Upload
c-kurtulus
View
219
Download
0
Embed Size (px)
Citation preview
ORIGINAL RESEARCH PAPER
Determination of the tectonic evolution of the Edremit Gulf basedon seismic reflection studies
C. Kurtulus Æ B. Dogan Æ F. Sertcelik ÆM. Canbay Æ H. M. Kucuk
Received: 4 May 2009 / Accepted: 8 August 2009 / Published online: 25 August 2009
� Springer Science+Business Media B.V. 2009
Abstract The Edremit Gulf, which developed during the
Neogene-Quaternary, is a seismically active graben in NW
Anatolia (Turkey) surrounded by the Sakarya continent.
The sedimentary deposits in the gulf overlie the bedrock
unconformably and can be separated into two parts as
upper and lower deposits based on similarity of their
seismic characteristics, and because the contact between
them is clear. The lower deposits are characterized in the
seismic profiles by the absence of well defined, continuous
reflectors and are strongly disturbed by faults. A tectonic
map and structural model of the Edremit Gulf was derived
from interpreting 21 deep seismic profiles trending NE–SW
and NW–SE within the gulf. Two fault systems were dis-
tinguished on the basis of this compilation. The NNW–SSE
trending parallel faults are low-angle normal faults formed
after compression. They controlled and deformed the lower
basin deposits. A syncline and anticline with a broad fold-
curvature length resulted in folds that developed parallel to
basin boundaries in the lower basin deposits. The ENE–
WSW trending high-angle faults have controlled and
deformed the northern basin of the Edremit Gulf. The folds
developed within the northern lower deposits originated
from the listric geometry of the faults. These faults are
normal faults associated with regional N–S extension in
western Anatolia. The Edremit Gulf began to open under
the control of low-angle NNW–SSE trending faults that
developed after the compression of western Anatolia in an
E–W direction in the early Neogene. Subsequently, regio-
nal N–S extensional stress and high-angle normal faults cut
the previous structures, opened the northern basin, and
controlled and deformed the lower basin deposits in the
gulf. As a result, the Edremit Gulf has not been controlled
by any strike-slip faults or the Northern Anatolian Fault.
The basin developed in the two different tectonic regimes
of western Anatolia as an Aegean type cross-graben from
the Neogene to Holocene.
Keywords The Edremit Gulf � Seismic reflection �Aegean cross-graben
Introduction
The Edremit Gulf is located between western Anatolia and
the south strand of the North Anatolian Fault in the NW of
Anatolia, where it is surrounded by the Sakarya continent
which developed to the south of the Intrapontide suture that
formed between the E and W of the Marmara region (Okay
and Tuysuz 1999) (Fig. 1b). Oligocene terrestrial and
Lower Miocene lacustrine sedimentary rocks formed as the
result of the closure of Tethys ocean, together with coeval
volcanic rocks to the south (Yılmaz 1997).
C. Kurtulus (&) � F. Sertcelik � M. Canbay
Engineering Faculty Department of Geophysics, Kocaeli
University, 41380 _Izmit-Kocaeli, Turkey
e-mail: [email protected]
F. Sertcelik
e-mail: [email protected]
M. Canbay
e-mail: [email protected]
B. Dogan
Engineering Faculty Department of Geology, Kocaeli
University, 41380 Kocaeli, Turkey
e-mail: [email protected]
H. M. Kucuk
Engineering Faculty Department of Geophysics, Dokuz Eylul
University, _Izmir, Turkey
e-mail: [email protected]
123
Mar Geophys Res (2009) 30:121–134
DOI 10.1007/s11001-009-9072-2
There have been a few studies related to the geology and
tectonics of the northern onshore region of the Edremit
Gulf, which is about 80 km long and broadens westward
from about 5 km across to more than 30 km (Fig 1a),
(Yılmaz and Karacık 2001; Saka 1979; Yaltırak and Okay
2004), but there is sparse information related to the tectonic
setting of the Edremit Gulf.
