SW Iran Research Articles

Ecological changes and depositional sequences during Cenomanian/Turonian platform evolution in the Zagros Basin, SW Iran; an interplay between tectonics and aquifer-eustasy

This study focuses on the facies associations and depositional sequences of a Cenomanian/Turonian (C/T) outcrop, spanning the upper part of the Sarvak Formation in the Izeh zone, Zagros basin, Iran. The significant variations in sedimentary facies of the studied succession suggest an evolution from a late Cenomanian open-shelf to an early Turonian ramp system. This change is believed to be response of transition in the tectonic regime of Arabian plate from a passive to an active margin during the late Cretaceous. Two partial and one complete third-order depositional sequences and also several fourth-order sequences and small-scale cycles were recognized in the studied section. The global correlation of the third-order sequences suggests that they were eustatically-driven. However, local tectonic activities overprint the eustatic signature from the latest Cenomanian. The association of transgressions with cooling and regressions with warming during the fourth-order sequences support the aquifer-eustasy model as a controlling factor for the sea-level fluctuations under C/T supergreenhouse conditions.

Biochemostratigraphy of an upper Albian–Turonian succession from the southeastern Neo-Tethys margin, SW Iran

A Neo-Tethyan upper Albian–Turonian (hemi-)pelagic carbonate succession (Sarvak Formation), accessible in outcrop in the Zagros, SW Iran, was investigated using sedimentology, microfacies analysis, planktonic foraminifera biostratigraphy, and carbon-isotope stratigraphy. The succession contains six biozones including Thalmanninella (Th.) appenninica, Th. globotruncanoides, Rotalipora cushmani, Whiteinella archaeocretacea, Helvetoglobotruncana Helvetica, and Marginotruncana schneegansi. Some of these biozones show variable stratigraphic positions throughout the Tethyan and Boreal realms that hinder correlation of the studied Iranian section with European reference sections. Therefore, the correlation of the existing biostratigraphic framework was complemented by carbonate carbon-isotope stratigraphy based on bulk carbonate material. Despite the low resolution of the presented carbon-isotope record, pronounced global events including the late Turonian Events, Cenomanian/Turonian Boundary (CTB) Event (OAE 2), and Albian/Cenomanian Boundary (ACB) Event can be distinguished. The δ13C excursions provide global synchronous time-lines for correlation. The distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these time-lines. The correlation tentatively suggests that the biostratigraphic datum marking the ACB is diachronous with an SE–NW trend. First appearance datum (FAD) of Th. appenninica varies from the upper Albian to the lower Cenomanian. The FAD of Th. globotruncanoides is also variable from the upper Albian to the lower Cenomanian. However, the middle Cenomanian–Turonian biozones including Rotalipora cushmani and Whiteinella archaeocretacea zones are synchronous. Elevated pCO2 contributed to the gradual increase of the SST (sea surface temperature) during the Cenomanian, and the dramatic climax at the earliest Turonian. This trend closely correlates with the change from the diachronous ACB-biozones to synchronous CTB-biozones. Possibly, increasing SSTs provided temperature-tolerance range for the species throughout different latitudes, and assisted their rapid distribution. Moreover, the warming raised the sea level from the latest Albian to Turonian that inundated landbridges, resulting in an enhanced marine circulation and faster distribution of planktonic species throughout the Neo-Tethys Ocean.

