نشریه رسوب شناسی کاربردی
پیاپی 19 (بهار و تابستان 1401)

The Pabdeh Formation as a source rock, with reservoir potential is located between Asmari and Bangestan reservoirs, is of great importance. In this study, the Pabdeh Formation (Paleocene-Oligocene age) was studied to determine the sedimentary and organic geochemical characteristics in the Mongasht anticline section, northwest of Izeh zone with a thickness of 797.2 m. To perform sedimentary geochemical studies, 40 micritic samples were selected for powder preparation and analyzed by Atomic Absorption Spectrophotometer (AAS). 26 samples were also selected for organic geochemical studies and were examined by Rock Eval 6. The results of sedimentary geochemical analysis and plotting data in related graphs such as strontium to sodium ratio show that the samples of the Pabdeh Formation in this section have originaly aragonite mineralogy. Based on the strontium/calcium ratio as well as the strontium/manganese ratio, this formation was affected by an open to a closed diagenetic system, which is due to the changes in the water-to-rock interaction. The Rock Eval 6 data indicate that the analyzed samples have no hydrocarbon generation potential, while the changes in these data at the lower and upper boundaries of the Pabdeh Formation and the Paleocene / Eocene boundary are well identifiable and can be used as sedimentary environment markers.

The Ilam Formation is one of the important reservoir units in the Zagros area. Integrated sedimentological and petrophysical studies have been used to evaluate its depositional and diagenetic history, sequence stratigraphy and, finally, reservoir quality in an oilfield in the Lurestan area. Facies analysis has resulted in the recognition of 4 microfacies including pelagic mudstone/marl, planktonic foraminifera mudstone/wackestone, microbioclast wackestone to packstone, and oligosteginids planktonic foraminifera wackestone/packstone. Petrophysical logs of two wells A and B (Neutron, Sonic, Gamma-ray, and Resistivity( are used to define lithology, porosity and water saturation in the Ilam Fm. Clean to argillaceous limestone was the main lithology of the Ilam Fm. in studied wells. The formation has microscopic pores (up to 15%) as dominant pore types. Based on the MRGC method, 5 electrofacies have been defined and correlated with core-based microfacies. Finally, six integrated reservoir zones have been differentiated and correlated in a sequence stratigraphic framework.

Early to Middle Triassic carbonate sequences of Elika formation in Zal Section (South of Julfa, NW Iran), consist of two different lithology: limestone and dolomite. The thickness of this formation is about 377 m and contains nine different units. The two upper units (8 and 9) are mainly dolomites with thickness of 78 m. The transition between limestone and thick-bedded dolomite in this formation is gradual with the presence of medium-bedded dolomitic limestone lithology. Petrographic results and geochemical analysis clearly show that these dolomites are mainly type I (dolomicrite). Dolomite crystals formed in shallow burial environment (reduction conditions), which affected by marine fluids with little chemical change during dolomitization. The result of XRD analysis in different types of dolomites shows that most of the dolomites of the Elika formation are so close to stoichiometric state and the amount of Mol/Percent of MgCO3 in these dolomites are between 46.7 to 50.4. The Elika dolomites deposited in shallow marine environments (supratidal to intertidal) with high rate of evaporation and salinity, which led to form very fine dolomite along with some silt-sized quartz. The presence of ooid, primary sedimentary structures such as lamination, along with low amount of Fe and Mn and high amount of Na and Sr prove mentioned sedimentation situation. High amount of Na in these dolomites possibly indicate the presence of clay minerals, which identified by SEM and XRD studies.

Shahbazan Formation with Eocene age is widely developed in Lorestan basin. In the study section, this formation with a thickness of 62 meters is located on the Kashkan Formation and is discontinuously below the Asmari Formation. The lithology of Shahbazan Formation in the study area includes dolomitic carbonate rocks. In order to study micro-facies, 60 samples of this section were collected and 20 samples were selected for elemental analysis. Based on field observations, lithographic and geochemical evidences based on elemental analysis by (EPMA) and (EDS) methods, two groups of dolomite were identified. Primary dolomites include dolomicrites in size between 4 to 10 microns that represent the formation of a tidal zone environment. Secondary dolomites include dolomicrosparite in size between 10 to 20 microns, dolosparites larger than 50 microns that is formed in a shallow to medium burial diagenesis environment due to the seepage of evaporated basin floor brines in to the carbonate platform on Shahbazan Formation in the study area. Low values of Fe versus high values of Sr and Na in dolomicrites, and high concentration of Fe in dolomicrosparite and dolosparite with some evidence such as intraclast, fenestral prosity and lack of evaporative minerals, indicate that these dolomites have been formed from the tidal model, seepage and then shallow to moderate burial. Geochemical evidence showed that the studied dolomites are non- stoichiometric, which can be explained the age of Shahbazan Formation.