The study area and its surroundings are significant places
for understanding the Neotectonic evolution of Turkey, and
consequently were considered by many authors. The North-
ern Anatolian Fault splinters into three strands around
Mudurnu (Bolu) to the east of the Marmara Sea (McKenzie
1978; Sengor 1979; Barka 1992; Taymaz et al. 1991; Bozkurt
2001; Kurtulus 2002; Yaltırak 2002). The northern strand
Fig. 1 a Simplified geological map of the surrounding of the Edremit
Gulf, and location of the seismic profiles (modified from Yılmaz and
Karacık 2001, Yaltırak and Okay 2004, Saka 1979). b Active
Tectonic map of Marmara Region (Yaltırak 2002)
122 Mar Geophys Res (2009) 30:121–134
123
enters the Gulf of Saros as NE–SW direction from the slope
of the Ganos mountain traversing the Marmara Sea west-
wards in E–W direction. The middle strand of the Northern
Anatolian Fault extends almost E–W along _Iznik Lake, to the
Gemlik and Bandırma Gulfs (Fig. 1b). This strand diverts at
the western part of the Bandırma Gulf and turns southwest-
ward into the Bandırma-Behramkale Fault Zone (BBFZ)
trending to the western part of the Edremit Gulf and con-
sisting of many strike-slip faults of varying lengths. The
southern strand of the Northern Anatolian Fault crosses
Yenisehir and extends from Bursa to Manyas, bending
southwest from the southern part of Uluabat Lake and elon-
gates in a NE–SW direction up to the southern part of Manyas
Lake (Fig. 1b). The fault turns into the direction of N45E just
to the SW of Manyas Lake and extends from Manyas to
Edremit (Barka and Hancock 1984; Barka 1992) (Fig. 1b).
The western Anatolian extensional regime developed a
series of NNW–SSE and E–W trending basins (Sengor
1987). Some authors proposed that these two sets of basins
trending along two directions were the result of strain in two
directions at different time during the Oligocene, and from
Late Miocene to Quaternary (Seyitoglu and Scott 1991;
Seyitoglu et al. 2002; Isık et al. 2003). The some other
authors proposed that the N–S trending basins were cut by
E–W trending basins during the Late Miocene and Qua-
ternary (Yılmaz et al. 2000; Gurer et al. 2001, 2006; Ko-
cyigit 2005; Kaymakcı 2006; Kocyigit and Deveci 2007).
The Kucukkuyu Formation was deposited in a lacustrine
area and comprises Oligocene conglomerate, sandstone and
shale. The region is also characterized by Oligocene Ay-
vacık Volcanics composed of andesite-latite and rhyolite-
dacite components formed on the northern margine of the
Edremit Gulf (Yılmaz and Karacık 2001; Genc 1998; Ka-
racık and Yılmaz 1998). The Hasanboguldu Formation
defines the Plio-Quaternary alluvial-fan facies (Yaltırak
and Okay 2004). Lower–Middle Miocene volcanic rocks
and laterally equivalent lacustrine units are exposed in the
southern Edremit Gulf (Yılmaz and Karacık 2001; Yılmaz
1997; Saka 1979). Regional transgression and regression
developed by change of sea—levels have been calculated
by determining the stratigraphic sequence and facies of the
upper Quaternary sediments in three basins trending NE–
SW located in the NE of Aegean Sea (_Isler et al. 2008).
The deformational structural data related to Paleotec-
tonic (pre-Cretaceous) and Neotectonic (Miocene and
afterwards) periods are formed to the north of the Edremit
Gulf (Yılmaz and Karacık 2001; Yaltırak and Okay 2004).
Thrust faults formed during the subduction of the Tethys
Ocean between Permian and Early Triassic and these have
been uplifted and folded during the Cretaceous deforma-
tion (Yaltırak et al. 2000). The Neotectonic period began
with the formation of NNE–SSW trending extensional
faults caused by a N–S trending compressional regime that
existed in Early-Middle Miocene. In addition to this, a
continuation of this shortening phase during this period
formed a fold axis trending E–W.
The N–S compression that began in the Late Miocene
formed oblique normal faults trending NE–SW and NNE–
SSW, and which had a dominant dip-slip component and a
small strike-slip component (Yılmaz and Karacık 2001).
Faults trending NE–SW that are observed north of the
Edremit Gulf and that control the Ezine Grabens, also
developed the Etili and Gulpınar Grabens (Fig. 1b). The
continuation of N–S compression triggered the develop-
ment of an erosional planar topography in the region. The
Kazdag Horst observed in the north of the Gulf of Edremit
was uplifted to the present elevation by E–W trending
faults. The Bayramic Graben, which is located north of the
Edremit Gulf is a subsidiary half-graben associated with
uplift of the Kazdag Horst. The age of the Edremit Graben
is not precisely dated. It may be estimated as being Pleis-
tocene-Quaternary because it was controlled by Late
Miocene-Early Pliocene structural elements (Yılmaz and
Karacık 2001).
One of the aims of this study is to determine which
tectonic regime and basin type opened the Edremit Gulf,
and to classify the basin deposits lithostratigraphically in
order to determine the relationship between the basin
deposits and the older bedrock. The other main research
objective is to determine the competing influences of the
Northern Anatolian Fault and the western Anatolian
extensional regime on the tectonic evolution of the Edremit
Gulf. The relationship between the opening of the Edremit
Gulf and the western Anatolian extensional regime or the
Northern Anatolian Fault was investigated. More generally,
the study area forms a model for determination of the
opening of a basin controlled by high angle normal faults.
