Tectonic Evolution of Southern part of the Mesopotamian Foredeep Basin

This study investigated the tectonic evolution of the southern part of the Mesopotamian Foredeep basin. Subsidence and sedimentation rates were calculated for six oil wells distributed on the tectonic subzones of the sedimentary basin through the use of restored thickness rates according to Backstripping Method for Cretaceous and Tertiary sequences. The consequence of this study indicates the subsidence and sedimentation rates changing vertically and laterally through geologic time. As shown, the sequences of Albain subcycle are wide subsidence and sedimentation rates especially for the Mauddud Formation at the Am-1well which located in the eastern part of the sedimentary basin (Tigris subzone), as well as for the sequences of Cenomanian-Early Turonian subcycle especially for the Ahmadi and Mishrif formations were increase in subsidence and sedimentation rate toward (Am-2 and Mj-3) wells. Both wells located within the Tigris and the eastern part of Zubair subzone. This is in accordance with the closure of the South Tethys Sea because of the influences of the Austrian and Subhersynian orogenies. Three unconformity surfaces determine clearly in the depositinal basin of incompatibility during the Early Turonian, Danian and Oligocene epochs. Those unconformities affects all tectonic subzones except for the Am-1well where it was not influences by the unconformity during the Oligocene epoch. The subsidence and sedimentation process continued at high rates, reflecting the large thickness of the eastern part of the basin in the Tigris subzone area. Sedimentation rates augment significantly at the well (AG-19), which indicates the effect of faults on the Tigris subzone. This affects the degree of maturation and the source of hydrocarbons in the sedimentary basin.


The Area of study
The study area consists of seven oil wells (Su-9, Ru-72, Mj-3, AG-19, Am-2, Kf-1, and Ns-1), which are distributed in the Zubair, Tigris and Euphrates subzones for Mesopotamian basin within the stable shelf as given in Figure (1) [1]. The study area is characterized by a thick sedimentary cover that increases toward east, short and large lengths folds with a northsouth direction in the southern part of the sedimentary basin and northwest-southeast in the eastern part of the sedimentary basin along the passive margin [2].

Tectonic Setting
At the end of the Middle Permian-Cenomanian period, the Arabian plate was exposed to an extension force between the Iranian and Turkish margins from the edge of the eastern and northern Arabian plate [3]. This resulted in the opening of the Sea of Neo-Tethys and the Southern Neo-Tethys during the Middle Permian-Early Triassic and Mid Triassic-Cenomanian respectively [1[. This has caused the formation of half-graben basins resulted by the Listric Normal Faults [4] and was associated with the deposition of the higher part of the megasequence (AP6) and cycle sequences of megasequence (Ap7) and megasequence (AP8) [1]. The end of the Jurassic period and the beginning of the Cretaceous era marked the Geodynamic inversion from extension to Compression [5] due to the closure of the Southern Tethys during the early Masteriachtian-Turonian period, which appeared in the Kemerian orogeny in the Berriasian epoch and the Austrian orogeny at the end of Albain epoch [4].
During this period, the deposited of sequences of the (AP9) were ended with a regional unconformity resulting from the Laramidian orogeny, which represents the first phase of the alpine orogeny where a continental-continental collision occurred and the ophiollite emerged on the edge of the plate during the Masteriachtian period [1]. During the Middle Paleocenerecent period, the new Tethys Sea closed, which reached its peak during the Pliocene period of the Alpine orogeny [6], and deposited of megasequence (AP10) and AP11 were separated by a

Methodology
The original thickness and restored thickness are considered using the Backstripping method, based on mathematical equations. The porosity calculated based on the linear equation for shallow depths as shown below [6]: As for the deep depths, the equation [7]) is used: : Porosity of the rock at depth (Z); e: The Basis of the Niberian Logarithms.
°: The porosity of the rock on the surface (Z = 0) based on [8].
C: The coefficient determines the porosity gradient with the depth and is also called the compaction constant (m-1).
The decompaction thickness is calculated according to the equation below: T d : The original thickness before compaction; T n : Current thickness.
Based on the original thickness and variations of the global sea level [10] , total subsidence was calculated according to [11]: We can also calculate the total subsidence and sedimentation rates according to [11]:

Results and discussion
The deposition of the Mesopotamian basin included four Megasequence of the Late Tithonian period to the present. Each megasequence contains a number of sequences. The sedimentation times of each sequence were utilized [13]. The following are the rates of subsidence and sedimentation for these sequences:

3-Megasequence (AP-11) Latest Eocene-Pliocene (36.5-0 M.A):
This megasequence is divided into three sequences:  located at the center of the basin, near the Tigris subzone , where the subsidence and sedimentation rate was very high. This means that the Zubair, Euphrates, and the northern part of the Tigris subzones were exposed to elevation due to movements along longitudinal and