Central Anatolia, Turkey

15 Pages·2013·2.42 MB·English

Turkish Journal of Earth Sciences Turkish J Earth Sci
(2013) 22: 778-792
http://journals.tubitak.gov.tr/earth/ © TÜBİTAK
doi:10.3906/yer-1207-2
Research Article
Paleomagnetic rotations in the Late Miocene sequence from the Çankırı Basin (Central
Anatolia, Turkey): the role of strike-slip tectonics
1 1, 2 1
Stella LUCIFORA , Francesca CIFELLI *, F. Bora ROJAY , Massimo MATTEI
1
Department of Sciences, Roma Tre University, Largo San Leonardo Murialdo 1, 00146 Rome, Italy
2
Department of Geological Engineering, Middle East Technical University, 06531 Ankara, Turkey
Received: 10.07.2012 Accepted: 29.11.2012 Published Online: 26.08.2013 Printed: 25.09.2013
Abstract: In this paper, new paleomagnetic and anisotropy of magnetic susceptibility (AMS) data from Miocene continental units of
the Çankırı Basin are presented, with the main goal of providing additional constraints on its deformational and rotational history
during the Late Cenozoic. AMS data indicate a tectonic origin for the magnetic fabric, suggesting that Upper Miocene units were still
involved in the deformation processes. Paleomagnetic data show that tectonic rotations in the Çankırı Basin do not show a symmetrical
distribution along the opposite edges of the basin, as expected from the observed Ω-shape. In particular, by combining our data with
those already published, we observe that tectonic rotations increase from the southern portion of the basin toward the north and
from the central part toward the basin margins. This distribution reasonably matches with a post-Late Miocene reactivation of the
Çankırı Basin margin fault systems, possibly related to the activity of the right-lateral North Anatolian strike-slip fault. In this tectonic
interpretation, the complex pattern of paleomagnetic rotations appears to be connected with a local block rotation mechanism due to
the activity of faults with strike-slip components of motion along the tectonic margins of the Çankırı Basin.
Key words: Paleomagnetic rotations, oroclinal bending, Central Anatolia, Neogene, strike-slip tectonics
1. Introduction the indentation of the Kirşehir Block against the Sakarya
In the last few decades, a large number of paleomagnetic continent. Also from this evidence, Mejiers et al. (2010)
studies have been carried out in Turkey, with the aim of proposed an overall tectonic model for the evolution of
defining the northward latitudinal drift of the different Central and North Turkey and suggested that deformation
microcontinents now amalgamated in the Anatolian was localized in the northern part of the central Pontides
region (e.g., Van Der Voo 1968; Sanver & Ponat 1981; during Late Cretaceous-Tertiary convergence between the
Evans & Hall 1990; Morris & Robertson 1993) and to different Anatolian blocks, resulting in oroclinal bending
shed light on the role of crustal block rotations along the lasting until the Paleocene. After that period, deformation
North Anatolian Fault Zone and within the Anatolian was mainly expressed by thin-skin thrust tectonics, which
Block (e.g., Saribudak et al. 1990; Platzman et al. 1994; propagated southwards and were concentrated in the
Michel et al. 1995; Tatar et al. 1995; Piper et al. 1996; Çankırı Basin, thus causing the present-day curved shape.
Gürsoy et al. 1997; Piper et al. 1997; Platzman et al. 1998, In this work, we present new paleomagnetic and
Piper et al. 2010). The role of paleomagnetic rotations anisotropy of magnetic susceptibility (AMS) data from
in the origin and tectonic evolution of curved tectonic Miocene continental units from the Çankırı Basin, with
structures and sedimentary basins has been partially the main objective of further constraining the time and
investigated in Central and Northern Turkey. Meijers et spatial distribution of tectonic rotations during Late
al. (2010) suggested that the curved shape of the central Cenozoic times. In particular, AMS and paleomagnetic
Pontides orogenic belt resulted from oroclinal bending measurements on the rock collection from the Çankırı
during the latest Cretaceous to earliest Paleocene times, Basin were carried out with a 2-fold purpose: to define the
whereas Kaymakçı et al. (2003), on the basis of structural timing of rotation in the Late Miocene sediments and give
and paleomagnetic data, suggested that the Ω-shape further constraint to the indentation mechanism proposed
of the Çankırı Basin (Central Anatolia) resulted from by Kaymakçı et al. (2003); and to determine the fabric of
opposite rotations along the basin margins, related to the Miocene sediments and to assess whether they have
* Correspondence: [email protected]
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a fabric dominated by sedimentary or tectonic processes. 2. Geological setting of the Çankırı Basin
Our results show that paleomagnetic rotations in the The Çankırı Basin is an important tectonic feature for
Çankırı Basin do not have a symmetrical distribution understanding the tectonic history of Central Anatolia,
along the opposite edges of the basin and, when considered due to its tectonic position at the contact between the
together with those published by Kaymakçı et al. (2003), Pontides and the Anatolide-Tauride Block (Figure 1a,
they do not fit with the indentation model considered to b). The tectono-sedimentary evolution of the Central
be responsible for the Ω-shape of the Çankırı Basin. We Anatolia basins has been mainly controlled by the
propose that the complex pattern of tectonic rotations progressive closure of the northern Neotethys Ocean, and
measured in the Çankırı Basin is due to strike-slip motion then by the initiation and subsequent deformation on the
along the basin margins, related to activity on the North North Anatolian Fault activity (Şengör & Yılmaz 1981).