For this reason, the locations of the faults and their inter-
action mechanism in the gulf were constrained, and the
geologic formations were detected accurately, based on
deep-penetrating multi-channel seismic reflection profiles
conducted by Turkish Petroleum Corporation (TPAO) in
1986 (Fig. 1a). These previous dataset had been obtained
for the purpose of gas and oil exploration, rather than to
investigate the tectonics of the Edremit Gulf.
Materials and methods
A total of 1,000 km of deep-penetrating, multi-channel
seismic reflection profiles was collected by Amaco-Turkey
Petroleum Co-Western Geophysical Co. in 1986 in the
Edremit Gulf, which we reinterpreted in this study
(Fig. 1a). These data were recorded using a DFS V
recorder at 6.0 s two-way travel time and a sampling rate
of 4.0 ms. Group and shot intervals, as well as array
Mar Geophys Res (2009) 30:121–134 123
123
lengths, were fixed at 25 m. 18 HP air-guns of 1,270 cu. in.
array and a 120 trace analog streamer were used. The data
were electronically muted to remove refracted arrivals
from shallow sediments. The predictive gap was fixed at
24 ms. The data were filtered with a high-cut 90 Hz 7208/
octave. The low-cut filter was out while recording. A time
variant filter (6, 10, 75, 90) for 0–1,000 ms, (4, 8, 65, 75)
for 1,000–2,000 ms, and (3, 6, 40, 50) for 2,000–6,000 ms
were applied before wave equation migration to remove
noise followed by a mute, Normal Move Out (NMO)
correction, velocity analysis and deconvolution. The time
variant filter was reapplied followed by wave equation
migration processing to obtain the final stack. The research
vessel was navigated using primarily Syledish and sec-
ondarily Loran-C and satellite.
Results
Bathymetry
A bathymetric relief map of the Edremit Gulf was prepared
by combining the echo sounder data and the deep seismic
reflection profiles (Fig. 2). The sea floor, which can be
characterized by a concordant morphology, continuously
deepens to the SW of the gulf. The water depth adjacent to
Lesbos Island is greater than 91 m. Four main ridges are
noticeable in the gulf. One of these is observed along the
northern marginal faults in the gulf, whereas the others are
associated with scarp locations where some fault throws are
observed.
Seismic profiles
Profile Pr2 is a regional line oriented in an NE–SW
direction in the north of the Edremit Gulf, as shown in
Fig. 3. The morphology of the faults is well preserved in
the basin sediments. The lower basin deposits, which are
folded and controlled by one or more faults, are charac-
terized by well-stratified reflections with a subparallel to
divergent internal configuration. They are often dissected
by north-dipping faults displaying listric planar shape to
the bedrock, such as between shot points (SP) 480 and 490;
SW-dipping faults generally show high angles between SP
380 and 480, and form listric planes in the lower parts of
the stratigraphy between SP 260 and 380. The folded basin
sediments observed on the cross-section of Profile Pr2,
which trends NW–SE, was deformed by a low-angle nor-
mal fault system that penetrates down to the bedrock. The
horizontal layers in the SW of Profile Pr2 trend towards NE
with high dip angles. This change in the stratal dips well
displays where the fault plane displays a listric geometry.
These fault planes trend NNW–SSE and deform the basin
units into N–S trending folds (syncline) with a wide fold
curvature length (Fig. 6). The faults numbered 1 and 2
observed on profile Pr2 cut the upper basin deposits as
normal faults with high-angle dip angles. The low angle
fault system in shallow depths shows a high angle orien-
tation at lower levels in the crust. The coeval faults are
observed at the SW end of Profile PR2.
The angles of the north-dipping normal faults observed
between SP 1300 and 1370 on Profile Pr3 decrease from
shallow to deep levels sub-seafloor (Fig. 4). High angle
normal faults dipping south between SP 1370 and 1540 are
recognized and the fault plane observed at SP 1650 folds
the layers with a listric geometry. The folded basin sedi-
ments and structural elements indicate the existence of a
fault period with low–high angles. Images of Fault 3
indicate that the stratigraphy of the upper parts of the basin
fill are controlled by high angle normal faulting.
Normal faults dipping both south and north are
observed between SP 240 and 300 on Profile Pr5 and
Fig. 2 Bathymetry map of the
Edremit Gulf
124 Mar Geophys Res (2009) 30:121–134
123
Fig. 3 Interpreted (a) and raw (b) seismic cross-section of Profile Pr2 (see Fig. 1a for location)
Mar Geophys Res (2009) 30:121–134 125
123
form a syncline in that area (Fig. 5). The north-dipping
faults observed between SP 110 and 240 have caused
folding of the basin sediments. The sedimentary layer
labelled (M1) and seen in the SW of cross-section is
deformed by faults that cause vertical throws up to 1.5
sec two way travel time.
