GeolCarp_Vol62_No6_489

www.geologicacarpathica.sk

GEOLOGICA CARPATHICA

, DECEMBER 2011, 62, 6, 489—500 doi: 10.2478/v10096-011-0035-6

Introduction

Paleozoic-Early  Mesozoic  parts  of  the  Arabian  Platform  or
Southeast  Anatolian  Autochthon  (SEAA)  (Göncüog˘lu  et  al.
1997)  unit  crop  out  in  the  Amanos,  Diyarbakôr-Hazro  and
Hakkari-Çukurca  regions,  from  west  to  east  (Fig. 1).  The
Hazro area is one of the important potential petroleum basins
in Turkey, known as an anticline structure (Hazro anticline).
It  comprises  the  best  preserved  and  continuous  outcrops  of
Middle Paleozoic-Lower Mesozoic sequences. Many studies
focused on the general and petroleum geology were conducted
in  this  area  (e.g.  Tolun  1951;  Yah

man & Ergönül 1959;

Kellog 1960; Schmidt 1964; Ag˘ral

& Akyol 1967; Lebküch-

ner 1976; Güven et al. 1982; Bozdog˘an et al. 1987; Çubukçu
& Say

1990; Perinçek et al. 1991). In addition to these, a

detailed book related to the stratigraphic lexicon of SEAA
units was published by the geologists of the Turkish Petro-
leum Company (Y

lmaz & Duran 1997).

The determination of diagenetic – very low-grade metamor-

phic characteristics of the Paleozoic aged sedimentary rocks by
means of the textural and mineralogical (crystallinity, poly-
type, b cell dimension) properties could supply valuable data
related to tectonic setting of the sequence and paleogeographic
evolution of a region (e.g. Merriman & Frey 1999; Merriman

Clay mineralogy of the Paleozoic-Lower Mesozoic

sedimentary sequence from the northern part of the Arabian

Platform, Hazro (Diyarbak

r, Southeast Anatolia)

ÖMER BOZKAYA

, HÜSEYIN YALÇIN

and HÜSEYIN KOZLU

Cumhuriyet University, Department of Geological Engineering, TR-58140 Sivas, Turkey; *bozkaya@cumhuriyet.edu.tr

Nig˘de Caddesi, 18/1, Dikmen/Ankara, Turkey

(Manuscript received November 15, 2010; accepted in revised form June 9, 2011)

Abstract: The Paleozoic—Lower Mesozoic units in the Diyarbak

r-Hazro region consist of sandstone (subarkose, quartz

arenite), mudstone, shale, coal, marl, dolomitic marl, limestone (biomicrite, lithobiosparite, biosparite with lithoclast,
dololithobiosparite, dolomitic cherty sparite) and dolomite (dolosparite, dolosparite with lithoclast, biodolosparite with
glauconite). These units exhibit no slaty cleavage although they are oriented parallel to bedding planes. The sedimentary
rocks contain mainly calcite, dolomite, quartz, feldspar, goethite and phyllosilicates (kaolinite, illite—smectite (I—S), illite
and glauconite) associated with small amounts of gypsum, jarosite, hematite and gibbsite. The amounts of quartz and
feldspar in the Silurian-Devonian units and of dolomite in the Permian-Triassic units increase. Kaolinite is more com-
monly observed in the Silurian-Devonian and Permian units, whereas illite and I—S are found mostly in the Middle Devo-
nian and Triassic units. Vertical distributions of clay minerals depend on lithological differences rather than diagenetic/
metamorphic grade. Authigenetic kaolinites as pseudo-hexagonal bouquets and glauconite and I—S as fine-grained flakes
or filaments are more abundantly present in the levels of clastic and carbonate rocks. Illite quantities in R3 and R1 I—S vary
between 80 and 95 %. 2M

+1M

illites/I—S are characterized by moderate b cell values (9.005—9.040, mean 9.020

A),

whereas glauconites have higher values in the range of 9.054—9.072, mean 9.066

A. KI values of illites (0.72—1.56, mean

1.03 2 °) show no an important vertical difference. Inorganic (mineral assemblages, KI, polytype) and organic matura-
tion (vitrinite reflection) parameters in the Paleozoic-Triassic units agree with each others in majority that show high-
grade diagenesis and catagenesis (light petroleum-wet gas hydrocarbon zone), respectively. The Paleozoic-Triassic se-
quence in this region was deposited in the environment of a passive continental margin and entirely resembles the Eastern
Taurus Para-Autochthon Unit (Geyikdag˘

Unit) in respect of lithology and diagenetic grade.

