نشریه علوم زمین
پیاپی 130 (زمستان 1402)

One of the common processes that lead to the formation and enrichment of precious metal deposits is boiling. The existence of a spatial relation between fluid boiling and deposition of precious metals is a valuable tool in exploration of epithermal deposits. Therefore, the investigating of the process occurrence in epithermal deposits will be able to predict the continuation of exploration trend. Chah-Morad epithermal gold deposit is located in 75 km northwest of Bazman in the Sistan and Baluchistan Province and in the Makran-Chagai Magmatic Arc southeast of Iran. The mineralization in the Chah-Morad deposit occurred in 3 stages and in quartz veins that exist between the altered argillic alteration zone and dacite and rhyodacite sub-volcanic rocks. Textural mineralogical and fluid inclusions studies indicate the occurrence of the boiling process in this deposit. The most important kinds of evidence for the occurrence of this process are: a) the presence of adularia, b) platy calcite texture, c) breccia, crustiform-colloform textures, d) different liquid-vapor ratios of fluid inclusions, e) the increase in the salinity of fluid inclusions with the decrease in homogenization temperatures, f) the coexistence of fluid inclusions with different salinities and g) co-existing liquid single-phase fluid inclusions with vapor single-phase fluid inclusions. Therefore, the existance of boiling is confirmed in the Chah-Morad deposit.

Ten tectono-sedimentary basins have been identified around the Paleotethys suture zone in NE Iran. These basins have been developed from the Lower Paleozoic to recent time in response to relative movements of the of Eurasia and Gondwana supercontinents. The recognized basins from ancient to modern are: 1) Paleozoic passive marginal basin of central Iran, 2) Devonian-Carboniferous platform basin of Turan plate, 3) Active continental margin basin (trench and foreland), 4) Permo-Triassic arc-related basins, (5) Upper Triassic-Lower Jurassic peripheral foreland basin, 6) Lower to Middle Jurassic intramontane basin, 7) Middle Jurassic rift basin, 8) Oligocene-Pliocene foreland basin and 10) Post orogenic molasses basin. Each basin has its own characteristics, and is formed in different tectonic setting during the evolution of the Paleotethys Ocean in NE Iran.

Many examples of tear faults are observed in Tabas block. These faults are usually seen in belts with active folds. In this research, an example of the mentioned faults has been studied. The axis of the Kamarmahdi anticline has a north-south trend. In the north of Kamarmehdi anticline, there is a fault with an approximate trend of N75E which does not have a clear shear sense on the ground, and the geological structures on both sides of this fault are also different. This research has been done to determine the shear direction of the said fault. For determining the shear sense of this fault, a geological map with a scale of 1:1000, was prepared and the boundary of the rock units and the folding axis are taken as a guide to calculate the fault shear direction. The amount of heave (143m) and throw (331m) of fault was determined after preparing the geological cross sections on both sides of the tear fault, using AutoCAD software. By determining the movement direction of the fault, the existence of the tear fault and its displacement has been proven, and the movement pattern of the formation of the tear fault has been presented.

Numerous mechanisms are active during folding in folded-thrust belts, such as the role of salt movement, the role of multiple detachments in sedimentary cover, interference between different phases of deformation, and the role of basement during folding. The performance of these mechanisms plays an important role in the formation of different structures and geological features in geological units and folds geometry. In this research, such structures have been introduced and studied in Takhteh, Nahreh and Kuh-e-Lar anticlines in the north of Fars Paleo-High during field observations and measurement of geometric features of anticlines such as Aspect ratio, axial distance and half wavelength. These structures mainly include growth strata, geometry of tectonic synchronous strata, structures associated with shallow detachment such as rabbit ear structures, faults that are themselves structures that control the geometry and kinematics of structures, and sulfur springs that related to faults and rheology of exposed formations. The present study shows that the anticlines have an aspect ratio less than ten and are part of the detachment folds in which the detachment horizons have played a role and have a dextral arrangement. The formation of these anticlines occurred at the same time, which will be connected to each other, and these anticlines are associated with basement faults. The location of these anticlines is suitable for the presence of hydrocarbons but the basement fault in the southern flank of Takhteh anticline may affect the reservoir. The presence of water gaps and wind gaps in the region is a sign of uplift and activity of the region.

