GEOLOGICA CARPATHICA, FEBRUARY 2006, 57, 1, 3—13
www.geologicacarpathica.sk
Sedimentary records of the extensional tectonic regime with
temporal cessation: Gümü hane Mesozoic Basin (NE Turkey)
CEMIL YILMAZ
1
and RAIF KANDEMùR
2
1
Karadeniz Technical University, Geology Department, 61080 Trabzon, Turkey; cyilmaz@ktu.edu.tr
2
Karadeniz Technical University, Geology Department, Gümü hane, Turkey; raif@ktu.edu.tr
(Manuscript received November 10, 2004; accepted in revised form June 16, 2005)
Abstract: The Gümü hane Mesozoic Basin is characterized by Lower—Middle Jurassic volcanic-siliciclastic sediments
( enköy Formation), Upper Jurassic—Cenomanian platform carbonates (Berdiga Formation) and Upper Cretaceous turbid-
ites (Kermutdere Formation). Four extensional periods (Lias—Dogger, Turonian—Coniacian, Late Campanian (?) and Early
(?) Maastrichtian) separated by two quiet tectonic periods (early Malm—Cenomanian and Santonian—Campanian) have been
defined in this sequence. The previous studies suggested that Mesozoic basins only formed by extensional movements in the
middle Cretaceous. Three extensional periods seperated by two quiet periods from the Cenomanian to the end of the
Maastrichtian in Gümü hane and NE Turkey were firstly proved by sedimentological findings in this study. The definition
of these periods depends on features such as (1) neptunian dykes in different levels, (2) shallow marine limestone,
(3) thinning-and-fining-upward sequences, (4) mixed faunal assemblages, (5) micro-turbiditic structures, (6) syn-sedi-
mentary fault, (7) grabens, half-grabens, (8) pelagic limestone, (9) calciturbidites, (10) laterally and vertically rapid
changes of the thickness and facies, (11) platform-to-basin transition and (12) monogenic breccias.
Key words: Jurassic—Cretaceous, NE Turkey, Gümü hane Basin, extensional tectonic regime, sedimentary record.
Introduction
The study area is located at the southern zone of the East-
ern Pontides, NE Turkey (Ketin 1966; Gedikoûlu et al.
1979; Yôlmaz et al. 1997), around the city of Gümü hane
(Fig. 1). The Gümü hane region has been studied by previ-
ous authors with respect to stratigraphy, paleontology,
tectonics and geotectonics (Tokel 1972; Eren 1983; Görür
et al. 1983; Bekta 1986; Bergougnan 1987; Taslô 1991;
Bekta et al. 1995; Robinson et al. 1995; Taslô & Özsayar
1997; Yôlmaz 1997, 2002; Yôlmaz et al. 1997; Yôlmaz &
Korkmaz 1999; Eren & Taslô 2002; Kandemir 2004).
There are different views on the geological evolution
of the Eastern Pontides. According to
engör et al.
(1984), the Eastern Pontides forms the eastern continua-
tion of the Rhodope-Pontide fragment. It is generally ac-
cepted that the Rhodope-Pontide fragment lies entirely
to the north of the neo-Tethyan oceanic sutures and
therefore it represents the northern margin of the neo-
Tethys Ocean. engör & Yôlmaz (1981) suggested that
the neo-Tethys Ocean was consumed from the Early Ju-
rassic to mid-Eocene by a northward-dipping subduc-
tion. In this view, the Black Sea represents the remnant
of a back-arc basin which opened to the north of the
Eastern Pontides during the Late Cretaceous. Okay &
Tüysüz (1999) and Okay et al. (2001) suggested that dur-
ing the Late Cretaceous period, northern and western
Turkey was comprised of two continents, the Pontides in
the north and the Anatolide-Taurides in the south, sepa-
rated by the neo-Tethyan Ocean. During the conver-
gence, the Pontides formed the upper plate, the
Anatolide-Taurides acted as the lower plate. However,
Dewey et al. (1973) and Bekta et al. (1984) suggested
that the Eastern Pontides were attached to a segment of
the neo-Tethys which was subducted towards the south.
