The South Marmara Fault

ORIGINAL PAPER

The South Marmara Fault

Xavier Le Pichon • Caner Imren • Claude Rangin •

A. M. Celal Sengor • Muzaffer Siyako

Received: 21 February 2013 / Accepted: 24 July 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract We use about 800 km of multichannel explo-

ration seismic reflection profiles of the seventies as well as

the results of three drill holes that penetrated the sedi-

mentary cover down to the Upper Cretaceous basement to

describe a continuous gently curvilinear, south-concave

zone of deformation about 10 km wide that extended over

the whole southern shelf of the Sea of Marmara from the

Gulf of Gemlik to the Dardanelles Straits in Lower Plio-

cene time, about 4 Ma. We call this zone of deformation

the South Marmara Fault (SMF) system and propose that

the SMF was then a branch of the dextral North Anatolian

Fault. This branch passed to the north of the Marmara

Island Eocene block and thus had a south-facing concavity.

This curvature resulted in a significant component of

shortening in the western part of the fault. The SMF was

deactivated at the end of Lower Pliocene, about 3.5 Ma,

except for its easternmost branch between the Gulf of

Gemlik and Imralı Island where about 5 mm/year of dex-

tral motion is still occurring today.

Keywords South Marmara Fault � Sea of Marmara �North Anatolian Shear Zone � Multichannel seismic

data

Introduction

The purpose of this paper is to introduce an hitherto

unknown element into the complex fault geometry asso-

ciated with what Sengor et al. (2005) called the North

Anatolian Shear Zone within which the active branches of

the North Anatolian Fault later became nucleated (Fig. 1a).

Since the work of Sengor (1979) and Sengor et al. (1985),

it has been known that the North Anatolian Fault has two

main active branches west of the Yenicaga depression, east

of Bolu (Fig. 1a).

An older, southern branch connects the Yenicaga fork

with the Pamukova basin, where a 22–26 km right-lateral

offset of the Sakarya River is observed (Sengor et al.

2005). From the Pamukova basin, the fault continues to the

Yenisehir pull-apart from which it goes through the

southern margin of the Bursa depression. A complex series

of right-lateral faults defines a broad, elongate basin, not

unlike the northern trough in the Sea of Marmara, called

the Mysian trough (Fig. 1a; Sengor et al. 2011). This

trough is dominated by the Manyas and Uluabat (also

written as Ulubat: all modern names in this paper are taken

from Anonymous 1977; ancient Apolloniatis) sub-basins

not dissimilar to the Central and the Tekirdag basins of the

Sea of Marmara (Le Pichon et al. 2001; MB and UB in

Fig. 1b, respectively). These are separated from the

southern coastal regions of the Sea of Marmara by a string

of mountain ranges: in the east, the Katırlı and Genc Ali

mountains form the western prolongation of the Avdan

Mountain and continue westward, via the solitary elevation

(600 m) south of Zeytinbagı (formerly Trilya), to the

Karadag. The latter culminates at an elevation of 833 m

(Erk 1944 Fig. 2; Anonymous 1977, sheet 323-D) and is

tilted to the south (Altınlı 1943) along a major, coast-

parallel normal-separation oblique fault. The topographic

X. Le Pichon � C. Rangin

College de France, Aix en Provence, France

C. Imren � A. M. C. Sengor (&)

Avrasya Yerbilimleri Enstitusu, Ayazaga, Istanbul Teknik

Universitesi, 34469 Istanbul, Turkey

e-mail: [email protected]

M. Siyako

Turkish Petroleum Corporation (TPAO), Ankara, Turkey

123

Int J Earth Sci (Geol Rundsch)

DOI 10.1007/s00531-013-0950-0

grain within this east–west trending range is north–north-

east and northeast, as in the Kapıdag Peninsula (classical

Arctonnesus).

Sedimentation in the Mysian trough began in the Pontian

(Late Miocene) with fluvial sediments and rapidly

developed into a lacustrine environment (Sengor et al.

2005). The southern branch of the North Anatolian Fault

runs out to the sea along a small rift that is located along the

Etili Fault Zone in the middle of the Biga Peninsula. It has a

geometry suggesting a pull-apart origin, although its

Fig. 1 a Map showing the setting of the SMF within the context of

the North Anatolian Shear Zone (Sengor et al. 2005). b A schematic

map showing the tectonic ecology of the newly discovered SMF.

Everything before the Miocene is here considered ‘‘basement,’’ i.e.,

the edifice all branches of the North Anatolian Fault had to disrupt to

come into existence. Black lines are medial Miocene to younger right-

lateral strike-slip faults (all belonging to the north Anatolian Shear

Zone). Blue lines mark the location of the faults belonging to the

SMF. Note that the northern branch of the North Antolian Fault

closely follows the contact between the Paleozoic of Istanbul and the

Sakarya basement and then jumps to follow the northern boundary of

the Intra-Pontide suture. It is clear that the fault has chosen here a

bimaterial boundary as it did farther in the east (see Sengor et al.

