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Late Pleistocene-Holocene evolution of the southern Marmara shelf and sub-basins: Middle strand of the North Anatolian fault, southern Marmara Sea, Turkey

Article (PDF Available) inMarine Geophysical Researches 35(1):69-85 · March 2014
DOI: 10.1007/s11001-013-9210-8
Denizhan Vardar at Istanbul University
  • 11.48
  • Istanbul University
Cenk YALTIRAK at Istanbul Technical University
  • 31.94
  • Istanbul Technical University
Hüseyin Tur at Istanbul University
  • 22.1
  • Istanbul University
Abstract
Although there are many research studies on the northern and southern branches of the North Anatolian fault, cutting through the deep basins of the Sea of Marmara in the north and creating a series of pull-apart basins on the southern mainland, little data is available about the geometrical and kinematical characteristics of the middle strand of the North Anatolian fault. The first detailed geometry of the middle strand of the North Anatolian fault along the southern Marmara shelf, including the Gemlik and Bandırma Bay, will be given in this study, by a combined interpretation of different seismic data sets. The characteristic features of its segments and their importance on the paleogeographic evolution of the southern shelf sub-basins were defined. The longest one of these faults, the Armutlu-Bandırma segment, is a 75-km long dextral strike-slip fault which connects the W–E trending Gençali segment in the east and NE–SW trending Kapıdağ-Edincik segment in the west. In this context, the Gemlik Bay opened as a pull-apart basin under the control of the middle strand whilst a new fault segment developed during the late Pleistocene, cutting through the eastern rim of the bay. In this region, a delta front forming the paleoshoreline of the Gemlik paleolake was cut and shifted approximately 60 ± 5 m by the new segment. The same offset on this fault was also measured on a natural scarp of acoustic basement to the west and integrated with this paleoshoreline forming the slightly descending topset–foreset reflections of the delta front. Therefore the new segment is believed to be active at least for the last 30,000 years. The annual lateral slip rate representing this period of time will be 2 mm, which is quite consistent with modern GPS measurements. Towards the west, the Bandırma Bay is a rectangular transpressional basin whilst the Erdek Bay is a passive basin under the control of NW–SE trending faults. When the water level of the paleo-Marmara lake dropped down to −90 m, the water levels of the suspended paleolakes of Bandırma and Gemlik on the southern shelf were −50.3 (−3.3 Global Isostatic Adjustment—GIA) and −60.5 (−3.3 GIA) m below the present mean sea level, respectively. As of today a similar example can be seen between the Sea of Marmara and the shallow freshwater lakes of Manyas and Uluabat. Similarly, the paleolakes of Gemlik and Bandirma were affected by the water level fluctuations at different time periods, even though both lakes were isolated from the Sea of Marmara during the glacial periods.
ORIGINAL RESEARCH PAPER
Late Pleistocene–Holocene evolution of the southern Marmara
shelf and sub-basins: middle strand of the North Anatolian fault,
southern Marmara Sea, Turkey
Denizhan Vardar Kurultay O
¨ztu
¨rk
Cenk Yaltırak Bedri Alpar Hu
¨seyin Tur
Received: 2 September 2013 / Accepted: 30 December 2013
ÓSpringer Science+Business Media Dordrecht 2014
Abstract Although there are many research studies on
the northern and southern branches of the North Anatolian
fault, cutting through the deep basins of the Sea of Mar-
mara in the north and creating a series of pull-apart basins
on the southern mainland, little data is available about the
geometrical and kinematical characteristics of the middle
strand of the North Anatolian fault. The first detailed
geometry of the middle strand of the North Anatolian fault
along the southern Marmara shelf, including the Gemlik
and Bandırma Bay, will be given in this study, by a com-
bined interpretation of different seismic data sets. The
characteristic features of its segments and their importance
on the paleogeographic evolution of the southern shelf sub-
basins were defined. The longest one of these faults, the
Armutlu-Bandırma segment, is a 75-km long dextral strike-
slip fault which connects the W–E trending Genc¸ali seg-
ment in the east and NE–SW trending Kapıdag
˘-Edincik
segment in the west. In this context, the Gemlik Bay
opened as a pull-apart basin under the control of the middle
strand whilst a new fault segment developed during the late
Pleistocene, cutting through the eastern rim of the bay. In
this region, a delta front forming the paleoshoreline of the
Gemlik paleolake was cut and shifted approximately
60 ±5 m by the new segment. The same offset on this
fault was also measured on a natural scarp of acoustic
basement to the west and integrated with this paleoshore-
line forming the slightly descending topset–foreset reflec-
tions of the delta front. Therefore the new segment is
believed to be active at least for the last 30,000 years. The
annual lateral slip rate representing this period of time will
be 2 mm, which is quite consistent with modern GPS
measurements. Towards the west, the Bandırma Bay is a
rectangular transpressional basin whilst the Erdek Bay is a
passive basin under the control of NW–SE trending faults.
When the water level of the paleo-Marmara lake dropped
down to -90 m, the water levels of the suspended paleo-
lakes of Bandırma and Gemlik on the southern shelf were
-50.3 (-3.3 Global Isostatic Adjustment—GIA) and
-60.5 (-3.3 GIA) m below the present mean sea level,
respectively. As of today a similar example can be seen
between the Sea of Marmara and the shallow freshwater
lakes of Manyas and Uluabat. Similarly, the paleolakes of
Gemlik and Bandirma were affected by the water level
fluctuations at different time periods, even though both
lakes were isolated from the Sea of Marmara during the
glacial periods.
Keywords Southern Marmara Sea Middle strand of the
North Anatolian fault High resolution seismic reflection
Multibeam Paleoshoreline
Introduction
The North Anatolian fault (NAF) is a 1,500-km-long in-
tracontinental transform fault (S¸ engo
¨r1979) and splits into
three branches (Barka and Kadinsky-Cade 1988) at the
eastern part of the Sea of Marmara (Fig. 1). These branches
D. Vardar (&)K. O
¨ztu
¨rk B. Alpar
Institute of Marine Sciences and Management, Istanbul
University, Vefa, 34116 Istanbul, Turkey
e-mail: denizhan@istanbul.edu.tr
C. Yaltırak
Department of Geological Engineering, Istanbul Technical
University, Maslak, 34669 Istanbul, Turkey
H. Tur
Department of Geophysical Engineering, Istanbul University,
Avcılar, 34850 Istanbul, Turkey
123
Mar Geophys Res
DOI 10.1007/s11001-013-9210-8
terminate against the normal faults at the northern Aegean
Sea where the westward escape of the Anatolian block
turns into anticlockwise rotational wedges (Yaltırak et al.
