Zagros Fold Belt Research Articles

Comprehensive source rock evaluation of the Kazhdumi Formation, in the Iranian Zagros Foldbelt and adjacent offshore

The Kazhdumi Formation is regarded as one of the most prolific hydrocarbon sources in the Zagros Foldbelt and adjacent offshore. Rock-Eval pyrolysis data were collected from 2300 rock samples of the Kazhdumi Formation in 64 wells (core and cutting) including 37 oil and gas fields and five outcrops. 200 Vitrinite reflectance measurements were carried out to calibrate and map thermal maturity over the study area. Palynofacies analyses and thermal history modeling were applied on the wells located in the study area.Based on the total organic carbon (TOC) map, the Kazhdumi Formation TOC values range from 0 to 11%. In the central part of Dezful Embayment, its average value is about 5%, while average TOC value of the Kazhdumi Formation is lower than 0.5% in Qatar-Gawbandi Paleo-high. Hydrogen index (HI) values represented types II and III kerogen for central part of the Dezful Embayment and Qatar-Gawbandi Paleo-high, respectively. Tmax ranges from 370 to 455 °C in the study area, the maximum and minimum values for this parameter are recorded in the central Dezful Embayment and central Persian Gulf anticlines, respectively. Vitrinite reflectance (VRr) map also confirms the concluded results of Tmax data. Reconstructed burial history and thermal modeling of three wells are also in full agreement with the results of other maturity evidence (Tmax and VRr). Palynofacies analyses revealed that this formation in the central Persian Gulf (South Pars Field) clearly represents the dominance of terrigenous elements which were resulted from a close proximity to a fluvio-deltaic source. However, towards the northwest, amorphous organic matter (AOM) dominates in central Dezful Embayment indicating a distal dysoxic-anoxic environmental condition.

Mineralogical and geochemical investigations of the Mombi bauxite deposit, Zagros Mountains, Iran

The Mombi bauxite deposit is located in 165km northwest of Dehdasht city, southwestern Iran. The deposit is situated in the Zagros Simply Fold Belt and developed as discontinuous stratified layers in Upper Cretaceous carbonates (Sarvak Formation). Outcrops of the bauxitic horizons occur in NW-SE trending Bangestan anticline and are situated between the marine neritic limestones of the Ilam and Sarvak Formations. From the bottom to top, the deposit is generally consisting of brown, gray, pink, pisolitic, red, and yellow bauxite horizons. Boehmite, diaspore, kaolinite, and hematite are the major mineral components, while gibbsite, goethite, anatase, rutile, pyrite, chlorite, quartz, as well as feldspar occur to a lesser extent. The Eh–pH conditions during bauxitization in the Mombi bauxite deposit show oxidizing to reducing conditions during the Upper Cretaceous. This feature seems to be general and had a significant effect on the mineral composition of Cretaceous bauxite deposits in the Zagros fold belt. Geochemical data show that Al2O3, SiO2, Fe2O3 and TiO2 are the main components in the bauxite ores at Mombi and immobile elements like Al, Ti, Nb, Zr, Hf, Cr, Ta, Y, and Th were enriched while Rb, Ba, K, Sr, and P were depleted during the bauxitization process. Chondrite-normalized REE pattern in the bauxite ores indicate REE enrichment (ΣREE=162.8–755.28ppm, ave. ∼399.36ppm) relative to argillic limestone (ΣREE=76.26–84.03ppm, ave. ∼80.145ppm) and Sarvak Formation (ΣREE=40.15ppm). The REE patterns also reflect enrichment in LREE relative to HREE. Both positive and negative Ce anomalies (0.48–2.0) are observed in the Mombi bauxite horizons. These anomalies are related to the change of oxidation state of Ce (from Ce3+ to Ce4+), ionic potential, and complexation of Ce4+ with carbonate compounds in the studied horizons. It seems that the variations in the chemistry of ore-forming solutions (e.g., Eh and pH), function of carbonate host rock as a geochemical barrier, and leaching degree of lanthanide-bearing minerals are the most important controlling factors in the distribution and concentration of REEs. Several lines of evidences such as Zr/Hf and Nb/Ta ratios as well as similarity in REE patterns indicate that the underlying marly limestone (Sarvak Formation) could be considered as the source of bauxite horizons. Based on mineralogical and geochemical data, it could be inferred that the Mombi deposit has been formed in a karstic environment during karstification and weathering of the Sarvak limy Formation.

