Geomorphology, Stratigraphy and Tectonics of the Mesopotamian Plain, Iraq: A Critical Review
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ISSN 0016-8521, Geotectonics, 2021, Vol. 55, No. 1, pp. 135–160. © Pleiades Publishing, Inc., 2021.
Geomorphology, Stratigraphy and Tectonics
of the Mesopotamian Plain, Iraq: A Critical Review
V. K. Sissakiana, N. Al-Ansarib, *, and N. Adamoc
a
University of Kurdistan Hewler, Erbil, A9422504 Iraq
b
Lulea University of Technology, Lulea, 97181 Sweden
c Consultant Dam Engineer, Sweden
*e-mail: nadhir.alansari@ltu.se
Received August 29, 2019; revised April 30, 2020; accepted May 26, 2020
Abstract—The Mesopotamian Plain is part of the Mesopotamia which extends for vast area bigger than the
plain. The plain is almost flat and vast lowland, which has clearly defined physiographic boundaries with the
other surrounding physiographic provinces. The plain is a huge accumulation geomorphologic unit, where
the fluvial, lacustrine, and the Aeolian landforms prevail; the fluvial units being the abundant among others.
However, estuarine and marine forms also are developed, but restricted to the extreme southeastern reaches
of the plain. The Mesopotamian Plain is covered totally by Quaternary sediments among which the fluvial
origin is the most prevailing and more specifically the flood plain sediments. The flood plain sediments are
the Holocene in age, whereas the Pleistocene sediments are restricted to alluvial fan sediments and river ter-
races. The flood plain sediments cover majority of the Mesopotamian Plain, whereas the alluvial sediments
are restricted to the northern–eastern, western and southern peripheral parts only. Different geomorpholog-
ical features indicate the Neotectonic activity in the plain, such as migrations of rivers due to growing of sub-
surface anticlines. The extreme southeastern part is covered by the tidal flat and sabkha sediments. Marshes
and shallow depressions are also covered by the Holocene sediments which are contaminated by the Aeolian
sediments. Mesopotamian Plain is a part of the Mesopotamian Foredeep which is a part of the Zagros Fore-
land Basin including the Zagros Fold-Thrust Belt. It is large continuously subsiding basin since the Upper
Miocene (11.62 Ma). The plain shows no structural features on the surface, except the main fault escarpment
representing the part of Abu Jir Active Fault Zone. However, the rolling topography, in the northern parts of
the plain indicates subsurface anticlines that are still growing up, such as Balad, Samarra, Tikrit and Baiji
anticlines indicating the Neotectonic activity. Moreover, many buried subsurface anticlines are present in dif-
ferent parts of the plain. All of them are growing anticlines and have caused continuous shift to Tigris and
Euphrates rivers and their distributaries indicating the Neotectonic activities. The minimum and maximum
subsidence amounts in the plain since the Upper Miocene are zero and –2500 m, respectively.
Keywords: fluvial sediments, Pleistocene, Holocene, marshes, alluvial fan sediments, aeolian sediments, ter-
races, subsurface anticlines, river migrations, Neotectonic activities, folds growth
DOI: 10.1134/S001685212101012X
INTRODUCTION mia and Lower or Southern Mesopotamia [59]. Upper
Mesopotamia, also known as the Jazirah (Al-Jazira
Mesopotamia is a historical region in West Asia situ- Plain), is the area between the Euphrates and the
ated within the Tigris-Euphrates rivers system. In mod- Tigris from their sources down to Baghdad [20].
ern days, roughly corresponding to most of Iraq, Lower Mesopotamia is the area from Baghdad to the
Kuwait, parts of Northern Saudi Arabia, the eastern Persian Gulf [59]. In modern scientific usage, the
parts of Syria, Southeastern Turkey, and regions along term Mesopotamia often also has a chronological con-
the Turkish–Syrian and Iran–Iraq borders [23] (Fig. 1). notation. In modern Western historiography of the
Mesopotamia, in modern times, has been more region, the term “Mesopotamia” is usually used to
generally applied to all the lands between the Euphra- designate the area from the beginning of time, until
tes and the Tigris, thereby incorporating not only parts the Muslim conquest in the 630s, with the Arabic
of Syria but also almost all of Iraq and Southeastern names Iraq and Jazirah being used to describe the
Turkey [27]. The neighboring steppes to the west of the region after that event [12, 27, 71].
Euphrates and the western part of the Zagros Moun- The Mesopotamian Plain, however, is different
tains are also often included under the wider term geographically, geologically and historically from the
Mesopotamia [20, 57, 71]. The further distinction is Mesopotamia. The Mesopotamian Plain represents
usually made between Upper or Northern Mesopota- part of the Mesopotamia, and nowadays it represents
135
136 SISSAKIAN et al.
Turkеy
unnamed
poak
Mosul Erbil
As Sutaymaniyah
Syria
Kirkuk
35° Iran
Samarra
Baghdad
Ar Ramadi
Jordan
Ar Rutbah
Karbaia Al Kut
An Najaf
An Nasiriyah
Al Basrah
Umm Qasr
30° Saudi
Arabia
Kuwait
0 50 100 km
0 50 100 m
40° 45°
Fig. 1. Location map showing geographic limits of the Mesopotamia (green dash line), and limits of the Mesopotamian Plain
(red dash line) added by the authors (after [37]).
the existing plain between the Tigris and Euphrates GEOMORPHOLOGY
rivers, which is limited south of Al-Fatha gorge in the OF THE MESOPOTAMIAN PLAIN
north. The alluvial plains along the Iraqi–Iranian bor-
ders in the east. From the west (northern part), it is Topography
limited by wadi Al-Tharthar and (southern part) the
eastern limits of the Western Desert; then extending The Mesopotamian Plain is mainly the flat and
with the northern limits of the Southern Desert (almost vast lowland, which has clearly defined physiographic
parallel to the Euphrates River), forming the southern boundaries with the surrounding physiographic prov-
limits of the plain. From the southeast, it is limited by inces as follows [10, 51]: The Low Amplitude Moun-
the upper reaches of the Arabian Gulf (Fig. 1). tainous Province from the north and east. From the
west, it is limited by Al-Jazira Plain and the Western
The age of the Mesopotamian Plain backs to the Desert Province. From the south it is limited by the
Pleistocene (2.558 Ma), and because the alluvial sedi- Southern Desert Province [68].
ments of the plain are not concerned in oil explora-
tions; therefore, very limited data is available from the The Mesopotamian Plain is a huge accumulation
drilled oil wells, as well from the water wells; since the geomorphologic unit, where the fluvial, lacustrine,
water wells very rarely encounter the Pleistocene sedi- and Aeolian landforms prevail. In the extreme south-
ments. Moreover, there is a large similarity between eastern reaches of the plain; however, estuarine and
the alluvial sediments of the plain and the underlying marine forms also are developed. Moreover, some ero-
Pre-Quaternary sediments [74]; especially, when the sional landforms are developed in different places, but
Bai Hassan Formation (Pliocene-Pleistocene, mainly are not well expressed. The geomorphic units are clas-
conglomerate and claystone) underlies the Mesopota- sified according to origin, geomorphic position, and
mian Plain sediments. lithology. Some of the units involve different geomor-
GEOTECTONICS Vol. 55 No. 1 2021
GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 137
40 42 44 46
N
Turkey
36 Mosul Arbil 100 km
Syria
Sulaimaniyah
Iran
34
Hor Al-Shuwaicha
Falluja
Baghdad
Iskandariya Hor Al-Dalmaj
Jordan
Hor Al-Sanaf
H
Iraq
32 G
Al-Najaf
D
K
Basrah
30
Saudi Arabia
Kuwait
Fig. 2. Map showing the rivers’ names and other geographical locations mentioned in the text, the authors added the data in the
map (after [37]). River names: Al-Hilla (H), Al-Diwaniya (D), Al-Ghar’raf (G), Karoon (K).
phic features, which are described briefly taking in ity of the Tigris and Euphrates Rivers, beside the foot-
consideration their order and importance. hill rivers (wadis) of Himreen Mountain.
