Tertiary evolution of the Sivas Basin, central Turkey

Tectonophysics, Elsevier

29

195 (1991) 29-46

Science Publishers

B.V.. Amsterdam

Tertiary

evolution

of the Sivas Basin, central Turkey

J.M.L. Cater a, S.S. Hanna

b, A.C. Ries ’ and P. Turner

d

u Earth ’ Ries-Coward

Sciences and Resources Institute, Unroersiiy of Reading, Innovation Centre, Reading RG6 2BX, UK h Department of Earth Sciences, Sultan Qaboos Unruersrty, P.O. Box 32486, Oman Associates Ltd., 70 Grosoenor Road, Coversham, Reading RG4 OES, UK, and Postgraduate Research Institute for Sedimentology, The University, P.O. Box 227, Whrteknighis, Reading RG6 2AB, UK ’ School of Earth Sciences, University of Birmrngham, Birmingham BlS 2TT, UK (Received

January

22,199O;

revised version accepted

February

20. 1991)

ABSTRACT Cater, J.M.L., Hanna, S.S., Ries, Tectonophysrcs, 195: 29-46.

A.C.

and

Turner,

P., 1991.

Tertiary

evolution

of the

Sivas

Basin,

central

Turkey.

The Sivas Basin is one of several basins in Turkey formed during closure of the northern branch of Neotethys in early Tertiary times. Cretaceous ophiolitic fragments and Eocene platform carbonates and volcaniclastics, transported northwards into the basin as olistoliths and grain-flow aprons, were incorporated into autochthonous Eocene turbidites and bioclastic limestones. The sequence as a whole was thrust northwards in late Eocene times. A southward-sloping terrestial foreland basin, related to northward-directed thrusting, developed during Oligocene times. A piggy-back basin developed on top of this thrust system. During the late Oligocene, the Eocene thrusts were reactivated, probably resulting in northward propagation of thrusts in the subsurface. In early and mid-Miocene times, the basin was floored by a thrust sheet which had been cut by N-S trending tear faults or oblique culminations as a result of non-uniform thrust advance in pre-Miocene times. These N-S faults were subsequently reactivated as extensional faults, radial to the thrust front, during early to mid-Miocene alluvial and shallow marine sedimentation. Later strike-slip displacement along the N-S faults was associated with the development of the Northern Boundary Fault of the Sivas Basin in late Miocene times, which is regarded as a left-lateral transpressive fault related to the North Anatolian Fault Zone.

Introduction

were

The Sivas Basin lies within

the Erzincan

in post-Late Cretaceous resulting in the Kirsehir

taceous-Palaeocene

the

Mesozoic

(Artan

and

Sestini,

1971;

Continued closure of northern Neotethys during the Eocene resulted in subsidence and the development of a remnant basin between the

but pre-Eocene Block, with its

0 1991 - Elsevier Science Publishers

onto

Yilmaz, 1981). Ophiolitic rocks were also obducted at this time onto the active margin to the north as part of an accretionary complex (Gansser, 1974).

cover of Mesozoic platform carbonates, moving northwards towards the Pontides. Closure of northern Neotethys resulted in Late Cretaceous to Palaeocene subduction-related talc-alkaline magmatism in the Pontides, with the concomitant development of the Black Sea basin behind this arc system (Dewey et al., 1986). Ophiolitic rocks 0040-1951/91/$03.50

southwards

platform carbonates, which led to the foundering of the passive margin during the Late Cre-

Suture

Zone, the latter marking the former location of northern Neotethys, which separated the Pontides to the north from the Anatolides (Kirsehir Block) to the south during the Cretaceous (Fig. 1). Palaeomagnetic data (Sanver and Ponat, 1980) suggest an anticlockwise rotation of the Kirsehir Block times,

abducted

Pontides

and

the

Kirsehir

Block

(Gorur

et al.,

1984). During or shortly after the collision of these blocks in the late Eocene, the dominant sense of thrust movement changed from south to north within the Sivas Basin. Since the mid-Miocene, continued convergence of the Arabian and Eurasian plates has resulted in B.V.

I.M.L. CATER

30

an Continent Gondwanaland Vardar Zone lntra-F~ntide Suture IAS lzmir-Ankara Suture ES Erzincan Suture ITS Intra-Tauride Suture SAS Sevan-Akera Suture C East Anatolia Accretionary

ET AL.

m VZ bps

Black

Sea

Complex

PLATFORM

Fig. 1. Schematic

map showing

the main tectonic

Tibetan-type crustal thickening of the Anatolian Block, with the development of the right-lateral strike-slip North Anatolian Fault Zone (Sengiir,

N.A.F.Z. E.A.F.Z. S. F. M.F.

features

of Turkey

(m~ifi~

1979) and the left lateral strike-slip East Anatolian Fault Zone (Dewey et al., 1986) (Fig. 2). The Anatolian Block, which lies between these two

e

North Anatolian Fault Zone East Anatolian Fault Zone

rL

Sivas Basin Northern Boundary Fault Malatya

Fig. 2. Sketch

from Sengor et al.. 1984).

Fault map showing

the main neotectonic

features

of central

Turkey

in relation

Thrust Strike -slip fault Approximate limit of the Sivas Basin to the Sivas Basin.

TERTIARY

EVOLUTION

OF THE SIVAS

BASIN,

31

TURKEY

Neogene,

N

Ortaki

km II-4

T

-

J

Malakkay

Oligo-MioL,,,, Eocene L. Cretaceous ophiolitic rocks L. Creta~eous/Palaeocene sediments Metamorphic complexes & granites Volcanic rocks Geological boundary -broken lines denote uncertainty Thrust/fault-broken lines denote uncertainty Asphalt or graded road

Fig. 3. Geological map of the western and central parts of the Sivas Basin (after Baykal and Erentoz. 1966).

major

strike-slip

faults,

is still moving

westwards

Pm-Eocene

rocks

to accommodate the continuing convergence between the Arabian and Eurasian plates. The Sivas Basin lies between 36” and 39” E

Pre-Cretaceous margins of the

and 39 o and 40 * N; this paper is confined and western parts of the basin.