Key words: geochemistry, mineralogy, diagenesis, phyllosilicate.

& Peacor 1999; Merriman 2005). These types of studies were
done during the past decade in Southern Turkey and provided
new scientific contributions to the interpretation of the evolu-
tion of the Taurus Belt (e.g. Bozkaya & Yalç

n 2000, 2004a,b,

2005, 2010; Bozkaya et al. 2002, 2006). The aim of this study
is to describe the diagenetic degree by means of clay mineral-
ogy of the Paleozoic-Lower Mesozoic sedimentary rocks of
SEAA units from the Arabian Platform, and to obtain some
additional data related to petroleum maturity zones.

Stratigraphy and lithology

Paleozoic-Early Mesozoic successions in the Hazro area

contain rock units called the Diyarbak

r, Tanin and Ç

g˘l

Groups which are divided into several formations and were
named in earlier studies (Schmidt 1964; Bozdog˘an et al.
1987; Perinçek et al. 1991; Y

lmaz & Duran 1997) (Fig. 2).

The Silurian—Early Triassic aged Diyarbak

r Group is made

up of Dada (Upper Silurian—Lower Devonian), Hazro
(Lower Devonian) and Kayayolu (Middle—Upper Devonian)
Formations. The Tanin and Ç

g˘l

Groups comprise Ka and

Gomaniibrik (Upper Permian) and Yoncal

, Uludere and

Uzungeçit (Lower Triassic) Formations, respectively.

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The Dada Formation, the lowermost unit in the area,

crops  out  in  the  rims  of  the  anticline,  is  an  approximately
80 m thick sedimentary sequence of Late Silurian—Early De-
vonian  age  (Bozdog˘an  et  al.  1987).  It  comprises  mainly  of
shale,  siltstone,  mudstone  and  sandstone  with  rarely  lime-
stone  intercalations.  The  organic  matter  types  and  contents
of this formation are evaluated as a potential source rock for
petroleum occurrence (Bozdog˘an et al. 1987).

The Early Devonian aged Hazro Formation which crops out

only  in  the  Hazro  area,  is  conformably  overlain  by  the  Dada
Formation, and involves different lithologies in the lower, mid-
dle and upper parts of the sequence. The lower and middle parts
of the formation are formed from dolomitic marls with dolomite
intercalations  and  mudstone,  sandstone  and  marls.  The  upper
parts  are  made  up  of  marls  intercalated  with  poorly  cemented
sandstones with petroleum and dolomite lithologies.

The Late Permian aged Ka Formation discordantly overlies

the Hazro Formation, and includes coal measures within the
quartz arenitic sandstones and coaly shales. High contents of
spores and pollen are characteristic for this formation (Ag˘ral

& Akyol 1967). Coaly levels are formed by four zones with
various thicknesses, namely 1.00, 0.15, 0.30 and 1.00 m.

The Late Permian aged Gomaniibrik Formation is passed to

the Ç

g˘l

Group with conformable boundary and divided into

three facies: A, B and C (Bozdog˘an et al. 1987). The A, and C
facies are composed of carbonate rocks, whereas B facies is
made up of siliciclastic rocks. Carbonate levels include fossil-
iferous limestone, dolomite, dolomitic marl and clayey dolo-
mites. Limestones are characterized by plentiful neritic fossils.
Petroleum leakages were first observed in the fissures of dolo-
mites during the field studies. Siliciclastic levels are represent-
ed by sandstone, mudstone and shale lithologies.