2005). The newly discovered SMF does the same thing in the south,

following the contact between the Sakarya basement and the Intra-

Pontide suture. This map shows how critically important it is to set

neotectonic features into the framework of paleotectonic ones to

establish what controlled the course of the former. The extent of the

Intra-Pontide suture in submarine areas is drawn by interpolating the

land-based observations, except south of the Lagoon of Buyukcek-

mece (just north of the letter N where it is written NAF), where the

seismic reflexion data show the edge of the Thracian basin clearly


123

northern part seems not to be faulted (Sengor et al. 2005).

The movement along this fault zone seems to have begun in

the Late Miocene as shown by the ages of the sediment

infills of the fault-related basins. In the Etili Rift, the basalts

associated with such sedimentary rocks give isotopic ages

of 9–8.4 Ma (Ercan et al. 1995; Aldanmaz et al. 2000).

This southern branch is still active, although it moves

much more slowly compared with the northern branch (at

most 5 vs. 22 mm/year). However, Sengor et al. (1985)

pointed out, and Le Pichon et al. (2003) concurred, that the

‘‘fragmented’’ nature of the southern strand shows that a

through-going main fault is yet to materialize, at least west

of Pamukova (Fig. 1a). This shows that this branch has

never been a fast moving fault and probably was overtaken

by its northern rivals before it could become a through-

going feature itself.

This has been a surprising feature of the southern strand,

because the northern strand did not materialize as a

through-going feature until at least the Late Pleistocene.

The question has long been which features then shared the

motion. This paper provides the answer: the North Ana-

tolian Shear Zone has another, now almost completely

abandoned intermediary branch, going from the Gulf of

Gemlik to the Strait of Dardanelles, skirting the Island of

Marmara to the north, which we here call the ‘‘South

Marmara Fault’’ (SMF) (Figs. 1a, b, 2). Its presence had

not been previously suspected, because it lies buried under

the Plio-Quaternary cover of the broad southern Marmara

shelf. Now, with the help of 800 km of previously

unpublished multichannel exploration seismic reflection

profiles of the seventies as well as the results of three drill

holes that penetrated the sedimentary cover down to the

Upper Cretaceous basement, we have unearthed the pres-

ence of this long, gently south-concave strike-slip SMF that

started moving in the later medial Miocene and deactivated

in the Early Pliocene (some 3.5 Ma ago).

Geologically, this remarkable feature seems to follow

mostly an old zone of material discontinuity, namely the

border between the Intra-Pontide suture zone with its broad

melanges of mainly Cretaceous to possibly earliest Paleo-

cene age with succeeding Paleocene-Early Eocene flysch

abutting the complex basement of the Sakarya continent to

the south (Sengor and Yılmaz 1981; for newer data cor-

roborating older observations, see Goncuoglu et al. 2008,

2012). That this coincidence is not perfect is a result of the

fact that the geometry of the suture/Sakarya contact is too

irregular with a wavelength that makes it impossible for a

strike-slip fault to follow. Interestingly, the northern, the

today-active, main strand of the North Anatolian Fault

seems to follow the northern bimaterial boundary of the

Intra-Pontide suture (there the coincidence is better,

because the suture boundary is straighter). In places (such

as near Bursa), there are indications from the juxtaposition

of older basement and Early Mesozoic ophiolitic melanges

that the today-active southern branch of the North Anato-

lian Fault probably also follows a suture, but an older,

Paleo-Tethyan one, namely that of the Karakaya (Fig. 1b;

see Sengor and Yılmaz 1981; Sengor et al. 1984; Okay

et al. 1996; Okay and Goncuoglu 2004).

As mentioned above, structurally, the SMF sits within a

high, bordered both to the north and to the south by normal

and extensional oblique faults. The northern boundary fault

Fig. 2 Synthetic structural map with locations of well holes and seismic profiles


123

of this high, which may be termed the Kara Dag High after

its most prominent eminence (833 m asl), is the SMF itself.

The southern limit is a series of disconnected normal faults

that drop toward the Mysian trough (Sengor et al. 2005).

South of the SMF, the basement consists of two main

units: a highly metamorphic gneiss ? marble association

that was deformed and metamorphosed about 384 Ma ago,

based on a single zircon dating using the Kober evapora-

tion technique (A. M. C. Sengor and A. Kroner, unpub-

lished data). This is everywhere tectonically overlain by

what is essentially an ophiolitic melange called the Kara-

kaya complex (Sengor and Yılmaz 1981; Sengor et al.

1984; Okay et al. 1996; Okay and Goncuoglu 2004).

Although Okay (2000) thought it represented the remnants

of an oceanic plateau, the components of the Karakaya

complex are far too diverse to allow such a facile inter-

pretation. It most likely represents partly the Paleo-Tethyan

suture and partly an ensimatic arc/marginal basin complex

that bordered it. The Karakaya was deformed during the

latest Triassic and earliest Jurassic and is overlain by the

sandstone of the Bayırkoy Formation that heralded a pro-

longed period of shelf sedimentation that lasted until the

end of the Cretaceous (Sengor and Yılmaz 1981).

