NE Iran Research Articles

Influence of rift geometry over successive post-rift sedimentation: Tectonostratigraphy of the eastern Kopeh Dagh Belt (NE Iran)

Well, seismic (2D and 3D) and AHe age data, complemented by field surveys, were analyzed with the objective of investigating the tectono-stratigraphic evolution of syn- and post-rift sedimentary basins in the eastern Kopeh Dagh Belt (NE Iran), a region well known for its important oil and gas occurrences. The study was focused on evaluating how and when the geometry of syn-rift structures influenced the development of the post-rift sedimentation. Our results show that the Middle Jurassic rifting stage influenced the geometry of the post-rift basins. Carbonate buildup of the Upper Jurassic (Mozduran reservoir) was formed in the low relief accommodation zones between the Middle Jurassic opposing half-grabens in parallel to the sedimentation of argillaceous carbonates within the adjacent troughs. This geometry was also transmitted to the Lower Cretaceous, affecting the deposition of a relevant siliciclastic system (Shurijeh reservoir). The role of rifting was crucial in the distribution of reservoir facies and the generation of the structural-stratigraphic traps in the study area, which were also affected by late tectonic inversion. Uplift and denudation is likely to have occurred up to Late Miocene.

From Gondwana rifting to Alpine orogeny: Detrital zircon geochronologic and provenance signals from the Kopet Dagh Basin (NE Iran)

The Kopet Dagh mountains in NE Iran exhibit a 7-km-thick continuous sedimentary sequence recording detritus from exposed surrounding terranes from the last 175 Ma. This work presents a multi-disciplinary geochronologic and provenance analysis in an attempt to identify and date major geologic events along the northern segment of the Tethys and reconstruct the regional tectonic history from Gondwana-related rifting until the Alpine orogeny. Sandstone framework, heavy mineral analysis, U-Pb dating of detrital zircons, and Hf-isotope ratio measurements on dated zircons from Triassic to Paleocene sandstones indicate three main tectonic events that include Early Silurian intracontinental rifting (opening of Paleo-Tethys), Early Carboniferous rifting of a back-arc basin (Aghdarband Complex), and Late Triassic collisional to post-collisional magmatism (Paleo-Tethys collision). Mineralogical and age peak considerations indicate that detritus was supplied from the south into the extensional Kopet Dagh Basin during Middle Jurassic, while Cretaceous to Paleocene sandstones show signs of increasing recycling.

Compositional and Geochemical Signatures of Oligocene volcanoclastic sandstones of Abbasabad-Kahak area, NE Iran: Implications for provenance relations and paleogeography

Petrography and geochemistry of sandstone for the lower Oligocene volcanic-related sandstones of Abbasabad-Kahak area, NE Iran, are detected to decipher provenance, tectonic setting and paleo-weathering of source areas. Lower Oligocene sandstones are grey in colour and host copper mineralization as bedded and lenticular, vein-veinlets and disseminated textures and structures. Texturally, sandstones are medium to coarse grained, moderately to poorly sorted and compositionally have abundance of volcanic lithic fragments. Sandstones are lithofeldspathic to feldspatholithic, leading to a provenance from the progressive dismantling of a magmatic arc. Geochemical signatures suggest a derivation from mafic-to-intermediate volcanic sources. CIA values (56–61 with the average of 57) indicate a low level of chemical weathering in source areas, which may reflect arid to semi-arid climatic conditions in source terrains. These sandstones, deposited in a remnant backarc basin, are the results of the post-Eocene extensional stage of a dismantling magmatic arc.