The surface of the Mesopotamia Plain is almost flat Seven units of alluvial origin are developed in the
with imperceptible gradient from the northwest to the Mesopotamian Plain of alluvial origin. They are
southeast. Its elevation drops southwards with an aver- described briefly hereinafter.
age of 1 m/1 km, in its northern sector from Baiji to
Balad towns. From Balad to Baghdad it drops 1 m/ each
3 km, and it decreases to 1 m/20 km south of Baghdad Fluvial Terraces
to the head of Arabian Gulf (Fig. 2). However, the plain The most extensive terraces recorded within the
is sloping down gradually, but more steeply than the Mesopotamia Plain are the fluvial terraces of the
slopes southwards from the foothills of Himreen Euphrates River, near Falluja town (Fig. 2). They are
Mountain. Along the eastern borders of the plain; it developed in two separate levels. The relics of the
slopes towards the flood plain of the Tigris River. In its higher terrace level are about 23 m above the recent
western borders, the plain slopes down from the desert water level of the river and along its right bank. The
plateaus to the Euphrates River’s flood plain. lower terrace level is recorded east of Falluja town and
near Iskandariyah town [74] (Fig. 2).
Geomorphological Units Alongside the courses of the foothill rivers (wadis),
The landforms of fluvial origin; mainly flood fluvial terraces are also developed at the outlets of the
plains are the most common accumulation forms in rivers (like Diyala, Galal Al-Nafut, Galal Har’ran,
the Mesopotamia Plain. They are related to the activ- Galal Badra, Chab’bab, and Al-Teeb, Note: Galal
GEOTECTONICS Vol. 55 No. 1 2021
138 SISSAKIAN et al.
43.25° E 45.75°
34.50° Salah Al-Din
1
N
2
Tharitar Lake
Diyala Diyala Governorate
Hit
Ramadi 3
4
5 Baghdad
32.75°
0 25 50 km
Karbala Wasit
Fig. 3. Satellite image [79] showing different alluvial fans of the Mesopotamian Plain (the authors’ interpretation). Alluvial fans
(red numbers): 1, Al-Fatha; 2, Al-Adhaim; 3, Diyala; 4, Eastern; 5, Ramadi Fan. Black arrows point to the alluvial fans; black
dash line refers to the limits of the alluvial fans.
means seasonal river) where they merge into the Mes- iments interfinger from east, west and south with Al-
opotamia Plain. Usually, two levels were recorded, the Fatha alluvial fan and Diyala alluvial fan sediments
surface of the higher level is around (7–18) m, above (Fig. 3).
the recent river bed. The lower level occurs few to 6 m (iii) Diyala. It is developed by the Diyala River
above the recent water courses. These terraces often when it enters the Mesopotamian Plain after living
pass gradually into the alluvial fan sediments, which Himreen Mountain. The length and width of the fan is
are very well developed alongside the eastern limits of about 175 and 85 km, respectively. The fans’ sediments
the Mesopotamian Plain. interfinger with different sediments (Fig. 3).
(2) Alluvial fans system in the eastern part of the
Alluvial Fans Mesopotamia Plain. This is a complex of alluvial fans
Four alluvial fan systems occur on the peripheral system developed on the eastern margin of the Meso-
parts of the Mesopotamian Plain; these are: potamian Plain alongside the foothill slopes in five
stages; as maximum (Fig. 3). The fans form continu-
(1) Alluvial fans system in the northern part of the ous belt of Bajada, with width exceeding 15 km. Sizes
Mesopotamian Plain. Three main individual alluvial and extensions of individual fan varies from few kilo-
fans are developed within this system, besides the fans meters to more than hundred square kilometers.
which merge laterally together to form Bajada along
the foothills of Himreen Mountain. The individual (3) Alluvial fans system in the western part of the
alluvial fans are described briefly hereinafter: Mesopotamia Plain. This system of alluvial fans is
developed at the outlets of the main valleys draining
(i) Al-Fatha. The fan is developed by the Tigris River the Iraqi Western Desert and the one developed by the
starting from Baiji town (Fig. 3). Jassim (1981) [40] Euphrates River (Fig. 3). Among these alluvial fans,
considered the gravel body as a fan latter on was proved only three are very large:
to be a large alluvial fan by Hamza et al. (1990) [34];
Yacoub et al. (1990) [78] and Yacoub (2011a) [74]. (i) Ramadi Fan developed by the Euphrates River,
(ii) Al-Adhaim. It is developed by Al-Adhaim (ii) Najaf–Karbala Fan developed by Wadi Lisan
River when it enters the Mesopotamian Plain after liv- and covers the Najaf–Karbala Plateau;
ing Himreen Mountain. The length and width of the (iii) Hab’bariyah Fans developed by some of the
fan is about 70 and 50 km, respectively. The fans’ sed- valleys draining the Iraqi Western Desert.
GEOTECTONICS Vol. 55 No. 1 2021
GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 139
4415 E 4745
Lorestan
Ramadi
3315 Al-Habbaniyah Baghdad
Hor
N Al-Shuwaicha Ira
n
Al-Razzazah
Karbala Wasit
Iraq
Hor
Al-Dalmay
Ab Najar
Al-Qadisiyyah
uJ Bahir
ir Maysan
t
Al-Najaf Amarah
ser
Hor
De
Hor
Al-Sanaf
ern
Ac Sand Al-Huwaiza
tiv Dunes
est
eF
An-Najaf
iW
au Central
3115 lt Samawah
q
zo Marshes
Ira
t
ser
n e Dhi Qar
De
Nasiriyah
ern
Al-Slalbar
Hor Al-Hammar
uth
Depresion
So
qi
Ira
Basrah
0 30 60 km
Basrah
Fig. 4. Landsat image [79] showing different features and forms within the Mesopotamian Plain (the authors’ interpretations).
The red dash line is the boundary between the Southern and Western Iraqi deserts.
(4) Alluvial fans system in the southern part of the (Fig. 2) is limited between two erosional cliffs of (6–
Mesopotamia Plains. This system of alluvial fans is 10) m height, above the surface of the flood plain. The
developed at the outlets of the main valleys draining sediments of the Euphrates River pass gradually into
the Iraqi Southern Desert. Among these alluvial only the sediments of Tigris River. Further downstream,
two are large fans: the Euphrates River starts to build its natural levees,
(i) Dibdibba Fan, which covers the major part of which attain few meters above the normal water level
the Dibdibba Plain [2], and SW of Basra city; of the river with variable width (1–3 km).
