Geopersia
Volume:13 Issue: 2, Summer-Autumn 2023

Sand dunes of the Quaternary age occupy large areas of Iran’s semiarid and arid regions. In this study, some 33 sediment samples were collected from the crest, the lee and stoss sides of the linear dunes of the southern part of Qazvin plain. Sedimentological, geochemical, and mineralogical investigations were carried out in order to identify the origin and probable source of the aeolian dune sands. Grain size analysis of the sediments shows that most of the aeolian sands are generally fine-grained, moderately well-sorted, fine skewed and leptokurtic. The textural, mineralogical and the geochemical results supported by the statistical approach indicate that the dune sands were mainly derived from the Quaternary flood plain with a minor contribution from alluvial and fluvial sands. Facies study leads to the determination of 4 facies in 2 facies associations, including: 1) medium-grained lithofacies (Sdpc, Sdl, and Sdm), and 2) gypcrete facies (G). The studied aeolian sands are characterized by the predominance of gypsum and quartz, and stable minerals together with sedimentary, metamorphic, and volcanic fragments, and a few unstable pyroxene and amphibole minerals. The sand dunes of the Qazvin Plain record a semi-arid to arid paleoclimate and the relatively stable tectonic background characterized by the mineralogical and geochemical composition and gypcrete facies in the dunes.

 Astaneh fault is one of the active and seismic faults in the southern part of eastern Alborz. Performance of seismic faults in carbonate rocks and favorable conditions causes the change in calcite and its conversion to lime or its thermal decomposition. If the environment is suitable for this deformation, after initial deformation, the primal volume is reduced, leaving the space available for depletion between deformed particles, which can be used as a key for this earthquake slip. During the Astaneh fault at the location where the fault occurred in the carbonates, after sampling the fault core and fault gouge, and photographing and studying them by SEM electron microscopy, the presence of Co2 exit bubbles and the reduction of calcite volume caused by the earthquake slip heat created was observed at the nanoscale and micro level. After observing the thermal decomposition of calcite in the gouge fault, the reduced volume of particles was calculated from the earthquake slip heat. With the proportion between this volume reduction and the temperature causing it the temperature resulting from the seismic slip causing this deformation is estimated for the sampling location and fault surface.

The existence of vast areas covered with aeolian sand in many regions of Iran has made the use of this type of soil inevitable in engineering projects. Considering the abundance of fine-grained soil in Khuzestan plain along with the aeolian sand, it is important to investigate the effect of the addition of fine-grained soil to aeolian sand to improve its dry density and bearing capacity. In the present research, different percentages of fine-grained soil were added to aeolian sand from Khuzestan plain to determine its effect on the maximum dry density (dmax), optimum water content (opt) and California bearing ratio (CBR) of the aeolian sand and fine-grained soil mixture. It was found that an increase in the percentage of fine-grained soil increased the dmax and decreased the opt. The CBR of the soil increased under tests performed at the optimum water content and decreased under saturated conditions. The highest CBR for penetrations of 2.5 and 5 mm (CBR (2.5) and CBR (5)) when the samples were tested at an optimum water content was for the sample where the ratio of the dry weight of the fine-grained soil (WS(F)) to dry weight of the aeolian sand (WS(S)) is equal 40%. Comparison of the results of the current and previous research showed that, in areas such as the Khuzestan plain in which fine-grained soil is available, the use of such soil for improvement of aeolian sand is appropriate.

Alvand heights can be considered a suitable site for reserving a significant volume of water. The main contributors to this potential are lithology (mainly comprised of igneous rocks and metamorphism), erosion performance, and tectonic forces regarding their roles in feeding hard formations. In the present study, the hydrogeology and hydrogeochemistry of water resources in Alvand heights are evaluated. Also, the effect of geological formations on the quality of these resources is investigated. For hydrogeochemical studies of water resources of hard formations of Alvand heights and their suitability for drinking, agricultural, and industrial uses in the study area, 27 water samples were collected from the region’s springs and subjected to chemical analyses. The predominant water type in all samples is the bicarbonate-calcium. Generally, the water quality of the springs for domestic and drinking purposes is in good condition in terms of hardness such that the samples have no permanent hardness and are soft water based on the total hardness. Based on various indicators (i.e., SAR, EC, Na+%, and RSC), the water quality of the springs was assessed as very good for agricultural use and irrigation. Evaluating these indicators showed that most springs have corrosive and invasive waters. Moreover, the hydrochemical composition of the region’s aquifers is mainly affected by geological and geochemical factors, including weathering of igneous rocks, metamorphism, feldspar minerals (especially plagioclase and orthoclase), and biotite.

