, horizontal
stack and attenuation level). Predictive deconvolution
was successfully applied on some of the seismic sections.
422
g. çi̇fçi̇ et al.
Fig. 1. Schematic map showing the study area in the general position of the Mediterranean Ridge and mud volcano areas in the Eastern
Mediterranean. The Mediterranean Ridge mud volcano belt is hatched. 1. Cobblestone-3 area; 2. Pan di Zucchero area; 3. Prometheus 2
area; 4. Olimpi area; 5. The United Nation Rise. Lines with solid and open triangles indicate the outer and inner deformation fronts of the
Ridge, respectively. M.A.P.>Messina Abyssal Plain; S.A.P.>Syrte Abyssal Plain; H.A.P.>Herodotus Abyssal Plain; P.T.>Pliny Trench;
S.T.>Strabo Trench; A.M.>Anaximander Mountains; F.R.>Florance Rise (Compiled by M. K. Ivanov, J. P. Foucher and A. F. Limonov,
UNESCO, 1996).
2. Geological Setting of the Mediterranean Ridge
The Mediterranean Ridge is interpreted as a large accretionary complex, which originated due to the northern subduction of the African lithosphere below the
Eurasian one and partial collision of those two continents, more precisely between the African and the
Aegean Microplate. The Mediterranean Ridge is undergoing a very strong compressional deformation,
and its structure is dominated by thrusts reverse faults
and strike-slipe faults with numerous compressional
folds. The edges of some thrust sheets are seen on
sidescan sonar sonographs as curvilinear escarpments
(Kenyon et al., 1982; Limonov et al., 1995). Judging
from the age and composition of the rock fragments
found in the mud breccia from mud volcanoes in western and central parts of the Mediterranean Ridge
(Cobblestone 3 and Olimpi areas), it is made up of a
wide variety of lithological rock types, ranging in the
age at least from the Middle Cretaceous to Holocene
(Limonov and Ivanov, 1996).
The average depth of the Mediterranean Ridge is
about 2100–2200 m, varying between 1200 m and more
than 3000 m. Its topography is characterized by small
closely spaced depressions and ridges (with a relief
50–100 m and a wavelength of 0.5–2 km) oriented
mostly parallel to the general trend of the ridge. Such
a pattern produces a ‘hummocky’ hyperbolic acoustic
reflection configuration. This special character of the
Mediterranean Ridge relates to the presence of Messinian evaporites at a shallow (100–400 m) depth below
the seafloor; they strongly influence the interstitial fluid
migration, pore water composition, and the pattern of
structural deformation of the ridge (Cita and Camerlenghi, 1990). The relationship between the development of the Mediterranean Ridge mud volcanoes and
the tectonic structure needs to be defined.
The presence of mud volcanoes in different areas
on the Mediterranean Ridge accretionary complex was
initially documented by Italian expeditions. Four mud
diapir and mud volcano areas have been documented
before the TTR-3 cruise: the Cobblestone (or Prome-
mud volcanoes and dome-like structures at the eastern mediterranean ridge
theus), the Pan di Zucchero, the Prometheus 2 and the
Olimpi areas (Figure 1). All of them are located in the
crestal zone of the Mediterranean Ridge (Camerlenghi
et al., 1992). The Olimpi and Prometheus 2 areas constitute a single zone. It is suggested that other known
areas (Cobblestone and Pan di Zucchero areas) belong
to the same zone which is referred to as ‘The Mediterranean Mud Diapiric Belt’. The phenomenon of the mud
volcanism is rather the rule than exception for the
Mediterranean Ridge accretionary complex as for
other similar tectonic features such as the Nankai
Trough accretionary prism (Taira et al., 1992) or the
Barbados accretionary complex (Le Pichon et al.,
1990). The dimensions of the mud volcanoes and the
depth of their roots seem to increase generally southward, from the inner deformation front to the Mediterranean Ridge crest. Two contrasting mud dome
structures in the Olimpi mud diapir field have been
drilled to test two hypotheses:
1. whether they formed as mud diapirs (i.e. intrusion),
or
2. as mud volcanoes (i.e. extrusion).