(ii) Al-Batin Fan, which was originated from Wadi (ii) Tigris River. The flood plain of the Tigris River
Al-Batin. between Baiji town and Tikrit city (Fig. 2) is limited
3 km within its meandering belt, in the northern sector
of the Mesopotamian Plain. Two flood stages with
Sheet Run-Off Plain height difference of (1.5–2) m can be recognized
This plain is the middle part of the piedmont plain. within the meandering belt. In the central sector of the
It has close connection with the peripheral part of the Mesopotamia Plain (Fig. 2, south of Baghdad–north
alluvial fans and terminates in Hor Al-Shuwaicha; a of Amara), the gradient of the Tigris River is less than
shallow depression located between the eastern allu- 5 cm/km. The most expressive morphological features
vial fans and Diyala Alluvial Fan (Fig. 4). The plain is in this plain are the abandoned river troughs, the relics
very flat and gently sloping towards the southwest, of old irrigation canals and hillocks; locally called
with average gradient of 1.1 m/1 km. The sheet run-off “Tells” which were ancient populated areas also called
plain is generally barren land; however, dense natural “Ishan.”
vegetation is grown alongside its boundary with the (iii) Adhaim River. This flood plain occupies the
alluvial fans [74]. northeastern part of the main f lood basin. Hamza
Flood plains. The flood plains of Euphrates, Tigris, (1997) [33] considered it as an alluvial fan (Adhaim
Shatt Al-Arab, Diyala, Adhaim rivers, and foothill riv- Fan) and the authors adopted Hamaza’s opinion
ers (wadis) are the major morphologic features of the (Fig. 3). Adhaim River had deposited four stages of
Mesopotamian Plain system and cover the majority of flood plain; the highest (older) stage has only wide
the plain. They differ in aerial extension, surface relief, extensions, whereas the others are restricted inside
and nature of development. the valley.
(i) Euphrates River. The upper reaches of the flood (iv) Diyala River. This flood plain is a flat terrain,
plain of the Euphrates River, near Al-Ramadi city very gently sloping towards south and southwest. Two
GEOTECTONICS Vol. 55 No. 1 2021
140 SISSAKIAN et al.
stages of flood plains are developed, the surface of the Units of Marine Origin
higher one, which is the most extensive is around 5 m,
whereas the second is around 3 m, above the present Only two units of marine origin are developed in
river level. the extreme southern parts of the Mesopotamian
Plain. They are described briefly hereinafter.
(v) Foothill rivers (wadis). Many foothill rivers (1) Tidal flat. The coastal muddy shore of the head
form distinct flood plains. They are developed in two of the Arabian Gulf is the tidal flat, which occupies the
stages: intertidal zone between the high and low tides, which
First, the higher stage forms the majority of the ranges between (1–1.5) m. The active tidal zone
flood plain system; its surface is (6–8 m) above the extends along the coast from Al-Fao to Um Qasir.
river level. The natural levees laterally pass to the (2) Tidal channels (creeks). These are one of the
sheet-run off plains. expressive degradational geomorphic features; the
Second, the flood plains are terminated in form of tidal channel system of Khor Al-Zubair. This system
small fan shaped deltas at the ends of river courses in resembles a course of meandering river and system of
shallow depression. dendritic tributaries; some of them suffer from the
Neotectonic activity where clear differences can be
(vi) Shatt Al-Arab. Shat Al-Arab is formed from seen through 50 years (the age differences is between
the joining of both Tigris and Euphrates Rivers after the two images). The tidal channels are the result of
leaving the marshes at Al-Qurna town (Fig. 2). It is both lateral and vertical marine water erosion effect into
rimmed by low natural levees of 1 m height above the unconsolidated sediments, mainly due to tidal action.
water level. Downstream of Basra, the flood plain However, Neotectonic activity cannot be disregarded
passes into estuarine sabkhas, on the right bank and the [66, 67] as can be seen from many indications (Fig. 5,
flood plain of Karoon River on the other side (Fig. 2). Points A-A1, B-B1 and C-C1). The tidal channels are
Two abandoned river troughs west of Shatt Al-Arab narrow and gradually widen towards the main chan-
flood plain are conspicuous morphologic features nel, Khor Al-Zubair, which reaches 1 km, in width.
most probably representing the former courses of
Shatt Al-Arab. The width and alignments of both
troughs are good indications for migration of the Shat Units of the Aeolian Origin
Al-Arab due to Neotectonic activity [70].
Only three units of the Aeolian origin are devel-
oped in the Mesopotamian Plain, especially in dry and
Shallow Depressions barren lands. These are sand dunes (Fig. 4), sand
sheets, and nebkhas.
One of the common morphological features in the
Mesopotamian Plain is the very flat and smooth shal-
low depressions. Their coverage areas vary from few Units of Degradational Origin
hundred square meters to many hundreds square kilo- The units are the result of fluvial or the Aeolian
meters. The more extensive shallow depressions are deflation; only two units are developed in the Meso-
those situated near the contact between the Mesopo- potamian Plain. These are fluvial degradational forms
tamian Plain and the Western and Southern deserts and the Aeolian deflation forms.
following Abu Jir Active Fault Zone; mainly repre-
senting sag depressions indicating Neotectonic activ-
ity. The largest one is Al-Slaibat Depression (Fig. 4). Units of Anthropogenic Origin
Marshes (ahwar) and lakes. In the northern and The Mesopotamian Plain was the cradle of civiliza-
central sectors of the Mesopotamian Plain, there are tion. Therefore, a lot of anthropogenic forms are pres-
many individual marshes and lakes (Fig. 4). The ent because of ancient human’s activities. These geo-
marshes and lakes system of the southeastern part of morphic forms are: irrigation canals, ancient settle-
the Mesopotamian Plain are rather complicated, and ments and artificial tells (hillocks). The irrigation canals
might be developed and survived not only due to tec- often form elongated earth dykes with variable lengths.
tonically active subsiding land [70]. Many researches An exceptional long and historical irrigation canal is Al-
[49, 64, 76] confirmed that the marshes region has Nahrawan Canal. It is considered as the longest, deep-
been more influenced by eustatic sea level changes and est, and largest irrigation canal ever built in the history
deltaic progradation, rather than tectonic events. The [19, 74]. Many isolated “tells” (hills) are distributed in
marshes are distributed on three main areas, named: the Mesopotamian Plain. Some of the prominent tells
Hor Al-Huwaizah (east of the Tigris River), Central reach the height of 10 m and cover an area of few square
Marshes (west of the Tigris River) and Hor Al-Ham- kilometers. Such tells are concentrated in groups, corre-
mar (south of the Euphrates River) (Fig. 4). The water sponding to main archeological sites (or buried settle-
depth varies from few decimeters to 2 m, exceptionally ments), like Babylon, Nippur, Al-Warka, Uruk, and Ur,
reaches (3–4) m, in Al-Hammar Lake. Erido [74] (Fig. 6). These settlements may indicate the
GEOTECTONICS Vol. 55 No. 1 2021
GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 141
(a) (b)
C
C1
A A1
B B1
2 km
Fig. 5. Tidal channels system of Khor Al-Zubair. (a) Aerial photograph (after [32]); (b) Satellite image (after [79]). Differences
due to the Neotectonic activity: points A, B, C, A1, B1, and C1.
extension of the gulf inside the Mesopotamian Plain; (2) Dibdibba Formation (Pliocene-Pleistocene).
representing the shore line [71]. The formation consists of sand and sandstone;
together with gravels. The age of the Dibdibba Forma-
tion is not ascertained yet (in Iraq), Sissakian and
STRATIGRAPHY Fouad (2012) [68] suggested Pliocene–Pleistocene
age depending on the age of the Bai Hassan Formation
Most of the previously carried out works confirm which is it age equivalent in the southern part of Iraq.
that the Stratigraphy of the Mesopotamian Plain is
limited to the Pleistocene Period, among them are: (3) Mahmudiya Formation (Pliocene-Pleistocene).
