Late Cretaceous extension and Palaeogene rotation-related contraction in Central Anatolia

24 Pages·2014·3.33 MB·English

by  Eldert L. Advokaat

InternationalGeologyReview,2014
Vol.56,No.15,1813–1836,http://dx.doi.org/10.1080/00206814.2014.954279
Late Cretaceous extension and Palaeogene rotation-related contraction in Central Anatolia
recorded in the Ayhan-Büyükkışla basin
Eldert L. Advokaata,b, Douwe J.J. van Hinsbergena*, Nuretdin Kaymakcıc,d, Reinoud L.M. Vissersa
and Bart W. H. Hendrikse
aDepartment ofEarthSciences,University ofUtrecht,Utrecht,TheNetherlands;bSEAsiaResearchGroup,Department ofEarth
Sciences,RoyalHollowayUniversityofLondon,Egham,UK;cMiddleEastTechnicalUniversity,DepartmentofGeologicalEngineering,
Ankara,Turkey;dPalaeomagnetic Laboratory‘FortHoofddijk’,Departmentof EarthSciences,University ofUtrecht,Utrecht,The
Netherlands; eCentreforGeodynamics, GeologicalSurveyofNorway (NGU),Trondheim,Norway
(Received10March2014;accepted10August2014)
5
1
20 TheconfigurationandevolutionofsubductionzonesintheEasternMediterraneanregioninCretaceoustimeaccommodating
y Africa–Europeconvergenceremainpoorlyquantitativelyreconstructed,owingtoalackofkinematicconstraints.Arecent
r
a
u palaeomagneticstudysuggestedthatthetriangularCentralAnatolianCrystallineComplex(CACC)consistsofthreeblocks
br that once formed an ~N–S elongated continental body, underthrusted below ophiolites in Late Cretaceous time. After
e
F extensionalexhumationanduponPalaeogenecollisionoftheCACCwiththePontidesofthesouthernEurasianmargin,the
12 CACCbrokeintothreefragmentsthatrotatedandconvergedrelativetoeachother.Here,wedatetheextensionandcontraction
8 history of the boundary between two of the rotating massifs of the CACC by studying the Upper Cretaceous–Palaeogene
3
6: Ayhan–Büyükkışlabasin.Wereportan40Ar/39Arageofanandesiteatthebaseofthesequencetoshowthatthedeposition
] at 0 sotfatrhteedCinAaCnCEm–Wetaemxoternpshiiocns.alTbhaeslionwaerorubnadsi7n2s.e1d1im±e1n.4ta6r.yTrhoeckbsawsinerdeeuvnecloopnefodrmcoanbtleymcpoovrearneedobuyslymwidi-tEhorceegnioenlaimleexsthounmesataionnd
si redbeds,followedbyintensefoldingandthrustfaulting.Twobalancedcross-sectionsinthestudyareayieldaminimumof17–
e
ersit 2H7ırkkmadoağfpbolostc-kmbido-uEnodcaernyea~nNd–sShoshworthteantinthge.WexetetnhsuisondaelmeoxnhsutmrataetitohneoCfetnhoezoCiAcCcoCmpprreedssaitoesnaclonllaitsuioren-orfeltahteedKıcroşnehtriarc–tNioinğ.deA-
niv platekinematicscenarioisrequiredtoexplaintheseobservationsthatinvolvestwoLateCretaceous–Palaeogenesubduction
U zonestothenorthandsouthoftheCACC,forwhichweshowapossibleplateboundaryconfiguration.
k
ni Keywords: Turkey; geodynamics;tectonics;basin; Ar/Ardating
k
e
T
u
og 1. Introduction accommodation of Africa–Europe convergence was more
D
a Closure of theNeotethyan oceanic domain was associated complex and was accommodated by multiple, partly syn-
Ort withthesubductionofoceanicandcontinentallithosphere chronous subduction zones; many different scenarios for
y [ belowcontinentalandoceanicplatesandledtoJurassicand thenumberandconfigurationsofsubductionsystemshave
d b younger deformation, magmatism, and metamorphism in been proposed (e.g. Stampfli and Borel 2002; Robertson
de theeasternMediterraneanregion(SengörandYilmaz1981; 2004;Okayetal.2006;BarrierandVrielynck2008;Moix
a
nlo Dercourt et al. 1986; Stampfli and Hochard 2009). In the et al. 2008; Lefebvre et al. 2013; Okay et al. 2013): the
w Aegean region, Late Cretaceous and younger Africa– kinematicreconstructionofsubductionsystemsintheeast-
o
D Europe convergence was accommodated along a single ernMediterraneanregionprovestobechallenging.
