جستجوی مقالات مرتبط با کلیدواژه « facies » در نشریات گروه « زمین شناسی »

Lignite Beds of Tabriz are among of the Neogene formations in the northwestern area of the Iran, which is spread in the eastern suburb of Tabriz. Its sedimentary facies includes facies groups of fine grains clastics, sandstones, limestones and facies of lignite, tuff and microfacies and petrofacies under them. In this study, two stratigraphic sections of these sediments in the eastern part of Tabriz were studied and 171 samples and 42 thin sections were collected and studied. XRD analysis for mineralogy and SEM electron microscopy for 3-dimensional studies were used to identify microfossils. Identified fossils include the genera and species of gastropods, Pelecypods, ostracods, fish, diatoms, charophyte algae, and foraminifera. The studied fossil assemblages includes species from freshwater to euryhaline and marine. The identified sedimentary environments include the lake basin environment, the shallow coastal environment and the marshy lake environment. In  the studied sedimentary strata, strong fossil evidence and sedimentological evidence of the marine environment are not observed, at least during its lifetime. Therefore, it is concluded that the marine taxis in these deposits remain and are adapted from a former marine environment.

This study was done to describe and interpret the facies, the provenance of sediments, pedogenesis processes, and the model of the Abyek alluvial fan in the northern margin of Qazvin Plain, using 45 sediment samples in the form of nine profiles and nine surface samples. The facies study led to the determination of six facies grouped into two facies associations including coarse-grained lithofacies (Gms, Gcs, Gci, Gcp/Gmp, Gmg, and Glns), and calcrete facies (Plc). This alluvial fan is dominated by the episodic matrix to clast-supported gravel (interbedded with a subordinate) and red, matrix-supported gravel which were deposited by non-cohesive debris flow. The results of granulometry analysis showed that the size of the sediments of the alluvial fan shows wide variations from gravel to clay, and the texture of the sediments of this alluvial fan is mainly gravel and sandy gravel with very poorly sorting and fine skewness. The study of macromorphology and micromorphology of calcrete showed that their occurrence was controlled by pedogenic processes. Micromorphological studies also revealed alpha and beta features such as coated grains, pisoid, laminar crust and strong brecciation.

In order to study of the Oligocene depositional sequences, a stratigraphic section of the equivalent deposits of the Qom Formation (for convenience in the continuation of the article, Qom Formation is mentioned) which is 330 meters in thickness has been nominated in northwest of the Hamedan. Facies analysis has produced eight microfacies related to the four facies belts of tidal flat, reef, slope and open marine. Base on lacking the sediment gravity flows, turbidity facies, and abundance in reef facies deposits, a carbonate shelf is proposed for Qom formation. In this research, two depositional sequences and three-sequence surfaces have been separated based on sequence stratigraphic studies (the first and third sequence surfaces being of the first type). A comparison of the relative sea-level change curve in the study area with the Oligocene-Miocene global sea-level change curve shows that sequences of the Qom Formation have acceptable compatibility with global changes in seawater level. Also, the comparison of the sequence boundaries of this study with the Zagros and European basins indicates that the Oligocene sequence levels of the Qom Formation which are identified in the Zagros basin, are well corresponded with the results of this study compare to the European one.

Lower Miocene deposits in Iran have a significant expansion. In Zagros and Central Iran, these sediments include Asmari and Qom formations, respectively. Due to its economic importance and especially the possibility of reservoir and cap rocks, many studies have been conducted on the Miocene deposits in areas with high hydrocarbon potential. However, in the high Zagros, due to the limited oil reserves, the Miocene deposits have been less studied. According to the geological map of Harsin in the northern parts of the high Zagros zone (Shahidi and Nazari, 1997), the Miocene deposits consist of carbonate and clastic rocks. In terms of lithology, especially the presence of clastic rocks, these deposits are very similar to the Qom Formation, but since they are located in the high Zagros zone, it may not be correct to refer to this formation. On the other hand, the lithology and appearance of these deposits are fundamentally different from the Asmari Formation. Therefore, in this paper, like the geological map of Harsin, they are called Miocene deposits. In this paper, the paleoenvironment and microfacies of Miocene deposits in the high Zagros have been studied.

