Zagros Thrust Belt Research Articles

Effect of stress on fracture development in the Asmari reservoir in the Zagros Thrust Belt

Development and production from fractured reservoirs require extensive knowledge about the reservoir structures and in situ stress regimes. For this, this paper investigates fractures and the parameters (aperture and density) through a combination of wellbore data and geomechanical laboratory testing in three separate wells in the Asmari reservoir, Zagros Belt, Iran. The Asmari reservoir (Oligo-Miocene) consists mainly of calcitic and dolomitic rocks in depths of 2000–3000 m. Based on the observation of features in several wellbores, the orientation and magnitude of the in situ stresses along with their influence on reservoir-scale geological structures and neotectonics were determined. The study identifies two regional tectonic fracture settings in the reservoir: one set associated with longitudinal and diagonal wrinkling, and the other related to faulting. The former, which is mainly of open fractures with a large aperture, is dominant and generally oriented in the N45°-90°W direction while the latter is obliquely oriented relative to the bedding and characterized by N45°-90°E. The largest aperture is found in open fractures that are longitudinal and developed in the dolomitic zones within a complex stress regime. Moreover, analysis of drilling-induced fractures (DIFs) and borehole breakouts (BBs) from the image logs revealed that the maximum horizontal stress (SHmax) orientation in these three wells is consistent with the NE-SW regional trend of the SHmax (maximum principal horizontal stress) in the Zagros Belt. Likewise, the stress magnitude obtained from geomechanical testing and poroelastic equations confirmed a variation in stress regime from normal to reverse, which changes in regard to active faults in the study area. Finally, a relationship between the development degree of open fractures and in situ stress regime was found. This means that in areas where the stress regime is complex and reverse, fractures would exhibit higher density, dip angle, and larger apertures.

Clay minerals study of the Kolosh Formation at selected sections from northern Iraq: Implications for provenance history

The mineralogical study using X-ray diffraction (XRD) supported by scanning electron microscopic (SEM) examination and energy-dispersive spectroscopy (EDS) on the claystone of the Kolosh Formation from northern Iraq was conducted to Shows the provenance history of rocks. Chlorite, montmorillonite, illite, palygorskite, and kaolinite were recorded in different amounts in the study area. The association of montmorillonite and chlorite in the claystone of the Kolosh Formation (Paleocene) refers to the marine environment. Chlorite and montmorillonite are the common minerals in the Kolosh Formation with less common of illite, kaolinite and palygorskite. These clay minerals are of authigenic, detrital and diagenetically origin, which are controlled mainly by the source rocks, paleoclimatic conditions and the burial diagenesis. The clay minerals assemblages refer to be derived mainly from Fe-Mg rich with minor Si-Al rich silicate minerals, which are very common in the ophiolites associated with the basic igneous rocks. These rocks composed the major lithological units in the Zagros Thrust Belt of NE Iraq.

Burdigalian-Langhian foraminifera of the northwest High Zagros Thrust Belt, southwest Iran

Abstract The foraminiferal contents of the lower–middle Miocene succession exposed in three sections in north Nur Abad on the northwestern side of the High Zagros Thrust Belt were studied. Assemblages of larger foraminifera from these sections can be referred to Zone SBZ 25 (and the Miogypsina globulus and Miogypsina intermedia subzones), which correlates with the Burdigalian Stage. For the first time, planktonic foraminifera documented from the Nur Abad area document Lang-hian deposits in the High Zagros, the upper 20 metres of the upper Sayl Cheshmeh section being characterised by the occurrence of planktonic foraminifera such as Globigerina concinna (Reuss), Globigerina diplostoma (Reuss), Globigerinoides obliquus (Bolli), Orbulina bilobata (d’Orbigny) and O.universa (d’Orbigny). This association characterises the Orbulina suturalis Interval Zone.