Some new seismic data and the results of scientific
drilling has supported the hypothesis of an eruptive
origin of the mud volcano deposits, although the
source of the mud is still debatable (Kopf et al., 1996).
The easternmost portion of the Mediterranean
Ridge has been crossed by some single- and multichannel seismic reflection profiles (Finetti and Morelli,
1973; Morelli, 1975; Ross and Uchipi, 1977; Woodside
and Williams, 1977) and by a few deep seismic refraction profiles (Lort, 1973; Malovitsky et al., 1975),
French PRISMED Program (Mascle et al., 1994;
Chaumillon and Mascle, 1995) and GLORIA mosaic
compiled by Kenyon et al. (1982). However, the eastern
part of the Mediterranean Ridge has been poorly investigated.
The tectonic transpression is partially accommodated by a strike-slip motion. Many linear topographic
features could be related to compressional deformations with a left lateral strike-slip sense. The deep structure of the ridge in the study area remains almost
unknown. Deep seismic profiles normally show a sharp
transition from the stratified, slightly disturbed seismic
sequences on the Herodotus Abyssal Plain to the
highly-deformed sedimentary cover on the ridge at the
western part of the study area, provisionally distinguished the A and B reflectors (at the top and bottom
of the Messinian evaporites, respectively). Malovitsky
et al. (1975) had determined the sedimentary sequence
from Paleozoic platform formations through Mesozoic
to Quaternary sediments, with a thickness of about
15 km. However, the oldest fragments of rock clasts
423
so far found among the mud breccia from mud volcanoes are no older than mid-Cretaceous (Limonov and
Ivanov, 1996).
3. Interpretation of the Seismic Profiles Across the
Eastern Mediterranean Ridge
Fifteen lines (PS-154 to PS-168) of high resolution
seismic survey were carried out along the Mediterranean Ridge from the Olimpi Area in the west to the
Florence Rise in the east (Figure 2). Most of lines
were concentrated in the southwestern part of the area
where some new mud volcanoes were discovered for
detailed observations. PS-157 follows the axis of the
Mediterranean Ridge and shows a wide area of cobblestone structures. PS-159 and PS-160 are situated
north of PS-157 along the Strabo Trench which is a
major sinistral strike slip fault subparallel to the
Hellenic Trench and the Mediterranean Ridge. The
zone between the two main profiles (PS-157 and
PS-159–160), is most probably the ‘backstop’ of the
accretionary complex of the Hellenic subduction zone.
PS-158 represents the eastern border of the area and
links the profiles PS-157 and PS-159.
PS-155 profile line connects the Olimpi mud volcano
field to the main investigated area of this study. The
line crosses the Napoli dome (Figure 3), which is the
most prominent tectonic feature. We expected to obtain a typical seismic image of a mud volcano that
could serve for calibration of similar features observed
on the other seismic sections. The relief along the line
is rather smooth, and the mud volcano is seen as a
large dome with a symmetric cross-section, surrounded
by a round zone of depression. The body of the mud
volcano is characterized by an acoustically transparent
seismic reflection pattern, and the seismic reflectors
nearby the feeder channel bend down beneath the mud
volcano. The characteristic M-reflector, interpreted as
the top of the Messinian evaporites which is very pronounced away from the mud volcanoes (Figure 4), is
absent around the Napoli dome for an area and more
than 10 km across. The presence of Messinian layers
at a distance from the mud volcano seems to be related
to faults. At the very end of the profile, the Messinian
probably pinches out again. The average thickness of
the evaporites can be estimated to be around
100–150 ms, although the bottom is not clearly detected, due to multiple diffractions.
