Sedimentology
Afshin Karimkhani-Bahador; Sadat Feiznia; Mohsen Aleali; Mehran Arian
Abstract
To prepare sedimentological data, 98 surface sampling stations have been designed from the seabed in the continental shelf in the southern part of the Caspian Sea and along the coast of Iran. Indicators such as the type and amount of sediment load transported to the sedimentation environment, the energy ...
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To prepare sedimentological data, 98 surface sampling stations have been designed from the seabed in the continental shelf in the southern part of the Caspian Sea and along the coast of Iran. Indicators such as the type and amount of sediment load transported to the sedimentation environment, the energy of waves and sea currents, as well as how the slope of the seabed changes, play a role in the production and diversity of the sedimentary facies. 9 sedimentary facies are the most abundant in the surface deposits of this area and on average, in the sediments of the continental shelf, there are 1% by weight of coarse-grained particles, 25% by weight of medium-grained particles and 74% by weight of fine-grained particles. The composition of sedimentary facies in this area is controlled by indicators such as the size of sedimentary particles, the amount of sedimentary load carried to the environment, the energy of waves and sea currents, and how the slope of the seabed changes. In the marine environment of the study area, sub-sedimentary environments, Backshore, Foreshore, Shoreface, Offshore transition zone and offshore can be identified. The two facies of slightly gravelly Mud and Mud are more abundant than other facies.
Enayatallah Haghfarshi; Peyman Rezaee; Seyed Reza Moosavi Harami; Mohammad Faridi
Abstract
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 ...
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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.
Stratigraphy and Palaeontology
Mahnaz Parvaneh Nejad Shirazi; M. Seddighi; P. Balicheh khorram abadi
Abstract
This study deals with lithostratigraphy, biostratigraphy, microfacies analysis, and depositional setting of the Jahrum Formation in Chellehgah Sepidan section, NW Shiraz. Vertical changes in lithological characteristics led to recognition of 15 lithotypes. The Jahrum Formation, in this area, rests conformably ...
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This study deals with lithostratigraphy, biostratigraphy, microfacies analysis, and depositional setting of the Jahrum Formation in Chellehgah Sepidan section, NW Shiraz. Vertical changes in lithological characteristics led to recognition of 15 lithotypes. The Jahrum Formation, in this area, rests conformably (with a gradational boundary) on the Pabdeh Formation and is overlain unconformably by the Asmari Formation. Micropaleontological analyses based on benthic foraminifera (Nummulites striatus, N. cf. fabianii, N. gr. bullatus-garganicus, Spiroclypeus sp.) suggest a middle-upper Eocene age for the formation. Facies analyses allowed to recognize the 6 facies (including 12 microfacies) for the examined strata. The results also suggest that the Jahrum Formation deposited in a homoclinal ramp.
Sedimentology
Umid Kakemem; Mohammad Adabi; Ehsan Dehyadegari
Abstract
Depositional texture, sedimentary structure and present fauna led to characterize twelve carbonate- evaporate facies. These facies were classified in three facies belts including tidal flat, lagoon and shoal. Developpment of tidal zones together with evaporate deposits and thrombolite facies (signs to ...
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Depositional texture, sedimentary structure and present fauna led to characterize twelve carbonate- evaporate facies. These facies were classified in three facies belts including tidal flat, lagoon and shoal. Developpment of tidal zones together with evaporate deposits and thrombolite facies (signs to a shallow depositional environment), the absence of continuous reef‐frame builders, high production of carbonate mud, absents of calciturbidite, tempestites deposits and slump structures are evidences for a homoclinal carbonate ramp setting. The facies based on petrophysical characteristics which is the results of depositional texture and diagenesis are classified in seven reservoir rock types. In which, the first rock type (RT1) has weak reservoir property and toward RT7 reservoir quality will increase. Facies variation related to sea level fluctuations led to subdivide the whole strata into two 3rd order sequences. Facies stacking patterns in the sequences characterized by subtidal facies (lagoon and shoal) tend to have the most reservoir quality that covered by evaporative (Mf1) and peritidal facies (Mf2 to Mf4) with low-reservoir quality. The most reservoir quality in both K1 and K2 reservoir zones is coincident with late TST, maximum flooding surface (mfs) and late HST in identified depositional sequences which is settled in high-energy shoal facies intervals.