In this model, the Black Sea represents a remnant of the
paleo-Tethys Ocean.
According to Gedik et al. (1996) the Early Jurassic ba-
sin in the Gümü hane area (NE Turkey) was controlled
by transtensional tectonics. Bekta & Çapkônoûlu (1997)
and Yôlmaz (1997) argued that Mesozoic basin in NE
Turkey was characterized by two rifting phases, Early Ju-
rassic and mid-Cretaceous in age. The first rifting is relat-
ed to break up of the Hercynian granitic basement,
whereas the latter is related to the break up or drowning
of the carbonate platform indicated by transition from
the platform carbonate environment to the pelagic facies.
The quiet tectonic period developed between these two
distinct rifting phases in the southern zone of the Eastern
Pontides is characterized by the deposition of thick and
widespread carbonates known as Eastern Pontide Car-
bonate Platform (Bekta et al. 1995) was broken up by
extensional tectonic movements during the mid-Creta-
ceous. This conclusion has been confirmed by Yôlmaz
(1997), Bekta et al. (1995, 1999), Rojay & Altôner
(1998) and Eren & Taslô (2002). According to Rojay &
Altôner (1998), the Jurassic—middle Cretaceous carbon-
ates in the Pontides were deposited in an Atlantic-type
continental margin facing the neo-Tethys to the south.
Kandemir (2004) emphasized that the Early-Middle Ju-
rassic
enköy Formation is represented by typical rift
sediments. Eren & Taslô (2002) suggested that the con-
tact between the shallow water limestones (Berdiga For-
mation) and overlying red pelagic limestones are
4
YILMAZ and KANDEMùR
separated by a hardground surface in the east of
Gümü hane. The same authors argued that this event is re-
lated to the break-up and subsidence of the Eastern Pon-
tide Carbonate Platform, during the formation of the Black
Sea back-arc basin. According to Bekta et al. (2001), mul-
tidirection neptunian dykes (NE—SW, NW—SE and E—W)
are consistent with the general trend of the paleofaults.
The previous studies (Robinson et al. 1995; Gedik et al.
1996; Bekta et al. 1995, 1999; Taslô & Özsayar 1997;
Yôlmaz 1997; Bekta et al. 2001; Eren & Taslô 2002) sug-
gested two extensional periods in the Jurassic—Cretaceous
span at Gümü hane and NE Turkey. However, obtained
data during this study prove that the Cretaceous sequence
in Gümü hane were not formed by only one extensional
movement indicated by previous studies but by more than
one. The evidence shows sedimentary records of three dif-
ferent extensional periods. These new findings are an
important contribution to knowledge of the tectonic de-
velopment of Gümü hane and NE Turkey.
This paper primarily deals with the sedimentary
records showing the cessation of extensional tectonic
movements in the Mesozoic sedimentary basin in the
Gümü hane region.
Stratigraphy of the study area
In the study area, five different lithostratigraphic units
have been identified (Fig. 1 and Fig. 2): 1 – Paleozoic
Gümü hane Granite and Pulur Metamorphites forming
Fig. 1. Geological map of the study area (after Yôlmaz 1997).
the basement, 2 – Early to Middle Jurassic rift-related
sediments and volcano-clastics (first rifting phase; Yôlmaz
1997), 3 – Late Jurassic to mid-Cretaceous platform car-
bonates (Eastern Pontide Carbonate Platform; Bekta et al.
1995), 4 – Middle to Late Cretaceous rift-related sedi-
ments (second rifting phase; Yôlmaz 1997), 5 – Eocene
volcano-sedimentary rocks.