The Yoncalô, Uludere and Uzungeçit Formations of Ç

g˘lô

Group are of Early—Middle Triassic age (Köylüog˘lu 1986), and
include mainly shale, limestone, dolomite, dolomitic marl and
sandstone lithologies. Brownish-green shales with claret red
sandstone interlayers in the lower levels are characteristic of the
Triassic units, as stated by Aç

kba (1978) for the Hakkari-

Uludere area. Limestones with brachiopods, pinky dolomite,
and green glauconite patched sandy limestone, white-pink sand-
stone and dolomitic marls were observed in the middle levels of
the Ç

g˘l

Group, whereas dolomite, sandstone and dolomitic

shales were found in the upper levels of the Ç

g˘l

Group.

Materials and methods

A total of 90 samples was collected along the measured

stratigraphic sections, and analysed by optical (OM) and
scanning electron (SEM) microscopy, vitrinite reflection
(VR) and X-ray diffraction (XRD) methods.

VR measurements were fulfilled on the coal and organic mat-

ter-rich samples through polished blocks by Orthoplan micro-
scope (Leitz-Wetzlar MPV-II) in the Department of Geological
Engineering, Hacettepe University (Ankara, Turkey).

XRD analyses were done using a Rigaku DMAX IIIC dif-

fractometer  in  the  Department  of  Geological  Engineering,
Cumhuriyet  University  (Sivas,  Turkey).  The  diffractometer
conditions  were  arranged  as  CuK   (1.541871

A), Ni filter,

35 kV,  15 mA,  speed  of  goniometer  = 0.5°/min,  step  0.01°,
0.02°, 0.04°, time constant = 1 and 4 sec, slits = 1° 0.15 mm,
1° 0.30 mm, 2  interval = 2 = 2—30°, 5—35°, 59—63°, 5—65°,
16—32°.  The  semi-quantitative  mineral  amounts  in  the  bulk
and clay fraction ( < 2 µm) of sedimentary rocks were calcu-
lated by the external method of Brindley (1980a).

Clay separation was done by the sedimentation method after

chemical dissolution (removing carbonate minerals), defloccu-
lation and sedimentation during 3 hours 40 minutes for 200 ml
clay suspension. Clay mud was mounted on glass and subjected
to air-drying, glycolating (16 h under 60 °C) and heating (4 h
under 490 °C) procedures before the XRD studies.

Identification of clay minerals, ordering types (R0, R1,

R3) and illite contents of illite—smectite (I—S) were deter-
mined by the method of Moore & Reynolds (1997).

Illite “crystallinity” measurements were performed on the

first peaks of illites (10

A), as the width of half of the peak

height (Kübler index (KI) – Kübler 1968; Guggenheim et al.
2002). Standard samples of Warr & Rice (1994) were used for
calibration (e.g. Bozkaya et al. 2006). In this study, KI values
were obtained from decomposed illite peaks owing to co-ex-
isting illite and I—S peaks as broad and asymmetrical shapes.
Because of the asymmetrical nature of illite peaks in the pres-
ence of I—S, KI values were measured from the symmetrical
extension of illite peaks, as reflected from the right sides of the
peaks to their left sides. KI values were correlated to full width
half maximum (FWHM) results of decomposed peaks from
X-ray diffractograms in which illite peaks could be separated
from I—S peaks, and an equation (KI = 0.669 FWHM + 0.056,
r

= 0.82) was obtained for conversion of FWHM to KI values.

The 211 peak (2 = 59.97°, d = 1.541

A) of quartz was tak-

en as the reference for the measurement of the d

060

values of

illites. The regression equation of Hunziker et al. (1986) was
used for the octahedral Mg+Fe contents of illite/muscovites.
Polytype  examinations  were  investigated  for  illite  and  kao-
linite  through  representative  peaks  proposed  by  Bailey
(1988).  Illite  polytype  proportions  were  calculated  by  peak
area ratios of Grathoff & Moore (1996). Peak areas were in-
dividually  determined  on  the  fitted  peaks  by  the  WINFIT
program  (Krumm  1996).  Illite  percentages  in  I—S  were  cal-
culated  from  Moore  &  Reynolds  (1997).  2   or  d

001

values

were detected from the decomposed peaks by the WINFIT
program. The results were also correlated with the calculated
patterns of the NEWMOD program (Reynolds 1985).

