Geological Environment and Engineering
Shirin Samani; Ali Uromeihy; Amirhossein Enayati; Imandokht Mostafavi; Misha Pezeshki
Abstract
Diagenetic processes in carbonate rocks can be considered as one of the most important factors influencing the inherent characteristics of this type of reservoir on a small as well as large scale. Considering the importance of knowing the mechanical characteristics of reservoir rocks in geomechanical ...
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Diagenetic processes in carbonate rocks can be considered as one of the most important factors influencing the inherent characteristics of this type of reservoir on a small as well as large scale. Considering the importance of knowing the mechanical characteristics of reservoir rocks in geomechanical modeling and its application in the exploitation and development of hydrocarbon fields, it is necessary to find out how lithological characteristics affect its rock mechanical behavior. In this study, the impact of two diagenetic processes (Dolomitization and Anhydrite cement) on the physical and mechanical characteristics (such as Uniaxial Compressive Strength, Young’s modulus, Cohesion, and Internal friction angle) of carbonate reservoirs of the Kangan Formation, are addressed. The evaluations have been done in two phases: i.e., lithological studies and rock mechanical tests. The results show that changes in mechanical properties are strongly influenced by diagenetic processes. The two main influential features on mechanical characteristics are dolomitization and anhydrite cementation, which strongly affect porosity, dominant pore type, and mineralogy. The results show that dolomitization in the studied samples has caused an increase in porosity and a decrease in strength and elasticity. While the presence of anhydrite has caused an improvement in the resistance characteristics with an opposite effect.
Stratigraphy and Palaeontology
Ali Asaadi; Ali Imandoust; Mehdi Sarfi; Mehdi Ghane Ezabadi
Abstract
The Lower Cretaceous Fahliyan Formation is one of the main oil reservoirs in the Persian Gulf. In this study, for investigating facies characteristics, depositional environment, diagenetic features, sequence stratigraphy and describing factors controlling reservoir quality, the integration of the results ...
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The Lower Cretaceous Fahliyan Formation is one of the main oil reservoirs in the Persian Gulf. In this study, for investigating facies characteristics, depositional environment, diagenetic features, sequence stratigraphy and describing factors controlling reservoir quality, the integration of the results from core description, petrographic studies, and petrophysical data was utilized. Nine main facies were recognized and grouped in four facies belts of lagoon, shoal, patch reef and shallow open marine, indicating deposition of the formation in a carbonate ramp platform. Various diagenetic processes that influenced facies, occurred in marine, meteoric, and burial diagenetic realms. Four main pore types have been identified in the reservoir that include interparticle, moldic, vuggy, and microporosity. From the sequence stratigraphy point of view, three third-order sequences which are correlatable within the Fahliyan Formation were identified. The development of grainstone and algal rudstone/floatstone in shoal/ patch reef sub-environment played an important role in developing the high reservoir. In view of their controls on reservoir quality and pore system, diagenetic features can be categorized into two classes: (1) diagenetic processes enhancing reservoir quality that include dissolution and fracturing, and (2) diagenetic processes reducing reservoir quality that include cementation and compaction.
Sedimentology
Mohammad Shalalvand; Mohammad Adabi; Afshin Zohdi
Abstract
In this study, the Late Paleocene Taleh Zang Formation in the southwest of Kermanshah hasbeeninvestigatedfor elemental geochemistry and effective diagenetic processes during burial. The thickness of the studied section is 282 meters that mainly composed of shallow marine limestones with interbedded of ...