There is a heterogeneous pre-Jurassic basement in the
southern part of the Eastern Pontides. It contains Paleozoic
massifs, made-up of granites and metamorphic rocks
(Fig. 2). The Jurassic in the Eastern Pontides is characteristi-
cally represented by a predominantly volcano-sedimentary
formation ( enköy Formation), which rests unconformably
over a heterogeneous basement. The enköy Formation is
2—2243 m thick and shows vertical and lateral facies changes
(Fig. 3a—e; Yôlmaz & Kandemir 2003). The enköy Forma-
tion starts with coal-bearing medium- to thick-bedded con-
glomerate and sandstone alternations. The formation is
characterized by Calcari Ammonitico Rosso facies with as-
sociations of ammonites, brachiopods, bivalves, gastropods,
belemnites, crinoids, foraminifers and nodular textures and
turbiditic volcanogenic sandstones-siltstones, tuffite, tuff,
pillow lava basalt, andesitic lavas, shale, and turbiditic
sandstones. These sediments pass upward into thick-bed-
ded, shallow marine Callovian—Cenomanian aged oolitic
platform carbonates (Berdiga Formation; Pelin 1977). The
enköy Formation is conformably covered by platform car-
bonates of the Berdiga Formation in the Eastern Pontides.
This platform carbonates consist of medium- to massive-
bedded, grey to yellowish limestones (Fig. 3f—i). The lower
5
SEDIMENTARY RECORDS OF THE EXTENSIONAL TECTONIC REGIME (NE TURKEY)
and middle parts of this formation are rich in oolites and
bivalve fragments, which are partly dolomitized. The up-
per part is characterized by the wackestones/packstones
containing abundant small benthic foraminifers, ostracods
and algae with chert nodules. The total thickness of the
formation varies between 300 and 500 meters. These se-
quences are covered by the Upper Cretaceous Kermutdere
Formation (Tokel 1972). Kermutdere Formation has a tran-
sitional contact with underlying platform carbonates. It
consists mainly of turbiditic sequences. The basal part of
the Kermutdere Formation consists of pelagic monogenic
breccias/conglomerates, calciturbidites and red lime-
stones, which contain a pelagic microfauna such as Glo-
botruncanidae. This basal part grades upward into an
alternation of thin-bedded turbiditic sandstones-marls-and
pelagic biomicrites. The thickness of the formation ranges
from 45 to 1200 meters. Kermutdere Formation is uncon-
formably covered by the Eocene Alibaba Formation (Tokel
1972). The formation consists of thick and widespread vol-
caniclastics and local nummulitic sandy limestones. For
Fig. 2. Columnar section of the study area.
6
YILMAZ and KANDEMùR
Fig. 3. Structures developed during the Lias-Dogger extensional tectonic period and structures developed during the Malm-Cenomanian quiet
tectonic period. (a) 1 – Paleozoic Gümü hane Granite, 2 – Lias-Dogger enköy Formation, lower part consists of limestone
of Calcari Am-
monitico Rosso (CAR) facies, (b) neptunian dyke in the Gümü hane Granite, (c) volcanic-siliciclastics in the enköy Formation, (d) mi-
croscopic view of the volcanic-siliciclastics, (e) microscopic view of the limestone (CAR), (f) limestones of the Berdiga Formation,
(g) sandy oolitic grainstone, (h) dolomitized limestone, (i) small benthic foraminiferal grainstone. Scale bar is 500
µm.
7
SEDIMENTARY RECORDS OF THE EXTENSIONAL TECTONIC REGIME (NE TURKEY)
ages of the Berdiga and Kermutdere Formations we follow
the biostratigraphic data of Taslô (1991), Taslô & Özsayar
(1997) and Eren & Taslô (2002).
Quiet and extensional consecutive tectonic periods
in the study area
Lithological and sedimentological characteristics of
the Mesozoic sequences in the Gümü hane area indicate
four extensional and two quiet tectonic periods (Fig. 2).
First period – Extensional Tectonic Regime (Early—
Middle Jurassic)
This period started with rifting of the Hercynian base-
ment in the Early Jurassic and ended in the Late—Middle
Jurassic with the deposition of platform carbonates. The
Early—Middle Jurassic extensional tectonic period is char-
acterized by deposition of the enköy Formation, which
consists of volcano and silici-clastic turbidites (Fig. 3b,d)
and fossiliferous limestones which developed in the Cal-
cari Ammonitico Rosso facies (Fig. 3a,e). Many cracks de-
veloped on the basement rocks are filled by neptunian
dykes of Liassic sediments (Fig. 3b). Volcanic and silici-
clastic turbiditic sequences are characterized by fining-
and-thinning upward sequences. The
enköy Formation
gradually passes upward into the sandy oolitic grainstones
of the Berdiga Formation.
