Iraqi Bulletin of Geology and Mining

The geomorphology of the Iraqi Low Folded Zone (LFZ) is reviewed in the present article. Narrow, elongated and elevated mountainous chains with highly rugged terrain, and the wide gently sloping flat plains with local slight undulation represent the main topographic features of the LFZ. These features reflect the main geological structural relief's and the action of different geomorphologic processes. Moreover, the surface of the study area is dissected by complicated drainage patterns with variable density; they drain the study area towards the main streams and rivers, and then ultimately toward the Tigris River. The water flow erosion is dominant and active processes, beside less affectively wind erosion.
A simplified geomorphologic map of the LFZ is compiled. This elucidates the spatial distribution of the main geomorphologic units and related morphologic features. The geomorphologic units are classified genetically into seven classes, which include different landforms. The recognized genetic units are; Structural-Denudational, Denudational, Fluvial, Solution, Evaporation, Aeolian, and of Man-made origins. Each of these units include different lithomorphologic landforms, which were developed as a result of weathering, erosion and deposition processes, in conjunction with tectonic, structural, lithologic, and climatic factors.
The present study revealed that the geomorphologic evolution of the LFZ was greatly influenced by the last phase of intensive orogenic movement that took place during Late Miocene – Pliocene, and continued during Quaternary Period with less intensity. During the Quaternary Period, the climate became leading factor in controlling the majority of geomorphologic processes, particularly the fluvial. The Quaternary long-term climatic changes are deduced by well developed river terrace stages along the Tigris River valley, in particular.

The Low Folded Zone is an integral part of the Western Zagros Fold – Thrust Belt of the Iraqi territory. Field, seismic and well data have been integrated to interpret the structural styles and geometries of the folds and the associated structures and their variations across and along the zone. It is concluded that the mechanical properties of the folded sedimentary pile as well as the presence or absence of early formed structural lines of weakness have exerted first order impact on the nature of the folding and faulting processes and their subsequent evolution in this structural domain. Moreover, the classical structural – mechanical grouping of the Zagros stratigraphy in southwest Iran appears not uniform and may show significant variation in the mechanical properties. Therefore, it is found that this grouping might be partially applied in Kirkuk region of the Low Folded Zone, whereas it is totally inapplicable in Mosul region of the zone.

The stratigraphy of the Low Folded Zone, in Iraq is reviewed. The oldest exposed rocks are Late Cretaceous in age, which belong to the Shiranish Formation, whereas the youngest are of Pliocene – Pleistocene age, which belong to the Bai Hassan Formation. The exposed stratigraphical column is represented by 24 formations. Moreover, ten main types of Quaternary sediments, which have wide geographic extent, are reviewed too.
The Cretaceous and Paleogene rocks are mainly of marine carbonates with rare clastics, the Cretaceous rocks represent synrift sediments. The Early Neogene (Oligocene) rocks form a complex of reef – back reef – fore reef and are restricted almost in the eastern, central and western parts of the involved area, especially in Qara Chouq anticline, with other restricted exposures in different parts. The Early and Middle Miocene rocks are mainly of marine origin, lagoonal carbonates and evaporate, respectively. The Late Miocene rocks, which represent the beginning of the continental environment, together with the rocks of Pliocene – Pleistocene consist of molasse sediments, deposited in sinking foredeep. The Quaternary sediments are well developed, especially Pleistocene river terraces of different stages, and polygenetic sediments that fill the synclinal troughs, with other different types.
For each exposed formation, the type locality, exposure areas, subsurface extension, main lithology (as described inform of members and/ or informal units), thickness, fossils, age, depositional environment, and the lower contact are described. The described lithologies of the formations by different authors from different localities are reviewed, with occasional remarks of the present authors. The main tectonic events and the paleogeography are reviewed briefly. Each formation is discussed, for majority of them the present authors' opinion are given, with many recommendations for future studies. Some new ideas dealing with many aspects for many formations including proposals for establishing new formations are given, too.