Results

Optical microscopy

On the basis of representative samples from the Paleozoic-

Lower  Mesozoic  sequence,  the  shales  and  siltstones  in  the
Dada  Formation of Late Silurian—Early Devonian age contain
quartz, feldspar, sericite, muscovite and high amounts of organ-
ic matter in some samples. Shales have sericitized clay matrix
and  serve  micro-lamination  (0.3—1.0 mm)  and  micro-orienta-
tion (Fig. 3a). Limestones with sparitic orthochems include mi-
critic  intraclasts  and  fossil  shells.  In  addition  to  extraclasts  of
quartz, feldspar and mica, rare glauconite occurrences were also

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feldspar  grains.  Carbonate  rocks  with  sparitic  orthochems
(dolosparite,  dolomitic  cherty  lithosparite,  dololithobiomi-
crosparite)  display  coarse  subhedral-euhedral  dolomite,  chal-
cedonic quartz and glauconite minerals. Algae fragments were
marked in the cores of the euhedral dolomite crystals in some
samples (Fig. 3c).

In the Upper Permian Ka Formation, quartz arenites sig-

nify no orientation texture, and contain mainly quartz and
feldspar and accessory muscovite, tourmaline, zircon and ap-
atite. The groundmass material is formed by iron-oxide min-
erals (hematite) in some sandstones (Fig. 3d).

In the Upper Permian Gomaniibrik Formation, the limestones

have biomicritic characteristics. The dolomites have coarse-
grained sparitic and partly microsparitic dolomite crystals. The
medium sorted and poorly cemented sandstones have subangu-
lar-subrounded quartz grains without orientation.

In the Yoncal

, Uludere and Uzungeçit Formations of the

g˘l

Group of Early—Middle Triassic age, sandy limestones

(lithosparite,  glauconite-bearing  lithosparite  and  lithobio-
sparite)  cover  quartz,  feldspar,  accessory  muscovite,  apatite,
tourmaline,  zircon,  goethite  and  opaque  minerals  as  extra-

clasts.  Spherical-ellipsoidal  granular  glauconite  occurrences
within the pores of carbonate rocks are typical of the Triassic
units.  Limestones  (biosparite,  glauconite-bearing  biosparite)
and dolomites (dolosparite, glauconite-bearing biodolosparite,
and  lithoclast-bearing  biodolosparite)  contain  euhedral  and
zoned dolomite and glauconite (as pore filling and roundish-
ellipsoidal)  occurrences  in  addition  to  fossil  shells  (Fig. 3e).
Sandstones (subarkose, quartz arenite) with sparry calcite ce-
ment  have  mono-  and  poly-crystalline  quartz  and  feldspar
(zoned plagioclase) grains without any orientation (Fig. 3f).

Scanning electron microscopy

This investigation was performed on the six samples includ-

ing carbonate and clay minerals. Illites and illite-rich I—S miner-
als are observed as coarse flakes and ribbon-like filaments
(5—10 µm) (Fig. 4a), whereas illite-poor I—S are seen as relative-
ly fine curved flakes (Fig. 4b). Hexahedral shaped jarosites and
their traces are also noticed together with illite-poor I—S in the
coaly shale samples. Kaolinites show the classic platy, pseudo-
hexagonal accordion- or book-like forms indicating typical au-

Fig. 4. SEM photomicrographs of the samples: a – Illite and illite-rich I—S aspects as long filaments and coarse flakes, respectively, in
shales (DBH-81, Dada  Formation, Silurian—Devonian); b – Illite-poor I—S as fine curved flakes associated with hexahedral jarosites in
the coaly shales (DBH-35, Ka  Formation, Upper Permian); c – Euhedral pseudo-hexagonal shaped kaolinite crystals with tightly pack-
aged book-like form and I—S as coarse flakes in sandstones (DBH-76, Dada  Formation, Silurian—Devonian); d – Rhombohedral dolomite
crystals and glauconites as fine-grained thin flakes on the dolomites (DBH-12, Yoncalô Formation, Triassic).