The Central Anatolian Crystalline Complex (CACC)
subduction zone below the Eurasian continental margin
in Turkey (Göncüoğlu et al. 1991) (Figure 1; also known
andwasassociatedwithaccretionofcontinentalandocea-
as the Kırşehir Block (Görür et al. 1984)) is a key region
nic (upper) crust to the overriding plate, forming an ele-
vated fold–thrust belt (Faccenna et al. 2003; van in our attempts to reconstruct the eastern Mediterranean
subduction zone configuration since the Late Cretaceous.
Hinsbergen et al. 2005, 2010; Jolivet and Brun 2010).
The CACC is a 200 km × 200 km × 200 km, triangular
Subsequently, during periods of slab rollback, the pre-
viouslyburiedandmetamorphosedpartsofthefold–thrust continentaldomainsurroundedbysuturezone(s)andbelts
of high-pressure (HP) metamorphic rocks that demarcate
beltbecameexhumedasaresultofwidespreadextensionof
former subduction zones.
the overriding plate (Dilek and Altunkaynak 2007, 2009;
To the north, the CACC is separated from the conti-
Dilek and Sandvol 2009; Edwards and Grasemann 2009;
nental Pontides of the southern Eurasian margin by the
Jolivetetal.2009;JolivetandBrun2010;vanHinsbergen
Izmir–Ankara–Erzincan suture zone (IAESZ) (Sengör and
and Schmid 2012). In Anatolia, however, the tectonic
*Correspondingauthor.Email: [email protected]
©2014Taylor&Francis
1814 E.L. Advokaat et al.
5
1
0
2
y
r
a
u
r
b
e
F
2
1
8
3
6:
0
at
si] Figure 1. Tectonic map of the eastern Mediterranean region, modified after Okay et al. (1996), Şengöret al. (2008), Pourteau et al.
site (2010),andvanHinsbergenandSchmid(2012).EF= EcemişFault.
r
e
v
Uni Yilmaz 1981). Along the IAESZ, a northern branch of the of the CACC, commonly referred to as the ‘Intra-Tauride’
k Neotethyan Ocean subducted since at least the Early subduction zone (Sengör and Yilmaz 1981; Dilek and
ni
k Cretaceous,asshownbyHPmetamorphicrocks,arcmag- Whitney 1997; Dilek et al. 1999; Parlak and
e
T matismanddeformationinthePontides,andtheevolution Robertson 2004; Clark and Robertson 2005; Barrier and
u
g ofaforearcbasinalong itssouthernmargin(Tüysüz etal. Vrielynck 2008; Robertson et al. 2009; Sarıfakıoğlu et al.
o
D 1995;Okayetal.2001,2006;Riceetal.2006;Kaymakcı 2013).
a
rt et al. 2009; Hippolyte et al. 2010; Okay et al. 2013). The The CACC itself exposes metasedimentary rocks that
O
[ CACCandoverridingophiolitesstartedtocollidewiththe underwent regional Barrovian metamorphism following
by Pontides in latest Cretaceous to Palaeocene time, shown ophiolite obduction of Late Cretaceous age (Santonian–
ed by a transition from forearc to foreland basin evolution Turonian, ca. 90–85 Ma) (Erkan 1976; Seymen 1981;
d
oa along the southern Pontide margin and formation of a Göncüoğlu 1986; Erdogan et al. 1996; Yalınız and
nl northward convex orocline in the Pontides north of the Göncüoğlu1998).Afterophioliteemplacementandregional
w
o CACC (Görür et al. 1984, 1998; Kaymakci et al. 2003, metamorphismfollowedtheintrusionofanUpperCretaceous
D
2009; Meijers et al. 2010) (Figure 1). beltofplutonsgeochemicallyconsistentwitharcmagmatism
FringingtheCACCtothesoutharebeltsofhigh-pressure, (Göncüoğlu1986;Kadiogluetal.2003, 2006;Köksaletal.