Kowsar station was implemented about 35 years ago in the Gareh Baygon plain of Fasa in Iran. Alluvial fan layer thickness, texture, permeability, total density, moisture, electrical conductivity and pH of sediments were investigated. The purpose of this study was to introduce suitable alluvial fans for floodwater spreading system and also to obtain the sedimentary properties of alluvial fans in the vertical column and a lateral comparison of its layers. After sampling, and experiments, the characteristics of the sedimentary layers of the three wells drilled in the alluvial fan were compared by the correlation method.The artificial recharge of the aquifer have changed the properties of the aquifer material in the depths.The infiltration clay has led to the formation of thin layers with a slight permeability (about 0.01 cm/m). The bulk density of sediments increased, their salinity increased and their acidity decreased, the calcium and magnesium cations increased and the moisture content of aquifer sediments increased significantly. Humidity, organic matter, micro and macro organic activity intensify the chemical weathering of sediment minerals.Generally, there are positive changes and there was no evidence of adverse effects of flood infiltration, such as the formation of saline interbeds or the formation of specific minerals. In arid regions, artificial recharge can not have a destructive effect on aquifers sediments. Provided that they are run in places without any special geological and sedimentary problems.

Transitional boundary of Cretaceous to Paleocene known as a hiatus due to laramid orogenic activities and is associated with detrital facies. There is an outcrop in the south part of the Yazd block which show continuity of sedimentation at the boundary of Maastrichtian to Paleocene. As a result of the importance of this boundary in Central Iran, the sedimentary sequence of Barremian-Paleocene was studied in the Yazd block, the Chahtorsh Section. Lithostratigraphic studied released the presence of carbonate and detrital sediments in this stratigraphic section. Facies analysis led to recognition of 15 sedimentary facies which deposited on a shallow carbonate ramp in four subenvironments, tidal flat, lagoon, shoal and shallow part of open marine. According to the four type 1 and 2 sequence boundary, four sedimentary sequences was divided in this section. The boundary between fist and second sequences recorded on of the longest discontinuity (Aptian- Maastrichtian) in Central Iran Semi continent while the Maastrichtian to Paleocene boundary, that is discontinue in most parts of Central Iran, is a continue boundary in this section. These results can be used in the paleoenvironmental reconstruction of Central Iran Semicontinent.

Possible sources of the dusts in the Khour and Biabanak were been investigated. For these purposes, 28 surface samples from this area were collected for sedimentology and mineralogy studies. Most of the surficial sediments of the area are fine sand, a few samples with silt and clay size; which are susceptible to wind erosion. Furthermore, climatology could facilitate a better understanding of natural hazards such as dust events. Climatic data for a period of 20 years (1991-2010) including rainfall, dust events, wind speed and directions obtained from Meteorological Organization of Iran were analyzed. Major wind directions are W and NE. Heavy minerals including pyroxene, biotite, amphibole, as well as some opaque minerals are recognized in these sediments, among which the pyroxene is more frequent than the others (1-1.2% av. in whole samples and up to 5-10% in heavy mineral fraction). Most of the pyroxene is augite. According to climatic conditions, overwhelming fine grain sediment particle size (less than 63 µ) of the area and predominant wind direction, the dusts might originate from west of the Khour and Biabanak. Detailed knowledge of dust provenance could aim to eliminate its environmental impacts. Hence, possible sources of dusts were examined. Majority of the sediment cover in the NE of Isfahan provenance are originated from acidic, intermediate and ultramafic rocks exposed in the Anarak area; altered ultramafic rocks of Proterozoic to early Palaeozoic in the Anarak-Khour; as well as ophiolites exposed along major faults such as Naein-Dehshir-Baft.

Mashalak River is located in the north of Iran and is one of the most important rivers leading to the Caspian Sea west of the Mazandaran province. To conduct environmental monitoring, 25 samples of sediments were collected from the Mashalak riverbed. The samples were analyzed by ICP-MS. A review of heavy metal concentrations suggested that the highest concentrations of heavy metals pertained to Vanadium, Chromium, Zinc, Nickel, Copper, Lead, Cobalt, and Molybdenum, respectively. According to Sediment Quality Guidelines (SQGS), Mashalak sediments are more likely to be contaminated with Chromium and Nickel. The enrichment index shows that Chromium and Nickel produce moderate pollution while other metals have low pollution. Using the Geo-Accumulation Index, only Chromium shows low to moderate pollution. Examining the ecological risk of heavy metals in the Mashalak River deposits suggests these deposits are not contaminated, indicating that the ecological risk of the area under study is low. The Principal Component Analysis (PCA) test results helped identify two main factors. The main factor includes such metals as Cobalt, Aluminum, Vanadium, Copper, Nickel, Zinc, and Chromium, which have both lithogenic and anthropogenic origins simultaneously, as the secondary factor includes the former.