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GEOLOGICA CARPATHICA, 2011, 62, 6, 489—500

thigenetic occurrences (Fig. 4c). The tight package of kaolinite
booklets reflects a high grade of diagenesis. Euhedral dolomites
show typical rhombohedral morphologies in carbonate rocks
(Fig. 4d). Clay occurrences as thin flakes were shown on the do-
lomite crystals. Illite was found not only as fine-grained flakes,
but also as ribbon-like filaments.

Organic petrography

According to organic petrographic investigations on a

shale  sample  of  the  Silurian  Dada   Formation  in  the  Derik
area  and  a  coal  sample  of  the  Ka   Formation  in  the  Hazro
area; the main components (macerals) are represented by vit-
rinite,  tellinite  and  inertinite.  Vitrinites  are  shown  as  thick
and  thin  bands  without  any  inner  texture,  whereas  tellinites
have  a  plant  texture.  Inertinites  are  characterized  by  light
grey colours in addition to plant texture as sieve (Fig. 5).

VR values in the samples of the Dada and Ka Forma-

tions, collected from the Derik and Hazro regions, respec-
tively, are measured as 1.32—2.29 Rm

oil

% (mean 1.75) and

0.49—0.66 Rm

oil

% (mean 0.55) for Dada and Ka Forma-

tions (Fig. 6). These values correspond to low volatile bitumi-
nous and sub-bituminous coal ranks of USA classification
(Teichmüller 1987), and their coalification ranks are consis-
tent with the catagenesis or high diagenetic grades (Merriman
& Frey 1999).

X-ray mineralogy

Bulk and clay mineralogy

The Silurian-Triassic sedimentary units in the study area are

formed of quartz, feldspar, calcite, dolomite, goethite, hematite,
jarosite, gypsum, gibbsite and clay (illite, kaolinite, I—S) miner-
als. The most common clay mineral associations are illite + I—S
and kaolinite + illite + I—S (Fig. 7). Illite and I—S with different
ordering types show the composed peaks with broad and asym-
metrical shapes. Individual peaks were decomposed by the
WINFIT program, and correlated and/or confirmed by calcu-
lated patterns created by the NEWMOD program (Fig. 8).

Fig. 5. Microscopic appearances of main maseral types: a – Coal sample of the Ka Formation (DBH-42, Hazro area); b – Shale sample
of the Dada Formation (MDK-89, Derik area).

Fig. 6. The frequency distribution
of VR values measured in the
samples of coal (DBH-42) and
shale (MDK-89).

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Fig. 7. XRD patterns of the typical clay mineral assemblages in the Hazro area: a – Illite + I—S; b – Kaolinite + illite + I—S.

According to decomposed peaks and their correlations with cal-
culated  patterns,  I—S  minerals  with  both  R1  and  R3  ordering
type accompany the illite. The illite contents of R1 and R3 I—S
are  70—85 %  and  90—95 %,  respectively.  R0  I—S  is  rare  and
found  only  in  two  calcareous  rocks  of  Triassic  units.  Glauco-
nite-bearing  samples  have  R3  type  glauconite—smectite  (G—S)
ordering in addition to glauconite. The smectite contents of G—S
from  pore-filling  authigenic  and  round-shaped  granular  types
are measured as 13 % and 10 %, respectively.

Crystal-chemical characteristics of clay minerals

The KI values, both measured directly on illite 10

A peaks

and converted from the FWHM values of decomposed illite
10

A peaks (Fig. 9), vary between 0.77—1.56 ( 2 °) for

Silurian-Triassic samples from the Hazro area (Table 1), and
reflect low and high diagenetic conditions. However, KI val-
ues for Silurian samples in the Mardin area range from 0.50
to 0.62 ( 2 °), and indicate completely high diagenetic con-

Table 1: Mineralogical properties of illite/I—S and glauconites (Italic values represent glauconite samples).