low-temperature (HP-LT) metasedimentary rocks, known as 2004;Ilbeyli2005;Boztuğetal.2007,2009a).Exhumationof
theolder,structurallyhigher,andhigherpressureTavsanliand the CACC metamorphics is documented by geochronology
the younger, structurally lower, and lower pressure Afyon andlow-temperaturethermochronologytooccurca.75–60Ma
zones(Okayetal.1996;OkayandTüysüz1999;Dilekand andwasinseveralplacesshowntohavebeenaccommodated
Whitney 1997; Pourteau et al. 2010, 2013; Whitney et al. by low-angle extensional shear zones and detachment faults
2011). Based on 40Ar/39Ar mica ages, and unconformably (Göncüoğlu 1986; Whitney et al. 2003; Köksal et al. 2004;
overlyingsedimentaryrocksofthesebeltsinwesternTurkey, Whitney and Hamilton 2004; Boztuğ and Jonckheere 2007;
aca.88–55Mahistoryofburialandexhumationwasinferred Boztuğetal.2007,2009b;Gautieretal.2008;Isiketal.2008;
forthesebelts,withtheseprocessesyoungingtowardsdeeper Isik2009;Lefebvre2011;Lefebvreetal.2011).
structural levels (Sherlock et al. 1999; Seaton et al. 2009; To unravel the plate tectonic configuration and geody-
Pourteau et al. 2013). These data have been interpreted to namic evolution of the Cretaceous–Palaeogene subduc-
inferasecondLateCretaceoussubductionzonetothesouth tion–collision history of Anatolia, it is essential to
International Geology Review 1815
b a
5
1
0
2
y
r
a
u
r
b
e
F
2
1
8
3
6:
0
] at c
si
e
sit
r
e
v
ni
U
k
ni
k
e
T
u
g
o
D
a
rt
O
[
y
b
d
e
d
a
o
nl
ow Figure 2. (a) Location of the Menderes Massif and the CACC in the Turkish orogenic system. (b) Simplified geological map of the
D CACC projected on a digital elevation model. The black rectangle indicates the area of study presented in Figure 2. (c) Simplified
tectonostratigraphiccolumnshowingtherelationshipsbetweenthemainunitsoftheCACC(nottoscale).SSZ,supra-subductionzone.
develop accurate kinematic reconstructions and, in parti- shear zones and detachment faults accommodated ~E–W
cular, to restore the Late Cretaceous configuration of the extension. This configuration is somewhat surprising,
CACC preceding its collision with the Pontides. Towards since Africa–Europe convergence in Late Cretaceous
this end, Lefebvre et al. (2013) recently carried out a times occurred in a NNE–SSW direction (Torsvik et al.
palaeomagnetic study of the granitoid belts in the 2012):itwouldsuggestthatahighlyoblique,N–Sstriking
CACC.Theirresultsdemonstratedthatthemassifcontains subduction zone may have existed that created E–Wover-
three internally palaeomagnetically coherent blocks (the riding plate extension.
Akdağ, Kırşehir, and Niğde-Ağaçören massifs, Figure 2) Lefebvre et al. (2013) proposed that the Central
that rotated relative to each other after latest Cretaceous Anatolian block rotations were accommodated along two
cooling of the granitoids (Figure 3). Correcting for these fault zones (Figure 3). One of these is the Savcılı thrust
rotations aligns the granitoid belts into a Late Cretaceous zone (Görüret al. 1998; Yürür and Genç 2006; Isik et al.
~N–S trend and suggests that documented extensional 2014), which should accommodate several tens of
1816 E.L. Advokaat et al.
5
1
0
2
y
r
a
u
r
b
e
F
2
8 1 Figure3. Present-day(right-handside)andLateCretaceous(left-handside)configurationofthemagmaticbeltsoftheCACCaccording
3 topalaeomagneticresults,modifiedfromLefebvreetal.(2013).ThefaultzoneparalleltotheSavcılıthrustzonewasproposedbythese
06: authorsasatranspressionalfaultzonethataccommodateda29.0±4.5°counterclockwiserotationoftheNiğde–Ağaçörenmassifinthe
at south relative to the Kırşehir Massif in the north, which would require ~40–60 km of total N(NE)–S(SW) shortening. If correct, this
si] wouldrestorethesenseofshearrecordedalongtheHırkadağdetachment(Lefebvre2011)intoatop-to-the-ELateCretaceousorientation.
