Abstract and Figures

The Zagros fold and thrust belt represents a tectonically significant area, and one of the richest areas in oil and gas reservoirs in the world. The Zagros fold and thrust belt is the deformational product of the Cretaceous-present day convergence of the Arabian and Iranian (Eurasian) plates (subduction and collision). The belt extends more than 2000 km from southern Turkey through the north and northeastern Iraq to the Strait of Hormuz in southwestern Iran. The Zagros fold and thrust belt is divided into two parts which are; Western part within Iraqi region and Eastern part within Iranian region. The western part of the Zagros fold and thrust belt has been traditionally subdivided into several structural zones that are generally striking parallel to the plate boundary. This is characterized by exposure of Late Ordovician to Pliocene-Pliestocene formations with different types of Quaternary Sediments. This research will concentrate on Western part of Zagros fold and thrust belt and the styles of structural classifications, which will aid to clarify and better understand the tectonic and structural history and evolution of the region. We have considered the last version of structural classification as the most relevant one to the reality, especially within outer platform (Unstable shelf). Where it divides the region into four structural zones, which are: Low Folded zone, High Folded Zone, Imbricate Zone, and Zagros Suture Zone and these zones were further divided to several subzones. This classification is based on the structural style and intensity of deformation, stratigraphy, mechanicalstratigraphy and tectono-stratigraphy of the deformed sequences, Age of deformation, surface physiography and morphology. The data used in the classification is more reliable, up to date and relevant.
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Journal of Earth Sciences and Geotechnical Engineering, vol.7, no. 2, 2017, 71-89
ISSN: 1792-9040 (print version), 1792-9660 (online)
Scienpress Ltd, 2017
The Tectonic and Structural Classifications of the
Western Part of the Zagros Fold and Thrust Belt,
North Iraq, Review and Discussion
Maher T. Zainy
1
, Nadhir Al-Ansari1, Tobias E. Bauer1 and Maria Ask1
Abstract
The Zagros fold and thrust belt represents a tectonically significant area, and one
of the richest areas in oil and gas reservoirs in the world. The Zagros fold and
thrust belt is the deformational product of the Cretaceous-present day convergence
of the Arabian and Iranian (Eurasian) plates (subduction and collision). The belt
extends more than 2000 km from southern Turkey through the north and
northeastern Iraq to the Strait of Hormuz in southwestern Iran. The Zagros fold
and thrust belt is divided into two parts which are; Western part within Iraqi
region and Eastern part within Iranian region. The western part of the Zagros fold
and thrust belt has been traditionally subdivided into several structural zones that
are generally striking parallel to the plate boundary. This is characterized by
exposure of Late Ordovician to Pliocene - Pliestocene formations with different
types of Quaternary Sediments. This research will concentrate on Western part of
Zagros fold and thrust belt and the styles of structural classifications, which will
aid to clarify and better understand the tectonic and structural history and
evolution of the region. We have considered the last version of structural
classification as the most relevant one to the reality, especially within outer
platform (Unstable shelf). Where it divides the region into four structural zones,
which are: Low Folded zone, High Folded Zone, Imbricate Zone, and Zagros
Suture Zone and these zones were further divided to several subzones. This
classification is based on the structural style and intensity of deformation,
stratigraphy, mechanicalstratigraphy and tectono-stratigraphy of the deformed
sequences, Age of deformation, surface physiography and morphology. The data
used in the classification is more reliable, up to date and relevant.
Keywords: Tectonic, Classification, Western Zagros Belt, North Iraq
1
Luleå University of Technology, Lulea, Sweden
72 Maher T. Zainy et al.
1 Introduction
During the end of the Proterozoic and beginning of the Phanerozoic (early
Paleozoic), the Arabian and several other continental micro plates including
Turkey, central Iran, Afghanistan, India and other smaller fragments collectively
formed part of the Paleozoic northern margin of the Gondwana supercontinent
which bordered the southern shore of the Paleo-Tethys Ocean[1] (Fig.1).
[2, 3 and 4] considered the end of the Paleozoic (Late Permian) and the beginning
of the Mesozoic (Early Triassic) to be dominated by rifting (sea - floor spreading)
of the northern margin of Gondwana. The microcontinents started to separate from
Gondwana drifting northeastwards and forming the Neo-Tethys Ocean, where the
Neo-Tethys continued to expand on the expense of the Paleo-Tethys shrinking,
and the final closure happened in Jurassic, when central Iran collided with Eurasia.
[5] considered the Mesozoic had witnessed the birth and the development of the
Arabian plate which borders the western shore of the Neo-Tethys Ocean [ 5 Fig.3-
14].
Figure 1: Supercontinent GONDWANA, early Paleozoic
(http://kingofwallpapers.com/gondwana.html).
The Arabian Plate is surrounded by several types of plate boundaries (Fig. 2).
These are: The western and southern boundaries of the plate represent passive
margins located at the rifting spreading ridges of the Red Sea and the Gulf of
Aden. The northwestern margin is located along the Levant transform fault along
the Dead Sea, and the Owen fractures at the southern margin of the Arabian Plate.
The south - eastern boundary of the Arabian Plate is represented by Makran
subduction zone, whereas the north and northeastern margin of the Arabian Plate
The Tectonic and Structural Classification of the Western Part of Zagros
73
is represented by the collision - subduction zones with Turkish and Iranian plates
[5, 6 and 7]. The resulting late Cretaceous basin is known as the Zagros foreland
basin [8, 9, 10 and 11].
[7] considered the Arabian plate is generally sub-divided into the Arabian shield,
Arabian shelf and the Zagros fold and thrust belt.
Figure 2: Main Tectonic sub-division of the Arabian plate and Location of Iraq
(http://africa-arabia-plate.weebly.com/arabian-plate.html).
Zagros fold and thrust belt locate to the north and northeast of the Arabian Plate
and is part of the Alpine- Himalayan belt. Zagros fold and thrust belt extends more
than 2000 km from southern Turkey through northern and northeastern Iraq to the
Strait of Hormuz in southwestern Iran. [9] considered this belt, as a result of
structural complexity of the belt, characterizes a 200 to 300 km-wide zone. It
includes a sequence of heterogeneous sedimentary cover strata, 7 to 12 km thick
and composed of alternating incompetent and competent layers, overlying
Precambrian crystalline basement with a complex pre-Zagros structural fabric
[9].It is the deformational product of the Cretaceous to present day convergence of
the Arabian and Iranian (Eurasian) plates [3, 5 and12]. [5 and 13] refers to the
present morphology of the Zagros fold and thrust belt as the result of its structural
evolution and depositional history. It is mountainous area, with very rugged
topography due to the presence of complicated structures and main thrust sheets.
