Turkish Journal of Earth Sciences - Universiteit Utrechtforth/publications/Uzel_2010.pdf · Batı Anadolu’ da Aktif Olarak Gelişen Süperimpoze Bir Havzanın Neotektonik Evrimi:

Turkish Journal of Earth Sciences

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doi:10.3906/yer-0910-11

Neotectonic Evolution of an Actively Growing Superimposed Basin in

Western Anatolia: The Inner Bay of zmir, Turkey

BORA UZEL, HASAN SÖZB L R & ÇA LAR ÖZKAYMAK

Dokuz Eylül University, Department of Geological Engineering, Tınaztepe Campus,

TR 35160, Buca- zmir, Turkey

Corresponding author: Bora UZEL (e-mail: [email protected])

Please cite this article as: UZEL, B., SÖZB L R, H. & ÖZKAYMAK, Ç. Neotectonic Evolution of an Actively Growing Superimposed Basin in Western Anatolia:The Inner Bay of zmir, Turkey Turkish Journal of Earth Sciences [Turkish J. Earth Sci.] (2010) [in press].

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Neotectonic Evolution of an Actively Growing Superimposed Basin in Western Anatolia: The Inner Bay of İzmir, Turkey

BORA UZEL, HASAN SÖZBİLİR & ÇAĞLAR ÖZKAYMAK


TR−35160, Buca-İzmir, Turkey

Corresponding author: Bora UZEL

(e-mail: [email protected])

Abbreviated title: Neotectonic Evolution of the Inner Bay of İzmir

Neotectonic Evolution of an Actively Growing Superimposed Basin in Western Anatolia:

The Inner Bay of İzmir, Turkey

BORA UZEL, HASAN SÖZBİLİR & ÇAĞLAR ÖZKAYMAK


TR−35160, Buca-İzmir, Turkey (e-mail: [email protected])

Abstract: The İzmir Bay is an actively growing shallow marine basin that is controlled by

NE, NW, N–S and E–W trending active faults, in the West Anatolian Extensional Province.

The bay of İzmir is a lazy L-shaped superimposed basin which topographically divided into

an E–W-trending inner bay and a NW-trending outer bay. The Inner Bay of İzmir is an

approximately 5–7-km-wide, 25-km-long asymmetric graben structure and it comprises (i)

upper Cretaceous–Paleocene basement, (ii) an older succession of lower- to upper- Miocene

basin fill, angularly unconformably overlain by (iii) a younger Plio–Quaternary basin fill. The

older succession contain a 0.5-to 1.5-km-thick, folded and coal-bearing continental volcano-

sedimentary sequence. The younger succession of the Inner Bay of İzmir include late

Pliocene–Pleistocene Görece formation and Holocene to recent alluvial fan, fan delta to

shallow marine deposits.

This study reveals that the İzmir Bay region was above sea level and the site of NE–SW

trending lacustrine environment associated with calc-alkaline to alkaline volcanism during the

early to late Miocene. By the late Pliocene the modern coastal areas of İzmir was concealed

beneath the waters of the Aegean sea by the creation of E–W trending Inner Bay of İzmir.

According to detailed geological mapping, geomorphological evidences and computer-

based kinematic analysis, the tectonic evolution of the basin since the early Miocene can be

divided into four stages. The former two extensional stages have resulted in the formation of

NE-SW trending lacustrine volcano-sedimentary basins; the third stage is characterized by

dip- to strike-slip faulting caused to deformation of the older basin fill units and the last

extensional stage operated since the Late Pliocene resulted in the opening of the Inner Bay of

İzmir.

Key words: The İzmir Bay, İzmir fault zone, Karşıyaka fault zone, Seferihisar fault zone,

fault kinematics, superimposed basin, western Anatolia.

Batı Anadolu’ da Aktif Olarak Gelişen Süperimpoze Bir Havzanın Neotektonik Evrimi:

İzmir İç Körfezi, Turkey

Özet: Batı Anadolu Genişleme Bölgesi içerisindeki İzmir Körfezi KD, KB, K–G ve D–B

uzanımlı faylar tarafından kontrol edilen ve aktif olarak gelişmekte olan sığ denizel bir

havzadır. Körfez topografik olarak D–B doğrultulu iç körfez ve KB-GD uzanımlı dış körfez

olmak üzere iki kısımdan oluşan L-şekilli superimpose bir havzadır. İzmir İç Körfezi yaklaşık

5–7-km genişliğinde, 25-km uzunluğunda, D–B gidişli ve bölgesel ölçekli açısal

uyumsuzluklarla birbirinden ayrılan (i) geç Kretase–Paleosen yaşlı temel kayaları, (ii) erken

Miyosen–erken Pliyosen yaşlı eski havza çökelleri ve (iii) Pliyo–Kuvaterner yaşlı genç havza

çökellerinnden oluşur. Eski havza çökelleri 0.5–1.5-km kalınlığındaki kıvrımlanmış ve

yüzeylemiş olan kömür içerikli karasal volkanosedimanter bir istif içerir. İç Körfeze ait genç

havza çökelleri Görece formasyonu ve güncel alüvyonal çökelleden yapılıdır.

Bu çalışma İzmir Körfez alanının erken–geç Miyosen zaman aralığında kalk-alkali ve

alkali volkanizmanın eşlik ettiği deniz düzeyi üzerindeki KD–GB uzanımlı gölsel havzayla

simgelendiğini göstermektedir. Geç Pliyosen’ den itibaren İzmir Körfezi Ege Denizi suları

altında kalmaya başlar ve böylece D-B uzanımlı İzmir İç Körfezi’ nin oluşumu gerçekleşir.

Detaylı jeolojik haritalama, jeomorfolojik veriler, bilgisayar tabanlı kinematik analiz

çalışmaları ve arazi gözlemlerine göre havzanın erken Miyosen’ de başlayan tektonik evrimi

dört evreye ayrılabilir. İlk iki evre KD–GB uzanımlı gölsel volkanosedimenter havzanın

oluşumunu sonuçlamıştır, üçüncü evre eski havza dolgusunun deformasyonuna neden olan

eğim atımlı ve doğrultu atımlı faylanmanın gelişimiyle karakteristiktir, geç Pliyosen’de

başlayan son genişleme evresi İzmir İç Körfezi’ nin açılmasına neden olmuştur.

Anahtar kelimeler: İzmir Körfezi, İzmir fay zonu, Karşıyaka fay zonu, Seferihisar fay zonu,

fay kinematiği, superimpose havza, Batı Anadolu.

Introduction

The İzmir Bay is a typical depression for the Aegean back-arc domain undergoing N–S

extension which is accommodated by active dip- to oblique-slip normal faults and strike-slip

faults. Major part of the modern depression is flooded by the waters of Aegean Sea, forming

the inner bay of İzmir. It is generally accepted that the Aegean Sea started to open as a NW–

SE trending narrow channel in the Serravalian–Tortonian, and widened under the influence of

N–S extensional regime in the Pliocene (Görür et al. 1995). However, western Anatolia next

to the Aegean Sea was the site of lacustrine basin sediments and terrestrial volcanism during

the Neogene time. In the late Pliocene–Pleistocene to Holocene, the Neogene basin in western

Anatolia was invaded while the İzmir Bay was the site of fan-delta to shallow marine

deposition. The back-arc tectonic environment of the Aegean subduction system has been the

sites of extensional back-arc basins since the Late Oligocene. These basins have been

described as a result of extension in response to the retreat of the subducting African plate

under the Eurasian plate (Jolivet 2001). GPS velocity vectors and earthquake slip vectors

show a counterclockwise rotation with southwestward motion of western Anatolian plate into

the Aegean realm along its boundary structures; dextral North Anatolian Fault Zone and

sinistral East Anatolian Fault Zone (Oral 1994; Louvari 2000; Reilinger et al. 2001;

McClusky et al. 2000, Aktuğ & Kılıçoğlu 2006; Figure 1a).