Sometime after the end of the Cretaceous and before the

Lutetian, the Sakarya Continent collided with the Rhodope-

Pontide south-facing ensialic island arc to the north along a

north-dipping subduction zone. The ophiolitic melanges of

the Intra-Pontide suture are overlain by the Korudag-Ganos

flysch wedge that accumulated during the Eocene in an

environment of a remnant fore-arc basin within a collision

zone. The Thrace basin overlies this remnant fore-arc area

(Gorur and Okay 1996; unpublished gravity observations

by the Turkish Petrolem Company, indicating the presence

of high density material south of the Strandja Massif,

contradict the interpretation by Elmas (2012), that the

Thracian basin is mostly underlain by the rocks of the

Rhodope Massif: Mr. Vasfi Erol, pers. comm., 1981).

Eastward, the flysch and melange fill of the suture zone

pinch out, and there seems to be much elision of suture

material because of an earlier, possibly Eocene–Oligocene

strike-slip tectonics. In the Armutlu peninsula, the Paleo-

zoic of Istanbul lies above the foredeep flysches of the

Sakarya Continent across a thrust contact that appears to

have cut right into the lower crust as, at the western tip of

the Armutlu Peninsula, it exposes what seem to be deep

crustal mafic high-grade metamorphic rocks (Akbayram

et al. 2012; that they may be lower crustal mafic rocks: Dr.

Kenan Akbayram, pers. comm. 2012. Dr. Akbayram also

informs us that he no longer subscribes to the Early Cre-

taceous collision hypothesis and has returned to the long-

held Early Cainozoic interpretation) of Late Proterozoic to

Early Paleozoic ages (Bozkurt et al. 2013a). Farther east,

some Paleo-Tethyan ophiolites are mixed in with the

younger, Permo-Triassic, oceanic rocks of the Intra-Pon-

tide suture in the Almacıkdag region (Bozkurt et al.

2013b).

Shortening, right across the entire area shown in Fig. 1b,

continued until the Early Miocene, when it was replaced by

the establishment of a complex extensional regime shortly

afterward, to be followed by the formation of a broad right-

lateral shear zone, the North Anatolian Shear Zone (Sengor

et al. 2005). When the shear motion began, the region

consisted of a strong basement in the north (The Strandja

and the Paleozoic of Istanbul zones) constituting the

Rhodope-Pontide arc massif (see Sengor and Yılmaz 1981).

The flysch/melange fill of the central part made up the Intra-

Pontide suture. Finally, in the south, a highly disrupted

basement containing bits and pieces of an old, Late Paleo-

zoic basement and the much softer rocks of the Karakaya

complex formed a stronger basement than the Intra-Pontide

suture, but weaker than that of the Rhodope-Pontide Frag-

ment (Okay et al. 1996; Okay and Goncuoglu 2004). Le

Pichon et al. (2003) already pointed out that the regions

south of the main northern strand of the North Anatolian

Fault in the Marmara region were now accommodating

more strain than the regions north of it and ascribed this

asymmetry to the disparate geological constitutions of the

areas. We shall see below that the individual branches of the

North Anatolian Fault sensitively pick out bimaterial

boundaries to nucleate on, a behavior theoretically pre-

dicted (cf. Weertman 1980; Andrews and Ben-Zion 1997;

Ben-Zion and Andrews 1998; Ben-Zion 2001).

Chronological arguments: borehole Marmara 1

Borehole Marmara 1 is situated near the northern edge of

the southern Marmara shelf, two-thirds of the way between

Marmara Island and Imralı Island, near the northern

extremity of seismic profile 32 (Fig. 2). The only infor-

mation we have on the results of the drilling comes from

the final well report (Marathon Petroleum Turkey Limited

1975) as samples of cuttings and cores no longer exist

according to the Turkish Petroleum Company (TPAO),

except for the Upper Cretaceous basement. The following

stratigraphic sequence was observed (Fig. 3).

Sea floor 126 m (0.166 s twt): Unconsolidated quaternary

recent clay.

Unit 1: 163–238 m (0.27 s) Post-Rift calcareous mud-

stones of Lower Pliocene age (Pannonian in report); mostly

unconsolidated.