Diagenetic processes in carbonate rocks can be considered as one of the most important factors influencing the inherent characteristics of this type of reservoir on a small as well as large scale. Considering the importance of knowing the mechanical characteristics of reservoir rocks in geomechanical modeling and its application in the exploitation and development of hydrocarbon fields, it is necessary to find out how lithological characteristics affect its rock mechanical behavior. In this study, the impact of two diagenetic processes (Dolomitization and Anhydrite cement) on the physical and mechanical characteristics (such as Uniaxial Compressive Strength, Young’s modulus, Cohesion, and Internal friction angle) of carbonate reservoirs of the Kangan Formation, are addressed. The evaluations have been done in two phases: i.e., lithological studies and rock mechanical tests. The results show that changes in mechanical properties are strongly influenced by diagenetic processes. The two main influential features on mechanical characteristics are dolomitization and anhydrite cementation, which strongly affect porosity, dominant pore type, and mineralogy. The results show that dolomitization in the studied samples has caused an increase in porosity and a decrease in strength and elasticity. While the presence of anhydrite has caused an improvement in the resistance characteristics with an opposite effect.

The Hauterivian-Barremian Gadvan Formation represents a depositional sequence in the central and eastern regions of the Zagros Mountains. Field surveys and petrography of 30 thin-sctions of this Formation in the Khaneh-Kat anticline togheter with wireline logs (gamma-ray and sonic) and 25 thin-sections analysis of two drilled wells in the Dashtak and Bandubast gas fields (Interior Fars area) indicate important events in the basin evolution, especially the changes in the sedimentation regime and platform evolution during the time period. The key point is upward grading of the thick-bedded layers, feature forming Berriasian-Valanginian carbonates into shale, marl and argillaceous limestone interbeds of the Gadvan Formation. The vertical changes is consisten with a prominent decrease in carbonate production and a definite change in the nature of the Fars platform. The intense bioturbation and mostly mud-dominated texture of skeletal limestone microfacies with significant occurrence of molluscs, green algae and benthic foraminifera in the cyclic alternations of shales and limestones indicate that the Gadvan Formation was deposited in a mixed carbonate-siliciclastic platform. The platform formed as the result of increased siliciclastics influx from the southern areas of the Zagros fold-thrust belt (clastic drowning of the platform) and the change of the Fahlyian oolithic-algal ramp into an environment consisting of an open lagoon and a muddy shelf. In the drilled wells, these changes correspond to a significant increase in gamma-ray and sonic wireline logs. The Khalij Member shows the regional continuity, implies a decrease of the (relative) siliciclastics supply and increase of carbonate production in the mixed platform. Considering the relative tectonic quiescence of the Interior Fars area during the Early Cretaceous, the mentioned changes can be the result of the interplay between tropical climate and short-term fluctuations in the context of global sea level rise.

In order to study  the Lower Cretaceous deposits' coral fossils, the Baghin section was chosen and sampled. This section consists of a sequence of green marl, limestone and shaly limestone deposits. In this section, diverse groups of microfossils (orbitolinids, algae and ostracods) and macrofossils (corals, echinoids, bivalves, brachiopods, gastropods,…) are present. The presence of diverse collection fossils, especially large orbitolinid foraminifera indicated a favorable environmental conditions and absence of planktonic foraminifera indicated shallow environmental conditions. Also, the presence of platycopid and podocopid ostracods and corals confirm the shallow, warm, light and suitable paleoecological conditions.

Pteriomorpha, Heterodonta, Paleoheterodonta and Anomalodesmata bivalves from the Kazhdumi Formation of the Geno and Gerash sections in the southeast of  Zagros Mountains are studied here. In order to this research, bivalve speies are identified and described as follow: Arctica angulata, Birostrina concentrica, Ceratostreon flabellatum, Crassatella manzourensis, Flaventia belviderensis, Granocardium productum, Gyrostrea delettrei, Illymatogyra africana, Mytiloides concentricus, Neithea dutrugei, Neithea sp. 1, Neithea sp. 2, Paraesa faba, Pinna cfcretacea, Pholadomya fabrina, Pholadomya vignesi, Protocardia hillana, Pterotrigonia scabra, Rhynchostreon suborbiculatum, Tenea delettrei, Venericardia deserti. Many of these species excluding Ceratostreon flabellatum, Illymatogyra africana, Neithea dutrugei and Pterotrigonia scabraare reported for the first time from Iran. Kazhdumi Formation disconformably overlies the top of the Dariyan Formation and underlies the Gurpi Formation.