The elevation ranges within study area from ( 500 - > 3500) m (a.s.l.), with very
complicated terrain.
This study deals with the western part of the Zagros fold and thrust belt, which
located within Iraqi region, along the Iraqi- Iranian and Turkish borders (Fig. 3),
the study area covers approximately 82000km2.
The main aim of the present study is to introduce all structural classifications of
the western part of the Zagros Fold and Thrust Belt and to shed light on the
74 Maher T. Zainy et al.
differences and similarities of aspects between them, and to delineate the most
relevant and scientifically accepted one from the author’s opinion; based on the
presented structural elements.
Figure 3: Location of the study area in Iraq.
2 Stratigraphic setting
The study area is characterized by various formations ranging from late
Ordovician to Pliocene - Pliestocene in age and overlain by different types of
Quaternary sediments [14]. [5] estimated the average depth of the basement to
approximately (8- 14) km indicating, the basement is deeper in the study area as
relative to other parts of Iraq territory.
The stratigraphic sequences are dominated by carbonates and clastics. The oldest
exposed rocks are represented by the late Ordovician (460-445 m.y.) Al khabour
formation mainly consists of sandstone, siltstone and shale. It is exposed in the
north part of Iraq, near Iraqi-Turkish [5].The youngest rocks in the study area are
represented by Pliocene - Pliestocene (3.0 m.y-10 th.y.) Bai Hassan formation
mainly consists of sandy conglomerates and sandstone [5 and 14]. The Paleozoic,
Mesozoic, and Cenozoic rocks comprise mainly marine carbonates with some
clastic materials.
The Tectonic and Structural Classification of the Western Part of Zagros
75
3 Structural classifications of the Zagros Fold and Thrust belt
Many researchers classified Zagros belt structurally into several zones. [13 and
15] was the first who introduce a regional structural classification of the Zagros
fold and thrust belt. He divided it into three parallel NW-SE trending structural
belts. The belts from NE to SW are; the thrust belt, Imbricated belt and the simply
folded belt. Later many other structural classifications were introduced,
representing modifications of the original concept of [13 and 15], we will
introduce some classifications hereinafter...
[16] considered the Zagros fold and thrust belt is bounded by two stable platforms
(Fig. 4). On the southwest is the Arabian platform and on the northeast is the
Precambrian metamorphic basement of central Iran. Moreover, he divided
stratigraphic Zagros column from bottom to top into five structural divisions:
1.Basement Group 2.Lower Mobile Group 3.Competent Group 4.Upper Mobile
Group 5. Incompetent Group.
[12] considered The Zagros orogenic belt of Iran is the result of the opening and
closure of the Neo-Tethys oceanic, and He divided it, from northeast to southwest,
of three parallel tectonic subdivisions: 1. The Urumieh-Dokhtar Magmatic
Assemblage; 2. The Sanandaj-Sirjan Zone; and 3. The Zagros Simply Folded Belt.
[3] divided the Zagros belt into five morphotectonic units based on the
topography, seismicity and exposed stratigraphy (including erosion and
sedimentation), each with their own characteristics and deformation style. These
five units are:1) the high Zagros thrust Belt, 2) the simple folded belt, 3) the
Zagros foredeep, 4) the Zagros coastal plain and 5) the Persian Gulf-
Mesopotamian lowland (Fig.5).
Figure 4: Tectonic settings of the Zagros fold and thrust belt showing the major tectonic
belts [modified after 16]
76 Maher T. Zainy et al.
Figure 5: Simplified transverse cross section of the Zagros active fold-thrust mountain
belt [modified after 3]
[17 and 18] divided the Zagros fold and thrust belt laterally into four main
longitudinal segments of changing width and morphology, from SE to NW there
are: Fars arc, the Dezful embayment and the Lurestan arc in Iran and the Kirkuk
Embayment in Iraq (Fig.6).
Figure 6: Tectonic Map of Zagros belt, shows the lateral divided laterally zones
Into four longitudinal segments
(https://en.wikipedia.org/wiki/Zagros_fold_and_thrust_belt)
[19] divided Zagros belt into NWSE trending structural zones (imbricated and
simply folded Belt) parallel to the plate margin separated by major fault zones
such as the High Zagros and Mountain Front Faults (Fig. 7). The Imbricated Belt
situated between the High Zagros and Zagros Main Reverse Faults and Simply
The Tectonic and Structural Classification of the Western Part of Zagros
77
Folded Belt lies to the southwest of the High Zagros Fault.
Figure 7: Structural setting of the Zagros fold-thrust belt showing the major fault zone
[from 19]
4 Structural classifications of the western part of the Zagros Fold
and Thrust belt
[20] divided the Zagros fold and thrust belt into a western part within the Iraqi
territory and an eastern part within the Iranian territory. It is important to mention,
that almost all of the classifications have focused on the Iranian part of the Zagros,
whereas the Iraqi part received only a very limited attention.
The western part of the Zagros fold and thrust belt has been traditionally
subdivided into several of structural zones and subzones that are generally striking
parallel to the plate boundary. Early divisions were linked more or less to oil
exploration activities [21, 22, 23and 24]. More detailed classifications were
introduced later by some researchers; we will introduce the structural
classifications hereinafter...
[25] divided Iraq based on (the outdated geosynclines theory and terminology)
into three tectonic units, whereas each of units was subdivided into tectonic
subzones which are:
a- Stable platform subdivided into Rutbah-Jezirah zone and Salman zone.
b- Unstable Platform subdivided into Mesopotamian zone, Foothill folded zone
and High folded zone.
c- Geosynclinal Area subdivided into external zone (Balambo-Tanjero and
northern thrust zone), central zone (Qulqula-Khwakurk and Penjwin-Walash
zones) and internal zone (Shalair zone) (Fig. 8). The western part of the Zagros
belt is including (b-c).