2012). All branches demonstrate different kinematic and
seismic appearance in the region. Starting from east to
west, the NAF bifurcates at the western side of 30.5°E
longitude (Fig. 1). The northern strand extends from the
city of Bolu to Izmit (S¸ engo
¨r1979). Then the southern
strand bifurcates in the Pamukova plain (Koc¸yig
˘it 1988).
Its northern segment, known as the middle strand of the
NAF (hereafter termed NAFMS), extends westward along
the Lake Iznik (O
¨ztu
¨rk et al. 2009), the Gemlik Bay
(Yaltırak and Alpar 2002a), southern coast of the Bandırma
Bay and then changes its direction by turning southwest-
ward at the eastern part of the Erdek Bay. Meanwhile the
southern strand of the NAF extends from the Pamukova
plain towards the Gulf of Edremit in the west (Fig. 1;
Yaltırak 2002).
Many studies have been devoted to the northern and
southern branches, which cut through the deep basins of the
Sea of Marmara in the north and create the Yenis¸ehir pull-
apart basin and the lakes of Uluabat and Manyas (Yaltırak
2002; Selim et al. 2013) in the south, respectively. How-
ever the geometry of the NAFMS under the sea and its
kinematic features, which are less active if compared to the
northern strand, have not been precisely studied previously.
The studies on the NAFMS have been mostly focused
on the faults in the Gemlik Bay and partly its western
approaches (Barka and Kadinsky-Cade 1988; Barka and
Kus¸c¸u 1996; Ergin et al. 1997; Alpar and C¸ izmeci 1999;
Aksu et al. 1999,2000; Yaltırak 2002; Yaltırak and Alpar
2002a; Adatepe et al. 2002;Gu
¨rer et al. 2003; Kurtulus¸ and
Canbay 2007; Kus¸c¸u et al. 2009). This basin was first
considered as a pull-apart system (Barka and Kadinsky-
Cade 1988; Barka and Kus¸c¸u 1996; Fig. 2a). The basin
developed during the Late Pliocene–Early Pleistocene
(Yaltırak and Alpar 2002a), and is mainly controlled by
west-trending dextral strike-slip faults aligned along the
middle strand of the NAF zone (Fig. 2b). These faults cut
the northwest-trending normal faults of the Thrace-Esk-
isehir Fault system (Fig. 1), which existed well before the
east-trending main strike-slip faults. The southern shelf
was uplifted tectonically due to the bending of the NAFMS
in Bandırma Bay (Fig. 2c) and eroded starting from the
Late Pliocene (Adatepe et al. 2002). On the basis of
extensive high-resolution shallow seismic survey, Kus¸c¸u
et al. (2009) outlined four major fault zones in the Gemlik
Bay, which are thought to be responsible for the formation
of Burgaz pull-apart basin and so-called Gemlik push-up
structure (Fig. 2d).
For Bandırma Bay, the only available seismic data
(Kavukc¸u 1990) indicated that the seabottom was divided
by NE–SW and E–W trending faults (Fig. 2d), indicating
an inward collapse which is still active.
In this context the depression fields of the Gemlik Bay,
including the Lake Iznik to the east (O
¨ztu
¨rk et al. 2009), and
the Bandırma Bay were developed on the transtensional
regions between the fault segments that evolved during Late
Fig. 1 Location map of the study area (Yaltirak et al. 2012). NAF North Anatolian fault, TEF Thrace-Eskis¸ ehir fault, EAF East Anatolian fault,
BFFZ Burdur Fethiye fault zone, DSF Dead Sea fault, IS Istanbul strait, CS Canakkale strait
Mar Geophys Res
123
Pliocene–Early Pleistocene under the control of right lateral
strike-slip faults along the NAFMS. Yaltırak (2002) defined
three en-echelon right-lateral fault segments bending
between the Gemlik and Bandırma Bay, which forms the
NAFMS under the sea. The bending causes N30°E-trending
tension in addition to the strike-slip motion. According to
Kurtulus¸ and Canbay (2007), Gemlik Bay is controlled by
the boundary faults, a number of inactive faults with normal
components, as well as by other active faults cutting
through the seafloor. The right-lateral strike-slip geometry
Fig. 2 Previous models proposed for the southern Marmara Sea;
apull-apart model based largely on morphology and bathymetry
(Barka and Kus¸c¸u 1996), bwest-trending dextral strike-slip faults
cutting the Thrace-Eskisehir fault system (Yaltırak and Alpar 2002a),
cthe faults causing tectonical uplift along southern shelf (Adatepe
et al. 2002), dan inward collapse in the Bandırma Bay which is still
active (Kavukc¸u 1990) and major fault zones in the Gemlik Bay
responsible for the formation of Gemlik push-up structure (Kusc¸u et al.
2009), ea main fault model which has a lazy-Z shape in the Gemlik
Bay and extends to Bandırma Bay (Kurtulus¸ and Canbay 2007)
Mar Geophys Res
123
of NAFMS deformed the bay as a small ‘‘lazy Z-shaped’
basin and Bandırma Bay as a ‘‘negative flower-structure’
basin. The tectonic setting between these two sub-basins, on
the other hand, was defined as pure strike-slip within an
E–W trending fault system (Fig. 2e).
