نشریه رسوب شناسی کاربردی
پیاپی 23 (بهار و تابستان 1403)

The studied section is located in the 113Km east of Birjand (25Km Asadiyeh City) and east of Pating Village. The mentioned sequence, aged Late Cretaceous, is totally 246m in thickness and mostly consists of thick and medium bedded limestones along rock units. The lower boundary has been limited by basal red conglomerate and the upper boundary has been covered by red-colored sandstone unit. In This research, based on both field and laboratory studies, the main components of carbonate rocks include both skeletal and non-skeletal grains and totally 7 carbonate microfacies have been determined which have been deposited within 3 facies belts including tidal flat, Semi-restricted lagoon and shoal. According to the obtained evidences from the microfacies analysis, the suggested depositional model for the Pating section is a homoclinal ramps type carbonate platform. All of the microfacies are mainly deposited in the inner part of the ramp slope. The obtained geochemical data from carbonate samples analysis indicate a calcitic original mineralogy and dominance of a closed diagenetic system for the studied sequence. Also, according to the geochemical data, a temperate climatic condition could be considered for the formation environment of this sequence which is confirmed by the Late Cretaceous Palaeogeographic global map. The studied limestone samples have been widely affected by different diagenetic processes that the most important of which are micritization, cementation, mechanical and chemical compaction, dissolution, neomorphism, replacement, fracturing and vein-filling cements that have been formed in a variety of marine, meteoric, shallow burial and uplift diagenetic environments.

in the north and east of the Lorestan basin. In this study, biostratigraphy, microfacies and paleoenvironment of the Taleh Zang Formation (Palganeh, 25; Pasan, 52 and Poshteh Jangal, 75 m thick) were investigated. Assemblages of larger foraminifera from Palganeh and Pasan sections can be referred to Zone SBZ 3 which correlates with the late Thanetian Stage. In view of the fact that we could not find any index microfossils in The Poshteh Jangal section, as to its stratigraphical position, we prefer an early Thanetian date (SBZ 3) for this section. The existing microfacies indicate an inner ramp environment for the Pelganeh and Poshteh Jangal sections and inner and middle shelf environments for the Pasan section. In addition, from the microfacies of the internal ramp, in the Poshteh Jangal section, only the microfacies of tidal flat and Lagoon are spread, but in the other two sections, in addition to these two microfacies, the microfacies of the open marine are also seen.

The Arc Section in the northwest of Birjand is located in the eastern Iran structural zone. The petrography and geochemistry of siliciclastic deposits of this section have been studied in order to determine the lithology and tectonic setting of the source area. Petrographic evidence of sandstone samples, including types of monocrystalline and polycrystalline quartz with non undulose and undulose extinction, the abundance of sedimentary rock fragments and to a lesser extent metamorphic and volcanic lithics, as well as drawing results of the modal analysis of these samples on the tectonic provenance diagrams show that the studied sandstones are the result of recycled orogeny and post collision. Also, based on the geochemical analysis of the major elements of the shale samples, these sediments originate from igneous rocks and belong to the collision tectonic setting. The sistan suture zone is placed between two continental blocks of Lut and Afghan. According to most researchers, subduction of the oceanic crust has played a very important role in the tectonic evolution of this region. The recent studies show that due to the westward subduction of the Sistan Ocean in the Early to Middle Cretaceous, the upper mantle was pushed under the Lut block and the collision between the Lut and Afghan blocks along the Sistan collision zone probably occurred in the Upper Cretaceous. Combining above data and comparing it with the tectonic evolution of the region shows that the results of this study can be used to reconstruct the paleogeography of this area.

In this research, the effect of monsoon phenomenon on the textural characteristics of the sediments of Iranian coasts of the Oman Sea was investigated. For this purpose, necessary sampling was done from 13 stations based on marine sedimentological standards. According to the amounts of sand, silt and clay in the pre-monsoon and post-monsoon samples, the sedimentary types of sand, clayey sand, sandy clay and clay were identified in the studied stations. Granulometric analysis showed that the amount of sand and clay in pre-monsoon samples of shallow and near-shore stations (Tiss, Desalination, Center of the Bay, Ramin, Beris and Pasabandar) range from 43 to 97 and 0 – 27%, respectively. On the other hand, these values change between 8 – 45% and 54 - 82 % in deep and offshore stations, respectively. The amount of sand and clay in post-monsoon samples of shallow and near-shore stations vary between 68% - 96% and 0% - 13%, respectively. The amount of sand and clay in deep stations and far from the coast in post-monsoon samples fluctuates between 8-22% and 58-86%. The amount of organic matter in sediments varies between 1 and 3% in most of the studied stations and is within the normal range. This amount showed a slight increase in Konarak and Ramin stations due to human pollutants and fine-grained sedimentary texture. The low amount of organic matter in the desalination station can be caused by the inflow of more saline wastewater into the bay environment

In this study, electrofacies analysis has been done using MRGC (Multi-resolution graph-based clustering) method to be used in static modeling. Then, the resulting facies was modeled and compared together by applying different geostatistical stochastic algorithms in Petrel software. Two electrofacies classes including reservoir and non-reservoir facies were determined which were used for facies modeling. Seismic data was also applied for seismic facies construction and also to construct trend maps for appropriate facies distribution. In order to investigate the effect of five applied different geostatistical algorithms used in facies modeling on porosity distribution, the constructed facies models were used for porosity modeling. According to this study, the uncertainty of electrofacies modeling without applying seismic data increases which in turn reduces the accuracy of porosity models. In addition, electrofacies modeling considering the sequential indicator simulation (SIS) algorithm and applying the seismic trend maps, enhance the accuracy of the porosity model. Moreover, construction the of seismic facies is considered the best method for facies modeling to be used for porosity modeling due to the high correlation coefficient between acoustic impedance and porosity.