Jassim et al. (1984, 1986 and 1990) [42–44]; Yacoub The Mahmudiya Formation consists of alternation of
(2011b) [75] and Sissakian and Fouad (2012) [64]. sand, silt and clay, with thin intercalations of marsh
However, some of the sediments such as Al-Fatha and lake horizons. The maximum thickness of the
Alluvial Fan, Al-Batin Alluvial Fan and other alluvial Mahmudiya Formation is 54 m, in a borehole drilled in
fans located along the eastern limits of the Mesopota- Hor Al-Dalmaj area, west of Kut city (Figs. 2 and 7).
mian Plain, and the first stage of terraces of the rivers The thickness decreases to less than 20 m on the west-
may have sediments older than the Pleistocene and ern margin of the Mesopotamia Fluvial Basin.
grade up to Late Pliocene. This assumption is sug-
gested according to the age of the Bai Hassan Forma-
tion (Pliocene–Pleistocene); since the rocks of the Pleistocene Sediments
Bai Hassan Formation are almost equivalent to the
oldest sediments of the above mentioned geological The Pleistocene Period, in the Mesopotamia Plain
units. It is worth to mention that due to lack of absolute was characterized by glacial and inter-glacial phases.
dating technique in Iraq; therefore, the used ages are The climatic oscillations with the Neotectonic activity
assigned depending on global events. However, some played an important role in the development of the
paleontological data are uses in dating, especially ostra- fluvial sediments in the Mesopotamian Fluvial Basin.
cods [42]. The geological units of the Mesopotamian The upper contact with the overlying Holocene sedi-
Plane are presented in Fig. 7, and are described briefly ments is diachronous and is not always clear. Three
mainly based on Yacoub (2011b) [74]. types of Pleistocene Period sediments are developed in
the plain. These are briefed hereinafter:
Sediments of the Mesopotamian fluvial basin. These
Pliocene-Early Pleistocene Rock Units sediments comprise of pebbly sand and sandy gravels,
Three rock units are exposed in the Mesopotamian sands, silts and silty clay, with prevailing sands fol-
Plain (Fig. 7). These are briefed hereinafter: lowed by silts. There is an impressive and traceable layer
of brown silty clay which has been considered as the top
(1) Bai Hassan Formation (Pliocene-Pleistocene). of the Pleistocene sediments, across the whole Meso-
The formation consists of alternation of conglomer- potamia Fluvial Basin by Yacoub et al. (1981) [76]. The
ate, claystone, pebbly sandstone, and siltstone. The thickness of the Pleistocene sediments across the Mes-
exposed thickness of the Bai Hassan Formation is opotamia Basin ranges from (40–174 m), the maxi-
highly variable. Hamza et al. (1990) [54] measured mum being located in Hor Al-Shuwaicha north of Kut
11.5 and 16 m in northeast of Tikrit city. city (Fig. 7).
GEOTECTONICS Vol. 55 No. 1 2021
142 SISSAKIAN et al.
Samarra Diyala River
Euphrates R. Baghdad
1
2 T. Uqair T. Jemdet Nasr
Sippar
Karbala 3: Kish
5: Mashkan-shapir
Babylon
Kut
Borsippa 2 Tigris River
Najaf Adab Susa
4 Amara
Nippur 8
Isin Umma
Karun-Karker R.
Shurrupak 6 9: Girsu
Samawa 10: Lagash
7: Uruk 11: Nina-Sirara
Larsa Nasiriya Quma
T. ‘Ubaid 12 13
Basra
Eridu Ur T. Lahm
Shatt al-Arab
10 50 100 200 km
Modern city Arab-
Modern watercourse Persian
Gulf ca. 4000 BCE Gulf
Fig. 6. Major archeological sites of the Mesopotamian Plain showing some archeological sites and hypothetical extent of the Per-
sian Gulf ca. 4000 B.C. (after [11, 63]).
Alluvial Fan Sediments reen Mountain and reaches almost the Tigris River in
the south (Fig. 3). The sediments are fine sand and silt
These sediments are the oldest Quaternary sedi- with lenses of fine conglomerate. The thickness of the
ments within the Mesopotamian Plain (Figs. 3 and 7). fan sediments is not recorded, but the authors believe
Four alluvial fan systems are developed surrounding it ranges from (5–5) m.
the Mesopotamian Plain. They are briefed hereinafter
and some of them are presented in Fig. 7. (iii) Diyala. It is a very large individual alluvial fan
deposited by Diyala River after leaving Himreen
(1) Northern alluvial fan system of the Mesopota- Mountain and reaches almost the Tigris River in the
mian Plain. Three main individual alluvial fans are south (Fig. 3). The sediments are fine sand and silt
developed within this system, besides the fans which with lenses of fine conglomerate. The thickness of the
merge laterally together to form Bajada along the foot- fan sediments is not recorded, but the authors believe
hills of Himreen Mountain: it ranges from (5–25) m.
(i) Al-Fatha. It is a huge alluvial fan in the north- (2) Eastern alluvial fan system of the Mesopota-
ern part of the Mesopotamia Plain (Figs. 3 and 7). mian Plain. This fan system includes all fans that are
The sediments are subdivided into two main litho- developed alongside the northeastern and eastern
logical units [78]. The lower unit is mostly gravels margins of the Mesopotamian Plain (Figs. 3 and 7).
and conglomerate, whereas the upper unit is gypcrete These sediments consist of unsorted and massive
and gypsiferous clastics unit. The thickness of these gravel beds with sand or mud matrix. The exposed
sediments ranges from (12–20) m, but may reach 40 m, thickness of the individual alluvial fan, along the banks
in Abu Dalaf vicinity north of Samarra city (Fig. 7). of the foothill rivers, reaches (5–6) m, however, the
The age of Al-Fatha Alluvial Fan is considered as the total thickness may reach 10 m and more. The age of
Pleistocene. the first four stages is considered as Pleistocene,
(ii) Al-Adhaim. It is a very large individual alluvial whereas the fifth stage represents the recent and sub-
fan deposited by Al-Adhaim River after leaving Him- recent fan sediments of the Holocene age.
GEOTECTONICS Vol. 55 No. 1 2021
GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 143
350
Tikrit 0 17.5 35 70 105 140 175 210 km
Adaim River
Al-Fatha
Aluvial Fan
Samarra
340
Mandali
Badra
Baghdad
Jabbab River
330
Karbala Kut
Al-Teeb
320 Najaf Diwaniya
Amara
Samawa
Nasiriya
310 Qurna
Hor-Al-Hammar
A
Aluvl-Batin Basrah
ial F
an
300
430 440 450 460 470 480
Quaternary Sediments Geological Formations
Aeolian Tidal Flat Dibdibba
Flood Plain Inland Sabkina Bai Hassan
Crevasse Splay Sheet Run-off Mukdadiya
Depression Fill Gypcrete Injana
Active Marsh Alluvial Fan Nfayil
Dry Marsh Al-Fatha Fan Conglomorate Fatha
Estuarine Sabkina
Fig. 7. Geological map of the Mesopotamian Plain (after [75]).
(3) Western alluvial fan system of the Mesopota- role in the development of these fans by changing the
mian Plain. This system is represented by three main gradient of the valleys due to activity of the fault.
alluvial fans; deposited at the peripheral parts of the
Western Desert [73, 77] (Figs. 3 and 7). The fans are (4) Southern alluvial fan system of the Mesopota-
Ramadi alluvial fan, Alluvial fan of Karbala-Najaf mian Plain. This system is represented by two main
Plateau, and Habbariyah Alluvial Fans. alluvial fans; deposited at the peripheral parts of the
The tectonic effect of the Abu Jir-Euphrates fault Western Desert. The fans are: alluvial fans of Al-Slai-
zone (apart from Ramadi fan) may also has played a bat Depression and Al-Batin alluvial fan.