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.

Toward 4D modeling of orogenic belts: Example from the transpressive Zagros Fold Belt

Latest developments in computer power and computational solutions open new ways to envision complex natural systems. Advances in high-resolution 3D geodynamic modeling, in particular, allow investigating tectonic processes such as transpression, which involve “normal” and “tangential” kinematics with respect to the bulk orogenic trends. We demonstrate that implementing the 4 dimensions (space and time) provides and constrains new answers to long-lasting discussions. As case study, we have chosen the Zagros Simply Folded Belt in Iran, which exhibits spatial variations of structural patterns from the homogeneously shortened, wide fold belt in the Fars to the narrower, higher elevated area in the Izeh. High-resolution, 4D numerical modeling shows how a low-viscosity décollement becoming frictional toward the Dezful embayment influences the exposed fold patterns. Results also emphasize the importance of an oblique backstop to produce en-échelon arranged folds where convergence-related and backstop-controlled folds are mingled in the transpressional orogen.

ACTIVE DEFORMATION DELINEATED BY GEOMORPHIC AND SEDIMENTARY RESPONSE OF RIVERS, CENTRAL ZAGROS FOLD – THRUST BELT, SW IRAN

The mountain generation in Iran is because of continental collision between the Arabian and Eur-asia plate. Southwestern Iran shows active shorten that its evidences is deformation of crust and frequent earthquakes. At depth, active basement of the Zagros fold-thrust-belt in southwestern Iran, which are covered by folding of the Phanerozoic sediments, affected by some blind thrusted faults that have seismic nature. The Zagros fold-thrust-belt can be divided into 4 lithotectonic units including Sanandaj-Sirjan Zone (SSZ), Imbricate Zone (IZ), Zagros Fold Belt (ZFB), and Molasse Cover Sequence (MCS); this dividing and classification is based on geomorphology landscape, drainage pattern, rate of tectonics and stratigraphic records. Each tectonic unit characterized by especial abnormal forces in river systems. Active tectonics has the most important role to control the river systems by changing of channels incline. Change in the drainage pattern, channels cut, longitudinal profile, anomalous changes of sinuosity, changing of the side form and forming of terrace, change of river direction, compact meanders, cutting of meanders and geomorphology features of the rivers are responds to the active tectonics of region that are studied using remote sensing, DEM and field observations. These parameters are used to understand the vertical movement in the study area. Existing structures, especially growing anticlines and blind thrusted faults in the Zagros fold-thrust-belt, which cut the river channels and sometimes put them in parallel, are used in the study of their effect on the longitudinal and transverse tilt of morphological changes.

SOURCE‐ROCK MATURITY, HYDROCARBON POTENTIAL AND OIL – SOURCE‐ROCK CORRELATION IN WELL SHORISH‐1, ERBIL PROVINCE, KURDISTAN REGION, IRAQ

The Shorish‐1 exploration well is located in Erbil Province in the Kurdistan region of Iraq, on the outskirts of Erbil City near the dividing line between the Low Folded and High Folded Zones of the Zagros foldbelt. The well penetrated rocks which are between Miocene and Late Triassic in age. The depositional environment, source potential and maturity of organic‐rich intervals within the well succession were investigated using 38 cuttings samples. All samples were analysed for bulk geochemical parameters (i.e. total organic carbon, total carbon, sulphur, Rock‐Eval). A subset of 13 samples was selected for biomarker analysis, pyrolysis – gas chromatography and isotope investigations. In addition non‐commercial oil and oil impregnations were investigated for oil‐source correlations.Source rocks occur in the Jurassic Sargelu and Naokelekan Formations and the lowermost Cretaceous Chia Gara Formation. Analytical results suggest that these source rocks were deposited in a carbonate‐rich, anoxic environment in an intrashelf basin setting with free H2S in the water column. Oxygen‐depleted conditions were favoured by salinity stratification. The average preserved TOC contents of the 100 m thick Sargelu Formation and the 25 m thick Naokelekan Formation are 2.2% and 4.6%, respectively. The TOC content of the Chia Gara Formation decreases upwards and averages 3.2% within its lower 40 m. Very high sulphur contents suggest the presence of kerogen Type II‐S, and that all the formations have generated sulphur‐rich hydrocarbons at relatively low maturities.In contrast to the oil impregnations within Jurassic strata, the oil and the oil impregnations within Cretaceous rocks are heavily biodegraded. Oil biomarker and isotope data indicate generation from the above‐mentioned Jurassic and Cretaceous source rock formations. As a result, generation from Triassic and Paleogene rocks can be excluded or is of negligible significance.Numerical models show that hydrocarbon generation rates from the Sargelu, Naokelekan and Chia Gara Formations peaked firstly at about 55 Ma (Paleocene/Eocene) and then again at 5 Ma before present (late Miocene/Pliocene). The first peak resulted from increased Paleocene subsidence, and the second peak was related to deep late Miocene/Pliocene burial. Hydrocarbon generation ceased during Recent uplift, during which ∼2000 m of the Late Neogene succession was eroded.