One of the most complete sedimentary successions of the Upper Permian-Lower Triassic is located at Zal section, in NW Iran. This section was examined in order to determine the microfacies changes and depositional environment in uppermost Permian and through the entire Lower Triassic. The microfacies change from deep deposits of the uppermost portion of the Paratirolites Limestone to the upper Changhsingian Boundary Clay post-extinction facies is sharp lithologically and in terms of faunal content. This change appears to be associated with shallowing but there is no evidence of erosion or subaerial exposure. Despite of the presence of microgastropod packstone and bioclastic wackestone with clotted appearance in their micritic matrix, which is indicative of microbial origin, at the beginning of Triassic at the Zal section, but no microbial buildups such as thrombolite are observable in the lowermost beds of the Elika Formation. Keratos sponge fabric, which has been previously reported only from the uppermost beds of the upper Changhsingian Paratirolites Limestone at Zal section, has been found both in uppermost Changhsingian Boundary Clay and in lowermost beds of the Lower Triassic Elika Formation as post-extinction facies. Upper Permian to Lower Triassic transition at Zal section is associated with considerable microfacies change from deep water setting to shallow water inner shelf setting. Microbial carbonates appear in the upper beds of the lower part and in the middle and upper parts of the Lower Triassic Elika Formation at Zal section and in a more limited way includes thrombolite, clotted micrite and cortoids.

The Dalan Formation is a carbonate sequence of Upper Permian age, which was widely deposited in Persian regions. Dalan Formation has been studied in the underground section of Kish 2, 1 and B2 wells of Kish Island gas field. Petrographic studies and facies analysis led to the identification of 12 microfacies deposited in a single-slope carbonate ramp and in 4 sedimentary sub-environments, including intertidal, lagoon, bariier and open sea areas. The important diagenesis processes that have affected the carbonate rocks of the Dalan Formation include micritization, cementation, anhydritization, compression, dolomitization and dissolution. Diagenesis minerals obtained in these deposits include three types of dolomite with replacement texture, two types of dolomite with cement texture, two types of anhydrite and two groups of calcite cement. Replacement type dolomite generally improves the reservoir quality and anhydrite reduces the reservoir quality by creating a layer by creating an obstacle in the path of hydrocarbon movement. Intercrystalline, interparticle and sheared porosity is the best type of porosity in the whole rock. The reservoir rocks were divided into 4 categories (RRTs-1 to RRTs-4) based on the analysis of the drilling core (SCAL data) and the description of thin sections. The first category is the best reservoir rock for storing and producing hydrocarbons, and the quality reservoir decreases towards the fourth category. According to the available data, the sedimentary environment cannot completely create the necessary conditions for the formation of reservoir-quality rocks, but mainly the final diagenesis along with diapirism determines the reservoir or non-reservoir formation.

The Oligocene – Miocene Asmari reservoir with 400 meters thickness in the Shadegan Oil Field consists of limestones and porous dolostones associated with sandstones, and shales. Dolomitization, as the most important diagenetic process, affected the Asmari reservoir and thus played a major role in the formation of the pore spaces structure, final flow capacity and heterogeneity of the Asmari reservoir. Dolomite types based on geochemical and textural characteristics, especially crystal size and shape includes: (i) very finely-crystalline, fabric-retentive dolomite (D1), (ii) fine to medium-crystalline, fabric-retentive dolomite (D2); (iii) medium to coarse-crystalline, fabric-destructive dolomite (D3); and (iv) very coarsely-crystalline, non-planar saddle dolomite (D4).Two types of fabric named fabric selective dolomitization and pervasive dolomitization were identified in dolomite crystals. Based on textural classification, 6 different textures including idiotopic, hypidiotopic or (idiotopic-S), xenotopic or non-planar-A (anhedral), idiotopic-C or planar-C (cement), porphyrotopic and poikilotpoic texture for dolomite crystals is identified. The mean concentration of strontium in dolomite samples is 483 ppm and the mean concentration of sodium is 1618 ppm which indicates the enriched amounts of strontium and sodium in these samples. The mean values of iron in dolomite samples are 3111 ppm and the mean concentration of manganese is 111 ppm. Dolomites (D1) with low Fe and Mn content may have formed during the early stages of diagenesis in an oxidizing environment. High amounts of iron and manganese in D3 and D4 dolomites indicate deposition in a reducing environment during shallow to relatively deep burial.