Anatolian Fault. During the Late Cretaceous-Paleogene, accretionary
26°E 30°E 34°E 38°E 42°E 33°30’N 34°00’N 34°30’N
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0
A R A B I A N 40° Miocene Units Thrusts
T A U R I D E S Oligocene Units Faults
P L A T E 3 Eocene Units Strike-slip faults
7
°N Paleomagnetic sites and measured
Mediterranean Sea 0 200 400 km Basement Units magnetic lineation
12 32 1 4
00 00 0 0
UU OO O O
SS BB B B
NNW SSE
x
? ? ? ? +++++++
+ +
not in scale
d) MMiioocceennee rmedu dcrloacsktiscs EOolicgeoncee nseeq sueeqnuceensces +++ CPrree-tOacleigooucse onpeh gioralintiitco mideslange
Figure 1. Tectonic setting (a) and geological sketch (b) of Eastern Mediterranean area. (c) Geological map of the Çankırı Basin.
Sampled sites and magnetic lineations from AMS measurements from this work are shown. (d) Simplified geological section cutting
the Çankırı Basin (its trace is indicated in Figure 1c). NAF, North Anatolian Fault; EAF, Eastern Anatolian Fault; CB, Çankırı Basin;
KFZ, Kızılırmak Fault zone; ESFZ, Ezinepazarı–Sungurlu Fault zone.
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prisms and fore-arc basins developed to be followed in fluvio-lacustrine deposits. The Late Pliocene-Quaternary
Eocene times by piggyback to peripheral basins (Şengör alluvial fan deposits and recent alluvium (fifth sequence)
& Yılmaz 1981; Rojay 1995; Görür et al. 1998). After the locally overlie all these units (Kaymakçı 2000).
closure of the northern Neotethys during the Miocene The main structures that shape the current geometry
(Gannser 1974; Şengör et al. 1981; Kaymakçı 2000; Şengör of the Çankırı Basin are the thrust and reverse faults
2003; Rojay et al. 2004), the Central Anatolian region was delineating its western and northern rims (Figure 1c).
characterized by the formation of narrow continental A belt of NNE-striking folds defines the eastern margin
basins (e.g., Ankara and Çankırı Basins) and extensive of the basin. In the south, the basin infill laps onto the
Neogene volcanism (e.g., Galatia and Cappadocia basement (Kaymakçı 2000). Other major structures
volcanic terrains). According to Kaymakçı et al. (2009),
affecting the Çankırı Basin are the right-lateral Kizilirmak
the Çankırı Basin first developed as a fore-arc basin
Fault zone (KFZ) and Ezinepazarı–Sungurlu Fault zone
from Late Cretaceous to Middle Paleocene times, and
(ESFZ). These are WSW–ENE oriented and displace the
then as a foreland basin during the Late Paleocene-Early
ophiolitic rim, the basement, and the basin infill, which
Miocene, straddling the İzmir-Ankara-Erzincan suture
included Late Miocene units indicating a post-Late
zone (Figure 1b). The Ω-shaped Çankırı Basin is bounded
Miocene tectonic activity (Kaymakçı et al. 2003).