The Cenomanian/Turonian boundary interval deep-sea deposits in the Zagros Basin (SW Iran): Bioevents, carbon isotope record and palaeoceanographic model

The Cenomanian/Turonian (C/T) boundary interval, spanning the upper part of the Sarvak Formation in the Zagros Basin (Izeh Zone), has been studied to determine the timing and the possible cause of biotic turnovers, coinciding with the intense environmental perturbations during the Oceanic Anoxic Event 2 (OAE2). The upper Cenomanian strata in the study section, composed of light-colour marlstone/organic-rich marlstone and shale bedding couplets, record fluctuations in microfossil assemblages and organic carbon contents. We suggest that the organic-poor layers, characterized by high abundance of radiolarians, were deposited during cold periods under surface water eutrophication (upwelling) and ventilated seafloor. In contrast, water column stratification during warm periods enhanced organic matter preservation and allowed deposition of organic-rich strata. Continued stratification and also increased runoff and primary productivity during warm intervals of OAE2 led to expansion of oxygen minimum zone (OMZ), which may have caused extinctions of deep followed by intermediate water planktic foraminifera. Such conditions may have led to significant decreases in the abundance and diversity of planktic foraminifera and dominance of the biserial genus Planoheterohelix (“Heterohelix” shift event). The δ13C curve in the study interval reveals the diagnostic features of global C/T boundary carbon isotope record, including three positive peaks (A, B and C) within the Whiteinella archaeocretacea Biozone. These carbon isotope features and the most important bioevents in the study section are stratigraphically listed below: 1- Highest occurrences (HOs) of Th. greenhornensis and Th. deeckei, 2- HO of R. cushmani and δ13C peak A, 3- HO of “G”. bentonensis, 4- Onset of “Heterohelix” shift event, 5- δ13C peak B, 6- δ13C peak C, 7- Filament event, 8- Lowest occurrence (LO) of H. helvetica, and 9- Holywell event.

Estimation of the current stress field and fault reactivation analysis in the Asmari reservoir, SW Iran

Knowing the current condition of the faults and fractures in a reservoir is crucial for production and injection activities. A good estimation of the fault reactivation potential in the current stress field is a useful tool for locating the appropriate spot to drill injection wells and to calculate the maximum sustainable pore pressure in enhanced oil recovery and geosequestration projects. In this study, after specifying the current stress state in the Gachsaran oilfield based on Anderson’s faulting theory, the reactivation tendency of four faults (F1, F2, F3, and F4) in the Asmari reservoir is analyzed using 3D Mohr diagrams and slip tendency factors. Results showed that all the faults are stable in the current stress state, and F2 has the potential to undergo the highest pore pressure build-up in the field. On the other hand, F3 has the proper conditions (i.e., strike and dip referring to σHmax orientation) for reactivation. Stress polygons were also applied to show the effect of the pore pressure increase on fault stability, in a graphical manner. According to the results, the best location for drilling a new injection well in this part of the field is the NW side of F2, due to the lower risk of reactivation. It was found that both methods of 3D Mohr diagrams and slip tendency factors predict similar results, and with the lack of image logs for stress orientation determination, the slip tendency method can be applied. The results of such studies can also be used for locating safe injection points and determining the injection pressure prior to numerical modeling in further geomechanical studies.

Trachyspermum reginei sp. nov. (Apiaceae) from southwest Iran

Trachyspermum reginei Ajani & Mozzaff. sp. nov., is described and illustrated as a new species from Chaharmahale Bakhtiari province, SW Iran. The new species differs from its closest relative T. confusum, endemic to Afghanistan, mainly by stem, leaf and fruit morphological characters. Its taxonomic relationships with T. podlechii and T. ammi are also discussed. The new species is threatened by different factors and its protection is recommended.

Jurassic igneous rocks of the central Sanandaj–Sirjan zone (Iran) mark a propagating continental rift, not a magmatic arc

AbstractJurassic igneous bodies of the Sanandaj–Sirjan zone (SaSZ) in SW Iran are generally considered as a magmatic arc but critical evaluation of modern geochronology, geochemistry and radiogenic isotopes challenges this conclusion. There is no evidence for sustained igneous activity along the ~1,200 km long SaSZ, as expected for a convergent plate margin; instead activity was brief at most sites and propagated NW at ~20 mm/a. Jurassic igneous rocks define a bimodal suite of gabbro‐diorite and granite. Chemical and isotopic compositions of mafic rocks indicate subcontinental lithospheric mantle sources that mostly lacked subduction‐related modifications. The arc‐like features of S‐type granites reflect massive involvement of Cadomian crust and younger sediments to generate felsic melts in response to mafic intrusions. We conclude that Jurassic SaSZ igneous activity occurred in a continental rift, not an arc. SaSZ igneous rocks do not indicate that subduction along the SW margin of Eurasia began in Jurassic time.