In the present paper we present new results from a
shallow high-resolution Chirp seismic study carried out on
the southern Marmara shelf, including the bays of Gemlik,
Bandırma and Erdek. On the basis of the active faults
observed on the seafloor and the morphological structures
Fig. 3 a Fault map of the Sea of Marmara region after Yaltırak
(2002). The faults along the southern margin of the Sea of Marmara
were modified depending on our interpretation in this study. Multi-
beam data of the Marmara deep basins and Tuzla region after Rangin
et al. (2002) and Go
¨kc¸eoglu et al. (2009), respectively. Arrows show
the horizontal velocity field from Ergintav et al. (2007). NAFNS North
Anatolian fault northern strand, NAFMS North Anatolian fault middle
strand, NAFSS North Anatolian fault southern strand, EMT eastern
Marmara trough, MMT middle Marmara trough, WMT western
Marmara trough, bbathymetric and topographic features of the study
area. KP Karabiga Promontory, KH Kapıdag
˘high, KR Kapıdag
˘ridge,
BB Bandırma Basin, SMS South Marmara sill, MH Mudanya high, IR
Imralıridge, IC Imralıcanyon, AH Armutlu high, GB Gemlik Basin,
clocation map of the seismic profiles
Mar Geophys Res
123
on the seismic and multibeam data, we propose a new
model explaining the Late Pleistocene–Holocene evolution
of the middle strand of the NAF along the southern Mar-
mara sub-basins and the paleogeographic development of
the study area.
Physical setting of the study area
The southern shelf of the Sea of Marmara covers a broader
area (4,194 km
2
) compared to the northern one and its
average width is 20 km (Gaziog
˘lu et al. 2002; Fig. 3a). The
sub-basins in the Bandırma Bay (-51 m) and in the
Gemlik Bay (-110 m) are the most distinct geomorphic
basins (Fig. 3b). Along the 290-km long southern coasts,
the study area covers three sub-basins, namely Erdek,
Bandırma and Gemlik, lined up between the Karabiga
Promontory in the west and Gemlik Village in the east.
The steep and uplifted shores observed between the
Kapıdag
˘Peninsula (?803 m) and Armutlu Peninsula
(?903 m) are mostly fault-controlled. The uplifted region of
Karadag
˘-Bandırma (?750 m), Mudanya (?550 m) and
Kurs¸unlu High-Gemic¸ Mountains (?520 m at the coast and
?1,278 m towards Lake Iznik) forms the most clearly out-
lined heights along the southern margin of the study area
(Fig. 3b). The southern mountains are parallel to the coast
and occur in front of the low-lying plains (\100 m) draining
the rivers of Kocasu, Go
¨nen and Biga into the Sea of
Marmara.
The sedimentary sequence on land ranges from Miocene
to recent. The pre-Miocene basement is made up of Cre-
taceous metamorphic rocks and Paleogene sedimentary
units. The basement is distributed over a broad area along
the coastal region; the Marmara Islands, Kapıdag
˘and
Armutlu Peninsulas, Karabiga, Karadag
˘, Kurs¸unlu, Muda-
nya and Gemlik (Fig. 4). The basement rocks were covered
with volcanic (Lower–Middle Miocene) and sedimentary
units (Upper Miocene—Pliocene) behind the coastal
mountains. Holocene alluvial units are dominant along the
regional rivers and around the lakes of Manyas, Uluabat
and Iznik. In the study area, the sedimentary sequences
consist of Lower Miocene to younger deposits, which
unconformably overlie the pre-Miocene to Miocene base-
ment cropping out on Marmara Island, Karabiga, Kapıdag
˘
and Armutlu Peninsulas (Fig. 4). The units, discordant to
each other, are in agreement with the Neogene formations
between the lakes Uluabat and Manyas as described by
Ergu
¨l et al. (1986). The sedimentary units over the folded
Miocene basement indicate variable character (Fig. 4)
(Marathon Petroleum Turkey 1976). Using single-channel
air-gun and deep-tow boomer profiles, Aksu et al. (1999)
defined acoustically reflective, lenticular, stratified and
cross-stratified deposits (Unit 2) rest on an angular
unconformity of sub-unconformity sediments (Unit 3). It is
overlain by widespread draping, locally onlapping and
acoustically transparent deposits of Unit 1.
Materials and methods
New high-resolution Chirp seismic data (Fig. 3c) were
collected in 2010 (350 km of track lines) and 2011
(650 km) using a Bathy 2010P
TM
Chirp sub-bottom pro-
filer and bathymetric echo sounder which provides high
performance sub-bottom survey capability usually for
shallow inland waterways by providing algorithms for peak
signal detection. The system uses 4 transducers in array
configurations to provide full power capability. The power
level, sweep bandwidth and detection threshold was
adjusted automatically during the survey. The travel times
were converted to depth values below the present mean sea
level using the typical interval velocities of 1,500 and
1,700 m/s, which have been found to be appropriate for the
water column and near-surface siliciclastic sediments (Eris¸
et al. 2007), respectively. The transmit pulse repetition rate
was 1 Hz dependent on the depth range (150 m) and also
on the selected pulse length which is short enough to
resolve thin layers covering the sub-bottom strata. The
penetration depths ranged from a few meters in coarse sand
near shore to about 60 m in finer-grained sediments. The
vertical resolution of 2–8 kHz source Chirp systems used
in this study equates to a theoretical vertical resolution of
0.125 m (assuming a compressional wave velocity of
1,500 m/s). The speed of the research boat was set to
7.0–7.5 km/h during the survey. The ship’s position and
heading provided with a Magellan Proflex 500 scientific
GPS were stored in data files. Following some basic data
processing sequences such as gain recovery and filtering
using Kogeo Seismic Toolkit 2.7, the seismic sections were
interpreted with the aid of seismic-reflection interpretation
software Kingdom Suite donated by Seismic Micro
Technology.
For a better interpretation, our seismic data were com-
bined with 3 different previous data sets (Fig. 3c) gathered
by two other seismic systems with different penetration and
resolution characteristics. The first interpreted data set was
the single-channel pinger (uniboom) data gathered by the
Department of Navigation, Hydrography and Oceanography
of Turkish Navy (SHOD) in 1979 (280 km) and 2,000
(150 km) (Tur and Ecevitog
˘lu 2000; Vardar 2006). Another
data set we re-interpreted was the air-gun single-channel
analog data collected under the Marmara Gateaway project
in 1995 (Aksu et al. 1999,2000; Yaltırak 2002). All of the
seismic data obtained from these previous studies were re-
interpreted here and all of the sections given in this paper
were not published before.