Unit Age KI ( 2 )

(mean)

060

(Å)

(mean)

/ (2M

+1M

) R0

N (nm)

(mean)

Yoncal

Triassic

0.81–1.14

(1.00)

0.81–0.90

(0.86)

1.5033–1.5053

(1.5041)

1.509–1.512

(1.511)

–

75–80

–

87–90

7–10

(9)

7–8

(8)

Kaş Permian –

–

– –

90 –

Gomaniibrik Permian

0.81–1.40

(1.03)

1.5008–1.5043

(1.5028)

35 –

70–80

6–11

(9)

Hazro Devonian

0.72–1.28

(0.93)

1.5013–1.5067

(1.5046)

40 –

75–85

7–13

(10)

Silurian–
Devonian

0.77–1.56

(1.16)

1.5028–1.5053

(1.5041)

40 –

75–85

90–95

7–11

(8)

Dadaş

Silurian 0.50–0.62

(0.56)

1.5003–1.5013

(1.5008)

45 –

12–14

(13)

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Fig. 8. Decomposition of compound peaks of illite and I—S by means of a – WINFIT and b – NEWMOD

programs.

ditions. The KI values of pore-filling authigenic and round-
shaped granular glauconites are determined as 0.81 and 0.90
( 2 °), respectively.

In addition to illites, the FWHM ( 2 °) values of decom-

posed peaks of R1 and R3 I—S are also measured together
with their d

001

(

A) values (Fig. 10). In general, decreasing

FWHM values accompany decreasing d

001

(

A) values, as a

result of regular transformation from smectite-rich I—S to il-
lite. Although the KI values show no remarkable differences

Fig. 9. Decomposition of illite + R1 and R3 I—S peaks and FWHM and KI values of illites obtained from resolved and unresolved 10

peak by assuming symmetrical reflection of the right-side of the peak: a – Dolomitic shale of Yoncalô Formation (Triassic); b – Dolomitic
marl of Gomaniibrik Formation (Permian).

between the formations, some were due to lithological vari-
eties (Fig. 11). Illites from clay-rich lithologies have gener-
ally  higher  KI  values  than  those  of  carbonate-rich
lithologies. Crystallite size (N) values, calculated from XRD
peaks  using  the  WINFIT  program,  vary  between  6  and
14 nm (Table 1), and indicate low- to high-grade diagenesis.
Silurian  samples  from  the  Mardin  area  indicate  the  highest
crystallite size values, reflecting relatively higher diagenetic
grades, similar to the KI values.

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Fig. 10. Variations of width and positions of decomposed peaks in illite and I—S (arrow
shows a direction of progressive transformations from R1 I- to illite).

In the Hazro area, the d

(060)

values of il-

lite and I—S minerals vary in a broad
interval of 1.5008—1.5053

A, which

correspond to octahedral Fe+Mg contents
of 0.35—0.58, indicating the composition
of  phengite-rich  white  K-mica.  Silurian
samples from the Dada  Formation in the
Mardin  area  have  relatively  lower  d

(060)

values (Table 1), and point to muscovite-
rich composition (Fe + Mg content is
0.35). The d

(060)

values of granular and

pore-filling glauconites are determined
as 1.5092 and 1.5115

A, respectively,

which are close to those of the ideal glau-
conite (1.512—1.517

A; Brindley 1980b).

Illite/I—S shows 2M

(35—45 %) and

(55—65 %) polytypes for Permian

and older units, and 2M

(55 %) and

Fig. 11. Vertical distributions of bulk and clay mineral distributions with some mineralogical parameters in the Hazro area.

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(45 %) for Triassic units. Glauconite and kaolinite have

completely 1M, and 1T kaolinite polytype with respect to the
representative peaks.