Shahbazan Formation is one of the Eocene carbonate units of Lorestan region. In present study, dolomitization models this formation were investigated by petrographic and geochemical (EDS) methods. The section under study is 71 m in the thickness and located at 65 km southwest of Khorramabad including carbonate and dolomitic carbonate rocks, and dolomite. The dolomites based on the texture are categorized into dolomicrite, dolomicrosparite, dolosparite, and filling of fractures, which except dolomicrite, the others are secondary. Dolomites of first type represent the formation in the tidal zone environment. In most cases, these dolomites are seen at the end of upwardly shallowing sequences, which indicate a drop in sea level. The secondary dolomites were formed in a shallow to medium burial digenesis environment as a result of seepage of evaporated basin floor sediments into the carbonate platform of the Shahbazan Formation. Low amounts of Fe and high amounts of Sr and Na in dolomicrites, high concentration of Fe and Mn in dolomicrosparites and doloasparites along with evidences such as algal laminae, intraclasts, fenestral porosity and absence of evaporate minerals indicate the formation of this dolomite from the model of tidal, seepage and the following shallow to medium burial. Low values of Sr and high concentration of Fe and Mn in coarse crystal dolomites can indicate the increase in the size of dolomite crystals and their recrystallization during burial. The absence of saddle dolomites probably indicates the non-interference of hydrothermal solutions and fluids during the process of dolomitization of Shahbazan Formation carbonates.

The present study investigates lithofacies and petrofacies in details and also reconstructs the depositional environment of the Paleocene siliciclastics of the Kerman Formation located in NE Central Iran, which is composed significantly of polymictic conglomerate bodies intercalated with some minor sandstone beds. Through detailed sedimentological studies (e.g., dominant grain size, degree of clast rounding and sorting, texture, and stratification), five lithofacies have been identified: clast-supported massive conglomerate (Gcm), matrix-supported massive conglomerate (Gmm), horizontally stratified conglomerate (Gh), horizontally bedded sandstone (Sh), and massive sandstone (Sm). Petrographic analysis revealed three petrofacies composed of petromict conglomerate, volcanic arenite, and feldspathic litharenite; gravels chiefly made up of basalt and andesite, as well as fewer limestone and agglomerated tuff. The lithofacies associations are related to sedimentary gravity flow (SG) and channel-fill sandstone bodies (CH) deposited in alluvial fan and braided fluvial systems. This research provides important insights into the sedimentary environments of the Kerman Formation.

The mud volcanoes of Sivan region are unique phenomena that are closely related to the folded and fine-grained sedimentary units of the Miocene. These mud volcanoes are in the form of eroded and inactive or semi-active cones, as well as mud ponds in the region. The results of the analysis of the sediment samples, in terms of texture, place them in the mudstone and clayey silt groups, in the Folk and Shepard classifications, respectively. Quartz, feldspars, mica, various heavy minerals, clay minerals (Illite and chlorite) and rock fragments (metamorphic, carbonate and volcanic) are the components of these sediments. Mineralogical evidence indicates the origin of sediments from metamorphic and possibly volcanic rocks of the region. The amount of calcium carbonate in the mud samples varies between 19 and 45%, and accordingly, the sediments of the mud volcanoes are calcareous mud, argillaceous marl, and marl. The formation of Sivan mud volcanoes can be related to some factors such as the presence of fine-grained sediments of Miocene, the thickness of sediments, and the influence of overburden pressures and regional tectonics. Also, the presence of a hidden salt dome according to the geological map as well as surface features can be effective factor in the formation and activity of the mud volcanoes in this area. In terms of the composition of sediment, water and formation mechanism, these mud volcanoes are comparable to mud volcanoes on the margins of the Caspian basin, which can be related to their sedimentation-tectonic conditions.

The Qanli laterite-bauxite horizon is located in the Central Iranian Zone, at a distance of 80 km from Zanjan city. The studied units at this area include sequences of the Ruteh and the Shemshak Formations. Based on sedimentary facies analysis and study of skeletal and non-skeletal allochems, it can be concluded that the sedimentary environment of this formation is a ramp-type carbonate platform. According to the fieldwork studies, the Qanli laterite-bauxite horizon is stratiform and and located at the final section of the Ruteh and below the Shamshak Formation. Mineralogical studies show that the laterite-bauxite horizon consists of hematite, goethite, boehmite and kaolinite with a few amounts of lipdocrosite, rutile, chlorite and ilmenite. Microgranular, pletiomorphic, flow-colloform, pisoidic, ooidic, peloidic and extraclast are the most important textures in these strata. Different chemical diagrams show that the laterite-bauxite horizon of Qanli deposit is located in the range of bauxite, bauxite clay and laterite. According to the mineralogical studies, it seems that the formation of laterite-bauxite horizon of Qanli occurred at pH between 3.5 to 6 and Eh about 0.4 to 0.7 and it has undergone moderate degrees of lateritization process. Current research indicate that the laterite-bauxite horizon of Qanli is the most similar to the karst bauxite deposits. Due to the expansion of Permian and Jurassic units in this area and nearby areas, the study and investigation of the Qanli laterite-bauxite horizon can be considered as an exploration key for similar areas in the Central Iranian zone.