Efficiency of seismic wave velocity and electrical resistivity in estimation of limestone rock mass quality indices (Q, Qsrm) (Case study: Asmari formation, SW Iran)

In this research, the relationship between P-wave velocity (Vp) and Electrical Resistivity (ER) parameters with rock mass quality indices is investigated; parameters such as rock mass quality classification (Q) and modified system for sedimentary rocks, known as Qsrm. For making predictive models, about 1200 data-sets extracted from sections drilled in Seymareh and Karun 2 Dam Sites (SDS and KDS) in Asmari Formation, south-west Iran. Statistical and fuzzy methods used to study the relationships between physical characteristics and rock mass quality. Since in Qsrm classification, the existence of cavities, layering and rock texture is considered in addition to the parameters considered in the Q classification; therefore, it provides a better description of rock mass and is closely related with Vp and ER parameters. The obtained equations for predicting Q and Qsrm showed the determination coefficients (R2) 0.48 and 0.67, respectively, and the coefficient of determination 0.86 for Qsrm calculated from the fuzzy model. Finally, Mean Absolute Deviation (MAD), Variance Accounted For (VAF) and Root Mean Square Error (RMSE) used to check the prediction performance of statistical and fuzzy methods. The results of the calculated errors also showed that fuzzy models are interesting because they have good accuracy for predicting Qsrm. In addition, by increasing the degree of karstifiction, the efficiency of the geophysical method for estimate of Q decreases rapidly, this is due to ignoring the cavities in these categories.

Dissocladella compressa n. sp., a new Dasycladale (green algae) from the Upper Maastrichtian of Iran

The new dasycladalean alga Dissocladella compressa is described from the lower part of the Tarbur Formation of SW Iran (Zagros Zone). The medium-sized representative of the genus is characterized by rather large primaries displaying slight vertical compression. It occurs in a foraminiferan-algal packstone associated with larger benthic foraminifera typically Omphalocyclus macroporus Lamarck, Loftusia sp., Siderolites cf. calcitrapoides Lamarck, and scattered corals. Associated algae include Trinocladus tripolitanus Raineri, Thyrsoporella longa Radoicic, Ovulites delicatula Elliott, accessory udoteaceans, and corallinaceans.

Pseudochablaisia subglobosa gen. et sp. nov., a new pfenderinid foraminifera from the Upper Cretaceous of Iran

A new microgranular-imperforate foraminifera, attributed to the family Pfenderinidae, is described as Pseudochablaisia subglobosa gen. et sp. nov. from the upper Maastrichtian Tarbur Formation (Zagros Zone, SW Iran). It occurs in inner platform wackestones/packstones associated with other larger benthic foraminifera (e.g., Loftusia, Omphalocyclus, Gyroconulina) and dasycladacean green algae (e.g., Cymopolia, Dissocladella, Thyrsoporella). Pseudochablaisia gen. nov. is compared with possible ancestral morphotypes, the Middle Jurassic to Oxfordian homeomorph Chablaisia Septfontaine, 1978 and sections of a taxon classically assigned to the middle-Late Cretaceous “Nezzazatinella” Darmoian (1976) which type-material is incompletely known from loose isolated specimens. These two homeomorphic taxa and the new genus Pseudochablaisia possess a trochospirally coiled test, with a pseudokeriothecal wall texture (sometimes hardly visible). The central structure of the test comprises an umbilical (“siphonal”) hollow columella in early stages continuing in a deep umbilical cavity in later stages. The chamber interior is occupied by a zone of coalescence of the septa and a septal button, lacking in sections of “Nezzazatinella".