A study on depositional environment, diagenetic history, and sequence stratigraphy of the upper Cretaceous successions of the boundary between the Central and Eastern Alborz zones is lacking. This study attempts to tackle this issue by analyzing a succession composed of 120 meters of medium- to thick-bedded limestones. Facies analysis led to the identification of facies associations of terrestrial, inner ramp (proximal, mid, and distal lagoon and shoal), mid ramp, outer ramp, and basin settings. According to the lateral and vertical changes in facies associations indicating gradual facies variations and the absence of large barrier reef organisms, a carbonate platform of ramp type with a bioclastic shoal is suggested for the studied succession. However, regarding the presence of turbidites in the transition of mid and outer ramp facies, a distally steepened ramp better suits the studied succession. Diagenetic study reveals products of eogenesis, mesogenesis, and telogenesis stages. Sequence stratigraphic analysis based on facies analysis and field observation denoted one 3rd-order depositional sequence, which its maximum flooding surface is equivalent to MFS K180 of the Arabian Plate (AP) with middle Maastrichtian age. A disconformity at the topmost of the studied succession correlates with the upper sequence boundary of megasequence AP9 around the Cretaceous–Paleogene boundary.

The transition zone (TZ) in an oil reservoir has traditionally been a volume of lesser interest compared to oil-saturated zone. Researchers have suggested that it can contain commercial hydrocarbon volumes. Therefore, this paper seeks to summarize the characterization methods of TZs for the assessment of oil production opportunities. Another goal is to summarize the potential methods of oil production from TZs. It is conceivable that TZs will produce both water and oil together. However, some surprising instances of dry oil (i.e., 100% oil, with no associated connate water) production, due to the formation of water clusters, have also been observed earlier. Also, oil can possibly be found below the current FWL. Characterizing TZs is more complicated compared to oil-saturated zone. TZs can show variable wettability and permeability characteristics due to several complex phenomena related to buoyancy, capillarity, diagenesis, cementation, and reservoir tilting. Careful TZ core characterization followed by reservoir simulation and oil production can increase the overall reserves. Methods for TZ characterization include petrophysical logs, geophysical analysis, and reservoir modeling. Analysis of core obtained from TZs using the centrifuge method can reveal the residual oil saturation and relative permeabilities, which can aid the prediction of future oil production. More complicated analyses include structure and stratigraphic geological models and basin modeling for hydrocarbon migration history. Possible oil production methods from TZs include CO2 injection, surfactant flooding, combined carbonated water and surfactant flooding, and smart well placement. We recommend including TZs that span several meters in depth as part of reserves calculation.

Qeshm Island is the largest island in the Persian Gulf, similar to a dolphin in shape. The island is located at the mouth of the Strait of Hormuz in Hormuzgan Province, Iran. The Island is dolphin-shaped, and most of the outcrops include sedimentary rocks. Qeshm is one of the most beautiful Islands of the Persian Gulf and due to its special geographic location has many beautiful natural and geological phenomena. Qeshm Island has a variety of cultural, handiworks, and local architecture as well as geological diversity. The geological formations of this belt may range from the late Precambrian to Cambrian in age and include diapirs called the Hormuz Series. Most of the mature salt diapirs formed in the Qeshm and the longest salt cave was created in the west of the island in a series of Hormuz Formation. The main geotourism attractions of the island include different forms resulting from erosion, as well as very attractive geomorphologic structures such as Star Valley, Khorbas Cave, Mangrove forest, Roof of Qeshm, and Chah-Kuh Gorge, Salt Cave, coral reefs, etc. Most of the landscapes are the product of wind and water erosion. Qeshm Island is one of the numerous places in Iran rich in many geologic, ecologic, cultural, and historic attractions and unique for geotourism and ecotourism. In addition to the geological and natural attractions of the region, the ancient and cultural features are included in the potential of the island’s tourism attraction. This study introduces geotourism attractions in Qeshm Island.

Groundwater is the most common source of water in many places especially arid regions. The quality of this valuable resource is highly important for human health. One of the essential topics in groundwater management is the area surrounding a pumping well from which groundwater is extracted. The extent of this area namely as capture zone or wellhead protection area, generally depends on factors such as the pumping rate, hydraulic conductivity, and well depth. In this research, the capture zones of 575 production wells in Abarkooh plain, located in Yazd province at central Iran, are calculated using WhAEM model for a travel time of 10-year, considering groundwater hydraulic gradient, hydraulic conductivity, recharge and aquifer thickness parameters. Furthermore, for the first time, a general equation of capture zone was developed using multivariate statistical regression method, which is based on the results obtained from WhAEM. The capture zones calculated by the new developed equation are relatively correlated with the results simulated by the WhAEM model with the correlation coefficient of about 51%. As the input parameters for the capture zone analysis are changing over time, the new developed equation by multivariate regression method can help to calculate the capture zone more effective and quicker. The calculated capture zones are essential for protecting groundwater resources, applying in remediation actions in the case of groundwater pollution.