Mar Geophys Res
123
Multi-beam bathymetric data were collected between
2004 and 2007 during the course of numerous cruises
onboard the TCG C¸ubuklu operated by SHOD (Go
¨kas¸an
et al. 2010). The system used (Elac-Nautik 1050 D multi-
beam sonar) operates with 56 beams at 50 kHz and employs
a fan of echo-sounders covering an angle of approximately
120°below the survey vessel. A Sercel NR-203 D-GPS was
used for positioning, the vessel speed being held at
15–18 km/h. The corrected data against the ship movements
were combined with previous bathymetric maps for the in-
sonified regions by multi-beam sonar and also with topo-
graphic elevations digitized from 1:25,000 topographic
maps. The combined data were then arranged in 1-m contour
intervals using ArcGIS 10 software. For a hillshade presen-
tation using ENVI software program the data were also
transformed into a digital elevation model (DEM) as raster
files with 30 930 m pixel size.
Results
In the present study, three seismic units were distinguished
from the high-resolution Chirp seismic reflection profiles
from Erdek Bay (Fig. 5a) and from the region between
Bandırma and Gemlik Bay (Fig. 5b). These units were
named C3, C2 and C1 starting from the sea bottom.
Unit C3: The uppermost seismic unit consists of weak
and internally parallel reflectors with coastal onlaps onto
Unit C2 (Fig. 5a, b). Unit C3 can be seen everywhere and
represents the sedimentation starting from the first marine
invasion. It has variable thickness depending on the riv-
erine inputs and geomorphic condition of depositional
environments; i.e., it is more than 25 m thick on the Ko-
casu River delta (Fig. 6a), 19 m in the Gemlik Basin in
Gemlik Bay and 12 m in Bandırma Bay. The unit becomes
thinner (\2 m) outwards of the Bandırma sub-basin where
the acoustic basement uplifted depending on the SEE
extension of an underwater ridge forming the small islands
to the east of Kapıdag
˘Peninsula. In Erdek Bay the maxi-
mum thickness can be reached in front of the Go
¨nen River
as well as at the SE part of the basin; slightly more than 19
and 13 m, respectively (Fig. 6a). Similarly the unit
becomes thinner outwards of Erdek Bay, *4 m between
Karabiga Peninsula and Pas¸alimanıIsland. Unit C3 has
variable thickness between the Kapıdag
˘Peninsula and
Marmara Island depending on the sea-bottom morphology
(Fig. 6a). Hiscott and Aksu (2002) dated the base of Unit
C3 as 9,900 year BP (see Fig 5c and their Figs. 7,8). On
the basis of 15–50 cm thick sapropelic layer at depths
ranging from 0.90 to 2.35 m below sea floor, the topmost
part of Unit C3 was deposited between about 4,750 and
3,500
14
C year BP during a high global sea-level stand
(C¸ag
˘atay et al. 1999).
Unit C2: This unit is characterized by discontinuous,
parallel to sub-parallel, undulating reflections (Fig. 5a,
b;7a, b, c). At some localities the unit includes some pro-
grading clinoforms; e.g. offshore Kocasu River (Fig. 7d).
Fig. 4 Simplified geological map of the study area and its surround-
ings (modified from Yaltırak 2002). The most detailed geological data
representing offshore sedimentary units can be obtained from the
Marmara-1 borehole, near the shelf edge northwest of the Imralı
Island (Marathon Petroleum Turkey 1976)
Mar Geophys Res
123
Unit C2 unconformably overlies a deformed acoustic
basement (see Unit C1). The base of Unit C2 forms a major
shelf-crossing unconformity surface developed during the
last glacial period. The topography of the sequence
boundary between Units C3 and C2 becomes deeper, as
much as 95 m, from the Kapıdag
˘Peninsula towards Gemlik
Bay (Fig. 6b), implying that the subsidence in the bay was
much faster than that in Bandırma Bay. The same sequence
boundary in Erdek Bay, on the western side, becomes
shallower with a gentle slope towards the northwest
(Fig. 6b). Although the average thickness of Unit C2 ranges
from 6 to 10 m, it disappears outside the Bandırma Basin
Fig. 5 Interpreted Chirp seismic profiles illustrating the seismic stratigraphic units C1, C2 and C3 aline E3-4 in Erdek Bay, bline 15 in the
Bandırma Bay (see Fig. 3c for locations), cseismic units compared with other studies
Mar Geophys Res
123
(Fig. 6c). Unit C2 was dated to 23,000 year BP by Hiscott
and Aksu (2002) (Fig. 5c). On the basis of spatial and
temporal distributions of terrestrial and freshwater taxa
Mudie et al. (2002) indicated that freshwater conditions
were dominant along the southern Sea of Marmara region at
10,800 BP. McHugh et al. (2008) defined that the age of
lacustrine sediments to the south of the relatively active
Imrali Basin (Fig. 3a) were *11,800 year BP.
The paleoshoreline between the Imrali Basin and the
western end of Armutlu Peninsula was -90 m (Fig. 8a)
which becomes shallower westward up to -82.5 m pos-
sibly due to relative tectonic uplift (Fig. 8b, c). This
represents that the maximum water level of the Marmara
paleo-lake was -82.5 m below the present mean sea
level. The ocean basins are getting slightly larger since
the end of the last glacial cycle because of post-glacial
rebound, also called glacial isostatic adjustment (GIA).