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In this study, the Late Paleocene Taleh Zang Formation in the southwest of Kermanshah hasbeeninvestigatedfor elemental geochemistry and effective diagenetic processes during burial. The thickness of the studied section is 282 meters that mainly composed of shallow marine limestones with interbedded of marl and dolomite. The main diagenetic processes affecting the TalehZangFormation include micritization, various types of porosity, cementation, dolomitization and compaction. Due to the texture and the abundance of unstable skeletal particles (green algae and bivalve), porosity and cementation aremorecommon among the identified processes. Microscopic and geochemical studies have shown that these processes have taken place in eogenesis and early mesogenesis stages in marine, meteoric and shallow burial environments. Evidences indicate that the carbonates of the TalehZangFormation didnot tolerate deep burial after the deposition during diagenesis. Fluids that affected the lower parts of the formation during burial were mainly marine. Moreover, tothetop ofthe sequence in addition to seawater less meteoric fluids have affected the marine carbonates of the Taleh Zang Formation during diagenesis. The high amounts of Sr/Mn (mean27/51) and Sr/Ca (mean 1/61) and also low Mn (mean 27ppm) and Fe (mean 78ppm) values indicate close digenetic system with low water/rock interaction for the carbonate samples of the TalehZangFormation.
Sedimentology
Elmira Shahkaram; Mohammad Hosein Adabi; Davood Jahani; Seyed Hamid Vaziri
Abstract
The Dalichai Formation is the first rock unit of the Middle Jurassic in the Alborz sedimentary basin that has occurred in a marine environment. The boundary of the Dalichai formation with Shemshak Formation is erosional unconformable while it is concordant with Lar formation. Due to lithological similarity, ...
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The Dalichai Formation is the first rock unit of the Middle Jurassic in the Alborz sedimentary basin that has occurred in a marine environment. The boundary of the Dalichai formation with Shemshak Formation is erosional unconformable while it is concordant with Lar formation. Due to lithological similarity, the boundary of the Dalichai formation with the Lar formation is unclear. It is also very difficult to identify the primary carbonates mineralogy, due to the effects of diagenetic processes solely on the basis of petrographic studies. We studied a section of Sharaf mountain with a thickness of 1420m and 149 samples was studied. The study of the major and minor elements, the Oxygen and Carbon isotopes, and plotting of these values against each other represents that the Dalichai formation have had original aragonite mineralogy, and the nonmarine diagenesis have had the highest impact on them. Plotting the Sr/Ca ratio versus Mn value, shows that these carbonates are affected in a semi-closed to open diagenetic system. Using Sr, Sr/Na, Sr/Ca, Oxygen and Carbon isotopes, the boundary of this formation with the Lar Formation is recognized in thickness of 1200m. The diagenetic environment temperature for this section limestones is 32.9ºC.
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.
Mostafa Moradi; Asadollah Mahboubi; Mohammad Khanehbad; Ali Ghabieshavi
Abstract
The Asmari Formation is the main reservoir rock for the Aghajari oilfieild. It is composed of about 400-meter limestone, dolostone and interlayers of sandstones. Study of 1200 meters drilling cores, 2800 microscopic thin sections, 12 SEM analyses along with 125 routine core tests in 5 cored wells indicate ...
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The Asmari Formation is the main reservoir rock for the Aghajari oilfieild. It is composed of about 400-meter limestone, dolostone and interlayers of sandstones. Study of 1200 meters drilling cores, 2800 microscopic thin sections, 12 SEM analyses along with 125 routine core tests in 5 cored wells indicate that the Asmari Formation was effected by various diagenetic processes such as micritization, compaction, cementation, fracturing, dissolution and dolomitization. Some of these processes (e.g. dissolution, dolomitization and fracturing) have constructive effects on the reservoir quality and created wide variety of porosity types including vuggy, intercrystaline and channel in upper parts of the Asmari Formation. Destructive diagenetic processes (micritization, compaction and cementation) have destroyed pore spaces and make the lower parts of the Asmari (specially zone 5) to a non-reservoir unit. Porosity-permeability plots on the Lucia's diagram show sandstones and carbonates rocks with interparticle porosities have good reservoir qualities and always plot on upper parts of classes 1-3. Samples with fracture porosity mainly plot on upper part of class 1. This shows fractures has no considerable role in promoting the porosity, but they strongly increase permeability. Dolostones and the rocks with vuggy porosity have plotted on classes 2 and 3 (high porosity, relatively high permeability). Paragenetic secession of the Asmari Formation shows the diagenetic processes occurred syn-sedimentary on sea floor, after sedimentation during the low-deep burry and uplift. The results of this study can be useful in detection of reservoir zones, increasing of hydrocarbon production and enhanced recovery of this oilfield.