Two surface sections of the Sarvak Formation in the Lurestan zone (Zagros fold-thrust belt) were examined to inspect the naturally occurring fractures. The inspected are located sections in the Surgah anticline and the Kuh-e-Charmi anticline; in the Ilam and the Kermanshah provinces respectively. The Sarvak Formation was carefully examined to record the fracture types, their spatial distribution, spacing and cross-cutting relationships. Detailed examinations were undertaken on 420 fractures, 40 core plugs porosity and P-wave velocity and 205 thin sections. Three genetic types of fractures including tectonic, pressure-solution and dissolution related fractures were identified. The tectonic related fractures include two main sets (namely with NW-SE and NE-SW trends). In addition, distinguished two types of stylolites include the bed-perpendicular and the tectonic stylolites (bed-parallel); that postdate the fractures (veins). The Sarvak Formation underwent various diagenetic processes in couple with fracturing. The pore types include microporosity, intergranular porosity, mold porosity and fracture-stylolite. Petrophysical measurements (performed on some core plugs prepared from surface block samples), show that the carbonates of the Sarvak Formation have low porosity (74% of the samples have less than 3%) and high compressional wave velocity (Vp), (96% of the samples have 6000 m/s), Therefore, it could be concluded that the Sarvak Formation is a tight interval in a reservoir aspect.

Various depositional and post-depositional factors interact to shape a reservoir, typically causing heterogenies in reservoir properties on different scales. This study investigates depositional and diagenetic factors controlling reservoir properties of the Asmari Formation as the most prolific reservoir rock in Iran. Data from six surface and 12 subsurface sections show that both primary and secondary factors governed reservoir quality. Lithology is the principal primary control, with major differences between siliciclastics and carbonates. Other primary controls include rock texture, facies, and depositional setting. Dolomitization, dissolution, and cementation are the main diagenetic factors that modify the original rock fabric. Dolomitization improved reservoir quality. Early diagenetic dissolution also enhanced porosity. However, the created spaces are separated vuggy and moldic pores with no effect on permeability. Cementation and compaction are major porosity-occluding processes. Anhydrite cementation degraded reservoir quality of oolites, one of the best productive facies of Asmari. Results show that tectonics, paleo-climate, and sea-level changes were allogenic controls on reservoir configuration. Lithology variations, as a principal control on reservoir quality, resulted from tectonic movements alongside sea-level oscillations. The diagenetic path—specifically dolomitization, dissolution, and cementation—was controlled by paleo-climate and sea-level changes. Hypersaline conditions prevailed during and after deposition, with major impacts on the reservoir quality (pervasive dolomitization and dissolution), were the consequence of combined paleo-climate and sea-level effects. Regional syn- and post-depositional tectonics created widespread fractured reservoirs with higher production rates than unfractured counterparts. The results of this study can assist in regional characterization of the Asmari reservoir throughout the Zagros area.

The assessment of recharge is one of the most important issues in management and planning of the groundwater resources. In this study, the amount of recharge to the Semnan alluvial aquifer was investigated using methods of water table fluctuations (WTF), chloride mass balance (CMB), water budget and stable isotopes. The parameter is highly important for managing this vital aquifer as over- exploitations for drinking, agricultural and industrial uses occurred, resulting in water table decline with an average rate of about 80 cm annually. Based on the results, the values of recharge into the Semnan alluvial aquifer are estimated about 4.4, 2.5 and 2.1 MCM/year by WTF, CMB and water budgetmethods, respectively. The isotopic data ( 18 O and 2 H) do not show any significant effects of evaporation on recharge process, confirming the main role of highland recharge in this arid-land aquifer. Combining results of the recharge studies in saturated zone of Semnan aquifer, yields annual rainfall recharge of about 3 MCM, which is about 5% of the annual precipitations.

The chronological and paleoenvironmental settings of the Sirenia-bearing strata in the Zagros Basin of Iran were studied in four sections. These sections, located in the Izeh (Asmari Formation), Interior Fars (Gachsaran Formation), and Coastal Fars (Mishan Formation) zones of the Zagros Basin, were investigated for the details of their micropaleontology, biostratigraphy, and microfacies. A total of 113 thin sections were analyzed. Fossils from the Asmari Formation and the Gachsaran Formation were younger (Burdigalian), while those from the Mishan Formation were older (Aquitanian). Thirteen carbonate microfacies were identified in three facies belts; tidal flat, inner ramp, and middle ramp. The tidal flat facies association included mudstone microfacies. Inner ramp facies association consisted of bioclast with porcelaneous tests wackestone, peloid and miliolids packstone to grainstone, bioclast and miliolids wackestone to packstone, benthic foraminifera grainstone, red algae with bryozoan and miliolids wackestone to grainstone, and echinoid and miliolid packstone to grainstone facies. Middle ramp facies association was comprised of red algae and meandrous coral packstone to rudstone, coral floastone, bioclast and bryozoan wackestone to packstone, echinoid and bryozoan packstone, bryozoan and benthic foraminifera wackestone to packstone, and echinoid and bioclast wackestone facies. A shallow carbonate ramp was identified as the habitats of sea cows in the Aquitanian-Burdigalian of the Zagros Basin.