نشریه رسوب شناسی کاربردی
پیاپی 21 (بهار و تابستان 1402)

This research is based on sedimentological study of 4 surface (Kabir kuh, Samand, Anjir and Anaran) and 8 subsurface wells in the Lurestan, North Dezful and Abadan plain with a total thickness of 1592 m. The Santonian – Lower Campanian Ilam Formation is a carbonate hydrocarbon reservoir in the Zagros fold – thrust belt, in SW Iran. Twenty microfacies were recognized based on microscopic study. Microfacies analysis led to the recognition of four facies belts including inner (shoal), mid, outer ramp, and basinal setting. Correlation of depositional environments together with lateral facies changes indicate deposition are distally steepend ramp. Deep marine and inner ramp facies are the most and least facies, respectively in the study area. As the distribution of inner ramp facies is very limited, it can only be recognized in wells from North Dezful and Abadan plain.The results obtained from facies together with analyses of wireline logs clearly shows a northward deepending of the depositional environment from Balarud Fault. Cementation, micritization, compaction, solution seams, neomorphism, disolution, fracturing, pyritization, phosphatization, gluconitization and bioturbation are the main diagentic processes. However, cementation is most dominant in shallow marine facies in the Abadan plain, whereas, pyritization, stylolite and fracture are the most prevailing processes in deeper marine facies of the Ilam Formation in Lurestan. There is a limited distribution of porosity, but the most dominant types are, interpartical, microporosity and fracture related porosity. The Ilam carbonates are mostly affected by shallow to deep burial diagenesis in Lurestan,

The study of Aptian-Albian sequence in many parts of the Zagros Basin and the Arabian plate has always been limited due to the discontinuity of sediments during this period. The Tang-e Maghar, located in the Dezful Embayment, is one of the few continuous sequences of the Aptian-Albian marine sediments on the Arabian plate, the study of which provides valuable information about the paleogeological status of this period. In this study, in addition to examining the trend of changes in% TOC and% CaCO3 values through the Aptian-Albian transition sequence in order to analyze the state of the oceans, sedimentary micro-losses have also been investigated using a thin section study. In the Tang-e Maghr section, the TOC level at the base of the albino turbulence has reached 5.8%, which indicates the presence of black shale in this section. This important finding, along with the biostratigraphic data of previous studies, in addition to determining the chronostratigraphic position of this shale, has made it possible to accurately match it with other black shale horizons in other sedimentary basins. Changes in CaCO3 levels have also been recorded in different layers with different values. The most important of these fluctuations in terms of paleoecological interpretations have been at the end of Aptian and the beginning layers of Albian, which is known for a significant decrease in CaCO3 levels. This combined with fossil data from previous studies can confirm the acidic conditions of seawater at the time of Aptian-Albian sediment deposition.

The distribution of microfacies in Ali Bashi and Zal sections and two studied sections in Hambast Valley is suggestive of open marine and deep environment in mid and outer ramp settings. Considering the faunal contents and microfacies type of the Wuchiapingian deposits in the study areas, the lower parts of the Wuchiapingian strata yield a mid ramp setting while their upper parts are characteristic of outer ramp setting. Based on previously obtained results from tectonic subsidence curves for Alborz and Abadeh, the Early Permian rifting event was followed by strong subsidence in Middle and Late Permian and was associated with an increasing subsidence from North (Alborz) toward South (Abadeh). The increasing tectonic subsidence was also caused the increased thickness of deposits in a N-S trend as the thickness of Wuchiapingian deposits in Abadeh area are more than four times than those of coeval deposits in Julfa area. This thickness increasing in Abadeh area is more evident in the lower Wuchiapingian deposits and the upper Wuchiapingian strata, Unit 6 of the Hambast Formation, has the same thickness as Upper Julfa Beds in Julfa area. Furthermore, the increasing of tectonic subsidence was led to sea level rising and deepening and caused the reduced size and diversity among brachiopods and abundance of small-sized ostracods and sponge spicules in the Upper Julfa Beds as well as pelagic fauna such as conodont and ammonoids in the Unit 6 of the Hambast Formation.