to the

margin,

the Akdag

Topo-

consist

of amp~bolite-facies

central

graphic maps at the scale of 1: 25,000 and 1 : 100,000 were used as base maps for the structural sections. The only available geological maps were the 1 : 500,000 Sivas sheet (Baykal and Erentoz, 1966; see Fig. 3) and a more detailed map of the central part of the basin published by Kurtman (1973). Stratigraphy and sedimentology The lithostratigraphy established during this study for the southwestern and central parts of the Sivas Basin is shown in Fig. 4.

rocks are Sivas Basin.

exposed On the

on the northern

and Sakardag massifs (Fig. 3) metasediments and

acid igneous rocks. On the southern margin near Malakkoy, calcareous schists and marbles structurally underlie recrystallized Upper Cretaceous or Palaeocene limestones. The age of these rocks and the age of the metamo~~sm which affects them are not known but both ages are assumed to be pre-Cretaceous. Upper Cretaceous-Palaeocene shallow-water platform carbonates outcrop on Tecer Dagi (Tecer Limestone) and Gurlevik Dagi (Gurlevik Limestone) on the southern margin of the Sivas Basin (Fig. 3). The base of these sequences is not exposed. At least 100 m of limestone occurs on

J.M.L.. CATER

32

S.W. MALAKKO’ w

ET AL.

W.CENTAAL SAMANKAYA n nn*nn silts

IIOCENE

Ribbon sane nnf,An,

Ribbon sands AhhhAAl Silts

1 “““““\ Calciturbidit

OCENE

Ribbon sands

Slope depoe I

PALAEOCE \ Calciturbidites

>RETACEOU!

. 3lope deposit; “““““” VVV”” “““““Y ““““” 3

’

’

L

Fig. 4. Generalized

lithostratigraphy

for the southwestern

and central parts of the Sivas Basin. The locations of the areas shown are shown on Fig. 3.

Gurlevik Dagi, where crinoids and rudists of Maastrichtian age are seen in life position. Kurtman (1973) suggested that the upper part of this sequence is Palaeocene. On Gurlevik Dagi, the limestones have a karstic upper surface encrusted with oysters and overlain by Eocene sediments. Ophiolitic rocks outcrop along the northern and southern margins tectonic blocks within the ophiolitic

of the basin and as small the basin. On the margins,

rocks appear

as serpentinized

ultra-

mafic blocks in a matrix of serpentinite or radiolarite. The age and direction of emplacement of this ophiolitic melange is poorly constrained. Artan and Sestini (1971) and Yilmaz (1981) assumed a Late Cretaceous emplacement age in the Sivas Basin, and Aktas and Robertson (1984) and

Hempton (1985) suggested a Late Cretaceous age for ophiolite abduction onto the southern Anatolide margin. The op~olitic melange was clearly emplaced prior to the Eocene; in the Cavarkoy area, the melange is stratigraphically overlain by nummulitic limestones and a similar relationship is recorded in the Beypinari area by Artan and Sestini (1971). The emplacement direction of the ophiolites

onto

the southern

margin

of the Sivas

Basin could not be determined in the field, but the ophiolites are assumed to have been derived from northern Neotethys and emplaced southwards onto the passive margin of the Kirsehir Block. The ophiolites on the northern margin of the basin are part of the southern Pontide accretionary complex of Gansser (1974).

TERTIARY

EVOLUTION

33

OF THE SIVAS BASIN. TURKEY

Bulucan

Calciturbidites _ _

Volcaniclastics

trichtian-Palaeocene

150Km

)

