Geomorphology, Stratigraphy and Tectonics of the Mesopotamian Plain, Iraq: a Critical Review

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: [email protected] 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 terraces. 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 geomorphological features indicate the Neotectonic activity in the plain, such as migrations of rivers due to growing of subsurface 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 different 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, terraces, 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 Ar Rutbah Karbaia Jordan 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 borders 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-

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40 42 44 46 N Turkey

Arbil 100 km 36 Syria Mosul Sulaimaniyah

Iran

34 Hor Al-Shuwaicha Falluja Baghdad

Iskandariya Hor Al-Dalmaj Hor Al-Sanaf H

Jordan 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

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43.25° E 45.75°

34.50° SSalahalah AAl-Dinl-Din 1 N 2 TharitarTharitar LLakeake

DiyalaDiyalaDiyalaDiyala GovernorateGovernorate HHitit RRamadiamadi 3 4 5 BaghdadBaghdad

32.75° 0 25 50 km KarbalaKarbala WasitWasit

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.

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4415 E4745 LorestanLorestan RRamadiamadi 3315 Al-Habbaniyah BBaghdadaghdad N Hor Al-Shuwaicha Iran

Al-Razzazah KKarbalaarbala WWasitasit IraqIraq Hor Al-Dalmay Al-QadisiyyahAl-Qadisiyyah Abu Jir NNajarajar Bahir MaysanMaysan Al-Najaf AAmarahmarah Hor Hor n Desert Al-Sanaf Active Fault zone Sand Al-Huwaiza Dunes An-NajafAn-Najaf i Wester SSamawahamawah Central 31 15 raq Marshes I DhiDhi QQarar NasiriyahNasiriyah Al-Slalbar Depresion Hor Al-Hammar

Southern Desert

Iraqi BBasrahasrah 03060 km BasrahBasrah

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 flood 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 developed in the Mesopotamian Plain, especially in dry and barren lands. These are sand dunes (Fig. 4), sand Shallow Depressions sheets, and nebkhas. One of the common morphological features in the Mesopotamian Plain is the very flat and smooth shallow 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 representing sag depressions indicating Neotectonic activity. 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

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(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 suggested 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).

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Samarra Diyala River

Euphrates R. Baghdad 1

2 T. Uqair Sippar T. Jemdet Nasr Karbala 3: Kish 5: Mashkan-shapir Babylon Kut Borsippa 2 Tigris River Najaf Adab Susa Amara Nippur 4 8 Umma Isin 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.

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350

TikritTikrit 0 17.5 35 70 105 140 175 210 km Adaim River

Al-FathaAl-Fatha AAluvialluvial FFanan SamarraSamarra 340

MandaliMandali

BBadraadra BBaghdadaghdad

330 Jabbab River

KarbalaKarbala KutKut Al-TeebAl-Teeb

320 NNajafajaf DDiwaniyaiwaniya AmaraAmara

SSamawaamawa NasiriyaNasiriya 310 QurnaQurna HHor-Al-Hammaror-Al-Hammar

Al-BatAl-B BasrahBasrah AAluvlu atinin viiaal Fan Fan

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.

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N Samawah Nasiriyah 0 50 km Al-Staibat W E 31° Depression Al-Batin Alluvial Fan S

A Iran Al-Salman Basrah Stage 1 Stage 2

Stage 3 30° Stage 4

Iraq

Kuwait KuwaitKuwait Saudi Arabia 29° Saudi Arabia

B 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-

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44°59′24″ E 45°16′48″

S.Sh. S.D. Euphrates River S.Sh. 31°19′12″ SawaSawa SamawahSamawah N LakeLake

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 2021 146 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: fluvial 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 flat. 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 fluvial 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 2021 GEOMORPHOLOGY, 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 divisions 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 opinion 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 2021 148 SISSAKIAN et al.