by Cretaceous ophiolitic mélanges at the northern and
western edges, by a N–S oriented left-lateral strike-slip
3. Sampling and methods
fault overprinted on an imbricated accretionary wedge at
For this study, we collected 162 oriented cylindrical samples
the western edge, and by the Kırşehir crystalline complex
from 7 sites (Figure 1c; Table 1). All the sampled sites
in the south (Figures 1c and 1d). The basin is filled with
belong to the Miocene continental succession comprising
4 km of Late Cretaceous to recent deposits, which can be
fluvio-lacustrine units, frequently in succession with
grouped into 5 sedimentary sequences (Kaymakçı 2000).
evaporites. In particular, sites have been collected from
The oldest sedimentary sequence consists of tectonically
the continental Tuğlu, Süleymanlı, and Bozkır Formations
intercalated Late Cretaceous deep marine sediments
(Late Miocene), which lie within the fourth stratigraphic
alternating with mafic volcanic rocks, volcano-clastic
sequence of Kaymakçı (2000). Four sites have been
rocks, proximal regressive shallow marine units, and
Paleocene littoral red clastic rocks and carbonates, which sampled from the Bozkır Formation (MN13–MN15,
represent the subduction history of the northern Neotethys Messinian-Lower Pliocene) which crops out in the central
in the region. The second sequence is a Late Paleocene to (BO01, BO03, and BO04) and western parts of the basin
mid-Oligocene, more than 1 km thick, regressive flysch (BO02). The sample sites are located on top of a hidden
to molasse type of succession intercalated with mafic to thrust fault, which cuts Oligocene sequences and is sealed
intermediate volcanic rocks and nummulitic limestones. by Middle-Late Miocene units (Figure 1d). At site BO02, a
The third sequence comprises a very thick (up to 2 km) 90-m-long stratigraphic section (64 samples) was sampled.
sequence of Late Eocene to mid-Oligocene continental red This section corresponds to the lower part of the Bozkır
clastic rocks and evaporites. The fourth sequence is up to Formation, close to the contact with the underlying
1 km thick and represented by Early Miocene to Pliocene formation (Süleymanlı Formation). The section is formed
Table 1. List of anisotropy factors computed at each site in the Çankırı Basin.
Site n/N K L F P’ T S D, I (K ) D, I (K ) e
m 0 min max 1,2
TU01 24/24 465 1.006 1.010 1.017 0.195 40°, 20° 259, 55 22, 21 8.0
SU01 8/10 1265 1.003 1.014 1.019 0.569 variable 197, 85 57, 4 34.8
SU02 12/12 442 1.007 1.014 1.022 0.328 348°, 10° 184, 84 36, 5 9.7
BO01 18/18 245 1.002 1.018 1.022 0.768 320°, 10° 222, 80 58, 10 27.4
BO02 64/64 121 1.003 1.026 1.032 0.759 variable 114, 77 22, 0.4 29.7
BO03 13/13 1170 1.007 1.070 1.086 0.791 178°, 27° 352, 60 253, 5 16.8
BO04 23/23 293 1.003 1.035 1.043 0.827 sub-horiz 118, 86 11, 1 44.3
n/N = measured/sampled samples; K = (K + K + K ) / 3 (mean susceptibility, in 10–6 SI units); L = K /K ; F = K /K ; Pj =
m max int min max int int min
exp {2[(η1 – η)2 + (η2 – η)2 + (η3 – η)2]}1/2 (corrected anisotropy degree; Jelinek, 1981); Tj = 2(η2 – η3) / (η1 – η3) – 1 (shape factor;
Jelinek 1981); S = bedding attitude (azimuth of the dip and dip values); η1 = lnK ; η2 = lnK ; η3 = lnK ; η = (η1 + η2 + η3) / 3; e :
0 max int min 1-2
semiangle of the 95% confidence ellipses around the principal susceptibility axes.