The pottery production from the Deh Dumen Bronze Age graveyard (South-Western Iran): a chemical, mineralogical and physical study

A collection of pottery vessels uncovered during the first season of excavations in the Deh Dumen Bronze Age graveyard (the second half of the third millennium BC) located in south-western Iran were studied by using chemical, mineralogical and physical techniques, with the aim to identify the pottery manufacturing process in this region. The site is located in a region of the Zagros fold and thrust belt that includes carbonate rocks and alluvial deposits. The pottery vessels found in the site present two different fabric types in their fresh surface: bright yellowish hue fabric (TYPE-1) and sandwich-like or black core fabric (TYPE-2) showing presumably different production techniques or workshops. Twenty-four samples from pottery sherds were selected and analysed by X-ray fluorescence (XRF), powder X-ray diffraction (XRD), polarized light microscopy (PLM), and field emission scanning electron microscopy (FESEM). Hydric tests were also performed. Samples were different according to their chemistry having distinguished calcium-rich and calcium-poor ceramics. Al2O3 and Fe2O3 were detected as the other main components of samples besides SiO2 and CaO. The mineralogical and textural characterisation revealed a fine-grained clayey matrix with quartz and feldspar grains in TYPE-1 potteries and large and small calcitic and clayey lumps inclusions in TYPE-2 potteries. Imprints of straw or other plants can be responsible for the higher porosity of some of the potteries. It was found that most of the potteries from the Deh Dumen graveyard were produced by means of a local and traditional pottery manufacturing technique, whilst others may have been produced in different places and transported to the graveyard as ritual offerings.

3-D Geothermal Model of the Lurestan Sector of the Zagros Thrust Belt, Iran

The Zagros thrust belt is a large orogenic zone located along the southwest region of Iran. To obtain a better knowledge of this important mountain chain, we elaborated the first 3-D model reproducing the thermal structure of its northwestern part, i.e., the Lurestan arc. This study is based on a 3-D structural model obtained using published geological sections and available information on the depth of the Moho discontinuity. The analytical calculation procedure took into account the temperature variation due to: (1) The re-equilibrated conductive state after thrusting, (2) frictional heating, (3) heat flow density data, and (4) a series of geologically derived constraints. Both geotherms and isotherms were obtained using this analytical methodology. The results pointed out the fundamental control exerted by the main basement fault of the region, i.e., the Main Frontal Thrust (MFT), in governing the thermal structure of the crust, the main parameter being represented by the amount of basement thickening produced by thrusting. This is manifested by more densely spaced isotherms moving from the southwestern foreland toward the inner parts of orogen, as well as in a lateral variation related with an along-strike change from a moderately dipping crustal ramp of the MFT to the NW to a gently dipping crustal ramp to the SE. The complex structural architecture, largely associated with late-stage (Pliocene) thick-skinned thrusting, results in a zone of relatively high geothermal gradient in the easternmost part of the study area. Our thermal model of a large crustal volume, besides providing new insights into the geodynamic processes affecting a major salient of the Zagros thrust belt, may have important implications for seismotectonic analysis in an area recently affected by a Mw = 7.3 earthquake, as well as for geothermal/hydrocarbon exploration in the highly perspective Lurestan region.

Discrimination of Geological Top-Formations by their Morphology through SAR Images and via Fractal Geometry implementation in IEM Backscattering Model(Case Study: Zagros Thrust Belt)

Discrimination of Geological Top-Formations by their Morphology through SAR Images and via Fractal Geometry implementation in IEM Backscattering Model(Case Study: Zagros Thrust Belt)

Geothermal Model of the Shallow Crustal Structure across the “Mountain Front Fault” in Western Lurestan, Zagros Thrust Belt, Iran