@

~~~~~~~a~~~~h

fTJ

Red beds

El

a

Debris flows and volcanistics

m

Alluvial

m

Fig. 5. Stratigraphy

and correlation

Conglomerate

of Eocene flysch sequences

Volcanic

rocks

Limestones

along the southern

margin

m

Evaporites E

n

Metamorphic basement

of the Sivas Basin.

Stromatolites mud-mounds Carbonate

a

platform

Pillow andesites & epiclastic volcaniclastics

Break of slope

Fig. 6. Paleogeographic

reconstruction

for the Eocene of the Sivas Basin.

J.M.L.

34

top of the Eocene sequence

Eocene deposits

of the basin, Eocene

rocks

southern

margin

variations

there

densed

are shown at

(Baykal

Eocene

mostly

occur at Agcakisla,

in Fig.

the

The

facies

5. The

con-

may

Erentoz,

be

partly

1966;

Gokten,

on the northern

margin

Slope deposits.

slope redeposition

to subaerial

al-

conglomerates occur at on the northern margin,

of the southern

margin,

clasts. Olistostromes

debris-flow

deposits margin

are

along

followed

lower energy,

as the slope stabilized.

to the slope deposits.

events

downThere is contrib-

The Maastricht-

large olistoliths

within

this sequence.

of the basin

is recorded

Infilling

and

towards

the

end of the Eocene.

and subaqueous

abundant

slope

ian and ?Palaeocene limestone ridges (i.e. Giirlevik Dagi and Tecer Dagi) and ophiolite ridges along the southern margin could represent very shallowing

where they are dominated

by ophiolitic

on the southern

of at least two volcanic

uting debris

up

nummu-

the development

unstable

of progressively

be-

passing

facies.

succession

of a northward-dipping, by a period

Subaqueous

or fan-delta and Bahgecik

the Eocene

of the Sivas Basin records

(Fig.

margin

beds of mid-Eocene marine

ET AL.

bioclastic

interbeds,

of shallow

com-

where they contain well-rounded (second-cycle?) metamorphic basement clasts, and along the length

southern

Overall,

evidence

luvial-fan Agcakisla

thicker

litic packstone

become

mudstone

and Bahqecik

prise: (I)

into coarser,

margin

on the southern

the turbidites

tween calcareous

in the Sivas Basin

Karacayir

deposits

along

Basin.

Malakkoy and

outcrops

3) The Eocene

exposed

of the Sivas

sequence

Palaeocene 1983).

are

CATER

the

(Fig. 5) and are best exposed

at

Samankaya and Tepehan (near Beypinari). They are dominated by ophiolitic and volcanic debris, along with slope-derived intraclasts. Widespread tabular aprons of coarse volcaniclastic sand, often containing large mud intraclasts, are also common along the southern margin. Slump folds in these rocks indicate palaeoslope to the north, and palaeoflow indicators record transport dominantly

Oligocene deposits During the Oligocene, the Sivas Basin comprised two sub-basins (Fig. 7) in which sediments of markedly different facies were deposited: (1) The Ortak5y sub-basin. In the southwestern part of the Sivas Basin, around Ortakiiy, about 140 m of Oligocene non-marine mudrocks and thin limestones conformably overlie relatively un-

to the north (Fig. 6); Gokcen (1981) suggests that the provenance area was largely composed of ophiolitic rocks.

deformed Oligocene

Eocene rocks

Miocene

limestones

(2) Basinaf deposits. The olistostromes volcaniclastic aprons are intercalated with

sequence since the Oligocene sequence elsewhere in the basin is up to 1500 m thick. The Ortakoy

and thin-

marine turbidites are conformably and

represent

(Fig. 8). The overlain by a condensed

bedded turbidites of basin-plain facies which record both down-slope and basin-axial flow direc-

area lies to the south of a line connecting

tions (Fig. 6). Some of these sediments are probably contourites. Calciturbidites occur throughout,

It is postulated that this lineament marks the northern limit of a thrust sheet developed in the

and are particularly common in the condensed sequence at Malakkiiy in the southwestern part of the Sivas Basin, where they are intercalated with mud-shales of hemipelagic origin.

late Eocene and that the Ortakoy sediments were deposited in a piggy-back basin located on the top of this thrust sheet.

(3) Limestones. On the northern margin of the Sivas Basin, Eocene limestones, containing reworked nummulites, show lateral facies variations from micritic mud mounds and bioclastic storm deposits in the Agcakisla area to the west, to sub-tidal stromatolites and bioclastic storm deposits near Karac;ayir to the east (Fig. 6). At the

Dagi, Tecer Dagi and the Caldag

massifs

Giirlevik (Fig. 7).

(2) The Ceiulli sub-basin. In this area, Oligocene is dominated by red and green

the silt-

stones and yellow sandstones of fluvial to lacustrine facies (Fig. 7). The sandstones are generally erosive-based, intraclastic and trough crossbedded, fining up into climbing-~ppled, crosslaminated sandstones and siitstones. Laterallyaccreted heterolithic units are common. The fin-

TERTIARY

EVOLUTION

OF THE SIVAS

BASIN.

TURKEY

35

1 BOIJNDARY

N

FAULT

ZONE a

q

0 : Fluvial sand-shale b-O sequence

-7,.

.‘o.

-.O

_ ‘,amankaya

/

y:.

/

.’

.‘o’

:..

.,

.o

.o.O

Red marls

El

Large shallow, ephemeral lakes

-

u -

‘0

f ‘o’ . , ,

v.C)rtakoy ORTAKij’. :7_-. “, ” YJB-BASIN ‘, ‘, _,’

m u

40Km

L

Fig. 7. Paleogeographic

reconstruction

R

-

4

of the Oligocene

Ophiolitic Limestones

of the Sivas Basin

ing-up cycles are generally capped by red and green siltstones and are typically 5-10 m thick.

sheet was still active during The dominantly southward

The

coarser

palaeoflow

and

limestone

units

contain

clasts,

serpentinite,

the ultramafic

quartzite clasts

being

more common in the lower part of the sequence. Palaeoflow recorded by cross-bedding in the channel fills is dominantly towards the south and southwest

suggesting

northern side unfossiliferous cracks

positional

melange

is not

Oligocene deposition. and southwestward

consistent

northward

with

thrust

major

syn-de-

displacement

along

the Caldag-Giirlevik line, although the structural data (below) clearly indicate that regional tectonic shortening

occurred

at the end of the Oligocene.

uplift of a source area on the

of the basin. The mudrocks are and show abundant desiccation

and pseudomorphs

of gypsum

and halite.

Towards the centre of the sub-basin, around Celllli, mudrocks are more common. Farther east, lacustrine ostracodal limestones occur in the Oligocene sequence near Bulucan (Fig. 8). The upper part of the sequence in the Celslli sub-basin consists of lacustrine shoreline facies with abundant wave-rippled sandstones recording storm events (Gokcen and Kelling, 1985). This sub-basin lies to the north of the CaldagGiirlevik thrust fault, and is here regarded as a foreland basin. It is not clear from the sedimentological data whether the postulated Eocene thrust