Lateral and depth variations of coda Q in the Zagros region of Iran

We have analyzed more than 2800 local earthquakes recorded by the Iranian National Seismic Network (INSN) and the Iranian Seismological Center (IRSC) to estimate coda wave quality factor, Q c , in the Zagros fold and thrust belt and the Sanandaj-Sirjan metamorphic zone in Iran. We used the single backscattering model to investigate lateral and depth variations of Q c in the study region. In the interior of Zagros, no strong lateral variation in attenuation parameters is observed. In SE Zagros (the Bandar-Abbas region) where transition to the Makran subduction setting begins, the medium shows lower attenuation. The average frequency relations for the SSZ, the Bandar-Abbas region, and the Zagros are Q c = (124 ± 11)f 0.82 ± 0.04, Q c = (109 ± 2)f 0.99 ± 0.01, and Q c = (85 ± 5)f 1.06 ± 0.03, respectively. To investigate the depth variation of Q c , 18 time windows between 5 and 90 s and at two epicentral distance ranges of R < 100 km and 100 < R < 200 km were considered. It was observed that with increasing coda lapse time, Q 0 (Q c at 1 Hz) and n (frequency dependence factor) show increasing and decreasing trends, respectively. Beneath the SSZ and at depths of about 50 to 80 km, there is a correlation between the reported low velocity medium and the observed sharp change in the trend of Q 0 and n curves. In comparison with results obtained in other regions of the Iranian plateau, the Zagros along with the Alborz Mountains in the north show highest attenuation of coda wave and strongest frequency dependence, an observation that reflects the intense seismicity and active faulting in these mountain ranges. We also observe a stronger depth dependence of attenuation in the Zagros and SSZ compared to central Iran, indicating a thicker lithosphere in the Zagros region than in central Iran.

Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

The isostatic modeling represents one of the most useful “geological” reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted “isostatic” Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub’ al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

Influence of surface processes and initial topography on lateral fold growth and fold linkage mode

Elongation of randomly distributed fold segments and their potential linkage are important for hydrocarbon exploration because it can greatly influence the morphology of the reservoir and both migration and accumulation of hydrocarbons in antiformal traps. Here we study the effects of surface processes and the presence of a topographic slope on the different linkage modes that can occur, and how these parameters affect the required horizontal offset for perturbations to link. The proposed numerical model represents a sedimentary cover detached over a much weaker basal decollement layer. The upper surface is modified by mass redistribution, which is achieved by a combination of fluvial and hillslope processes. Several series of simulations were performed: (1) without surface processes or regional slope, (2) with regional slope only, (3) with fluvial incision and hillslope processes, and (4) with hillslope processes only. Model results show that the presence of a regional slope reduces the critical distance required for the transition between linkage and no linkage modes, whereas erosion and redeposition of sediments, on the contrary, increase this distance. The location of the saddle point, where fold segments link, and its vertical distance to the crests of the anticlines are different compared to the case without erosion or initial topographic slope, which potentially can affect the morphology of hydrocarbon traps. Moreover, both erosion and redeposition of sediments enhance the fold elongation (growth along the fold axis), once the erosion velocity exceeds the folding velocity. Model results have been compared to the Zagros Fold Belt.