GEOTECTONICS Vol. 55 No. 1 2021
144 SISSAKIAN et al.
N
0 50 km Samawah Nasiriyah
Al-Staibat W E
31° Depression
Al-Batin Alluvial Fan S
A
Ira
Al-Salman Basrah
Stag
n
Stag e1
e2
Stag
e3
30°
Sta
ge
4
Ira
q
Ku
wa Kuwait
it
Sa
29° ud
iA
rab Sa
ia ud
iA
rab
B ia
44° 45° 46° 47° 48°
Fig. 8. Al-Batin alluvial fan (after [70]). Note the transversal fault A–B and the dissected lineaments. Gradient map of the Global
Multi-resolution Terrain Elevation Data 2010 (GMTED2010) 7.5arc-second spatial resolutions (after [70], modified).
The desert valleys which have deposited these fans River Terraces
show no abrupt change in slope and the deposition is The river terraces include:
a result of the change in channel width and loss of the
(1) Euphrates River Terraces are well developed
load volume; as the stream flows out over the fan [18]. along the cliffs bordering the river flood plain; from
However, the tectonic effect of the Abu Jir-Euphrates Ramadi to east of Falluja, and further to southeast in
Fault Zone may also play an important role in the Iskandariyah vicinity (Fig. 7);
development of these fans. The three main fans are
described hereinafter: (2) River terraces developed in the eastern margin
of the Mesopotamia Plain.
(i) Alluvial Fans of Al-Slaibat Depression. These The lithology of the terraces differs at different parts
are located south of Nasiriya city deposited by differ- of the plain. This is attributed to the exposed rocks in
ent valleys such as Al-Qusiar, Sdair, Ghwair valleys the catchment area, river size and its location inside the
which drain large parts of the Southern Desert into plain. The terraces of the Euphrates River consist of
the Al-Slaibat Depression which is a sag depression highly gypsiferous gravely sand. The age is Early Pleis-
along the active Abu Jir Fault Zone (Fig. 4). They tocene. The higher terrace of the Diyala River is com-
comprise of fairly cemented gravels rich in carbonate posed mainly of carbonates and chert with rare sand-
rock fragments. The age of the sediments is consid- stone, igneous and metamorphic rocks. The age is Mid-
ered as Late Pleistocene, according to their geomor- dle Pleistocene. The presence of the stages deduces big
phological position. climatic oscillation during the Pleistocene and associ-
ated with continuous subsidence of the Mesopotamia
(ii) Al-Batin Alluvial Fan. It is an ideal alluvial fan fluvial basin [75]. The age estimation depends on global
of a desert plateau with distinct four stages. The events and as correlated with the sediments of the Bai
feeder channel of the fan is wadi (valley) Al-Batin Hassan Formation of Pliocene–Pleistocene age.
(Fig. 8). The fan consists of gravely sand and gyp- Pleistocene-Holocene sequence. The sedimentary
crete. The coverage area of the fan is about 10842 km2. units of this sequence have different origins, such as flu-
The exposed thickness of the fan sediments reaches vial, deluvio–fluvial and evaporitic. Three different
up to 10 m, its age is Pleistocene [5]. The four stages units are developed; they are mentioned hereinafter.
of the fan (Fig. 9) can be correlated with the four
alluvial fan stages of the Eastern Mesopotamia Plain
Fans System. The western limits of the fan are dis- Sheet Run-off Sediments
sected by a transversal fault which also dissects three The sediments consist of alternating of sand, silt
NW-SE trending lineaments indicating the Neotec- and silty clay. The thickness of these sediments ranges
tonic activity (Fig. 8). from (1–15) m. The sheet run-off sediments are con-
GEOTECTONICS Vol. 55 No. 1 2021GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 145
44°59′24″ E 45°16′48″
S.Sh.
S.D. Eup
hra S.Sh.
tes R
iver
31°19′12″ Sawa Samawah
N Lake
S.Sh.
S.D.
Samwa
Cement Plant
31°12′54″
0 2.5 5.0 km S.D.
Fig. 9. Satellite image [79] showing creeping of sand dunes (S.D.), sand sheets (S.Sh.)
nected originally with the alluvial fans and foothill flu- During the late Holocene, the irrigation artificial
vial system (Fig. 7), in addition to the sheet wash activ- canal systems have greatly influenced the flood plain
ity [75]. sediments and were contaminated by reworked sands
(1) Slope sediments. In the eastern margin, the slope and silts. Both ancient and modern river branches of
sediments consist of gypsiferous sand and loam with the Tigris and Euphrates rivers are bifurcated at the
gravels and rock fragments with thickness of (3‒4) m. lower parts of the plain, forming extensive deltas/cre-
Whereas in the western margin they consist of pebbly vasse splays along the northern and western margins of
coarse grained sands with thin lenses of brown silty clay, the marshes in the Southern Mesopotamia Plain [75].
and Aeolian admixture; with thickness of (0.5–2) m. The flood plains of the main rivers Euphrates, Tigris,
and Shat Al-Arab are briefly described hereinafter:
(2) Gypcrete. The gypcrete is often developed on the (i) Euphrates River flood plain. It consists mainly
top of the Pleistocene sediments, such as river terraces of silty clay with few pebbles. The silty clay is brown
and alluvial fans, or mantling the Late Neogene forma- with common massive bedding, and is rich in second-
tions, surrounding the Mesopotamia Plain (Fig. 7). ary salts. Marsh deposits also occur indicating the
Gypcrete is highly gypsefoerous soil, well compacted presence of shallow depressions which were filled bt
and hard, usually (0.3–4) m in thickness. these deposits.
(3) Holocene sequence. The majorirty of the (ii) Tigris River flood plain. It consists of muddy
Mesopotamia Plain is covered by Holocene sedi- sand, fine to medium and even coarse grained.
ments (Fig. 8). They represent the uppermost Between Baiji and Samarra towns, pebbles occur too.
sequence (about 15–20 m) of the Quaternary sedi- Southwards, the sediments are greatly influenced by
ments of the Mesopotamia Basin. The Holocene the sediments provided by Adhaim and Diyala, and
started (11700 years ago) after the end of the last plu- foothill rivers. The crevasse splay sediments are well
vial phase of the Pleistocene, which was marked by a developed and cover extensive areas (Fig. 7). The sed-
considerable warming up of the climate. Eight differ- iments are composed of fine to medium sand with less
ent lithological units are developed within the Holo- silt and mud.
cene Sequence (Fig. 7), they are briefed hereinafter: (iii) Shatt Al-Arab flood plain. It consists of silty
(4) Flood plain sediments. These sediments are the clay and clayey silt. Whereas, downstream from Basra,
most widely spread over the Mesopotaimian Plane Shatt Al-Arab receives sediments mainly from Karun
(Fig. 7) forming the flood plain sediments of the rivers River.