Lower and middle Miocene

deposits

The Miocene rocks of the Sivas Basin show complex thickness and facies changes, some of which are summarized in Figs. 9 and 10. The sequences in various parts of the basin scribed below from west to east. (1) Ortakiiy

area. The condensed

are de-

Oligocene

se-

quence in this area passes conformably up into 5 m of non-marine mudrocks and thin limestones of Miocene age, overlain by 20 m of limestones which pass laterally eastwards into widespread evaporites of early Miocene age. The apparently slow sedimentation rate, the conformable contact with the underlying Oligocene rocks and the difference in

J.M.L. CATER

36

facies seen in this area relative basin,

are

all

“piggy-back” area.

Since

displacement

consistent model

there

with

piggy-back

is no clear

sub-basin basin

Miocene

located

and

Tremp-Graus

contain

Ortakoy of thrust the

setting to the Miocene

and

bedding

recording

sequence

contains

facies.

point

and

evaporites

Samankaya

areas.

Lower

topping

in this area pass up into more

abundant

than 400 m of coarse sandstones and red nonmarine silt-shales (Fig. 9). The sand bodies are

Ortakiiy

with

fines were preserved

Celhi

Bulucan

200 i! E

:0

Eocene

\ /Eocene /

EJ

150Km

WE

Red siltstones and fine sands (Flood plainllacustrine)

Fig. 8. Generalized

stratigraphy

The flood-

deposited accretion

cross-beds.

indicate

was common,

rmit

W+

lateral

channel-fills

of the channels

directions.

were

the epsilon

incross-

because

by on The

that overand

the

of a slow

rate of lateral migration of the channel-belt. The serpentinite clasts record late Oligocene uplift of

Samankaya

Palaeocene‘\

structures

40% fine-grained

sandstones

rivers,

winged

flow

clasts

are not nota-

and planar-tabular

diverse

bars producing

abundant

(2) Yenikbj,

show internal

about

The

bases, and

and quartzite

These sand bodies epsilon

trough,

high-sinuosity

of the Southern

serpentinite

debris.

cluding

plain

Pyrenees. Miocene

abundant

with reverse-graded

bly intraclastic,

as a former

on top of an inactive Basins

winged,

and plant

deposition

sediments,

can be regarded

commonly

postulated

evidence

in the Sivas Basin during

thrust sheet, in an analogous Jaca

the

for the Oligocene

of these lower and middle Ortakijy

to the rest of the

ET AL.

and correlation

of the Oligocene

in the Sivas Basin.

TERTIARY

EVOLUTION

01

THE SIVAS

BASIN.

TURKEY

:! Yenikhy

37

Samankaya

Karayh

I

Fig. 9. Generalized

stratigraphy

w -_-----A

Top not

____-----h

fi A

A A

h A

A A

and correlation

A h

A A

h A

A

A

HAFIK

h

A

at

expo8ed

of the Miocene

least

150-200m

1’

in the Sivas Basin.

A

FOR?vlA;lON

E

-_-_---____

A

A

h ‘E&O’&

A

A

--

A

A

AA

AA,f,a;y -

_---------e-w-

----

-m----e--_

,I

c

-

-

_-

AA

Datum *~tJlc Horizon -

-

-

----

I

-

-

-_‘7c_G

Oligocene

--

-

-

_

-

-

--

I

Oligocene

I F Siiley -

m -

.Y/

-

Coarse

-m

Fine

rautr

elastics

to medium

sands

,

Fig. 10. Schematic

cross-section

of the central

part of the Sivas Basin showing growth

faults.

thickness

and facies variation

Skm

in Miocene

,

rocks across

38

J.M.1

2

-0

---_----

---

--_--1

.-

L_‘L --1’ -__ Ah

ZJ

Sands and conglomerates Fined

w4

4

ET AL.

Akpinar Coastal Marine sequence

$

b)

CATER

5Km

Evaporites

3

Marine

silts

red

and

beds

sands

E

(c)

Alluvial Ian transport and progradation direction

grained

iJ

N Main fluvial ~transport direction /

\ \ 3 Marine reworking of fan deltas?

n = 57

s

”

=81

Fig. 11. (a) Facies variations in the Karayun Sand Body (K.S.B.). (b) Palaeoflow data from the Lower K.S.B. (c) Palaeoflow data from the Upper K.S.B.

an ultramafic source area, possibly the Caldag massif to the south. (3) Area south of Siuas. The basal Miocene in this area is represented by 50 m of evaporites and limestones overlain by a 1400 m sequence dominated by red and green siltstones with gypsum

pseudomorphs, calcareous palaeosols and rootlets, interbedded with fining-upward sand bodies with erosive bases, including winged channel-fills (Fig. 9). The sand bodies are highly intraclastic and contain abundant plant debris including large tree fragments. They show trough cross-bedding pass-

TERTIARY

ing

EVOLUTION

up into

plane

cross-lamination. heterolithic mon

in

OF THE

and

Multistorey sequence.

sandstones

suggests

units

gypsum

study

units suggesting

of

the

sandstones

is overlain

which

a meandering

pass up into green marine to-

to be laterally-equivalent ltaic sandstones

records

meandering

floodplain

area of high subsidence area

discharge may

fluvial type in a

rate and arid

have

been

more

the N-S east

trending

of this

fluvial

origin.

They

mudrocks

which

seem

overlain

and

Upper

Fault

(Fig. 10). To the beds

are

coarse sand bodies,

the

Karayun

and Sand

fine-grained

red

Bodies

member

(KSB)

separated

may have been locally forested. (4) Area southeast of Siuas. The 1400 m thick

the Lower KSB are unimodal (Fig. llb), while those in the Upper KSB are bimodal (Fig. 11~).

fluvial sequence south of Sivas passes, km, eastwards into 55 m of evaporites

Both units contain erosive-based, stacked tabular sand bodies rich in intraclasts and serpentinite,

within 5 and silt-

a

towards

humid, in view of the abundance of plant debris in the sandstones: alternatively, the channel belts

Karayun

by

the de-

thins rapidly

evaporites

by two prominent

Lower

above

west (Fig. 10).

Karayun

fault,

lateral-accretion

to those

farther

100

by 400 m of

show

To the east, this sequence

of highly-fluctating source

m of massive tabular

pers. commun.,

deposition

The

and

of the channel-filling

(A. Bromley,

1988). This thick sequence

climate.

stacks

are very com-

that flow was dominantly

the southwest

(5) Kuruyiin ureu. To the west of Karayiin,

climbing-ripple

Detailed

and provenance

TURKEY

channel

accretion

palaeoflow wards

BASIN.

bedding

lateral this

SIVAS

stones capped by a 30 m thick marine algal grainstone unit (Fig. 10). These limestones pass up

limestone

and

commonly

pass up from dewatered

and/or exposed

bedded and plane-bedded stones, but in the Upper