The listric shape of Faults 4 and 5 in the basement rock
(Kazdag Dome) have caused folding between SP 180 and
320 on Profile Pr13 within the basin sediments (Fig. 6).
The high angle faults that trend ENE–WSW in the cross-
section are observed in the shallow levels of the upper
basin deposits. The basin sediments between SP 320 and
400 on Profile Pr13 were also folded because of the listric
character of the faults.
North-dipping, high-angle faults are observed
between SP 300 and 530, and SP 80 and 160 on Pro-
files Pr15 and Pr16 respectively. In contrast, the south-
dipping Faults 6 and 7 that were observed between SP
390 and SP 400 on Profile Pr15 have a listric character
in the lower part of basin deposits (Fig. 7). The faults
which deform the gulf and accommodate the opening of
the northern basin are observed as high-angle faults, as
depicted in seismic profile Pr15 (Fig. 7). The upper part
of the basin sediments, which are horizontal, are
Fig. 4 Interpreted (a) and raw (b) seismic cross-section of Profile Pr3 (see Fig. 1a for location)
126 Mar Geophys Res (2009) 30:121–134
123
Fig. 5 Interpreted (a) and raw (b) seismic cross-section of Profile Pr5 (see Fig. 1a for location)
Mar Geophys Res (2009) 30:121–134 127
123
deformed by high-angle normal faults, while covering
the folded lower part of basin fill unconformable. Faults
6 and 7 indicate that the initial source of the defor-
mation in the area is low-angle normal faulting. The dip
directions of the layers indicated by (M2) in the basin
sediments are related to the fault planes that formed
an asymmetrical syncline with a long fold-curvature
length. because listric geometries were observed
between SP 230 and 260 on Profile Pr16 (Fig. 8).
Layer (M3) forms an asymmetrical syncline in the fol-
ded basin unit between SP 400 and 470 on Profile Pr18
(Fig. 9). The south and north-dipping faults between SP
100 and 290 on Profile Pr18 generally show high angles.
The upper parts of the basin sediments cover the older units
with an angular-unconformity.
Seismic stratigraphy
Formations were distinguished by considering the reflec-
tion configurations (Sangree and Widmier 1979; Sheriff
1980). The mapped Neogene to Holocene formations may
be divided into a number of seismic layers. Different
coeval formations are known to outcrop over the sur-
rounding regions of the Edremit Gulf. Although the seismic
layers have been delineated using unconformities and their
correlative conformities, we avoided giving names to the
layers because we could not establish every layer, because
the lack of borehole data that represents the stratigraphic
units deposited during the Neogene period.
The lower (Neogene), upper (Holocene) parts of basin
sediments and bedrock formations are well observed in the
Fig. 6 Interpreted (a) and raw (b) seismic cross-section of Profile Pr13 (see Fig. 1a for location)
128 Mar Geophys Res (2009) 30:121–134
123
seismic profiles (Figs. 3, 4, 5, 6, 7, 8 and 9). The top of the
sequence consists of sedimentary layers that are charac-
terized by well-defined, continuous and parallel reflections.
The average velocity of this formation is V = 1,909 m/s
while its thickness ranges 47–379 m. The lower basin
deposits consist of a series of parallel to subparallel, obli-
que and sigmoid reflections. From bottom to top, four
lithostratigraphic layers may readily be distinguished.
They are medium to thinly-bedded and rather uniform. The
average velocity of the lower basin deposits is
V = 2,783 m/s, while its thickness is estimated at 490–
2,000 m. The unit overlies the volcanic bedrock uncon-
formable, and is cut by several faults (Fig. 10).
The bedrock comprises chaotic bedding, as evidenced
by numerous hyperbolic acoustic returns. Internal reflec-
tions in the bedrock are finely banded, discontinuous to
rarely chaotic.
Tectonic and seismicity
Because the investigation area, the Edremit gulf, is one of
the western Anatolian basins and is located in the tran-
sition zone between the Aegean and Marmara regions, it
is debatable which tectonic regimes, Northern Anatolian
Fault strike-slip or West Anatolian extensional are more
dominant in the region and which tectonic stress caused
the faults that formed the bathymetry of the gulf. We
determined that the three basins trending NE–SW and
observed in the northern part of the region, close to the
Biga Peninsula at which Fig. 1b, as well as two ridges
originated as a result of the effects of tensional and strike
slip faults detected in the seismic cross-sections (_Isler
2005). The modern micro-earthquake activity in the
investigation area is very strong (Tan et al. 2008)
(Fig. 11).