Unit 2: 236–1264 m (0.27–1.35 s) Average velocity

1.90 km/s Lower Pliocene (Pannonian in report) foreset

beds of fluvio-deltaic thickly interbedded sandstones


123

(average porosity, 42 %) and mudstones. Dipping on seis-

mic sections is to the SSE. Multiple level soft sediment

slumping is common, consistent according to the report,

with active faulting during deposition. Namık Cagatay

(private communication, February 8, 2011) considers that

the fauna mentioned in the report is not diagnostic of precise

stratigraphic ages. He identifies unit 2 with the Alcıtepe

Formation on the basis of the presence of foreset beds and

calcareous sediments. Cagatay states: ‘‘On land, Alcıtepe

Formation around Canakkale, Gallipoli Peninsula and Gulf

of Saros appears to comprise both Messinian and Lower

Pliocene according to the nanoplankton data of Melinte

(Melinte-Dobrinescu et al. 2009; Armijo et al. 1999; Armijo

et al. 2000).’’ Melinte-Dobrinescu et al. (2009) attribute

Alcıtepe to the post-Messinian as they believe that it lies on

top of what they consider to be the Messinian unconformity.

However, Namık Cagatay and Mehmet Sakınc have re-

examined the data and they cannot corroborate the exis-

tence of the unconformity presumed by Melinte-Dobrinescu

et al. (2009). They emphatically state that the question

remains open. Sengor and Le Pichon earlier examined the

outcrops in western Gallipoli Peninsula and they too could

not locate an unconformity under Alcıtepe. It could be that

the canyon filled by the sediments that was observed by

Armijo et al. (1999) is not representative of the deformation

of the Alcıtepe Formation in general.

Unit 3: 1264–2174 m (1.35–1.9 s) Average velocity

3.3 km/s Lower Pliocene mudstone oxidized and vari-

colored, with subordinate layers of sandstone (25 %

average porosity). Both the porosity of the sand layers and

the average velocity show that this unit is significantly

more consolidated than unit 2. Parallel bedding is identified

on seismic profiles according to the report, which states

that this unit may be Lower–Upper Miocene (Sarmatian–

Tortonian) at the base. These deposits appear to have been

deposited in a ‘‘fluvial, alluvial plain, claypan environ-

ment’’ A layer of red tuff is present at 1829 m Cagatay

(same personal communication as above) tentatively attri-

butes the tuffs to the 9.7 Ma alkali basalt volcanic activity

known in this area (Cagatay et al. 2006). Thus, unit 3 might

be the equivalent of the Kirazlı Formation, which is Upper

Miocene. It appears to have been deposited in a quieter

environment than unit 2.

Unit 4: 2174–2275 m (below 1.9 s) Below a major

unconformity lie uppermost Cretaceous (Campanian–Ma-

astrichtian) limestones. Similar Upper Cretaceous lime-

stones were penetrated by wells on the Gallipoli Peninsula

and crop out on the Imralı Island. Thus, the whole sequence

of Paleocene–Eocene–Oligocene–Lower and Middle Mio-

cene is missing and was presumably eroded, which is hardly

surprising this close to the suture. This unconformity coin-

cides with the acoustic basement that is well identified on the

seismic sections. The absence of the Eocene was a surprise

for the drillers as the Eocene Formation was the main target

of the well as they did not know about the suture.

To conclude, well Marmara 1 (Fig. 4) shows that after a

period of strong erosion, a rifting phase with relatively fast

Fig. 3 Logs of drill holes Marmara 1, Isıklar 1, Doluca 1. For each well, log to the right and seismic section to the left


123

subsidence occurred there during Upper Miocene (11 to

10?–5.3 Ma?) and that it continued into the uppermost

Miocene–Lower Pliocene (Alcıtepe Formation, 5.3?-3.7 to

3.4 Ma?) during which foreset beds of fluvio-deltaic

thickly interbedded sandstones and mudstones that might

correspond to the Gilbert deltas described by Melinte-

Dobrinescu et al. (2009) were deposited. The source of

sediments was to the NW. Tectonic activity appears to

have been significantly stronger during the deposition of

this unit. The rifting phase was terminated when the Lower

Pliocene fresh water calcareous mudstone of unit 1 was

deposited, probably corresponding with the ConkbayırıFormation, which is younger than 3.7–3.4 Ma (Yaltırak

et al. 2000) Fig. 5.

The shelf east of Marmara Island

We now use the stratigraphy of Marmara 1 well, located on

seismic profile 32, at the northern limit of the southern shelf

basin and the southern limit of the Marmara basin, as a key

to interpret seismic section 32 and to extend this interpre-

tation eastward and westward over the whole shelf, using

adjacent seismic reflection profiles (see Fig. 2). This inter-

pretation enables us to map a deformation zone, about

10 km wide that can be followed along the whole shelf,

from the Gemlik Bay to the east to the Dardanelles Straits to

the west. We call it the SMF system (Fig. 2). The acoustic

basement, which coincides with the post-Upper Cretaceous

erosional unconformity, can be identified throughout the

section. Unit 3 (the Upper Miocene Kirazlı Formation)

which is 900 m (0.55 s) thick at the well increases to nearly

2 km (1.1–1.2 s) to the south of the southern shelf basin.

