نشریه رسوب شناسی کاربردی
پیاپی 16 (پاییز و زمستان 1399)

Loess deposits are unconsolidated sediments with mainly coarse silt, without stratification with high permeability that are mostly yellow to light brown colour. Golestan Province in northeast of Iran is one of broadest loess area in Iran that connects loesses of middle asia to urasia. In this research, texture characteristics and quantity of silt, sand and clay are compared in 2 methods (sieve- hydrometry and laser diffractometry), in 16 sampling station. Data correlation in particle measurements between sand, silt and clay in these methods are a bit different. There is weak correlation between sieve- hydrometry and laser, in loess sediments of  the study area; except sand, there are very weak correlation between silt and clay that can be realated to different measurement methods. Analysis of hydrometry is based on speed of sediment deposition particles and settling velocity is assumed to be constant, density of particles is considered equal to quartz and particles are considered spherical and smooth. Results shows that the amount of clay particles in hydrometry method are much more than laser method, which is related to different mineralogy of clays. This causes overestimation of platy particles in hydrometry method. Laser particle sizer measures medium particle diameter but sieve shows large particle diameter. This is the reason of different measurements between sand size sediments.

Arjan plain lake is one of the most important and valuable ecosystems in Fars Province possessing an area of more than 1000 hectares in 65 km southwest of Shiraz. Twenty samples were taken from the lake bed for identifying sediment textural characteristics of this seasonal lake. The particle size distribution of this deposit is 73% clay, 15% silt and 12% sand. In other words, these deposits are in the category of clay and sandy clay. Other textural features of these deposits include weak to moderate sorting, negative skew (towards coarse grains), very leptokurtic to platykurtic, fine to semi-rounded roundness, and medium to high sphericity. Mud cracks and typical gradual classification are the predominant sedimentary structures in these deposits. The main calcite and quartz minerals and dolomite, halite, feldspar, montmorillonite are sub-minerals of Arjan plain lake deposits. Fifteen types of heavy minerals were detected in these deposits. Histological characteristics show that the particles formed by these sediments are transported by river and wind processes and are deposited in a calm and low energy lake environment.

The purpose of this study is to determine the characteristics of sediments laid down in South Golbaf Playa and their influence on the formation of pseudokarstic bodlands in this area, as well as to investigate development of these badlands. For this purpose, textural, mineralogical and chemical (pH, EC, ESP and SAR) characteristics of the sediments were determined. These data revealed that the deposits are mainly comprised of erodible loams (mudrocks). According to field evidence, filling of the tectonic depression with sediments led to overflowing of surficial runoff as well as creation of gullies on the surface of playa. These events caused drainage and contraction of sediments and the appearance of fissures. The entry of runoff into these fissures and the consequent erosion led to creation of pseudokarstic badland.

Soil erosion and land subsidence in Iran have become known and important issues. Recently, the vital arteries of urban and interurban areas include the nation's power line face with secondary effects of soil erosion and land subsidence. In this research, the place of power line and different upstream marls (M1, M2, M3 units) from Eshtehard to Bouin-Zahra area were studied from a sedimentology erodibility and geoelectric point of view. In the laboratory, granulation, calcimetry, electrical conductivity, Aterberg limits, type and the amount of different elements and clay minerals were determined. The types of erosion include surface, furrow, stream, and trench erosion on the Upper Red Formation deposits and Quaternary sediments. The results show that the area is covered by highly erodible marl and contains abundant non-cohesive silt particles, alkali cations, and soluble anions. A silty layer about one-meter-thick is located on the surface substrate consisting of dense clay and on the clayey sand layer and due to high erosion, they cause large tunnels and gullies that go towards the electric towers. The clay mineral of this layer is montmorillonite with highly sensitive to soil erosion factors. Geoelectric studies show this layer as well as sandy layers deposited in 45m and more depths. The main reason for the general subsidence of this region can be considered as water extraction for the steel industry in the Eshtehard region, which has been used as a driving force to create cracks and erosive cracks in the soil.

The Pabdeh formation which is organic matter-rich in its certain layers in some of the oil fields and can be considered as a source rock, has been studied to illuminate the effect of clay minerals and hydrocarbon generation on the primary migration of hydrocarbons of this formation in one of the wells in the Karanj oil field. Based on the rock-eval and XRD results and electron microscopy images before and after heating the selected samples and creation of artificial thermal maturation, it was determined that the illitization in conjunction with hydrocarbon generation process has responsibility for migration of hydrocarbons through the source rock, a process referred to as primary migration. In fact, by maturing the immature source rock in the laboratory trough heating, the illitization process by releasing water, brittle minerals such as quartz and illite and also hydrocarbon production cause local pressure until it reaches the rock’s fracture strength. Therefore, the microfractures initiate preferably in low-strength pathway with a high smectite/illite contentthat converted to brittle minerals (illite and quartz) and could explain primary migration in Pabdeh source rock in Karanj oil field.