This study shows the existence of at least two generations of basins that are superimposed

in the İzmir bay region. The term of “superimposed basin” is used for a basin type which

includes at least two sediment fills of dissimilar age, origin, facies, internal structure, and

deformational pattern (Koçyiğit 1996). This terminology was mostly adapted on

understanding of multi-deformational history of hydrocarbon-bearing basins and salt tectonics

(Liangjie et al. 2001). In Turkey, many superimposed basins located mostly in or adjacent to

active strike-slip fault zones (e.g. North Anatolian Fault Zone) cutting across suture zones

(Koçyiğit & Kaymakçı 1995; Koçyiğit 1996). This type of basin has a key role in

understanding the deformational phases which responsible for the formation and deformation

pattern of the basin. To verify this, 1/25.000 scaled field geological mapping was carried out

at the inner coastal parts of the İzmir Bay. During the field studies the lithostatigraphical units

and their geological structures were mapped and a number of fault sets were studied in order

to collect kinematic data for paleostress analyses. This contribution allows us (i) to outline the

distribution of superimposed main rock units that episodically forming on each other, (ii) to

establish main faults which are responsible for each deformation phase (iii) to know how and

when the inner bay of İzmir begin to form, and (iv) to show a validity of superimposed basin

including sedimentary packages of different age and orientation on the basis of stratigraphic

and structural data. This work is also important for the active tectonics of İzmir city and

surrounding area where several seismic events happened in the past.

Tectonic Framework of the Region

The basement in the study area is represented by the Bornova flysch zone, whose sedimentary

sequence was strongly folded and dynamically metamorphosed during the early Tertiary

Alpine orogenic event (Erdoğan 1990; Okay & Siyako 1993; Okay et al. 1996; Okay &

Altıner 2007). West of the Bornova flysch zone is represented by a well-defined metamorphic

core complex, the Menderes massif, while east of the zone is characterized by platform

carbonates of Paleozoic-Mesozoic age (the Karaburun platform). These basement rocks are

unconformably overlain by Miocene volcanosedimentary basins having E–W and NE–SW

orientations (Figure 1 & 2).

Field-oriented studies in western Anatolia revealed that the E–W trending Miocene basins

are bounded by approximately E–W-oriented low- and high-angle normal faults (Koçyiğit et

al. 1999; Bozkurt 2000, 2001; Sözbilir 2001, 2002; Bozkurt & Sözbilir 2004, 2006; Emre &

Sözbilir 2007; Çiftçi & Bozkurt 2007, 2008, 2009). The low angle normal faults (detachment

faults) that are kinematically linked with a crustal-scale metamorphic core complex, the

Menderes massif, and approximately E–W and NE–SW dissecting basins form the most

prominent features of western Anatolia (Hetzel et al. 1995; Bozkurt & Oberhansli 2001;

Gessner et al. 2001; Isik & Tekeli 2001; Ring et al. 2003 and references therein; Figure 1).

Detachment fault systems in this province are associated with domal uplift of the Menderes

metamorphic core complex of the lower plate and the formation of asymmetric

supradetachment basins in the upper plate. However, there are some studies revealing the

presence of a number of NE–SW trending strike-slip faults controlling the NE-trending

Miocene deposition on the western Anatolian crust onshore (Kaya 1981; Genç et al. 2001;

Kaya et al. 2004; Erkül et al. 2005a; Uzel & Sözbilir 2006, 2008; Kaya et al. 2007; Sözbilir et

al. 2008) and offsore (Ocakoğlu et al. 2004, 2005). This transversely orientated strike-slip-

dominated zone that accommodated the lateral termination of E–W-trending graben-faults,

linking spatially discrete loci of extension, includes the İzmir-Balıkesir Transfer Zone (Figure

1b). Along the zone, the main structural contacts between the tectonostratigraphic units were

reactivated as transtensional shear zones and resulted in NE–SW trending elongated basins of

Miocene age. Several strike-slip faults have moved contemporaneously with the normal faults

which resulted in alongated Cumaovası basin, south of the study area (Uzel & Sözbilir, 2008).

Therefore, the İzmir-Balıkesir Transfer Zone has been described as a NE-trending strike-slip

dominated zone of weakness limiting the eastern coastlines of the Aegean Sea that lies

between Balıkesir and İzmir cities (Okay & Siyako 1991; Ring et al. 1999; Sözbilir et al.

2003a 2003b; Erkül et al. 2005b; Kaya et al. 2007; Sözbilir et al. 2007; Özkaymak & Sözbilir

2008; Uzel & Sözbilir 2008). Thus, the structural evolution of the İzmir Bay region has been

controlled to a large extend by reactivation of ancient tectonic structures.

The İzmir Bay

The morphology of the Aegean coast of Anatolia is characterized by numerous bays (Figures

1b & 2). From south to north, these are the NE-directed Fethiye, E–W-directed Hisarönü, E–

W-directed Gökova, NE-directed Güllük, E–W-directed Kuşadası, NNW-directed Sığacık, E–

W- to NW-directed İzmir, NE-directed Çandarlı, NW-directed Dikili, and E–W-directed

Gökova Bays. The İzmir Bay which is one of the most distinctive bays of the Aegean Sea

located to the western coast of Anatolia. It’s a lazy L-shaped basin controlled by NE-, NW-

and E–W-trending active faults and can be divided into two depressions based on their surface

and subsurface morphology: the Inner Bay and Outer Bay (Figures 2 & 3). The leg of the

‘‘L’’ defines the Outer Bay of İzmir (Aksu et al. 1987; Sayın 2003; Sayın et al. 2006). It is

about 20-km-wide, 40-km-long, NW-trending basin, bounded by the Karaburun Peninsula to

the southwest and the Foça high and the Menemen plain to the northeast. Along the onshore

Urla-Mordoğan district, there are a series of NW-trending islands and intrabasinal highs.

Here, the Outer Bay of İzmir partitioned with another depression named the Gülbahçe Bay.

The base of “L” interpreted as the Inner Bay of İzmir is approximately 5–7-km-wide and 25-

km-long E–W-trending basin (Figure 3). The fault pattern and seismicity of the İzmir region

has previously been analyzed for earthquake hazard assessment (summarized and published in

İzmir Earthquake Scenario and Master Plan - Radius Project), basin formation and fault

kinematics. Their interrelationships are still open questions. Thus, we present our field-based

geological data and surface/subsurface morphological observations on the Inner Bay of İzmir

that can shed light on its tectonic evolution.

Surface and Subsurface Morphology

The Inner Bay of İzmir is an E–W-directed depression clearly outlined on topographic

elevation map of the region (Figure 3a). The horst of the Inner Bay of İzmir includes three

topographic domains: (i) the Yamanlar High to the north and (ii) the Seferihisar and (iii)

Nifdağı Highs to the south of the bay. The top point of the Yamanlar High is the Kara

Mountain with an altitude of 1076 m. The Yamanlar High has a typical volcanic morphology

which is characterized by a radial drainage pattern (Figure 3b). The top point of the

Seferihisar High is the Tekke Mountain of 1017 m altitude. The northern part of the Tekke

Mountain is characterized by dendritic drainage pattern including approximately north-

flowing rivers. To the NE-side of the Tekke Mountain, the north-flowing rivers suddenly

change their orientation to the NW-direction, which may indicate the presence of a NW–SE

trending fault in the footwall of the İzmir fault zone. The onshore part of the İzmir Bay is

characterized by the E–W-trending Bornova plain which is bounded by Nifdağı High to the

south.

On the subsurface bathymetric map of the İzmir Bay, it is also clear that the İzmir Bay

has two different depression areas: a NW-trending Outer Bay and an E–W-trending Inner Bay

(Figure 3b). Based on bathymetric data carried out by previous studies (Akyarlı et al. 1988;

Alpar et al. 1997; Sayın 2003; Sayın et al. 2006), the maximum water depth is about 70 m in

the Outer Bay, and about 20 m in the Inner Bay. The Inner and Outer Bay depressions are

separated by a narrow threshold named as the Yenikale strait.

Stratigraphy

The rock units exposed in the study area are divided into three groups as (i) the basement, (ii)

older basin fill and (iii) younger basin fill (Figures 4 & 5). Brief descriptions of these units are

given below.

Basement Units

The basement of the basins around Izmir city is characterized by a series of NE-trending

discontinuities, identified in outcrops in the Seferihisar, Spildağı, Nifdağı, and Yamanlar

Mountains. The Bornova mélange (also called the ‘Bornova flysch zone’) forms the basement

of the Miocene to Quaternary units. The Bornova mélange is believed to be related to the

closure of Neotethys Ocean during the late Cretaceous-Paleocene time interval (Erdoğan

1990; Okay & Siyako 1991). It is composed of various-sized blocks of Mesozoic limestones,

cherts, submarine volcanics and serpentinites embedded in a flysch-type sedimentary matrix

(Okay et al. 1996). The Bornova mélange has undergone significant deformation, with a very

low metamorphic grade (Erdoğan 1990; Okay & Siyako 1993; Okay & Altıner 2007). The

details of the stratigraphy of the pre-basin-fill units lie outside the scope of this paper, and the

reader is referred to the most recent literature (Erdoğan 1990; Okay & Siyako 1993; Okay et

al. 1996; Bozkurt & Oberhansli 2001; Okay & Altıner 2007; Okay 2008) for further reading.