Second Period – Quiet Tectonic Regime (Late Jurassic—
Cenomanian)
This period corresponds to the deposition of the plat-
form-type shallow marine limestones of the Berdiga For-
mation, which make up a small part of the Eastern
Pontide Carbonate Platform (Bekta et al. 1995). The Ber-
diga Formation consists of medium- to massive-bedded,
grey to yellowish limestones (Fig. 3f). The lower and mid-
dle parts of this formation are rich in oolites (Fig. 3g) and
bivalve fragments, which are partly dolomitized (Fig. 3h).
The upper part of the formation is characterized by the
presence of packstones/grainstones containing abundant
small benthic foraminifers (Fig. 3i), ostracods and algae
with chert nodules. The total thickness of the formation
varies between 300 and 500 meters.
Third Period – Extensional Tectonic Regime (Turonian—
Coniacian, Figs. 4—6)
This period is characterized by break-up of the carbonate
platform and accumulation of monogenic breccias/con-
glomerates and calciturbidites (lower part of the Kermutdere
Formation) during the Early Turonian. The carbonate plat-
form broke up to form grabens and half-grabens (Fig. 4). At
the base of these grabens monogenic breccias/monogenic
conglomerates were deposited (Fig. 5A, Fig. 6a,b). These are
poorly and thickly bedded, unsorted monogenic limestone
breccias involved different stratigraphic levels of the plat-
form carbonate. However, some of the clasts are derived
from volcanics of the enköy Formation (Fig. 6b). These
monogenic breccias are grain-supported with a small
amount of matrix including benthic and pelagic foramin-
ifers (Fig. 5A,C). The matrix consists of red or grey mi-
crite and fine-grained clasts with a composition similar
to the larger components. The fossil assemblage shows a
mixture of benthic and pelagic fauna derived from near-
by submarine highs. The calciturbidites consist of nor-
mally-graded wackestones and packstones containing
debris of small benthic foraminifers, echinoderms, bryo-
zoans, pelagic foraminifers and sand-sized lithoclasts de-
rived from the Berdiga Formation with pelagic matrix
(Fig. 5B,D,E). The subrounded-angular clasts were de-
rived from the platform edge and transported down the
slope into the more pelagic slope facies by the turbiditic
currents. The limestone breccia and calciturbidite se-
quences are vertically arranged in thinning-and-fining
upward megacycles (Fig. 5B). The upper level of the Ber-
diga Formation includes many neptunian dykes, which
are filled by overlying sediments (Fig. 6e,f). The mono-
genic breccias/monogenic conglomerates and calcitur-
bidites which developed during the third extensional
tectonic period are overlain by thin-bedded, red pelagic
limestones.
Fourth Period – Quiet Tectonic Regime (Santonian—
Campanian)
This period is characterized by pelagic foraminiferal pack-
stones/wackestones, which are predominantly represented by
red to dark grey, dense, fine-grained limestones with pelag-
ic foraminifers and less abundant radiolarians (Fig. 7a,c).
The base of this unit also contains calcarenite with suban-
gular grains in an argillaceous lime mud matrix. The con-
tact between the platform carbonates and red pelagic
limestone corresponds to a hardground surface (Eren &
Taslô 2002) which is characterized by vertical burrows, rud-
istid bivalves (Requienia sp.), neptunian dykes filled by
red pelagic limestones, and syn-sedimentary normal faults
(Fig. 6c,d,e,f). The pelagic foraminiferal wackestones/pack-
stones were deposited on a slope to open-marine environ-
ment, as suggested by the fauna and sedimentary textures.