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LUCIFORA et al. / Turkish J Earth Sci
by grayish clays and silty clays interbedded with thick layers of 5–10 mT up to 100 mT. The characteristic remanent
of gypsum. Two sites (SU01–SU02) have been sampled in magnetization (ChRM) was resolved from the orthogonal
the northwestern part of the basin from the Messinian vector projections and their equivalent directions were
(MN13) Süleymanlı Formation to the south of a thrust calculated by principal component analysis (Kirschvink
belt where the Cretaceous ophiolitic mélange is thrust 1980). For each site, the mean direction was computed
onto Eocene and Oligocene red clastics, and Miocene red using standard analysis (Fisher 1953).
clastics are steeply tilted (Figure 1d). Finally, a stratigraphic The measurement of the low-field AMS was also carried
section (TU01) has been sampled in the northeastern part out. AMS represents a cheap, rapid, and nondestructive
of the basin. The section is composed of fluvio-lacustrine technique for the characterization of the mineral fabric
sediments formed by clays and sandy clays intercalated of rocks (Hrouda 1982). AMS is defined by a second-rank
with sandy layers from the Tuğlu Formation (Tortonian, tensor and approximated geometrically by an ellipsoid
MN9–12). with principal axes K , K , K , in which the highest
max int min
At each site, cores were drilled with an ASC 280E petrol- intensity of magnetization is induced along the long axis
powered portable drill and oriented in situ by a magnetic (K ) and the weakest intensity along the short axis (K ).
max min
compass, corrected to account for the local magnetic A range of parameters has been defined quantifying the
declination according to the NOAA National Geophysical magnitude of anisotropy and for defining the shape of
data center. From each core, 1 to 3 standard (25 mm in the ellipsoid (see Table 1; Jelínek 1981; Hrouda 1982).
diameter × 22 mm in height) cylindrical specimens were
The magnitude of lineation L of the ellipsoid is defined as
cut. All magnetic measurements were carried out at the
K /K ,and the magnetic foliation F is defined by K /
Roma Tre University and Istituto Nazionale di Geofisica e max min int
K . The anisotropy degree and the shape parameter are
Vulcanologia (INGV, Rome) paleomagnetic laboratories. min
expressed by parameters P’ and T, respectively. AniSoft
In order to identify the main magnetic carriers in these
software (Chadima & Jelinek 2009) was used for these
sediments, rock magnetic analyses on selected specimens
calculations.
were carried out, which included:
1) The measurement of hysteresis properties using
4. Results
a MicroMag alternating gradient magnetometer (AGM
4.1. AMS results
model 2900, Princeton Measurements Corporation)
The distribution of magnetic susceptibility values (K )
with a maximum applied field of 1 T. From hysteresis m
indicates a range of 100–500 × 10–6 SI for the majority
cycles, after subtraction of the paramagnetic high-field
of the specimens (Figure 2a). This suggests a significant
susceptibility after saturation, we calculated the coercive
paramagnetic contribution of the clay matrix to the bulk
force (B), the saturation remnant magnetization (M ),
c rs susceptibility. However, some specimens show higher
and the saturation magnetization (M).
s susceptibility values (up to 2400 × 10–6 SI in site SU01),
(2) Stepwise acquisition of isothermal remanent
suggesting a major ferromagnetic content in these samples.
magnetization (IRM) and subsequent backfield DC
The L parameter ranges between 1.002 and 1.007, whereas
demagnetization (both in a succession of fields up to 1 T),
the F parameter ranges between 1.01 and 1.07 (Figure 2b;
measured on the same samples on the Micromag AGM.
The coercivity of remanence (B ) was computed from the Table 1). P’ values are less than 1.1 and T values are all
cr
backfield demagnetization curves. positive (Figure 2c). The shape of the ellipsoid is mainly
(3) The measure of the variation of susceptibility with oblate with a well-developed magnetic foliation recognized
temperature in some representative specimens. by well-grouped K axes in most cases (Figure 3). The
min
The natural remanent magnetization (NRM) was main magnetic susceptibility directions for each site are
analyzed using 2G Enterprises DC-SQUIDs cryogenic generally tightly grouped (Figures 3b–3g), with only TU01
magnetometers, installed within a magnetically shielded characterized by a girdle distribution of K and K axes
int min
room. The NRM of one specimen per core was measured (Figure 3a).