The older basin fill

The Miocene stratigraphy of the older basin fill can be subdivided into a lower and an upper

volcano-sedimentary sequence, separated by a regional angular unconformity (Figures 4 & 5).

The lower volcano-sedimentary sequence is well-exposed within and beyond the northern

margin of the incipient Inner Bay of İzmir, and along the Orhanlı fault zone (Figure 4). It is

moderately folded and cross-cut by normal and strike-slip faults. This sequence, consisting

primarily of conglomerates at the base, limestones, mudstones, and sandstone-shale

alternations, unconformably overlies the basement rocks. It consists of three sedimentary units

overlain by the Yamanlar volcanics. The basal section of the lower sequence is here firstly

named as the Kızıldere formation (Figures 5 & 6). Around the Menemen, a basal

conglomerate overlies an erosional surface of sandstone-shale alternation of the Bornova

mélange. The dominant lithology of the formation is made up of brownish-red, thick bedded

to massive, poorly to moderately sorted polymictic conglomerates. Clasts are in range of

pebble size and were mainly derived from the Bornova mélange. The conglomerates alternate

with gray-reddish-brown colored sandstone, siltstone and shale. Upward in the sequence, the

formation ends with a yellowish brown lacustrine limestone level. The Kızıldere formation

can be interpreted as an alluvial to fluvial sequence overlain by lacustrine carbonates.

At the southern sector of the Inner Bay of İzmir, the lithology of lower sequence

characterized by the Çatalca formation (Genç et al. 2001), which is composed of laminated

siltstones, sandstones and shale alternations including lignite lenses and thin bedded

conglomerate levels. The formation is interpreted as a lacustrine-fan delta facies and dated as

lower−middle Miocene based on paleontological and palynological studies (Akartuna 1962;

Kaya 1979, 1981; Genç et al. 2001; Sözbilir et al. 2004; Uzel & Sözbilir, 2008). The lateral

equivalent of the Çatalca formation north of the İzmir Bay is the Sabuncubeli formation,

cropping out between the Bornova and Kayadibi villages and north of Beşyol village. It is

composed of thick bedded conglomerate, sandstone and mudstone alternation with limestone

lenses toward the top (Figure 6b).

The overlying unit is made up of calcalkaline volcanic rocks known as the Yamanlar

volcanics, which conformably rest on the sedimentary rocks described above (Kaya 1979,

1981). In the study area, the Yamanlar volcanics are composed of several lavas, pyroclastic

rocks, dykes and domes of dacitic, andesitic, rhyolitic and basaltic compositions. K-Ar ages of

19.2–14.7 Ma have been reported for the Yamanlar volcanics (Borsi et al. 1972; Savaşçın

1978; Ercan et al. 1996), indicating an early to middle Miocene age.

The upper volcano-sedimentary sequence is exposed at Cumaovası basin and NE of

Bornova district. According to field observations and geological mapping, it is slightly

deformed, folded and faulted. In the northern sector, the sequence begins with the Kızılca

formation resting unconformably on the Yamanlar volcanics. The Kızılca Formation is a

package of terrestrial clastic rocks, intercalated with lacustrine carbonate levels. The

formation is made up of brown, poorly sorted alluvial conglomerates at the base, passing

upwards into greyish-brown sandstones and mudstones. The alluvial conglomerates contain

clasts derived from the Yamanlar volcanics and lacustrine carbonates of the lower volcano-

sedimentary sequence and the Bornova mélange. The succession ends with a light-grey and

yellowish-white clayey limestone intercalation at the top and is gradationally overlain by a

carbonate-dominated sequence forming the Yaka formation. At the transitional contact

between these two units, the Beşyol basalt is located. The Beşyol basalt is characterized by

dark-brownish colored olivine basalt lavas showing peperitic texture at the contact with the

lacustrine carbonate of the Yaka formation. The age of this formation is accepted as late

Miocene according to the stratigraphic correlation of the successions in the neighboring

basins (see Cumaovası basin, Uzel & Sözbilir 2008).

In the southern sector, the upper volcano-sedimentary sequence begins with the Ürkmez

formation (Eşder & Şimşek 1975; Genç et al. 2001) which is dominated by red conglomerate

and sandstone alternated with lacustrine limestone lenses. Upward in the sequence, lithology

displays a fining-upward profile where the conglomerates are replaced gradually by gravels,

sandstones and mudstones. According to Genç et al. (2001), the Ürkmez formation is of latest

middle(?)–late Miocene in age, and is interpreted as alluvial fan and lateral fan deposits

interfingering with low energy lacustrine facies. These clastic rocks are interbedded with

lacustrine limestones of the Yeniköy formation in the upper parts of the unit (Eşder & Şimşek

1975; Genç et al. 2001). The Yeniköy formation consists of sandstone, mudstone and

claystone alternations with thin lignite seams. Upward, the sequence is dominated by thin- to

medium-bedded lacustrine limestones and green laminated claystone alternations. These are

interbedded with pyroclastic rocks of the Cumaovası volcanics (Eşder & Şimşek 1975;

Özgenç 1978; Genç et al. 2001). The outcrops of the Cumaovası volcanics are aligned in

NNE–SSW direction forming ‘central volcanics’ for the basin. The Cumaovası volcanics

yielded 11.5–9 My K/Ar ages (Borsi et al. 1972; Özgenç 1978; Genç et al. 2001). They are

mostly rhyolitic pyroclastic rocks and lava flows with local domes. Genç et al. (2001)

suggested that the Cumaovası volcanics begin with air fall tuffs of about 15 m thickness,

forming early products of the volcanic activity. They are overlain by pyroclastic flow

deposits, which are commonly composed of fragments of angular lava within a pumice

matrix. These are intercalated with rhyolitic lavas, locally including obsidian and perlites.

The younger basin fill

The older basin fill of Miocene age is unconformably overlain by the Plio–Quaternary

younger basin fill of the Inner Bay of İzmir. It consists of two successions: (i) Plio–

Pleistocene alluvial fan deposits (Görece formation), and (ii) Holocene alluvium and fan-delta

to shallow marine deposits (Figures 4 & 5).

The Görece formation is exposed along the strike-slip and normal faults such as

Seferihisar, İzmir, Orhanlı, Buca, Yaka and Değirmendere faults (Figure 4). It is characterized

by red colored semi consolidated continental clastics which are made up of reddish-brown

sandstone and conglomerate alterations. It begins with a basal conglomerate on an erosional

surface of the volcano-sedimentary sequence. The unit is made up of alternations of poorly

bedded, poorly- to moderately sorted reddish-brown conglomerates and poorly bedded,

moderately sorted yellowish-brown sandstone. Based on sedimentary and geometric

characters, the Görece formation can be considered as an alluvial fan deposition including

proximal, middle-distal and alluvial plain parts of the fan system (Uzel & Sözbilir 2008). No

paleontological data have been acquired from the Görece formation. Close to the study area,

Sözbilir et al. (2004) defined the Plio−Pleistocene Sütçüler formation in the Kocaçay basin,

which may probably be correlated with the Görece formation. Plio−Pleistocene sediments

exposed along most of the western Anatolian grabens can also be correlated with the Görece

formation (Koçyiğit et al. 1999; Yılmaz et al. 2000; Sarıca 2000; Seyitoğlu et al. 2002;

Koçyiğit 2005; Rojay et al. 2005; Emre & Sözbilir 2007; Ersoy & Helvacı 2007).

The Holocene alluvium and fan-delta to shallow marine deposits are the uppermost

sediments in the study area, which are restricted by normal faults to the south and north of the

Inner Bay of İzmir. This unit is made up of coarse-grained alluvial-fan deposits, coarse- to

fine-grained fluvial deposits and fine-grained fan-delta and shallow marine sediments. The

alluvial-fans are controlled by the İzmir fault to the south and the Karşıyaka fault to the north.