An engineering geological assessment for the Darband dam site, NE of Iran, using eight rock mass classification systems

An engineering geological assessment for the Darband dam site, NE of Iran, using eight rock mass classification systems

Classification of synoptic weather clusters associated with dust accumulation over southeastern areas of the Caspian Sea (Northeast Iran and Karakum desert)

• Determination of weather clusters associated with high dust-AODs over northeast Iran/Karakum desert. • Six identified weather clusters from PCA with highest frequency in spring. • The dust hotpot areas are attributed to convergence of northerly and southwesterly winds over NE Iran. • The Siberian High and Qibla wind in central Iran modulate the dust accumulation. • Changes in position, intensity and expansion of the upper-level subtropical jet modulate the dust distribution. In this study, daily-mean total and dust aerosol optical depth (TAOD, DAOD, respectively) obtained from the Monitoring Atmospheric Composition and Climate (MACC) and meteorological fields from ERA-Interim reanalysis are used to identify spatial patterns of dust accumulation over northeast Iran and Karakum Desert during 2003–2012. The most dust-affected area is defined using highest variances of DAOD by S-mode and weather clusters by T-mode principal component analysis (PCA). Six weather clusters are classified via the statistical analysis, associated with high DAOD values, with larger frequency in spring, while PC1 (41 cases) dominates in summer. The results show that changes in the intensity and expansion of the Siberian/European high-pressures in spring modulate strong northeasterlies or northwesterlies over Central Asia, which are associated with frontal dust storms over the desert areas (Aralkum, Karakum). In addition, dynamic conditions associated with the sub-tropical jet stream and the Iranian trough, and combined with convective conditions at areas of thermal lows in east Iran, create a strong southwesterly wind – called Qibla – over the Iranian Plateau. These two contrasting wind regimes converge over northeast Iran/Karakum Desert, facilitating dust accumulation over the area. In summer, northerly winds dominate over Central Asia, but the absence of Qibla flow allows them to traverse till the north coast of the Arabian Sea, where they converge with the southwest monsoon flow. The accumulation of dust over northeast Iran/Karakum is lesser than that over Pakistan and Thar desert. Furthermore, the upper-level sub-tropical jet stream moves northward in summer, with core over Turkmenistan/Uzbekistan.

The oxic Coniacian-Santonian interval in the Kopet-Dagh Basin (NE Iran): Carbon isotope and benthic-planktic foraminiferal assemblages at the time of the last Cretaceous OAE

A middle Coniacian-middle Santonian interval has been studied in the Kopet-Dagh Basin (NE Iran) to reconstruct the paleoenvironmental conditions in the eastern part of Tethyan realm at the time of the last Cretaceous Oceanic Anoxic Event (OAE3). This succession is composed of a chalky limestone unit, sandwiched by light gray calcareous mudstone and marlstone beds. The δ 13 C curve indicates several minor positive shifts up to 1‰ in the studied section that is correlative to other carbon isotope curves from the Tethys and Boreal realms. A prominent upward increase of P/B ratio in the studied section suggests a relative sea-level rise toward the Santonian. Lithology (low carbonate contents) and faunal contents (high %benthic and higher infaunal benthic foraminifera) reveal that the lower part of the studied section was deposited in a neritic environment influenced by continental-derived nutrients and mesotrophic to eutrophic conditions. Enhanced carbonate contents, higher diversity of benthic foraminifera and dominance of epifaunal taxa suggest more oligotrophic conditions and/or higher oxygen concentrations in the interval equivalent with a δ 13 C positive shift, caused by a transgression phase at this time. The overlying deposits are characterized by the maximum flooding surface and the highstand phase. The stratification of water column and more oxygen consumption in this interval resulted in higher abundance of infaunal benthic foraminifera and decline of carbonate production in a bathyal environment. • Coniacian/Santonian boundary interval was deposited under oxic conditions in the E Tethys. • No black shales or anoxia mark this inferred OAE3 interval. • Sea-level fluctuations control foraminiferal assemblages in this study. • The δ 13 C curve reveals the diagnostic features of global Co/Sa boundary record.