following progressive stepwise demagnetization using At the site scale, a tectonic control on the magnetic
thermal and alternating field (AF) procedures. The thermal fabric is well recognizable, even when the primary
demagnetization was carried out using small temperature sedimentary fabric is still preserved, as is the case in
increments (50 °C up to 300 °C and 30 °C above 300 °C) most of the sites (Figure 3). A well-defined magnetic
until the NRM decreased below the limit of the instrument lineation is defined, which parallels the main structural
sensitivity or random changes of the paleomagnetic trends documented in the area (Figure 1c). The central
directions were observed. Stepwise AF demagnetization part of the basin is characterized by ENE-WSW trending
was carried out using a set of 3 orthogonal AF coils magnetic lineations, parallel to the main fold axes that
mounted inline on the 2G Enterprises system, with steps characterize this area. In the western border, magnetic
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100 1.1
80 1.08
60 1.06
n
me L
ci40 1.04
e
p
S
20 1.02
a) b)
0 1
0 400 800 1200 1600 2000 2400 1 1.02 1.04 1.06 1.08 1.1
K (10–06 SI) F
m
1
0.5
T0
-0.5
c)
-1
1 1.05 1.1 1.15
P'
Figure 2. Magnetic parameters of analyzed samples in the Çankırı Basin. (a) Frequency distribution of the mean
susceptibility (K ) values for the entire set of specimens; (b) site-mean magnetic lineation L vs. site-mean magnetic
m
foliation F diagram; (c) site-mean degree of anisotropy P’ vs. shape factor T diagram.
lineations are oriented NNE-SSW and reflect the change between 0.2 and 0.3 T, suggesting the dominance of a
in fold axis orientation, which in this area is NNE-SSW. In low coercivity ferromagnetic mineral such as magnetite,
the eastern part of the basin, magnetic lineation is NNE- whereas other samples (TUGLU32, TUGLU37) do not
SSW–oriented, which is almost parallel to the trend of the saturate at 1 T, suggesting the coexistence of low coercitivity
thrusts in this area. Collectively, these data suggest that (magnetite) and a high coercivity ferromagnetic mineral
the magnetic fabric developed in a compressional tectonic such as hematite. These results are also confirmed by
setting and that magnetic lineations follow the geometry thermomagnetic analyses, which show a sharp decrease in
of the main thrust faults in the basin. magnetic susceptibility between 400 and 600 °C, indicative
4.2. Magnetic mineralogy and demagnetization of the of the presence of magnetite, and a small tail in magnetic
NMR susceptibility above this temperature indicating the
Representative examples of hysteresis loops are shown in presence of hematite (Figure 4f).
Figure 4. Results from these analyses indicate magnetic The intensities of the NRM vary by more than 3 orders
saturation (M) values from 0.001 to 0.1 Am2/kg. In some of magnitude. In some samples, NRM was found to be too
s
samples, a paramagnetic contribution due to the clay weak to measure accurately (NRM < 10–5 A/m) or unstable
matrix was observed (gray curves in Figures 4a, 4c, and after the first demagnetization steps. These samples were
4d). Figure 4a shows a hysteresis loop weakly developed, excluded from further paleomagnetic evaluation (Table
indicating the presence of low coercivity minerals, such as 2). Most of the samples are characterized by a single
magnetite. Figure 4b shows a typical wasp-waisted shape, component of magnetization with both normal (Figures
which suggests the occurrence of a mixture of 2 minerals 5a–5d) and reversed (Figures 5e–5h) polarity. The normal
with different coercitivity values. Loops in Figures 4c polarity ChRM has been isolated between 180 and 630–
and 4d are characterized by a well-developed hysteresis 670 °C (Figures 5a, 5b, and 5c) or between 10 and 100
and a more open shape, which suggest the presence of a mT (Figure 5d), suggesting the presence of both hematite
mineral with higher coercivity, probably hematite. IRM and magnetite. Reversed polarity samples are generally
curves (Figure 4e) confirm the presence of ferromagnetic characterized by a normal polarity viscous component,
minerals with different coercivity. Some samples (SULE18, which is completely removed at 180–230 °C (Figure 5f),
SULE31, SULE19, TUGLU10) reach 90% saturation values or at 10 mT (Figure 5g), and by ChRM, which has been
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LUCIFORA et al. / Turkish J Earth Sci
N N N
TU01 SU01 SU02
N = 8
N = 12
N = 24
a) b) c)
N N N
BO03 N = 13
BO01
N = 18
BO02
N = 64
d) e) f)
N N 0% N
0% 5%
2% 10%
4% 15%
6% 20%
8% 25%
BO04 N = 23 10% 30%
Kmax Kmin
N = 166 N = 166
g) h) i)
Figure 3. Mean magnetic susceptibility directions for samples analyzed in this study. (a)–(g) AMS plots with data plotted on
lower hemisphere, equal-area projections, in geographic coordinates. Squares and circles represent maximum and minimum axes,
respectively. Bedding planes (when detectable) are also represented. (h), (i) Contouring plots of K (pole to magnetic foliation)
min
and K (magnetic lineation), respectively.