e
sit
r
e
v kilometres shortening to accommodate the palaeomagne- presumably Palaeozoic to Lower Cretaceous sedimentary
Uni tically determined ~30° rotation between the Kırşehir and protoliths (Göncüoğlu et al. 1992; Kocak and Leake
nik Niğde–Ağaçörenmassifs(Lefebvreetal.2013)(Figures2 1994). These are tectonically overlain by the Central
k and 3). In this article, we test that prediction by studying Anatolian Ophiolites, with Turonian–Santonian crustal
e
u T the structural and stratigraphic evolution of the Ayhan– ages (Seymen 1981; Yalınız and Göncüoğlu 1998; Floyd
og Büyükkışla basin that lies within the postulated Savcılı et al. 2000; Yalınız et al. 2000; Lefebvre et al. 2011),
D
a thrustzone(Figures2and3)andaimtoobtainconstraints intrudedbyaregionallyextensivesuiteofgranitoids,with
rt on the timing of central Anatolian rotational deformation. local gabbros and syenitoids (Figure 2) with published
O
y [ TheAyhan–Büyükkışlabasinislocatedadjacenttothe ages covering the ca. 95–75 Ma interval (Göncüoğlu
b Hırkadağ massif, along the northern edge of the counter- 1986; Kadioglu et al. 2003; Whitney et al. 2003; Köksal
d
e clockwise rotated Niğde–Ağaçören massif. The basin etal.2004;Boztuğetal.2007,2009a;Lefebvre2011).An
d
a
o exposes a folded and thrust faulted stratigraphy of volca- 84.1 ± 0.8 Ma U/Pb monazite age from migmatites in the
wnl nic, continental clastic, and shallow marine and lacustrine Kırşehir Massif was interpreted to date peak metamorphic
o
D calcareous rocks, with a presumed Late Cretaceous to conditions in the CACC (Whitney and Hamilton 2004).
post-mid Eocene age range (Göncüoğlu et al. 1993; Becausethegranitoidsuitesdidnotexperiencetheintense
Köksal and Göncüoğlu 1997; Köksal et al. 2001). Here, prograde to syn-peak metamorphic deformation character-
wereporttheresultsfrommappingofthestratigraphyand isticoftheCACCmetamorphics,thepre-85Mamagmatic
structure of the Ayhan–Büyükkışla basin, geochronologi- ages may be incorrect (Lefebvre et al. 2013).
cal dating of its volcanic content, and cross-section The tectonic causes of exhumation of the high-grade
restoration of its compressional history. We evaluate our metamorphic rocks of the CACC remain only locally
results within the context of the Late Cretaceous– resolved, but are consistent with a key role of extensional
Palaeogene kinematic evolution of Central Anatolia and denudation (Whitney and Dilek 1997; Gautieret al. 2002,
the subduction zone configuration inferred from that. 2008;Isiketal.2008;Isik2009;Lefebvre2011;Lefebvre
etal.2011).Followinginitialpostulationsthatextensional
exhumation occurred in the Miocene (Whitney and Dilek
2. Geological setting
1997), subsequent evidence has demonstrated that the
The oldest and tectonostratigraphically deepest rocks in timing of extensional exhumation is mainly Late
the CACC comprise metasedimentary rocks with Cretaceous to perhaps Palaeocene in age (~75–60 Ma)
International Geology Review 1817
(Boztuğ and Jonckheere 2007; Gautier et al. 2008; Isik volcanics of a Late Cretaceous age (Aydın 1985; Gökten
et al. 2008; Boztuğ et al. 2009a; 2009b; Isik 2009; and Floyd 1987; Kara and Dönmez 1990; Göncüoğlu
Lefebvre et al. 2011). Extension-related deformation was et al. 1993) (Figure 4). These mafic volcanics are prob-
overprintedbycontractionaldeformationthatdevelopedin ably magmatically cogenetic and consequently contem-
the localized zones of folding and thrust faulting, such as poraneous with the İdiş Dağı syenite (Köksal et al.
theSavcılıthrustzone,ofwhichrecentclaymineraldating 2001). Clastic sedimentary rocks and volcanics with a
ingougessuggestedthatithasbeenactivebetween46–40 presumed Late Cretaceous age are also exposed in the
and 29–22 Ma (Isik et al. 2014), and the Çiçekdağı syn- central part of our study area around Ayhan between the
cline and Çiçekdağı basin that formed between 39 and İdiş Dağı and Hırkadağ blocks (Atabey 1989) (Figure 4).
35 Ma (Gülyüz et al. 2013) (Figure 2). Overlying the continental clastic series in the Ayhan area
To the southwest and southeast of the Ayhan– are Eocene nummulitic limestones, dated as Lutetian
Büyükkışla basin, the study area of this article (Figure 4), (48.6–40.4 Ma in the timescale of (Gradstein et al.
metamorphic and plutonic rocks are exposed in the 2004)) based on their alveolina and nummulite content
Hırkadağ massif and in the İdiş Dağı block, respectively, (Göncüoğlu et al. 1993), overlain by unfossiliferous
exposing amphibolite-facies metasedimentary rocks, (probably lacustrine) marls. Eocene limestones are wide-
5
1 intruded by granodiorites and syenites (Whitney and spread in central Anatolia and frequently unconformably
0
y 2 Dilek 2001; Lefebvre 2011). In the southeast of the cover exhumed metamorphic basement of the CACC
ar study area, near Göynük village, a thrust fault emplaces (e.g. Göncüoğlu et al. 1991; Gülyüz et al. 2013).