The alluvial fan deposits are characterized by gray to yellowish-brown colored debris flow

sediments which are commonly poorly sorted, poorly bedded to massive, matrix-rich, and

matrix-supported to clast-supported, unconsolidated composition. The matrix is an unsorted

mixture of sand and reddish-brown mud. The maximum clast size ranges from pebble to large

isolated boulders (260 cm), and the clasts are derived from the underlying basement rocks and

ancient basin fill units. The alluvial fan deposits interfinger with alluvial plain deposits toward

the basin depocentre. The alluvial plain deposits are difficult to recognize, because of the

scarcity of adequate exposures and high settlements in the area. The fluvial deposits are

coarse- to fine-grained axial river deposits carried by the Kavak River. The lateral fans and

the axial river deposits, are controlled by the present-day drainage system in the region,

interfinger laterally and vertically with deltaic deposits and are typical valley fills. The Gediz

delta which is developed by the alluvial deposits of the Gediz River forms an oblique alluvial

plain with respect to the orientation of the İzmir Bay. It is difficult to recognize, because of

their poor exposures and show a record of complex interplay of alluvial and marine

sedimentation. Alluvial fans of diverse size also are present in the southern part of the Inner

Bay of İzmir. The largest alluvial fan has been deposited by the present Ilıca River which has

also formed a fan delata prograding northward. Shallow marine deposits have been

accumulated as medium to fine clastics in the submarine part of the bay. However, available

subsurface data are insufficiently detailed to constrain the thickness, geometry and lithofacies

of submarine sediments.

Faults

A large number of the strike-slip and oblique to dip-slip normal faults are established and

mapped around the Inner Bay of İzmir; these are NE–SW, NW–SE, N–S and E–W trending

fault sets (Figure 4). Detailed analyses of Neogene to Quaternary faults in the study area

enable us to recognize a pre-existing zone of weakness that intermittently reactivated and is

active today. Many of the dip- to strike-slip faults that initiated during the early history of the

Miocene basin formation have become inactive, and older basin fill has been uplifted on the

footwalls of younger faults. Relative chronologies of faulting events were established by

using qualitative observations (e.g. superposition of slickensides on the same fault surface).

NE–SW-trending Faults

The NE–SW trending faults are mostly well exposed as short (0.5–2 km) and long (>20 km)

fault segments. The long segments can be followed along mountain ranged and have formed

the basin margin of the Miocene depressions, whereas the short segments mostly cut and

displaced rocks of the Bornova mélange, together with the Miocene units as well. Two well

known fault zones in the southern sector bound the Seferihisar High from the western and

eastern sides: these are the Seferihisar (SFZ) and Orhanlı fault zone (OFZ), respectively.

The SFZ lying between Sığacık Bay and Güzelbahçe district is a 2–5-km-wide, 30-km-

long and NE-trending dextral fault zone (Figures 4 & 7; İnci et al. 2003; Ocakoğlu et al.

2004, 2005; Emre et al. 2005; Sözbilir et al. 2008). At the northern termination, it consists of

a series of parallel and sub-parallel fault segments. It enters into the study area at the Yelki

town in N20OE strike and cuts the basement rocks of Bornova mélange and Holocene alluvial

deposits. There are also a series of actively growing lateral alluvial fans aligned along the

fault segments (Figure 7). Towards the north, the strike of the fault changes to N40–50OE and

connected to the İFZ. Holocene activity of the fault is evidenced by the dextral offset of

drainage systems of up to 100 m (Emre et al. 2005). Moreover, an intermediate-magnitude

(MW= 5.7) earthquake that struck on April 10, 2003 supports the recent dextral strike-slip

activity of the SFZ (Akyol et al. 2006; Figure 4). Along the northern termination of the SFZ,

the fault segments have a strike of N30–50OE and average dips of about 70–87O to the NW.

The slickenlines on the fault planes show a rake angle ranging from 03O to 32O (Figure 8).

When the SFZ come close to İFZ it bends to the east and their fault planes have a rake angle

up to 70O.

The OFZ forms the western margin of the Cumaovası basin, and is also the most

prominent structure in the region located to the south of İzmir city (Figures 2 & 4). It bounds

the Seferihisar High to the east. It may be traced for about 45 km, between İzmir Bay in the

north and Kuşadası Bay in the south. The fault zone includes several dextral fault segments

extending mainly in a NE−SW-direction. The main motion along the slip surfaces is dextral

strike-slip. However, there are some geomorphological and structural evidence for the

presence of an earlier sinistral strike-slip motion (Uzel & Sözbilir 2008). Typical tectonic

landforms, such as systematically deflected stream channels and ridges, shutter ridges, and

fault scarps, are recognized along segments of the OFZ. On the basis of their morphological

and structural features, it is interpreted that the early sinistral offsets are later overprinted by

dextral offsets. In addition to that, several hot springs occur in the central part of the fault

zone, implying that the fault zone provides effective conduits for the geothermal field. This

indicates that the hot springs in the area are associated with active faults (Uzel & Sözbilir

2008). Recent activity of the OFZ is also evidenced by 6 November 1992 Doğanbey

Earthquake (Tan & Taymaz 2001; Figure 4).

N–S-trending Faults

The N–S faults are steeply dipping, and are mainly of strike-slip nature (Figures 4 & 9). Some

of these show clear evidence of early left-lateral slip reactivated by later right-lateral motion.

In the southern sector, NW of Altındağ two sets of slip lines on the fault planes were

recognised, and slip lines with rakes 10ON are superimposed by striations with an average

rake of 25OS (Figure 10a). The length of this fault is approximately 2 km. The fault cuts

trough Miocene lacustrine limestone and is in turn cut by approximately E−W trending

normal faults of the İFZ. To the southeastern part of the study are, between Işıkkent and

Gökdere village, there is a straight fault zone with a N–S trend, for about 6 km. To the east of

Buca district, several NE–SW trending dextral strike-slip faults splaying out from the main

fault zone cut, and these displaced the unconformity between the Bornova mélange and the

overlying Neogene units (Figures 4 & 9). There are also several oblique-slip normal faults

along the west side of the main fault and are en echelon or oblique to the trend of the main

fault. The en echelon faults are stepply dipping and have normal separation. Some of the

faults have nearly horizontal slickenside striae that are interpreted as consequences of

oblique-slip. Structural evidence for N–S-trending srike-slip faults comes from the northern

section around Akgedik tepe where N–S dextral strike-slip faults cut and displaced Miocene

lacustrine limestones, and display cross-cutting relationsips with the NE–SW trending dextral

strike-slip faults (Figures 10b-d &11).

The N-S trending strike-slip faults may have acted as extensional tear faults (cross-faults)

separating areas that may have experienced different amount of extension. According to Kaya

(1979 & 1981) and Kaya et al. (2004 & 2007), the NE–SW and N–S trending faults were

inherited from old zones of weakness of Paleocene age. These Paleocene faults a) have

significant vertical movements, b) later acted as growth faults during the early Miocene,

because they are responsible for variation in thickness of the Miocene volcano-sedimentary

units, c) were a zone of weakness that aligned volcanic centers, and d) reactivated

intermittently until recent time as indicated by overprinted slickenlines.

NW–SE-trending Faults

The NW–SE trending fault system consists of a set of about high-angle faults, aligned in an

average of N45OW direction, which represent geologically and geomorphologically

prominent structures in the uplifted domain. The presence of two sets of striations on slip

surfaces suggest that some of the NW–SE trending faults reactivated: the fault once operated

as a strike-slip fault, then a normal fault.

The length of this fault system is approximately 10 km. This fault set forms the

nortwestern margin of the Bornova plain. It comprises a series of parallel to sub-parallel

oblique-slip normal faults with minor amounts of dextral and sinistral strike-slip component.

There is also pure sinistral strike-slip component which pre-date the oblique-slip movements.

It is represented by an approximately 2-km-wide shear zone. The fault set starts in east of

Doğanlar villages as two paralel segments forming the northeastern margin of the modern

Bornova plain and intermittenly continues to the northwest in the form of discontinuous

strands of parallel to sub-parallel fault segments. Some of these segments are oblique-slip

normal faults facing towards the basin and formed step-like morphology lowered toward the

basin. Similar NW–SE trending high-angle normal faults are mapped in the southern sector,

South of Balçova district. This fault is cut and displaced by an E–W trending segment of the

İFZ.