The Zagros thrust belt is a zone of deformed crustal rocks well exposed along the southwest region of Iran. To obtain a better knowledge of this mountain chain, we elaborated a 2D model reproducing the thermal structure of the “Mountain Front Fault”. This study, which is focused on the Lurestan region, is based on a model made by merging published sections and available information on the depth of the Moho. We present the isotherms and the geotherms calculated using an analytical methodology. The calculation procedure includes the temperature variation due to the re-equilibrated conductive state after thrusting, frictional heating, heat flow density data, and a series of geologically derived constraints. In order to perform the temperature calculations, the crustal structure in the Lurestan region is simplified as composed of two domains: A lower unit made by crystalline basement and an upper unit including all the lithostratigraphic units forming the sedimentary cover. The resulting model is compared with the numerical results obtained by previous studies to improve the description of the thermal structure of this geologically important area.

ORIGIN AND DISTRIBUTION OF CLAY MINERALS IN THE MUDSTONES OF THE KOLOSH FORMATION INRAWANDOZ AREA, NORTHEASTERN IRAQ

The mudstone/ shale units constituted 60% of the Kolosh Formation of 170 m thickness, which were studied and the clay minerals were identified to conclude the origin and paleoclimate. The studied area is located near the suture of Zagros Thrust Ophiolite Zone in NE Iraq. Kolosh mudstones contain chlorite, vermiculite, illite, nontronite, serpentine with varieties of mixed-layer clays. These clay minerals are of detrital and diagenetic origin, which are controlled mainly by the source rocks, paleoclimatic conditions and the burial diagenesis. Some of chlorite, chlorite/ vermiculite mixed layer, nontronite and smectite refer to hydrothermal origin comes from submarine basaltic flows and the high-temperature pore waters.The distribution of the clay minerals in the stratigraphic section of the Kolosh Formation controlled by episodic thrusting, episodic volcanic eruptions and interbedded sedimentary rock units. These are controlled by the changes in the paleoclimatic conditions, chemical weathering and the diagenetic processes.The clay mineral assemblages refer to be derived mainly from Fe-Mg rich minerals with minor Si-Al rich silicate minerals, which are very common in the ophiolites and associated basic volcanic rocks. These rocks composed the major lithological units in the Zagros Thrust Belt of NE Iraq.

Petrography and geochemical constrain on dolostones of the Shahbazan Formation in Lorestan (Iran)

The Shahbazan Formation (Fm.) was deposited in the Lorestan subzone of the Zagros Basin during middle to late Eocene, which presently is part of the Zagros fold and thrust belt. The Shahbazan Fm. consists of limestone and dolostone beds, which hosts some considerable hydrocarbon occurrences in the Zagros basin. In the present study, the reference Mamulan and Murani sections in the Lorestan province were studied. A total of 330 samples were collected. Petrographic examination of stained sections (alizarin red S and potassium ferricyanide) allowed differentiating five types of dolomites within the Shahbazan Fm. Within the Mamulan section, three distinct types where defined including dolomicrite (D1), associated by evaporites, peloides, intraclast, and algal laminites; dolomicrosparite (D2), with well-preserved algal laminites; and limpid dolosparite (D3) locally embedded within poikilotopic anhydrite. The Murani section comprises fabric-destructive dolosparite (D4), pore-filling dolomite (D5), as well as D1. Some fractures of the Shahbazan Fm. were occluded by evaporites and calcite spars in the Mamulan and Murani sections, respectively. The pore-filling (D5) dolomite displays a fine zonation pattern under CL, which may reflect successive growth stages during shallow to relatively burial diagenesis. According to microfacies analysis, seven microfacies including dolomudstone (F1), dolomitized bioclast–intraclast wackestone to packstone (F2), dolomitized lime mudstone (F3), interbedded laminated lime mudstone and evaporites (F4); dolomitized peloid packstone to wackestone (F5); dolomitized intraclast bioturbated wackestone (F6); bioclast miliolid wackestone to packstone (F7), as well as various anhydrites (e.g., nodular and laminated) were recognized which suggest intertidal–supratidal depositional setting for the Shahbazan Formation. ICP-MS analysis on some selected samples of the D1, revealed their chemical composition with an average for Fe of 1291 and 185 ppm, for Na of 644 and 650 ppm, for Sr of 125 and 185 ppm, and a Mg/Ca ratio of 0.57 and 0.505, for Mn of 23 ppm (only for Mamulan section) in the Mamulan and Murani sections, respectively. Relatively high Mg/Ca ratio suggests that these dolomites might be originated from salt waters. The Sr/Ca vs Mn suggests a relatively semi-closed diagenetic system. Variable Fe and Mn contents are probably due to reaction with meteoric water.