u
br syenites of the İdiş Dağı block over continental clastic The Eocene and older units in the Ayhan area are
Fe sedimentary rocks that intercalate with mafic volcanics unconformably overlain by a series of folded and thrust
12 that were correlated to regionally occurring (Karahıdır) faulted red fluvial conglomerates, covering the northern
8
3
6:
0
at
]
si
e
sit
r
e
v
ni
U
k
ni
k
e
T
u
g
o
D
a
rt
O
[
y
b
d
e
d
a
o
nl
w
o
D
Figure4. GeologicalmapoftheAyhan–Büyükkışlabasin.ThestratigraphicunitsthatwemappedareoutlinedinFigure5.Forprofiles
A and B, see Figure 9. CAG, Central Anatolian Granites; CAM, Central Anatolian Metamorphics; GzL, Gözsu Tepe Limestone;
KV,Karahıdırvolcanics.
1818 E.L. Advokaat et al.
half of the study area around Büyükkışla (Figure 4). The 3.1. Yeşilöz Formation
age of the Büyükkışla basin fill is Lutetian or younger, as
The Ayhan area exposes an ~4 km-thick stratigraphy with
it covers the limestones, and is generally assumed to be
internal low-angle unconformities. The volcanics interca-
Oligocene (Atabey 1989), but no independent age data latingatthebaseoftheYeşilözFormationwerepreviously
exist. In the north of the study area (Figure 4), Eocene assigned to the ‘Göynük volcanoclastic olistostrome’
limestones and marls are exposed, and the northern con- (Köksal and Göncüoğlu 1997), described as containing
tact between the Büyükkışla redbeds and Eocene lime-
continental clastic sedimentary rocks, blocks of volcanics
stones was previously mapped as an unconformity as well as blocks of İdiş Dağı syenite. Our observations
(Atabey 1989). The study area is bounded in the south
suggest, however, that such an amalgamation is restricted
by a normal fault that has Miocene (Tortonian) and to a zone of ~50 m thickness below the İdiş Dağı thrust
younger volcanic tuff, commonly referred to as the
fault, and that this lithology represents a tectonic mélange
Ürgüp Formation of the Cappadocian volcanic province,
related to post-depositional thrust faulting, not olistostro-
in its hanging wall (Atabey 1989; Mues-Schumacher and malprocesses.ImmediatelynorthofGöynük,asuccession
Schumacher 1996; Viereck-Goette et al. 2010). In places, of intercalating purple and yellow lavas, stratified tuffs,
subhorizontaltuffsunconformablycoverallpreviousunits
5 conglomerates, and redbeds show that the volcanics form
01 in the study area. an integral part of the Yeşilöz Formation stratigraphy.
2
y In addition to the Karahıdır volcanics, we subdivide
ar the Yeşilöz Formation into seven members that have
u
br been mapped separately to highlight the basin’s structure
12 Fe 3T.heLoiltdheossttrpaatritgorafpthhey sotfratthigeraApyhhyan––BteürmyüedkktıhşelaYBeaşisliönz (Y1M–7e)m(FbiegrurYe15)c.onsists of alternating dark-grey mud-
38 Formation and intercalating ‘Karahıdır’ volcanics – is stone without fossils and lens-shaped sandstones. It only
6:
0 exposed in the Ayhan and Göynük area (Figure 4). The crops out in the central southern part of the basin with an
] at overlyingnummuliticlimestonesandmarlsareassignedto exposed thickness of 250 m, tapering out to the W. It was
esi theMucurFormation.Theunconformablyoverlyingseries probably deposited in a fluvial environment.
sit of ~5 km of red conglomerates and sandstones define the The overlying Member Y2 consists of purple and red
r
ve Büyükkışla Formation. conglomerates and intercalated sandstones that can be
ni
U
k
ni
k
e
T
u
g
o
D
a
rt
O
[
y
b
d
e
d
a
o
nl
w
o
D
Figure5. FaciesdiagramshowingtheregionalandverticalrelationshipsbetweenthemetamorphicbasementoftheHırkadağBlockand
thestratigraphyofthe Ayhan–Büyükkışlabasin.