Geochemical characterisation, volumetric assessment and shale-oil/gas potential of the Middle Jurassic–Lower Cretaceous source rocks of NE Arabian Plate

ABSTRACT The Middle Jurassic–Lower Cretaceous strata of the NE Arabian Plate contain several prolific source rocks providing the charge to some of the largest world-class petroleum systems. They are located within the Zagros Fold Belt and Mesopotamian Foreland Basins covering the northern, central and southeastern parts of Iraq, Kuwait and western and southwestern Iran, particularly the Lurestan and Khuzestan provinces. These source rocks include the Bajocian–Bathonian Sargelu, the Callovian–Lower Kimmeridgian Naokelekan and the Upper Tithonian–Lower Berriasian Chia Gara formations of Iraq and their chronostratigraphic equivalents in Kuwait and Iran. They have charged the main Cretaceous and Cenozoic (Tertiary) reservoirs throughout Iraq, Kuwait and Iran with more than 250 billion barrels of proven recoverable hydrocarbons. These formations represent the transgressive system tracts of sequences deposited within deep basinal settings and anoxic environments. They are dominated by black shales and bituminous marly limestones, with high total organic carbon (TOC) contents (ranging from 1–18 wt%), and by marine Type IIS kerogen. Their Rock-Eval S2 yields may reach up to 60 mg HC/g Rock, particularly along the depocentre of the Mesopotamian Foreland Basin. The immature hydrogen index (HI) values might have been up to 700 mg HC/g TOC, whereas the present-day observed values vary depending on the location within the basin and the present-day maturity. The Source-Potential Index (SPI; i.e. mass of hydrocarbons in tons, which could be generated from an area of 1 sq m in case of 100% transformation ratio) averages around 2–3, but can even reach up to 14–16 along the basins’ centres. The Sargelu and the overlying Naokelekan-basinal Najmah formations (and their equivalents) could represent the best potential shale-gas/shale-oil plays in Iraq, Kuwait and Iran, due to their organic richness, favourable maturity and the presence of regional upper and lower seals. The estimated oil-in-place for the potential Sargelu shale-oil play in Iraq only is around 1,300–2,500 billion barrel oil-equivalent (BBOE) and in Kuwait is about 7–150 BBOE.

Age determinations of Cretaceous sequences based on calcareous nannofossils in Zagros Thrust and Folded Zone in Kurdistan Region-Iraq.

The studied area is located in Northern Iraq in the Kurdistan Region, in the North-&#x0D; Western part of the Zagros Fold belt. This study concentrates on the biostratigraphic&#x0D; approach using nannofossil analysis to identify the age of the formations that have&#x0D; deposited during Cretaceous period in Kurdistan Region-Iraq. The sedimentary&#x0D; sequences in Kurdistan region exhibit many lateral and vertical environmental and facies&#x0D; changes. Previously most of the works to recognize the age of the formations were&#x0D; concentrated on the Foraminifera zonation. In the present study, attempts have been&#x0D; made to review the age of the formations and the contact between them by using&#x0D; nannofossil analysis technique. Nannofossils assemblage Chia Gara Formations show&#x0D; that conformable contact situation between Jurassic-Cretaceous. The contact is between&#x0D; Late Tithonian Chia Gara and Berriasian- Valanginian Balambo formations. In Kurdistan&#x0D; during Hauterivian-Barremian the outer shelf sediment of Sarmord Formation deposited&#x0D; that conformably overlay Balambo Formation. The Qamchuqa Formation is a&#x0D; heterogeneous group of limestone. The lower part is belongs to the Aptian to Albian&#x0D; periods, while The upper part of the Qamchuqa limestone is generally dolomitized,&#x0D; therefore, the existed nannofossils even within the locally thin marl layers are destroyed.&#x0D; The Dokan Formation, which appears along the Dokan dam, is a Cenomanian age. The&#x0D; Kometan Formation is represented an Early Turonian age. The top of the Kometan&#x0D; limestone is characterized by a hard ground most possibly indicating a hiatus. The&#x0D; sequence of marl-Limestone of Shiranish Formation we dated Early to Late Campanian.&#x0D; Toward north the Early to Late Campanian part of Shiranish Formation can be locally&#x0D; replaced by the reefal Bekmeh limestone Formation. Very rare nannofossils were found&#x0D; in the marly intercalations of the Bekmeh limestone indicating at least a Late Cretaceous&#x0D; age. The Shiranish/Tanjero formations boundary lies within the Upper Campanian. The&#x0D; age of Tanjero Formation ranges from Late Campanian to Late Maastrichtian.