Euphrates, Tigris, Diyala, Adhaim and foothills
streams (rivers and or wadis) built up vast flood plains
in the Mesopotamia Plain. The sequence consists of Shallow Depression Fill Sediments
alternation of sand, silt and silty clay, which are verti- These sediments represent the infilled sediments in
cally and horizontally interfingering by gradual to shallow depressions in the lower parts of the Meoso-
abrupt boundaries. Marshy horizons exist within the potamian Plain [75]. These sediments differ in dimen-
subsurface sequence of the flood sediments. The aver- sions and geomorphic position and in origin as well.
age thickness of the sediments is (15–20 m). These sediments are generally fine silts and clays,
GEOTECTONICS Vol. 55 No. 1 2021146 SISSAKIAN et al.
grayish brown and greenish grey colored. The high stratigraphic units: lower fluvial sandy unit, estuarine/
biological activity is a characteristic feature repre- marine unit, and upper fluvial-lacustrine unit.
sented by moderate amount of mollusk shells and (5) Anthropogenic and irrigation canal sediments.
humificated organic matter. The thickness of these The main effective human activities on these sediments
sediments does not exceed 1 m and the age is Holo- in the Mesopotamia Plain are the irrigation canal sys-
cene. Local marshes could be developed in central tem (both ancient and recent), ancient settlements, and
parts of some depressions, where enough supply of artificial tells (hillocks). They are mainly concentrated
water is available to keep the growth of marsh vegeta- in the ancient cities and along the main abandoned river
tion [75]. courses and/or irrigation canals (Fig. 6). The sediments
(1) Marsh and lake sediments. The modern consist of fine clastics of different origins, mixed with
marshes and lakes represent significant sedimentary brick and pottery fragments. The irrigation canal sed-
environments in the southern part of the Mesopota- iments consist of coarse grains; the thickness does not
mian Plain. They cover vast areas in the southern part exceed 1 m; but may reach several meters. Since the
of the Mesopotamian Plain (Fig. 7). The thickness of Old Sumerian (2400–2000 B.C.) or may be back to
the marsh and sub-marsh soil does not exceed one Early Dynastic Period (3000–2300 B.C.), the irriga-
meter, but locally reaches more than one meter. The tion canals were existed in the Mesopotamia Plain on
age of the modern marsh sediments is late Holocene a very primitive stage [39]. The major canal systems
they were developed after the last retreat of the Holo- were existed with high degree of prosperity during the
cene sea (2900 ± 550 years B.P. [7]). The presnt fauna Sassanian (226–636 A.D.) and the Abbasid times
in these sediments represent fresh stagnant water, in (636–1700 A.D.); the bulk of the preserved ancient
shallow aquatic environment. Three types of sedi- canals in the Mesopotamia Plain belong to more
ments are developed, these are marsh sediments, fresh recent time interval.
water lake sediments, and salt water lake sediments. (6) Aeolian sediments. The Aeolian sediments of
(2) Inland Sabkha. The main inland sabkhas are different forms are characteristic of the arid and semi-
restricted to the shallow depressions; especially those arid climatic conditions, which were prevailed during
located along the western and southern margins of the Holocene Epoch. Their influences have increased,
Mesopotamian Plain (Fig. 7). Generally, most of sab- especially during the Late Holocene, and recently
khas are rich in sulfates, mainly gypsum. The sabkha became more effective. The Aeolian sediments are
consists of vary-colored fine clastics dominated by widely spread in the Mesopotamian Plain; as a thin
reddish brown silty clay with powdered gypsum layers discontinuous sand sheet, Nabkhas and as large sand
(5–10 cm thick). The thickness of Sabkha sediments is dune fields. In the Mesopotamia Plain, three Aeolian
less then 0.5 m and may reach to more than 1 m [75]. fields are developed (Figs. 7 and 9). The thickness of
the sand sheets does not exceed one meter. Whereas,
(3) Estuarine and marine sediments. The extremely the thickness of Barchan fields reaches 5 m, and
southeastern part of the Mesopotamia Plain (Fig. 7) exceptionally may attain (25–30) m, in southwest of
represents the coastal region at the head of the Ara- Samawa city (Figs. 4 and 9). The bulk of the Aeolian
bian Gulf. It is characterized by three main sedimen- sediments are accumulated during the late Holocene,
tary environments, these are: f luvial plain of Shat Al- and may be slightly earlier. The influences of the wind
Arab and Karun River sabkha, estuarine sabkha, and activities are intensively increased during the last four
tidal f lat. decades. Accordingly, large rural and agricultural lands
The age of these sediments is probably late Holo- were effected (Fig. 9) causing one of the serious desert-
cene and continue to recent time; as indicated from ification problems in the whole Mesopotamian Plain.
scattered marine fauna and brackish water mollusks
and small oysters [75].
TECTONICS, STRUCTURAL GEOLOGY
(4) Subsurface estuarine/marine sediments. The AND NEOTECTONICS
complete Holocene sequence of sediments is pre- OF THE MESOPOTAMIAN PLAIN
served in Amara, Nasiriyah and Basra areas (Fig. 7).
The contact between the Holocene and Pleistocene Tectonics and Structural Geology
sediments is based on a brown silty clay with coarse Mesopotamian Plain is a part of The Mesopota-
crystalline gypsum of f luvial origin [75]. These sedi- mian Foredeep which is a part of Zagros Foreland
ments consist of fine to medium grey; alternated with Basin including the Zagros Fold-Thrust Belt. The
brownish and greenish grey silty clay and clayey silt. plain is a large continuously subsiding basin since the
The thickness of these sediments is (5–12) m. The Upper Miocene (11.62 Ma), it is covered by thick Qua-
age of these sediments is the Holocene, depending ternary sediments [50, 68]. Therefore, the plain shows
on the faunal assemblages [35]. However, Aqrawi no structural features on the surface, except a main
(1993 and 2001) [7, 8] using C14 dating determined fault escarpment that extends from south of Al-Najaf
8350 ± 230 years B.P., which means Middle Holocene. city to south of Nasiriya city [67, 68]. However, the
The Holocene sediments are divided into three litho- rolling topography, in the northern parts of the plain
GEOTECTONICS Vol. 55 No. 1 2021GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 147
indicates subsurface anticlines that are still rising up, tonic divisions of Iraq, and considered the present day
such as Balad, Samarra, Tikrit, and Baiji anticlines [2]. “Mesopotamia Plain” as the entire Mesopotamian
The Mesopotamian Plain forms the central and the Basin. Actually, the Mesopotamia Foredeep (Basin) is
southern parts of Iraq (Fig. 1). Many researchers like larger than that of the Mesopotamian Plain, which
Dunnington (1958) [25]; Ditmar (1971) [24]; Iraqi– forms only a part of the basin. The present day Meso-
Soviet Team (1979) [38], and Buday (1980) [15] con- potamia Foredeep (Basin) extends from northeast
sidered the plain as a part of the Unstable Shelf of the Syria to the Straits of Hormuz. It consists of two
Arabian Platform. Buday and Jassim (1984 and 1987) domains, the first is terrestrial and covers parts of
[16, 17] referred to this area as the Mesopotamian northeast of Syria, Iraq, and parts of Kuwait and the
Zone considering it as a separate structural unit within coastal plains of Iran. The marine is represented by the
the Unstable Shelf (Fig. 10a). Al-Kadhimi et al. (1996) Arabian/Persian Gulf Basin (Berberian, 1995 [6];
[3] followed almost Buday and Jassim (1987) [17] in Alshrhan and Nairn, 1997 [12]; Brew, 2001 [14]; Shar-
their tectonic divisions of Iraq (Fig. 10b). Jassim and land et al., 2001 [65]; Alavi, 2004 [1] and Fouad and
Goff (2006) [41] considered the Mesopotamian Zone Nasir, 2009 [30]). The current authors would like to
as a part of the Stable Shelf of the Arabian Platform clarify the statement of Fouad (2012) [29] by referring
(Fig. 10c). However, Fouad (2012) [29] considered the to Figure 1 from our research that illustrates the Mes-
Mesopotamian Plain within the Outer Platform opotamia Foredeep and the Mesopotamian Plain
(Unstable Shelf) of the Arabian Plate (Fig. 10d). It is (Fig. 1).
worth to mention that in all considered tectonic divi-
sions of Iraq the Mesopotamian Plain is considered to Neotectonics
represent the entire Mesopotamia Basin (or foredeep)
(Fig. 10). We adopted the opinion of Fouad (2012) [29] Generally, in Iraq the concept of Obruchev (1948)
in considering of the Mesopotamian Plain (Fig. 10d) [60]; Pavlides (1989) [61], and Koster (2005) [47] is
as a portion of the major Mesopotamia Foredeep considered in defining the Neotectonic movements.