In this study, a combination of petrographic and major element geochemistry of siliciclastic deposits of Lower Permian Doroud Formation in the Zal section in south of Jolfa has been used to investigate the provenance, tectonic setting and paleo-weathering. The thickness of Doroud Formation in Zal section is 112 m consisting of micro conglomerate, red sandstone and shale. Thirteen samples of sorted and medium grained sandstones were examined by point-counting method and 6 samples were examined for determination of their major elements by X-ray fluorescence (XRF) method. The studied samples are frequently sublithic-arenite in composition. The study of the amount and type of monocrystalline and polycrystalline quartz and using of discrimination function, indicate that the parent rocks of these deposits are predominantly metamorphic, felsic igneous rocks as well as sedimentary recycled. The presence of chert in petrographic studies has also confirmed the effect of sedimentary recycling from older formations. Petrographic and geochemical studies also indicate the cratonic origin and tectonic setting of the passive continental margin at the time of sediment deposition of the Doroud Formation. Determination of chemical index of alteration (CIA) indicates intense weathering and humid climate in the provenance area, which is consistent with the paleogeography of the Iran in Permian. It seems that factors such as the a long-distance transport on the Arabian Craton, the recycling of older formations and also the humid climate at the time of the deposition of the Doroud Formation, together, have played significant role at the relatively high maturity of this sandstones.

The present study has focused on the lithology and mineralogy of the Bangestan reservoir shale unit, 5 meters thick at the 45 m below the upper boundary of Sarvak formation, located in the Lali oil field, to clear the existing lithostratigraphic ambiguities which refer it as a tongue of the Surgah Formation. After examining the petrophysical logs to determine the exact location of these deposits and core descriptions, the petrography was performed, and XRD analyses to recognize the mineralogy of the total sample as well as clay minerals. Core studying indicates that the unit is pyrite bearing gray shales. Moreover, based on petrography, the studied samples are argillaceous and fossil-free mudstone. The results of the XRD analysis show that the mineralogy of these deposits is mainly clay minerals, calcite, quartz, and pyrite. The samples' average abundance of clay minerals is 56%, and the most frequent ones are the mixed-layered clays (illite/smectite), illite, and kaolinite, respectively. The SEM images often exhibit clay minerals of detrital origin. Due to the lack of fossils, the age of this unit was determined based on its stratigraphic position, which is surrounded by the Sarvak Formation deposits of the Cenomanian age and is distinguished from the Sorgah Formation (Turonian- Santonian age). Due to the absence of deep-marine organisms in this unit and the identification of lagoon and shoal carbonate microfacies in its surrounding layers, a calm and reducing lagoon environment is attributed to these sediments, which is against the deep marine of the Surgah Formation.

The Persian Gulf is one of the most prominent postglacial landscape changes in the world. The basin has recorded the Holocene climate changes and sea level fluctuations in its sedimentary sequences. Therefore, the study of the Persian Gulf’s Holocene sediments is of great importance. Understanding the postglacial climatic and oceanographic condition requires the discrimination of post-depositional disturbances from syn-depositional processes that are controlled by climatic and oceanographic conditions. In this regard, we used two short sediment cores obtained from the deepest parts of the Persian Gulf (PG) and Strait of Hormuz (SH) using a gravity corer to investigate the most important disruptors of the Holocene sedimentary sequences. Sedimentological studies along with X-ray images and high-resolution photographs were implemented on two well radiocarbon-dated short sediment cores. The radiocarbon results show that the sediments are disturbed in both cores. The SH core shows repeated age reversal and evidence of liquefaction. The PG core, on the other hand shows evidence of age reversal on top and a hiatus at the base. We assumed that the late-Holocene SH sedimentary sequence is more prone to be disturbed by earthquake while gas venting and relatively strong bottom currents are also influential. On the other side, bioturbation is more responsible for sediment disturbances in PG during the Mid to late Holocene. It is suggested that before starting comprehensive studies on the PG sediments, sedimentary structures are investigated to determine any disturbances in the sequence