max
isolated between 280 and 630–670 °C (Figures 5f and 5h) coordinates, all the sites have a mean direction distinct
or at 10–100 mT (Figure 5g). from the geocentric axial dipole (GAD) magnetic field
Site-mean paleomagnetic directions are illustrated in direction (D/I = 0/56.5° and D/I = 180/-56.5° for normal
Figures 6a–6g and listed in Table 2. All the sites have a and reversed directions, respectively), which suggests that
well-defined mean direction with α < 11.3°. Sites BO01, they have not undergone recent overprint. At site BO02,
95
BO02, BO03, and TU01 have normal polarity, whereas both normal and reversed polarities were observed. Data
sites SU01 and SU02 show reversed polarity. In geographic from this section do not pass the bootstrap reversal test
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LUCIFORA et al. / Turkish J Earth Sci
0.01
0.15 a) 0.008 b)
0.1 0.006
g) g) 0.004
k k
2m/ 0.05 2m/
A A 0.002
nt ( 0 nt ( 0
e e
m m
mo mo−0.002
c −0.05 c
eti eti−0.004
gn TUGLU10 gn
Ma −0.1 TUGLU10 Ma−0.006 TUGLU37
TUGLU10 cor TUGLU3cor
−0.008
−0.15
−0.01
−1 −05. 0 0.5 1 −1 −05. 0 0.5 1
Magnetic field (T) Magnetic field (T)

0.1 c) d)
0.1
g)0.05 g)
k k0.05
2m/ 2m/
A A
nt ( 0 nt ( 0
e e
m m
o o
m m
etic −0.05 etic −0.05
n n
ag ag SULE18
M SULE19 M SULE18
SULE19 −0.1 SULE18corr
−0.1 SULE19corr

−1 −05. 0 0.5 1 −1 −05. 0 0.5 1
Magnetic field (T) Magnetic field (T)
1 25
0.9 e) f)
0.8 20
0.7
M/M max00..56 eptibility15
c
0.4 SULE18 us10
SULE31 S
0.3 SULE19
TUGLU24
0.2 TUGLU32 5 TU02
TUGLU10
warming
0.1 TUGLU37
cooling
0 0
0 0.2 0.4 0.6 0.8 1 0 100 200 300 400 500 600 700
Magnetic field (T) Temperature (°C)
Figure 4. Magnetic mineralogy analysis of the analyzed sediments from the Çankırı Basin. (a)–(d) Hysteresis loops for representative
samples. Gray curves represent the hysteresis loops before paramagnetic correction. (e) IRM acquisition curves showing the presence
of both low-coercivity and high-coercitivity minerals in the analyzed samples. (f) Thermal susceptibility curve for TU02 specimens.
Solid (dashed) line corresponds to the measure on warming (cooling).
(Tauxe et al. 1991), indicating that normal and reverse be due to a viscous component acquired during a more
polarities are not antipodal (Table 2). We interpret this to recent period superimposed onto the normal polarity
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E, Up N, Up E, Up
a) b) c)
180°C
670°C 630°C
N S W E N S
180°C 630°C
BO0423 BO0410 BO0419
Unit = 1.04 e-03 A/m Unit = 8.78 e-04 A/m Unit = 1.12 e-03 A/m
Horizontal Horizontal Horizontal
180°C
W, Down S, Down W, Down
E, Up N N, Up
d) e) f)
10 mT 10 mT 230°C
100 mT
N 100 mT S W E W 670°C E
Up Down
BO0313B BO0217B SU0102
Unit = 1.05 e-02 A/m Unit = 7.11 e-05 A/m Unit = 6.07 e-04 A/m
Horizontal Horizontal Horizontal
W, Down S S, Down
N, Up E, Up
g) h)
10 mT
280° C
630° C
100 mT
W E N S
BO0255B SU0204
Unit = 1.23 e-04 A/m Unit = 1.86 e-04 A/m
Horizontal Horizontal
S, Down W, Down
Figure 5. Vector component diagrams (Zijderveld diagrams, in geographic coordinates) for the progressive thermal and AF
demagnetization of representative samples (demagnetization step values are in °C and mT, respectively). Empty and solid symbols
represent projection on the vertical and horizontal planes, respectively.