Sedimentology
Yazdan Golestan; Umid Kakemem; Mohammad Adabi; E. Dehyadegari
Abstract
Carbonate-evaporate succession with siliciclastic sediments and mixed siliciclastic carbonate deposits of Asmari-Pabdeh reservoir in Karanj Oil Field with Oligo-Miocene in age was studied to determine diagenesis, microfacies and original carbonate mineralogy. Micritization, dissolution, compaction, neomorphism, ...
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Carbonate-evaporate succession with siliciclastic sediments and mixed siliciclastic carbonate deposits of Asmari-Pabdeh reservoir in Karanj Oil Field with Oligo-Miocene in age was studied to determine diagenesis, microfacies and original carbonate mineralogy. Micritization, dissolution, compaction, neomorphism, cementation and dolomitization are the main diagenesis processes that effect Asmari-Pabdeh successions. Petrographic studies led to identification of three types of dolomite such as dolomicrite, dolomicrosparite and dolosparite, in which dolomicrosparite and particulary dolospatite caused increase in reservoir quality. Eleven carbonate-evaporate microfacies were identified. These deposited in four major environments comprises of tidal flat, lagoon, carbonate shoal and open marine. Sedimentary environment of the Asmari Formation recognized as a homoclinal ramp. Diagenetic studies reveal impact of marine, meteoric and burial diagenesis on the deposits. Geochemistry of minor and major elements reveal original aragonite mineralogy for carbonates of the Asmari Formation. The high Sr/Mn and Sr/Ca and minor amounts of manganese implying close diagenetic system with low Water/Rock interaction for the Asmari Formation succession.
H. Hoseini; N. Kohansal Ghadimvad; M. Zamani Pedram; M. R. Majidifard; A. R. Shahidi
Abstract
Accumulation of Shemshak group lithofacies have been started during Early-Cimmerian orogeny from middle of Late-Triassic and ended with Middle- Cimmerian discontinuity dating Millde-Jurrasic. So the mostly Siliciclastic and occasionally Marin lithostratigraphic unite has evidences of two major tectonic ...
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Accumulation of Shemshak group lithofacies have been started during Early-Cimmerian orogeny from middle of Late-Triassic and ended with Middle- Cimmerian discontinuity dating Millde-Jurrasic. So the mostly Siliciclastic and occasionally Marin lithostratigraphic unite has evidences of two major tectonic events as orogenic activity at lower and upper border of sequence. Therefor the lower contact of Shemshak group is composed of Middle-Triassic platform carbonates known as Elika formation which distinguished with Plaeokarsts including bauxit and laterit horizons and the upper contact with parallel unconformity with Delichay formation fossiliferous marls and carbonates of Bajocian stage (Middle Jurrasic). Results of deposition environment and facies studies have shown that the mentioned siliciclastic group (Shemshak) composed of three major facies, 22 subfacies and have been deposited in three different environments including Fluvial (Terrestrial), mid-tidal and shallow marine environments. The vertical changes of facies have declared that the sequence has formed due to erosion of Early-Cimmerian uplands and have experienced progess of shallow marine. The existing shallow marine sediments in the end of Shemshak group states that, in comparison with surrounding area , clastic sediments of end of Shemshak cycle, because of erosional cycles of Middle-Cimmerian orogeny, befor deposition of Delichay marine formation, have been eroded.
Sedimentology
Afshin Zohdi
Abstract
In this study, for the first time stratigraphy and depositional history of the Routeh Formation have been evaluated in west of Zanjan (Agh-Bolagh section). These deposits with thickness of 102m consist of limestone, dolomitic limestone with the less frequency of thin-bedded calcareous shales. This sedimentary ...