Tracing of hydrothermal ore forming process in the Sorkhvand manganese deposit, Kermanshah Province, Iran

The Sorkhvand manganese deposit is located in the Zagros thrust belt, close to the Kermanshah ophiolite melange. This ophiolite records the early stage of Neo-Tethys evolution in the western part of Tethyan realm. In the study area, Mn-mineralization occurs as irregular lenses or interlayers with radiolarian cherts within the Cretaceous radiolarite-bearing mudstones. The present work is an attempt in order to characterize the geochemical process involved in manganese mineralization. Mineralogically and texturally, the Sorkhvand manganese deposit is analogous to that of Tethyan manganese occurrences, comprising three generation of Mn-ores including syngenetic (pyrolusite), diagenetic (braunite-pyrolusite), and late-stage epigenetic mineralization (pyrolusite). The significant geochemical characteristics such as high Mn content (6.35–67.64 wt%; average 33.4 wt%), low concentration of Fe (0.18 to 8.4 wt%; average 2.26 wt%), high Ba (14–3445 ppm, average 1038.3 ppm), LREE > HREE, and negative Ce anomalies (Ce/Ce* = 0.58–1.02; average 0.74) with a negative Eu anomalies (Eu/Eu* = 0.48–0.91, average 0.67) reveal a primary distal hydrothermal source for mineralization. Also, the prevailing of oxic conditions (V/V + Ni = 0.11–0.52), absence of sulfide minerals coupled with relative enrichment of some bioessential elements (e.g., Co) suggest that manganese segregation from hydrothermal ore-bearing solutions may be related to microbial activity influenced by bacterially mediated reactions.

Gas leakage hazard zonation of Masjed-i-Soleiman area, Zagros, Iran, using GiT

The shallow Masjed-i-Soleiman (MIS) oil field is situated at the Dezful Embayment in the Zagros Fold and Thrust Belt in southwestern Iran. The shallow depth of this oil field and multiple fractures has resulted in many gas leakages causing a significant pollution in residential areas around the area. In order to define the extent of the gas leakage, data sets such as surface structures, underground contour map, detected gas leakages, lithology, digital elevation models and population density were compiled using of remote sensing techniques and field investigations. The data were then added as layers in a geographic information system, which were overlaid form comparisons and used to construct a gas leakage hazard zonation map. This study shows that the central part of the MIS area, around the See-Berenj, Naftoon and Darre-Khersun districts, is a high-risk area, because of the shallow depth of gas caps, localizing of popular habitation and the high density of fractures and gas leakages.

Isotopic analysis, hydrogeochemistry and geothermometry of Tang-Bijar oilfield springs, Zagros region, Iran

This study is focused on warm and cold springs in Tang-Bijar oilfield of southern Iran. The springs emerge from fractures and faultlines within the carbonate and evaporitic rocks of Zagros Thrust Belt (ZTB) and vary in temperature between 20 and 44°C. Chemical analyses define three main chemical water associations reflecting different hydrochemical processes including: (1) Ca-HCO3,(2) Mg-SO4 and (3) Na-Cl. Based on isotope analysis, meteoric water is the origin of these spring waters. Two distinct hydrogeological systems are postulated: a deep moderate-temperature (40 to 45̊C) geothermal system recharged by meteoric waters mixed with oilfield brine and a shallow cold aquifer system related to local groundwater.