There, the basement has been downfaulted by more than

2 km, mostly during the Upper Miocene (Kirazlı). In the

central part of the section, the basement has been uplifted by

more than 1 km, after the rifting, forming a 10-km-wide

anticlinal fold. The consequent uplift led to the erosion of

unit 2 as well as the upper part of unit 3 near the summit of

the anticline. This folding was contemporaneous with the

formation of the broad zone of deformation of the SMF

system, while the uppermost SE dipping foreset beds of unit

2 (uppermost Miocene–Lower Pliocene Alcıtepe Forma-

tion) were still being deposited to the south. It is important

to note that the source of the sediments during the deposi-

tion of units 2 and 3 was to the NW and not to the south.

The quality of the seismic profile is not such that the

style of deformation can be unambiguously determined.

However, the central part of the deformation zone, near the

apex of the uplifted basement, coincides with a flower

structure that we interpret as compressive. Figure 1 shows

that this zone of deformation can be followed both west-

ward to the Marmara Island and eastward to the ImralıIsland. Profile LD 70 (Fig. 6), between profile 32 and

Marmara Island, demonstrates that the uplift of the base-

ment by 1.5 km increases westward toward Marmara

Island and that both units 2 and 3 above the anticline have

been conformably folded and strongly eroded. Thus, the

uplift occurred near the end of Lower Pliocene. Profile 60

(Fig. 7), halfway between profiles 70 and 32, confirms the

strong uplift and folding of the basement as well as its

conformable Upper Miocene–Lower Pliocene cover. This

deformation is definitely post-unit 3 (Kirazlı) and probably

contemporaneous with the deposition of the upper part of

unit 2 (Alcıtepe). The interpretation to the north of shot

point 300 is tentative but there is no doubt that a post-

Alcıtepe EW normal fault marks the edge of the shelf to the

north. Figure 8 shows a NW/SE chirp profile across the

northern part of profile 60 near shot point 230, which

displays eroded sedimentary layers with a component of

dip to the SE. These eroded layers most probably belong to

the lower part of unit 2.

The Marmara Island (ancient Proconnesus), to the west,

is made up of north-dipping metamorphic thrust sheets

interlayered with metagranitoid intrusions dated by

Ustaomer et al. (2009) as Lutetian (47.6 ± 0.2 Ma). The

pluton underwent severe brittle-ductile deformation, fol-

lowing its mid-Eocene emplacement, with the development

of both a N-dipping foliation and an WNW-ESE doubly

plunging stretching lineation. These structures indicate a

top to south motion and record the formation and the

tightening of the Intra-Pontide suture (Ustaomer et al.

2009). The seismic profiles to the east of Marmara Island

indicate that Marmara Island must have been uplifted and

broadly warped by about 1.5–2 km near the end of Lower

Pliocene. An examination of a slope map of the island

confirms the broad EW anticlinal upwarp of the island. We

do not have the information necessary to determine

Fig. 4 Simplified log of Marmara 1 well


123

whether part of the SMF system entered the northern part

of Marmara Island, possibly reactivating the Eocene

thrusts, or whether the whole zone of deformation was

deflected to the north of the island, on the edge of the shelf,

to avoid the Kapıdag Peninsula-Marmara Island basement

block. This is because the later normal faulting that created

the present Marmara basin at the end of Lower Pliocene

had encroached on and at least partly obliterated the SMF

system immediately north of the Marmara Island.

At the eastern extremity of the part of the area we have

just discussed, the zone of deformation appears to enter the

northernmost Imralı Island. An examination of a slope map

of Imralı Island shows that the southern two-thirds of the

island appear to form a broad NS fold, while the northern

extremity is marked by an EW elevated high with steep

topography to the north, most probably coinciding with

major EW faults. The sharp bend of the SMF system, from

EW to SE, near Imralı Island may coincide with a change

from a principally reverse component of motion to the west

to a normal one to the east. This change would be expected,

as the main motion on the SMF system was dextral.

Unfortunately, as for the northern Marmara Island, the later

normal faulting that created the present Marmara basin and

now roughly coincides with the edge of the shelf has also

encroached on and partly obliterated the earlier deforma-

tion zone immediately north of Imralı Island, as it did north

of Marmara Island. Furthermore, although profiles 14 and

9a to the east of Imralı confirm the presence of the SMF

system east of Imralı Island (see Fig. 2), the style of

deformation is difficult to unambiguously characterize.