[26] divided the Iraqi territory into three main zones, which are 1- the Stable Shelf
2- the Unstable Shelf 3- the Geosyncline, then subdivided it into zones and
subzones (Fig. 9). This classification depends on (Geophysical data,
78 Maher T. Zainy et al.
Morphological style, and the sedimentary cover).
[5] divided the Iraqi territory into a Stable Shelf, an Unstable Shelf and the Zagros
suture zone (WZFTB including unstable shelf and Zagros suture zone) (Fig. 10),
they furthermore subdivided the unstable shelf from SW-NE into the foothill zone,
the high folded zone, and the imbricate zones. Additionally, they subdivided the
Zagros suture zone from SW-NE into three parts, which are the Qulqula-
Khwarkurk zone, Penjwin-Walash zone and Shlair zone. These classifications
depend on (the rocks type, ages of rocks, thickness of the individual zones and
their structural evolution).
[7] divided the Arabian plate into: a)-Arabian shield and b)-Arabian shelf. They
furthermore divided the Arabian shelf into two parts. (an unfolded zone and a
folded zone). Additionally, they divided the Iraqi territory from NE to SW into
five parts: 1- thrust zone, 2-folded zone (high folded zone and low folded zone), 3-
Mesopotamian zone (Mesopotamian Basin, Mesopotamian Basin with strike-slip
faulting and Mesopotamian Basin with salt), 4- Salman zone (Salman zone and
Salman zone in east of Khleisia, 5- Rutba-Jezira zone (Rutbah subzone and Jezira
subzone) (Fig. 11). They furthermore considered thrust zone and folded zone
within western part of Zagros belt. The western part of the Zagros fold and thrust
belt including zones (1, 2 and 3).
Figure 8: Tectonic Map of Iraq [modified after 25]
The Tectonic and Structural Classification of the Western Part of Zagros
79
Figure 9: Tectonic Map of north part of Iraq [modified after 26]
Figure 10: Tectonic Map of Iraq [modified after 5]
80 Maher T. Zainy et al.
Figure 11: Structural elements map of the Iraq [modified after 7]
[27] divided the Iraqi territory into two main tectonic segments (Figs. 12 and 13).
These are: 1) Arabian platform part (within WZFTB), 2) the Shalair terrane of the
Sanandaj Serjan Zone of the Eurasian plate (within the EZFTB). The former
lacks any kind of metamorphism and volcanism, except within the Zagros Suture
Zone. Moreover, he divided the Arabian plate form part into two main tectonic
divisions, which are 1) Inner Platform (Stable Shelf) to the southwest, which is
less affected by Alpine deformation and remained relatively stable, 2) Outer
Platform (Unstable Shelf) to the northeast, which is involved by the deformation.
Later on he divided the Outer Platform into two tectonic units, which are 1)
Mesopotamia Foredeep, 2) Western Zagros Fold-Thrust Belt. Farther on then he
divided WZFTB according to the modern tectonic concepts into four tectonic
zones (Fig.14), which are from SW to NE 1) Low Folded Zone ; consists of series
of gentle to open folds of Pliocene-Pleistocene age, 2) High Folded Zone; consists
of large number of tight and overturned folds mainly with southwest vergence, 3)
Imbricate Zone; consists of autochthonous Paleozoic to Mesozoic platformal and
marginal sedimentary units that have been deformed more intensely with the
development of series of imbricate fans and, 4) Zagros Suture Zone; consists of
allochthonous Cretaceous- Eocene nappes of ophiolite, radiolarites and volcano-
sedimentary rock that have been thrusted over the platformal and marginal
sediments of the Arabian plate [20], and then he divided some of the zones into
subzones.
The Tectonic and Structural Classification of the Western Part of Zagros
81
This tectonic classification is based on the structural style and intensity of
deformation, age of deformation, stratigraphy, mechanical-stratigraphy and
tectono-stratigraphy of the deformed sequences.
Figure 12: The Tectonic Divisions of Iraq [from 27]
Figure 13: Tectonic classification of Iraq [modified after 28]
82 Maher T. Zainy et al.
Figure 14: The tectonic subdivisions of the western Zagros fold and thrust belt
[from 4]
5 Tectonic Units
The Outer shelf (unstable shelf) has been subsiding since the opening of Neo-
Tethys in the Early Cretaceous and [5] considered the maximum subsidence
occurred during the late Cretaceous. [29] reported that the deformation within the
Zagros fold and thrust belt includes both accumulated cover and basement rocks.
The western Zagros fold and thrust belt is composed of a (7 to 12) km thick
Neoproterozoic and Phanerozoic sedimentary sequences [13].
The western Zagros fold and thrust belt was divided by [20] to several sub tectonic
units, they are, from SW to NE:-
5.1. The Low Folded Zone
The Low Folded Zone of the Western part of Zagros belt is the largest zone. It is
about 700 Km long and 100 Km wide. Its coverage area is about 56930 Km².
Structurally this zone contains number of folds of variable sizes and geometries.
The folds extended NW SE trend though most of the zone, but gradually
changes to E W trend northwestward towards the Turkish territory. Almost all
the anticlines in the eastern part exhibit reverse faulting that has caused over-
ridding on the NE limbs on the SW limbs, especially in Kirkuk Subzone [27].
The Low Folded Zone forms the first topographic and morphological front of the
(WZFTB) [27]. It is located between the Mesopotamia Foredeep from the
southwest and the High Folded Zone from the northeast [4, 11] (Fig.14).
The Low Folded Zone knows in Iranian Region with different names such as the
Zagros deformational front [6 and 30] and the Zagros Mountain Front [3 and 31].
The exposed rock units within this zone extend from Late Cretaceous in age,
The Tectonic and Structural Classification of the Western Part of Zagros
83
which belong to the Shiranish formation to Pliocene Pleistocene in age, which
belong to the Bai Hassan formation. The exposed stratigraphical column is
represented by 24 formations [32].
Based on field, seismic and well data [4 , 27] subdivided the Low Folded Zone
into two subzones, which are (Kirkuk Subzone in the SE, and Mosul Subzone in
the NW) (Fig.13).