Therefore the elevations of seismic units and paleoshor-
elines may be adjusted for GIA which is -0.3 mm/year
for this region (Toscano et al. 2011). In that case the
paleoshoreline between the Imrali Basin and the western
end of Armutlu Peninsula was between -93.5 and
-86.0 m with GIA. The Imrali ridge located between the
Marmara and Gemlik paleo-lakes caused a water-level
Fig. 6 a Isopach map showing sediment thicknesses of Unit C3. PI
Pas¸alimanıIsland, AI Avs¸a Island, KP Kapıdag
˘Peninsula, BP Biga
Peninsula AP Armutlu Peninsula, bdepth to the sequence boundary
between Units C3 and C2, cisopach map showing sediment
thicknesses of Unit C2 dpaleoshoreline of the study area representing
the time period of 30,000–11,300–11,000 year BP. BR Biga River,
GR Gemlik River, KR Kocasu River, BL Bandırma Lake, SMS South
Marmara Sill, IR ImralıRidge, IC ImralıCanyon
Mar Geophys Res
123
Fig. 7 Interpreted Chirp
seismic profiles illustrating athe
paleoshoreline and NAFMS
segments in Bandırma Bay,
bthe pressure ridge, NAFMS
segments and paleoshoreline in
Bandırma Bay cpaleoshoreline
in Gemlik Bay, dthe Armutlu
Bandırma segment in front of
the Kocasu River eE–W
trending fault south of Marmara
Island fnorthwest trending
normal faults in Erdek Bay. See
Fig. 3c for locations. ABS
Armutlu Bandırma segment,
NBS new Bandırma segment,
KES Kapıdag
˘Edincik segment,
BL Bandırma Lake, GL Gemlik
Lake
Mar Geophys Res
123
difference of 23 m (at least) between these two aquatic
environments.
Unit C1: This is the deepest sedimentary package con-
stituting the folded basement in the Chirp data. The inter-
face between Units C1 and C2 represents the upper surface
of the Early–Middle Pleistocene sediments identified in the
sea (Fig. 5a, b). Its internal stratification varies throughout
the study area from parallel divergent to undulating
reflections depending on the topography. Unit C1 represents
the deposits on the shelf formed during a period of relatively
faster sea level rise. This unit corresponds to Unit 1 defined
by Kus¸c¸u et al. (2009) and Unit 2b defined by Yaltırak and
Alpar (2002a) (Fig. 5c), which is older than 30,000 year.
Paleoshoreline
The Sea of Marmara is a transcontinental water passage
between the Mediterranean and Black Seas. The water
exchange between these two seas is controlled by two
respective sills. The first is located in the Strait of Istanbul
(Bosphorus) and the other is offshore S¸ arko
¨y to the east of
the Strait of C¸ anakkale (Dardanelles). Their depths are -35
and -70 m, respectively. These sills prevented a seawater
connection between Black Sea and Mediterranean Sea
during the later Quaternary (Stanley and Blanpied 1980)
while the sill in the Dardanelles also controlled the water
level of the Sea of Marmara during global lowstands
(Smith et al. 1995). Thus the water-level fluctuations of the
Sea of Marmara, limited in magnitude by the sill depth of
the Strait of Dardanelles, are small in amplitude (e.g.,
70 m) but enough to change its condition into a lacustrine
paleoenvironment (Aksu et al. 1999; Yaltirak 2002;
C¸ag
˘atay et al. 2002; Aksu et al. 2002; Kaminski et al.
2002). If we consider that the elevation of a paleoshoreline
has not changed since deposition, then the measured ele-
vation is equal to the sea level at that geological period. So
the evolution time of the paleoshoreline outlined from our
seismic data was defined regarding the bathymetric relation
between the sub-basins and the Sea of Marmara, as well as
considering the global sea-level curve given by Bard et al.
(1990,1996,2010) and Stanford et al. (2011).
The paleo-lake shoreline was identified depending on the
termination of lake deposits (Unit C2) on the coastal region
and the terrace-shaped geometry of the upper surface of Unit
Fig. 8 Interpreted seismic pinger (uniboom) profiles, oriented north–
south, illustrating the Armutlu-Bandırma segment (ABS) and the
paleoshorelines of the paleolake Gemlik (GL) and paleolake Marmara
(ML) aline 1–23, bline 39–59, cline 61–90, dline 120–145. See
Fig. 3c for locations
Mar Geophys Res
123
C2. This surface becomes shallower westward, from Gemlik
Bay to Bandırma Bay (Fig. 6b). In Erdek Bay it gets shallower
northwestward gradually with a slight slope (Fig. 6b). The
paleoshoreline could also be identified on the multibeam data
if it is integrated with some normal faults trending along the
shoreline; e.g. at the eastern part of Gemlik Bay (Fig. 7c).
Since the paleoshorelines correspond to 11,000–11,300 year
BP when the sea level overtopped the southern Marmara sill,
the total GIA correction was approximately 3.3 m for the
paleoshorelines. Considering GIA these shorelines, in other
words the highest terrace levels, were located at -50.3 m
(-53.6 m with GIA) in Bandırma Bay (Fig. 7a, b) and
-60.5 m (-63.8 m with GIA) in Gemlik Bay (Figs. 7c; 8a–
d).
The coastal features of a paleolake were outlined on the
seismic sections and occupied the basin in Gemlik Bay and
extended into the front of the Kocasu River mouth (Fig. 6d).
The paleolake was receiving drainage and fed by the paleo-
rivers in the region. To the east of ImralıIsland a long and
relatively narrow underwater valley at -60 m (-63.5 m
with GIA) water depth is the most outstanding sea-bottom
feature on the multibeam bathymetric map (Fig. 3b). This
canyon’s role can be explained by the existence of this
paleolake, as it must carry the lake waters into the deeper
basins of the Sea of Marmara and control the level of the
paleolake. The seismic data show another isolated paleolake
located in the vicinity of Bandırma Bay (Fig. 6d). It was
possibly discharging westward into Erdek Bay through a
water passage between the Kapıdag
˘Peninsula and its
mainland, which was closed by Belkis Isthmus at least
2,500 years BP (Ardel and Inandik 1957). On the multi-
beam bathymetry, some small-scale seafloor mounds
observed at the easternmost part of Erdek Bay (Fig. 6d)
may be dependent on an outward flow coming from the
Bandırma paleolake. The development of Belkis Isthmus,
which is placed on top of the highest part of an autoch-
thonous ridge lying between the Bandırma and Erdek
depression fields, is not well known. It is made up of two
opposite coastal spits, which are developed seaward from
the shores into the sea utilizing suitable promontories of the
autochthonous ridge, and then separated the bays of Ban-
dırma and Erdek. The swamp area in the central part was a
remnant of a lagoon (Ardel and Inandik 1957).