Fig. 7 Interpreted (a) and raw (b) seismic cross-section of Profile Pr15 (see Fig. 1a for location)
Mar Geophys Res (2009) 30:121–134 129
123
The tectonic map of the Edremit Gulf was defined by
interpreting the 21 seismic profiles trending NE–SW and
NW–SE in the gulf (Fig. 12). Two fault systems were
mapped out in the Edremit Gulf. The fault map of the
Edremit Gulf defined by our work with structural
parameters obtained from seismic profiles allows us to
test which tectonic model is most appropriate to explain
the opening of the gulf. The data indicate two fault sys-
tems developed in different directions, origins and peri-
ods. The first fault system observed on Profiles Pr2, Pr3
and Pr5 was mapped using the other seismic profiles with
same direction and bathymetric data. These faults were
formed as a parallel set trending NNW–SSE, W–SW
dipping and generally low angle normal faults controlled
and folded the lower part of the basin sediments along an
axis trending NNW–SSE. According to ages determined
by Yılmaz and Karacık (2001) in the stratigraphic
sequences in the area of land to the north of the gulf, the
age of the faults is generally early Neogene. The normal
faults represent the response to an initial compressional
regime that formed a series of N–S trending grabens
under the effect of breakaway faults developed after
Fig. 8 Interpreted (a) and raw
(b) seismic cross-section of
Profile Pr16 (see Fig. 1a for
location)
130 Mar Geophys Res (2009) 30:121–134
123
western Anatolian compression (Sengor 1979; Sengor and
Yilmaz 1981; Yılmaz et al. 2000). However, these faults
show similarities with the fault system observed by Yal-
tırak and Okay (2004), in the onshore region on the
northern side of the gulf, and which caused the elevation
of both the Kucukkuyu Formation and the Kazdag Massif,
since the beginning of the Kucukkuyu Formation with the
end of the Kazdag Massif rise is simultaneously, in lower
Miocene (_Inci 1984). This fault system formed three
consecutive scarps parallel to the direction of the faults in
the bathymetry of the Edremit Gulf. The second group of
fault system observed in Profiles Pr13, Pr15, Pr16, Pr18
was mapped using the other seismic profiles collected in
the same direction, as well as with bathymetric data.
These faults controlled the basin in the north of the region
and are high-angle normal faults trending ENE–WSW.
The wide fold-curvature length folds that trend NE–SW in
this period (may be Early Miocene), which are younger
than that in which the first group faults system developed
were mapped using both the seismic profiles and the 3-D
bathymetric data. The 3D digital elevation model map
obtained from the batimetric map of the Edremit Gulf
shows the fault scarps indicated by S1, S2, S3 (Fig. 12)
and controlled by NNW–SSE oriented low-angle normal
faults and Scarp S4 which was controlled by ENE–WSW
trending high-angle normal faults in the gulf.
This most recent period of Western Anatolian Neotec-
tonics is characterized by the basin boundary trending in an
E–W direction. The folds of these basins are formed by
high angle normal faults, which also controlled and
deformed the lower and upper basin sediments in the Ed-
remit Gulf (Fig. 7). The fault planes are seismogenic and
form part of the western Anatolian extensional regime.
This interpretation is consistent with ENE–WSW trending
pure normal fault plane solutions obtained by England
(2003) (Fig. 11).
Fig. 9 Interpreted (a) and raw (b) seismic cross-section of Profile Pr18 (see Fig. 1a for location)
Mar Geophys Res (2009) 30:121–134 131
123
These two fault systems began to open the Edremit Gulf
along low-angle normal faults, which were formed after
compression and presumably dating from the begining of
Neogene. With the start of sedimentations of lower
deposits in the basin, NNW–SSE trending fault scarps were
formed similar by the development of tectonic origin of the
basins trending NE–SW direction (Bozkurt 2000, 2003).
The Edremit Gulf takes its present shape after the earlier
fault scarps were cut by ENE–WSW trending faults
developed as a result of a regional N–S extensional regime
within western Anatolia. The Edremit Gulf with this tec-
tonic geometry and bathymetry developed during two dif-
ferent stress periods within western Anatolia, like an
Aegean-type cross-graben shape.
Discussion
This study examines how the Edremit Gulf was opened and
if the southern branch of the Northern Anatolian Fault or
the western Anatolian extensional regime had any effect on
the development of the gulf as evidenced from the seismic
reflection profiles collected in the gulf.