laterally into 40 m of coarse sandstones farther to the southeast. The latter, which

contain abundant echinoids and oysters, show large scale sigmoidal cross-stratification dipping south and southeast and are overlain by finergrained sandstones with low-angle planar crossbedding dipping east. The top of the sequence is cut by channels filled with intraclastic sandstone which fines up into green marls with sandy interbeds less than a metre thick. The thick, non-marine sequence

south of Sivas

often

(Middle

Sand Body) (Fig. 11 a). Palaeocurrents

pebbly,

quartzite

grading

clasts.

Individual trough

transitionally

contains desiccation-cracked siltstones and thin sand units with wave and current ripples. Marked thinning of the sequence, particularly and Middle KSB, occurs laterally

in the Lower towards the

Karayun and Akpinar faults (Figs. 10 and 11). On the eastern side of the Akpinar Fault, up to pass up into non-marine overlain

barrier,

which

subsidence

beyond

it to the east and allowing

a

marine transgression to spread into this area. The echinoid-rich sandbody is of deltaic origin, the large-scale sigmoidal cross-beds recording progradation of the delta-front slope towards the east and southeast. The delta developed when sedimentation from the north and west over-topped the intervening barrier, and was abandoned due to a reduction in elastic supply. The sands were then reworked on an east-facing shoreline and eroded by fluvial or tidal currents. The overlying green marls probably record another marine transgression, but laterally equivalent facies have not been identified farther west.

the

sandstones. The Upper KSB also shows some herringbone cross-stratification. The Middle KSB

100 m of evaporites

from balancing

cross-

up from

and green mudrocks

sedimentation

units

sandstone into red siltKSB, the siltstones are

passes abruptly into marine deposits across an area of low subsidence which acted as a partial preventing

in

marine,

coarsen

upward

well-sorted,

with intense

bioturbation

lar and sigmoidal The sequences

in

by marine regular

red

mudrocks cycles

into

inverse-graded sandstones and rare low-angle tabu-

cross-bedding (Fig. lla). on both sides of the Akpinar

Fault pass up into green marine mudrocks which are not affected by lateral thickness variations (Fig. lo), and therefore appear to post-date vertical displacement on the fault. These sequences are laterally equivalent to the green marine mudrocks above the deltaic sandbody farther west, This complex facies association results from the interaction of marine transgression and syn-sedimentary subsidence variations across NNW-SSE to N-S trending growth faults (Fig. 12). The

.I.M.L CATER

40

ET AL.

Zara

rAXrakials

Mud-dominated

red beds

red beds

Sand-dominated Marine

muds

Syn-sedimentary

fault 1

Fig. 12. Palaeogeographic

reconstruction

meandering fluvial sequence in the west is abruptly replaced across the Karayiin Fault by coarse, tabular pebbly sandstones of the Lower KSB which are interpreted as braided alluvial channel deposits. Their geometry and unimodal current patterns suggest that the channels were confined by the NNW-SSE

to N-S

trending

faults to a linear

of the Miocene

sands as linear bars and tidal-channel fills. At about this time, the Upper KSB was being deposited, which was less confined by the NNW-SSE to N-S trending faults and may have had a fan-like morphology. The bimodal current directions and possible

herringbone

have been highly cross-bedded

differential

subsidence

con-

tinued during deposition, while the reduced grain-size indicates a reduction of elastic input from the south. Despite this, conditions remained non-marine in this area, possibly due to low relative sea level at this time. These deposits may correlate with the non-marine mudrocks towards the base of the Akpinar sequence farther east. This latter sequence records a marine transgression after deposition of the basal non-marine sequence. Coarser sediment then extended to the Akpinar area, causing deposition of reworked

cross-bedding

in the Upper

KSB sequence suggest some marine reworking of the fan. Deposition of the Upper KSB seems to

member

that

1

in the Sivas Basin.

belt (Fig. 12), and that a fan morphology did not develop. The shape of the overlying fine-grained shows

20km

mudstones

energetic;

sandstones are interpreted

the dewatered grading

up into

as debris-flow

the basal parts having dewatered tional during flow. Eventually,

trough pebbly deposits,

and become tracrenewed marine

transgression led to the deposition of green mudrocks throughout the area, by which time the syn-sedimentary subsidence variations had stopped. (6) ~~~ai~i area. In this area a high-angle (up to 90 o ) unconformity separates the Oligocene from a Miocene sequence comprising a thin basal conglomerate overlain by 150 m of algal grainstones.

TERTIARY

The

kVOLUTION

conglomerate

presumably tion

event.

during

pebbles, area which

the late Oligocene

echinoids cross-beds

probably

marine

serpentinite

from a provenance

The algal

rhodoliths, sigmoidal quence

contains

derived

was uplifted

41

OF THE SIVAS BASIN. TURKEY

grainstones,

deforma-

which

contain

and bivalves, show low-angle dipping southeast. This se-

records

the migration

of sub-

bars of tidal or storm origin, with the basal

conglomerate

representing

a winnowed

lag de-

The limestones marls

calated

with

are overlain a sparse

by 300 m of bluemarine

fauna,

inter-

with thin (ca. 1 m) shelly coquinite

beds,

rich in derived bivalves and brachiopods, which were colonized by epifaunal oysters and Bryozoa. Flute

casts indicate

transport

from the north

and

west. The sequence passes up into > 200 m of red beds, which coarsen up from bioturbated sideritic and rootletted siltstones to tabular sandstones with trough cross-bedding dipping to the southeast and east. These are capped by two thin gypsiferous layers separated by 140 m of red siltstones and thin tabular sandstones. This 640 m sequence records

the progradation

shoreline eventually

from

of a fan-delta

the W/NW

leading

into

to terrestrial

or elastic

a marine floodplain

basin, and

playa conditions. The sequence correlates with the Karayun sequence up to or including the Upper KSB. It is overlain by 300 m of green sandy mudstones and yellow marls of marine origin, laterally equivalent to the green marine mudrocks seen elsewhere. (7) Bulucun

area. The basal Miocene

sequence