Petrography and geochemistry analysis of the sandstones of the Ojaggheshlagh Formation (Late Eocene-Early Oligocene) of the Moghan Basin, was carried out to evaluate their tectonic setting, climate, weathering degree, and parent rock. Sandstones include litharenite and feldspathic litharenite and minor arkose and greywacke. In a general view, sandstones are immature, characterized by the poorly sorted and poorly rounded grains including volcanic fragments and feldspars and minor heavy minerals, mica, monocrystalline quartz and clay minerals. Geochemical diagrams including discriminate function, TiO2 vs. Al2O3, TiO2 vs. Zr, as well as trace elements diagrams/data as La/Th vs. Hf, Zr/Sc and Th/Sc indicate a predominantly basic to intermediate (and minor acidic) volcanic parent rocks for the Ojaggheshlagh sandstones. Low chemical index of alteration plus SiO2 vs. Al2O3+K2O+Na2O and Al2O3-CaO+Na2O-K2O diagrams emphasis sub-arid climate and short transportation distance of the Ojaggheshlagh sandstones from the source area, which led to the preservation of the unstable minerals and poor compositional and textural maturity of the Ojaggheshlagh sandstones of the Moghan Basin. Al2O3/SiO2 vs. Fe2O3+MgO, K2O/Na2O vs. SiO2 and La-Th-Sc diagrams and La/Th and Th/Sc content reveal an island arc tectonic setting The archived results of the paper are useful for the paleogeographical and tectono-sedimentary reconstruction of the Moghan Basin.

In this study, the lowermost part of Akhore Formation with Middle Eocene age at the Shurab section, in the north Naein, east Isfahan has been studied. In this research, a stratigraphic section with 505 meters thickness is measured and ten lithostratigraphic units differentiated and composed of a thin basal conglomerate followed by the alternation of mostly purple sandstones and shales.This succession covered the Naein Ophiolite Complex,. Lithofacies analysis led to the identification of six coarse-grained facies (Gcm, Gp, Gh, Gci, Gmg, Gmm), two medium-grained (Sm, Sh) and three fine-grained (Fl, Fm, Fsm) as well as pedogenic fearute (P). Lithofacies studies led to identification of five facies associations which have been deposited in the sub environments of Sediment Gravity flow (SG), Sandy-bedform (SB), Floodplain (OF), Gravel-bar (GB), Foreset macroforms (FM) for braided river. The study of this succession provides us with important information on the geodynamic evolution of central Iran during the Middle Eocene.

The upper Permian–Lower Triassic Dalan and Kangan formations comprise two of the most important hydrocarbon reservoirs in the Persian Gulf. The goal of this study is to analyze sedimentary microfacies and establishing a conceptual depositional model and the sequence stratigraphy framework of the upper Dalan and the Kangan formations in central and eastern oil fields Persian Gulf. According to petrographical studies carried out on 3651 thin sections, fifteen carbonate microfacies associated with tidal flat, lagoon, shoals and open marine depositional settings were identified. Microfacies analysis and their vertical and lateral changes, gamma-ray response as well as comparison with the ancient and modern analogues suggest a gentle carbonate ramp as the depositional model for the studied successions. Comparison of the microfacies abundances in the studied oil fields revealed dominance of the shallower depositional setting in the central field studied well compared to those of the eastern oil fields which indicates a northeast-ward deepening paleo-dip of the sedimentary basin. Five third-order depositional sequences were established; three sequences labeled here as USD1, USD2 and USD3 in the upper Dalan Formation and two sequences in the Kangan Formation namely KGS1 and KSG2. The sequences comprise TST and HST system tracts, separated by sequence boundaries and maximum flooding surfaces. While the sequence boundaries were identified based on the sedimentary successions or microfacies indicative of relative sea level fall, the maximum flooding surfaces were recognized based on occurrence of deepest microfacies in the sequences. Correlation of the established sequences in the studied wells represents an overall shallowing upward depositional pattern.