The regional seismic line PS-156, is oriented from
E–SE to W–NW and cuts across the northern part of
the UN Rise area which is called this site as a discrete
area of mud volcanism and to call this ‘United Nation
Fig. 2. Location of the Seismic profiles (PS-156–157, 160–162, 168), OKEAN lines in the study area. Also sampling sites are shown outside the United Nation Rise. Bathymetry after
IOC-UNESCO (1981).
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g. çi̇fçi̇ et al.
mud volcanoes and dome-like structures at the eastern mediterranean ridge
425
Fig. 3. Seismic Test Profile across the Napoli mud volcano from Olimpi mud volcano field to the investigation area. The shape of the dome
and body of the mud volcano is generally symmetrical, although there is no symmetry in the surrounding structures – the sediments are very
much deformed by faults and folds.
Rise’ in celebration of the fiftieth anniversary of
this organization in 1995. A V-shaped valley 1.7 km
wide is observed as well as on the PS-161 line. Its
northern wall marks as a high backscattering line,
parallel to the seismic line on its ORETECH records
(Figure 4).
The section of profile 156 crossing the northern part
of the UN, displays a very complex seafloor topography including a relief up to 300 m. The inner structure appears also complex, and it is often impossible
to discriminate between the Plio-Quaternary (Pl-Q)
sediments and the underlying reflectors. The Pl-Q layer
appears generally very thin, below the resolution of the
seismic section, and that strongly deformed bedrocks
(Messinian or older strata) are almost outcropping.
A very strong M-reflector as well as the seabottom
topography appear almost horizontal along Line 156
(right part of Figure 4a) and chaotic reflections are
observed and the topography is characterized by
cobblestone structures. Such seafloor topography produces hummocky, hyperbolic acoustic reflections,
masking all reflections from the deeper part of the
seismic sections (Limonov et al., 1994).
An unknown feature (Figure 4a) corresponds to a
large flat-topped dome showing an internal acoustic
window. The feature has a more than 100-m thick
cover of the Pl-Q sediments, and well-stratified low
frequency reflectors are recorded downsection. This
structure may have some connection with the buried
mud volcano on the ORETECH line. The profiler data
indicate a dome-like shape for this volcano that is
nearly 2 km across. It has a marked circular shape in
plain view (Figure 4b).
The PS-159 seismic line is subparallel and close to the
Strabo Trench but in the cobblestone area. Here the two
standard units referred to the Messinian are replaced in
a short distance by a single low-frequency unit with
high-amplitude reflectors. This profile illustrates alternates between intensively deformed zones and weakly
disturbed sections. The characteristic feature of this line
is the abundance of thrust features of potential ‘reverse
flower structures’ (Figure 5a), which are evidence for
strike-slip displacements. We believe this is probably due
to the proximity of the Strabo shear zone. Transcurrent
faults are also seen on OKEAN records from this area
(Figure 5b). There are some drastic changes in the struc-
Fig. 4a. V-shaped valley and a flat-topped dome of an unknown nature (may be assumed to be a mud dome) and the transition from accretionary complex passing through the SW
edge of the Strabo Trench in PS-156.
426
g. çi̇fçi̇ et al.
Fig. 4b. Top: Probable buried mud volcano on the northern slope of the United Nation Rise. Bottom: 6.5-kHz profiler record.
mud volcanoes and dome-like structures at the eastern mediterranean ridge
427
Fig. 5a. The Reverse Flower Structure in seismic profile-159.
428
g. çi̇fçi̇ et al.
Fig. 5b. Some drastic changes in the structural trends are seen, which are probably caused by transcurrent strike-slip faults.
mud volcanoes and dome-like structures at the eastern mediterranean ridge
429
Fig. 6a. Top: ORETECH image of the Stoke-on-Trent mud volcano and one main flow. Bottom: 6.5-kHz profiler record.
430
g. çi̇fçi̇ et al.