The sedimentary succession of Cenomanine-Turonian, which is introduced by Sarvak Formation, is the most important hydrocarbon (reservoir) formation of Abadan plain. Reservoir facies of this formation show variable temporal and spatial distribution in this time period due to tectonic and sedimentary conditions. In this study, using subsurface seismic data and well data (petrophysical logs and core thin sections), and also comparison with surface outcrops data of Izeh zone, facies, sedimentary environments and diagenetic changes of Sarvak Formation have been studied and analyzed in the framework of sequence stratigraphy. Investigation lateral and vertical variations of facies belts and sequences indicated sedimentation of Sarvak Formation on a rimmed carbonate shelf and intra-platform basins. By examining the changes and geometries of sedimentary-seismic facies along with well, paleontological and petrophysical data and comparison with outcrops, four third-order sedimentary sequences have been separated in the Sarvak Formation (Cenomanian – Turonian interval) with an average age of about 4 million year. These sequences include K120, K130, and K135 in the early Cenomanian, mid Cenomanian, and late Cenomanian respectively, and the K140 sequence is in the early to mid-Turonian. This study showed that distribution and migration of system tracts are consistent with the reservoir zones of Sarvak Formation. The best reservoir facies are in Highstad Systems Tract (HST) which are grain-supported, high porosity and permeability and are subjected to diagenetic processes such as dissolution and karstification. The K135 Sequence forms the best hydrocarbon-containing reservoir facies of shoal, rudist, and channel type in the area.

River sedimentology provides significant basic data for river engineering projects (sediment transport and channel stabilit.( Most of these data are collected after careful study of bedform, texture and facies analysis along with architectural elements (Hey et al., 2015). Downstream grain size changes are complex in a gravelly bed river and often do not follow a simple sediment graft model. The processes affecting the sediment degradation process in rivers are selective sorting, wear and sedimentation rate of lithological units of the catchment (Ruset, 1978). Mianroud river is located in the southeast of Iran, which is one of the very low rainfall areas with an average annual rainfall of 63.6 mm and has a dry climate. Severe and short-term showers play a very important role in the occurrence of large floods in the Mianrud catchment area. In this area, factors such as diversity of different faults, geomorphic controls (river flow, basin slope, ...), hydraulics (water discharge), and sedimentology (sediment production, transfer and re-sedimentation) control the main parameters of the river (Sin Ciana and Pasternak, 2017.( This paper presents the textural changes of sediments, rock facies and architectural elements and sediment model in a rugged mountain river.

Mishan Formation with a thickness of 395 meter which is composed of limestone, marly limestone and marl and early to middle Miocene age (Burdigalian-Langhian), has been measured and sampled in order to study the sedimentary environment and sequense stratigraphy in Bavarian stratigraphic section in the south of Kavar, Fars province. The Mishan Formation is located on the red evaporative and clastic sequence succession of the Razak Formation and under the clastic and carbonate succession of Agha Jari Formation (Miocene-Pliocene age). Based on the characteristics of petrographic features, field evidence, as well as examining the abundance and distribution of foraminifera and other other allochems and orthochems, eighteen microfacies packages were identified in six sub-environments or sedimentary zones (Facies zones) including tidal flat, lagoon, shoal, pach reef, shallow and deep open marine can be placed. The absence of barrier reefs (which are typical of rimmed platforms) and re-deposited carbonates and also gradual conversion of microfacies into each other and the existence of wide areas of tidal, indicate that the sedimentary sequence in this section was deposited on a homoclinal ramp carbonate platform. The sedimentation of limestone-marl deposits of Mishan Formation on the evaporite-clastic sedimentary rocks of Razak Formation, indicate the last transsgresion of the sea water during the Miocene age of the Zagros Basin. The investigation of the sequence stratigraphy of this Formation in the research section has led to the identification of four third-order sedimentary sequences with sequence boundaries of the second type.