Further east, in Gemlik Bay, Kuscu et al. (2009) have

mapped a set of active dextral faults that are in the direct

Fig. 5 Seismic section 32. See location in Fig. 1. Bottom TPAO

seismic section. Top Line drawing. Thick black, Upper Cretaceous

basement. Green, Upper Miocene (Kirazlı) rifting faults at the origin

of the southern shelf basin. See location of Marmara-1 well. Red,

Lower Pliocene (Alcıtepe) mostly reverse and transcurrent faults

associated with the formation and evolution of the SMF. Blue, post-

Alcıtepe normal faults associated with the subsidence of the Marmara

basin to the north. Note the Lower Pliocene uplift of the central part

of the section, which is syntectonic with the activity of the SMF Fault

(Fig. 1)

Fig. 6 Seismic section 70. See location in Fig. 1. Bottom TPAO

seismic section. Top Line drawing. See Fig. 4 for legend. Note that

units 2 and 3 are folded conformably with the uplifted Upper

Cretaceous basement. The uplift and consequent folding is syn- to

post-Alcıtepe


123

prolongation of the SMF system. Gasperini and Polonia

(2009) have evaluated a rate of 5 mm/year for the dextral

strike-slip across the Gemlik Bay. It is thus probable that

the SM Fault extended eastward into the Gemlik Bay and

that the portion east of Imralı Island is still active today and

now extends northwestward into the southern slope of the

Marmara basin. In a recent IODP meeting, Gunay Cifci and

Seda Okay presented a high-resolution seismic profile near

Imralı Island which may indicate that this present activity

of the SMF extends somewhat west of Imralı (Pierre

Henry, personal communication, October 2012).

The shelf west of Marmara Island

As mentioned above, the SMF system is offset to the north

as it enters the Marmara Island uplift. Most of it has

probably been reactivated to form the slope of the Marmara

basin at the end of Lower Pliocene. Further west, the SMF

can be recognized again to the NW of Marmara Island,

coming out of the southern Tekirdag basin, near 40�400Nand 27�200E. It is then abruptly offset by 5 km to the SSW

along a fault near 27�25�E. This NNW/SSE fault appears

to mark the western limit of the broad basement uplift to

which the Kapıdag Peninsula, the Marmara Island, and a

set of smaller islands belong (Fig. 2).

West of this fault, starting with profile 99, the SMF

system can be precisely mapped with the help of closely

spaced seismic profiles and two wells that penetrated the

whole sedimentary sequence, Doluca-1 borehole on profile

102 and Isıklar-1 borehole on profile 114 (Figs. 2, 3, 9, 10).

Unfortunately, the detailed final reports of the two wells

are not available any more. However, records at TPAO

indicate that below 54 m of water, Doluca-1 drill hole

penetrated a Middle Miocene Formation described as

Gazhanedere and reached the basement immediately below

it at a depth of 800 m (Fig. 2). The basement is described

as ophiolitic melange and was penetrated over a thickness

of 300 m. It is considered to be pre-Neogene. Thus, the

whole Neogene sedimentary section below the Middle

Miocene is missing, as in borehole Marmara-1. The

Gazhanedere Formation is stratigraphically below the

Upper Miocene Formation and corresponds to the Middle

Miocene (Burdigalian to Serravallian, 17–10 Ma, Cagatay

et al. 2006). If the identification is correct, the Upper

Miocene (Kirazlı Formation) and the Lower Pliocene

(Alcıtepe Formation) have been eroded to the north of

Fig. 7 Seismic section 60. See

location on Fig. 1. Bottom

TPAO section. Top line

drawing. See Fig. 4 for legend.

Note the strong uplift and

folding of the basement and its

sedimentary cover to the south

with the apex of folding just

south of shot point 300. The

profile is more difficult to

interpret to the north and the

interpretation we propose there

may be discussed

Fig. 8 Chirp profile across the northern portion of profile 60 from

cruise Marnaut (courtesy of Pierre Henry 2010). Note the eroded

sedimentary layers with a component of dip to the SE. They probably

belong to unit 2


123

profile 102 (Fig. 8) but are present in the central part of the

profile where they have been affected by steep thrust and

presumably dextral faulting of the SMF system. A pre-

sumably Upper Pliocene to Pleistocene section uncon-

formably overlies the Lower Pliocene and Upper to Middle

Miocene layers affected by the deformation. Thus, the

activity of the SMF system most likely has the same age

west of Marmara Island as it has east of it.

Fifteen km west of profile 102, profile 114 (Fig. 10) is

calibrated by borehole Isıklar-1 (Fig. 3). The drill hole

penetrated below 68 m of water, 278 m of conglomerate,

sandstone, and mudstone described as the Upper Miocene

Gazhanedere Formation with an average velocity of 2

155 m/s and thus poorly consolidated. However, as men-

tioned above, the Gazhanedere Formation corresponds to

the Middle Miocene but in the absence of samples and

detailed stratigraphic descriptions, the validity of this dating

cannot be verified. Then, the drill hole penetrated 239 m of

turbidites of the Upper Eocene Ceylan Formation, 110 m of

limestones of the Upper–Middle Eocene Sogucak Forma-

tion, and 136 m of clastics of the Middle Eocene Koyunb-

aba Formation. The average velocity of this 485 m. Eocene

sequence is 3 465 m/s. The Eocene Formation is thus much

better consolidated than the Miocene sediments deposited

on top of it after an important episode of erosion. Finally,

the drill hole penetrated over 32 m of basement described as

ophiolitic melange (as in Doluca – 1) with an average

velocity of 4 000 m/s. Profile 114 shows that the well was

drilled on top of an anticlinal warp that resulted in the

erosion of the Upper and Late Miocene layers. Reverse

faults forming a flower in the summit area of the anticlinal

warp are post-Middle Miocene and probably of the same

Late Lower Pliocene age as further east. The difference

there is that the Eocene is still present as in the Gelibolu

Peninsula area to the north.