Tectonic Geomorphology of Iran’s Salt Structures

Iran has a various salt structures that their tectonic geomorphology is subject of this paper. Geologic situation of salt structures in Iran have determinate. According to age and geological setting of salt deposits that revealed by tectonic geomorphology methods, salt structure provinces of the Central and Southern Iran have been distinguished. Also, critical concepts of salt diapirism in the Southern Iran and Central Iran salt basins have explained. Therefore, Central Iran’s salt diapirs have triggered by tectonic forces, but salt diapirism in the Southern Iran has triggered by halokinesis, then it has effected by tectonic forces, especially in Zagros fold and thrust belt.

Genesis of the Nasirabad manganese occurrence, Fars province, Iran: Geochemical evidences

The Nasirabad manganese occurrence is located to the south of the Neyriz in the Fars province. Structurally and lithologically, this occurrence lies in the southwest part of the Zagros Thrust Belt and was deposited as Mn-nodules and interconnected ore-bearing interlayer's with radiolarite cherts in the vicinity of the Neyriz ophiolites. The present work deals with the geology and geochemistry of the Nasirabad manganese occurrence with a discussion of its genesis. High Mn/Fe (average 18.85) and high Ba (average 28,830ppm) with low Pb (2.0ppm) and LREE>HREE, Lan/Ndn (average 4.5), Dyn/Ybn (average 1.2) and negative Eu anomaly suggest distal hydrothermal source. The Co/Zn (average 2.2), Ce/La ratio (average 0.67) and trace element discrimination diagrams indicate hydrothermal–hydrogenous processes. Y/Ho ratio (average 24.85) and strong positive correlation coefficient between major oxides and some high field strength elements (HFSE) like; TiO2 vs Fe2O3 (r=0.98), Al2O3 vs Zr (r=0.97), Al2O3 vs Fe2O3 (r=0.98), Zr vs K2O (r=0.98), Nb vs TiO2 (r=0.92), Th vs Fe2O3 (r=0.76), Th vs MgO (r=0.86) reveal the presence of volcaniclastics and (or) terrigenous detritals of mafic composition being deposited into the depositional basin. It seems that intermittent interlayering of mafic detrital material derived from volcanic eruption of the Neyriz island arc directly affected the physicochemical conditions of hydrothermal ore precipitation in this basin and consequently the Nasirabad manganese ores represent hydrothermal–hydrogenous geochemical characteristics. The Nasirabad is an example of non-sulphidic, oxic Mn-mineralization. Similar trend between the enrichment and depletion of some bioessential elements (e.g., Mn, As, Ba, Sr, Co, Ce) might have been resulted from selective sequestering of metal ions by microbial processes and hence hydrogenous characteristics may also be the result of biogenetic processes. Moreover the high dilution of distal hydrothermal exhalations by sea water cannot be ruled out.

Multi-attribute ant-tracking and neural network for fault detection: a case study of an Iranian oilfield

Fault detection is one of the most important steps in seismic interpretation in both exploration and development phases. A variety of seismic attributes enhancing fault visualization and detection have been used by many interpreters. Geometric seismic attributes such as coherency and curvature have been successfully applied in delineating faults in sedimentary basins. Seismic attributes are often sensitive to noise and it is necessary to reduce noise and enhance the seismic quality before computing the attributes. In this study, after enhancing the quality of the seismic data, several different seismic attributes sensitive to discontinuities such as similarity and curvature were computed and applied to a 3D seismic dataset and their effective parameters were explained. Ant-tracking as an algorithm that captures continuous features was used to improve fault visualization. Ant-tracking was applied to different fault-sensitive attributes and their results were compared. Also artificial neural networks were used for combining multiple attributes into a single image to allow us to visually cluster different fault-sensitive attributes. The area of this study was an oilfield in the South West of Iran lying in the Zagros thrust belt. Results showed that the similarity and the most-positive curvature could detect faults and fractures more properly than the other attributes and applying the ant-tracking algorithm provided better interpretable information for studying faults and subtle faults. Results proved that applying ant-tracking to the most-positive curvature attribute was more acceptable than the dip attribute or even the similarity in this field. Also by an unsupervised neural network, different ant-tracking volumes were integrated into one volume and faults with more probability were clustered in one group.