(Figs. 1 and 10). Sissakian and Deikran (1998) [67] adopted the opin-
ion of Obruchev (1948) [60] and constructed the Neo-
Mesopotamian Plain is a part of the Mesopota- tectonic Map of Iraq. The constructed map shows that
mian Foredeep which is a part of Zagros Foreland the Mesopotamian Plain is a subsiding basin. The
Basin including the Zagros Fold–Thrust Belt [28], basin has NW-SE trend with oval shape. The maxi-
which is the product of the structural deformation of mum subsidence in the basin is about 3000 m as mea-
the Zagros Foreland Basin, whose present day rem- sured on the top of the Fatha Formation (Middle Mio-
nant is the continental Mesopotamia and the Marine cene). The subsiding basin extends from east of Al-
Persian Gulf Basin [6, 12, 28, 29]. The Mesopotamia Khalis town, for about 30 km, to west of Badra town,
Foredeep is a continental basin which lies between the for about 10 km (Fig. 11).
Zagros deformational front fro and the stable interior
part of the Arabian Platform [28]. The Mesopotamia The basin is asymmetrical with very steep eastern
Plain occupies the central and the southern parts of rim. This asymmetry is a typical of foreland basins
the Mesopotamia Foredeep within Iraq. It is a depo- formed due to the plate collision manifesting the shape
center due to subsidence in the Neogene, and a signif- of the subsiding foreland basin formed due to the colli-
icant basin of alluvial sediment accumulation in the sion of Arabian and Eurasian Plates in front of the rising
Quaternary, with maximum estimated subsidence to Zagros Mountain. Such asymmetry also indicates tec-
be about 3000 m [67]. tonic tilting of the basin [62]. The length of the basin, in
Iraq is about 540 km, whereas the width is variable; it is
Three genetic types of folds (which are developed 80 km, in the extreme northern part, 200 km between
in the extreme southern part of Mesopotamia Plain) Hilla city and Badra town, 230 km between Samawa
occur in the Mesopotamia Plain [28], these are fault- city and Ali Al-Gharbi town, and 40 km near Basra city
related folds, simple buckle folds, and north–south (only the included part in Iraq) (Fig. 11).
trending folds.
There are many uplifted areas within this huge con-
These folds are following the old inherited fractures tinuously subsiding Mesopotamian Basin which are
of N-S Arabian trend. They are long, broad and with still active indicating the Neotectonic movements.
low amplitudes; such as Zubair and Rumaila structures. However, these areas are not shown in Fig. 11 due to
However, according to Colman-Saad (1978) [22], the the scale limitations. These areas are evidenced by
folds are related to the movement of salt substratum. many Quaternary landforms, like topographic indica-
No surface indication exists to indicate faults in the tions, abandoned river channels, shifting of river
Mesopotamia Plain. However, the network of NW– courses, active and inactive alluvial fans. Such features
SE trending faults were developed in south of Bagh- are evidences for Neotectonic activities (Al-Sakini,
dad. These faults are of normal type and forming a 1993 [4]; Markovic et al., 1996 [52]; Mello et al., 1999
complex set of grabens; some of them were partially [58]; Kumanan, 2001 [48]; Bhattacharya et al., 2005
inverted, forming anticlinal folds [31]. Fouad (2012) [13]; Jones and Arzani, 2005 [45]; Philip and Virdi,
[29] relied upon that almost all of the mentioned tec- 2007 [62], and Woldai and Dorjsuren, 2008 [72]). The
GEOTECTONICS Vol. 55 No. 1 2021148 SISSAKIAN et al.
39 43 47 39 43 47
(a) Turkey (b) Turkey
37 37
Syria Syria
Iran Iran
33 Baghdad 33
Baghdad
Sa Sa
ud ud
ia ia
Ar Ar
ab ab
ia K 0 100 km ia K
29
0 100 km uw
29
uw
ai ai
t t
Eugeosyncline Miogeosyncline Geosyncline/Thrust Region
Eugeosyncline Miogeosyncline Eugeosyncline Unstable Shelf
Unstable Shelf Stable Shelf Miogeosyncline High Folder zone
High Folder zone Salman zone Stable Shelf Foothill zone
Foothill zone Rutba-Jezira zone Salman-Hadhar zone Mesopotamian zone
Maaniya-Rutba zone
Mesopotamian zone
39 43 47 39 43 47
(c) Turkey (d) Turkey
37 37
Syria
Syria
Iran Iran
33
Baghdad 33 Baghdad
Sa Sa
ud ud
ia ia
Ar Ar
ab ab
ia K 0 100 km ia K
29
0 100 km uw
29 uw
ai ai
t t
Unstable Shelf Stable Shelf Arabian Plate
Zagros Suture zone Mesopotamian zone Outer Platform Inner Platform
Mesopotamian Fore deep Western Desert Subzone
Imbricate zone Salman zone Basra Subzone Southera Desert Subzone
High Folder zone Rutba-Jezira zone Al-Jazira Subzone
Eurasian Plate
Foothill zone Western Zagros Fold-Thrust Belt Shalair
Low Folder zone Imbricat zone (Sanandaj-
Sujan)
High Folder zone Stature zone Terance
Fig. 10. Main tectonic division zones of Iraq. Fragments: (а) (after [16]), (b) (after [3]), (c) (after [61]), and (d) (after [4]), mod-
ified from [70].
majority of the uplifted areas, within the Mesopota- trend changes to NW-SE. Another fact is that the distal
mian Plain represent nowadays oil fields. Their trends parts of the majority of the alluvial fans, both active and
differ in the plain, in the southern part they have N-S inactive, which are developed in the eastern margin of
trend, whereas in the central and northern parts the the plain, are parallel to those uplifted areas [31].
GEOTECTONICS Vol. 55 No. 1 2021GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 149
43 44 45 46 47 48
35
Tikril
Eu
ph
ra
34
tes
Ri
Baghdad
ve
A
r
2 B
5 00
Ramadi 2
Baghdad Ti 000
gr
is
Ri 33
ve 150
r 0
Fialla
Karbala Kut
1
00
C
0
1 2 D
5
50 00
0
2 0 0
0
Najaf
50
Diwantiya 32
Amara
500 Contour lines of
Subsided areas
Samawa
Middle-Late Miocen Ze
ro 31
Sea Level Nasiriya
Thrust fault
Basrah
Abu Lir-Euphrates fault
100 km
30
A B C D
Zero
500 m
1000
1500
2000
2500
3000
100 200 km 100 200 km
Fig. 11. Neotectonic map of the Mesopotamian Plane and two cross sections A–B, C–D (after [67], modified).