Fifth and Sixth Periods – Extensional Tectonic Regime
(Campanian—Maastrichtian, Fig. 7)
These periods developed in the upper level of the Ker-
mutdere Formation, which consists of siliciclastic turbid-
ites. The unit has a great lateral extent with a remarkably
uniform lithology and thickness in the study area. It is com-
posed mainly of turbiditic sandstone-argillaceous lime-
stone-marl alternation. The clasts of turbiditic sandstone
were derived from the Gümü hane Granite (quartz, feldspar),
enköy Formation and Pontide volcanic arc (Fig. 7b,d,e),
and include abundant pelagic microfossils (globotrun-
canids). Extensional features are seen between the top of the
red pelagic limestone and the base of the siliciclastic tur-
bidites. In this level, the top strata of the red pelagic lime-
8
YILMAZ and KANDEMùR
stone include multi-micro- and macroscopic sized neptunian
dykes which are filled by siliciclastic turbidites (Fig. 7b,d,e).
Structures of the sixth extensional tectonic period are
developed in the middle-upper level of the siliciclastic
turbidites. This level includes neptunian dykes filled by
coarse-grained siliciclastic turbidites from the overlying
sediments (Fig. 7f,g). This event shows that the exten-
sional tectonic regime became intensified during the
deposition of the siliciclastic turbidites.
Discussion and conclusions
Thick and widespread sediments were deposited in the
earliest Jurassic to Late Maastrichtian interval controlled
by the extensional tectonic regime with temporal cessa-
tion in the Gümü hane Mesozoic sedimentary basin
(Fig. 2). The records of the first extensional period which
controlled Early—Middle Jurassic sedimentary basin are:
break-up of the Hercynian basement and development of
Fig. 4. Structures developed during the Turonian—Coniacian extensional tectonic period.
9
SEDIMENTARY RECORDS OF THE EXTENSIONAL TECTONIC REGIME (NE TURKEY)
Fig. 5. Structure developed during the Turonian—Coniacian extensional tectonic period. A – Monogenic breccias at the base of the
graben. B – Calciturbidites. C – Microscopic view matrix of the monogenic breccias (G – Globotruncana sp.). D, E – Microscopic
view of the calciturbidites (G – Globotruncana sp.). Scale bar is 500
µm.
the horst and grabens, neptunian dykes filled by Liassic
sediments, rapid sudden lateral and vertical changes of
the facies and thickness, fining-and-thinning upward se-
quence. The passage between the enköy Formation and
the Berdiga Formation is characterized by a decrease of
the siliciclastic component and increase in the carbonate
component. This fact also suggests slowing down of the
extension. The sedimentary characteristics of the thick
and widespread Berdiga Formation, deposited in a shal-
low marine environment, records the quiet tectonic peri-
od. The Late Jurassic—Cenomanian quiet tectonic period
is replaced by strong extension during the Early Turonian.
The Turonian—Coniacian re-deposited sediments show
rapid changes in lithology as well as in thickness. Mono-
genic limestone breccias and calciturbidites character-
ized by an abrupt facies transition from shallow platform
to deep basin are common. Poorly-organized monogenic
breccias may indicate debris flows resulting from cata-
10
YILMAZ and KANDEMùR
strophic flows generated by failure along steep fault
scarps (Mullins & Van Buren 1979; Cossey & Ehrlich
1979; Snavely 1981; Eberli 1988; Rudolph et al. 1989;
Santantonio 1993; Szulczewski et al. 1996). Mid-Upper
Cretaceous rocks of the Gümü hane region recorded geo-
logical processes that occurred during the break-up of
the Eastern Pontide Carbonate Platform, which existed
throughout the Late Jurassic to Cenomanian. They indi-
cate transition from a platform to a basin related to a
rifting phase. A thinning-and-fining upward megacycle
indicates vertical aggradation and extensional tectonic
period of the re-deposited sequence in the rift basin
(Boillot 1983; Eberli 1987, 1988; Enos & Stephens
1993; Santantonio 1993; Yôlmaz 1997; Yôlmaz & Kork-
maz 1999; Graziano 2000). The benthic foraminiferal
packstones/grainstones of the Berdiga Formation, lime-
stone breccias, calciturbidites and pelagic foraminiferal
wackestones/packstones
correspond
to
platform-slope
paleoenvironments, while siliciclastic turbidites of the
Kermutdere Formation represent basin paleoenviron-
ment.