Seismic reflection studies carried out in the Edremit
Gulf indicate that: (1) Two fault systems exist. One fault
set consists of the transtensional boundary faults trending
NNW–SSE and which are the source of the basin. These
faults allow the preservation of the lower part of basin
sediments. The other fault set is made up of high-angle
normal faults that originated from detachment faults
developed during ENE–WSW trending compression. (2)
The NNW–SSE trending faults are generally seen to have a
low dip and show a listric geometry towards bedrock
whereas, the ENE–WSW trending faults in the Edremit
Gulf are arranged parallel with the normal faults observed
on land north of the gulf.
The first period of faulting in the northern Edremit Gulf
is the Oligo-Miocene detachment faulting with low dip-
angle related to back-arc extension (Rotstein 1985). The
Plio-Quaternary period is characterized by parallel normal
faults that cut the older units and structures (Beccaletto and
Steiner 2005). This interperation is in a good agreement
with the present and historical seismic activities observed
around the Edremit Gulf, as depicted in Fig. 11. The tec-
tonic geometry determined in our study is consistent with
the results of Yaltırak and Okay (2004) and Beccaletto and
Bonev (2005) in which they stated that the ENE–WSW
trending high-angle normal faults cut and deformed the
Oligo-Miocene, Lower Middle Miocene, Upper Miocene
and Pleistocene units located around the Kazdag uplift. (3)
The basin deposits overlying the basement rocks were
distinguished as upper and lower deposits. The lower
deposits are folded and their ages were interpreted as being
Miocene if they correlated with similar units on land
whereas the upper deposits of the basin are generally
horizontal and their ages may be Plio-Quaternary.
Basins formed by the control of strike-slip faults are
separated distinctly from basins controlled by normal faults
with their particular geometries. In this sense, listric normal
faults were observed in the south, while parallel strike-slip
Fig. 10 Thickness map of the
Neogene formation in the
Edremit Gulf
Fig. 11 Seismicity of the North Western Anatolia. Red and whitecircles represent historical and instrumental period earthquakes,
respectively, Tan et al. (2008). Fault plane solution is from England
(2003)
132 Mar Geophys Res (2009) 30:121–134
123
dominant E–W faults were detected in the north of the
seismic cross-section conducted in the west of the Edremit
Gulf (Guney Boztepe et al. 2001). We thus conclude that
structural and bathymetric elements associated with strike-
slip faults were not distinguished in the Edremit Gulf. The
sea-bottom topography of a region controlled by strike-slip
or normal faulting shows some differences (Barka and
Kadinsky-Cade 1988). For example, depressions located in
the Marmara Sea (Cınarcık, Middle Marmara, Tekirdag
Basins) were developed under the influence of strike-slip
faulting are delimited by ridges (push-ups) from each other
(Le Pichon et al. 2001; Armijo et al. 2002; _Imren et al.
2001). These ridges represent the compressional compo-
nent of the strike-slip tectonics (Okay et al. 1999; Rangin
et al. 2004). In addition, the seismic studies conducted in
the Gulf of Gemlik located along the middle branch of the
North Anatolian Fault indicated that the axis lengths of the
basins were equal to each other, so that the basin is a lazy-s
shaped pull-apart basin formed by strike-slip fault defor-
mation (Kurtulus and Canbay 2007). In contrast, there is no
such ridge evolution in the Edremit Gulf developed from
the basins controlled by the parallel normal faults of which
E–W axis is longer than that of N–S axis.
Conclusions
The results of our study show that the contact relation
between bedrock and the main basin-fill sedimentary units
can be determined from seismic reflection profiles. These
units were divided into two groups as lower and upper
basin deposits. The downward concave geometry of the
observed fault planes that control the geometry of the lower
part of the basin-fill deposits caused folding along an axis
trending NNW–SSE. The Edremit Gulf began to open in
the Early Miocene after the compression of the western
Anatolia ceased. Extension was in an approximately E–W
direction along NNW–SSE trending low angle normal
faults that control the geometry of the lower synrift
deposits. At end of Neogene and during the Holocene,
high-angle ENE–WSW trending normal faults developed
due to N–S extension of western Anatolia, thus causing
formation of the northern basin and cutting the previous
structural elements. Within the study area we did not
observe the North Anatolian Fault or deformational evi-
dence of any strike-slip faulting. The Edremit Gulf was
controlled by low-angle, parallel normal faults trending
from E to W, while its northern boundary was controlled
and deformed by high-angle normal faults that cut the
faults that controlled the geometry of the gulf, which
developed as an Aegean type cross-graben from Neogene
to Holocene.
Acknowledgments The author is grateful to Peter Clift for his
fruitful discussions and suggestions that improved the paper.