There is a NW–SE trending depression in the NE of northern sector between Çiçekli and

Yaka villages (Figure 11). This depression forms the western end of the Quaternary

Kemalpaşa basin. The depression is bounded by the Çiçekli and Yaka faults from south and

north, respectively. The Yaka fault is a 200-m-wide, 5-km-long high-angle normal fault,

which dips at an average angle of 65OSW with a minor dextral strike-slip component. Upper

volcano-sedimentary units are displaced by a northern up-thrown footwall block and a

downfaulted block exhibiting Quaternary sediments, which are tectonically juxtaposed along

the fault. The Çiçekli fault is the southern basin-bounding structure forming the western end

of the Kemalpaşa fault zone. It is a 500-m-wide, 6-km-long, graben-facing normal fault cross-

cutting the NE–SW trending fault zone west of Çiçekli village. The fault displays locally

well-preserved striated fault planes that clearly showing that the Çiçekli fault is an oblique-

slip normal fault dipping at an average of 70ONE, with a minor sinistral strike-slip

component.

E–W-trending Faults

The E–W trending faults are mostly oblique- to dip-slip normal faults and are well exposed

along the northern and southern margins of the Inner Bay of İzmir. There is some structural

evidence, however, for the presence of an earlier strike-slip motion along some of the E–W

trending fault segments. They can be followed along the mountain range and have formed the

basin margin of the Quaternary depression.

The İFZ is the southern incipient margin-bounding structure of the Inner Bay of İzmir. It

is an approximately 2–4-km-wide, 40-km-long, E–W-trending and range-front active normal-

fault zone (Figures 4, 7 & 13a). It bounds the Seferihisar and Nifdağı Highs to the north and

consists of two main fault sets lying between Güzelbahçe and Altındağ villages. Through

Balçova to Güzelbahçe villages, the western fault set of the İFZ is made up of a number of

segments trending approximately in an E–W direction (Figures 7 & 13b). In this section, the

İFZ has corrugations with variable size wave lengths, reaching km-scale amplitude. Their

map view shows a basin-ward-facing step-like fault pattern which is convex to north.

Towards the east, where the eastern fault set of the İFZ enter into Altındağ village in a

WNW–ESE-direction, it includes several en-echelon-arranged synthetic and antithetic fault

segments, dipping to the north and south, respectively (Figure 9). Here, the İFZ cuts the

basement rocks of the Bornova mélange and sedimentary rocks of the older basin fill units,

while its northernmost segment separates the Holocene alluvial deposits from the older rocks.

Holocene lateral alluvial fan sediments growing on the hanging wall of the İFZ are back-tilted

towards the fault.

In the easternmost segment of the fault zone we measured two differently orientated

striation sets on the same slip surface of the İFZ (Figure 13c, d), which strike in

approximately E–W and dip 75ON. The younger set is represented by slip lines with rakes of

79–88OW and overprints an older striation set with an average rake of 10OE. There, the

observed two slickenside lineation with different plunges and slip senses on the same fault

plane suggest that the strike-slip surface was overprinted with dip-slip movements.

The northern sector of the bay between Bayraklı and Karşıyaka district is bounded by the

Karşıyaka fault zone (KFZ) which is an antithetic fault to the İFZ (Figure 4). It is a 0.5–2.5

km-wide, 20-km-long, approximately N80OW- to E–W-trending normal fault zone which is

characterized by a concave, curvilinear range-front fault trace to the south. The hangingwall

of the KFZ comprises the modern basin fill units, while the footwall includes the Bornova

mélange and volcano-sedimentary rocks of the lower sequence. The fault zone displays a

well-developed step-like morphology. There are also a series of actively growing lateral

alluvial fans aligned parallel to the fault. The observed fault planes are trending N80OW,

dipping an average of 60O to SW. Through the village of Bornova, it runs between the

sedimentary rocks of the lower and upper units, N80OW in strike, and it is characterized by an

oblique-slip normal fault dipping to the south. Between Bornova and Naldöken villages, the

fault trends in NW–SE direction and include two closely spaced fault segments.

Folds

The folds observed within the study area comprise a series of anticlines and synclines. These

folds of various sizes characterize the internal deformation of the older basin fill units. Two

types of fold-to-fault relationships have been mapped: folding parallel to the normal-fault

traces, and folds lying oblique to the strike-slip fault traces (Figures 9 & 11).

The E–W-trending folds are well exposed between the Bornova and Beşyol villages where

they are nearly parallel to NW–SE trending normal faults (Figure 11). They are large, open,

gently northwest- to southeast-plunging folds with gently to moderately dipping limbs.

Towards northern parts of the study area folds is open with interlimb angles around 130O. The

origin of the mapped folds can be explained in two ways: (1) a NE–SW-directed compression

that postdates the sedimentation of the Yaka formation, (2) they may be resulted from

extensional tectonics as similar to fault-bend longitudinal folds mapped in the basin fill of the

Gediz graben (Sözbilir 2001, 2002; Çiftçi & Bozkurt 2008). Unfortunately, this study was not

able to document certain evidence for reason of this folding due to limited distribution of this

deformation.

Several folds have been mapped that are associated with strike-slip faults and typically are

arranged in en echelon patterns oblique to the principal direction of shear in which Miocene

rocks are folded into en echelon, NE–SW trending anticlines and synclines that die out within

approximately 2 km (Figure 9). Typically, en echelon folds are distributed in a relatively

narrow zone adjacent to strike-slip faults. The general trend of the folds indicates a NW–SE-

directed compression direction, possibly attributed to the formation of the strike-slip faults.

Paleostress Analysis of Fault-slip Data

Methodology

In this section we aim to better constraining the tectonic evolution of the Bay of İzmir area by

combining field-based structural data with the computer-based paleostress inversion method.

Numerous methods have been developed for the paleostress inversion in graphically (Arthaud

1969; Alexandrowski 1986; Kratz 1988) and numerically (Carey & Brunier 1974; Angelier

1979, 1984, 1990; Etchecopar et al. 1981; Armijo et al. 1982; Gephart & Forsyth 1984;

Michael 1984; Reches 1987; Marrett & Almandinger 1990; Will & Powell 1991; Yin &

Ranalli 1993; Hardcastle 1989; Fry 1999; Ramsey & Lisle 2000; Yamaji 2000; Delvaux &

Sperner 2003; Zalohar & Vrabec 2007). We used the Direct Inversion Method (INVD) of

Angelier (1990), because it is more effective in multistage deformed areas and have been

more widely used (example Vandycke & Bergerat 2001; Brahim et al. 2002; Saintot &

Angelier 2000; Bergerat et al. 2007).

The first step of the analysis in this study was careful data collection in the field. Multi-

stage deformation features, block rotation and heterogeneous fault plane data makes the

specification of local deformation more complex. Thus, the structural observations such as

displacement of stratigraphy, style of fault zone deformation, type and rake angle of

slickenline, direction and dip angle of fault plane, shear sense through the fault and

overprinting and cross-cutting relationships of the features were noted for the identification

and separation of deformation phases correctly. The second step is the computation of local

stress tensors using the fault slip data sets. This computer-based method is based on the

assumption that the rigid block displacement is independent and that striations on a fault plane

are parallel to the maximum resolved shear stress (τ) applied on this fault. The results include

the orientation of principle stress axes that σ1, σ2, and σ3; maximum intermediate, and

minimum principal stress axes, respectively. The stress ratio ( ) describing the relative stress

magnitudes of the calculated mean stress tensor defines by the formula [ = (σ2 – σ1) / (σ3 –

σ1)], it is also another output of this computation. The stress regime is determined by the

nature of the vertical ones: extensional when σ1 is vertical, strike-slip when σ2 is vertical and

compressional when σ3 is vertical. Delvaux et al. (1997) suggest that the stress regimes also

vary in function of the stress ratio ranging in 0- to- 1: radial extension (σ1 vertical, 0 < <

0.25), pure extension (σ1 vertical, 0.25 < < 0.75), transtension (σ1 vertical, 0.75 < < 1 or

σ2 vertical, 1 > > 0.75), pure strike-slip (σ2 vertical, 0.75 > > 0.25), transpression (σ2

vertical, 0.25 > > 0 or σ3 vertical, 0 < < 0.25), pure compression (σ3 vertical, 0.25 < <

0.75) and radial compression (σ3 vertical, 0.75 < < 1).