Effects of late diagenesis on primary reservoir quality of a quartz arenite unit: a case study from the lower Cretaceous successions of SW Iran

In this study, a sandstone interval of the lower Cretaceous successions in SW Iran is analyzed regarding the effects of late diagenesis on the alteration of primary reservoir quality and pore system. Petrological and geochemical analyses indicate dominant quartz mineralogy (quartz arenite) deposited in distributary channel and mouth bar environments which is embedded in delta front to prodelta argillaceous sediments. Rather than mineralogy and some remaining primary (intergranular) porosity, several late (burial) diagenetic processes including multi-phase carbonate cementation, chlorite cementation, and chemical compaction, affected the reservoir quality. Most of the diagenetic processes had a decreasing effect on the primary reservoir quality. All recognized diagenetic features are related to burial diagenesis of the surrounding open marine shales (clay mineral transformation) and expelled diagenetic fluids.

BURIAL, TEMPERATURE AND MATURATION HISTORY OF CRETACEOUS SOURCE ROCKS IN THE NW PERSIAN GULF, OFFSHORE SW IRAN: 3D BASIN MODELLING

This study presents a 3D numerical model of a study area in the NW part of the Persian Gulf, offshore SW Iran. The purpose is to investigate the burial and thermal history of the region from the Cretaceous to the present day, and to investigate the location of hydrocarbon generating kitchens and the relative timing of hydrocarbon generation/migration versus trap formation. The study area covers about 20,000 km2 and incorporates part of the intra‐shelf Garau‐Gotnia Basin and the adjacent Surmeh‐Hith carbonate platform. A conceptual model was developed based on the interpretation of 2700 km of 2D seismic lines, and depth and thickness maps were created tied to data from 20 wells. The thermal model was calibrated using bottom‐hole temperature and vitrinite reflectance data from ten wells, taking into account the main phases of erosion/non‐deposition and the variable temporal and spatial heat flow histories. Estimates of eroded thicknesses and the determination of heat‐flow values were performed by burial and thermal history reconstruction at various well and pseudo‐well locations. Burial, temperature and maturation histories are presented for four of these locations. Detailed modelling results for Neocomian and Albian source rock successions are provided for six locations in the intra‐shelf basin and the adjacent carbonate platform. Changes in sediment supply and depocentre migration through time were analyzed based on isopach maps representing four stratigraphic intervals between the Tithonian and the Recent. Backstripping at various locations indicates variable tectonic subsidence and emergence at different time periods.The modelling results suggest that the convergence between the Eurasian and Arabian Plates which resulted in the Zagros orogeny has significantly influenced the burial and thermal evolution of the region. Burial depths are greatest in the study area in the Binak Trough and Northern Depression. These depocentres host the main kitchen areas for hydrocarbon generation, and the organic‐rich Neocomian and Albian source rock successions have been buried sufficiently deeply to be thermally mature. Early oil window maturities for these successions were reached between the Late Cretaceous (90 Ma) and the early Miocene (18 Ma) at different locations, and hydrocarbon generation may continue at the present‐day.

Style and timing of salt movement in the Persian Gulf basin, offshore Iran: Insights from halokinetic sequences adjacent to the Tonb-e-Bozorg salt diapir