Three sections of Miocene deposits are studied, located 23 km south of Harsin (Figure 1). Fig. 1. Locality map of the studied area. In the present study, a total of 130 sections were taken. Thin sections were prepared from rock samples and isolated fossils were isolated from soft samples. Texture properties and fossil assemblages in thin sections were examined and identified by a polarizing microscope.BiostratigraphyBased on foraminiferal distribution, the following assemblage zones are recognized:1) Indeterminate Zone I: In view of the fact that we unable to find any index microfossils, comments on the age of this zone are difficult, which explains why this is here referred to as an indeterminate zone.2) SBZ25: Larger benthic foraminiferal zone SBZ 25 can be divided into two subzones; those of M. globulina and M. intermedia.2-a) M. globulina Subzone: This is defined by the FO of M. globulina at the base and the FO of M. intermedia at the top. It is regarded as a common global index for the Burdigalian Stage.2-b) M. intermedia Subzone: This is defined by the stratigraphical range of M. intermedia, which is considered to be a characteristic form for the middle-upper Burdigalian (Cahuzac & Poignant, 1997). 1) Indeterminate Zone II: In view of the fact that we could not find any index microfossils in this zone, we here refer to it as indeterminate zone. As to its stratigraphical position, we prefer an early Langhian date for this zone.2) Orbulina suturalis Interval Zone: Planktonic foraminifera are frequent to dominant in the upper part of the Sayl Cheshmeh section. Based on their vertical distribution, a single biozone has been recognized. This is defined by the FO of O. suturalis (Brönnimann, 1951) and ends right below the conglomerate/sandstone levels of Pliocene age

Depositional model:

Based on the field observations, petrographic studies and textural characteristics as well as the abundance and distribution of foraminiferal fauna and other components, 7 carbonate microfacies have been identified. These carbonate microfacies were deposited in4 facies belts including lagoon, margin facies, upper slope facies and lower slope facies (Fig. 2). Fig. 2. Depositional model for the platform carbonate of the Miocene deposits in the Harsin area, High Zagros Zone The stratigraphical position and vertical and lateral dispersion of different facies along with textural features and skeletal composition, and the presence of coral reef reefs and sudden change of facies and the absence of large tidal zones of Miocene deposars in Harsin area indicate that this sequence deposited on a rimmed carbonate platform.

The Sarvak Formation was deposited on shallow-marine carbonate platforms under the controls of tectonic and eustatic changes during the Upper Cretaceous in the Zagros area. It forms on of the most important reservoir intervals in SW Iran. Complex depositional setting and diagenesis history have resulted in a heterogeneous carbonate reservoir. This study, integrates the results of petrographic (facies and diagenesis) studies with petrophysical and reservoir data (core porosity-permeability and wireline logs) to evaluate the controls of depositional and diagenetic processes on the distribution of reservoir quality in the Sarvak Formation. Ten hydraulic flow units are determined using the FZI concept. Twelve reservoir and non-reservoir (baffle and barrier) units are identified using the Lorenz approach. Finally, dominant depositional facies and diagenetic alterations are evaluated in each HFU and reservoir zone. Results of this study showed that meteorically-dissolved rudist-dominated facies and high-energy facies of shoal complexes formed the best reservoir units in the Sarvak Formation. In sequence stratigraphic point of view, these zones are located in the RSTs of third-order sequences, beneath the disconformity (paleoexposure) surfaces. In contrast, the compacted and cemented mud-dominated facies concentrated in the TSTs and around the maximum flooding surfaces (MFS) formed the non-reservoir units of the Sarvak Formation.

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.

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.

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 Kopet-Dagh sedimentary Basin that crops out from NE Iran to Turkmenistan was formed as an intracontinental Basin due to the southeastern extension of the South Caspian Basin by Neotethyan back-arc rifting after the closure of the Palaeotethys and the early Cimmerian Orogeny (middle Triassic). A thick sedimentary package (10 kilometers) consisting of five transgressive- regressive super-sequences from Jurassic to Miocene time is deposited in the Eastern part of the sedimentary basin that is mainly controlled by NW-SW running major faults. The Cretaceous sequence in the Kopet-Dagh Basin is divided into nine formations, mainly composed of sandstones, conglomerates, mudstones, limestones, and dolomites with minor amounts of evaporates (Afshar-Harb, 1979). The regional trend of the Kopet-Dagh sedimentary basin was northwest-southeast during the Cretaceous. After the deposition of thick, red siliciclastic sediments of the fluvial system during the Early Cretaceous, a suitable condition for the deposition of carbonate sediments (named as Tirgan Formation) was provided as a result of major marine transgression during the Barremian-Aptian stages. The Tirgan Formation is one of the most widespread Upper Cretaceous formations in the eastern Kopet-Dagh that unconformably overlies the fluvial sediments of the Shurijeh Formation and is overlain by a sharp contact of the Sarcheshmeh Formation.