During the inversion process, for the separation of heterogeneous data, we used some

estimates: ANG and RUP values. The allowable maximum misfit angle (ANG), average angle

between observed slip and computed shear was taken as 20O. The acceptable maximum

quality estimator value (RUP), ranging from 0% (calculated shear stress parallel to actual

striae with the same sense and maximum shear stress) to 200% (calculated shear stress

maximum, parallel to actual striae but opposite in sense) was taken as 75%. The fault plane

data having more than these limited values was separated from the data set. After this

separation the local stress tensor was re-computed. Additionally, at one location we computed

a P-T (pressure-tension) plot using the Angelier software to the compare between the fault

plane data and the focal mechanism solution of a recent earthquake occurred in the study area.

We give the paleostress analysis results and local meanings briefly below. The readers are

referred to Angelier (1979, 1984 & 1990) and Angelier et al. (1982) for more details of stress

inversion procedure.

Paleostress Reconstruction

In order to reconstruct the kinematic development and geological history of the Inner Bay of

İzmir, 65 fault-slip data from 7 locations were collected for paleostress computation. In two of

these locations, overprinting slickensides were noted. Figure 14 and Table 1 gives

reconstruction plots for the study area and shows the subsets of the data together with the

orientation of the calculated principal stress axes and other outputs.

In the southern margin of the Inner Bay of İzmir, we have studied well-exposed fault

surfaces at three localities (sites 1 & 2) along the NE-trending SFZ and OFZ (Figures 8 and

14). The stress field orientations at site-1 along the strike of SFZ suggest a NNE–SSW-

directed extension associated with a WNW–ESE compression (Figure 14 and Table 1). The

calculated principle stress axes are characterized by nearly vertical σ2, as 001O/57O and by

nearly horizontal σ1, as 100O/06O; whereas σ3 is gently oblique, as 194O/33O. The maximum

ANG and RUP values are 13 and 32, respectively. The computed value of = 0.524 is

inferred that, these stress tensors are associated with the pure strike-slip type deformation.

At site-2 on the OFZ, crosscutting relationships and superposition of successive striae in

fault planes show that sinistral faulting was reactivated as dextral faulting (Uzel & Sözbilir

2008). The older kinematic structures including sinistral shear sense are determined in site-2s

(Figure 14 & Table 1). The paleostress computation results of fault-slip measurements for

early phase of sinistral strike-slip faulting suggest a subvertical σ2 (53O) but gently plunging

in σ1 and σ3 (17O and 32O). According to the results of younger dextral movement on the OFZ

(site-2d), the dip of the principle stress axes are similar to early phase that have 77O, 06O and

11O, respectively. For both of strike-slip phase the values for ANG are generally low (05O and

09O), indicating a good fit between the calculated tensors and measured striations, but the

RUP rates were calculated as 45% and 29%.

Site-3 includes data from NW-trending faults at the south of Kayadibi villages (Figure

14). The computed orientations of the principle stress axes (σ1, σ2 and σ3) are 315O/78O,

110O/10O and 200O/05O, respectively. And the ANG and RUP values were calculated as 10O

and 29%, respectively. The projection of the fault-slip shows the NE–SW-directed, pure

extensional ( = 0.431) stress regime (Table 1).

The fault-slip data collected from site-4 along the İFZ include nearly vertical σ1 (76O)

trending at 153O, whereas σ2 and σ3 axes have attitudes of 298O/11O and 030O/08O,

respectively (Figure 14 and Table 1). The allowable maximum misfit angle and the acceptable

maximum quality estimator values were calculated as 09O and 30%, respectively. The rate of

(0.332), between 0.250 and 0.750, represents the local paleostress tensors for the NE–SW-

trending pure extensional deformation in the SW rim of the Inner Bay of İzmir.

In site-5, another location along the İFZ corresponds to the reactivation of older fault

planes (see the ‘Faults’ section above). Older structures including dextral shear indicators are

determined in site-5d. The paleostress results are characterized by tensors with a subvertical

σ2 (301O/71O) that is inferred a pure strike-slip and/or transpressional deformation ( = 0.278,

as very close to 0.250). Moreover, the maximum and minimum principle stress axes were

calculated as 129O/18O and 038O/02O, respectively. The values for ANG and RUP are

generally low, indicating a good fit between the calculated tensors and measured striations.

The reconstruction plot shows NE–SW-trending extension associated with NW-SE

compression in this area. On the other hand, the younger kinematic structures collected at

site-5n, are characterized by subvertical σ2 (71O) trending at 301O, whereas σ2 and σ3 axes are

very slight and calculated as 073O/06O and 341O/16O, respectively. The fault populations are

homogeneous (the ANG and RUP values are very low) and well distributed, with dominant

movement planes parallel to the İFZ. The computed tensors and calculated are reported to

the NNW–SSE-directed pure extensional regime (Figure 14 and Table 1). Additionally, the

reconstruction P-T (pressure-tension) plot of the site-5n and the 16.12.1966 İzmir Earthquake

focal mechanism solution where very close to site-5 location have almost similar P-T pole

points and areas.

We used kinematic data from Yaka and Çiçekli faults at site-6. The orientations of the

computed principal stresses are as follows: σ1 is almost vertical and oriented as 334O/82O, σ2

and σ3 are nearly horizontal and oriented as 96O/04O, and 187O/07O, respectively. The quality

values of the data slightly high (ANG=20O, RUP=43%), but still under the limits. According

to calculated rate and projection results show an N–S-directed pure extensional regime

around the northeastern part of the Bornova plain.

The site-7 comprising seven fault-slip measurements from KFZ mainly indicates a pure

extensional regime with a well constrained, steep and nearly N–S σ1 orientation (Figure 14

and Table 1). The calculated principle stress axes, that σ1, σ2 and σ3 have attitudes 341O/79O,

121O/09O and 212O/07O, respectively. Despite the allowable maximum misfit angle and

quality estimator values are under the limits (15O and 49%). The paleostress reconstruction

results are suggested that the northern margin of Inner Bay of İzmir formed in a NE–SW-

trending extensional stress regime.

Based on the chronology using lithostatigraphical records and superimposed kinematic

structures, the history of stress states can be separated in four stages. Phase 1 and 2 which are

described by syn-sedimentary information from the Miocene lower and upper volcano-

sedimentary sequences. They likely controlled the Miocene deposition and have been related

with regional N–S extensional tectonism (see also Koçyiğit et al. 1999; Lips et al. 2001;

Sözbilir 2001, 2002; Bozkurt & Sözbilir 2004). In study area, Phase 3 is characterized by the

early movement obtained from the NNE-SSW (plot 2s) and E-W trending (plot 5d) faults. The

paleostress results show that the Phase 3 is associated with local NW–SE extensional and

NE–SW-trending compressional regime. Phase 4 is represented by paleostress plots 1, 2d, 3,

4, 5n, 6 and 7 characterized by dextral movement on NE-trending faults and normal- and/or

oblique-slip movement on NW and E–W-trending faults. The calculated stress parameters

comprise the NNW–to NE-trending extension associated with E–W compression. The focal

mechanism solution of the 16.12.1966 İzmir Earthquake is also supporting that the study area

was formed under this recent NNE-directing extensional stress stage (Figure 14c).

Tectonic Evolution of the Inner Bay of İzmir

Recent studies suggested that the tectonic history of İzmir bay region in the late Tertiary was

characterized by motion along NE–SW running shear zone (İBTZ), belonging to a larger

strike-slip system that forming the structural contact between the Aegean region and western

Anatolia (Bozkurt & Sözbilir 2004; Uzel & Sözbilir 2008; Özkaymak & Sözbilir 2008;

Sözbilir et al. 2008, 2009) The tectonic history of the İBTZ can be traced back to the Late

Cretaceous, when a transform fault between the Neotethys Ocean and the Anatolide-Toride

carbonate platform was active. The transform fault led to deposition of flysch-like sediments

(the Bornova mélange) along the fault zone during the late Cretaceous to Paleocene (Okay et

al. 1996). Several studies suggest that the lateral movement on the IBTZ has also been

contemporaneous with the Miocene regional extension, thus it can be defined as a divergent

strike-slip zone (Uzel & Sözbilir 2008).