Tectonic processes have controlled the platform-ta-
lus to basin transition, especially by the means of a
structural discontinuity located at the platform-talus
boundary. This faulted margin is very similar to rift edg-
es or passive continental margins (Boillot 1983; Masse
& Luperto-Sinni 1987; Eberli 1988; Altôner et al. 1991;
Miller & Heller 1994; Rosales et al. 1994; Bekta et al.
1995; Yôlmaz 1997; Bekta et al. 2001; Koçyiûit & Al-
Fig. 6. Structures developed during the Turonian-Coniacian extensional tectonic period. (a, b) Monogenic breccias/conglomerates at
the base of the Turonian—Coniacian re-deposited sequence, vertical burrows (c) and rudistid bivalve (d) on the hardground surface,
(e) hardground surface and red pelagic limestone, (f) neptunian dyke filled by red pelagic limestone.
11
SEDIMENTARY RECORDS OF THE EXTENSIONAL TECTONIC REGIME (NE TURKEY)
Fig. 7. Structures developed during the Santonian—Campanian quiet tectonic period, Campanian extensional tectonic period and Maas-
trichtian (?)extensional tectonic period. (a) Contact between red pelagic limestone and siliciclastic turbidites, (b) micro-and macro-nep-
tunian dykes which were filled by siliciclastic turbidites, (c) microscopic view of the red pelagic limestone, (d, e) micro-neptunian
dykes which are filled by siliciclastic turbidites in the pelagic foraminiferal wackestone, (f—g) neptunian dyke in the siliciclastic turbid-
ites which were filled by overlying coarse-grained sediments. Scale bar is 500
µm.
tôner 2002). On the other hand, Okay & ahintürk (1997)
interpreted this phase as related to the northward em-
placement of an ophiolitic melange, mapped in the
southern parts of the Eastern Pontides.
Neptunian dykes are observed at four different levels
in the Mesozoic sequence. These levels are the basement
of the
enköy Formation on the Hercynian basement
(Fig. 3b), the basement of the red pelagic limestones on
the Berdiga Formation (Fig. 6e,f), the top of the red pe-
lagic limestones (Fig. 7b,d,e) and middle level of silici-
clastic turbidites (Fig. 7f,g). They are filled by overlying
sediments. This fact supports the interpretation of four
extensional tectonic regimes.
Neptunian dykes give valuable information on struc-
tural dynamics. Neptunian dykes from the Fundy Rift
Basin, Early Jurassic platform carbonates in Italy, Malm—
Early Cretaceous platform carbonates in southern Spain,
Triassic in Greece, Liassic in Yugoslavia and Oman, mid-
Cretaceous sedimentary rocks in Turkey were studied
(Füchtbauer & Richter 1983; Martire 1990; Schlische &
Ackerman 1995; Bekta & Çapkônoûlu 1997). Winterer &
Sarti (1994) explained that neptunian dykes can develop
in opening cracks that occur in the breaking, collapsing
platform as a result of normal fault systems developing
under the extensional tectonic regime.
The ophiolite and melange slabs were emplaced onto the
southern margin of the Eastern Pontides during the Cenom-
anian—Turonian in the regions Maden (Bayburt) and Kelkit,
approximalety 70—80 km further southeast, indicating that
this period corresponded to a major compression (Okay &
ahintürk 1997; and the references cited). However our
findings clearly point to an extension in the Gümü hane re-
gion during the same period. This fact clearly testifies that
some domains of an orogenic belt can undergo extension
while the other parts concurrently undergo compression, as
suggested by McKenzie (1978), Kimura & Tamaki (1986),
Bekta (1986), Uyeda (1991), Robinson et al. (1995), Bek-
ta et al. (2001) and Golonka (2004).
To sum up all these features point to an extensional
tectonic regime with temporal cessations.
Acknowledgment: We thank Prof. Dr. A. Okay and Prof.
Dr. M. Gaetani for revision of the English and construc-
tive critical reviews. We also thank Assoc. Prof. Dr. C.
en and Prof. Dr. . Çapkônoûlu who improved the En-
glish of the text.
12
YILMAZ and KANDEMùR
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