Three-dimensional Subsurface Modeling and Classification of Mineral Reserve: A Case Study of the C-North Iron Skarn Ore Reserve, Sangan, NE Iran

Three-dimensional Subsurface Modeling and Classification of Mineral Reserve: A Case Study of the C-North Iron Skarn Ore Reserve, Sangan, NE Iran

The Fourier transform infrared spectroscopy (FTIR) analysis for the clay mineralogy studies in a clastic reservoir

The complete characteristics knowledge of clay minerals is necessary in the evaluation studies of hydrocarbon reservoirs. Ten samples taken from two wells in a heterogeneous clastic gas reservoir formation in NE Iran were selected to conduct the transmission Fourier transform infrared spectroscopy (FTIR) tests for the clay mineralogy studies. The FTIR analysis showed that there were clear signs of clay minerals in all samples. The wavenumber region of the clay minerals in FTIR tests was detected to be 3621, 3432, 1034, and 515 cm−1 for illite, 3567, 3432, 1613, 1088, 990, 687, 651, and 515 cm−1 for magnesium-rich chlorite, 3700, 3621, 3432, 1034, 687, and 463 cm−1 for kaolinite, and 3567, 1088, 990, and 463 cm−1 for glauconite. After screening of samples by the FTIR method, the samples were then analyzed by powder X-ray diffraction (PXRD), wavelength dispersive X-ray fluorescence (WDXRF), and scanning electron microscopy (SEM). The PXRD and SEM result showed illite was by far the most common clay present. Kaolinite, magnesium-rich chlorite, and traces of smectite and the mixed-layer clays of both the illite–smectite and chlorite-smectite types were also recognized. The combination of PXRD and WDXRF results could quantify the clay abundances in the each well too. It was concluded that the FTIR analysis successfully could show the absorption bonds of all constituent clays. However, the infrared absorption spectra of mixed-layer clays overlapped those of the respective constituents of each mixed-layer minerals. This can be considered as the evidence of the usefulness of FTIR technique in the screening of the samples for the clay mineralogy studies.

Biostratigraphy and geometry of the Lower Cretaceous Tirgan and Taft formations from NE and Central Iran (Northern Tethyan margin): Critical discussion of recently published comments

Biostratigraphy of the Tirgan and Taft formations (Lower Cretaceous successions) from the Kopet-Dagh Basin (NE Iran) and Yazd Block (Central Iran) has been described using the benthic foraminifera and colomiellids, which calibrated with the stable isotope records. They have demonstrated that ages at the base and top of the formations are diachrone, and these successions start in the Berriasian? or the lower Valanginian and end in the upper Aptian or the Albian. Evidence for this diachrony in ages has been provided by geometry of the Tirgan and Taft formations, showing explicit onlap patterns for the deposits. Furthermore, comments have been recently published on some benthic foraminifera and age models of the Tirgan and Taft formations by Schlagintweit (2021). Here, we explain about accuracy of the palaeontology of these species and demonstrate that discussion on the age models is wrongly addressed.

Disentangling climate signal from tectonic forcing: The Triassic Aghdarband Basin (Turan Domain, Iran)

The Middle–Upper Triassic Aghdarband Basin, NE Iran, consists of a strongly deformed marine and non-marine stratigraphic succession, deposited along the southern margin of Asia in a highly complex tectonic context related to a back-arc setting. The youngest deformed units of the Aghdarband area consist of a rather monotonous sequence of brown-colored shales, with intercalations of siltstones and fine-grained sandstones forming the Miankuhi Formation. The shale-dominated Miankuhi Formation rests on an unconformity surface, separating it from the underlying Sina Formation. A multidisciplinary study based on sedimentological, palynological, and paleobotanical data permits to reconstruct the depositional environments, sedimentary evolution, and paleoclimate conditions of the upper Sina and the lowermost Miankuhi formations. The palynological association of the lowermost part of the Miankuhi Formation yielded sporomorphs of the latest early Carnian to early late Carnian age. Qualitative and quantitative analyses document a shift from xerophytic associations in the upper Ladinian (upper Sina Formation) to hygrophytic assemblages in the Carnian (lower Miankuhi Formation). This increase in hygrophytic elements is also observed in coeval Tethyan outcrops at the same latitudinal belt, suggests a more humid climate in the lower part of the Miankuhi Formation, and correlates this part of the succession with a record of the Carnian Pluvial Episode. The sedimentological and stratigraphical analyses show an evolution from prodelta to delta setting in the upper Sina Formation, then an unconformity enhanced by an interval of fluvial deposits with histosol levels in the basal Miankuhi Formation, in correspondence with the hygrophytic assemblages. The unconformable boundary between the Miankuhi and the Sina formations is, consequently, interpreted as a result of the sea-level fall associated with the humid climate shift, occurring in close association with the first effects of the Eo-Cimmerian Orogeny along the suture zone, taking to a regional reorganization of the basins architecture and the end of volcanic activity in the back-arc region. The main deformations related to the Eo-Cimmerian event thus, correspond in the Aghdarband Basin to the tectonic event that deformed the Miankuhi Formation. This event is probably older than the middle Norian (217.1 ± 1.7 Ma) but younger than the late Carnian, testifying to a diachronicity in the record of collision along the Iranian Cimmerian blocks and Southern Laurasia according to the different considered structural positions. • Stratigraphical and sedimentological revision of Upper Triassic strata from NE Iran • Palynological studies assignm the basal Miankuhi Formation to the Carnian age • Paleobotanical data show clear evidence of the Carnian Pluvial Episode in Iran • The best available estimation of the onset of Eo-Cimmerian event in NE Iran