39 43 47 39 43 47 Turkey Turkey 37 (a) 37 (b)

Syria Syria

Iran Iran 33 Baghdad 33 Baghdad

Saudia Arabia Saudia Arabia

0 100 km Kuwait 0 100 km Kuwait 29 29

EugeosynclineMiogeosyncline 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 Turkey Turkey 37 (c) 37 (d)

Syria Syria

Iran Iran 33 Baghdad 33 Baghdad

Saudia Arabia Saudia Arabia

0 100 km Kuwait 0 100 km Kuwait 29 29

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 Al-Jazira Subzone Rutba-Jezira zone 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]), modified 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].

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43 44 45 46 47 48

Tikril

Euphrates River

A Baghdad B 2500

Ramadi 2000 Baghdad Tigris River 33 1500

Fialla Karbala 1000 Kut C 500 1500 2000 D 250 Najaf Diwantiya 32 Amara 500 Contour lines of Subsided areas Samawa Middle-Late Miocen Zero 31 Sea Level Nasiriya Thrust fault Basrah Abu Lir-Euphrates fault 100 km 30

ABCD 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.

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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 0445.44015.2 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 anticline 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.

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43.36° E 43.54°

AAl-Dawrl-Dawr 34.27° N

34.15°

0 5 10 km SamarraSamarra

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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N N 32.26° 32.30° N N KutKut

32.25° 32.24°

32.20° 32.22°

32.15°

32.20°

32.10° Al-HayAl-Hay

06312 km 0 1 2 4 km 32.18° 45°50′ 45°55′ 46°0′ 46°5′ 45°52′ 45°54′ 45°56′ E Fig. 13. Satellite image [79] showing abandoned courses of Al-Ghar’raf River (blue color on the right fragment); Ox-bow lake (white line on the right fragment); the enlarged red rectangle (the right fragment); approximate location of Ahdab subsurface anticline (white dashed line on the left fragment).

N 31°20′ N Al-SamawaAl-Samawa AAl-Khidhirl-Khidhir

31°10′ A

NasiriyahNasiriyah 31°00′ UUrr

B 30°50′ EriduEridu

30°40′ 10 km

45°10′ 45°20′ 45°30′ 45°40′ 45°50′ 46°0′ 46°10′ E 46°20′

30°54′ N 31°9′ N B A 30°51′ 31°6′

45°20′ 45°24′ 45°28′ EE46°9′ 46°12′ 46°15′ Fig. 14. Satellite image [79] of the Euphrates River between Samawa and Nasiriya cities (the authors’ interpretations). Note the abandoned river courses in two captions (A and B), and the locations of Eridu and Ur archeological sites. Approximate location of Al-Samawa subsurface anticline (white dash line).

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40 42 44 46

Supergiant Oilﬁeld Turkey Other Oilﬁeld Oil Pipeles

T1-2A Principle Gas Pipeles 36 Syria IT-2

Iran T1-1A K2

T-1 34 K3

Baghdad PS-4 Iraq Jordan 32

PS-3

PS-2 N 30 Saudi Arabia

100 km IPS-2 Kuwait

Fig. 15. Distribution of oil and gas fields along the courses of the Tigris and Euphrates rivers (after [46]). All the subsurface anticlines are oil fields.

Figure 20 represents abandoned ancient course of ties (cultivation) others are hindered by sand dunes, the Euphrates River. We believe it is due to the growth and others are very old; therefore, their traces are very of Al-Batin alluvial fan. Sissakian et al. (2017) [70] difficultly visible on satellite images. confirmed the Neotectonic activity of the Al-Batin alluvial fan’s area. Figure 21 represents abandoned ancient course of Umm Al-Binni Lake the Euphrates River. We believe it is due to the growth of the Al-Samawa subsurface anticline (Fig. 15) and The Southern Mesopotamia is characterized by the effect of active Abu Jir Fault Zone (Fouad, 2012) vast marshlands of shallow-water lakes and vegetated [29]. We also believe that Al-Slaiabt Depression is a mashes (locally called Ahwar) mostly covered by reeds remnant of an old marsh through which the Euphrates (Aqrawi, 1993 [7]; Aqrawi and Evans, 1994 [9]). River was passing; it represents a sag depression along Among those Ahwar, tens of open lakes of different the active Abu Jir Fault (Figs. 18 and 21). sizes and shapes are developed and scattered across the It is worth to mention that there are tens of aban- southern parts of the Mesopotamian Plain. One of doned river courses and/or ancient irrigation channels these lakes is called the Umm Al-Binni Lake (Fig. 22). within the Mesopotamian Plain. All of them belong to It is located about 40 km south of the Amara city and the Tigris River and its distributaries, and the Euphra- about 45 km north of the present confluence of the tes River, and very rarely to Shat Al-Arab (Fig. 19). Tigris and Euphrates rivers at Qurna Town. The centre Some of them are almost vanished due to man activi- of this lake is defined by 31°14′29″ N and 47°06′21″ E