This study is focused on two stratigraphic sections in the Eastern Kopet-Dagh in northern Iran. Ninety thin sections were examined to identify fine-scale physical characteristics (mineralogical composition and fossil contents). Lithology, grain size, and sedimentary structures were recorded.

Based on sedimentological features, sixteen facies are recognized that grouped within five facies associations consist of deep and shallow open marine (FA), shoal (FB), lagoon (FC), and Tidal flat (FD). Deep open marine facies include green-gray fissile (sandy-silty) shale and shallow open marine facies are mainly consist of bioclastic wackestone, ooid/peloid bioclastic floatstone, sandy intraclastic floatstone, sandy intraclastic bioclastic float-rudstone, and sandy peloid bioclastic grainstone. The main constituents in this association are brachiopods, bryozoans, echinoderms, oysters, orbitolinids, intraclasts, ooids, and peloids. Micrite envelopes and borings are the common features in this association. The skeletal elements display high fragmentation, preferentially horizontal orientation, and fining up-ward fabrics. Green-gray fissile shale is deposited in a low energy depositional setting below weather wave base (SWWB), periodically affected by storm waves, suggested by the presence of the siliciclastic grains. The skeletal elements of the shallow open marine facies offer a shallow full open marine setting between SWWB and fair-weather wave base (FWWB) (Bovar-Arnal et al., 2009). High fragmentation, preferentially horizontal orientation, and fining upward skeletal elements suggest the storm-generated shell concentrations. Low energy periods of the sedimentary environment (post- and pre-storm phase) are indicated by micrite envelopes and borings. Shoal association consists of ooid grainstone and sandy ooid grainstone facies with predominantly well-sorted fabric. The main sedimentary structures in this association are sigmoidal cross-beds, wave ripples, cross lamination, and planar cross-beds with the erosional surface. These sediments are deposited in medium-high energy shoal settings above FWWB in the inner ramp environment suggested by well sorting of the elements and predominantly grainstone facies (Bachmann & Hirsch, 2006; Brandano et al., 2012). The sedimentary structures clearly show that tidal currents controlled the association's deposition in a sandy shoal environment. Lagoon association includes sandy mudstone, bioclastic wack-packstone, sandy ooid wackestone, sandy peloid packstone, intraclast, ooid float-rudstone, ooid/peloid pack-grainstone, ooidal bioclastic float-rudstone with main ooids, peloids, benthic foraminifers, echinoderms, and minor content of green algae, bivalves, brachiopods as well as siliciclastic grains that are commonly floated in the micritic matrix. These sediments are mainly deposited in a semi-restricted to restricted (sandy mudstone) lagoon setting above FWWB. The periodical water circulation suggested by the mixture of the open marine (echinoderm, brachiopods) to more restricted and brackish water elements (ostracodes, benthic forams), floated within the micritic matrix (Colombie & Strasser, 2005; Bachmann & Hirsch, 2006; Bovar-Arnal et al., 2009). The tidal flat association mainly consists of peloids, benthic foraminifers, and ostracods surrounded by flat microbial laminations. The flat geometry of the microbial lamination and the presence of the peloids and benthic foraminifers as the main elements in this association demonstrate a flat substrate in a tidal flat setting of the most internal part of the carbonate platform.

In a general view, petrography and field observations, facies associations relationship, and vertical trend of the studied successions suggest Tirgan sediments in the Kopet-Dagh basin are deposited in shallow to the deep marine environment with tidal flat, lagoon, shoal, and shallow to deep marine facies zones. These sediments were deposited in a homoclinal ramp characterized by gradationally vertical changes in the facies associations and abundant storm deposits. This carbonate system was influenced by storm (shallow marine zone) and tidal (shoal zone) currents suggested by the storm-generated shell concentrations, wave ripples, cross laminations, and sigmoidal cross-beds.