Land use is one of the most important methods to prevent soil erosion. Land use changes are inevitable due to development in watersheds. In this study, in order to determine the interaction effect of land use, rainfall intensity and erosion in deposits of Aghajari and Gachsaran formations, a part of Margha and Kuhe Gach watersheds of Izeh city with an area of 1609 and 1202 hectares were selected. A sampling of runoff, sediment, infiltration, and runoff and erosion threshold in both formations was carried out at 13 points with three replicates in range, agriculture and residential land uses of Aghajari and Gachsaran formations at rainfall intensities of 0.75, 1, and 1.25 mm/min using Kamphorst rainfall simulator. The results showed that in both formations, the interaction effect of different land use and rainfall intensity has significant effects on runoff, sediment, and infiltration and runoff and erosion threshold. In general, in Aghajari and Gachsaran formations, the interaction effect of land use and rainfall intensity in all erosion components in eight cases and land use in two cases and rainfall intensity in three cases have significant effect. Therefore, the interaction effect of land use and rainfall intensity has the most effective in erosion components and also land use has the least effect on erosion components.

According to facies analysis and sedimentological data integrated with statistical analysis, five microfacies (MF) and two lithofacies (LF) are identified in the Sargelu Formation (Middle Jurassic), exposed in the Lurestan sub-basin. The facies associations indicate the presence of three sunenvironments including the basin / shelf, slope and middle shelf facies belts with pelagic/hemipelagic sedimentation, periodically influenced by depositions of turbidites and tempestites. The sequence of identified sedimentary facies shows that among the main factors controlling the facies character, two factors of oxygen content and intra-basinal flows are the most important ones affecting the deposits of the Sargelu Formation. Statistical investigation on the distribution of size and skewness of Posidonia-containing microfacies, especially Posidonia Wackestone – Packstone (MF-G) also confirms that the Sargelu Formation deposited in a low-energy basin–outer shelf setting and high energy slope and middle shelf facies belts. The widespread occurrence of intervals containing Posidonia species was linked to nutrient supply and oxygen supply by marine currents. Differences in the Posidonia distribution pattern in the Wackestone – Packstone microfacies (MF-G) led to the decomposition of this microfacies into four subfacies (MF-G1, MF-G2, MF-G3, MF-G4), which differ in the patterns of statistical skewness and the position of sub-facies along the depositional profile. In this regard, the left-skewed distribution points toward the slope, whereas the right-skewed distribution points to the middle shelf, and the bimodal-skewed distribution indicates the outer basin/shelf subenvironment.

The Olig-Miocene Asmari Formation is one of the most important reservoir rocks in Zagros basin and composed of carboantes rocks and locally sandstone and evaporates in southwest Iran. In this research, microfacies, depositonal environemt and diagenetic processes of this formation in a well in Qaleh Nar field have been investigated. Thin section studies indicates that this formation mainly consist of dolomite and limestone. Based on petrographic analysis 3 facies association have been identied in the studied interval namely A, B and C which includes 10 microfacies. The microfacies are attributed to tidal flat (upper intertidal and intertidal), lagoon and shoal. The lack of great barrier reefal microfacies, abundant oolithic microfacies and wide distribution of tidal flat indictes that the Asmari Formation was deposited in a carbonate homoclinal ramp. Sedimentological studies indicate that different diagenetic processes have been affected on the studied interval including cementation, anhyiritzaiton, neomorphism, micritization, bioturbation, dissolution, compaction and dolomitization. These processed have been occurred in three diagenetic environments including marine, meteoric and burial. Among all, dolomtiztion, dissolution and fractureing have positive effects on porosity and enchance reservoir quality, with cementation and anhyritzation have negative effect on it.

Lower Cretaceous carbonate rocks (Taft and Abkouh formations) in the south of Yazd host lead, zinc and barite ore deposits. Diagenetic processes after deposition in these carbonates have caused the formation of these deposits. The main diagenetic processes affecting these sediments include compaction, brecciation, neomorphism, cementation, dissolution, dolomitization and replacement. The dolomitization and replacement process has led to the formation of lead, zinc and barite ore deposits. Hydrothermal fluids through the active and normal faults have provided the conditions for the formation of these deposits in the carbonate rocks of this area. The formation of the ore deposit occurred during two stages of mesogenesis and telogenesis. In the mesogenesis stage and in the burial conditions, first dolomite is formed and after the entry of hydrothermal fluids and supply of necessary elements, the replacement has created sulfide minerals. During the telogenesis stage, some parts of the formed sulfide deposits are re-exposed to meteoric fluids, leading to the formation of oxide ore deposits.