Sedimentology
Mohadeseh Janbaz; Hassan Mohseni; Alireza Piryaei; Rudy Swennen; Bizhan Yousefi Yeganeh; Hassan Soradeghi Sufiani
Abstract
Middle-late Eocene Shahbazan Formation is exposed in the Lurestan area (Zagros region). The diagenetic features have been studied based on the data from five surface sections and four additional exploration wells. This investigation was carried out on the petrography of 700 thin sections, Cathodoluminescence ...
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Middle-late Eocene Shahbazan Formation is exposed in the Lurestan area (Zagros region). The diagenetic features have been studied based on the data from five surface sections and four additional exploration wells. This investigation was carried out on the petrography of 700 thin sections, Cathodoluminescence on 40 thin polished samples, Scanning Electron Microscope on six samples and Electron Probe Micro-Analysis on 11 thin polished sections. the most conspicuous diagenetic processes affected on the Shahbazan Formation are dolomitization, cementation, neomorphism, physical and chemical compaction, dissolution and dedolomitization, of which dolomitization is the most important. Dolomite distribution in studied sections suggest that fluid flow was probably toward SW of studied area, since the extend of dolomitization waning in this direction. Since the dolomites of the Shahbazan Formation are overlain by the Asmari Formation, the dolomitization predates deposition of the Asmari Formation and occurred in eogenesis. Majority of calcite cements deposited before dolomitization in eogenesis, excluding parts of the blocky and poikiotopic calcite which may form in telogenetic and mesogenetic realms respectively. Degrading neomorphism occurred in marine realm. Part of dissolution occurred in meteoric vadose of eogenesis. Compaction commenced in meogenesis with increasing over burden due to deposition of the Shahbazan Formation and culminated after deposition of the Asmari and Gachsaran Formations. Telogentic processes caused dissolution and dedolomitization of the Shahbazan Formation due to exhumation. by the exception of dedolomitization and neomorphism, other diagenetic features are occurred in all studied sections.
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
L. Azad Shahraki; H. Rahimpour Bonab; M. Ranjbaran; A. Kangazian
Abstract
The Lower Cretaceous (Neocomian) carbonates of the Fahliyan Formation are considered as important reservoir rocks in the Zagros Basin. In this study, the sedimentary successions of this formation in Lar (620m thick) and Khami (517m thick) anticlines, located in the Izeh zone, were investigated to analyze ...
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The Lower Cretaceous (Neocomian) carbonates of the Fahliyan Formation are considered as important reservoir rocks in the Zagros Basin. In this study, the sedimentary successions of this formation in Lar (620m thick) and Khami (517m thick) anticlines, located in the Izeh zone, were investigated to analyze microfacies, depositional environment, and diagenetic phenomena. Based on petrographic studies, 16 microfacies related to five facies belts of tidal flat, lagoon, carbonate shoal, mid ramp and outer ramp were recognized. Grainstone microfacies were found more abundant in the Lar stratigraphic section than the Khami section. Lack of turbidite deposits and reefal facies, and transitional changing of the facies show that the Fahliyan Formation was deposited in a homoclinal carbonate ramp. Abundance of mud dominated facies and rarity of high energy facies (like shoal facies) show that the ramp was a leeward one. According to petrographic studies, the main diagenetic features of the carbonates were micritization, cementation, dissolution, neomorphism, compaction, fracturing, and dolomitization. Due to deposition in the photic zone and high sedimentation rate, the thickness of the Fahliyan Formation in both stratigraphic sections is considerable, but based on the drawn isopach map, the thickest succession of the formation is found in the Lar section. Therefore, the Lar area is considered as the depocenter of the Fahliyan Formation. Difference in the thickness of the Fahliyan successions of Lar and Khami, most probably, is caused by the syndepositional activity of the north-south trending basement faults (like Kazeroon fault) in the region. Also, difference in the quantity of the burial compaction of the carbonate successions (caused by facies and diagenetic differences) played a role in secondary (burial) thickness changes.