References
Armijo R, Meyer B, Navarro S, King G, Barka A (2002) Asymmetric
slip partitioning in the Sea of Marmara pull-apart: a clue to
propagation process of the North Anatolian Fault. Terra Nova
14:80–86
Barka AA (1992) The North Anatolian Fault Zone. Annales
Tectonicae 6:174–195
Barka AA, Hancock HL (1984) Neotectonic deformation patterns in
convex northwards arc of the North Anatolian Fault in the
Geological evolution of the eastern Mediterranean. Specical
Publication ed by Dixon, JG; Robertson AHF Geol Soc London
763–773
Barka AA, Kadinsky-Cade K (1988) Strike–slip fault geometry in
Turkey and its influence on earthquake activity. Tectonics
7:663–684
Beccaletto L, Bonev N (2005) Bivergent extensional un-roofing in
northwest Turkey: kinematic evidence of Kazdag massif In:
International Symposium on the Geodynamics of Eastern
Mediterranean: active Tectonics of the Aegean Region. Abs
Istanbul, Turkey 53
Fig. 12 Tectonic map of the
Edremit Gulf
Mar Geophys Res (2009) 30:121–134 133
123
Beccaletto L, Steiner C (2005) Evidence of two-stage extensional
tectonics from the northern edge of the Edremit Graben (NW
Turkey). Geodyn Acta 18(3–4):283–297
Bozkurt E (2000) Timing of extension on the Buyuk Menderes
Graben western Turkey and ıts tectonic implications. In: Bozkurt
E, winchester JA, Piper JDA (eds) Tectonics and magmatism in
Turkey and Surrounding Area 173. Special Publications, Geo-
logical Society London, London, pp 385–403
Bozkurt E (2001) Neotectonics of Turkey—a synthesis. Geodyn Acta
14:3–30
Bozkurt E (2003) Origin of NE trending basins in western Turkey.
Geodyn Acta 16:61–81
England E (2003) The alignment of earthquake T-axes with the
principal axes of geodetic strain in the Aegean region, Turkish. J
Earth Sci 12:47–53
Genc SC (1998) Evolution of the Bayramic magmatic complex
northwestern Anatolia. J Volcan Geother Res 85(23):3–249
Guney Boztepe A, Yılmaz Y, Demirbag E, Ecevitoglu B, Arzuman S,
Kuscu _I (2001) Reflection seismic study across the continental
shelf of Bababurnu promontory of Biga Peninsula, northwest
Turkey. Mar Geol 176:75–85
Gurer A, Gurer OF, Pince A, _Ilkısık OM (2001) Conductivity
structure along the Gediz Graben, west Anatolia Turkey: tectonic
implications. Int Geol Rev 43(12):1129–1144
Gurer OF, Sangu E, Ozburan M (2006) Neotectonics of the SW
Marmara region, NW Anatolia, Turkey. Geol Mag 143:229–241_Imren C, Le Pichon X, Rangin C, Demirbag E, Ecevitoglu B, Gorur N
(2001) The North Anatolian Fault within the Sea of Marmara: a
new evaluation based on multichanel seismic and multi-beam
data. Earth Planet Sci Lett 186:143–158_Inci U (1984) Demirci ve Burhaniye bitumlu seyllerinin stratigrafisi
ve organik ozellikleri. Bull Geol Soc Turk 5(2):7–40
Isık V, Seyitoglu G, Cemen _I (2003) Ductile–brittle transition along
the Alasehir detachment fault and its structural relationship with
the Simav detachment Menderes massif western Turkey. Tec-
tonophysics 374:1–18_Isler EB (2005) Late Quaternary stratigraphy and tectonic evolution
of the northeast Aegean Sea. MSc Thesis, Memorial University
of Newfoundland, 259 pp_Isler EB, Aksu AE, Yaltırak C, Hicott RN (2008) Seismic stratig-
raphy and Quaternary sedimentary history of the Northeast
Aegean sea. Mar Geol 254:1–17
Karacık Z, Yılmaz Y (1998) Geology of ignimbrites and the
associated volcano-plutonic complex of the Ezine area, north-
western Anatolia. J Volcan Geother Res 85(25):1–264
Kaymakcı N (2006) Kinematic development and paleostress analysis
of Denizli basin (w Turkey): implications of spatial variation of
relative paleostress magnitudes and orientations. J Asian Earth
Sci 27:207–222
Kocyigit A (2005) The Denizli graben-horst system and the eastern
limit of western Anatolian continental extension: basin fill,
structure, deformational mode, throw amount and episodic
evolutionary history, SW Turkey. Geodyn Acta 18(3–4):
167–208
Kocyigit A, Deveci S (2007) N-S trending Active Extensional
structure, the Suhut (Afyon) Graben: Commencement Age of the
extensional Neotectonic Period in _Isparta Angle SW Turkey.