directions, which has not been possible to isolate. For this correction (Dec. = 3.4°, Inc. = 52.4°, k = 24.76, α =
95
reason, we do not include the normal polarity samples in 12.4°) than before bedding correction (Dec. = 6.3°,
the calculation of the mean direction for site BO02. When Inc. = 56.8°, k = 21.31, α = 13.4°) (Figure 6h). These
95
all sites are considered together, mean paleomagnetic results, together with the presence of both normal and
direction from the basin is better grouped after bedding reversed polarity sites, permit consideration of the ChRM
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N N N N
BO01 BO02
a) b)
BTC ATC BTC ATC
n = 7 n = 8
ATC
Dec. = 330.9° Dec. = 329.2° Mean rev. Mean rev.
Inc. = 49.7° Inc. = 39.8° Dec. = 182.5° Dec. = 152.9°
k = 50.4 k = 50.3 Inc. = -76.7° Inc. = -57.1°
α95 = 8.6° α95 = 8.6° k = 12.6 k = 25.1
α95 = 16.2° α95 = 11.3°
BO03 BO04
c) d)
BTC ATC
BBTTCC AATTCC n = 13 n = 20
Dec. = 10.8° Dec. = 19.9° Dec. = 6.9° Dec. = 6.9°
Inc. = 35.1° Inc. = 60.9° Inc. = 45.7° Inc. = 45.7°
k = 17.9 k = 17.9 k = 31.7 k = 31.7
α95 = 10.1° α95 = 10.1° α95 = 5.9° α95 = 5.9°
SU01 SU02
e) f)
Dec. = 205.3° Dec. = 201.7° n = 10 BTC ATC n = 9
Inc. = -53.9° Inc. = -48.6°
k = 110.4 k = 110.1
α95 = 4.6° α95 = 4.6°
Dec. = 196.9° Dec. = 191.2°
Inc. = –56.7° Inc. = –47.7°
k = 60.6 k = 60.5
α = 6.7° α = 6.7°
95 95
BTC ATC
ATC
TU01 TOTAL
g) h)
BTC ATC
BTC ATC
Dec. = 11.5° Dec. = 25.6° N = 7 N = 7
Inc. = 71.5° Inc. = 52.8° Dec. = 6.3° Dec. = 3.4°
k = 19.9 k = 19.8 Inc. = 56.8°
Inc. = 52.4°
α = 7° α = 7° k = 21.31
95 95 k = 24.76
n = 23 α95 = 13.4° α95 = 12.4°
Figure 6. (a)–(g) Equal-area projection of the site-mean directions (red circles) from the Çankırı Basin; (h) Çankırı Basin-mean
direction (violet circle). White and black symbols represent projection onto upper and lower hemisphere, respectively. Ellipses are
projections of the α cone about the mean directions. BTC and ATC indicate data before and after tectonic correction.
95
magnetic components isolated in the Çankırı Basin as a rotated during the last 10 Ma (Besse & Coutillot 2002). For
primary magnetization, and therefore suitable for tectonic this reason, as reference direction we adopt the GAD field
interpretation. Eurasia is not believed to have significantly direction (in both normal and reversed polarity states),
786
LUCIFORA et al. / Turkish J Earth Sci
33°30’ 34°00’ 34°30’
A F
N
0’
0
°
1
4
B’
B’
SU01 KAL
INC3
SU02 A’
Çankiri
ESK
KFZ
BO02 INC2 UR
30’ BO03
°
0
4
TU01
BO01
BO04
YES
A
HAM2
DAN
KUC Sungurlu E S F Z
00’ HAL1 B
°
0
4
HAM3
SUN
B
GUV
Miocene
Kaymakci et al. (2003) This study
Oligocene
10 km
Eocene
Kirikkale
Figure 7. Paleomagnetic declinations (and relative confidence limits) from this study and from Kaymakçı et al. (2003).
A-A’ and B-B’ (gray area) represent the 2 traces along which paleomagnetic rotation distribution was evaluated (see
Figure 8).
assuming a negligible difference between Tortonian and 5. Discussion
present times. The resulting paleomagnetic rotations are Analysis of AMS can be used to establish the sedimentary
reported in Figure 7 and Table 2, together with previous and tectonic history in weakly deformed sediments
results from Çankırı Basin published by Kaymakçı et al. (Tarling & Hrouda 1993). In the last 50 years, numerous
(2003), and will be discussed in the following section. studies have shown that AMS can be related to mineral and
787