Compositional and Geochemical Signatures of Oligocene Copper-Bearing Sandstones of Abbasabad-Kahak Area, Ne Iran: Implications for Provenance Relations and Paleogeography

Compositional and Geochemical Signatures of Oligocene Copper-Bearing Sandstones of Abbasabad-Kahak Area, Ne Iran: Implications for Provenance Relations and Paleogeography

The trace fossil Gyrolithes lorcaensis from the Lower Cretaceous of the Kopet-Dagh Basin, NE Iran

The helical, vertical trace fossil Gyrolithes lorcaensis is described from marine to marginal-marine deposits of the Lower Cretaceous of the Sarcheshmeh Formation near the city Kalat-e-Naderi in the Kopet-Dagh Basin. This is the first report of Gyrolithes from Iran and thus expands the geographic range of this trace fossil. G. lorcaensis is characterized by its unique morphometric parameters, a small burrow size and whorl radius, which distinguishes it as the smallest Gyrolithes ichnospecies. The most likely producers of the Iranian Gyrolithes were crustacean decapods, which is supported by the paleoenvironment (shallow and warm water ramp) in which it is found. The function of the spiral structure in the described Gyrolithes of the Sarcheshmeh Formation can be explained as a permanent dwelling structure with the main purpose of farming bacteria via increasing the surface area of the burrow margin that allows more microbial activities. The small burrow dimensions may reflect reduced burrower body size in response to the dysoxic to anoxic conditions suggested by sedimentological evidence.

Application of self-organizing map (SOM) and K-means clustering algorithms for portraying geochemical anomaly patterns in Moalleman district, NE Iran

In this paper, in order to reveal the regional geochemical patterns of regularly sampled stream sediment data, we have employed the K-means and self-organizing map (SOM) as clustering methods in the Moalleman district, northeast Iran. Initially, a set of analyzed elements of geochemical data was subjected to isometric log-ratio (ilr) transformation to address the closure problem related to geochemical data, then, ordinary principal component analysis (PCA) was utilized for recognizing the internal relations between selected elements (As, Au, Cu, Pb, Sb and Zn). Subsequently, the K-means and SOM as unsupervised clustering methods were applied based on PC1 (Cu-Pb-Zn aggregation) and PC2 (Au-As-Sb aggregation) to distinguish different populations of multi-element geochemical indicators. In this regard, Silhouette Width (SW) was implemented for computing the optimal cluster number in K-means clustering method. In the next step, due to the presence of numerous copper mineral deposits/occurrences in the study area, we opted to implement the supervised SOM on ilr-transformed values of Cu-Pb-Zn elements for delineating high anomalous zones. For this purpose, a confusion matrix based on training and out-of-bag (OOB) data was developed for the supervised SOM model and the results indicated the accuracy of 96.27% and 94.26%, respectively. Moreover, success-rate curves were used for assessing the overall performance of K-means and SOM (unsupervised and supervised) models. Experimental outcomes represented the superiority of SOM models (especially the supervised SOM) over K-means in delineating the geochemical anomaly targets which can be used as an effective and powerful tool for discovering the complex patterns among variables in exploratory geochemical data.