At the beginning of the Miocene, while western Anatolia was characterized by a core

complex mode of extension during which supradetachment basins were formed and

extension-related deformation caused pervasive mylonitisation of the footwall, with top- to-

the NNE ductile, then brittle shear (Koçyiğit et al. 1999; Lips et al. 2001; Sözbilir 2001,

2002; Bozkurt & Sözbilir 2004), the study area was the site of lacustrine sedimentary

environment associated with calc-alkaline volcanism (Phase 1). It begins with coarse-grained

alluvial fan facies (Kızıldere formation) dominate the vicinity of the NE-trending SFZ and

OFZ, and graded into finer fractions of fluvial or stratigraphically upward facies of lacustrine

sediments (Çatalca formation; Figure 5). Yamanlar volcanic suite, were also exposing in this

depositional period, and represent the early to middle Miocene terrestrial volcanism (Figure

15). The older volcano-sedimentary succession is unconformably overlain by younger

lacustrine deposits of middle to late Miocene age (Figure 15 b). The early to late Miocene

period was of extensional/transtensional origin, and contains more than 1500 m of volcano-

sedimentary deposits. It evolved from a series of NE–SW trending basins to a single

lacustrine basin partly connected with the Aegean Sea (Phase 2).

Following the late Miocene tectonic activity, the region was deformed under the different

tectonic forces that arised after sedimentation of the Yaka formation, thus postdating the

region-wide late Miocene lacustrine sedimentation. During the early Pliocene the area

underwent normal- to strike-slip dominated tectonics that deformed the region-wide lacustrine

limestones, and resulted in tilting and local folding of the Miocene units (Figure 15c). The

relatively through-going NE–SW trending strike slip faults bring the rock units of Bornova

flysch zone into contact with strata of the Miocene formations. Most folds where developed

are parallel, oblique or en echelon to the main faults.

A new tectonic phase (Phase 4) that produced the first product of the Inner Bay of İzmir

took place in the Late Pliocene or Early Pleistocene, which resulted from approximately N–S-

trending tensional effects associated with E–W contraction (Uzel & Sözbilir 2008). This

second system is characterized by alluvial fans formed along the fault-controlled margins and

grades basin-ward into finer fractions of alluvial plain, delta and marine sediments; it is

controlled by NE-trending strike slip and E–W-trending normal faults on both margins of the

Inner Bay of İzmir. During this stage the Miocene sediments and some of the older strike-slip

faults were cut by the İFZ and KFZ to form the Inner Bay of İzmir. Based on the results

obtained from seismotectonic studies (Zhu et al. 2005, Akyol et al. 2006), the present

direction of tension in the area was determined to be NE–SW (Figure 15d).

Discussion and Conclusion

This study shows the existence of two basin formation of different age and orientation in the

İzmir bay region. The older basin is represented by a NE–SW trending depression that filled

with lower to upper Miocene lacustrine sedimentary units intercalated with calc-alkaline to

alkaline volcanic rocks. The younger basin cut across the older one and is characterized by the

E–W to NW–SE trending İzmir bay filled with Plio-Quaternary alluvial fan-fan delta to

shallow marine sediments. Today, major part of the basin is flooded by the waters of Aegean

Sea, forming the inner bay of İzmir.

In the İzmir region to the west of Menderes metamorphic core complex, the stratigraphic

and structural record is compatible with the interpreted episodic deformation. Detailed

mapping of Miocene volcano-sedimentary units also demonstrates a two-phase history of

volcanism. The oldest lower–middle Miocene calc-alkaline volcanic rocks are reminiscent of

many sections around the inner bay of İzmir. Younger volcanic episode was synchronous with

the onset of middle to late Miocene strike-slip deformation in the Cumaovası basin (Uzel &

Sözbilir 2008). These findings imply that middle to late Miocene extension in western

Anatolia is a distinct, younger period of faulting that is superimposed on the older, early–

middle Miocene distribution of extended domains. This resut is compatible with episodic

extension suggested by several studies (Koçyiğit et al. 1999 & 2000; Bozkurt & Sözbilir

2004, 2006; Uzel & Sözbilir 2008; Özkayamak & Sözbilir 2008) in contrast to Seyitoğlu &

Scott (1992) who claimed continuous extension in western Anatolia since late Oligocene.

In general, the main direction of horizontal principal stress axis (σ3) is relatively constant

in west Anatolian extensional province (Koçyiğit et al. 1999; Sözbilir 2001, 2002; Bozkurt &

Sözbilir 2004, 2006; Çiftçi & Bozkurt 2007; Uzel & Sözbilir 2008; Özkaymak & Sözbilir

2008), however westwards; the stress regime evolves locally into pure strike-slip in the İzmir

bay region by the end of Miocene time. Some authors argued that regional extension ceased in

the early Pliocene (5 Ma), after which the stress regime changed to a subhorizontal

compressional stress field that induced an N–S shortening (Koçyiğit et al. 1999). During this

phase the entire Aegean and Anatolian region was affected. Some workers consider that the

subduction along the Aegean trench during the Pliocene was closely related to the

compressional phase referred to above (Mercier 1981; Angelier et al. 1981). However, local

folding of the older basin fill units may be related to the extensional longitudinal folding or

possibly attributed to the formation of the strike-slip faults. Further work should be done for

the cause and nature of the early Pliocene deformation phase operated in western Anatolia.

The paleostress constructions of the younger fault-slip data at st-1, 2, 3n, 4 & 5d,

collected from basin margin faults of the Inner Bay of İzmir suggest that the post Pliocene

deformation of the region is consistent with an NNW- to- NE-trending extension and

approximately E–W compressional regime (Figures 14 & 15). The last stage corresponds to a

pure extensional regime in the area of the Inner Bay of İzmir and to a strike-slip regime in the

Cumaovası and Urla basins. The last four tensors of the İzmir bay region are stratigraphically

constrained to the late Pleistocene-Holocene period. They show a combination of pure strike-

slip movement along steeply-dipping NE–SW trending SFZ and oblique-normal movements

along E–W striking İFZ. In site 7, a set of fault planes with slickensides that affect the

Yamanlar volcanic give a tensor compatible with the last stress regime which resulted in the

formation of the Inner Bay of İzmir.

Acknowledgements

This work is a part of PhD Thesis undertaken by Bora Uzel at Institute of Natural and Applied

Sciences in Dokuz Eylül University. We are gratefully thank to Yalçın Ersoy, Ökmen Sümer

and Fuat Erkül for their constructive discussions and help during the fieldwork. This study

was supported by Dokuz Eylül University Scientific Research Foundation Grant BAP-Project

No: 2007.KB.FEN.039. This manuscript benefited from helpful reviews by Douwe J.J. van

Hinsbergen and an anonymous reviewer.

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ÖZKAYMAK, Ç. 2008. D-B uzanımlı İzmir Fayı ile KD-uzanımlı Seferihisar Fayı’nın

birlikte çalıştığına dair veriler: İzmir Körfezi’ni oluşturan aktif faylarda kinematik ve

paleosismolojik çalışmalar, Batı Anadolu. [Evidence for a kinematically linked E-W

trending İzmir Fault and NE-trending Seferihisar Fault: Kinematic and paleoseismogical

studies carried out on active faults forming the İzmir Bay, Western Anatolia]. Türkiye

Jeoloji Bülteni 51 (2), 91–114.

SÖZBILIR, H., KAYMAKÇI, N., LANGEREIS, C., UZEL, B., ÖZKAYMAK, Ç., ÖZKAPTAN, M. &

GÜLYÜZ, M. 2009. Transfer zonlarının jeolojik evrimi ve bu zonların Batı Anadolu’daki

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Figure Captions

Figure 1. (a) Simplified map showing the major Neotectonic elements and plate tectonic

configuration of eastern Mediterranean. DFZ – Dead Sea Fault Zone, PFB – Palmyride

Fold Bend, EAFZ – East Anatolian Fault Zone, NAFZ - North Anatolian Fault Zone,

CAFZ – Central Anatolian Fault Zone, EPF – Ezinepazarı Fault, TGF – Tuzgölü Fault,

İEFZ – İnönü-Eskişehir Fault Zone, AFZ – Akşehir Fault Zone, G – Bay of Gökova,

BMG – Büyük Menderes Graben, GG – Gediz Graben, İ – Bay of İzmir, SG – Simav

Graben, E – Bay of Edremit, NAT – North Anatolian Through, TFZ – Thrace Fault

Zone, WAEP – West Anatolian Extensional Province (redrawing from Taymaz et al.

2007 and complied from Şengör et al. 1985, Barka 1992, Bozkurt 2001, Koçyiğit &

Özaçar 2003; Kaymakçı et al. 2007 and our observations). Large arrows indicate

relative plate motion directions with respect to Eurasia. Source of seismic data are

from Tan et al. (2008). (b) Simplified geological map showing the Neogene-

Quaternary basins in the western Anatolia with main tectonic lines and distribution of

the Neogene−Quaternary deposits (modified from MTA 2002, Geological map of

Turkey, scale 1:500 000; Bozkurt 2000, 2001). İBTZ: İzmir-Balıkesir Transfer Zone.