Cenozoic tectonic evolution of Asia: A preliminary synthesis

Asia has been a major testing ground for various competing models of continental deformation due to its relatively well-understood plate boundary conditions in the Cenozoic, exceptional exposure of active structures, and strain distribution, and widespread syn-collisional igneous activity as a proxy for the thermal state of the mantle and crust. Two Cenozoic orogens dominate the continent: the Himalayan–Tibetan orogen in the east induced by the India–Asia collision and the Turkish–Iranian–Caucasus orogen in the west induced by the Arabia–Asia collision. The development of the two orogens was accomplished by shortening in the early stage followed by strike-slip faulting and extension in the late stage. In the Himalayan–Tibetan orogen, shortening across two discrete thrust belts at 55–30 Ma in southern and northern Tibet created a large intracontinental basin (the Paleo-Qaidam basin) in between. Subsequent crustal thickening and a possible thermal event in the mantle (e.g., convective removal of central Tibetan mantle lithosphere) may have raised the elevation of this early intra-plateau basin up to ~ 2–3 km to its current height. Collision between India and Asia also caused lateral extrusion of southeast Asia between 32 Ma and 17 Ma. The latest stage of the India–Asia collision was expressed by north-trending rifting and the development of trench-facing V-shaped conjugate strike-slip faults in central Mongolia, central Tibet, eastern Afghanistan and southeast Asia. In the Turkish–Iranian–Caucasus orogen, early crustal thickening in the orogenic interior began at or prior to 30–20 Ma. This style of deformation was replaced by strike-slip faulting at ~ 15–5 Ma associated with further northward penetration of Arabia into Asia, westward extrusion of the Anatolia/Turkey block, and rapid extension across the Sea of Crete and Sea of Aegean. The late stage extension in both orogens was locally related to extensional core-complex development. The continental-margin extension of east Asia was developed in two stages: initially in a widely distributed zone that has an east-west width of 500–800 km during 65–35 Ma, which was followed by localized extension and opening of back-arc basins associated with the development of spreading centers at 32–17 Ma (e.g., Japan Sea or East Korea Sea, Bohai Bay, and South China Sea). Opening of the back-arc basins could be induced by (1) rapid eastward migration of the western Pacific trench system or (2) oblique subduction of Pacific plate beneath Asia that had produced a series of en echelon right-slip primary shear zones linking with back-arc spreading centers oriented obliquely to the strike of the nearby trench. Since ~ 15 Ma, the eastern margin of Asia became contractional in the east–west direction, as indicated by the collapse of back-arc basins in the western Pacific and the development of fold-thrust belts along the eastern continental margin. Coeval with the contraction is widespread east–west extension in Siberia, North China, and the Tibetan plateau. The above observations can be explained by a change in boundary condition along the eastern margin of Asia that allowed the thickened Asian continent to spread eastward, causing east-west extension in its trailing edge and east-west compression in its leading edge. In west Asia, continental-margin extension started at about 25–20 Ma in the Aegean and Cretan regions, which was associated with a rapid southward retreat of the Hellenic arc. The complex evolution of Cenozoic deformation in Asia may be explained by a combined effect of temporal changes in plate boundary conditions, thermal evolution of the upper mantle perturbed by collisional tectonics, and the built-up of gravitational energy through crustal thickening and thermal heating. Although the past research in Asia has treated the India–Asia and Arabia–Asia convergence as separate collisional processes, their interaction may have controlled the far-field Cenozoic deformation in Asia. The most pronounced result of this interaction is the creation of a northeast-trending 300–400-km wide and > 1500-km long zone of northwest-striking right-slip faults, which extends from the Zagros thrust belt in the south to western Mongolia in the north and links with the active Tian Shan and Altai Shan intracontinental orogens. Cenozoic deformation and coeval igneous activity spatially overlap with one another in the Himalayan–Tibetan and Turkish–Iranian–Caucasus orogens. A large Cenozoic magmatic gap exists between Tibet in the south and Mongolia in the north where Cenozoic deformation has not been associated with any coeval igneous activity. Finally, Cenozoic igneous activity is always associated with Jurassic–Cretaceous magmatic arcs, suggesting a causal relationship between the early arc magmatism and later syn-collisional magmatism.