[4] mentioned the folds within Kirkuk Subzone are long, narrow, asymmetrical,
disharmonic structures, and the folds are NW SE trending. They are frequently
associated with thrust faults, where their back limbs have been thrusted
southwestwards over their forelimbs.
Within Mosul Subzone the folds are relatively short, broad, asymmetrical to
slightly, non-disharmonic structures and not associated with thrusting. The folds
are NW SE trending in the southeastern part of the region, but change to E W
direction in the northwestern part.
5.2. The High Folded Zone
The High Folded Zone is located between the Imbricate Zone to the north and
northeast and to the south and southeast by the Low Folded Zone (Fig.14). Its
coverage area is about 15827 Km². The zone extends from the Iraqi Iranian
borders where the folds are tending NW SE, but gradually changes to E W as
the folds continue northwards towards the Iraqi Turkish borders. Structurally the
Zone contains a number of high amplitude, short wavelength anticlines with
different dimensions, forming high rugged anticlinal mountains separated by deep
and narrow synclinal valleys [27].
[5] estimated the average depth of the basement by to be (~ 8) Km. That mean the
basement is shallower in the High Folded Zone as compared to its depth in the
Low Folded Zone.
5.3. The Imbricated Zone
The Imbricated Zone is topographically a narrow and high zone. Structurally this
zone consists of a series of southwest directed thrusts and elongated tight folds
[27]. The oldest exposed rocks in Iraq located in this zone, which is Al-Khabour
Quartzite formation (Late Ordovician). It is extending from the high folded zone
in the SW and Zagros suture zone in the NE. It is characterized by intense folding
and thrusting. [5] considered the imbricated zone can be subdivided into two sub-
zones (Fig.10), which are:
5.3.1. Balambo-Tanjero Subzone
[5] reported Balambo-Tanjero subzone formed due to the opening of the Neo-
Tethys during late Jurassic time. It is a narrow belt, a proximately 25 km wide
trending NW-SE, and extending from the Iranian border in the SE to the Turkish
border in the NW. Balambo-Tanjero subzone is intensely folded and faulted [5]. It
is characterized by lower and upper Cretaceous deposits.
84 Maher T. Zainy et al.
[5] mentioned Balambo-Tanjero subzone is subdivided into two belts, the NE part
representing a depression with Tertiary clastics sediments and the SW part where
Tertiary clastic sediments are absent.
5.3.2. Northern (Ora) Thrust Sub-Zone
Northern (Ora) Thrust Subzone is an approximately 15 km wide, E-W trending
belt within Iraqi territory. [33] suggested that the Triassic rocks are equivalent to
the metamorphic rocks of the Shalair zone, whereas [5] considered these rocks to
be part of the Northern Thrust Zone.
5.4. Zagros Suture Zone
This is the most complex and least studied tectonic zone in Iraq. The thrust zone in
Iran is also known as the Crush zone. It includes the igneous and metamorphic
rocks in Iraq, with other Triassic Miocene sedimentary rocks [5]. The
relationships between the established tectonostratigraphic units are poorly studied
and the vague naming of rock units prevents a regional comparison [34].
The Zagros Suture Zone is divided by [5, 28] into two tectonic subzones within
the Iraq territory these are:-
5.4.1. Qulqula-Khuwarkurk Subzone
Rocks in the Qulqula-Khuwarkurk Zone are formed during the Late Cretaceous
[5]. They consist of radiolarian chert, mudstone and limestone, and igneous rocks
towards NE. The basement is approximately-14 km deep [5]. The main structures
are recumbent and isoclinal folds, thrusts and reverse faults. [5] subdivided this
sub-zone into three blocks, an outer, central and inner blocks.
5.4.2. Penjween-Walsh Subzone
[5] mentioned the Penjween-Walsh Subzone represents the central, main Neo-
Tethys. It formed during the Cretaceous and extends along the Iraq-Iran border,
thrusted over the Qulqula-Khwarkurk subzone and the Balambo-Tanjero Subzone.
The thickness of the Cretaceous and Tertiary rocks is approximately 8km and the
main structures are represented by thrust sheets [5].
5.5. Shalair (Sandaj-Sirjan) Subzone (Terrane)
[2, 5 and 27] Shlair Terrane as an integral part of the Sandaj-Sirjan Zone (Eurasian
(Iranian) Plate), representing the widest part of the Zagros suture zone. The zone
consists of metamorphic and igneous rocks with Triassic Miocene sedimentary
rocks [14]. The thickness totals at approximately 5 km and it represented higher
thrust sheets in Iraq. The W boundary of the zone is a thrust fault [5]. [27]
mentioned the terrane is separated from the Arabian plate by the Zagros Main
Thrust, and contains many E W trending structures.
The Tectonic and Structural Classification of the Western Part of Zagros
85
6 Discussion
The Zagros fold and thrust belt is divided into two parts which are a western part
within the Iraqi territory and an eastern part within the Iranian territory. Almost all
previous works focused on the Iranian part of the Zagros (EZFTB), whereas the
Iraqi part (WZFTB) have had received only a very limited attention.
The Iraqi part of the Zagros belt has been divided into several structural zones.
Early classifications were related with oil exploration activities [21, 22, 23 and
24]. After that many sub classifications were presented later by [25 and 26]. All of
them classified based on the same principles by separating the fold belt into a
major roughly NW SE trending longitudinal zones, (assigned as Foothill Zone,
High Folded Zone, and the Geosynclinal Area) [4], the regional tectonic zones
were subdivided into smaller and smaller subzones that in sometimes inconsistent
with each other and was a very complicated, special in tectonic classification of
[26]. [5 and 7] have presented another classification, which is the same as that of
[25], but with minor modification. It is noteworthy, that all these differences
structural classifications are due to using differences between the used structural
criteria used in the classifications. All the researchers divided Iraqi territory into
Stable shelf and unstable shelf and considered Abu-Jir fault zone the limit between
them.
[28 ] have introduced a new tectonic classification to the Iraqi territory, he used
the first time the term Inner Platform (Stable Shelf) and Outer Platform (Unstable
Shelf) (Fig.12).