Structural setting and new fault segment
The NAFMS is made up of three segments between Ban-
dırma and Gemlik Bays (Fig. 9). The easternmost segment
is on land and is known as the Genc¸ali fault between the
southern coast of Lake Iznik and Mudanya. A west-trend-
ing active fault cuts the uppermost seismic unit C3 at the
eastern part of Gemlik Bay and extends towards the deep
basin of Gemlik Bay, in front of the northern part of the
Genc
¸ali delta and parallel to the coastline (Fig. 9). This
active fault was interpreted as a ‘‘new segment’’. At present
the Genc¸ali fault is no longer active and its slip has been
transferred to the new segment.
The second segment is an active fault, 75 km long from
the northern margin of Gemlik Bay to the southern part of
Bandırma Bay (Figs. 7a, b, d;8a–d). This segment, called
the Armutlu-Bandırma segment (ABS), is made up of three
sub-segments separated by small offsets. Such step-overs
are common features on long strike-slip fault systems.
In Bandırma Bay, the NAFMS makes a big offset
toward the southeastern shores of the Kapıdag
˘Peninsula
and is connected to the Edincik Fault along the southern
flank of the Erdek Bay trough (Fig. 9). It is called the
Kapıdag
˘-Edincik segment (KES) (Fig. 7a, b). The angle
between the KES (N59E) and the ABS at the south of
Bandırma Bay (N75E), which is 16°(Fig. 9), caused a
pressure ridge in the central part of Bandırma Bay
(Fig. 7b). Another N85E trending fault, the New Bandırma
Segment (NBS), is active and cut through the deepest part
of Bandırma Bay (Figs. 7a, b, 9).
Fig. 9 The structural model proposed for the study area on the basis of seismic reflection and multibeam bathymetric data. GF Genc¸ali fault,
ABS Armutlu-Bandırma segment, KES Kapıdag
˘-Edincik segment, NBS new Bandırma segment
Mar Geophys Res
123
Even though there are some secondary faults of the
NAFMS affecting the sediments at the southeastern margin
of Erdek Bay, most of the structural elements in this
westernmost basin are northwest-southeast trending normal
faults (Fig. 9) and are not deforming the seismic units
defined in this study (Fig. 7e, f). Another strike-slip fault
system (Fig. 7e), however, crosses and affects the sedi-
ments to the south of Marmara Island (Fig. 9).
Discussion
Unit C2 was deposited on the acoustic basement (Unit C1)
between 30,000 and 11,000–11,300 year BP, when the sea
level was below the southern Marmara sill (-51.2 m without
-3.3 m GIA). Parallel to subparallel, occasionally sigmoid
and oblique reflections of Unit C2 represent riverine and
lacustrine depositional environments. Its deposition depends
on the water depth and sea floor morphology. Unit C2 was
mentioned with different nomenclature in previous studies
(Fig. 5c); Unit 2 accreting sand bars by Aksu et al. (1999),
Unit 3-D2 by Yaltırak and Alpar (2002a) and Unit 2 by
Kus¸c¸u et al. (2009). Considering the depth of the S¸ arko
¨y sill
(-70 m) and the sea-level records given by Stanford et al.
(2011), the post glacial connection of the Sea of Marmara
with the Aegean Sea occurred between 12,350 and
12,800 year BP (Fig. 10). The paleoshorelines of the early
Holocene lake in the Gemlik basin (-60.5 m below present
mean sea level without GIA) and the Marmara lake margin
(which changed between -83 and -90 m below present
mean sea level, without GIA) at the Imrali Basin (Fig. 8a–c)
are directly related to this event. Unit C3 started to be
deposited on the southern Marmara shelf after sea level
overtopped the southern Marmara sill (Fig. 6d). In the pre-
vious studies this unit was also called a transparent Unit 1
mud drape (Aksu et al. 1999), Unit 3-D1 (Yaltırak and Alpar
2002a) and Unit 3 (Kus¸c¸u et al. 2009; Fig. 5c).
Two large paleolakes in Gemlik and Bandırma Bays can
be traced from the paleoshorelines at -60.5 m without
-3.3 m GIA (Figs 7c, 8a–d), -50.3 m without -3.3 m
GIA (Fig. 7a, b) and from the multibeam bathymetry where
the shorelines are fault controlled (Fig. 6d). This setting is
similar to the present topographic conditions observed
between the Sea of Marmara and the shallow freshwater
lakes in the southern Marmara region, which are deposi-
tional areas on the courses of main rivers. With an elevation
of 15 m above the present mean sea level, Lake Manyas
reaches a depth of 3 m. On the other hand, the water level of
Lake Uluabat is ?1 m above sea level, since it is connected
to the Sea of Marmara by the Kocasu River (Fig. 4).
The boundaries of the paleolake we defined in Gemlik
Bay are somewhat different than those given by Yaltirak
and Alpar (2002a, their Fig. 11J). The Gemlik paleolake
was fed by the surrounding rivers and discharged into the
ImralıBasin located to the east of ImralıIsland (Fig. 6d),
similar to the Kocasu River connecting the Lake Uluabat to
the Sea of Marmara today (Fig. 4).
The paleolake in Bandırma Bay, on the other hand, was
not controlled by rivers. It was discharging into Erdek Bay
via a paleo-channel located at the southern margin of the
Kapıdag
˘Peninsula before the modern isthmus was devel-
oped (Fig. 6d). The lack of any erosional truncation surface
related to a paleoshoreline in Erdek Bay and the paleo-river
observed on the multibeam data indicate that a riverine
regime was dominant in the region with poorly drained
marsh areas and plains during early phase of sea level rise
(Fig. 6d).
Contrary to a single fault segment as proposed by Ku-
rtulus¸ and Canbay (2007), the NAFMS is a right-lateral
strike-slip fault that is made up of three main segments in
the sea with step-overs (Fig. 9). The Armutlu-Bandırma
segment cuts through the seismic units C1 and C2
(Figs. 7a, b, d, 8) and partly affects the uppermost marine
sediments (Unit C3) younger than 11,000–11,300 year BP
(Fig. 8a, b, d). As far as it is known no big earthquakes
have occurred on this segment for the last few thousand
years (e.g., Guidoboni 1994; Ambrasseys 2009).