Paleogene Molluscan Communities in the Kopet-Dagh Basin, NE Iran

Paleogene Molluscan Communities in the Kopet-Dagh Basin, NE Iran

Mineralogy and trace elements geochemistry of the RoudMajan kaolin deposit, northwest of Torbat-e Heydarieh, NE Iran

Mineralogy and trace elements geochemistry of the RoudMajan kaolin deposit, northwest of Torbat-e Heydarieh, NE Iran

Geochemical and Isotopic Evolution of Late Oligocene Magmatism in Quchan, NE Iran

AbstractMagmatic activity that accompanied the collision between Arabia and Eurasia at ∼27 Ma, provides unique opportunities for understanding the triggers and magma reservoirs for collisional magmatism and its different styles in magmatic fronts and back‐arcs. We present new ages and geochemical‐isotopic results for magmatic rocks that formed during the collision between Arabia and Eurasia in NE Iran, which was a back‐arc region to the main magmatic arcs of Iran. Our new zircon U‐Pb ages indicate that collisional magmatism began at ∼24 Ma in the NE Iran back‐arc, although magmatism in this area started in the Late Cretaceous time and continued until the Pleistocene. The collisional igneous rocks are characteristically bimodal, and basaltic‐andesitic and dacitic‐rhyolitic components show significant isotopic differences; εNd(t) = +4.4 to +7.4 and εHf(t) = +5.4 to +9.5 for mafic rocks and εNd(t) = +0.2 to +8.4 and εHf(t) = +3.4 to +12.3 for silicic rocks. The isotopic values and modeling suggest that fractional crystallization and assimilation‐fractional crystallization played important roles in the genesis of felsic rocks in the NE Iran collisional zone. Trace element and isotopic modeling further emphasize that the main triggers of the magmatism in NE Iran comprise a depleted to the enriched mantle and the Cadomian continental crust of Iran. Our results also emphasize the temporal magmatic variations in the NE Iran back‐arc from Late Cretaceous to Pleistocene.

Cenozoic Dextral Shearing Along the Arusan Sector of the Great Kavir–Doruneh Fault System (Central Iran)

AbstractThe structural analysis of large intracontinental wrench faults is fundamental for deciphering the long‐term evolution of continental crust in complex areas in terms of their geodynamic evolution and large‐scale crustal block displacements. In this contribution, we demonstrate a pre‐Miocene dextral activity of the present‐day left‐lateral Great Kavir ‐ Doruneh Fault System (GKDFS, Central Iran), one of the major intracontinental active strike‐slip faults extending from the Afghan border to the Nain region between Central Iran and the Sanandaj‐Sirjan Zone. We document important dextral shearing recorded along a segment of the GKDFS, the Arusan Fault System (AFS), located east of Jandaq, close to the present‐day active trace of the GKDFS. The AFS include several ENE‐WSW striking strands exposed for a length of more than 50 km, which couple pre‐Cretaceous ophiolites and metamorphic basement units with the Cretaceous succession of the Khur basin. The fault shows transpressional structures consistent with a dextral shear including thrusts and en échelon folds affecting the Cretaceous carbonate units. Paleostress reconstruction based on mesoscopic fault analysis and related folds geometry allowed to establish vorticity parameters indicating that deformation occurred close to a total simple shear regime with a calculated Wk between 0.9 and 1. The enormous Meso‐Cenozoic dextral displacements occurred along the AFS and along the entire GKDFS are attested by the up to several hundreds of kilometers offset of the Paleotethys suture zone, from NE Iran to the western border of Central Iran.