International Geology Review 1819
tracedallalongthewesternandsouthernpartsofthebasin Member Y6isexposed inthe eastern part of thebasin
(Figure 4). Its thickness increases from ~600 m in the and comprises ~100 m of 1–2 m-thick bedded limestones
southeast to ~825 m in the southwest. The member con- (mudstones), without macroscopically observable fossils.
sistsofcross-bedded,finingupwardsandstones,andupto Thesequenceisinterpretedasalacustrinedepositlaterally
5 m-thick lenticular conglomerate beds that erode the equivalent with the lacustrine rocks of Member Y5.
underlying strata. The conglomerates are clast-supported, Finally, Member Y7 consists of 250 m of red sand-
with sub-angular 10–50 cm clasts solely consisting of stonesandmudstone.Therelationshipwiththeunderlying
volcanic debris. Palaeocurrent directions in fluvial sand- limestones is unknown, because the only contact with the
stones of this member are variable towards W and S (in limestones is a thrust fault. The sequence consists of 0.5–
present-day coordinates). The unit is interpreted as alter- 2 m-thick beds of coarse cross-bedded orange sandstones.
natingbraidedfluvialanddebrisflowdepositsconstituting The sequence is interpreted as fluvial.
a continental clastic fan system. At the west bank of the
Kızılöz river, andesite lavas intercalate with Member Y2,
and we collected a sample (21-05) for 40Ar/39Ar geochro- 3.2. Mucur Formation
nology (Figure 5). The Mucur Formation overlies the Yeşilöz Formation
5
1 Member Y3 overlies the underlying purple conglom- with an ~5° angular unconformity and consists of two
0
y 2 erates, and the contact between these units in the west of members (not specified as separate members on the map
ar the basin shows an ~15° angular unconformity. Member of Figure 4). Member 1 is exposed around Ayhan and
u
br Y3 consists of ~1200 m of sandstones and blue-grey comprises an ~200 m-thick sequence of 0.5–1 m thick,
e
F mudstones without fossils. The member tapers out to the grain-supported beds of nummulites and alveolinae, and
2
1 E, where it is exposed in small lenses only, and may ~10 m-thick beds of pelecypoda and nummulites. These
38 interfinger with Member Y4. Its lower 150 m consists of fossils clearly demonstrate a shallow marine environment.
06: regular alternations of ~30 cm-thick, yellow, carbonate- In Ayhan village, Göncüoğlu et al. (1993) assigned a
at rich, fine- to medium-grained sandstones intercalated with Lutetian (48.6–40.4 Ma) age for these limestones.
si] 2–4 m-thick siltstone and claystone layers. The upper Member M1 is also found in the north and west of the
e
sit ~1000 m consists of alternating blue mudstone and very study area, e.g. around Hacıbektaş and Avuç, where it is
er fine-grained yellow sandstone. Slump structures are found in thrust fault contact above the Büyükkışla
v
ni common (Figure 6). The basal sandstone preserves Formation. Around Avuç, the limestones are conformably
U
k syn-sedimentary normal faults, suggesting a roughly overlain by Member M2, which consists of white to grey
kni E–W direction of extension in their present orientation marls and mudstones with abundant organic matter frag-
Te (Figure6).Thepalaeoenvironmentisinterpretedasfluvial ments, alternating with sandstones and unfossiliferous
u
g for the basal sandstones and lacustrine for the upper limestones, generally of up to ~30 cm thick. The max-
o
D 1000 m. imumobservedthicknessofMemberM2is~300minthe
rta Member Y4 consists of an ~625 m-thick sequence of east of the study area. The member contains frequent
O
red sandstones. In the west, the base of the succession large-scale (tens of metres in size) slumps. This sequence
[
by consists of medium- to coarse-grained, thick-bedded (1– was previously suggested to be deep marine (Göncüoğlu
ed 2 m) grey sandstones. Upwards, fine- to medium-grained et al. 1993), but the absence of marine fossils and the
ad 5–15 cm-thick laminated sandstones occur that intercalate abundant presence of organic matter lead us to interpret a
o
nl with 5–50 cm-thick red siltstones. Intheeast,themember lacustrine palaeoenvironment instead.