In recent years, continental ichnology has gained great importance in the stratigraphy, basin analysis and paleogeography studies and widely used in understanding environmental parameters and paleoecological conditions. The study area in the Birjand city is a part of the sedimentary-structural zone of eastern Iran and includes alluvial sedimentary deposits with Neogene age. Based on the previous studies, the above-mentioned alluvial deposits include conglomerate, sandstone and mudstone lithofacies which were deposited in the fluvial system based on their textural features and sedimentary structures. Lithofacies, facies associations and the abundance of sediment gravity flow and channel-fill deposits, in the studied alluvial deposits indicate the existence of a braided fluvial system close to the source during the Neogene time. Field observations of the sand and mud deposits of the studied alluvial terraces indicate the presence of continental trace fossils in these sediments. Based on the observed burrows of these sediments, two Coprinisphaera and Skolithos ichnofacies and six distinct ichnogenus can be distinguished in these continental deposits, which confirm the deposition of these sediments in the adjacent parts of active channel and floodplain of fluvial system.

Paleocene-Eocene succession in the Shiraz region includes Sachun and Jahrom-Pabdeh formations. In order to study petrography, sedimentary environment, and sequential stratigraphy, 4 stratigraphic sections of Beiza, Sadra (auxiliary), Sarvestan, and Shahneshin were selected and analyzed. Based on field studies, manual samples, and detailed microscopic study, 800 thin sections prepared from the studied samples were identified as 23 microfacies and lithofacies deposited in a homoclinal carbonate ramp model. This model the time evolved to steepened ramp sedimentary environment model. By studying about 1700 meters of Paleocene-Eocene sediments, 9 depositional sequences were identified and separated depending on the location of the sections under study in sequence stratigraphy. During the Paleocene and FSST systems tract formation toward to southwest of the study area (Sarvestan section) evaporites sediments in the lower part of Sachun formation correlative deposited the equivalent of Pabdeh formation in the outer ramp. The evolution of steepened carbonate ramps in shallow parts of the carbonate platform of Jahrom Formation and in deeper parts of the Pabdeh formation was deposited in the Middle Paleocene to Middle Eocene period. In the HST systems tract and high carbonate production rate (Highstand Shedding) in the sloping part of the environment calciturbidite has been deposited as a layer between the Pabdeh Formation. Studies show that the facies of Sachun Formation in the study area gradually changes from west to evaporitic-marly facies to marl, limestone, dolomitic limestone, and purple shale facies.

The purpose of this research is to determine the sedimentary environment of alluvial terraces south of Khorramabad to Poldokhter using structural elements and limiting surfaces. In line with this goal, 4 sections were identified and studied. The cuttings are located at distances between 60 and 80 kilometers south of Khorram Abad towards Poldokhter. The studies conducted on these sections lead to the identification of 10 rock facies, including 4 gravelly rock facies (Gm, Gms, Gp, Gt), 4 sandy rock facies (Sm, Sp, St, Sh) and 2 rock facies. Flower (Fsm, Fm), 13 structural elements including (GB, HS, C/S, LHF, LCS, CVs, DIs, TCS, OF, CH, SB, SHF, LIS) and 6 limiting levels of rank 1 to 6 became. According to rock faces, limiting surfaces and structural elements under channel environments, channel bars, point bar, wide cuts (crevasse splay), natural embankments (levee).) and flood plain subenvironment were determined for the alluvial terraces south of Khorramabad to Poldokhtar. Structural elements CH, GB, C/S, LHF, SHF were observed in the studied alluvial barracks in abundance, which indicates a river environment with low twist for the studied alluvial terraces, which alternates between at times, it was attacked by strong and destructive floods, and the coexistence of flood channels indicates that they are periodic.