[25 and 26] (Fig.8 and 9) considered the WZFTB is located within the Unstable
Shelf and Geosynclinal area, then they subdivided these zones into subzones,
which are considered Mesopotamian, Low Folded Zone and High Folded Zone
within Unstable Shelf. Moreover, they divided the Geosynclinal Area into:
Balambo Tanjero, Northern thrust, Qulqula-Khuwarkurk and Penjwin- Walash
subzones within Geosynclinal area.
[5] considered WZFTB located within unstable shelf and Zagros suture zone and
considered Mesopotamian within stable shelf, whereas[20 and 27] considered the
Mesopotamia Zone belongs to the Outer Platform. It is worth mentioning that [5]
were more detailed than [20 and 27], in Imbricate Zone, they divided it into
several subzones, which are from SW to NE Balambo-Tanjero Subzone and
Northern (Ora) Thrust Zone (Fig 10). Also considered Shlair Zone within
WZFTB, whereas [20 and 27] considered Shlair as a Terrane and it belongs to
Eurasian (Iranian) Plate (EZFTB), which is more relevant.
According to the personal opinion of the authors the tectonic classification of [28]
is the most relevant one and clearer one; especially, within the Outer Platform
(Unstable Shelf) which is classified it based on the structural style and intensity of
deformation, stratigraphy, mechanical stratigraphy and tectono-stratigraphy of the
deformed sequences. However, the western part of the Zagros fold and thrust belt
of Iraq has been subdivided by [20 and 27] into four parallel structural zones
trending NW SE (Fig.14). The zones, from SW to NE are: Low Folded Zone,
86 Maher T. Zainy et al.
High Folded Zone, Imbricate Zone, and Suture Zone, with increasing
deformational intensity northeastward toward the Arabian Plate margin. Also he
divided the main zones into subzones, depending on field, seismic and well data.
He divided the Low Folded Zone into two sub-zones, which are Kirkuk Subzone;
in the SE and Mosul Subzone; in the NW. The Suture Zone is divided into two sub
zones: Qulqula-Khuwarkurk Subzone; in the SE and Penjween-Walash Subzone;
in the NW. Based on the difference in mobility and activity, he subdivided
Mesopotamian Foredeep into three subzones: Al-Jazira Subzone; in the NW,
Mesopotamia Subzone; in the middle and Basra subzone; in the SE. Moreover, he
divided the Inner Platform into two subzones: Western Desert Subzone and
Southern Desert Subzone; based mainly on the morphology and physiography of
the area.
We can considered the classification of [28] is the most relevant one, this
assumption is based on the following facts: 1) All previously existing
classifications; apart from that of [5] have used the old abandoned theory of
Eugeosyncline, 2) [5] considered the Mesopotamia Plain to be in the Stable Shelf
(part) ignoring the presence of tens of subsurface anticlines that follow the
tectonic regime of Zagros Fold. Those subsurface anticlines have N S trend in
the southern part of Iraq, then gradually change to NW SE trend, which are the
same trends of Zagros Fold style, 3) [25] have considered the Mesopotamian Plain
to be part of the Unstable Shelf (part), but [5] changed their opinion in this
consideration, 4) All previous Tectonic maps has considered Wadi Al-Tharthar as
a contact between the Stable and Unstable Shelves (parts), attributing that to the
presence of Al-Tharthar Fault. Accordingly, the Jezira area was considered within
the Stable part, whereas, Fouad considered it to belong to the Unstable Shelf
(Outer Platform) and to be part of the Mesopotamia Foredeep. Moreover, the
Jezira area includes many subsurface anticlines that Follow Taurus Folding style,
this phenomenon was considered by [28] for his assumption. It is worth
mentioning that [35] confirmed the absence of Al-Tharthar Fault by means of
detailed mapping, 5) [28] has used more detailed geological maps; updated maps
at scale of 1:250 000 (2012 2014), which were not available to other authors, 6)
[28] has used high quality satellite images that show more detailed data than other
authors, and 7) [28] has the opportunity of field observation, checking and
confirming the acquired data in 2006 2012.
7 Conclusions
This study has achieved the following conclusion: The tectonic maps of the Iraqi
territory were reviewed and a comparison of the given classifications by different
authors during many decades (1984 2014) are discussed and presented. The most
relevant classification for the tectonic style of the Iraqi territory is considered that
presented by [28]. This assumption is based on: 1) The used data is more reliable
and relevant, since it presents the most updated available data, 2) The majority of
The Tectonic and Structural Classification of the Western Part of Zagros
87
the acquired data was checked in the field, 3) High quality satellite images were
used to recognize and interpret the tectonic and structural forms and aspects, and 4)
More well and seismic data were used in defining the contacts between the tectonic
zones and subzones.
ACKNOWLEDGEMENTS. The author extends his sincere thanks to Mr.
Varoujan Sissakian for reviewing of the manuscript and his critical discussion,
comments and notes that have amended the manuscript, without his contribution,
this manuscript wouldn’t be in its current form.
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... These zones include, from SW to NE, the Low Folded Zone (or Foothills), the High Folded Zone, and the Imbricated Zone ( Fig. 2a) (Jassim and Goff 2006). According to Zainy et al. (2017), the Imbricated Zone can be further subdivided into two zones, namely the Balambo-Tanjero Subzone and the Northern (Ora) Thrust Subzone. This latter subzone is approximately 15 km wide and trends E-W in the border area of Northern Iraq and Turkey (Balaky et al. 2016;Edilbi et al. 2017;Zainy et al. 2017). ...
... According to Zainy et al. (2017), the Imbricated Zone can be further subdivided into two zones, namely the Balambo-Tanjero Subzone and the Northern (Ora) Thrust Subzone. This latter subzone is approximately 15 km wide and trends E-W in the border area of Northern Iraq and Turkey (Balaky et al. 2016;Edilbi et al. 2017;Zainy et al. 2017). ...
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... It was compared with them in the table below. The relationship of D. zeynepiae with the very distant Zagros Mountains species is interesting in terms of biogeography; however, the fact that Habib-i Neccar Mountain, where the habitat is located, is at the western end of the Zagros fold and thrust belt system (Zainy et al. 2017) is a clue that may explain the relationship (Fig. 14). ...
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A new Dionysia species, D. zeynepiae, is described from Antakya, a Mediterranean province in southern Turkey. It differs from all other known species of the genus by the presence of the trifid corolla lobes (vs. entire, emarginate or bifid lobes). This is the most western and most separated population of this mostly Irano-Turanian genus, which is distributed mainly in the Zagros Mountains (Iran) and adjacent areas. The floral morphology of the heterostylous flowers is also described in detail.