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31°50′ Amarah N AR AR

AR 2

31°40′ 1

AR 3

04 8 16 km 46°50′ 47°00′ 47°10′ E

Fig. 16. Satellite image [79] showing river courses. Indicated: rivers (yellow numbers) Tigris (1), Al-Majar (2), Al-Kahla’a (3); abandoned river courses (AR), and approximate location of Al-Dujaila subsurface anticline (white dash line).

3200 Missan N

3150 AR Amarah

AR 3140

AR 3130

05 10 km 20 3120 4610 4620 4630 4640 4650 4700 E4710

Fig. 17. Satellite image [79] showing abandoned river course (AR), most probably of Al-Gharaf River. Approximate location of Rafidain subsurface anticline (white dash line); green dot is a small village. coordinates. The Umm Al-Binni Lake is, however, shape that contrasts with the shape of other sur- almost dry nowadays. rounded lakes in the region. Master (2001) [53] and The previous studies of the Umm Al-Binni Lake Master and Woldai (2004 and 2006) [55, 56] proposed mentioned that it is an impact of meteorite crater (e.g. that the alleged Umm Al-Binni impact had been Master, 2002) [54]. He suggested that this 3.4 km responsible for the sudden climate change and cata- diameter, dry lake may be a meteorite-impact crater strophic events around 2200 BCE; including the col- due its nearly circular and slightly polygonal rimmed lapse of the Sumerian civilization.

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N 3200 AR N Najaf

AR 3140

AR SD

3120 Samawa

3100 015 30 60 km 4420 4440 4500 4520 4540 E

Fig. 18. Satellite image [79] showing abandoned river course (AR) of the Tigris and Euphrates Rivers and large sand dunes field (SD). The the Abu Jir Fault Zone (red dash line).

4814 E

Al-SeebaAl-Seeba

AR AR

3114

N AR AR

AR 5 km

Fig. 19. Satellite image [79] showing abandoned river courses (AR) of Shat Al-Arab due to the growth of Siba subsurface anticline. Approximate location of Siba subsurface anticline (dash black line).

Sissakian and Al-Bahadily (2018) [69] investigated sidence of the basement faulted blocks, as the distribu- the origin of the Umm Al-Binni Lake using geophysi- tion of the lakes is mostly controlled by such basement cal data and remote sensing techniques. The results of tectonic zones of weakness. The straight northeastern magnetic and gravity analyses showed that the Ahwar and southwestern rims indicate that the lake is tecton- area of southern Mesopotamia, including the Umm ically controlled, and since the lake is developed in the Al-Binni Lake, was subjected to the differential sub- fluvial sediments of the Mesopotamian Plain of Qua-

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3040

N AR

3035

0 2.5 5.0km 10

4710 4715 4720 4725 E

Fig. 20. Satellite image [79] showing abandoned river course (AR) of the Euphrates River due to the growth of Al-Batin alluvial fan, note the ancient cliff of the river at two points (Cl). Black arrows point to the extension of the alluvial fan.