in the Bulucan area overlies an erosion surface cut into the Oligocene sequence and consists of evaporites 15-150 m thick which contain scattered peridotite pebbles. This sequence passes up into > 200 m of thick-bedded, tabular sandstones and conglomerates which in turn are overlain by 50 m of silty sandstones of meandering fluvial origin,

to the north

red siltstones equivalent elsewhere These

and west, the higher parts

pass up into 300 m of green and

marine

to the

limestones,

green

marine

and

apparently

mudrocks

seen

in the Sivas Basin. complex

facies

ficult to reconstruct

variations

the Miocene

make

it dif-

palaeogeography

of the Sivas Basin. The sketch shown in Fig. 12 is probably areas

posit. green

Farther

of the sequence

over simplified, outside

Karayiin-Celllli

the

due to a lack of data for

well

region.

constrained

The linear

facies belts were due to fault-block

Sivass

trends

of the

control.

Upper Miocene deposits In many parts of the Sivas Basin, the early to mid-Miocene deposits are unconformably overlain by > 200 m of massive gypsiferous evaporites, known informally as the Hafik Formation. These evaporites contain rare serpentinite pebbles, anhydrite nodules and “chicken-wire” textures indicating shallow, probably marine, conditions. The serpentinite

clasts

ophiolite-bearing Gunyamac,

indicate thrust

renewed sheets

uplift

of the

to the south.

north of Hafik, the evaporites

At

pass up

into 50 m of large-scale, trough cross-bedded marine bioclastic grainstones. The latter were transported to the south and west and are interpreted as tidal or storm-reworked submarine sand-wave deposits. These sequences have not been dated but the thick evaporites of the Hafik Formation may correlate with the thick Messinian evaporites of shallow-water origin which are widespread the Eastern Mediterranean region.

throughout

Pliocene deposits

lateral accretion units, on point bars building

The plateau northwest of Sivas comprises c. 350 m of conglomerates, sandstones and non-marine limestones of post-Miocene age. These are later-

into westward-flowing channels. This meandering fluvial sequence includes burrowed calcareous mudstones, limestones with non-marine bivalves and gastropods and thin allochthonous coal seams, recording interfluvial lacustrine and swamp deposition.

ally equivalent to non-marine limestones exposed on the southern edge of the basin between Samankaya and Altinyayla and east of Ulas. These deposits form at least two flat erosional terraces, one 100 m above the other, the upper one being 400 m above the level of present-day lakes in the

containing well-developed 4 to 8 m thick, deposited

J.M.L. CATER

42

area, suggesting

considerable

uplift

since the early

planes dipping developed

NE-SW

ture cleavage,

Structure The central mapped

part

in detail

of the Sivas Basin

and structurally

has been

may be divided

into three areas (Fig. 13):

to N-S

folds, thrusts

tures affect Eocene

The southernmost

structure

Anticline,

a south-dipping

NlOO o E and

dips

Maastrichtian-Palaeocene thrust over ophiolitic

in this area is the

a hangingwall

62”s.

thrust The

anticline which

fold

limestones melange. The

re-

strikes

and extensional cleavage.

thrust

horizon.

in the central

contact

is

an extensional

fault

or a

representing

a major

de-

However,

part

as-

rocks.

Eocene-Oligocene

either

faults,

All these struc-

and Oligocene

the

being

collement

of Area

stones, which dip consistently

north

of Keka Tepe

2, Oligocene

sand-

north-northeast,

rest

by

on an erosional unconformity cut into folded and thrust Eocene turbidites and ophiolitic units. The

which are melange in

presence of this marked topographic unconformity, with erosional relief of > 800 m (Fig. 5)

is cored

turn has been thrust northwards over Oligocene shales and these shales are folded into a footwall syncline southern

or frac-

with a fracture places

with a regionally

are cut by later NNW-SSE

northerly-dipping

to

the south (Fig. 13). penetrative

trending

tectonic,

Buyukyilanli

trending

sociated In

Area I

lated

-C 45 o towards

These folds, which are associated

Pliocene.

ET AL.

related to a south-dipping thrust. limb of this syncline strikes N50”E

dips 16-22 o N. Hence northward-directed ing affected rocks as young as Oligocene.

The and

thrust-

demonstrates

a compressional

uplift in pre-Oligocene coaxial compressional

event with localized

times followed by a later event which affected Ol-

igocene rocks and tightened the pre-existing tures in the Eocene sequence.

struc-

Area 3 Areu 2 This area is characterized

by large wavelength,

thrust-related, doubly-plunging, asymmetric folds with axes trending E-W to ENE-WSW and axial

The central-northern consists almost entirely and shales of Miocene ping Oligocene

part of the Sivas Basin of evaporites, sandstones age, except for steeply-dip-

shales and sandstones

q Miocene q Ohgocene s

E0CWW Maastrichtian & Palaeocene

Fig. 13. Diagram

to show the nature

and trend of the main structural

elements

of the Sivas Basin

exposed

in

TERTIARY

EVOLUTION

OF THE

the core of the Celalli the Oligocene basal

rocks

limestone

The contact

the overlying

of

Miocene

(up to 90 “) angular further

localities

ophiolitic

lower Miocene

in the blocks

sediments

that the ultramafic

evidence

of

Basin,

ser-

the observed

Sivas

structurally

underlie

or evaporites,

implying

rocks were tectonically

the late Oligocene.

Miocene

43

TURKEY

deformation.

pentinized

The

Anticline.

with

recording

At several

during

BASIN,

is a marked

unconformity, Oligocene

SlVAS

influx

uplifted

This is consistent

of ultramafic

clasts

with

in early

fault is associated during

and

middle

Miocene

sediments

in

Area 3 are cut by steeply-dipping or vertical, N-S to NNW-SSE trending faults, e.g. the Karayiin and Akpinar Faults. These faults were clearly active during early Miocene tial subsidence of several

times, causing differenN-S aligned blocks as

with thrusts

and folds

strike-slip

displace-

left-lateral

ment along the fault. Most of these strike-slip wards into upper Miocene some evidence

faults die out northsediments. There is

of late Miocene

strike-slip

displace-

of Karayiin a left-lateral ment, e.g., northwest fault cuts near vertical mid-Miocene rocks (the KSB).

Elsewhere,

Miocene

rocks

of

the

to localized

structures,

upper

zones

suggesting

ductile

of de-

of cover rocks above zones of continu-