The Late Jurassic Arab Formation is one of the main oil reservoirs in the Middle East. To investigate factors reservoir quality controlling, the integration of the results from geological and petrophysical data was utilized. Ten main facies were recognized and grouped in five facies belts of tidal flat, intertidal, lagoon, shoal, and shallow open marine, indicating deposition of the formation on a homoclinal carbonate ramp platform. The diagenetic processes occurred in marine, meteoric, and burial diagenetic realms. According to the frequency within the reservoir, five main pore types comprising intercrystalline, interparticle, vuggy, moldic, and microporosity were determined. Four third-order depositional sequences which are correlatable with four reservoir zones (A–D) of the Arab Formation were identified. The development of grainstone facies played an important role in high reservoir potential intervals. In view of their controls on reservoir quality, diagenetic features can be categorized into two classes: (1) diagenetic processes enhancing reservoir quality that include dissolution, dolomitization, and fracturing; (2) diagenetic processes reducing reservoir quality including cementation, evaporate mineralization, overdolomitization, and compaction. Considering its layer cake nature, it is possible to use petrophysical logs for the correlation of different reservoir zones, and depositional sequences between the studied wells.

The outcrops of the Sarvak Formation of the Khartu and Rashtalu anticline in southeastern Zagros have been studied of biostratigraphy, paleoenvironment and sequence stratigraphy. Six biozones were identified in Sarvask Formation in studied area (Middle Albian to Upper Cenomanian). Based on field observations, three stratigraphic units can be distinguished in both sections. Five facies were identified in ten microfacies in four facies belts. Carbonate sequence of the Sarvak Formation in the sections in a ramp (inner, middle and outer ramp) that includes lagoon, barrier, front barrier and open marine belts. Tectonic processes and the location of the sedimentary basin and the rate of entry from outside the basin on the ramp have been affected. Three third-order sequences have been identified, which have decreased to the upper basin depth. So that the diversity of habitats in the environment of Sarvak Formation was higher in Rashtalu section, while the fossil diversity in Khartu section was less.

The Sarvak Formation at the age of Late Albian-Middle Turonian is the most important carbonate reservoir rock in Abadan plain area in the southwest of Iran. The carbonate rocks of this formation have different and complex reservoir properties due to their tolerance to different diagenetic conditions and environments. This formation in the Darquain oil field mainly consists of white to cream limestone with thin interbedded of cream-colored argillaceous limestone and shale. The purpose of this study is to identify facies, interpret the sedimentary environment, identification of diagenetic processes, and their effect on the quality of the Sarvak reservoir in the Darquain oil field. For this reason, about 600 thin microscopic sections belonging to cores of wells No. 32 and 33 of this field were studied. Widespread laboratory studies show that the Sarvak Formation consists of 9 facies associated with a homoclinal carbonate ramp platform. The most important diagenetic processes in the Sarvak Formation are cementation, dolomitization, dissolution, mechanical and chemical compaction, micritization, and fracturing, which all occurred in marine, meteoric, and burial diagenetic environments. The porosity of the Sarvak Formation in the Darquain oil field is about 10% to 15% and the permeability is variable between 0.1 to 100 milliDarcy. Based on the available evidence, the reservoir quality of this formation is generally good.

In order to determination of biozones, facies types and sedimentary model, the Posht Darband stratigraphic section of the Qom Formation with a thickness of 330 meters located in the northwest of Hamedan, structural zone of the Sanandaj- Sirjan, has been considered. On the basis of field observations, Qom Formation is composed of medium to thick-bedded limestone (Member a) and alternation of sandy limestone, sandstone and green marl (Member b). According to paleontological study, seventeen genera and nine species of benthic foraminifera and other skeletal components are introduced from the Posht Darband section and consequently, Lepidocyclina - Operculina - Ditrupa Assemblage zone has been recognized in the Qom Formation. Facies analysis (Variety in fauna features, fabrics, and sedimentary textures) has produced eight microfacies related to the four facies belts of tidal flat, reef, slope and open marine. Base on abundance in reef facies deposits including coral boundstone, algae and bryozoan, an open shelf is proposed for the Qom Formation. The vertical distribution column of the facies types (without considering the possible erosion phenomenon) suggests that the facies changes in member "a" are gradual, but in member "b" they were rapidly, with facies retrogradation and progradation.