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In this study, for the first time stratigraphy and depositional history of the Routeh Formation have been evaluated in west of Zanjan (Agh-Bolagh section). These deposits with thickness of 102m consist of limestone, dolomitic limestone with the less frequency of thin-bedded calcareous shales. This sedimentary sequence with an unconformity overlies the quartz-bearing sandstones of Doroud Formation and is overlain by a laterite-bauxite horizon below the vermiculate-bearing limestone of Elika Formation. The main components of Routeh Formation contain different kinds of algae, small benthic foraminifera and with a less frequency echinoderm and brachiopod debris. Based on filed and laboratory studied eight sedimentary facies have been distinguished into the Routeh Formation. These facies due to the different types of allochems, texture and fossil content display a shallow-water marine environment during deposition of the Routeh Formation located at Palaeotethys passive southern margin. The absence of re-sedimented deposits like: turbidites, presence of micrite at the most of facies, lack of continues reefal facies and gradual facies change indicate that the Routeh Formation possibly were deposited in a ramp carbonate platform. Due to great diversity and abundance of algae and benthic foraminifera, this carbonate ramp is referred to as an “algae and foram-dominated carbonate ramp system”. Field observations, facies analyses and sequence stratigraphy studied led to the identification of one-third order depositional sequence into the Routeh Formation. This depositional sequence separated by type-1 sequence boundaries at below with quartz-bearing sandstones of Doroud Formation and at the top with laterite-bauxite horizon between Routeh and Elika formations
Z. Alishavandi; H. Rahimpour-Bonab; A. Kadkhodaei; M. Arian
Abstract
The Sarvak Formation deposited in the North to Northeastern margin of the Arabian Platform during the Mid-Cretaceous (Albian-Turonian), and is extensively encountered in the Folded Zagros of southwestern Iran. It is the most important reservoir unit after Asmari Formation in Iran. Petrography of microscopic ...
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The Sarvak Formation deposited in the North to Northeastern margin of the Arabian Platform during the Mid-Cretaceous (Albian-Turonian), and is extensively encountered in the Folded Zagros of southwestern Iran. It is the most important reservoir unit after Asmari Formation in Iran. Petrography of microscopic thin sections in studied wells led to determination of nine microfacies that deposited in 3 sub-environments; restricted lagoon, lagoon-open marine and shoal in an interior part of carbonate ramp. Petrographic studies revealed that since deposition, the Sarvak Formation experienced several diagenetic realms including marine, meteoric, burial and telogenetic diagenetic environments. Location of the studied wells shows that the relative depth of the Sarvak Formation ramp decreases from the east to the west. Also, the results show that the Sarvak reservoir quality affected by various diagenetic processes such as micritization, dissolution, dolomitization, cementation, stilolitization and fracturing. These diagenetic successions are mainly restricted to the upper and lower parts of the Cenomanian-Turonian disconformity. Meteoric water infiltration below this disconform boundary and related karstification led to development of moldic and vuggy porosity a long with reservoir quality increase. Based on the sequence stratigraphic study, three third-order sequences were recognized in the middle Cenomanian to middle Turonian part of the formation. The results of this research show that the reservoir quality distribution in this unit is primarily controlled by depositional facies so that the rudist microfacies (grainstone, floatstones and rudstones) have the best primary reservoir qualities though, it has also been drastically improved by dissolution in paleoexposure surface
R Farokhnejad; B Esfandiari; A Motamed
Abstract
In this paper the Fajan Formation of Paleocene age with a thickness of 172.5 meters is studied in northwest Shahroud (Eastern Alborz). Main lithology of this formation, at the studied section, consists of conglomerate and sandstone. The formation disconforably overlain upper Cretaceous limestones ...
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In this paper the Fajan Formation of Paleocene age with a thickness of 172.5 meters is studied in northwest Shahroud (Eastern Alborz). Main lithology of this formation, at the studied section, consists of conglomerate and sandstone. The formation disconforably overlain upper Cretaceous limestones and its upper boundry with Ziarat limestone of Eocene age is of transitional type. Dominant lithology of mentioned formation, at the studied section, consists of polymodal and polymictic orthoconglomerate which contains rounded to subrounded grains. These clastic grains are generally oval to spherical in shape and originated from limestone, sandstone and chert materials. Paleocene Conglomerate is characterized by two distinc lithofacies: clast-supported massive gravel (Gcm) and clast-supported horizontally stratified gravel (Gh) which are formed in a braided river system. This subject is interpreted by evidances as condensed texture gravels, imbrication fabric that indicate on one hand paleocurrent, non-existence of fossil by reason of oxidation conditions of sedimentary environment, sandstone lenses that have through cross bedding (St) and existence of gravels that are mostly rounded to subrounded and denote distance from origin. Abundant bed load mostly rang in size from pebble to cobble and partially boulder, gravelly beds with long extended lateral spread and lack of flood plain muddy sediments, are reasons in distinguish between recognized sedimentary environment and meandering river. The studied Sandstone layers are described by ripple marked sand (Sr) and planar-cross-bedded sand (Sp) which contain sublitharenite and quartzarenite type are deposited in tide-dominated deltaic system.Interpretation criteria are propounded by means of interference ripple mark that prove direction change of current bearing clastic particles, rounded to subrounded sands that can present repeated reworking of grains after deposition in sedimentary environment, well sorting, high textural maturity, insignificant matrix as criterion in distinction specified delta from other deltaic environments and herringbone cross bedding which is the most important evidence of tidal currents.