Geochemical investigation, oil–oil and oil–source rock correlation in the Dezful Embayment, Marun Oilfield, Zagros, Iran

Geochemical analysis of crude oils from Bangestan and Khami reservoirs, and potential source and reservoirs rocks from the Marun Field in the Dezful Embayment, Zagros Fold Belt Iran show that the Kazhdumi Formation (Fm.) is likely to be thermally mature (at least in the oil window) across the entirety of the Marun field, and that it has excellent generative potential as a source rock. Geochemical data also suggest the Pabdeh Formation has remarkable generative potential but is not thermally mature at the crest of the Marun field, although it is likely to be thermally mature in synclinal regions to the NE and SW. The Gurpi Formation, while thermally mature (early oil window) has marginal generative potential. It is notable, therefore, that oils from the Bangestan and Khami reservoirs have biomarker characteristics that do not match bitumen obtained from the Kazhdumi Formation. Examples of this include the ratio of diasteranes to steranes, the proportions of different carbon numbered hopane homologues and the ubiquitous occurrence of alkylated-trimethyl-benzenes. These biomarker characteristics could only have been imparted to the Bangestan and Khami oils by a source rock other than the Kazhdumi Formation. This contrasts with the stable isotope composition of the Bangestan and Khami oils which suggest correlation to the Kazhdumi Formation. Biomarkers are a quantitatively minor fraction of oil, thus it is possible that the biomarker characteristics of the oils was created by mixing Kazhdumi-bitumen with other petroleum from the Gurpi and Pabdeh formations. This could happen if 1) multiple oil charges from different source kitchens filled the same reservoir, or 2) if oil migrated vertically from the flanks and crossed the Gurpi and Pabdeh formations – both of which have been considered regional seals. Both scenario 1) or 2) would point to a filling history more complicated than previously conceived.

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.

Analysis of natural fractures and effect of deformation intensity on fracture density in Garau formation for shale gas development within two anticlines of Zagros fold and thrust belt, Iran

Abstract Shale-gas production depends on natural and hydraulic fractures to flow it to well. A major part of source rocks in the Zagros Fold Belt was deposited during Neocomian time; the lowermost part of the Garau Formation has charged the Early Cretaceous Petroleum System of the Lurestan subzone, which has a potential of being as a shale-gas resource. These source rocks are widely distributed in the Lurestan Depression and in the NW part of the Dezful Embayment. Knowing factors which control fracture intensity and fracture length in each area are important in drilling into shale-gas resources. In this regard, a very dense and accurate field data acquisition on fracture sets, orientation, length, as well as bedding thickness, texture and lithology was carried out in Early Cretaceous Garau Formation and basal Sarvak Formation within two anticlines with different structural settings (Kabir-Kuh and Khoram-Abad). According to our analyses, we have identified 2 fracture systems: (1) an orthogonal fracture system: set A in Khoram-Abad anticline and sets A and B in the Kabir-Kuh anticline and a longitudinal fracture set: set B in Khoram-Abad anticline and sets C and D in the Kabir-Kuh anticline, (2) an oblique fracture system: sets C and D in Khoram-Abad anticline and set E in the Kabir-Kuh anticline. The normal faults and stylolites (prior to stylolitization) in the study area of Kabir-Kuh anticline had formed in response to extension stress regime and the transverse fractures in the study area of Khoram-Abad anticline are Early Cretaceous to Late Oligocene in age, then the transverse fractures and their orthogonal stylolites in Kabir-Kuh anticline and longitudinal and oblique fracture systems in the Khoram-Abad anticline have formed from Early Miocene to Middle Late Miocene, while longitudinal and oblique fracture sets in the Kabir-Kuh anticline have formed since Middle Late Miocene. We suggest that there have been two phases of counterclockwise rotations in orientation of the stress fields that had produced these fractures. The rotations in the stress field have probably occurred due to rotation of the Arabian plate during its convergence to the Eurasian plate which had changed the orientation of fractures. These rotations forming some range of fractures with different attitudes, that now with recent direction of impression apply by the Arabian plate those fractures which generate in the past would have shown different reaction. In our study area in addition to transverse fracture sets which originated near parallel to maximum horizontal stress, one set of oblique fractures is the second normal fracture set which is reactivated in response to fluid pressures, prior to origination of new hydraulic fractures. In the Lurestan structural province, deformation intensity is increased from the Kabir-Kuh anticline in the southern part of the Lurestan structural province to the Khoram-Abad anticline in the northeastern part of the province. In the Kabir-Kuh anticline, lithology has played the most important role in fracture intensity, so that in some places even with increasing bedding thickness, we observe an increase in fracture intensity instead of the expected decreasing fracture intensity. While in Khoram-Abad anticline bedding thickness has the most important effect on fracture intensity, and lithology has a minor role. In both investigated areas, fracture length is increased with changing texture from mudstone to wackstone and also from wackstone to packstone.