Discussion

Vertical distributions of clay minerals

Bulk and clay minerals show relatively different abun-

dances  and  assemblages  in  respect  to  the  vertical  distribu-
tions  (Fig. 11).  Quartz  and  feldspar  are  found  in  higher
amounts in the Silurian—Lower Devonian units, whereas the
dolomite content is high in Middle Devonian—Triassic units.
Goethite in Upper Permian—Triassic, hematite and gibbsite in
Devonian,  jarosite  in  Devonian—Upper  Permian  and  gypsum
in Triassic units are detected. Kaolinite is decisive in the Sil-
urian—Devonian  and  Upper  Permian,  whereas  I—S  is  domi-
nant in the Lower Devonian and Triassic in higher amounts.
Glauconite is encountered only in Triassic units. The miner-
alogical distributions in the studied units are related to litho-
logical  differences  rather  than  to  age  and  maturation,  thus
kaolinite is found in higher amounts in the clastic-rich lithol-
ogies, but I—S is rich in carbonate-rich lithologies.

Origin and occurrences

Although the abundances of illite and kaolinite depend

upon the lithological variations, as kaolinite and illite are re-
spectively dominant in clastic- and carbonate-rich lithologies,
they have diagenetic (authigenic) rather than of detrital origin.
Their diagenetic origin was confirmed by the presence of
glauconite, dominance of sericitized groundmass, the absence
or negligible amounts of detrital micas and clay shapes (flake,
filament and euhedral pseudo-hexagonal booklets).

In addition to the fabric properties of the studied rock sam-

ples, the crystal-chemical characteristics of illite and I—S
(KI, dominance of 1M

polytype), illite contents of I—S,

firmly packaged kaolinite booklets and vitrinite reflectance
data indicate their occurrence under high-grade diagenetic
conditions. The peak position (

A) and FWHM ( 2 °) values

of illite and I—S (R1 and R3) show a regular distribution from
R1 I—S to illite; this indicates a progressive transformation of
smectite to illite. Thus, the association of illite, R1 and R3 I—S
indicates that illites have a diagenetic origin rather than be-
ing inherited from fine-grained detrital micas. This approach
was also confirmed by the presence of I—S in quite low
amounts in the clastic-rich lithologies.

Glauconite firstly detected in Triassic rocks during this

study  is  an  indicator  for  marine  environments  (e.g.  Tucker
2001;  Flügel  2004),  and  indicates  a  relatively  shallow  envi-
ronment  (shelf)  with  a  low-rate  of  sedimentation  (Amorosi
1995; Chafetz & Reid 2000; El Albani et al. 2005). It is ob-
served within the pores in the carbonate-rocks and roundish or
ellipse-shaped  intra-clastic  particles  in  the  extraclast-bearing
carbonate rocks. These textural relationships indicate the glau-
conites  were  developed  in-situ  (authigenic)  and  transported
within the same basin (e.g. Amorosi 1993). According to min-
eralogical  variations  of  the  different  types  of  glauconites

(Fig. 3e), they have a relatively regular ordering compared to
transported glauconites because of the defecting crystal-chem-
ical structures during transportation. Additionally, the current
and ancient glauconite-bearing carbonate rocks have signifi-
cant differences that limit a decisive use of the medium shelf-
deep water or low-sedimentation-rate environments (e.g.
Chafetz & Reid 2000; El Albani et al. 2005).

Paleogeographic and tectonic settings

The studied series reflect almost homogeneous deposition

and  lithification  under  low-  to  high-grade  diagenetic  condi-
tions. In these types of sequences, which had not suffered in-
tense  diagenesis/metamorphism,  the  vertical  and  lateral
distributions  of  clay  minerals  can  be  used  to  describe  the
depositional history of the sedimentary rocks (e.g. Chamley
1989;  Ingl

s & Anadon 1991; Ingl

s & Ramos-Guerrero

1995).  In  general,  clay  mineral  assemblages  in  ancient  se-
quences  are  controlled  by  lithology,  depositional  environ-
ments,  paleoclimate  and  topography,  etc.  Clay  mineral
associations (kaolinite, illite/I—S, glauconite) in the Paleozoic—
Lower  Mesozoic  sequence  in  the  Hazro  area  mainly  exhibit
post-burial  (diagenetic)  conditions  rather  than  detrital  input.
According to optical- and electron-microscopic observations,
both  kaolinite  and  I—S  are  completely  of  authigenetic  origin,
and were precipitated within the pores during diagenesis. The
dominance  of  kaolinite  seems  to  be  related  to  a  depositional
environment close to low latitudes under tropical climate con-
ditions (e.g. Biscaye 1965; Griffin et al. 1968).