... The western part is subdivided into the following four structural zones from SW to NE: Low Folded Zone, High Folded Zone, Imbricated Zone, and Thrust Zone. These zones are generally striking northwest-southeast, and are further divided to several subzones that belong to the Unstable Shelf in Iraqi Geotectonic division (Jassim and Goff 2006;Fouad 2010Fouad , 2015Vaseghi et al. 2016;Zainy et al. 2017;Abdulnaby 2018). The sedimentary cover in the ZFTB is about 12 km thick, including Lower Cambrian to Pliocene Formations (O'Brien 1957;Lawa et al. 2013). ...
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... These structural zones include, from SW to NE, the Low Folded Zone (or Foothills), the High Folded Zone and the Thrust Zone (Jassim & Goff 2006). In a recent review, Zainy et al. (2017) noted that the Thrust Zone could be considered to be a subzone (i.e. the North ern (Ora) Thrust Subzone) within the Imbricated zone, with this latter zone being subdivided into two sub zones, namely, the Balambo Tanjero Subzone and the Northern (Ora) Thrust Subzone. The Banik section, which was examined as part of this study, is located near the boundary between the High Folded Zone and the Thrust Zone (Fig. 3). ...
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Lithological, petrographic, and geochemical analysis of the Middle to upper Jurassic succession (i.e. Sargelu and Naokelekan formations) from northernmost Iraq were undertaken with the aim of providing an updated discussion for their sedimentary and diagenetic histories, as well as examining the evaporation proxies and paleoredox conditions under which these two formations were deposited. Lithologically, the Sargelu Formation comprises massive dolomites, interbedded with shales, rare cherts and one single limestone bed, whilst the Naokelekan Formation consists of shales overlain by limestones and one single dolomite bed. Petrographic analysis of both formations revealed the presence of rare ostracods, bioclastic fragments as well as calcispheres. Five main microfacies were recognized, including bioclastic wackestone, mudstone, dolorudite, dolarenite and dolomicrite microfacies.
... These structural zones include, from SW to NE, the Low Folded Zone (or Foothills), the High Folded Zone and the Thrust Zone (Jassim & Goff 2006). In a recent review, Zainy et al. (2017) noted that the Thrust Zone could be considered to be a subzone (i.e. the North ern (Ora) Thrust Subzone) within the Imbricated zone, with this latter zone being subdivided into two sub zones, namely, the Balambo Tanjero Subzone and the Northern (Ora) Thrust Subzone. The Banik section, which was examined as part of this study, is located near the boundary between the High Folded Zone and the Thrust Zone (Fig. 3). ...
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Lithological, petrographic, and geochemical analysis of the Middle to upper Jurassic succession (i.e. Sargelu and Naokelekan formations) from northernmost Iraq were undertaken with the aim of providing an updated discussion for their sedimentary and diagenetic histories, as well as examining the evaporation proxies and paleoredox conditions under which these two formations were deposited. Lithologically, the Sargelu Formation comprises massive dolomites, interbedded with shales, rare cherts and one single limestone bed, whilst the Naokelekan Formation consists of shales overlain by limestones and one single dolomite bed. Petrographic analysis of both formations revealed the presence of rare ostracods, bioclastic fragments as well as calcispheres. Five main microfacies were recognized, including bioclastic wackestone, mudstone, dolorudite, dolarenite and dolomicrite microfacies. The shales comprise clay minerals assemblages (illite/muscovite and kaolinite) with some quartz, alkali feldspar and rare pyrite. The Sargelu Formation was probably deposited in a shallow-marine environment. In contrast, the Naokelekan Formation is hypothesized to be deposited in a restricted shallow-lagoon environment. Palaeoredox indicators suggest that both formations were accumulated under anoxic conditions, most probably in silled basins where water circulation was restricted. Tectonic activity thus resulted in basin compartmentalization across the region, which also explains the marked differences which are often observed. 3
... Current seismicity and folding indicate that this deformation is still active (Jackson et al. 1981;Berberian 1995;ANSS 2018). The belt extends more than 2000 km from southern Turkey through northeastern Iraq to the Strait of Hormuz in southwestern Iran (Zainy et al. 2017). The belt is up to 300 km wide and is dominated by numerous large "whaleback" and smaller anticlines as well as localized thrust faults which trend NNW-SSE parallel to the general strike of the Zagros. ...
... As magnetic method, the NS faults can be distinguished. It seems that there are other faults of northwestern trends where these features could be corresponding to the transversal, NW faults that mentioned by other researchers (Buday and Jassim, 1987;Hijab and Aldabbas, 2000;Jassim and Goff, 2006;Sissakian et al., 2014;Zainy et al., 2017). Naturally, these geological lineaments have been formed the result of a collision between the Eurasian and Arabian Plates, where most Iraq's structures have taken NW-SE trend (Sissakian et al., 2014). ...
... Current seismicity and folding indicate that this deformation is still active (Jackson et al. 1981;Berberian 1995;ANSS 2018). The belt extends more than 2000 km from southern Turkey through northeastern Iraq to the Strait of Hormuz in southwestern Iran (Zainy et al. 2017). The belt is up to 300 km wide and is dominated by numerous large "whaleback" and smaller anticlines as well as localized thrust faults which trend NNW-SSE parallel to the general strike of the Zagros. ...
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The biggest nine well-known natural ponds in the highest elevations of Zagros thrust zone in the northeast of Erbil, Kurdistan region, Iraq, have been taken and synthesized with RS and GIS techniques to reveal the spatial and temporal distribution of the ponds, and to explore the sustainability of these ponds. ENVI 5.1 software was used to detect pond surface area and shapes in different seasons and for 33 years. RS was used to detect land surface temperature (LTS), but GIS was used for maps and calculations of pond area variation. Geology of the area is very complex; formations are different in genetics, age, thickness, and extensions. The regional tectonic forces highly deformed the succession and extension of the geologic for- mations. i.e. The forces that had made the mountains were very strongly affected the layers and the geologic formations, resulting in many types of folds, faults, over- turning layers, thrusting, and many other highly deformed structures. Water-bearing formations are of restricted extensions due to the deformations, with limited and local productivity. The aquifers moved to face impermeable rocks or surface, dis- charging springs, ponds, and rivers. The ponds are sustaining permanently due to the following reasons: most of the ponds are located on semi-impermeable deposits, weather and LTS throughout the year are less than 25°C, high relative humidity and low evaporation, and they are recharging by direct groundwater and snowmelts.