The variations in the rate of salt rise is reflected in the sedimentary sequences adjacent to salt diapirs and provides insights into the style of salt movement-sedimentation interaction and the timing of halokinetic phases. Episodic movement of salt diapir is defined by wedge- and tabular-shaped salt-related sedimentary strata (halokinetic sequences) adjacent to the diapir. Detailed mapping of depositional strata on 2D seismic sections adjacent to salt diapirs on the Tonb-e-Bozorg Island (Persian Gulf, SW Iran) reveals the presence of a series of sedimentary sequences related to the halokinetic activity of two salt source layers, the Hormuz and Fars salts, respectively. The Hormuz salt deposited in the uppermost Proterozoic, mobilized in the Lower Paleozoic and then continued to move periodically to present and to create the deep salt structures in the Tonb-e-Bozorg region. The Fars salt deposited in the Lower Miocene and then started rising, and created the central salt structure, the Tonb-e-Bozorg Island, and several peripheral ring-like salt structures around the island. Our results reveal that both the salt layers within the Tonb-e-Bozorg region grew by downbuilding and continued to move periodically by passive and active diapirism to the present. Salt movement-sedimentation interaction during salt diapirism influences petroleum play and therefore is of interest in petroleum geoscience.

Index-based evaluation of pollution characteristics and health risk of potentially toxic metals in schools dust of Shiraz megacity, SW Iran

The concentrations of eight potentially toxic metals (i.e., As, Co, Cr, Cu, Cd, Ni, Pb, and Zn) and their contamination levels in dust collected from some schools of Shiraz city, Iran, have been studied in this work. The pollution of studied metals was assessed using ordinary pollution indices (i.e., PI, Igeo, and EF). The results of calculated pollution load index (PLI) revealed that the contamination status can be more likely attributed to the anthropogenic activities in this region. The results also indicated that traffic and combustion of fossil fuels as well as industrial activities are primary sources that rised heavy metals concentration in school dust. The noncancer risk of individual metals for both children and adults followed the decreasing trend of Pb > Cr > As > Ni > Cd > Cu > Zn > Co and Cr > Pb > As > Cd > Ni > Cu > Zn > Co, respectively. The HI value of Pb and Cr for children is very close to the safety limit, while HI values of other studied metals were fallen in the safe level. In terms of carcinogen risk, Cr, As, and Pb presented in the major of schools were found to be within the cancer threshold limit. However, the cancer risk of exposure to Cd, Ni, and Co was the lowest and could be neglected. The findings indicate that more investigations should be spend on potentially toxic metal contaminations in Shiraz schools, especially for Cr, As, and Pb.

Assessment of the engineering geological characteristics of the Bazoft dam site, SW Iran

The geotechnical parameters and permeability of the Bazoft dam site were investigated. The bedrock of the Bazoft dam site belongs to the Asmari and Jahrum (Eocene, Oligocene and Miocene) formations. Rock mass rating (RMR) and geological strength index (GSI) classification systems were used to evaluate the dam site. Physical, mechanical and dynamic tests were performed on samples in a rock mechanics laboratory. Shear strength parameters and geotechnical parameters of the rock mass were determined. The results of Lugeon tests for determining rock mass permeability were in the range of 10–30. Based on the RMR, the dam site is located in the ‘good’ category. Finally, the relationship between Lugeon, the number of joints and rock quality designation ( RQD) of the rock mass was evaluated using statistical analysis for 24 exploratory boreholes with a total length of 3400 m. The values of these parameters were determined and analysed using equations, tables and reports in sections of 5 m along the borehole. The results showed that the relationship between Lugeon with RQD and the joint number is an exponential equation with a good correlation coefficient. Multiple linear analysis also showed high accuracy of the estimated Lugeon based on RQD and joint number.

The "avatars" of Triloculina laevigata Orbigny, 1826, generic and specific attribution

A new dasycladalean alga is described as Uteria naghanensis n. sp. from the late Maastrichtian Tarbur Formation of the Zagros Zone, SW Iran. It is a small to medium-sized, rather well calcified species with small articles each bearing one fertile ampulla, alternating with close-set verticils of numerous sterile laterals. Another characteristic is its comparably wide main axis. The genus Uteria Michelin was so far only known from the Paleogene (Danian-Lutetian). The discovery of U. naghanensis n. sp. in inner platform wackestone of the Tarbur Fm. documents the origination of the genus already in the uppermost Cretaceous within an area belonging to the Arabian Plate.