ing strike-slip The marked

deformation

is restricted

folds and thrust formation

times. lower

strike-slip generated

displacement

at depth.

northern margin of the Sivas Basin is by a prominent near-vertical, north-facing

fault scarp separating south from ophiolitic

Miocene melange

sediments to the and Eocene sedi-

ments to the north. Near Bahqecik (Fig. 13) the fault zone dips c. 45” N with ?Late Cretaceous

shown by abrupt thickness and facies changes in the Miocene sediments (Fig. 10). This syn-sedimentary displacement, which continued until the

pillow lavas thrust southwards over Eocene pink limestones, which in turn are thrust over Miocene

end of early or mid-Miocene times, was mainly extensional with little evidence of strike-slip dis-

evaporites. Hence Northern Boundary

placement

ping

during

sedimentation.

The N-S to NNW-SSE Lineament is the dominant

trending Suleymaniye structural feature of

reverse

in this area this Fault) is a steep

fault;

steeply-dipping

however

normal

fault (the north-dip-

elsewhere

fault

it

is a

with downthrow

to

Area 3. It dies out southwards and does not affect the structures in Area 2. Two sets of en-echelon

the south. NW-SE

trending

ated

the

folds are related to this lineament: a dominant set trending NE-SW, e.g. the Celllli Anticline, and a

orientation of these folds and the fact that they die out away from the fault, imply some left-lateral

minor

strike-slip

set trending

N-S

to NW-SE,

i.e. parallel

to

the Suleymaniye Lineament. Associated minor ENE-WSW to NE-SW trending thrusts, e.g. near Tavsanli, affect middle to upper Miocene green marine mudrocks and are associated with co-generated hangingwall anticlines and footwall synclines. There are also a number of extensional and strike-slip faults associated with the Suleymaniye Lineament. ENE-WSW to E-W trending extensional

faults are seen, e.g., on the western

the Suleymaniye Lineament, faults, trending roughly parallel

side of

while strike-slip to the Suleymaniye

Lineament, are seen at Bulucan, Akpinar and around Karayiin (Fig. 13). Most of these show left-lateral displacements. The Celhlli Anticline is bounded to the west and east by NE-SW trending faults which display almost horizontal slickensides. Farther west, to the north of Ortakiiy, a

with

Boundary along

Fault. with

folds

Boundary

displacement

the fault

consistent

en-echelon

Northern

along

Horizontal

are associFault.

‘ the

The

Northern

slickensides

present

zone in the west of the area strike-slip

displacement.

are The

Northern Boundary Fault is best interpreted as a left-lateral transpressive strike-slip fault, which probably has an earlier history of down-to-S extensional displacement. The NNW-SSE to N-S trending which are well developed in the central Sivas Basin, probably or tear faults, associated

originated

structures, part of the

as lateral

with a thrust

ramps

sheet which

lay to the north of a postulated Eocene thrust sheet with a tip-line marked by the CaldagGiirlevik lineament. If this Eocene thrust sheet was actively being uplifted during Oligocene sedimentation, it follows that the more northerly thrust sheet was formed by northward thrust propa-

J.M.L. CATER

44

gation

during

the

event. These N-S active

as

Miocene

late

structures

growth

associated

compressional

then continued

faults

sedimentation.

these same structures faults

Oligocene during During

early

along the Northern

to

mid-

as strike-slip

left-lateral

Boundary

Late Eocene

to be

the late Miocene

were reactivated with

ET AL.

Incipient’thrusts

displacement

Fault.

Latest

Eocene

S

Summary On

the

southern

Maastrichtian

margin

limestones

Tecer Dagi are overlain litic melange. rocks

were

times

over

carbonates

of the

by thrust

It is assumed abducted

Sivas

of Giirlevik

Basin

Dagi

and

slices of ophio-

that

these ophiolitic

southwards

in pre-Eocene

Maastrichtian-Palaeocene which form the northern

Oligocene S Ghevik

platform margin

of the

Tauride (Kirsehir) Block. The base of the limestones is not exposed in the Sivas Basin, so it is not known whether these rocks are autochthonous or are olistoliths in a melange. Continued closure of Neotethys resulted in the formation of a narrow remnant basin in the Sivas region which filled rapidly, mainly with gravityflow deposits, during the Eocene. The reversal of polarity to north-directed thrusting in the late Eocene may be explained by means

of a gravity

collapse basin

sliding

of Palaeogene

as major

model

slope

northward-moving

involving

deposits gravity

the

into

the

End-Oligocene-Miocene s

0

N

Miocene

K?i

q Oligocene q Eocene (Bah~ecik Conglomerates

Maastrichtianl Palaocene

l?l5 Ophlolitlc

at base

)

cl

melange

Continental

crust

slides,

along reactivated abduction-related thrust planes (Fig. 14). During additional stacking of slide material, the distal parts of these slide planes may well have developed into compressional “surge zones” which dipped to the south. The latter could have propagated upwards through the stack of gravity-slides during the increased tectonic compression at the end of the Eocene, leading to north-directed thrusting. The remnant basin filled and became emergent prior to the Oligocene. The basal Oligocene unconformity records uplift and erosion of the basin fill at the end of the Eocene. The basin was then sub-divided by a thrust tip-line running from Giirlevik Dagi to the Caldag, with a piggy-back basin situated to the south of this line. The widespread Oligocene evaporites deposited above the Eocene turbidites are comparable in age and

Fig. 14. Schematic

diagram

illustrating

for the evolution

a gravity

sliding

model

of the Sivas Basin.

setting to the Eo-Oligocene sequence in the Tuz Golu Basin farther west, where an Eocene remnant basin fill is capped by evaporites (Gorur et al., 1984). Thrust reactivation

during

the late Oligocene

caused renewed northward movement of slices of ophiolite and Eocene sediments. The occurrence of coarse serpentinite clasts in the lower Miocene sediments records uplift of the thrust sheets in the south. Farther north, the foreland basin underwent differential subsidence during Miocene sedimentation. Marked facies and thickness variations indicate that the floor of the basin was divided into N-S elongated fault-bounded blocks. It is

TERTIARY

EVOLUTION

suggested sheet

that

which

pression; narrow

45

OF THE SIVAS BASIN, TURKEY

the basin