... Current seismicity and folding indicate that this deformation is still active (Jackson et al. 1981;Berberian 1995;ANSS 2018). The belt extends more than 2000 km from southern Turkey through northeastern Iraq to the Strait of Hormuz in southwestern Iran (Zainy et al. 2017). The belt is up to 300 km wide and is dominated by numerous large "whaleback" and smaller anticlines as well as localized thrust faults which trend NNW-SSE parallel to the general strike of the Zagros. ...
Chapter
Roughly 44% of the world’s total known hydrocarbon resources are located in North Africa and the Middle East, from Algeria in the west to the Zagros region of Iran in the east. This includes more than 200 giant fields in the Middle East. North African basins, mainly in Algeria, Libya, and Egypt, contain 4% of the world’s oil and gas reserves and nearly 40 giants. The most recent giant field resides in the offshore Levantine Basin. In this chapter, the region’s geological history and petroleum systems are reviewed, including descriptions of the regional habitats and stratigraphy of the main reservoirs and source rocks. 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Multiple marine transgressions across a low-relief continental platform were interrupted by at least four glacial events: Late Ordovician (Hirnantian), Silurian, Carboniferous, and Early Permian. Deposition of siliciclastics predominated throughout the Paleozoic whereas carbonates were much less common. The most important tectonic event was the mid-Carboniferous Hercynian composite-orogeny, which caused major uplift and erosion. The Hercynian represented the final closure of Paleotethys and produced many fault blocks and arches that would later host many of the major hydrocarbon accumulations of North Africa and eastern Arabia. The Mesozoic–Cenozoic sedimentary sequence similarly consists of eustatically and tectonically controlled depositional cycles along the newly formed passive margin of Neotethys. Triassic to mid-Cretaceous facies along North Africa are almost everywhere shallow marine, nearshore, deltaic, and continental. Neotethys reached its maximum extent in the Late Cretaceous at which time carbonate sequences dominated. In addition to the Hercynian Orogeny, two other compressional events had major consequences on North Africa–Arabia petroleum systems. The closing of Neotethys began in the late Santonian (~84 Ma) and the convergence between Eurasia and Africa–Arabia sent pulses of compressional deformation across the plate. This corresponded to the first phase of the complex Alpine orogenic cycle and caused folding, basin inversion, and strike-slip faulting along the African–Arabian Neotethyan margin (the “Syrian Arc”), and thrusting and ophiolite obduction in Oman. Compression was renewed at the end of the Maastrichtian and continued into the early Paleocene, followed by even stronger effects in the Late Eocene. Eruption of the Afar plume at about 31 Ma marked the beginning of a new phase of continental rifting that had dramatic effects on all aspects of the geology of the region. The Gulf of Aden ruptured first in the Early Oligocene, followed by the southern Red Sea in the Late Oligocene. At the Oligocene–Miocene transition, the remainder of the Red Sea north to the Gulf of Suez underwent a regional dike event and accompanying extensional faulting. Initiation of the Gulf of Aqaba—Dead Sea transform plate boundary occurred in the Middle Miocene, completing formation of the independent Arabian plate. The Neotethys Ocean also ceased to exist in the Middle Miocene following a collision between Eurasia and the Arabian plate to form the Bitlis–Zagros suture and fold belt. The Arabian plate was progressively tilted to the northeast as a result of both uplift and rifting of Arabia from Africa, and structural loading of the northeast margin by the Zagros fold belt. Recent tectonic activity is mainly concentrated along the Maghrebian Alpine Belt, the offshore Nile Delta, the Red Sea–East African (or “Afro-Arabian”) Rifts Province, the Aqaba–Dead Sea–Bekaa sinistral strike-slip fault zone, and some major intra-plate fault zones including the Guinean–Nubian, Aswan, and central Sinai lineaments. Our review of the petroleum systems of North Africa and Arabia is brief and includes only highlights of the hydrocarbon occurrences found across this broad and complex region. Based on the age of source rocks, it is possible to distinguish an Infracambrian Petroleum System, Palaeozoic-related Petroleum Systems, and linked Mesozoic–Cenozoic Petroleum Systems. The sedimentary fill contains numerous source rocks, some of them with exceptional quality and regional distribution, such as the Silurian “hot shale”. Producing reservoirs are found in both siliciclastics and carbonates. The proximity and juxtaposition of source rocks with thick reservoirs minimized the need for complex oil migration pathways, but also facilitated hydrocarbon expulsion and migration over long distances. Huge amounts of evaporites and shales are present, providing excellent lateral and ultimate top seals. Hydrocarbons are trapped in literally all stratigraphic units from the fractured Neoproterozoic basement to the youngest Pliocene–Quaternary sediments.
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Iraq Geological Survey is committed to update the published geological maps, almost periodically and as data are available for updating. Among the updated maps is the Geological Map of Iraq, at scale of 1: 1000 000. It is the 4th edition. The 3rd edition was made in 2000 (Sissakian, 2000), whereas the 1st and 2nd editions were made in 1986 and 1990, respectively (Jassim et al., 1986 and 1990). The new map is attached to this article in A3 size.
Book
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The Petroleum Geology of Iraq by A. A. M. Aqrawi, J. C. Goff, A. D. Horbury and F. N. Sadooni ISBN: 978-0-901360-36-8 424 pages +xvi Format: hardback Publisher: Scientific Press Ltd., PO Box 21, Beaconsfield, Bucks, HP9 1NS, UK This book presents a comprehensive, up-to-date appraisal of the reservoir rocks, source rocks, seals and traps that control Iraq’s petroleum resources. Early chapters review the history of the oil industry in Iraq and outline Iraq’s tectonic setting and evolution. A five-chapter section on stratigraphic elements, arranged by megasequence, is followed by an assessment of Iraq’s petroleum systems. The book provides an invaluable source of information for petroleum geologists and other researchers.