4600 E

NasiriyahNasiriyah AR 3100 N

SD AR

10 km

Fig. 21. Satellite image [79] showing abandoned river course (AR) of the Euphrates River. Note Al-Slaiabt Depression (SD) which was most probably an old marsh filling one of the sag depressions. ternary age; therefore, it is considered as the Neotec- a vast plain covered by Quaternary sediments; mainly tonic activity. fluvial origin with different types. The main fluvial types are the flood plain, terraces and alluvial fan sediments. The flood plain and alluvial fan sediments usu- CONCLUSIONS ally interfinger with each other. The eastern and south- The main conclusions from the current work can ern (Al-Batin) alluvial fans are of malty stage fans; be summarized as follows: The Mesopotamian Plain is whereas those of the northern (Al-Fatha, Al-Adhaim

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40 42 44 46

Turkey 47 05 42 47 06 47 E N N Arbil 100 km Syria Mosul 36 Sulaimaniyah 311518 Iran N

UB 34 Baghdad

Iraq Jordan 32 Al-Najaf 311330 500 m

Basrah 30 Saudi Arabia Kuwait

Fig. 22. (Left) Satellite image [79] showing the location of Umm Al-Binni Lake (UB); (Right) Geographic location of Umm Al-Bunny Lake. Red arrow points to the lake on the map [57]. and Diyala), western (Ramadi and Karbala–Najaf) The Mesopotamian Plain is a part of the Mesopo- fans are of single stage fans, all have typical fan tamia Foredeep of the Zagros Foreland Basin and is a shapes; except Ramadi fan which has longitudinal part of the Zagros Fold–Thrust Belt. The plain covers shape. This is attributed to the geomorphic nature of the central part of Iraq and extends south eastwards. It the surrounding areas of the fan which has limited is a large continuously subsiding basin since the Upper the fan’s shape; rather than the sediments size which Miocene (11.62 Ma). No structural features can be plays big role in shaping of the fans. In the extreme seen on the surface, except a main fault escarpment southern part, the tidal flat and sabkhas prevail cov- that represent Abu Jir Active Fault Zone. The rolling ering large areas between Shat Al-Arab and the Ara- topography, in the northern parts of the plain indicates bian Gulf. The Aeolian sediments also cover vast subsurface anticlines that are still growing up, such as areas in forms of sand dunes, Nebkhas, and sand Balad, Samarra, Tikrit and Baiji anticlines. Moreover, sheet; especially well developed between the Tigris many buried subsurface anticlines are present in dif- and Euphrates rivers. Due to climatic changes, the ferent parts of the plain which have contributed in coverage areas are extending forming desertification. changing the river courses; continuously. The Neo- The marshes are also special geomorphic forms being tectonic activities of the Mesopotamian Plain which deposited in special environment within the southern are everywhere in the plain. The maximum and min- parts of the Mesopotamian Plain. Their locations imum subsidence amounts in the plain are (<3000 were changed periodically with the changes of the and 2500>) m below sea level and (<250 and Zero>) m river courses and climatic fluctuations during Pleis- below sea level, respectively. The maximum and min- tocene and even Holocene. imum rates of subsidence during the Neotectonic period are (315.0 and 63.5 m/100 years X 10‒4), The Mesopotamian Plain is part of the large Meso- respectively. The plain is still active tectonically and potamia; it is continuously sinking basin filled mainly will continue in subsidence within the main Mesopo- by alluvial sediments. The flood plain sediments being tamian Foredeep in front of the rising Zagros Moun- the most abundant followed by alluvial fan sediments tains and being part of the Zagros Foreland Basin. deposited along the rims of the plain and some river terraces. In the extreme south eastern part of the plain, the tidal flat sediment and sabkhas are prevailing. ACKNOWLEDGMENTS Because the age of the oldest sediments of the plain are of Plio-Pleistocene age which is the same age of the The authors would like to express their sincere thanks to rocks which underlie the plain; like Bai Hassan, Dib- Prof. Vladimir G. Trifonov (Geological Institute of the dibba and Mahmudiya formations; therefore, the con- Russian Academy of Sciences, Moscow, Russia) for his tact between the sediments of the plain and underlying valuable and constructive comments which amended the geological formations remains not clear. paper.

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