The northwest–southeast faults in Gemlik Bay have
evolved over the Thrace-Eskisehir Fault system (Fig. 1).
They were cut through by the NAFMS, giving way to the
formation of extensional step-over geometry. Under the new
tectonic regime, Gemlik Bay opened as a pull-apart basin
between the Genc¸ali fault and Armutlu-Bandırma segment
(Fig. 9), similar to the 30°extensional sidestep model given
by Dooley and McClay (1997). This is in agreement with the
models proposed by Barka and Kus¸c¸u (1996), Yaltırak and
Fig. 10 The elevation of the ridges controlling water connections in
the Sea of Marmara depicted on the glacio-eustatic sea level changes
for the last 20,000 year BP given by Stanford et al. (2011). See Fig. 1
for S¸ arko
¨y sill level and Fig. 3b for southern Marmara sill and Imralı
ridge
Mar Geophys Res
123
Alpar (2002a) and Gasperini et al. (2011). The pull-apart
system, which started to evolve with the Genc¸ali fault,
transformed into a new regime (NS) parallel to the evolution
of the paleolake of Gemlik at 30,000 BP when the sea level
was -60.5 (-3.3 m GIA) (Fig. 11a) and the NAFMS took
over a new fault between Lake Iznik and Gemlik Bay
(Fig. 9). The mouth of the main stream which formed the
Genc¸ali delta at that time was located somewhere to the
north of the actual Kocadere stream delta at the eastern edge
of the bay (Fig. 11b). The delta front, which was forming the
eastern coastline of the paleolake, was cut through by the
W-trending new segment (Fig. 9). A right-lateral narrow
Fig. 11 a Sequence
stratigraphic interpretation of
observed stratigraphic
architecture and proposed
chronostratigraphic framework,
based on correlation of seismic
units in Gemlik Bay with late
quaternary glacio-eustatic sea
level changes. Sea level curve
after Chappell and Shackleton
(1986) and Bard et al. (1990),
recent 20,000 year is from
Stanford et al. (2011)bseismic
lines given in Fig. 12 (Kusc¸u
et al. 2009) superimposed on the
multibeam bathymetry, cthe
total displacement occurred on
the shoreline of the progressive
delta during the last
30,000 years on the multibeam
bathymetry map
Mar Geophys Res
123
and rectilinear slip of the paleoshoreline can be seen on the
morphobathymetric data, with an offset of 60 ±5m
(Fig. 11c). Considering the evolution of the Gemlik paleolake
of during the last 30,000 year BP, the lateral slip rate on the
NAFMS corresponds to 2 mm/year, which is consistent with
geodetic models given by Straub et al. (1997), McClusky et al.
(2000), Meade et al. (2002) and Ergintav et al. (2007).
Using the same lacustrine delta displacement on a lobate
topographic high, Gasperini et al. (2011) estimated the hor-
izontal slip rate for the NAFMS on the order of 4 mm/year.
The researchers suggested that the delta front was inactive
and passively displaced by the NAFMS when marine con-
ditions started 11,000 year BP. However, there was no sea
connection between the Gemlik and Marmara paleolakes
when the sea level was below -60.5 m. Therefore the
coastline of the isolated paleolake stayed approximately at
-60.5 m (with a slight decrease and subsequent increase)
when global sea level was below the Imrali canyon’s depth.
In that case the deltaic sequence above -60.5 m in the
seismic sections was started at 30,000 BP and ended
(drowned) at 11,300–11,000 year BP. This can be supported
by the lacustrine delta front representing a descending tra-
jectory progressive morphobathymetric shoreline as
observed on sections 20, 21 and 22 in Fig. 12. During the
development of the progressive shoreline of the Gemlik
paleolake, the upper parts of the progressive deltas were
eroded at some localities and a natural scarp was formed in
front of the delta lobe to the west (Line 23 in Fig. 12). The
age of the erosion surface of the natural scarp, where we
calculate the total offset on multibeam bathymetry, is
30,000 year. Therefore we suggest the horizontal slip rate for
the NAFMS was on the order of 2 mm/year. In addition, the
core Marm05–124 of Gasperini et al. (2011) is close to the
mouth of the modern Kocadere stream, which cannot rep-
resent such a displacement (Fig. 11b). Naturally the core
locality represents only a coastal plain at 11,000 year BP
which was later drowned by the rising sea-level in the Sea of
Marmara. Therefore the estimated slip rates given by
Gasperini et al. (2011) and their calculation for the amount of
stress accommodated along the NAFMS are not consistent
Fig. 12 Re-interpreted shallow Chirp seismic profiles published by
Kusc¸u et al. (2009). The data are recorded on the topographic high of
the lacustrine delta drowned after the last episode of sea level rise and
given in Fig. 11b. Yellow lines show the new segment developed on
the NAFMS while the red arrows show the prograding foresets of the
lower and upper chronostratigraphic boundaries. NS new segment
Mar Geophys Res
123
sufficiently either with the available geodetic models (Straub
et al. 1997; McClusky et al. 2000; Meade et al. 2002; Er-
gintav et al. 2007) or with other interpretations on total dis-
placement (Yaltırak 2002; Yaltırak and Alpar 2002a).
Bandırma Bay is interpreted as a rectangular transpres-
sional basin developed under the control of the 16°angle
difference between the segments of Kapıdag
˘-Edincik and
Armutlu-Bandırma, which are bordering the shorelines of
the Kapıdag
˘Peninsula and the southern coastline of the
bay, respectively (Fig. 9). Considering the faults affecting
the younger deposits and bordering the pressure ridge
(Fig. 7b), a younger W-trending fault (NBS) was mapped
between the oblique segments of Kapıdag
˘-Edincik and
Armutlu-Bandırma (Fig. 9). In large scale similar mor-
phological elements to those in the Bandırma Bay can be
seen in the western Marmara trough (Yaltırak 2002; Yal-
tırak and Alpar 2002b). The difference between these
basins in their size and depths can be explained by the
faster lateral movement of the NAFNS (19 mm/year)
according to that of NAFMS (2 mm/year). Meanwhile the
transpressional deformations experienced by strike-slip
shear and component shortening due to southwestward
bending of the faults, in concordance with the horizontal
velocity field (see GPS vectors in Fig. 3a; Ergintav et al.