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ABSTRACT The stratigraphy of the Low Folded Zone, in Iraq is reviewed. The oldest exposed rocks are Late Cretaceous in age, which belong to the Shiranish Formation, whereas the youngest are of Pliocene – Pleistocene age, which belong to the Bai Hassan Formation. The exposed stratigraphical column is represented by 24 formations. Moreover, ten main types of Quaternary sediments, which have wide geographic extent, are reviewed too. The Cretaceous and Paleogene rocks are mainly of marine carbonates with rare clastics, the Cretaceous rocks represent synrift sediments. The Early Neogene (Oligocene) rocks form a complex of reef – back reef – fore reef and are restricted almost in the eastern, central and western parts of the involved area, especially in Qara Chouq anticline, with other restricted exposures in different parts. The Early and Middle Miocene rocks are mainly of marine origin, lagoonal carbonates and evaporate, respectively. The Late Miocene rocks, which represent the beginning of the continental environment, together with the rocks of Pliocene – Pleistocene consist of molasse sediments, deposited in sinking foredeep. The Quaternary sediments are well developed, especially Pleistocene river terraces of different stages, and polygenetic sediments that fill the synclinal troughs, with other different types. For each exposed formation, the type locality, exposure areas, subsurface extension, main lithology (as described inform of members and/ or informal units), thickness, fossils, age, depositional environment, and the lower contact are described. The described lithologies of the formations by different authors from different localities are reviewed, with occasional remarks of the present authors. The main tectonic events and the paleogeography are reviewed briefly. Each formation is discussed, for majority of them the present authors' opinion are given, with many recommendations for future studies. Some new ideas dealing with many aspects for many formations including proposals for establishing new formations are given, too.
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The geological setting of the Mesopotamia Foredeep within the tectonic framework of Iraq, has been reviewed and redefined according to the modern concepts of foreland basins, and new structural boundaries are introduced. The Mesopotamia Foredeep, which is the present day expression of the terrestrial part of the Zagros Foreland Basin, is an integral part of the Zagros Fold – Thrust Belt that lies between the deformational front of the Zagros orogenic belt and the stable interior of the Arabian Platform. The Mesopotamia Foredeep is an elongated epicontinental basin formed above an earlier plat formal and marginal basin. Accordingly, the Phanerozoic stratigraphic sequence of the basin can be broadly categorized into three major tectono-stratigraphic assemblages; Cambrian – Early Permian intraplate assemblage, Late Permian – Middle Cretaceous Neo-Tethys passive margin assemblage, and Late Cretaceous – present foreland basin assemblage. The Mesopotamia Foredeep is a mobile tectonic zone and contains several buried structures including folds, fault and diapiric structures. Recent activity of some of these structures is recorded through their effects on the Quaternary stratigraphy and present geomorphological landforms.
Article
Most of the known oil accumulations of Northern Iraq probably originated by upward migration from earlier, deeper accumulations which were initially housed in stratigraphic or long-established structural traps, and which are now largely depleted. The earlier concentrations had their source in basinal sediments, into which the porous, primary-reservoir limestones pass at modest distances east of the present fields. Development of the region favored lateral migration from different basinal areas of Upper Jurassic and Lower-Middle Cretaceous time into different areas of primary accumulation. Important factors affecting primary accumulation included: (1) early emergence and porosity improvement of the reservoir limestones, followed by burial under seal-capable sediments; (2) the timely imposition of heavy and increasing depositional loads on the source sediments, and the progressive marginward advance of such loads; (3) progressive steepening of gradients trending upward from source to accumulation area; (4) limitation of the reservoir formations on the up-dip margin by truncation or by porosity trap conditions. In late Tertiary time, large-scale folding caused adjustments within the primary reservoirs, and associated fracturing permitted eventual escape to higher limestone reservoirs, or to dissipation at surface. The sulfurous, non-commercial crudes of Miocene and Upper Cretaceous reservoirs in the Qaiyarah area are thought to stem from basinal radiolarian Upper Jurassic sediments, which lie down dip, a few tens of miles east of these fields. Upper Cretaceous oils of Ain Zalah and Butmah drained upward from primary accumulations in Middle Cretaceous limestones, which were filled from basinal sediments of Lower Cretaceous age situated in a localized trough a few miles northeast of these structures. The huge Kirkuk accumulation, now housed in Eocene-Oligocene limestones, ascended from a precedent accumulation in porous Middle-Lower Cretaceous limestones, which drew its oil from globigerinal-radiolarian shales and limestones of the contemporaneous basin, a short distance east of the present field limits. Eocene-Oligocene globigerinal sediments, considered by some the obvious source material for Kirkuk oil, seemingly provided little or no part of the present accumulation. The reservoir formation may have been filled from these sources, to lose its oil by surface dissipation during the erosional episode preceding Lower Fars deposition. Upper Cretaceous basinal sediments probably contributed nothing to known oil field accumulations, though they may have subscribed to the spectacular impregnations of some exposed, Upper Cretaceous reef-type limestones. Neither Miocene nor pre-Upper Jurassic sediments have played any discernible role in providing oil to any producing field. Indigenous oils are thought to be negligible in the limestone-reservoir formations considered.
Article
In the simply folded belt of the Zagros Mountains, a sequence of Precambrian to Pliocene shelf sediments about 12 km thick has undergone folding from Miocene to recent time. Much of the section (6,000 to 7,000 m), consisting of Cambrian to Miocene rocks, forms a single structural lithic unit, the Competent group. It is bounded above and below by detachment zones in evaporite deposits. The author examines the way the rocks of the simply folded belt reacted to the deformation, the fundamental causes of which are not discussed. The intention is to show how the structures of the simply folded belt illustrate some of the general principles of structural geology, and to use these principles to interpret the structures at depth.
Article
Early orogenic movements resulted in consolidation of Precambrian basement and formation of vast Iranian platform considered to be extension of Arabian shield; only epeirogenic movements affected region during Paleozoie, which is represented by typical platform deposits; however, most of Iran went through all stages of complete Alpine orogeny in spite of prevailing platform character in preorogenic time; important trends in Alpine structural plan clearly were inherited from Precambrian structures; numerous structural zones are recognized which differ in structural development and present tectonic style.