w
o consists of conglomerate, coarse sandstones, and silt-
D
stones. Conglomerates consist mainly of volcanic debris
with ~5–10% granite and quartzite pebbles. The sequence 3.3. Büyükkışla Formation
is interpreted as deposited in a fluvial environment. The Büyükkışla Formation is a monotonous, ~5 km-thick
Member Y5 unconformably overlies Y4 with a low- sequence of red siltstones with lenticular bodies of sand-
angle unconformity and consists of 400 m of dark-red stone and conglomerate. The base of the stratigraphy
sandstones, thinning to 200 m eastwards. The sequence directly north and south of the exposures of the Yeşilöz
comprises one white-coloured sandstone of 20 m thick- Formationcontainstwoadditional members with different
ness, consisting of very coarse sandstones, followed by a colours, convenient for structural mapping. Hence, we
poorly exposed sequence of fine laminated dark-red subdivide the stratigraphy into three members (B1–3).
sandstones. The top of the formation is formed The lowermost Member B1 overlies the Mucur and
by intercalations of fine-bedded siltstone and claystone. Yeşilöz Formations and the Hırkadağ metamorphic base-
The sequence is interpreted as a transition from a fluvial ment with an angular unconformity. In the south, the
environment represented by the sandstones to a contact between Member B1 and the Yeşilöz Formation
lacustrine environment represented by the siltstone and is a normal fault, and northeast of Ayhan, the Yeşilöz and
claystone. Mucur Formations are probably thrust faulted over the
1820 E.L. Advokaat et al.
5
1
0
2
y
r
a
u
r
b
e
F
2
1
8
3
6:
0
at
]
si
e
sit
r
e
v
ni
U
k
ni
k
e
T
u
g
o
D
a
rt
O
[
y
b
d
e
d
a
o
nl
w
o
D
Figure6. (a)Slumpfoldingand(b)syn-sedimentarynormalfaultingintheYeşilözFormation.(c)NormalfaultbetweentheKarahıdır
volcanics and the Yeşilöz Formation (Member Y2) in the southeast of the Ayhan area. Tapering features in Member Y2 show syn-
sedimentary activity; (d) To the west, the normal fault is not visible, but instead, post-sedimentary thrust faults deform the Yeşilöz
Formation.
Büyükkışla Formation (Figure 4). North of the Ayhan up of 5–30 cm sized pebbles of metamorphic rocks and
basin, Member B1 is ~450 m thick and consists of dark- granites. Pebble imbrication and cross-bedding indicate
red conglomerates and mudstones. The sequence contains easterly directed palaeoflow (Figure 7). The basal con-
a 150 m-thick conglomerate succession at the base made glomerates are followed by a 300 m-thick sequence of
International Geology Review 1821
Figure7. PalaeocurrentdirectionsintheAyhan–Büyükkışlabasin,showingdominantlyE–W-orW–E-trendingpalaeocurrents.Forthe
Büyükkışla Formation, this is parallel to the fold axis of the Killik syncline. For the Yeşilöz Formation, this is parallel to the syn-
5
1 sedimentarynormalfaultsinthe basin,with somepalaeocurrentdirections towardsthesouthernN-dippingnormalfault ofFigure6c.
0
2
y
r
ua 5–20 cm-thick fine-grained sandstone beds intercalated andinverseisochrondiagrams.Statisticsonboththespec-
r
eb with 5–50 cm-thick lignites, which are locally mined. trum and the inverse isochron indicate some minor dis-
F
2 We have been unable to derive pollen from these lignites turbance of the Ar isotope system. We define a plateau
1
8 for age dating. The sequence is interpreted as an alterna- according to the following requirements: at least three
6:3 tion of braided fluvial and debris flow deposits. Upwards, consecutive steps, overlapping at the 95% confidence
at 0 the palaeoenvironment was dominated by fluvial deposits level, together comprising at least 50% of total 39Ar and
] and marshes. mean square of weighted deviates (MSWD) less than the
si
e Member B2 consists of a 300 m-thick sequence of two-tailed Student T (Stud-T) critical value. We use the
rsit olive-green sandstones and mudstones, with a 100 m- weighted York-2 method to calculate the inverse isochron
e
niv thick sandstone at the base. It is succeeded by 200 m of results, with statistically valid isochrons having a MSWD
U alternating ~20 cm-thick fine-grained sandstone beds and value less than the two-tailed F-test critical value. For
nik 0.5–2 m-thick claystone layers. Lenticular sandstone sample 21-05, a weighted mean age of 72.06 ± 1.78 Ma
ek bodies are erosive, 5–10 m thick, and 20–30 m wide. (2σ) was determined (Figure 8) for 81.83% of the cumu-
T
u Cross-beds in the sandstone layers indicate westerly lative 39Ar. The ages and uncertainties for the three steps
og palaeoflow(Figure 7). MemberB2 isinterpreted toreflect included in the calculation almost overlap at the 2σ level,
D
a a fluvial depositional environment, with channelled sand- but with a MSWD of 5.854 and a Stud-T value of 4.303
Ort stone bodies and claystone-dominated overbank deposits. they do not constrain a true plateau. Steps 1–4, represent-
y [ Member B3 is not further subdivided and comprises ing 91.61% of the cumulative 39Ar, yield a statistically
b
d thetop~4kmofthesuccession.Itisdominatedbyorange valid (i.e. MSWD of 2.888 below the F-test value of
de fluvial sandstones, mudstones, and conglomerates, includ- 2.997) inverse isochron age of 72.11 ± 1.46 Ma (2σ).