Production of hydrogen sulfide in various oil and gas reservoirs has been reported around the world. Hydrogen sulfide is one of the major challenges in the operation and refining process of oil and gas. Therefore, determining the origin and mechanism of hydrogen sulfide production in gas and oil reservoirs is great importance. Due to the relative increase in hydrogen sulfide concentration in the gas field studied and its possible problems in downstream process facilities and the gas refinery, the source of hydrogen sulfide production has been investigated. The ability to predict the presence of hydrogen sulfide in non-drilled material would be a good idea to reduce the risk of exploration and production. In this research, detailed geological and comprehensive laboratory studies (petrography and isotopic gas, gas condensate, water) were performed in different parts of the field to determine the source of hydrogen sulfide. According to petrographic studies, the conversion of anhydrite to calcite was observed at the upper depths of the Upper Dalan Formation. Geochemical evidence, such as increased nitrogen content, lighter CO2 isotope composition and heavier isotopic composition of hydrocarbon compounds, as well as isotopic evidence of sulfur in rock and gas, suggest a thermochemical sulfate reduction process. Negative values of the sulfur gas isotope as well as the burial history and presence of dark condensates in the studied field indicate the role of bacterial sulfate reduction and thermal cracking in organic matter with less impact for H2S production.

The Gaschsaran Formation, is one of the major and important stratigraphic units in Iran, and is regarded as substantial Asmari cap rock thuse, is significant economically. Generally, the Gaschsaran Formation with a thickness of 1200 to 1600 m, is present in South of Dezful embayment. The studied area is located in the Gachsaran oilfield, which consists of the Gachsaran member 1 with a thickness of 40 m. This research is focused on lithological variations, depositional fabrics together with the depositional environment in the well No. x in the Gachsaran oil field. The main sedimentary fabrics, as a result of gypsum to anhydrite transformation, occurred in this formation during diagenetic processes and lath fabrics, as well as flow fabrics, present in this formation. Based on the field investigation along with well logging data, the studied area involved reversed anticline, and variations in units indicate member 4 as anticline core as a result of other strata shortening. Three carbonates, evaporite, and shale facies are recognized based on their allochems, fabrics, texture, and lithology in the studied section. The studied facies represent a carbonate-evaporite platform involving sabkha and salt pan, tidal flat and lagoonal depositional environments during Miocene. Geochemical analysis, X-Ray-EDX, and SEM data revealed freshwater flooding, evaporative concentration, and desiccation stages during evaporite deposition. The Br element variation along the stratigraphic column indicated water entrance and evaporation occurred during evaporite deposition in this formation.

The pollution of heavy metals not only affects directly the physical and chemical features of soil and reduces biological activities and access to nutrition materials in soil, but also is considered a danger for human health. The finding from geo-accumulation index of serpentine soil samples shows that the intensity of serpentine soil is classified in the range of no pollution to average regarding chromium and nickel. In addition, the pollution bar index of chromium and nickel is more than 1 proving the inappropriate soil quality and soil pollution of the region. However, nickel has the most considerable value. The average value of EF proving the region shows enrichment for the chromium and nickel elements. According to the Pearson correlation coefficient, there is a high correlation between cobalt, chromium, and nickel that indicating the equal source or similar geochemical behavior of the elements toward each other. According to the geostatistics values such as geo accumulation, enrichment factor, and pollution bar in the studying area, is pollution in nickel and chromium elements. Pearson correlation coefficient reveals that there is a high correlation among cobalt, chromium, and nickel proving the same origin. Making a zoning map of heavy metal density in the region soil demonstrates that the high density of the elements in some stations is related to geological factors. Cluster analysis shows the division of the elements into 7 clusters. Besides, the elements with the structural relationship are related in the next subcategories. Clusters 6 and 7 together indicate the same origin for these elements.