Figure 2. Simplified geological map of coastal part of western Anatolia with main tectonic

lines and actively growing basins modified from Kaya (1981), MTA (2002), Bozkurt

(2001), Emre et al. (2005) and Uzel & Sözbilir (2008). ORFZ – Ortaköy fault zone,

OFZ – Orhanlı fault zone, SFZ – Seferihisar fault zone, GFZ – Gülbahçe fault zone,

İFZ – İzmir fault zone, KFZ – Karşıyaka fault zone, MFZ – Manisa fault zone, MEFZ

– Menemen fault zone, ZBFZ – Zeytindağ-Bergama fault zone, KMG – Küçük

Menderes graben, CB – Cumaovası basin, GG – Gediz graben, MB – Manisa basin,

BG – Bakırçay graben, KB – Kuşadası Bay, SB – Sığacık Bay, İBİ – Inner Bay of

İzmir, OBİ – Outer Bay of İzmir, ÇB – Çandarlı Bay.

Figure 3. (a) The surface morphology map of the İzmir Bay and surrounding region.

Topographic data were obtained by a Digital Elevation Model (DEM) image with ~90

m ground resolution. This figure was adapted from Global Mapper Program

(www.globalmapper.com). (b) Simplified drainage map of İzmir Bay region with

main parts of the İzmir Bay and catchment areas prepared from THGK (2000,

1:100.000 scale topographic map of Turkey). Bathymetric data simplified from Sayın

(2003) have ~5 m precision. MS – Mordoğan strait, YS –Yenikale strait, HL – Homa

Lagoon, PL – Pelikan Lagoon, UI – Uzun Island, HI – Hekim Island.

Figure 4. Detailed geological map of Inner Bay of İzmir and surrounding area. Note the black

stars show the epicenter of recent earthquakes; 1- 16.12.1966 İzmir, 2- 06.11.1992

Doğanbey, and 3- 10.04.2003 Seferihisar Earthquakes. KFZ – Karşıyaka fault zone,

İFZ – İzmir fault zone, SFZ – Seferihisar fault zone, OFZ – Orhanlı fault zone, ORFZ

– Ortaköy fault zone, DF – Değirmendere fault, KSF – Kısıkköy fault, BFZ – Buca

fault zone (compiled from MTA 2002; Sözbilir et al. 2003b; Tan et al. 2008; Uzel &

Sözbilir 2008 and this study).

Figure 5. Generalized columnar section of the study area including the radiometric age data

from the volcanic rocks (compiled from Kaya 1981; MTA 2002; Uzel & Sözbilir 2008

and this study; the age data from Borsi et al. 1972; Ercan et al. 1996; Genç et al. 2001

and references therein).

Figure 6. Field photos of the older and younger basin fill units. (a) The reddish sandstone and

conglomerate alternation of the Kızıldere formation (b) Field photograph of the main

unconformity between flysch-type highly deformed rocks of the Bornova mélange and

the overlying Miocene sediments of the Sabuncubeli formation. Note the NW–SE

trending faults are cut and display this boundary. (c) The top sections of the Kızılca

formation including the light-grey and yellowish-white clayey limestone and

sandstone alternation. (d) Field view of the Yaka formation. (e) Reddish continental

clastics of the Görece formation. (f) Field photo of the erosional surface between the

recent alluvial deposits and Miocene sediments.

Figure 7. (a) Detailed geological map of Güzelbahçe area (modified after Sözbilir et al.

2008). (b) a geological cross-section showing the structural configuration of the

southern rim of the inner bay of İzmir.

Figure 8. (a) Field photograph showing the morphologic contrast and linkage of the

Seferihisar and İzmir fault zones (view to SE). (b-e) Fresh slip-planes of the

Seferihisar fault zone indicating the nearly horizontal slickenlines where cuts the

basement and basil fill rocks.

Figure 9. (a) Detailed geological map of eastern segment of İzmir fault zone, around Buca-

Altındağ area. İFZ – İzmir fault zone. (a) Geological cross-section showing the

slightly folded and dip- to strike-slip faulted upper sedimentary sequence. Note the

angular unconformity between the upper sedimentary sequence and the underlying

rocks of the Bornova mélange.

Figure 10. Field photographs showing outcrops of N–S-trending faults which cut and

displaced the limestone strata of Yeniköy formation (a) Reactivated fault as shown by

superposed sets of striae. Note the dextral lineations (2) superimposed on the sinistral

(1) strike-slip. (b-d) Two slip-planes of the N-S faults on the Miocene sediments

indicating nearly horizontal slickensides.

Figure 11. (a) Detailed geological map of Bornova area. ÇF – Çiçekli fault, YF – Yaka fault.

(b) Geological cross-section showing the angular unconformity between the lower and

upper sedimentary sequence. Note the Plio-Quaternary basin fill deposits

superimposed on the older basin fill units.

Figure 12. Field photographs showing outcrops of NW–SE-trending normal and oblique-slip

faults. (a) The fault scarp and (b) close-up view of the fault zone cutting the Yamanlar

volcanics at the SW of the Kayadibi village. Note the rake of the slip lines suggests

that motion along the fault is normal with minor amount of dextral component. (c) The

nearly strike-slip striae along a NW-trending fault where it curves to the N–S-

direction. (d) A fault plane with superimposed striae on the limestone of the

Sabuncubeli formation. Note the normal-slip lineations superimposed on the sinistral

strike-slip. These crosscutting relations of different kinematic markers give a good

relative age determination of kinematic phases.

Figure 13. Field photographs of the E-W-trending İzmir fault zone. (a) The step-like

morphology, basin-ward-facing steep fault scarp reflecting an active normal-slip

character of fault zone (view to S, between the Balçova and Narlıdere villages). (b)

Fresh fault-planes of the İzmir fault zone indicating the nearly vertical slickenlines

where cuts the basement rocks. (c & d) In the easternmost segment of the fault zone

we observed and measured two differently orientated striation sets on the same slip

surface of the İzmir fault zone. There, the observed two slickenside lineation with

different plunges and slip senses on the same fault plane suggest that the strike-slip

surface was overprinted with dip-slip movements.

Figure 14. (a) Studied stations on the meso-scale faults of the Inner Bay of İzmir and

paleostress plots including lower hemisphere equal area projection of the fault planes,

slickenlines and stress orientations. Note the black star shows the epicenter of

16.12.1966 İzmir Earthquake. (b) Application of the pressure-tension diagram

(Angelier, 1990) to site-5n fault-slip data; lower hemisphere equal area projection. The

shaded parts are show pressure area. (c) Lower hemisphere equal area projection plots

of the focal mechanism solutions of 16.12.1966 İzmir Earthquake (Tan et al. 2008).

The shaded parts are compressional quadrants. Pressure and tension axes are plotted

with black and white circles respectively.

Figure 15. Geological evolution of the Inner Bay of İzmir. (a) early-middle Miocene:

formation of NE-SW trending depression filled with the older lacustrine sediments and

calc-alkaline volcanics, (b) middle-late Miocene: the younger infill began to form

under the control of NE-SW trending strike-slip faults that caused to deposition of

lateral alluvial fan facies overlying by a regional wide lacustrine carbonates, (c) early

Pliocene: uplift and deformation of the older basin fill units under the conrol ofdip- to

strike-slip faults, (d) late Pliocene-Holocene: formation of the E-W trending normal

faults together with NE-SW trending strike-slip faults resulted in the opening of the

inner bay of İzmir.

Figure 16. An integrated figure of 3D blok diagram and geological cross-section of the Inner

Bay of Izmir.

Table1. Characteristics of stress states used to reconstruct stress regimes as illustrated in

Figure 14. # – number of fault slip data; DO and PO – trends and plunges of stress axes

in degrees; φ – ratio of stress magnitude differences [φ=(σ2-σ3)/(σ1-σ3)]; ANG – the

average angle between observed slip and computed shear, in degrees (acceptable with

ANG<20O); RUP – criterion of maximum quality value for the ‘‘INVD’’ method

(acceptable results with RUP < 75%).

Figure 1 (Uzel et al.)







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Table 1(Uzel et al.)

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