In order to reconstruction of sedimentary conditions and paleogeography of Qom Formation, one stratigraphic outcrop in the Northeast of Mahneshan has been studied. In this study, microfacies analysis and microfossil investigations have been carried out on Forty-seven samples from one hundred sixty-two meters of sedimentary rock layers. Qom Formation in this section, is composed of carbonate, clastic and volcanoclastic layers that covers the andesitic strata of the Karaj Formation with a disconformity boundary and overlayed by clastic strata of the Upper Red Formation with gradual boundary. Microfacies analysis led to identification of one lithofacies (grain supported conglomerate) and three microfacies (1- Algal coral bioclast packstone, 2- Carbonate volcaniclastic and 3-Pelagic wack/packstone) that are related to the open carbonate shelf, submarine channels and submarine volcano in this section. Fossil investigations lead to identification if seventeen species of foraminifera fossils and two biostratigraphical zones. Based on foraminiferal index fossils (Borelis melo curdica, Meandropsina iranica, Praeorbulina glomerosa), Burdigalian-Langhian have been proposed as relative age for these strata. Facies change throw the stratigraphic column show deepening upward trend (during Langhian) in this study that can be correlated with paleogeographic events and relative sea level rise in Langhian age in this area.

The late Cretaceous Ilam Formation in the western part of the Zagros basin (W Iran) was inspected in two outcrops (namely Mehdiabad and Kuh-e Varzarin sections) which are located in the Ilam province (in the Zagros fold belt). The purpose of this research was to identify the lithofacies, microfacies and depositional environment of the Ilam Formation. This formation consists of limestone and argillaceous limestone which comprise three microfacies (planktonic foraminifera wackestone/packstone, planktonic foraminifera-benthic bivalve wackestone/packstone/rudstone, benthic-planktonic foraminifera wackestone/packstone/rudstone that were deposited in two facies zones (c.f. slope and toe of slope). Evidence of the gravity flow including basal truncation (erosional) surface of beds, normal grading, weak amalgamation, abundant deep-water facies, coupled laminae, relatively thick gravite beds, mixed planktonic (deep water) and benthic (shallow water) biota, large scale slump folds and deformed structures, attest the influence gravity flows which transported the shallow water sediments into the deep setting. Poor quality of the outcrops and lack of well-preserved sedimentary structures makes it impossible to discriminate between various types of sediment gravity flow deposits (gravites). Gravites are observed only in the toe of slope facies zone. This facies zone in turn is classified into three parts including upper, middle and deep parts according to the texture and the argillaceous limestone beds thickness. Due to ack of platform top deposits, it was not possible to distinguish the carbonate platform type (ramp versus shelf type). However, the overwhelming resedimented carbonate facies points toward a carbonate shelf rather than a ramp.

Shurijeh Formation (Neocomian - Barremian) is the main hydrocarbon reservoir in north east Iran. Most gas reservoir production place in zones B and D of this formation. In this study, comprehensive petrographic and petrophysical studies were performed to understand the factors controlling the reservoir quality of this formation. With respect to the petrographic studies, well log data, evidence achieved from the core and drill cuttings, five primary facies (petrofacies), including microconglomerate, sandstone, claystone/shale, sandy dolomudstone, and dolomitic- sandy dolomitic ooid grainstone / hybrid, were identified in the deposits of Shurijeh Formation. Sedimentary facies of the Early Cretaceous reservoir in the studied wells belong to the upper part of the supratidal zone, intertidal zone, lagoon, braided river (longitudinal bars) and meandering river (flood plain and oxbow lake). In this study, based on porosity and permeability data, 4 units of Hydraulic flow units (HFUs) were identified using flow zone indicator (FZI) method. The results of this study showed that the diagenetic processes like dissolution, dolomitization and chemical compaction (stylolites and dissolved vein) are related to the grain supported facies including micro-conglomerate, sandstone and dolomitic- sandy dolomitic ooid grainstone / hybrid and hydraulic flow units (HFU4) and hydraulic flow unit (HFU3) that have the best reservoir quality are connected. The results of this study showed that the diagenetic processes like dissolution, dolomitization and pressure dissolution (stylolites and dissolved vein) are related to the grain supported facies including micro-conglomerate, sandstone and dolomitic- sandy dolomitic ooid grainstone / hybrid and hydraulic flow units 4 and 3 that have the best reservoir quality are connected. Diagenetic processes of cementation (Silica, carbonate and anhydrite) and alteration of feldspars are associated with the dominant mud facies including claystone/shale, sandy dolomudstone of hydraulic flow units 2 and 1 which have the lowest reservoir quality.