Exploring the High Zagros (Iran): a challenge for geophysical integration

The purpose of a combined geological and geophysical study in the High Central Zagros area near the townships of Lordegan and Yasuj was to find answers to the following main questions: ■ Is the High Zagros Fault (HZF) an overthrust fault? ■ Are there vertically separated structural/ tectonic units in the ‘Complex’ Foreland of the Zagros? ■ Are there possible hydrocarbon exploration targets beyond the HZF? While Bosold et al.(2005) have published the results of a geological study, this paper focuses on the geophysical contribution to the above questions. Integration of seismic and potential field geophysical methods played a key role in this study. The area of investigation is located in the Zagros Fold-Belt (‘Complex’ Zagros Foreland), close to one of the oldest and richest oil and gas provinces in the world and the Zagros Thrust-Belt (High Zagros). Most of the oil and gas fields were discovered in the ‘Simple’ Zagros Fold-Belt in front of the Mountain Front Fault (MFF), which marks the front of the ‘Complex’ Zagros Foreland. Decades of successful activity of the petroleum industry have led to the acquisition of extensive knowledge of this area, whereas the orogenic zones further into the interior of the Zagros have been studied to a much lesser extent. The higher degree of structural complexity in combination with rugged surface topography is one of the main reasons. In the area between the Mountain Front Fault (MFF) and the High Zagros Fault (HZF) little seismic has been acquired previously and few wells have been drilled. These wells are often based exclusively on surface geology without seismic control, many of them having resulted in petroleum discoveries. North of the HZF, however, no data other than detailed surface geological mapping have ever been acquired prior to this study. In 2000, the exploration team of RWE Dea realized that new or previously undetected exploration plays could be present in the ‘Complex’ Zagros Foreland or even in the High Zagros adjacent to the established petroleum province. In 2001 a profirst posed two and a half year joint study programme in the Lordegan-Yasuj area was agreed with NIOC.

Structural Controls on Source Rock Distribution and Maturation in Southeast Turkey: ABSTRACT

Production from the western part of the Zagros fold and thrust belt southeastern Turkey is characterized by high-sulfur (2-3%) oils from middle Cretaceous Mardin Formation. The oils are generated from two carbonate sources, one from the middle Cretaceous passive margin sequence and one deposited as a part of the Upper Cretaceous foreland basin sequence. Both sources are associated with transgressive events coincident with two recognized Cretaceous oceanic anoxic events in Cenomanian-Turonian and Coniacian-Santonian. Geochemical markers in the oils substantiate the restricted, anoxic conditions characteristic of their source rock deposition. During the Upper Cretaceous compressional event, horsts formed buttresses to advancing oceanic thrust sheets. The oceanic thrust sheets consisted of the Karadut and Kocali formations, oceanic equivalents of the Mesozoic shelf. The middle and Upper Cretaceous source facies were rapidly and deeply buried by the tectonically thickened thrust sheets adjacent to the buttresses. Thick burial by the oceanic rocks was critical for thermal maturation of the sources. Geohistory modeling shows generation occurred during the Tertiary coincidental with tectonic activity that probably allowed oil migration to occur along new or reactivated Cretaceous faults.