M.R Rahmani; R Moussavi – Harami; M Arian
Abstract
Dariyan formation is one of the oil reservoirs in the south pars field. This formation has been studied in wells SPO-1, SPO -2 and Spo-3. Thickness of Dariyan formation in mentioned wells are 109, 113 and 114 meters respectively. Based on the studies of thin sections from the Dariyan formation of three ...
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Dariyan formation is one of the oil reservoirs in the south pars field. This formation has been studied in wells SPO-1, SPO -2 and Spo-3. Thickness of Dariyan formation in mentioned wells are 109, 113 and 114 meters respectively. Based on the studies of thin sections from the Dariyan formation of three above mentioned wells, nine carbonate and one detrital facies have been identified within four facies associations including tidal flat (Mudstone), lagoon (Bioclast mudstone to wackstone, Bioclast peloid wackstone to packstone, Bioclast peloid packstone to grainstone, Algal boundstone), Mid ramp (Echinoid mollusk wackstone to packstone, Orbitolina wackstone to packstone, Framestone, Floatstone) and outer ramp (Shale). Facies studies indicate that Dariyan formation has been deposited in a homoclinal ramp.The Dariyan formation has been affected by four diagenetic stages, including marine, meteoric, burial and uplift. The most important identified diagenetic processes are micritization, bioturbation, geopetal, physical and chemical compaction, cementation, neomorphism, replacement, dissolution, fracturing and filling. Among the all diagenesis process, dissolution and fracturing are the major processes improving reservoir quality. In Contrary, physical compaction and especially cementation are the main processes redusing reservoir quality. Dissolution process with generating secondary porosity consists of vuggy and moldic, has important effect on increasing of porosity. Most of the dissolution features have been produced during the meteoric diagenesis and less through burial diagenesis. Dissolution process with develop the vuggy pores caused to connect them in some case and also affected on fractures , stylolites and previous diagenetic cements in upper and lower members of daryian formation which eventually has been increased permeability and reservoir quality. Also, Fracturing, the main other diagenetic process with connect the some individual vuggy and moldic pores together has effective role to increase the permeability and reservoir quality in upper and lower parts of Dariyan formation.
M Khanjani; S.R Moussavi-Harami; H Rahimpour-Bonab; M.R Kamali; A Chehrazi
Abstract
The Santonian – CampanianIlam Formation is one of the major reservoirs of Bangestan Group in the Zagros petroliferous basin. In the Siri Alvand Oilfield located in the Persian Gulf this formation with a total thickness of 130 m, consists of limestone. In this study, microfacies, depositional environments, ...
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The Santonian – CampanianIlam Formation is one of the major reservoirs of Bangestan Group in the Zagros petroliferous basin. In the Siri Alvand Oilfield located in the Persian Gulf this formation with a total thickness of 130 m, consists of limestone. In this study, microfacies, depositional environments, diagenetic processes and sequence stratigraphy of the Ilam Formaton in Siri Alvand oilfield was studied. Based on thin sections studies, 8 microfacies and 4 facies associations were identified that deposited in a homoclinal carbonate ramp environment. On the basis of petrographic studies, the main diagenetic processes affected these rocks include bioturbation, cementation, dissolution, dolomitization, stylolitization, pyritization and fracturing. The most important cement types in this formation are bladed calcite, fine equant calcite, drusy mosaic calcite, coarse blocky calcite and syntaxial calcite overgrowth. Sequence stratigraphic studies led to recognition of four third order depositional sequences in the Ilam Formation that all of them terminated to the type 1 sequence boundary. Finally, facies and diagenetic processes intensity were studied in each sequence.