Tectonic and stratigraphic evolution of Zagros and Makran during the Mesozoic–Cenozoic, edited by P.Leturmy and C.Robin. Geological Society Special Publication, London, 330. No. of pages: 355. Price UK£95.00. ISBN 978‐1‐86239‐293‐9 (cloth).

This volume is welcomed, given the recent ‘warming’ of relationships between Iran and the ‘western’ world that is resulting in more requests for geological cooperation in both directions. Most articles relate to the fruition of an international mega-project carried out during an intense period activity in the previous thawing of relations with Iran between 2003 and 2006. Leturmy and Robin commence their volume with an introduction that adequately sets the scene for the subsequent technical papers. Eight of these are structurally focussed, with the last five being related to stratigraphic and petroleum geological issues. In a brief review, such as this, I have chosen to mention just a few of these papers. Hatzfeld et al. outline recent advances in understanding the kinematics of the Zagros Mountains by use of GPS and Quaternary geological features, notably with reference to the Kaizerun Fault Zone, showing that deformation includes both basement and cover sediments. Regard et al. detail the structural and stratigraphical lateral transition between the Zagros orogenic belt and the Makran accretionary prism/trench subduction zone complex. A right-lateral motion is identified in which the Makran is thrust over the Zagros, along a crustal plane that dips to the NE. Navabpour et al. outline the evidence for Mesozoic extensional brittle tectonics in Interior Fars, of particular relevance when combined with an appreciation of palaeogeographic evolution of the same interval. Aubourg et al. present new magnetic fabric data from the Fars province that relate to the Neogene compression of the Zagros margin. They identify, in addition to the Late Miocene–Pliocene event, an earlier Early Miocene age event where many structures were initiated. Emami et al. examine the regional structure of the Mountain Front Flexure in Lurestan, notably the S-shaped Pusht-e-Kuh Arc with constituent Anaran anticline and its subvertical forelimb. They identify a significant collapse of the anticline with development of deep and narrow half-graben within the fold belt system. Robin et al. focus on the Mesozoic deepwater carbonates from the southern Tethyan passive margin. This contains a detailed synthesis of data from radiolarian assemblages, in addition to comprehensive logging of outcrop stratigraphy and integration of results, into an elegant synthesis of one of the unusually long-lived areas of deepwater deposition along the NE margin of the Arabian Plate. Piryaei et al. are more stratigraphically selective and discuss the influence of Late Cretaceous tectonic processes in Fars Province, showing the evolution from passive margin into an active, compressional one. Bordenave and Hegre present a masterful review of the impact of the multiple (five) petroleum systems of the Zagros and its foreland on the distribution of oil and gas fields. The first four are long-lived and have long migration paths, pre-dating the main late Cenozoic compression and trap development, with the fifth being syn-orogenic and characterized by much more localized and vertical, fracture-fed migration. Criticisms of the volume are few. The main omission, no doubt due to inaccessibility during the main phase of research, is the absence of any synthesis of the remaining third of the Zagros fold belt within Iraq and its relationship to the Taurides. Otherwise, writing is clear and concise, and there is a reasonable balance of papers. I recommend the volume as a comment on the state of our knowledge of both the Iranian Zagros and Makran (pre-2010), which will be exceedingly useful as and when opportunities to work arise in this fantastic and legendary part of the world.

Oil biomarkers, isotopes, and palynofacies are used for petroleum system type and migration pathway assessments of Iraqi oil fields