Enhanced velocity-based pore-pressure prediction using lithofacies clustering: a case study from a reservoir with complex lithology in Dezful Embayment, SW Iran

The primary goal of this paper is to improve accuracy and reliability of the conventional Bowers and Tau methods in a reservoir with complex lithology. We demonstrate the capability of the proposed method through a case study in a reservoir in the Southwest of Iran. Velocity based pore pressure prediction methods are widely accepted as a routine technique in the petroleum industry. Despite recent improvements, still, literature suffer from inconsistencies and uncertainties mostly arise from velocity anomalies due to complex lithostratigraphic setting or presence of various formation fluids. Our proposed workflow aims to address those issues and improve the accuracy of the estimations by clustering the input data into zones with specific geomechanical characteristics. We hypothesis each major zones at the offset test wells might have distinct Normal Compaction Trend with a different empirical constants. Thus, Bowers and Tau methods should be calibrated for each cluster rather the whole stratigraphic column. The clustering task was done by statistical analyses of a suite of well logs and validated with core derived lithologies. Several clustering techniques namely K-means, basic sequential algorithmic scheme, single, and complete linkage hierarchical were applied and compared to find the best algorithm. We found that the self-organizing map (SOM) method provide the best results by maximizing lithology likelihood within each cluster and improve the efficiency of the Bowers and Tau methods. Satisfactory results of this study offer a safe ground for implementation of the proposed method in other sedimentary basins.

Assessment of temperature and rainfall changes in the Karoun River basin

An increase in greenhouse effect leads to climate change, a rise in sea levels, higher heat waves, an increase in extreme climatic frequency, an increase in wildfire risks, and other consequences pregnant with several different natural hazards. In Karoun River basin, SW Iran, climate change is likely to affect nearly every aspect of surface and underground water. The outputs from representative concentration pathways (RCPs) are applied in simulating the maximum and minimum temperature and rainfall changes in this basin. The assessments are tested based on the ability of models in reproducing the regional climatological trends. The best goodness of fit among RCP scenarios is involved through RCP 4.5. The simulated results of each scenario indicate a significant increase above 1 °C in the minimum temperature during warm months over most areas of the basin. The change in maximum temperature at most stations is linked to seasonal cold to warm transition months of the year. A reduction in autumn and winter rainfall and an increase in spring rainfall are expected for the coming three decades. The changes in rainfall pattern lead to a higher 24-h maximum precipitation which increases flooding probability especially at discharges greater than 2000 m3/s.

Structural analysis of the Aghajari and Pazanan anticlines, Dezful Embayment, SW Iran

In the present study, seismic profiles and well data were used to provide detailed deformational patterns through the Aghajari and Pazanan anticlines located in the Zagros fold and thrust belt. A suite of 32 and 26 seismic profiles obtained from the Aghajari and Pazanan anticlines, respectively were examined. Furthermore, some 50 well data upon top of drilled formations were applied to prepare depth contour map of the relevant formations in these two anticlines. These asymmetric anticlines with a northwest-southeast trend and en-echelon pattern host considerable oil reserve in the Dezful Embayment. The fold axis of these anticlines are not identical above and below the upper detachment level (the Middle Miocene Gachsaran Formation). Progressive deformation caused thinning and escape of incompetent layers of the Gachsaran Formation from the crest of the anticlines toward adjacent synclines. A main deep-rooted fore-thrust within middle detachment level (the Lower Cretaceous Garu Formation) also cuts up-section toward the foreland and flattens in the Gachsaran detachment. Furthermore, a back-thrust cuts up from the main thrust into the hinterland. The shortening percentage was estimated in 58 seismic profiles across the Pazanan and Aghajari anticlines, by averaging of the Asmari, Sarvak and Fahlian Formations’ top restoration. The maximum and minimum amount of shortening is about 11.1 and 8.5 percent, respectively which is slightly less than those reported along the Dezful Embayment. The Hendijan High is the most important structure between the Aghajari and Pazanan anticlines which imparted considerable changes in basin fill facies. These changes presumably affected the folding geometry of the area, since it is similar to the fault bend folding geometry through the Hendijan High wherein exhibit fault propagation folding geometry on its both flanks. There is an anomaly and discontinuity in the depth contour maps of the Asmari and Fahlian formations which separated the northwest termination of the Pazanan anticline from the rest of the structure. Reasonably, it is better to consider it as southeast continuation of the Aghajari anticline, which is similar to the most anticlines with en-echelon pattern.