Fig. 6b. Top: ORETECH image of the Dublin mud volcano (arrow) and one main flow. Bottom: 6.5-kHz profiler record.
mud volcanoes and dome-like structures at the eastern mediterranean ridge
431
Fig. 6c. Discovered Dublin and Stoke-on-Trent mud volcanoes in PS-160. In its middle a column of strong reflections appears which is overlain by high-frequency reflections. They
sometimes show the M-reflector, which is louvered by a system of conjugated faults. This is covered by a layer of low-frequency chaotic reflections.
432
g. çi̇fçi̇ et al.
Fig. 7. Two huge intrusions which gives some signs of a mud diapirism (dome-like structures).
mud volcanoes and dome-like structures at the eastern mediterranean ridge
433
Fig. 8a. Geological overview of the new mud volcano area of the United Nation Rise at the Eastern Mediterranean Ridge. (D): cobblestone areas, SMV: Stoke-on-Trent mud volcano,
DMV: Dublin mud volcano, (1): inner deformation front, (2): high backscattering spots on OKEAN data, (3): SW edge of high seafloor deformations area>‘United Nation Rise’,
(V): V-shaped valley.
434
g. çi̇fçi̇ et al.
Fig. 8b. General geological interpretation of the main seismic profiles (PS-156, 160–162 and 164) in the study area of the United Nation Rise at the Eastern Mediterranean. The
difference between the area of high seafloor deformation and the area with typical cobblestone seafloor topography is seen. Some dome-like structures (?!) and discovered Dublin
(MVD) and Stoke-on-Trent (MVS) mud volcanoes are marked.
mud volcanoes and dome-like structures at the eastern mediterranean ridge
435
436
g. çi̇fçi̇ et al.
tural trends, which could be related to the presence of
large transcurrent faults (Limonov et al., 1996). Sometimes we observe a combination of both deformations.
The positive flower structure resembles to some extent
the mud volcanoes or Agas domes (following the terminology of Hovland and Judd, 1988), but without
acoustic masking, normally seen below such structures
as consequences of gas saturation. They show an average width of 2–4 km and represent positive topographic
features on the seafloor topography.
The seabottom topography in the PS-160 line is rather rough and induces a chaotic seismic facies;
M-reflector is hardly detectible. Two mud domes however were recognized on this line. They mark on the
ORETECH record as isometric black spots and display an internal seismic structure similar to the domelike structures. The Stoke-on-Trent mud volcano and
one of its main mudflows extends along the profile,
over a distance of 2.4 km (Figure 6a). A large mudflow
can be observed spreading in a northwestern direction.
The volcano and its mudflow appear as an area of
markedly high backscattering, which is related to the
presence of mud breccia virtually uncovered by pelagic
mud on the seafloor. The Stoke-on-Trent mud system
is characterized by a strong reflection shown on the
subbottom profiler. Its surface is flat to gently domed.
The Dublin mud volcano is characterized by high
backscattering and is narrow, only 300 m, but a much
larger area of the seafloor is highly reflective, as shown
by subbottom profiler (Figure 6b). The low backscatter
may indicate substantial coverage with pelagic mud
and thus appears as an older eruptive event rather
than one thought tobe more recent, responsible for
the high backscattering spot at the center of the Dublin
mud volcano. This area of low backscattering but high
reflectivity on the subbottom profiler record is gently
domed (Foucher et al., 1996). These two features were
sampled by gravity cores. The Stoke-on-Trent mud
volcano is characterized by a symmetric dome of about
7.5 km in width. They contain in the central part of
an area by strong reflections, and are overlain with
high-frequency reflections. Reflectors appear to bend
down due to a system of conjugate faults; in some areas
the M-reflector can be seen. The feature is underlain by
low frequency chaotic reflections (Figure 6c).