In order to study the biostratigraphy of the Gurpi Formation in Fars province and northwest of  Nour Abad Mamasani, the Murgah stratigraphic section with 159 m thickness (in the most western part of the Paskuhak anticline) has been sampled. In this section, the Gurpi Formation with 140 m thickness predominantly consists of grey argillaceous limestones and shale. This formation rests disconformably upon thick layered limestones with hematite nodules of the Sravak  Formation and also at the top, disconformably overlies on the Purple shale of the Pabdeh formation. In the biostratigraphic study of the Gurpi Formation, 46 species and 16 genera of planktonic foraminfera have been identified which is subdived into 8 biozens. Based on the identified biozones the age of the Gurpi Formation in the Murgah section is Santonian-Late Maastrichtian. Due to the main hiatus which encompasses Late Maastrichtian to Selandian, the K/Pg boundary in this section is not recorded. Furtermore based on petrographic studies 3 microfacies have been deposited in the open marine parts of a carbonate platform.

In this research, petrography and geochemistry of the sandstones of Padeha formation (Early-Middle Devonian) in Asu section, 40 km eastern Gonabad, located in Lut block have been studied. In this section, the thickness of Padeha formation is 210 m which is composed of siliclastic rocks. After field studies, 30 medium-grained sandstone samples were selected for point-counting and 10 sandstone samples were selected for geochemical analysis. The results of mineralogical studies show that monocrystalline quartz is the main phase and zircon and tourmaline minerals are the secondary phase. Based on the calculated percentages of point counting data, the composition of these sandstones has been detected as quartzarenite and sublitharenite. Petrographical evidence, such as, well rounded monocrystaline quartzs with straight extinction, lacking of plagioclase and low percentages of K-feldspar, ferromagnesian minerals, overgrowth silica cement, existence of rounded zircon and tourmaline imply craton interior and sediment recycled provenance. Moreover, using modal analysis data, (Qm95.5, F0.8, Lt3.6) and (Qt99.1, F0.8, L0) diagrams support this provenance. Based on geochemical data in discriminating tectonic diagrams, the Padeha Formation sandstones are deposited on a continental passive margin. These studies indicate that the studied sediments are likely deposited in the transition between the transformations of rifted margin to passive continental margin of Paleo-Tethys.

Carbonate-hosted base metal deposits are an important source of the world lead and zinc resources in Iran and were formed in late Proterozoic to Cenozoic age.  The Changarzeh Pb±Ag deposit with Middle Triassic faulted-dolostone, is located 75 km northeast Esfahan Province, southern part of the MEMB. Mineralization occurs as two hypogene (sulfide) and supergene (oxide, carbonate and silicate), orebodies. Sulfide mineralization with cavity filling, vein-veinlets and replacement textures is mainly composed of galena, sphalerite, pyrite and tetrahedrite-tennantite series. According to mineral chemistry data, FeS mol% content in sphalerites varies from 1.14 to 3.88 mol%, which corresponds to intermediate sulfidation state (LogfS2≈ -13). The Co/Ni ratio in pyrites varies from 0.12 and 0.25, which belong to sedimentary to hydrothermal fluids. The temperature and salinity values ​​of fluid inclusions in sulfide mineralization of the Changarzeh deposit are closely related to the composition of FeCl2-MgCl2 basinal brines (combination of paleo-oceanic waters and trapped high-brine fluids in cavities of rocks), which mixed by meteoric water in final mineralization stage. Considering all the evidence such as tectonic setting, dolostone host rock, silicification and dolomitic alterations, simple sulfide ore mineral, lithological-structural controls, marine sulfates as the main source of sulfur and metals released from the lower sedimentary bedrock, it can be said that the Changarzeh deposit is most similar to the Mississippi Valley Type (MVT) deposits.

The carbonate- siliciclastic sediments of the Mobarak Formation (Lower Carboniferous) at the Kahang area with 222 m thick, is composed of thick-bedded shale and thin-bedded limestone in the lower part, thin-medium- bedded limestone in the middle part, thick-bedded shale intercalated with limestone in the upper part of sequence and thick, massive conglomerate at the uppermost of the section. Based on petrography, geometry, macrofossil contents and trace fossil evidences (in the fieldwork observations), as well as microfossil and textural characteristics (in the laboratory studies), determination of 15 carbonate and one siliciclastic facies was possible. These facies are deposited in six facies zones include tidal flat, lagoon, shoal and patch reef in the inner ramp, middle ramp, ramp slope and deep ramp. The massive conglomerate facies is deposited in an upper shoreface- onshore setting. Templates facies as slope break related turbidite facies (crinoid packstone), intercalated within deep ramp facies (spiculite mudstone) display this carbonate-siliciclastic sequence is deposited in a carbonate platform of distally steepened ramp. The lateral changes in the facies and thickness of the sedimentary successions of the Mobarak Fm. display a generally deepening trend from south-south western to the N-NE of the Alborz Basin during deposition of the Mobarak Fm. in lower Carboniferous.