The Low Folded Zone extends in the northern and northeastern parts of Iraq. It is roughly of oblong shape, and elongated from northwest to southeast. It is characterized by thick sedimentary cover, and well defined folding system. The folding system is characterized by a series of narrow and elongated anticlines of different amplitudes, trending NW – SE, separated by broad synclines, which usually are occupied by synclinal valleys, except Sinjar Mountain at the western side has a trend of E – W. The broad synclinal valleys form the major groundwater basins, and they are filled by sedimentary sequence ranges in age from Late Miocene to Recent.
The Low Folded Zone is divided into thirteen hydrogeological Sub provinces, which are: Sinjar – Rabee'a, West Tigris River, Khazir – Gomel, Dohuk – Alqosh, Erbil, Altun Kupri, Dibiga, Makhmour, Kirkuk – Hawija – Tuz Khurmatu, Cham Chamal – Qadir Karam – Qara Too, Kalar – Khanaqeen, Qara Tappa – Al-Sa'adiyah and Mandili – Zurbatiya – Teeb.

The main water bearing formations at the western part of the Low Folded Zone; west of the Tigris River are represented by: Injana and Fatha formations, and Quaternary sediments. While Bai Hassan and Mukdadiya formations are considered as the main water bearing formations in the other parts; to the east of the Tigris River, beside Injana Formation and Quaternary sediments.
The source of recharge water within the Low Folded Zone is mainly from direct rainfall, and from the High Folded Zone at the northeast. The Mesopotamia Plain and Al-Jazira Area represent the discharge zones to the Low Folded Zone. The general trend of the groundwater movement at the western part of this zone is mainly from north and northwest towards south and southeast, while at the eastern part, the main direction of flow is from north and northeast towards south and southwest, with local different directions due to topographic and structural characteristics of the area. There is a hydraulic continuity between water bearing formations within this zone, depending on the piezometric relations of the water-bearing layers throughout the area.
The depth of the groundwater increases at the high lands and at the flanks of the synclines, and decreases at the central parts of the basins and at the discharge areas. The transmissivity of aquifers often increases at the central parts of the synclines and along river courses, and within the alluvial fans, as more permeable sediments are available.

The salinity of the groundwater increases generally from north to south. It increases from the high lands, which represent the recharge areas, towards the discharge areas along the Mesopotamia Plain and Al-Jazira area. The quality of the groundwater is mainly bicarbonate at the recharge areas, and becomes sulphatic at the discharge areas. The hydraulic conditions
and chemistry of aquifers within the Low Folded Zone are closely linked to the stratigraphic, lithologic, structural and topographic characteristics of the water bearing formations. According to the hydrogeological evaluation of the Low Folded Zone, it can be considered as the most promising zone for groundwater development in Iraq.

The Low Folded Zone of Iraq is rich in a variety of mineral resources and industrial rocks, developed over the history of Paleogene and Neogene marine and non-marine depositional processes. The Fatha Formation (Middle Miocene) is the most important minerogenic rock unit in this zone. Native sulfur is the remarkable mineral resource; the identified sulfur resources are the largest of its kind in the world. Raw materials for cement industry are present in sufficient quantities, as well as gypsum and gravel – sand aggregates. Rock salt deposits in the center of two main Early and Middle Miocene evaporitic basins were intersected in several wells in considerable thicknesses within the Dhiban and Fatha formations.
Interesting deposits of bentonite “sensu stricto” were identified, as well as occurrences of palygorskite, phosphate and Fe-oxyhydroxides (after pyrite). Paleogeography, tectonic settings and climatic conditions were important factors in the development of primary syngenetic deposits such as limestone, gypsum and rock salt in addition to some phosphate occurrences. Whereas, biochemical and chemical epigenetic alterations were important factors in the development of some other mineral deposits located in the Low Folded Zone, such as native sulfur and bentonite, together with some mineral occurrences including palygorskite and Fe-oxyhydroxides.