Concentration, contamination level, source identification of selective trace elements in Shiraz atmospheric dust sediments (Fars Province, SW Iran).

Geogenic dust is one of the most important environmental hazards in Iran. This study investigated the concentration, contamination level, potential sources, and ecological risk and human health assessment of Shiraz atmospheric dust, the largest city in southern Iran. Contents of atmosphericdust sediments geochemistrywere determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The mean concentrations of the elements in atmospheric dust are Zn (106.6mg/kg), Cr (98.4mg/kg), Ni (68.1mg/kg), Cu (40.5mg/kg), Pb (30.6mg/kg), As (4.5mg/kg), and Cd (0.28mg/kg). Except As and Cd, levels of all other elements in dust sedimentssamples were higher than corresponding background world soils. In comparison with the concentrations of studied heavy metals in Shiraz urban street dust, the concentrations of heavy metals in Shiraz atmospheric dust were substantially at low levels. Based on Enrichment Factor (EF) and Geo-accumulation index (Igeo), Shiraz atmospheric dust is moderately to minimally polluted by selected heavy metals. The values of risk index (RI) for seven heavy metals in all dust samples were 146.2 and 130.8, which were lower than 150, indicating that ecological risks posed by studied elements in atmospheric dust were moderate. Human health risk assessment (non-carcinogenic) suggested that of the three exposure pathways, ingestion of atmospheric dust was the major pathway exposure to heavy metals in dust, followed by skin contact. The hazard index (HI) values for all studied heavy metals decreased in the following order: Cr > Pb > Ni > Cu > Zn > Cd for both children and adults. Cr and Ni contribute most to health risk posed by atmospheric dust exposure for both children and adults, and Cd, Zn, and Cu have smaller contributions. The result of cancer risk assessment suggested that Cr, Ni, and Cd were all below the safe level. Principal component analysis (PCA) indicated that grouped Cd, Ni, and Zn and grouped Cr, Cu, and Pb could be controlled by two different types of anthropogenic source. Whereas, As and Zn were controlled by both human and geogenic sources.

Structural characteristic of a thrust system related gneiss dome of the Zagros hinterland-fold-and-thrust belt: The Sourian and Tutak metamorphic complexes, SW Iran

The Zagros hinterland fold-and-thrust belt left eye-catching features during its evolutionary episodic processes. As such features, the Tutak gneiss dome consists of exhumed middle crust including the Sourian and Tutak metamorphic complexes, which are lied on its edges and core respectively. In spite of several studies were carried out on the two mentioned metamorphic complexes, the structural nature of the dome, not correctly identified, yet. Therefore, the main purpose of this study is to highlight clues about formation mechanism of the Sourian and Tutak metamorphic complexes through structural and microstructural analyses and cross section reconstructions. Based on the fieldwork data, three main deformation phases concordance to the multiphase regional deformation of the Zagros hinterland fold-and-thrust belt, impressed the Sourian and Tutak metamorphic complexes resulted to development of multiple fold generations with interference pattern. According to the constructed cross section and microstructural analyses, it seems that Jian and Sourian major thrusts were controlled the exhumation of the Tutak gneiss dome (thrust-related gneiss dome) along a hybrid channel with producing a duplex thrust system.