Chelken Formation (Lower and Middle Pliocene) which represents a siliciclastic nature in Javarom Section (south of the Ghaemshahr city) was studied. This formation comprises three sets of conglomerate, sandstone and mudstone, which are usually arranged in fining upward sequences. According to the nature of fining upward sedimentary sequences, sedimentological characteristics and structural features, it is proposed that the Chelken Formation was deposited in a fluvial environment. Conglomeratic facies are mainly clast-supported, sandstone facies are represented by quartz arenite and lithic arenites and mudstone facies are carbonate-clastic in nature. According to the paleo-currents analyses, a north and northeastward direction is proposed for the paleocurrents deposition of  this formation.

The Ilam Formation (Coniacian? –Santonian), is among the most important oil reservoirs of the Abadan Plain, SW Iran. Despite its reservoir significance, there is no comprehensive knowledge about the geological characteristics and factors controlling reservoir quality. In this study, the Ilam Formation is investigated using detailed core description, thin section study, and conventional petrophysical well log data to explain facies characteristics, sedimentary environment, and presenting the sequence stratigraphic framework. Accordingly, a total of 280 m of cores in four key wells from three oil fields as well as 620 thin sections were described and studied. The results of facies analysis lead to the recognition of 12 microfacies grouped in four facies belts including lagoon, shoal, shallow and deep open marine and two siliciclastic petrofacies (shales) related to brackish water and shallow lagoonal environment, which deposited in a carbonate ramp. Frequency analyses of facies associations and petrophysical well log signature indicate that the sedimentary basin was deepening to the east. Based on the identified sequence boundaries and maximum flooding surfaces, one third-order sequence in the studied interval was recognized and correlated by using the petrophysical well log data in all studied wells. The maximum flooding surfaces are discriminated by the development of deep-marine facies and also high gamma-ray responses on the well logs.

The Kazhdumi Formation is a Middle Cretaceous whose base in the Abadan plain is composed of sandstone, shale and limestone, and is equivalent to the Burgan Formation in Arab countries. In this study, we investigated the reservoir quality of one of the major oilfields of the Abadan plain using thin sections, core data such as hydrocarbon impregnation, porosity, permeability, and well logs. According to petrographic studies, 4 sedimentary microfacies and 5 lithofacies have been identified in the Burgan Formation deposited in the carbonate ramp to the Delta. Diagenesis processes include dissolution, fracture, cementation, dolomitization, condensation, glaconite, hematite and pyrite occurring in three marine, meteoric and burial environments. Among the diagenesis processes, dissolution and fracture have had a special role in enhancing reservoir quality, and cementation, dolomitization and compaction have been the most important determinants of reservoir quality studied. Core studies and wellbore diagrams show that the sandstone and carbonate facies have the highest and the lowest amount of porosity, permeability and hydrocarbon impregnation, respectively, and the Chilean facies is in terms of reservoir quality between these two facies. Quartz Arenite rock facies was identified as the main reservoir zone in the studied oil field.

The Permian deposits (Doroud Formation) are exposed in a wide area of central Alborz. A stratigraphic section of Permian deposits in the Eram section (South Neka) has been selected for the study of facies, depositional environments, sequence stratigraphy, and diagenetic processes. The 320 m thick Doroud Formation in the study area mainly consists of intercalation of limestones and sandstones. Field and petrographic studies of thin sections led to identifying four siliciclastic petrofacies and three carbonate microfacies. These facies are deposited in four facies belts, including fluvial, coastal, lagoon, and shoal. The low diversity of facies and the gradual change of facies belts, the absence of turbidites, and the absence of large barrier reef indicate that the Permian deposits in the study area were deposited on a carbonate ramp. Also, based on the absence of turbidite deposits of a deep marine environment, it can be deduced that the depositional environment of the Doroud Formation is homoclinal. Two third-order depositional sequences have been identified in the studied interval of the Doroud Formation. Different diagenetic processes have been affected on the studied interval in the study area, most notably dolomitization, cementation, mechanical and chemical compaction, pyritization, fracturing, and neomorphism.