From the shelf west of Marmara Island

to the Dardanelles Straits

The available seismic profiles allow us to trace the SMF

system to 26�500E, off the Biga Peninsula, just east of the

entrance to the Dardanelles Straits. The dating of the post-

Miocene tectonics of the area around the Dardanelles

Straits has been the subject of several studies recently

(Armijo et al. 1999; Yaltırak et al. 2000; Armijo et al.

2000; Sengor et al. 2005; Sen et al. 2009; Melinte-Dob-

rinescu et al. 2009). All studies relate the tectonics to the

Ganos branch of the dextral North Anatolian Fault

(Fig. 11). All note the significant folding and thrusting of

the SW Thrace basin within the Gelibolu area extending

into and beyond the Dardanelles Straits that involve Upper

Miocene deposits, with steep, up to vertical dips, tight

secondary folds, and locally reverse faults and thrusts.

Fig. 9 Seismic section 102.

See location in Fig. 1. Bottom

TPAO seismic section. Top Line

drawing. Doluca-1 well is close

to the northern extremity of the

profile. Thick black, Upper

Cretaceous basement. Red,

Lower Pliocene (Alcıtepe)

mostly reverse and transcurrent

faults associated with the

formation and evolution of the

SMF. Note the strong erosion of

the Late Miocene section at the

northern end of the section and

the absence of the whole

Neogene section, the acoustic

basement coinciding in well

Doluca-1 with what is described

as an ophiolitic melange of

probable Upper Cretaceous age


123

These structures, kilometers to tens of kilometers long, are

subparallel to each other and to the trend of the Dardanelles

Straits and of the Ganos Fault. They are thus also subpar-

allel to the SMF system, having the same curvature.

Immediately north of the Dardanelles Straits, a promi-

nent anticline is bordered to the south by a thrust fault

called the Anafartalar Fault. Most of the studies propose

that the main tectonic event there took place during the

deposition of the mid-Pliocene (3.7–3.4 Ma) ConkbayırıFormation in an alluvial fan environment in front of the

transpressional Anafartalar thrust (see Yaltırak et al. 2000;

see also Sen et al. 2009). Armijo et al. (1999, 2000) do not

agree as they claim that the significant unconformity is at

the base of the older Alcıtepe Formation, that they pro-

posed to be post-Messinian, and that the Alcıtepe Forma-

tion is essentially undeformed. Thus, the end of tectonic

activity for them would coincide with the end of the

Messinian and be 5.3 Ma, not 3.7–3.4 Ma. But this claim

does not appear to us to be substantiated (see our discus-

sion above) and we do not follow their interpretation.

The data that we have discussed above lead us to propose

that at least part of the latest to post-Miocene deformation in

the Dardanelles Straits and in the Gelibolu area to the north

of it is due to the extension of the SMF system in the

Dardanelles area and not to the initiation of the present

Ganos branch of the North Anatolian Fault. However, there

is the possibility that as the SMF system was abandoned, the

fault jumped northward by about 15 km in this area and

initiated the Ganos branch of the North Anatolian Fault that

is remarkably parallel to the SMF system west of Marmara

Island and that deformation of both systems overlap.

We stress again that our data suggest that this defor-

mation is post-Alcıtepe and thus about 3.5 Ma and not pre-

Alcıtepe, or about 5.3 Ma as proposed by Armijo et al.

(1999). We believe that an investigation should be made of

whether the canyon filled by the Alcıtepe sediments that

was observed by Armijo et al. (1999) is not representative

of the deformation of the Alcitepe Formation in general.

Discussion and conclusion

The one clear and significant result of this study is the

discovery of a hitherto unknown and now largely dead

Fig. 10 Seismic section 114.

See location in Fig. 1. Bottom

TPAO seismic section. Top Line

drawing. Isıklar-1 well lies in

the middle of the profile. Thick

black, Upper Cretaceous

basement. Red, Lower Pliocene

(Alcıtepe) mostly reverse and

transcurrent faults associated

with the formation and

evolution of the SMF. Note the

erosion of the uppermost

Miocene and the Lower

Pliocene in the central part of

the section


123

branch of the North Anatolian Fault. It lies between the

highly active northern branch and the weakly active (but

still capable of generating magnitude 7 earthquakes on a

possibly demi-millenial repeat time in any one locality)

southern branch. The new fault, which we here call the

SMF, is located within a relative high, as opposed to the

location of the northern and the southern branches that are

located within deeps.