Rate of the Neotectonic Movements Mesopotamian Plain (Fig. 11), we divided the plain
in the Mesopotamian Plane into five parts:
(1) the Eastern Edge which extends along the Iraqi-
Sissakian and Deikran (1998) [67] have calculated Iranian borders until the latitude 31° N;
the rate of the subsidence and uplift During the Neo- (2) the Northern Edge which extends few kilome-
tectonic period (11.62 Ma) in the whole Iraqi terri- ters north of the latitude 34° N;
tory depending on the constructed Neotectonic Map
of Iraq. The rate of subsidence in the Mesopotamian (3) the Western Edge which extends almost along
Plain was calculated by dividing the amount of the the Euphrates River until the latitude 31° N;
subsidence by the values of the maximum and mini- (4) the Southern Edge which extends south of the
mum contour values by 11.62 Ma (The age of the latitude 31° N;
Upper Miocene, I.C.S., 2012 [36]). In order to calcu- (5) central part which covers the area between the
late the rate of the subsidence in different parts of the Tigris and Euphrates rivers.
GEOTECTONICS Vol. 55 No. 1 2021150 SISSAKIAN et al.
Table 1. Amounts and rates of subsidence in the Mesopotamian Plain
Subsidence amounts and rates during
Neotectonic (11.62 Ma) Pleistocene (2.588 Ma) Holocene (0.0117 Ma)
Mesopotamian
subsidence (‒m) subsidence (‒m) subsidence (‒m)
Plain parts
min max amount amount
rate, mm/ years min max min max
750 2500
1 167.04 555.36 1.14 2.52
0.000635 0.000315
0 2000
2 0 445.44 0 15.2
0 0.000161
0 250
3 0 55.68 0 1.90
0 0.000215
0 250
4 0 55.68 0 1.90
0 0.000215
0 1000
5 0 222.72 0 7.60
0 0.000806
1—Eastern Edge, 2—Northern Edge, 3—Western Edge, 4—Sothern Edge, 5—Central part, (after [67]).
The minimum and maximum subsidence amounts are related to huge floods which back to tens of centu-
are recorder in the five parts of the Mesopotamian ries when the course (channel) of the river is changed,
Plain (Fig. 11 and Table 1). The minimum and maxi- especially in meandering areas. Another case is con-
mum rates of the subsidence during the Pleistocene and struction of irrigation channels during ancient civiliza-
Holocene periods are also calculated by dividing the tions (Ellison, 1978) [26].
subsidence amounts by the 2.588 and 0.0117 Ma which
are the durations of Pleistocene and Holocene, Among the main abandoned channels, is the chan-
respectively (I.C.S., 2012) [36] (Table 1). The Zero nel between the Tigris and Al-Ghar’raf rivers (Fig. 13).
line which represents the Middle Miocene level runs This abandoned channel is either the old course of the
almost along the Western Edge of the plain (Fig. 11). Tigris River or that of Al-Ghar’raf River. The authors
believe that the growing of the subsurface Ahdab anti-
cline was the main reason for abandoning of the chan-
Neotectonic Indications nel. Many authors (Al-Sakini, 1993 [4]; Mello et al.,
The following Neotectonic indications are recorded 1999 [58]; Bhattacharya et al., 2005 [13], and Philip
in the Mesopotamia Plain. and Virdi, 2007 [62]) recorded such cases as the Neo-
(1) Topographic indications. Samarra subsurface tectonic activity.
anticline (Fig. 12) is the most obvious topographic
indication in the Mesopotamian Plain for the pres- The Euphrates River also had abandoned its course
ence of a growing subsurface anticline. The area is in different places and more than once (Al-Sakini,
covered by Quaternary sediments (Sissakian and 1993) [4], he claimed two abandoned courses. The
Fouad, 2012) [88], but the presence of the anticline is first one is west and south of the present course.
proved by geophysical studies (C.E.S.A., 1992 [21] Whereas, the second one runs east of the present
and Al-Kadhimi et al., 1996 [3]). The morphology of course. For the former course, only small part is clear
the area indicates a double plunging anticline (Fig. 12). (Fig. 14). The authors found many indications for this
Such Quaternary landform is clear indication for the course (Fig. 14) which are far from the locations of
Neotectonic activity (Markovic et al., 1996) [52]. Erido and Ur archeological sites (Fig. 14). But, they
(2) Abandoned river channels. Abandoned chan- are supposed to be located along an ancient river (Elli-
nels of the Tigris and Euphrates Rivers can be seen in son, 1978) [26]. However, no clear indication can be
different places within the Mesopotamian Plain. The seen from the satellite images for this course, because
reason for abandoning the rivers their channels is a mat- the supposed course is either vanished by cultivation
ter of debate. In the Neotectonic view, it is attributed to or covered by the active sand dune fields, between
the growing of subsurface anticlines. However, some Diwaniyah and Nasiriya cities.
GEOTECTONICS Vol. 55 No. 1 2021GEOMORPHOLOGY, STRATIGRAPHY AND TECTONICS 151
43.36° E 43.54°
Al-Dawr
34.27°
N
1
34.15°
0 5 10 km
Samarra
Fig. 12. Satellite image [79] showing Samarra subsurface growing anticline. Black dash line with rombus is the axis of Samarra
anticline; number 1 in rectangle is the High way number; red cross is the center of the image.
Changing of the River Courses Figure 17 represents abandoned ancient courses. It
is very difficult to decide whether it belongs to the Tigris
The Tigris and Euphrates and their distributaries River or the Euphrates River, because it is almost in half
have changed their courses within the Mesopotamian distance between the present river courses. We believe;
Plain; the most significant changes were during the however, it most probably belongs to the Tigris River.
Holocene (0.0117 Ma). This is attributed to the fact The change in the course is due to the growth of the
that the indications for the changes of the courses subsurface Rafidain, Gharaf and Al-Nasiriya anticlines
during Pleistocene (2.558 Ma) are almost vanished (Fig. 15). Gharaf and Al-Nasiriya subsurface anticlines
due to weathering and erosional process, and man are south (out) of Fig. 17. Another possibility is the old
activities. course of Al-Gharaf River.
Many authors (mentioned above) have assumed Figure 18 represents abandoned ancient courses of
different changes in river courses; each postulated own the Tigris and Euphrates Rivers. Those which are east
opinion in reconstructing of ancient courses. Some of of the Longitude 45○18′ belong to the Tigris River,
them even presented the ancient courses. However, whereas those to the west belong to the Euphrates
Al-Sakini (1993) [4] presented excellent maps for the River. The change in the course of the Euphrates River
ancient courses of the Tigris and Euphrates Rivers. He is due to the growth of Al-Samawa subsurface anti-
assumed that all changes in the river courses are cline (Fig. 15) and active Abu Jir Fault Zone. Those of
attributed to the growing of subsurface anticlines in the Tigris River is not related to Neotectonic activities,
the Mesopotamian Plain which are shown in Fig. 15. since no subsurface anticline is recorded in the area
We have selected many examples from the ancient (Fig. 15). It may be an ancient irrigation channel, part
courses within the Mesopotamian Plain. However, of it is covered by active sand dunes field.
some of the abandoned river courses may represent Figure 19 represents abandoned ancient courses of
artificial irrigation channels constructed during Shat Al-Arab (the conflict of the Tigris and Euphrates
ancient civilizations (Ellison, 1978) [26]. rivers). Two main abandoned courses can be seen
Figure 16 represents abandoned ancient courses of indicating that Shat Al-Arab is moving eastwards. We
the Tigris River and its distributaries. We believe the believe it is due to the growth of the Siba subsurface
change in the course is due to the growth of the sub- anticline (Fig. 15). Sissakian et al. (2017) [70] also
surface Al-Dujail and Kumait anticlines (Fig. 15). The confirmed Neotectonic activity from the concerned
Kumait subsurface anticline is south (out) of Fig. 16. area as related to the upper reaches of the Persian Gulf.
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