M khanjani; S.R Moussavi-Harami; H Rahimpour-Bonab; M.R Kamali
Abstract
The Albian - Turonian Sarvak Formation, the second major reservoir formation in south and southwest Iran is composed of mainly carbonate rocks. In this study, the upper part of Sarvak Formation in Siri Oil Fields was studied to determine facies, depositional environments, diagenetic processes and sequence ...
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The Albian - Turonian Sarvak Formation, the second major reservoir formation in south and southwest Iran is composed of mainly carbonate rocks. In this study, the upper part of Sarvak Formation in Siri Oil Fields was studied to determine facies, depositional environments, diagenetic processes and sequence stratigraphy analysis. The facies analysis led to the recognition of 12 microfacies in 5 facies associations, which deposited in a homoclinal carbonate ramp environment. The main diagenetic processes affected carbonates of this formation are bioturbation, micritization, cementation, dissolution, dolomitization, stylolitization, pyritization and fracturing. The most important cements in this formation are fine equant calcite cement, drusy mosaic calcite cement, coarse blocky calcite cement and syntaxial calcite overgrowth cement. Three third order sequences recognized in sequence stratigraphic studies for the upper part of Sarvak Formation taking into account of facies and diagenetic events in a sequence stratigraphic framework.
S. Parham; M. R. Kamali; F. Fayazi
Abstract
The Dalan Formation (Upper Permian) is mainly composed of limestone and dolostone with minor evaporite interbeds. Upper carbonates of the Dalan Formation constitute one of the main gas reservoirs in the Zagros fold thrust belt especially in the Fars and the Persian Gulf. The upper part of the Dalan Formation ...
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The Dalan Formation (Upper Permian) is mainly composed of limestone and dolostone with minor evaporite interbeds. Upper carbonates of the Dalan Formation constitute one of the main gas reservoirs in the Zagros fold thrust belt especially in the Fars and the Persian Gulf. The upper part of the Dalan Formation consists of oolitic grainstone with high reservoir quality. Based on sedimentological studies in the upper Dalan unit, seven microfacies have been recognized. This microfacies have been deposited in warm, arid intertidal, lagoon and shoal. They deposited in a homoclinal ramp. Different diagenetic process affected this unit are bioturbation, micritization, neomorphism, replacement, dolomitization, anhydritization, mechanical and chemical compaction, cementation, dissolution and fracturing. Based on the evidence like widespread dissolution, formation of moldic and vuggy porosity and precipitation of different types of meteoric cements and based on paragenetic sequences, it can be concluded that the studied interval, have not buried after the deposition, but at least some parts like oolitic shoal exposed subearially and was affected by meteoric diagenesis that was followed by deep burial diagenetic environment.
M. Hosseini-Barzi; M. Saeedi
Abstract
The sandstones of Padeha Formation with 390m thickness in section of Samirkooh in Kerman, Zarand have been studied to illuminate their provenance, tectonic provenance, diagenesis by omitting the effect of diagenetic process on sandstone composition. In this direction, petrography of 91 thin sections, ...
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The sandstones of Padeha Formation with 390m thickness in section of Samirkooh in Kerman, Zarand have been studied to illuminate their provenance, tectonic provenance, diagenesis by omitting the effect of diagenetic process on sandstone composition. In this direction, petrography of 91 thin sections, modal analysis of 30 appropriate samples, and use of SEM and EDX analyses of 6 sandstone samples were accomplished .We can point to diagenetic processes including mechanical compaction, coating hematite around the detrial grains (eogenetic stage) and growing up authigenic cholorite and illite, chemical compaction, quartz cementation, dolomite cementation, dedolomitization, albitization of feldspar and corrosion of grains by dolomite cement (mesogenetic stage) and fracturing as well as filling them by calcite, quartz and anhydrite cement (telogenetic stage). We studied tectonic provenance of these sandstones using Qt92 F7 L1, Qm77 F 7 Lt 16, Qp92Lvm4Lsm4, after recognition of diagenetic process and omitting their effect on the results of modal analysis. These results show quartzolithic facies with cratonic, recycled orogen and rifted continental margin tectonic provenance. Using diamond diagram drawn based on particulars quartz grains and also petrographic evidences in these sandstone, we can say that these sandstone derived from multi provenance. The log Qt/F+RF vs. Qt/F+RF climate diagram and QRRF triangle indicate humid climate during deposition of the Padeha Formation.