Both the northern and southern Marmara branches

should be slightly extensional in the present system if you

apply the average Anatolia/Eurasia rotation to both (see

Fig. 5 of Le Pichon and Kreemer 2010). Indeed, these two

faults became segmented and developed deeps along them

that are wedge basins and negative flowers, the Cınarcıkbasin in the eastern part of the Sea of Marmara being the

largest of these basins. On the other hand, in this rotational

system, the part of the SMF east of Marmara Island should

be extensional and west of it compressional, which is

approximately what one observes. This is because the SMF

had to bend around the Kara Dag High.

But why did the main fault within the Marmara Shear

Zone did migrate northward from its initiation in Mid-

Miocene to the present? As the slip rate increased along the

NAF, as proposed by Sengor et al. (2005), the orientation

of the Hellenic subduction progressively changed from

southward to southwestward and the northwestern end of

the Hellenic subduction consequently migrated northward

to its present position. This led to the northward migration

of the prolongation of the NAF in the Marmara–Aegean

area to join the northward migrating northwestern

extremity of the Hellenic subduction (see Fig. 5 of Le

Pichon and Kreemer 2010).

The evolution we propose is that in the medial Miocene,

the Marmara shear zone formed of numerous roughly east–

west orientated dextral fault segments which functioned in

various ways of across-strike strains, but always dextrally

in along-strike strains. Some rotated individually, others

with their neighbors. This process is seen today in its

incipient form along the southern strand where there is no

through-going fault similar to the one along the very active

northern strand. But the main motion was progressively

transferred northward, first to the SMF, that seems to have

died shortly or immediately after it had become a through-

going feature, because the northern branch had started

taking up more and more of the motion for the reasons we

have proposed above.

Our conclusions were written before the January 8,

2013, earthquake that occurred at 16:16:06 local time and

had an Mw = 6.2. The following information about this

earthquake and its largest aftershock was kindly supplied

by Dr. Dogan Kalafat of the Kandilli Observatory in

Istanbul. The hypocenter was given as 8.4 km. The earth-

quake occurred on the direct southwesterly continuation of

the SMF and showed a pure right-lateral strike-slip. The

largest aftershock (Mw = 4.6) had exactly the same char-

acteristics and occurred on the same fault some 10 km to

the northeast of the main shock. All other aftershocks

cluster around the southwestern extension of the SMF.

There is very weak seismicity along the rest of the SMF,

showing that such faults do not die at once. Segments of

them remain active, as the latest Aegean earthquakes

referred to above show and most likely they take up motion

from neighboring segments. There is hardly a serious offset

at the occidental termination of the southernmost branch of

Fig. 11 The synthetic structural map of Fig. 1 with locations of well

holes and seismic profiles is complemented by a bathymetric map

over the Sea of Marmara and a topographic map on land. Structures in

the Sea of Marmara are after Le Pichon et al. (2001). The structures

on land in the SW Thrace basin are after S. Sen et al. (2009).

Structures in the Gulf of Gemlik are after I. Kuscu et al. (2009)


123

the North Anatolian Fault and this has long concerned

those studying the westernmost part of the southernmost

branch of the North Anatolian Fault. We propose that this

is because the southernmost branch transfers its offset to

the occidental end of the SMF across a series of poorly

known wrench fault segments in the westernmost part of

the Biga Peninsula.

The data presented in this paper have very important

implications for the evolution of strike-slip shear zones, in

other words entire keirogens. In both orogens and taphro-

gens, faulting progresses either in a forward (forefolding) or

in a backward (backfolding) sense and after a time, both

senses are seen simultaneously at both flanks of an orogen or

a taphrogen. This is because gravity influences faulting as

faulting changes the potential energy of rock masses. Keir-

ogens do not in principle change the potential energy of the

rock volumes they affect, and the spatial evolution of faulting

in them is much more irregular and is controlled mainly by

strain hardening or strain weakening and the presence of pre-

existing weak zones and by the forces applied at the

boundaries. In the case of the North Anatolian Shear Zone,

the presence of the Intra-Pontide and the Karakaya sutures

has profoundly affected the placement of the major fault

strands. In the western part of the Biga Peninsula, the pres-

ence of several strands of serpentinite screens, possibly

formed by former, collision-related escape structures

repeating parts of the Intra-Pontide suture, may have facili-

tated motion transfer from the southern branch to the SMF.

Acknowledgments This project was initiated in October 2003

during a visit by Xavier Le Pichon and Caner Imren to TPAO in

Ankara. We thank TPAO for access to seismic lines shot on the

southern shelf of the Sea of Marmara in 1974 and 1975 and to the

reports of drill holes Marmara 1, Doluca 1, and Isıklar 1. We thank N.

Cagatay and M. Sakınc for important information and advice con-

cerning the stratigraphy of boreholes; we thank P. Henry, C. Grall,

and members of the College de France team for valuable discussion.

We thank Erdin Bozkurt and Bernard Mercier de Lepinay for their

useful reviews.

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Documents

The South Marmara Fault