Two wide features which can be reported as mud
diaprisms, are seen in Figure 7. They look like domelike structures having heights of about 170 m and 280 m,
respectively. On the OKEAN data, they mark as isometric black spots. These features may correspond to large
mud volcanoes. The inner seismic structures of domelike features are very similar to mud volcanoes. Many
diffraction patterns seen in the cobblestone area have
no correlation and coherency among their reflections.
Below a high reflection zone (thickness of approximately 130–135 msec) a few strong low-frequency reflections are detected. Such a pattern can be observed
as a consequence of intervening events at the wall of the
mud channel which contains gas and pull-down effects.
4. Discussion
The geological interpretation of seismic profiles PS-156,
160–162 and 164 in the area show some differences
between the area of high seafloor deformation and
the area with typical cobblestone seafloor topography
(Figure 8a and b). The UN Rise complex structure is
particularly evident in the highly dissected seafloor
topography with sharp, variable relief and sudden
changes of the structural trends. This can be explained
by a combination of the tectonic compression caused
by the motion northwards of the African Plate and a
probable tectonic escape from the west, where Africa
and Europe are in direct collision (Cita and Camerlenghi, 1992). The rise is characterized by recent, active
tectonic movements. The general tectonic pattern there
is dictated by the presence of a system of major sinistral
strike-slip faults, which is parallel to the fault system
of the Strabo Trench. These faults are very young
and are clearly displayed in seafloor relief as steep
escarpments. In fact, mud volcanoes are also related
to these large faults and these are covered by unconsolidated sediment.
Although there is evidence for the presence of mud
volcanism east of the Olimpi area, this phenomenon
is not as widespread as in the central and western parts
of the Mediterranean Ridge. The main reasons for this
are thought to be:
(i) the presence of a relatively thick layer of the plastic
Messinian evaporites, which prevent the breakthrough of mud brecia onto seafloor and
(ii) a weaker compressional tectonic stress, affecting
the accretionary prism in this part of the Mediterranean Ridge (Limonov et al., 1996).
There is a relationship between the Mediterranean
Sea to world climate and potential of mud volcanoes
to release greenhouse gases like methane and disturb
the Mediterranean water circulation. The information
provided by the mud breccia is important for several
reasons. Little is known about the deep geology of the
Mediterranean Ridge because of difficulties below the
rough surface and ambiguous Messinian salt using
geophysical methods. The eruptive products of the
mud volcanoes provide information about the rocks
at the lower depths. They may also give information
mud volcanoes and dome-like structures at the eastern mediterranean ridge
about hydrocarbon potential in the deeper part of the
accretionary prism. Whether the mud volcanoes are
an environmental or social hazard is also important
and should be investigated. If mud volcanoes are as
violent in eruption in the deep sea as they have been
observed on land (in cases where large craters are
created with diameters in the area of 1 kilometer ), they
could cause tsunamis (J. F. Woodside, pers. commun.).
437
Muhsin Köktaş, Eolco Felser and Rachel Huber for
cooperation and thanks also go to Jean Paul Foucher
for helpful discussions. Also we would like to express
our great thanks to the people who were involved in the
acquisition of the seismic data and to the scientists
Leonid Akentiev and Sergey Kraskovsky. Without their
hard work it would not have been possible to obtain the
data. We thank the Joint Editor, J.-C. Sibuet and the reviewers for their suggestions to improve the manuscript.
5. Conclusions
References
Interpretation of the high resolution seismic lines of the
Eastern Mediterranean was carried out using images as
an acoustic characteristic of mud volcanoes. New mud
volcanoes, and probably mud domes were discovered
in the UN area which rises from 250 to more than
700 m above the surrounding seafloor. The complex
structure can also be explained by the general setting
of the UN area. It is situated just in the kink point,
west of which we observe a strong lateral south-north
compression of the accretionary prism. To the east,
there is more strike-slip motion due to a combination
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structures including discovered mud volcanoes. We
suspect that such a picture may be produced by interference events between the wall of the mud volcano
and by the presence of gas-rich sediments.
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