Monitoring Sand Drift Potential and Sand Dune Mobility over the Last Three Decades (Khartouran Erg, Sabzevar, NE Iran)

Aeolian sediments cover about 6% of the earth’s surface, of which 97% occur in arid regions, and these sediments cover about 20% of the world’s lands. Sand drifts can harm sensitive ecosystems; therefore, this research has aimed to study wind regimes and the monitoring of sand drift potential and dune mobility in the Khartouran Erg (NE Iran). The study investigated 30 years of wind speed and direction to better understand sand dune mobility processes using the Fryberger and Tsoar methods. The results of the wind regime study showed that the eastern (33.4%) and northeastern (14.3%) directions were more frequent, but the study of winds greater than the threshold (6 m/s) in winter, spring, and autumn indicated the dominance of eastern and northern wind directions. Findings of calm winds showed that winters (40.4%) had the highest frequency, and summers (15%) had the lowest frequency; the annual frequency was 30%. The average wind speed in summers was the highest (4.38 m/s), and, in the winters, it was the lowest (2.28 m/s); the annual average wind speed was 3.3 m/s. The annual drift potential (DP = 173 VU) showed that it was categorized as low class, and the winds carried sand to the southwest. The monitoring of drift potential showed that there was a sharp increase between 2003 and 2008, which could have been attributed to a change in wind speeds in the region. Unite directional index, the index of directional variability, has been alternating from 0.3 to 0.6 for 30 years. Furthermore, monitoring of sand mobility recorded a value from 0.1 to 0.4, and the lowest and highest values were registered from 0.08 to 0.9, with an average of 0.27. Finally, it can be concluded that sand dunes have been fixed for a long time, and the intensity of the mobility index is affected by climate changes.

An ecological and hydrochemical study of three springs in NE Iran with the emphasis on diatom diversity

Springs are complex and taxa rich ecosystems. Diatom assemblages have received very little attention in spring ecosystems in Iran; hence, the diatom assemblage in three selected springs in northeast Iran, were investigated using multivariate analysis together with hydro chemical measures. For this purpose, water and diatom samples collected during four seasons of 2019. Hydrochemistry results revealed that water-rock interaction is the most important factor in changing the water chemistry of studied springs and their waters produced from carbonate reservoir rocks (mainly calcite). As a result, Ca-HCO3 is predominate water type in all three springs. In this study, 75 diatom taxa identified, from which 55 were included in the analysis. Cluster analysis based on diatoms relative abundance, clustered samples in two major groups and third small group. Results of the indicator species analysis for groups and DCA analysis were in the absolute conformity. Results revealed that the diatom assemblage dominated by combination of early colonizer taxa, spring indicator taxa and cosmopolitan taxa; most of them also reported from different spring types. The results also showed that the spring’s diatom composition influence by size and morphology of the springs.

Detrital Zircon Age Constraints on the Evolution of Paleo‐Tethys in NE Iran: Implications for Subduction and Collision Tectonics

AbstractThe timings of the onset of oceanic spreading, subduction and collision are crucial in plate reconstructions, but not always straightforward to resolve. The Paleo‐Tethys evolution dominated the Paleozoic‐Early Mesozoic tectonics of West Asia, but the timeline of events is still poorly constrained. We present new detrital zircon ages from the Binalud Mountains of NE Iran, in order to determine the timing of tectonic events in the region, and the wider implications for regional tectonics, paleogeography and climate change. Consistent age patterns in Paleozoic clastic rocks show a dominant provenance from the Neoproterozoic basement of northern Gondwana. We interpret this as deposition on a long‐lasting passive continental margin after the initial spreading of the Paleo‐Tethys Ocean. Central Iran‐Eurasia collision caused coarse clastic deposition of the Mashhad Phyllite in a peripheral foreland basin on the Paleozoic sequence of the northern Central Iran Block. The Mashhad Phyllite yields age clusters at 450–250 Ma and 1,900–1,800 Ma, with a clear provenance from a long‐lived continental arc at the active Eurasian margin since the latest Ordovician. Analysis of the age spectra allows us to constrain the maximum depositional age of the Mashhad Phyllite as no later than 228 Ma. This age provides a tight constraint on the timing of initial collision between Central Iran and Eurasia, which also coincides with the Carnian Pluvial Event (CPE). Our new timing evidence of collision reinforces the previous speculation on the Paleo‐Tethys closure as a causal mechanism for the CPE.