Iraqi Bulletin of Geology and Mining

This study deals with defining of landforms, morphogenetic processes and climatic fluctuations during the continental phases through the Tertiary and Quaternary periods, based on the available data obtained from the geological studies of the Iraqi Jazira Area. The study shows that the present surface of Al-Jazira Area is ascribed to a rejuvenated plateau within the Mesopotamian Depression Province, which originated from influence of destruction and construction processes during two continental phases. The first phase, which started after the sea regression in Oligocene, had produced older plateau, it is characterized by prevailing of denudation processes in humid semiarid climate. The second phase, which started during the initial influence of the last Alpine movements in Late Miocene, gave rise to younger plateau. It is characterized by climatic fluctuations (between wet – arid and semiarid), prevailing of denudation – deposition – chemical weathering and periodical activity of vertical movements, which contributed in development of twenty seven landform assemblages, attributed to seven morphogenetic units of variable origins. The younger plateau witnessed intensive denudation processes and evolution of two peneplains, salt marshes, karsts and surface drainage system.
The study regarded that Tharthar and Chagh Chagh rivers were ancient tributaries of the Euphrates River during Pleistocene – Holocene, which were dried later on, due to neotectonic activities in Sinjar mountain and climatic changes. The developments of ancient rivers, as well as genesis of Tharthar Depression, salt marshes, halcrete and calcrete have been discussed. Moreover, a new geomorphological map for the Iraqi Jazira Area is constructed depending on this study.

A comprehensive tectonic and structural analysis of Al-Jazira Area (including Khleissia Heigh) using seismic, drill-hole and surface geological data is carried out, and some new obtained information is introduced. Though it lacks significant surface structures, Al-Jazira Area is dominated by a network of subsurface intracontinental ENE – WSW and NW – SE trending Late Cretaceous rift basins with Campanian – Maastrichtian synrift sediments. Several geological evidences point out to the recent activity of Khleissia Graben after a considerable period of quiescence.
The nature of the stratigraphic sequence and the associated truncations reflect that the area was a subject to a repeated geological activity during the Mesozoic Era, but became almost stable during most of the Paleogene – Neogene Period. However, by considering its Late Mesozoic – Cenozoic stratigraphic and structural evolution, and its relation to the main tectonic zones of the Iraqi territory, Al-Jazira Area has been regarded as the northwestern extension of the Mesopotamia Foredeep of the Unstable Shelf of the Arabian Platform rather than a part of the Stable Shelf as proposed earlier.

The available stratigraphic data, including subsurface data, have been integrated to infer the stratigraphical evolution of the Miocene Basin in Al-Jazira Area, Northwest Iraq. The exposed rocks within the stratigraphic column are represented by four formations: Anah (Late Oligocene) Euphrates (Early Miocene), Fat'ha (Middle Miocene) and Injana (Late Mioccene). Moreover, twelve main types of Quaternary sediments are recognized. Whereas, the drilled wells in the area encountered five rock units of Miocene age (Euphrates, Dhiban, Jeribe, Fat'ha and Injana formations).
The stratigraphic sequence reflects the environmental changes progressively from marine, brackish and fresh water, respectively. The Miocene Basin incorporates sediments of two successive marine sedimentary cycles (Euphrates and Fat'ha formations), each cycle starts with sea oscillation, which delineate type and distribution of the sediments. The last sea regression was commenced in the Late Miocene due to the final phase of the Tethyan Sea closure that led to deposition of Injana Formation (Late Miocene) in fluvio – lacustrine environment, contemporaneously with cycles of terrigenous – continental clastics (pre-molasse facies). The molasse facies of Pliocene (Mukdadiya Formation) is not deposited in Al-Jazira Area due to influence of initial upheaval of the Sinjar anticline in that time.
The vertical tectonic movements were common in the Miocene Basin since late Early Miocene till Quaternary, as indicated by the development of Dhiban and Jeribe formations (subsurface) and the cyclicity of Fat'ha and Injana formations, as well as the presence of four levels of valley terraces.

The Iraqi Jazira Area is generally a flat terrain of less rugged topography with scattered hills. It is dissected by shallow wadis with presence of numerous salt marshes. The drainage is either internal into the marshes, swamps and sabkhas, or originating at the slope of the main structures. The recharge sources of the groundwater in the Jazira Area are mainly direct infiltration and/ or run off, from the intermittent wadis in form of percolation in shallow aquifers. The main water bearing formations in the area are Fat'ha and Injana formations in addition to Quaternary sediments. The groundwater discharge areas occur along Tharthar Lake and Sabkhas.
The regional trend of the groundwater movement in the Jazira Area is generally from north towards south, southeast and southwest. However, locally, the flow of the groundwater takes different directions depending on geological setting, topographic and structural features. The depth of the groundwater reaches some tens of meters in the northern parts, while it is near the surface or as seepage within the discharge areas, along Tharthar Valley and Tharthar Lake and at low lands of salt marshes.
Salinity of the groundwater in the Jazira Area increases, generally from the recharge areas, in the northern parts towards the discharge areas. The quality of the groundwater is mainly sulphatic with chloride and bicarbonate water types in some areas. According to the hydrogeological interpretations, the promising zones of good water qualities and quantities are fixed in Injana Formation, within the northern parts of the Jazira Area near the recharge areas.

Al-Jazira Area is located at the northwestern part of Iraq, it is covered by Euphrates, Fatha and Injana formations of Miocene age. Oligocene is represented by Anah Formation that is exposed as narrow strip near Rawa town along Euphrates River. These formations consist of limestone, marl, claystone, gypsum, sandstone and siltstone. Gypcret, sand and gravels of Quaternary sediments are present as thin cover. Limestones of Anah and Euphrates formations are mostly exposed on both sides of Euphrates River with high purity of calcium carbonate and are present with an economic potential for cement, glass, sugar industries, building purposes and road construction. The surface exposures of gypsum of Fat'ha Formation, which cover wide parts of Al-Jazira Area, are partly altered to gypcret; it is of good quality suitable for high grade plaster industry. Although most of the claystones of Fat'ha Formation are of bad quality, but there are some claytones suitable for bricks manufacturing. Sandstones of Injana Formation mostly contain calcareous cementing materials or claystones, secondary gypsum is also present as cementing material in some places; therefore they are not suitable for building purposes. Pleistocene terraces exposed on the banks of the main valleys and near Euphrates River are suitable for building purposes. Salt pans are mostly related to fractures aided the percolation of ground waters, which dissolve the evaporites (gypsum and salt beds) of Fat'ha Formation, leading to karstification and subsidence. Sulphur is one of the mineral showings that has been exploited by the locals in the past, but with no economic importance now days, it is present in the gypsums of Fat'ha Formation near Rawa city.