formed

during

in this model thrust-sheet

was floored

by a thrust

iate Oligocene

the N-S

segments,

blocks

separated

com-

The N-S

Boundary

by lateral

The

with the relative along

blocks und~~ent

during

growth

Miocene

movements

faults

differen-

being accommodated cover

above

the tear faults/lateral

culminations.

These growth

faults were reactivated

by strike-slip

motion

late

Miocene

(e.g. the Akpinar

Fault),

in the

and

by inversion

ping normal

may

Left-lateral Boundary echelon strike-slip

Fault folds

displacement

displacements Fault Zones

the subsurface.

Anatolia

is consistent

compression

with the

of the region

the northern

dur-

along

is suggested located

Miocene

edge

the Northern

by the oblique

south

of

probably fault.

displacement

it was

south-dip-

times onwards.

the

may

fault.

occurred

same time as reverse displacement left-lateral

that

of a pre-existing

displacement

at this Northern

reverse fault.

suggests

fault which formed

probably represents renewed tear faulting during a mid- to late Miocene phase of thrust movement in This model

the

as a steeply-dipping

i.e. it is a transpressive

tectonic

initiated

dip of the fault

also have undergone some strike-slip displacement during earlier Miocene times. This reactivation

apparent

areas). Compression

also

of the Sivas Basin from Eocene

sedimentation,

in the Miocene

Fault

steep

formed

elongated

subsidence

and Akpinar

probably

represent

ramps or tear faults. tial

Karayiin time

enThe

at the

along the fault,

The component be related

of

to the

along the North and East Anatolian as a result of westward “escape” of

during

crustal

shortening

from

mid-

times.

ing the Miocene, which was responsible for periods of uplift of elastic source areas and prograda-

The onset of strike-slip displacement along the North Anatolian Fault Zone in Ed-Miocene times

tion

(Sengor,

of

major

elastic

systems

(as

seen

in

the

1979) may provide

an explanation

Fig. 15. Block diagram to illustrate the geometry of the main structural features of the Sivas Basin

for the

46

J.M.I..

differential

subsidence

The orientation the new E-W

across the N-S

of these strike-slip

may have been

faults,

subjected

westward

thrust

to extensional

The sulted

relative

sheets underlying end

Boundary

Fault

to the fault-segmented

and

structures

in Fig. 15. The reverse acteristic

stress at

Block to the north

tectonics

Oligocene,

in complex

to

recorded Miocene

gives the basin

of a structural

in end times,

re-

which are illustrated

component

on the North

a geometry

“triangle

zone”,

chari.e. an

area of intense compressional activity between rigid blocks, with structures verging towards the centre of the basin. This compression is related to the northward migration of the Arabian Plate. The continued intense compression of the Sivas Basin area phases

also seems

to have resulted

of uplift during

Baykal,

F. and

Geological

in at least

two

the Pliocene.

Erentoz, Map

J.F.,

C., 1966.

of Turkey.

Mad. Tetk. Arama Dewey,

M.R.,

A.M.C.,

1986.

sphere:

the

collision

zone. In: M.P. Coward

and Dave Moulton. We wish to thank John Smewing and Andrew Mann for their valuable contribution as the “advance

party”

to the field area.

Gansser,

A., 1974. The ophiolitic

lem on Tethyan Gokcen,

examples.

Gokcen,

region

evolution

A.H.F.,

J.E. Dixon and A.H.F. Evolution Artan,

U. and

Karababa 76: 72-89.

Robertson

of the Eastern

Sot. London,

1984. The Maden

of a Neotethyan

active

(Editors),

Mediterranean.

Complex, margin,

In:

The Geological

Spec. Publ.. Geol.

storm-influenced

Sestini.

G., 1971. Geology

area (S&as province).

of the Beypinari-

Mad. Tetk. Arama

Enst.,

London,

19:

melange,

a worldwide

prob-

Guneyindeki

Paieojen

Evrimi.

Istifinin

YerbiIimle~,

8:

G., 1985. Oligocene Turkey):

shelf to evaporitic

basin.

deposits

of the

evolution

from

Geol. Rundsch.,

74: 139-153. Gokten,

E., 1983. Sarkisla(Sivas)

tigrafisi

ve jeolojik

guney-guneydogusunun

evrimi.

Bull. Geol.

Sot.

stra-

Turkey,

26:

167-176. Gorur.

N., Oktay,

F.Y., Seymen,

Pataeo-tectonic

evolution

I. and Sengiir,

Turkey:

sedimentary

closure.

In: J.E.

Dixon

Hempton,

record

and

Evolution

the Bitiis suture

near

basin

of

A.H.F.

a Neo-Tethyan (Editors),

Mediterranean.

17: 455-466. and deformation

Lake

1984.

complex,

Robertson

of The Eastern

, 1985. Structure

M.R.

A.M.C.,

of the Tuzgoiu

Central

Hazar,

history

southeastern

of

Turkey.

Geol. Sot. Am. Bull., 96: 233-243. Kurtman,

F.,

Jeolojik

1973.

Sivas-Hafik-Zara

ve tektonik

yapisi.

ve lmrali

Mad.

Tetk.

bolgesinin

Arama

Enst.,

80:

l-32. Sanver.

M. and Ponat,

paleomanyetik Istanbul Sengiir,

age,

E., 1980. Kirsehir

bulgular,

Yerbihmleri,

A.M.C.,

and

A.M.C.,

the

London,

Yilmaz,

Turkey,

iliskin

rotasyonu.

2: 231-238. tectonic

Anatotian

transform

significance.

Y. and Sungurhr, Cimmerides:

termination Robertson

Eastern

fault:

J. Geol.

Sot.

O., 1984. Tectonics

nature

of Palaeo-Tethys (Editors),

Mediterranean.

and evolution

The Geological Spec.

of

In: J.E. Dixon Publ.,

Evolution Geol.

Sot.

17: 77-112.

A., 1981. Tokat

Karisigin

ve dolaylarina Masifinin

136: 269-282.

and A.H.F. of

Kirsehir

1979. The North

offset

the western

Yilmaz,

17: 3755402.

Sot.

(Sivas, Centrai

of the Mediterranean G. and Robertson,

Geol.

ve Paleocografik

S.L. and Kelhng,

Zara-Hafik

Sengor,

SE Turkey:

young

l-25.

London,

Aktas,

litho-

Anatolia-a

Eclog. Geol. Helv., 67: 479-507.

S.L., 1981. Zara-Hafik

sedimantolojisi

its

References

F. and

and A.C. Ries (Editors),

Publ.,

Spec. Publ., Geol. Sot. London,

sions were held in the field with Gurhan Aktas, Lorie Dunne, Gilbert Kelling, Andrew Mackay

Saroglu,

3-36.

The Geologica

This work was funded by Amoco Turkey Petroleum Company through a grant awarded to the Earth Sciences and Resources Institute, University of South Carolina. Interesting and fruitful discus-

of the

1:500,000.

of continental

of Eastern

Spec.

text

Scale

W.S.F.,

Shortening

neotectonics

Tectonics.

Sheet. 116 pp.

Kidd,

@rgiSr,

ET AL.

Explanatory

Sivas

Enst., Ankara,

Hempton,

Collision

the Sivas Basin.

compressional

Eocene,

perpendicular

system, suggests that they

this time, as the rigid Pontide moved

tear faults.

CATER

Ic Yapisi 24: 31-36.

ile Sivas Arasindaki

Bolgede

ve Yerlesme

Bull. Geol.

Yasi.

Ofiyohti Sot.