Stratigraphic-lithological, textural and mineralogical data

from  the  Paleozoic—Lower  Mesozoic  sedimentary  units  in
the Hazro area introduce the sediment accumulation and dia-
genesis in a shallow marine environment without major vol-
canic  and  tectonic  activities.  Inorganic  and  organic
maturation  remains  at  the  diagenetic  level,  which  indicates
the typical passive margin conditions (e.g. Robinson 1987).
In addition to these, iron-(hydr)oxide minerals, phengitic il-
lite  and  glauconite  occurrences  represent  iron-rich  neo-
formed clays, which are also characteristic for shallow shelf
environments within the passive continental marginal basins
(Merriman 2005). Both stratigraphic-lithological and miner-
alogical characteristics of the sequence offer significant sim-
ilarities  to  the  Paleozoic-Mesozoic  sequence  of  the  Eastern
Tauride  Belt  (Bozkaya  et  al.  2002;  Bozkaya  &  Yalçôn
2004b), that represents a typical passive continental margin.

Conclusions

The Silurian-Triassic sequence from the Hazro region in-

cludes carbonate and clastic rocks with roughly fabric orien-
tation  parallel  to  bedding  without  cleavage,  which  shows
textural maturation of diagenetic grade. According to miner-
alogical data, the carbonate and clastic rocks mainly contain
calcite,  dolomite,  feldspar,  goethite  and  phyllosilicate  (ka-
olinite,  illite,  I—S,  glauconite),  and  rarely  gypsum,  jarosite,
hematite and gibbsite. The vertical distributions of minerals
are seen to be related to lithology rather than diagenetic mat-
uration. The presence of hematite-jarosite in the Silurian-De-

499

CLAY MINERALOGY OF THE PALEOZOIC—LOWER MESOZOIC SEDIMENTARY SEQUENCE (ANATOLIA)

GEOLOGICA CARPATHICA

GEOLOGICA CARPATHICA, 2011, 62, 6, 489—500

vonian and goethite and gypsum in the Permian—Triassic
units indicate that oxidation or shallow environmental condi-
tions are dominant for the younger units.

Regarding the clay mineralogical distribution, clastic-rich

lithologies (sandstone, siltstone) contain high amounts of au-
thigenetic euhedral kaolinite crystals as cement and pore fill-
ing  that  indicate  a  period  of  erosion  under  high  energy
conditions with high detrital input and indirectly the relative-
ly  low  pH  conditions.  However,  carbonate-rich  lithologies
(dolomite,  limestone,  marl)  represent  relatively  low-energy
conditions  with  sporadic  detrital  input  under  the  high  pH
condition,  so  they  contain  high  amounts  of  I—S.  In  other
words,  the  organic  data  and  crystal-chemical  characteristics
of phyllosilicate minerals indicate high diagenetic conditions
and show no remarkable differences through the sequence.

Consequently, mineralogical distributions in the sequence

are related to variations of lithological and/or micro-environ-
mental conditions, and the units were deposited and petrified
on a passive margin setting under tropical climate condi-
tions, so that they resemble the Eastern Taurus Autochthon
(Geyikdag˘

Unit, Özgül 1976) from southern Turkey.

Acknowledgments: This study is supported by the Scientific
Research Found of Cumhuriyet University under the project
number M-235. The authors thank Fatma Yalç

n (Cumhuriyet

University) for laboratory studies, Dr. A. I

hsan Karayig˘it

(Hacettepe  University)  for  measurements  of  organic-matter
reflectance,  Tug˘rul  Tüzüner  (Turkish  Petroleum  Corpora-
tion) and other technical staff for electron microscope inves-
tigations.  We  are  grateful  to  two  anonymous  referees  for
reviews and suggesting valuable comments.

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