a
o ing matrix-supported conglomerate layers of up to 3 m Again, some minor disturbance of the Ar isotope system
nl
w thickness. These layers have moderately sorted, semi- is indicated by the 40Ar/36Ar ratio, which at
Do rounded pebbles ranging in size from 4 to 10 cm. The 254.48 ± 22.87 (2σ) is lower than the atmospheric ratio.
pebble content is diverse and in the lower part of the The weighted mean plateau age and the inverse isochron
sequenceconsistsmainly ofvolcanicsandsomereworked age nevertheless completely overlap.
sandstone, but higher in the sequence (near Sarılar) also
fragmentsofnummuliticlimestonewerefound.Sandstone
layersaretypically~20cmthick,withgrainsizesbetween 5. Structure
medium and very coarse sand. At the base of the succes- 5.1. Present-day structure
sion, pebble imbrication and cross-beds indicate E-direc-
The angular unconformity between the Büyükkışla
ted palaeoflow (Figure 7). The unit is interpreted as an
Formation and the underlying formations (Figure 4) sug-
alternating braided fluvial and debris flow deposit.
gests that the Yeşilöz and Mucur Formations have experi-
enced at least one deformation phase more than the
Büyükkışla Formation. Therefore, we first describe the
4. 40Ar/39Ar geochronology deformation accommodated in the Büyükkışla Formation
Plagioclase was separated from sample 21-05 for and then summarize the deformation in the area around
40Ar/39Ar geochronology. Figure 8 displays the spectrum Ayhan that exposes the older formations.
1822 E.L. Advokaat et al.
30
25
20
a
C 15
K/
10
5
0
100
8
90
80
5
4
3
a)
M
5 ge ( 70 2
201 A 1 SWteeipg h3t e- d5 m(3e.2a n– a4g.5e W72).06 +/– 1.78 Ma (2σ) 6
ry 60 Step 3 - 5 overlap at 2σ level
ua MSWD 5.854, Stud-T 4.303
br 81.83% of cumulative 39Ar
e
F
2 50
1
8
3
06: 40
at 0 20 40 60 80 100
] Cumulative %39Ar
si
e
sit
r
e
v
ni
U
0.0045
k
kni 0.0040
e
T
u 0.0035 Trapped
g component
Do 0.0030
by [Orta 3640Ar/Ar 00..00002205 20
d 0.0015 Step 1 - 4 (2.0 – 3.8 W)
e Inverse isochron age 72.11 +/– 1.46 Ma (2σ)
d
oa 0.0010 40Ar/36Ar intercept 254.48 +/– 22.87 (2σ) 26
nl MSWD 2.888, F-test 2.997
ow 0.0005 91.61% of cumulative 39Ar Total fusion point 52
D 45 38
0.0000 32
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 0.045
39Ar/40Ar
Figure 8. Step heating release spectra for sample 21-05 (plagioclase) from the Karahıdır volcanics. Each age bar is plotted at 95%
confidencelevel.ThenumbersabovetheagebarscorrespondtotherownumberintheAppendix.Thebottompanelshowstheinverse
isochrondiagram,with numberscorrespondingtothelaser powerinWatts.
A cross-section through the western part of the study N-dipping stratigraphy (Figure 10a). To the north, this
areaisshowninprofileAofFigure9.TheHırkadağmassif stratigraphy is deformed into the 15 km-wide asymmetric
is bounded to the south by the Miocene and younger S-vergent‘Killik’syncline(Figure10b).Northofthehinge
Kızılırmak normal fault, with Cappadocian volcanics in its ofthesyncline,scatteredoutcropsinarivervalleybetween
hangingwall(Göncüoğluetal.1993;Toprak1994).Tothe Killik and Avuç expose redbeds with gradually steepening
north, the Büyükkışla Formation unconformably overlies S-dipping bedding. Previously, these have been mapped as
metamorphicrocksoftheHırkadağmassifandhasagentle the Yükseli Formation with volcanic ash deposits with an