R. Haftlang; M. Afghah; S. A. Aghanabati; M. Parvaneh Nezhad Shirazi
Abstract
Lithological and biological Sequences of Cretaceous in Bahar section, Located in South Esfahan (147 m. true thickness) include grayish olive green pencil- like shales containing Budantysras Ammonites (Albian) interbedded with limy shales. which are covered by glauconitic Sandy Limestone (Early Turonian) ...
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Lithological and biological Sequences of Cretaceous in Bahar section, Located in South Esfahan (147 m. true thickness) include grayish olive green pencil- like shales containing Budantysras Ammonites (Albian) interbedded with limy shales. which are covered by glauconitic Sandy Limestone (Early Turonian) (with erosional discontinuity). These sandy limestones are wackestone and rarely greenstone, according to Dunham classification. Based on Biozone divisions, this unit is related to Biozone No. 27 presented by Wynd (1965) and it is equivalent to Sarvak Formation in Zagros. Marly limestone and limestone containing Inoceramus bivalve interbedded with marl dating back to Late, Middle Touronian- Late Touronian- Coniacian to Early Santonian are younger equivalents of this section which can be equaled to Surgah Formation. According to Biozone divisions, this unit is equivalent to Biozone No. 28 presented by Wynd (1965) and also based on Dunham classification, the unit is packestone and partly boundstone. The lower Contact of the unit is Concordant and Continuous with glauconitic sandy limestone and its upper Contact is Continuous and Concordant with marl and interbeddings of Limestones dating back to Santonian- Campanian. By comparing Bahar Section with South eastern Lorestan section (Poshte jangal anticline), (Azadbakht, 2015), the following results were obtained: From Litho/bio stratigraphical view, thick to thin-bedded Limestones (Light to dark gray) interbedded with marl in Poshte jangal anticline are Correlated with Inoceramus limestone and marly Limestone interbedded with marl in Bahar Section. They are dated back to EarlyTuronian to Early Campanian.Due to Strong similarity of Lithostratigraphy and biostratigraphy between Bahar section located in Southern Esfahan (Central Iran) and section of Poshte jangal anticline located in Southeast of Lorestan, it can be deducted that a branch of Lorestan Sea has advanced in Turonian- Coniacian times and some parts of Southern Esfahan has been covered by the sea.
N Shahverdi; H Rahimpour- Bonab; M.R Kamali; B Esrafili- Dizagi
Abstract
The Albian-TuronianSarvak Formation is one of the main oil reservoirs in south and southwest Iran that hosts significant amount of hydrocarbon resources in this region. Facies analysis in seven oil fields of Persian Gulf led to identification of 7 microfaceis that are deposited in four facies belts in ...
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The Albian-TuronianSarvak Formation is one of the main oil reservoirs in south and southwest Iran that hosts significant amount of hydrocarbon resources in this region. Facies analysis in seven oil fields of Persian Gulf led to identification of 7 microfaceis that are deposited in four facies belts in a homoclinal ramp platform. Studies show that there is major facies variation in Sarvak carbonates of offshore Zagros. The rudist-bearing facies are mainly developed as major reservoir facies in the eastern Persian Gulf (Siri Fields) and replaced with mud-dominated lagoonalfacies in central and western sectors of considered area (Hendijan, Bahregansar, Balal and Lavan Fields). There are positive correlation between paleogeographic position of rudist buildups and configuration of Sarvak reservoir in the Persian Gulf. Main diagenetic processes that effected facies of this formation are neomorphism, bioturbation, micritization, dolomitization, dissolution, cementation, stylolitization and fracturing. During diagenesis, rudist-dominated facies are selectively dissolved and led to development porosity and reservoir quality in the Siri Fields. Generally, diagenesis is slightly impacted reservoir properties in the central and western parts oil fields, although, dolomitization is improved reservoir characteristics in the Bahregansar Field. Petrophysical evolution of studied intervals suggests that good reservoir intervals are associated with rudist-bearing facies. As well, there are decreasing trend in both porosity and permeability values from top of formation downwards, particularly in Siri fields. This trend is attributed to effect of meteoric diagenetic under the Turonian unconformity. In conclusion, our studies indicate that occurrence and evolution of rudists had main impact on diagenetic modification and reservoir potential of Sarvak Formation.