2007), resulted in oblique shear in both basins. If Bandırma
Bay had been deepened as a transtensional basin due to
step-over geometry, then the deepest part of the basin and
the thickest deposits would have been at the NE margin of
the basin and in front of a NW–SE oriented normal fault. In
contrary the deepest sea bottom and the thickest deposits
are located at the western margin, where Bandırma Bay
becomes narrow. Therefore the development of the Ban-
dırma Basin depends on the existence of a thrust compo-
nent in addition to the strike-slip components of the
boundary faults.
The NWW–SEE trending normal faults in Erdek Bay
have no effect on the seismic units C2 and C3 (Figs. 7e, f, 9).
These faults may have developed before the NAF regime
when the TEF was active in the region. Moreover, Erdek Bay
developed as a passive basin, even though the southeastern
margin of Erdek Bay is under the control by the secondary
faults of the NAFMS.
Conclusion
The seismic data taken from southern Marmara sub-basins
present three seismic units which indicate that the Sea of
Marmara experienced fluctuations in sea level. The most
characteristic seismic unit is made up of lacustrine-fluvial
sediments (Unit C2) overlying unconformably an acoustical
basement (C1) and overlain by the internally parallel
reflectors of marine deposits (C3). Following the post-
glacial connection of the Sea of Marmara with the Aegean
Sea (12,350–12,800 year), two paleolakes were still in
Gemlik and Bandırma Bays, respectively. Considering
global isostatic adjustment, which is about 3.3 m for the last
11,000 years, the water levels in these lakes were limited by
the sill depth of the Southern Marmara Sill, and can be
rounded to -55 m. This sill controlled the marine incursion
of these sub-basins by the Sea of Marmara until
*11,300–11,000 years BP depending on the modelled sea-
level probabilities given by Stanford et al. (2011). Before
the marine incursion the shorelines of the Gemlik and
Bandırma paleolakes were located approximately -64 and
-54 m below the present sea level, respectively. The
Gemlik paleolake was discharging into the Imralıbasin via
the Imralıcanyon which was approximately -63 m bmsl.
Gemlik Bay opened between the Armutlu-Bandırma
fault segment and the Genc¸ali Fault as a pull-apart basin.
The northwest-southeast trending fault systems, which are
bounding the bay and extending into the Sea of Marmara,
were developed on the remnants of the Thrace-Eskisehir
Fault. This active pull-apart system was cut through with a
new W-trending fault segment extended from the Lake
Iznik into Gemlik Bay for at least the last 30,000 years. Its
right-lateral offset on the lacustrine delta drowned after the
last episode of sea level rise is 60 ±5 m, which corre-
sponds to a slip rate of 2 mm per year.
The Armutlu-Bandırma segment of the NAFMS, which
is 75 km long from the northern margin of Gemlik Bay to
the southern part of Bandırma Bay, is made up of three sub-
segments separated by short oversteps. The western sub-
segment of Armutlu-Bandırma is divergent to the Kapıdag
˘-
Edincik segment forming a rectangular transpressional
basin. A new west-east trending fault (NBS) cuts this
system causing a pressure ridge at the southern margin of
Bandırma Bay. Finally, Erdek Bay in the west is a passive
basin under the control of northwest-southeast trending
faults.
Acknowledgments This study was supported by the Scientific
Research Fund of Istanbul University under the projects of O
¨NAP-
2914 for Chirp data acquisition in Erdek Bay and around the Marmara
Islands, TP-6527 for seismic profiling between Bandırma and Gemlik
Bays and UDP-36083 for a travel grant. We thank the officers and
crew, as well as the scientists and technicians onboard the TCG
C¸ ubuklu and TCG C¸es¸me of the Turkish Navy, Department of
Navigation, Hydrography, and Oceanography, for multibeam and
seismic data. The authors thank to Dr. Ali Aksu for seismic lines from
Marmara Sea Gateaway project and research assistant Irem Elitez for
her drawings of topographic and bathymetric maps.
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Project
The main scope of this project is to determine and model the near surface deformations and its related structural elements of the northern branch of the North Anatolian Fault (NAF), which is the mo…" [more]
Project
Earth sciences studies carried out in the Marmara Sea shelves are inadequate. In particular, land-sea interactions of structural elements pose a significant threat the civil life due to the possibl…" [more]
Article
October 2002 · Marine Geology
    The Gemlik Bay is developed as a pull-apart basin during the late Pliocene-early Pleistocene mainly controlled by west-trending dextral strike-slip faults along the middle strand of the North Anatolian Fault zone, with the NW-trending Thrace-Eskişehir Fault playing secondary role. The North Anatolian Fault reached the eastern Marmara Sea ∼3.5 Ma ago, where its middle strand intersected the... [Show full abstract]
    Conference Paper
    November 2007
      Lake Iznik is a fresh water lake in the Marmara region and located on a highly tectonically active region along a plate boundary. Numerous destructive earthquakes occurred in the last 2,000 years, a few events accompanied with some abnormal waves. Due to its thick sedimentary deposits, high resolution seismic reflection data can only show uppermost sedimentary and tectonic processes. The... [Show full abstract]
      Article
        High resolution Chirp and Sparker data allowed definition and mapping of distinct seismic units in the shallow sediment record (~100 ms) acquired from the southern exit of the Bosphorus Strait; a dynamic depositional environment. The bottommost unit observed in the Chirp data (unit-3) is made up of marine-lacustrine sediments thinning seaward and onlaps the basement rocks which are represented... [Show full abstract]
        Article
          The EIznik Basin is an active depression created by a series of faults developed in relation to the Middle Strand of the North Anatolian Fault (NAFMS). The most important of these faults is the oblique Sölöz fault, which runs parallel to the NAFMS. It is interpreted as a releasing bend, and plays a crucial role in the evolution of the 75-m-deep ellipsoid-shaped depression in the southern part... [Show full abstract]
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