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.
R. Moussavi-Harami; A. Mahboubi; A. Kheradmand; H. Zandmoghadam
Abstract
For interpretation of paragenetic sequence and post depositional history of siliciclastic sediments of Dahu Formation (Late Camberian), two stratigraphy sections were measured at Dahuieh (type section) and Gazuieh in the NE and E of Zarand, with the thickness of 240 and 227 meters, respectively. The ...
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For interpretation of paragenetic sequence and post depositional history of siliciclastic sediments of Dahu Formation (Late Camberian), two stratigraphy sections were measured at Dahuieh (type section) and Gazuieh in the NE and E of Zarand, with the thickness of 240 and 227 meters, respectively. The diagenetic processes affected these sediments, during three stages eogenesis, mesogenesis and telogenesis, including compaction, cementation, alteration, dissolution, fracturing and vein filling. Clay mineral study within sandstone and mud rocks of Dahu Formation led to identification of two groups of clay as illite and cholerite. Illite form 90% of clay minerals in these sediments that are mostly formed during burials and clay mineral diagenesis as well as alteration and dissolution of potassium feldspar. The interpreted paragenetic sequence shows that a large number of diagenetic processes act in the mesogenetic stage. Physical compaction and hematite cement have operated in eogenetic stage, while other processes such as chemical compaction, silica and dolomite cement, feldspar alteration, sericitization, ilitization and chloritization, dissolution of feldspars and cherts have occurred in mesogenetic stage. The fractures and calcite vein filling have formed in telogenetic stage during uplifting. We hope that this information can be used for evaluation of post depositional and burial history of similar sediments in local and regional scale.
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.
H. Mohseni; S. Khodabakhsh; A. H. Sadr; F. Aliani
Abstract
Bisotun inscription located on the mid-way of Hamedan- Kermanshah road (40 km to Kermanshah city), is carved on limestone cliffs exposed in the area. Dissolution of the inscription caused serious damage to the most important heritage of the country. The area comprises massive gray limestones of the Lower ...
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Bisotun inscription located on the mid-way of Hamedan- Kermanshah road (40 km to Kermanshah city), is carved on limestone cliffs exposed in the area. Dissolution of the inscription caused serious damage to the most important heritage of the country. The area comprises massive gray limestones of the Lower Cretaceous as a part of high Zagros thrust belt. Accordingly, the limestones are extensively tectonized and two main joint sets are developed in the area. Joint study was performed in an area of one km around the inscription. Thereby, it is revealed that these joint sets had impact on the dissolution of limestones. Limestone beds containing inscription are composed of mudstone to bioclastic algal wackestones. Original mineralogy of these algal bioclasts was aragonite. A few foraminifers and pellet also occur in some samples. Extensive jointing and unstable original mineralogy of limestone components lead to the dissolution of limestones in a meteoric condition. Evidences such as moldic, vuggy, canal, and cavern porosity suggest a meteoric diagenetic environment. Vugs up to centimeter scale in the field observations are evidences of karstification in the area. Jointing and dip direction of the bedding plane cut across the middle part of the inscription; conduct the corrosive rainfall precipitation toward the inscription surface. Consequently dissolution pit and holes were developed on it. Apparently the only practical way for remediation is to keep the inscription surface away from these corrosive waters. Considering the dip direction of the bedding plane, jointing on limestones and karstification in the area, it is recommended to drain the waters from bedding plane through a canal in a considerable distance from the inscription surface.