N Kohansal-Ghadimvand; Sh Gholipouri; P Ghazanfari; R Mahari
Abstract
The aim of this study is to determine microfacies and diagenetic processes of the Mobarak Formation with the age of early Carboniferous in Valiabad section, at Karaj-Chalus road. The thickness of the formation at this section is 339 m and consists of limestone with intercalations of shale and marl. ...
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The aim of this study is to determine microfacies and diagenetic processes of the Mobarak Formation with the age of early Carboniferous in Valiabad section, at Karaj-Chalus road. The thickness of the formation at this section is 339 m and consists of limestone with intercalations of shale and marl. According to lithological characteristics, the MobarakFormationis subdivided into 8 rock units and is disconformably overlain by the Lalun Formation and underlain by Dozdeband Formation. Thirteen microfacies have been recognized on the basis of depositional texture and petrographic analysis. These carbonate facies belong to four major sub- environments including beach/tidal flat, lagoon, barrier/sand shoal and open marine. The formation deposited in a homoclinal carbonate ramp.
A Abdi; M.H Mahmudy Gharaie; M Kariminia; A Karimi Bavandpur; M Mohajjel
Abstract
In Kermanshah Radiolarites, Jurassic to late Cretaceous in age, three sedimentary facies including tempestite, pelagic mudstone, and radiolarian wackestone-packstone were identified. Each of these sedimentary facies accompanies by ichnofacies, which reveal the depth and energy of the environment. In ...
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In Kermanshah Radiolarites, Jurassic to late Cretaceous in age, three sedimentary facies including tempestite, pelagic mudstone, and radiolarian wackestone-packstone were identified. Each of these sedimentary facies accompanies by ichnofacies, which reveal the depth and energy of the environment. In the tempestites (including calclithite bed, flat pebble conglomerate and hummocky cross stratification) the trace fossils with Domichnia such as Thalassinoides can be observed, which indicate the energetic conditions at the time of sedimentation. Trace fossils found in pelagic limestone units have Pascichnia and Fodinichnia. These Trace fossils include Planolites, Chondrites and Helminthopsis, which indicate distal Cruziana ichnofacies and show low energy condition. As a result of increasing of depth in siliceous deposits, the trace fossils with Pascichnia and Chemichnia including Scolicia, Helminthopsis, Gyrochorte and Chondrites, and Thalassinoides become dominant, which are indicative of the transitional zone between the distal Cruziana ichnofacies and the Zoophycos ichnofacies. The sedimentary facies and the present ichnofacies are indicative of the sedimentation of these deposits in the transitional zone between the middle and the outer ramp.
M Karavan; A Mahboubi; H Vaziri-Moghaddam; R Moussavi-Harami
Abstract
The Oligocene Qom Formation deposits in NW Central Iran (NE Delijan) are widespread in NE-SW trend.Four members of the Qom Formation (unknown, a, b& c1) in the study area consist of mainly marly limestone, limestone, sandy limestone and a minor amounts of sandstone. It disconformablyoverliesthe Lower ...
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The Oligocene Qom Formation deposits in NW Central Iran (NE Delijan) are widespread in NE-SW trend.Four members of the Qom Formation (unknown, a, b& c1) in the study area consist of mainly marly limestone, limestone, sandy limestone and a minor amounts of sandstone. It disconformablyoverliesthe Lower Red Formation and the upper boundary is covered by the recent alluvium. Based on the benthic foraminifers assemblage, these deposits are attributed to Oligocene (Rupelian- Chattian). Petrographic considerationled to identification of 12 carbonatemicrofacies and one sandstone facies that may have been deposited in a homoclinal ramp and in 4 sub environments including tidal flat, lagoon, bioclastic bar and open marine. Sequence stratigraphy analysis led to identification of 8 3rdordersdepositional sequences bounded by type I and type II sequence boundaries. Comparison between interpreted relative sea level curve with global sea level curve showsreasonable correlation with the lower and upper sequence boundaries of this formation and also Rupelian- Chattianboundary and the differences in other sequence boundaries can be related to local tectonic activity in the sedimentary basin of Qom Formation and the local sea level changes.