Analysis of δ13C aromatic and saturated hydrocarbons plus extracts from source-rock plots in graphical diagram as well as δ13C% and C28/C29 ratio of source-age sterane biomarkers of 300 scattered crude oil samples have enabled this study to assess groupings of hydrocarbons into families related to sedimentary basins in Iraq. Oil sources include Middle Jurassic strata of Sargelu Formation in the Zagros fold belt of North Iraq and eastern part of Mesan Governorate with Middle Jurassic as well as Upper Jurassic/Lower Cretaceous Chia Gara Formation in the North East based on a C28/C29 ratio of nearly 6 and 8, respectively. Mesopotamian Basin oil sources comprised mainly of Upper Jurassic/Lower Cretaceous Sulaiy Formation above the Upper Jurassic lower regional seal of the Gotnia Anhydrite except were thinned and faulted with a C28/C29 ratio that ranges between 5 and 9, which could cause mixing with Middle Jurassic Sargelu Formation oil. Middle Triassic oil in North West Iraq is recorded within Kurra Chine Formation with a C28/C29 ratio of 4, while Lower Palaeozoic oil sources are recorded in West Iraq. On the other hand, one formation may have multiple pay zones of Jurassic and Lower Cretaceous sources, such as Zubair and Yamama formations. The kerogens of the source rocks are confirmed by chemical analytical studies of pyrolysis and by microscopic studies of palynofacie types of the disseminated organic matters. PetroMod software basin modeling for hydrocarbon generation and palynomorphs for source-rock age assessments are discussed too. Oil accumulations in the reservoirs are assessed in this study using petrophysical properties to obtain hydrocarbon filling of the rocks and trapping dynamically mobile hydrocarbons in structural and stratigraphic traps in structural cross section and seismic sections. Petroleum system framework, interpreted in this study, could be used for hydrocarbon exploration and for mineral genesis of sulfur deposits through systematic studies and analysis in the proposed oil field especially when they are plotted on seismic section images for assessing the extent of source and reservoir rocks, and hence predicting hydrocarbon migration paths and finding new reservoirs and pay zones.

Sedimentological evidence for the Late Holocene sea level change at the Enjefa Beach exposures of Kuwait, NW Arabian Gulf

The mid-late Holocene drop in relative sea level has resulted in the deposition and progradation of coastal facies along the Enjefa Beach in Kuwait, NW Arabian Gulf. These coastal facies display various depositional subenvironments, including landward foreshore beach, tidal channel, shallow tidal channel, and coastal sand flat. The foreshore beach facies consist of dominantly planar laminated beds. Main tidal channel subenvironments are interpreted for the trough cross-bedded facies. The shallow tidal channel deposits are composed of variable oriented planar wedge-shaped and ripple cross-bedded facies. The coastal sand flat deposits consist of extensively burrowed beds with a large network of Ophiomorpha burrows. These exposures are overlain by the recent continental deposits of rubbles and artificial infill. The mere exposed occurrence of these rocks as well as the above facies stacking pattern reflects progradation as a result of relative drop in sea level. Based on the carbon dating of these sediments, the last phase of the relative sea level drop likely occurred around 1,800 years ago. Neotectonics of local structuring, due to the regional northeastward movement of the Arabian Plate under the Zagros Fold Belt, might have a role in this sea receding

Influences of surface processes on fold growth during 3‐D detachment folding

AbstractIn order to understand the interactions between surface processes and multilayer folding systems, we here present fully coupled three‐dimensional numerical simulations. The mechanical model represents a sedimentary cover with internal weak layers, detached over a much weaker basal layer representing salt or evaporites. Applying compression in one direction results in a series of three‐dimensional buckle folds, of which the topographic expression consists of anticlines and synclines. This topography is modified through time by mass redistribution, which is achieved by a combination of fluvial and hillslope erosion, as well as deposition, and which can in return influence the subsequent deformation. Model results show that surface processes do not have a significant influence on folding patterns and aspect ratio of the folds. Nevertheless, erosion reduces the amount of shortening required to initiate folding and increases the exhumation rates. Increased sedimentation in the synclines contributes to this effect by amplifying the fold growth rate by gravity. The main contribution of surface processes is rather due to their ability to strongly modify the initial topography and hence the initial random noise, prior to deformation. If larger initial random noise is present, folds amplify faster, which is consistent with previous detachment folding theory. Variations in thickness of the sedimentary cover (in one or two directions) also have a significant influence on the folding pattern, resulting in linear, large aspect ratio folds. Our simulation results can be applied to folding‐dominated fold‐and‐thrust belt systems, detached over weak basal layers, such as the Zagros Folded Belt.