Turk J Earth Sci 16:391–416
Kurtulus C (2002) Determination of geology seismic stratigraphy and
tectonism of the _Izmit Gulf by a seismic reflection study (in
Turkish). J Appl Earth Sci Kocaeli Univ 2(1):47–57
Kurtulus C, Canbay M (2007) Tracing the middle strand of the North
Anatolian fault Zone through the Southern Sea of Marmara
based on seismic reflection studies. Geomarine Lett 27:27–40
Le Pichon X, Sengor AMC, Demirbag E, Rangin C, _Imren C, Armijo
R, Gorur N, Cagatay N, Mercier de Lepinay B, Meyer B,
Saatciler R, Tok B (2001) The active main Marmara Fault. Earth
Planet Sci Lett 192:595–616
McKenzie DP (1978) Active tectonics of the Alpine-Himalayan belt:
the Aegean Sea and surrounding regions. Geophys J R Astron
Soc 55:217–254
Okay A_I, Tuysuz O (1999) Tethyan Sutures of Northern Turkey. J
Geol Soc Lond 156:475–515
Okay A, Demirbag E, Kurt H, Okay N, Kuscu _I (1999) An active,
deep marine strike–slip basin along the North Anatolian fault in
Turkey. Tectonics 18(1):129–147
Rangin C, Le Pichon X, Demirbag E, _Imren C (2004) Strain
localization in the Sea of Marmara: propagation of the North
Anatolian Fault in a now inactive pull-apart. Tectonics 23(2):
TC2014. doi:10.1029/2002TC001437
Rotstein Y (1985) Tectonics of the Aegean Block: rotation side arc
collision and crustal extension. Tectonophysiscs 117:117–137
Saka K (1979) Edremit Korfezi ve civarı Neojeni’nin jeolojisi ve
hidrokarbon olanakları. TPAO Project Report 1342, p. 17
Sangree JB, Widmier JM (1979) Interpretation depositional facies
from seismic data. Geophysics 44:131–160
Sengor AMC (1979) The North Anatolian transform Fault: its age,
offset and tectonic significance. Jour Geol Soc London 136:
269–282
Sengor AMC (1987) Cross-faults and differential stretching of
hangingwalls in regions of low-angle normal faulting: examples
from western Turkey. In: Coward MP, Dewey JF, Hancock PL
(eds) Continental Extensional Tectonics, 28. Special Publica-
tions, Geological Society, London, pp 575–589
Sengor AMC, Yılmaz Y (1981) Tethyan evolution of Turkey: a plate
tectonic approach. Tectonophysics 75(3-4):3-4
Seyitoglu G, Scott B (1991) Late Cenozoic crustal extension and
basin formation in west Turkey. Geol Mag 128(2):155–166
Seyitoglu G, Cemen _I, Tekeli O (2002) Discussion extensional
folding in Alasehir (Gediz) Graben western Turkey. J Geol Soc
Lond 159:105–109
Sheriff RE (1980) Seismic stratigraphy. International Human
Resources Development Corporation, Boston
Tan OM, Tapırdamaz C, Yoruk A (2008) The Earthquake Catalogues
for Turkey, Turkish. J Earth Sci 17:405–418
Taymaz T, Jackson JA, McKenzie DP (1991) Active tectonics of the
North and Central Aegean Sea. Geophys J Int 106:433–490
Yaltırak C (2002) Tectonic evolution of the Marmara Sea and its
surroundings. Mar Geol 190(1/2):493–529
Yaltırak C, Okay A_I (2004) Edremit Korfezi kuzeyinde Paleotetis
birimlerinin jeolojisi. _ITU Dergisi/d muhendislik 3(1):67–79
Yaltırak C, Alpar B, Sakınc M, Yuce H (2000) Origin of the Strait of
Canakkale (Dardanelles): regional tectonics and the Mediterra-
nean—Marmara incursion Marine Geology. Mar Geol 164:
139–156
Yılmaz Y (1997) Geology of Western Anatolia. In: Schindler C,
Pfister M (eds) Active Tectonics of northwestern Anatolia- The
Marmara Poly-Project. A multidisciplinary approach by space-
geodesy, geology hydrogeology, geothermics and seismology.
vdf Hochshulverlag AG an der ETH, Zurich, pp 31–53
Yılmaz Y, Karacık Z (2001) Geology of northern side of The Edremit
Gulf and its tectonic significance for the development of the
Aegean grabens. In: Bozkurt, E (Ed), Neotectonics of Turkey.
Geodyn Acta 14, 31–43
Yılmaz Y, Genc SC, Gurer F, Bozcu M, Yılmaz K, Karacık Z,
Atunkaynak S, Elmas A (2000) When did the Western Anatolian
Grabens begin to develop? J Geol Soc Lond 173:353–384
134 Mar Geophys Res (2009) 30:121–134
123