A. M. Ali Khasi; M. Hosseini Barzi; M. Shadan
Abstract
Determination of sedimentary environment, provenance and tectonic setting of Ab-Haji Formation sandstones (Lower Jurassic) have been carried out in Cheshmeh Bakhshi and Sartakht-e-Shotoran sections which are located in Kalmard Block. Facies analysis of sedimentary facies in mentioned sections implies ...
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Determination of sedimentary environment, provenance and tectonic setting of Ab-Haji Formation sandstones (Lower Jurassic) have been carried out in Cheshmeh Bakhshi and Sartakht-e-Shotoran sections which are located in Kalmard Block. Facies analysis of sedimentary facies in mentioned sections implies three clastic faceis associations including delta plain, delta front and prodelta and two carbonate facies, relevant to bar. The obtained results from modal analysis and geochemical data point to cratonic tectonic setting and presence of qurtzose rocks in the source area in the course of recycling processes. Moereover, using the tectonic discrimination diagrams suggest that Ab-Haji sandstones have been deposited in a passive continental margin. The calculated chemical index of alteration (CIA) and the plagioclase index of alteration (PIA), based on major element oxides, denote moderate to intense weathering in the hinterland. This consequence is conformed with the modal analysis and petrographic evidence referring to humid and semi-humid climate.
M. A. Salehi; M. H. Adabi; H. Ghalavand; M. Khatibi-Mehr
Abstract
The Fahliyan Formation with the age of Lower Cretaceous (Berriasian-Hauterivian) were studied for microfacies analysis, diagenesis and original carbonate mineralogy in the type section at Fahliyan Anticline and subsurface section in well number 55 of Gachsaran Oil Field. Petrographic studies led to the ...
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The Fahliyan Formation with the age of Lower Cretaceous (Berriasian-Hauterivian) were studied for microfacies analysis, diagenesis and original carbonate mineralogy in the type section at Fahliyan Anticline and subsurface section in well number 55 of Gachsaran Oil Field. Petrographic studies led to the recognition of 10 microfacies that were deposited in four facies belts: tidal flat, lagoon, shoal and open marine. The observed facies patterns indicated a carbonate rimmed-shelf depositional environment. Recognition of different type of cements shows that the Fahliyan Formation has mostly undergone meteroric diagenesis. Major and minor elements and carbon and oxygen isotope values indicate that aragonite was the original carbonate mineralogy in the Fahliyan Formation, and suggests that alteration occurred in a closed diagenetic system, with low water/rock interaction.
M. H. Adabi; M. Khatibi Mehr; A. Moallemi; A. Sadeghi; M. A. Salehi
Abstract
The Ziyarat Formation is an Upper Paleocene to Middle Eocene carbonate sequences, located in North of Tochal Village (south-east of Tehran), near Emam Zadeh Abdollah. The Ziyarat Formation with the total thickness of 212.5 m conformably overlies the Fajan conglomerate and is overlain by greenish tufaceous ...
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The Ziyarat Formation is an Upper Paleocene to Middle Eocene carbonate sequences, located in North of Tochal Village (south-east of Tehran), near Emam Zadeh Abdollah. The Ziyarat Formation with the total thickness of 212.5 m conformably overlies the Fajan conglomerate and is overlain by greenish tufaceous siltstone of the Karj Formation. Petrographic studies led to the recognition of 11 microfacies. Different facies and evidences such as the absence of reefal facies, calciturbidite deposits, and widespread tidal flat deposits indicate that the Ziyarat Formation was deposited in a homoclinal carbonate ramp environment. Micritization, cementation, compaction, neomorphism, dissolution, dolomitization, fracturing and silicification are the major diagenetic processes in the Ziyarat Formation, occurring in meteoric and burial diagenetic environments. Major and minor elements and oxygen and carbon isotope values indicate that Ziyarat carbonates were deposited in a shallow warm water tropical environment and original carbonate mineralogy was aragonite. Bivariate plots of Mn versus Sr/Ca and δ18O illustrate that Ziyarat limestones were affected by open system diagenesis with high water/rock interaction. Early burial diagenetic temperature calculation based on heaviest oxygen isotope values of micrite and δw of Eocene seawater of 0.85 SMOW, shows that temperature was around 39˚C. Cathodluminescence studies of carbonate cements illustrated dull luminescence, because these carbonates afftected by both meteoric and burial diagenesis, and thus typical yellow to orange luminescence and zonations, evidence of meteoric diagenesis, are absent. This statement is confirmed by isotropic evidences.