Tectonics of the Musandam Peninsula and northern Oman Mountains: From ophiolite obduction to continental collision

ABSTRACT The tectonics of the Musandam Peninsula in northern Oman shows a transition between the Late Cretaceous ophiolite emplacement related tectonics recorded along the Oman Mountains and Dibba Zone to the SE and the Late Cenozoic continent-continent collision tectonics along the Zagros Mountains in Iran to the northwest. Three stages in the continental collision process have been recognized. Stage one involves the emplacement of the Semail Ophiolite from NE to SW onto the Mid-Permian–Mesozoic passive continental margin of Arabia. The Semail Ophiolite shows a lower ocean ridge axis suite of gabbros, tonalites, trondhjemites and lavas (Geotimes V1 unit) dated by U-Pb zircon between 96.4–95.4 Ma overlain by a post-ridge suite including island-arc related volcanics including boninites formed between 95.4–94.7 Ma (Lasail, V2 unit). The ophiolite obduction process began at 96 Ma with subduction of Triassic–Jurassic oceanic crust to depths of &amp;gt; 40 km to form the amphibolite/granulite facies metamorphic sole along an ENE-dipping subduction zone. U-Pb ages of partial melts in the sole amphibolites (95.6– 94.5 Ma) overlap precisely in age with the ophiolite crustal sequence, implying that subduction was occurring at the same time as the ophiolite was forming. The ophiolite, together with the underlying Haybi and Hawasina thrust sheets, were thrust southwest on top of the Permian–Mesozoic shelf carbonate sequence during the Late Cenomanian–Campanian. Subduction ended as unsubductable cherts and limestones (Oman Exotics) jammed at depths of 25–30 km. The Bani Hamid quartzites and calc-silicates associated with amphibolites derived from alkali basalt show high-temperature granulite facies mineral assemblages and represent lower crust material exhumed by late-stage out-of-sequence thrusting. Ophiolite obduction ended at ca. 70 Ma (Maastrichtian) with deposition of shallow-marine limestones transgressing all underlying thrust sheets. Stable shallow-marine conditions followed for at least 30 million years (from 65–35 Ma) along the WSW and ENE flanks of the mountain belt. Stage two occurred during the Late Oligocene–Early Miocene when a second phase of compression occurred in Musandam as the Arabian Plate began to collide with the Iran-western Makran continental margin. The Middle Permian to Cenomanian shelf carbonates, up to 4 km thick, together with pre-Permian basement rocks were thrust westwards along the Hagab Thrust for a minimum of 15 km. Early Miocene out-of-sequence thrusts cut through the shelf carbonates and overlying Pabdeh foreland basin in the subsurface offshore Ras al Khaimah and Musandam. This phase of crustal compression followed deposition of the Eocene Dammam and Oligocene Asmari formations in the United Arab Emirates (UAE), but ended by the mid-Miocene as thrust tip lines are all truncated along a regional unconformity at the base of the Upper Miocene Mishan Formation. The Oligocene–Early Miocene culmination of Musandam and late Cenozoic folding along the UAE foreland marks the initiation of the collision of Arabia with Central Iran in the Strait of Hormuz region. Stage three involved collision of Arabia and the Central Iran Plate during the Pliocene, with ca. 50 km of NE-SW shortening across the Zagros Fold Belt. Related deformation in the Musandam Peninsula is largely limited to north and eastward tilting of the peninsula to create a deeply indented coastline of drowned valleys (rias).

Mineralogy and geochemistry of alteration induced by hydrocarbon seepage in an evaporite formation; a case study from the Zagros Fold Belt, SW Iran

Leaking hydrocarbon and associated fluids produce a reduced environment which initiates diagenetic reactions in the rocks and soils overlying hydrocarbon reservoirs. This article introduces mineralogical and geochemical alterations induced by hydrocarbon seepages in the Gachsaran evaporite Formation, Masjed Soleiman, Zagros Folded Belt, SW Iran, using various geochemical methods. X-ray diffraction (XRD) analysis revealed two dominant groups of mineralogical changes in the anomalous zone including: (1) spotty occurrences of jarosite, natroalunite, and sulfur; (2) simultaneous decrease of sulfate and increase of carbonate. The δ13C values of carbonate phases vary between −8.9‰ and −32.3‰ which support a partial contribution of hydrocarbon in these phases. pH measurements of rock samples indicated that hydrocarbon seepage causes decrease of pH, though not very significantly. However, pH in areas that show ongoing sour hydrocarbon seepage among rarely pure gypsum beds decrease to −0.09 which produces acid sulfate soil. Trace element concentrations indicated that Cr, Co, Ni, V, Cd, U, Cu, and Zn increase in various patterns around the hydrocarbon seepages excepting the areas with very low pH.