Yahya Djamour; S. Tabibi; M. M. Hossainali
Abstract
The accuracy of GPS derived positions in short term measurements largely depends on the better modeling of residual errors which is normally reduced in long term measurements by averaging the obtained results. To increase the accuracy of the movements obtained through the analysis of high rate data in ...
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The accuracy of GPS derived positions in short term measurements largely depends on the better modeling of residual errors which is normally reduced in long term measurements by averaging the obtained results. To increase the accuracy of the movements obtained through the analysis of high rate data in geophysics applications, systematic errors in the existing measurements in the corresponding frequency range should be reduced. Calibration techniques and the error reduction are based on the repeatability of the system constellation. For example, those errors affecting the resulting accuracy of the high rate positions in the time scales of 10-600s depend much on the constellation geometry of the GPS satellites and GPS stations. Since the satellite orbits are fixed, those errors are highly repeatable in time. This characteristic is the base for the development of sidereal filtering techniques for reducing this kind of errors. It is assumed that the repeatability occurs based on the nominal repetition period of the satellites; however, the true time of this repeatability varies even for each satellite. In this paper the mean period is estimated as 23h, 55m, and 55s and used for the noise reduction of time series of the relative displacement. By using this period, noises with frequencies less than 0.01Hz of high rate GPS positions have been reduced significantly. Accessible co-seismic displacements are reduced to less than 4mm in horizontal components and less than 10mm in the vertical components.
M Allameh; B Torabian
Abstract
Farrokhi Formation is a Cretaceous rock unit in Central Iran that lithologically contains lime, marl and marly lime accompanied by layers of fossiliferous limestones. This formation lays conformably over the Haft-Tuman Formation, while its upper boundary is disconformable with Chupanan Formation. In ...
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Farrokhi Formation is a Cretaceous rock unit in Central Iran that lithologically contains lime, marl and marly lime accompanied by layers of fossiliferous limestones. This formation lays conformably over the Haft-Tuman Formation, while its upper boundary is disconformable with Chupanan Formation. In this study, 23 rock samples from marl segment of the Farokhi Formation were prepared palynologically and their various palynological constituents were characterized and quantified by percent. Assessing the organic elements of formation demonstrated fair preservation of organic matters in marl segments and allowed determination of the sedimentation rate and oxygen content. Palynofacies investigation signifies that marl segment has been deposited in shallow to open marine environment with medium energy, and one palynofacies has been diagnosed for it. According to typical dinoflagellate cysts, a warm and rather shallow environment with medium energy and variable salinity is suggested for the period of sedimentation of the marl segment.
N Saboor; M.R Ghassemi; M Eskandari; A Nazari.F; M Ghorashi; F Seenaian
Abstract
Depending on their structural maturity, seismogenic faults, , may rupture in one segment or as multiple segments; they also may show different slips on their segments. Mature faults break in long ruptures with small slip, while immature faults rupture as short segments but are more energetic. On the ...
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Depending on their structural maturity, seismogenic faults, , may rupture in one segment or as multiple segments; they also may show different slips on their segments. Mature faults break in long ruptures with small slip, while immature faults rupture as short segments but are more energetic. On the other hand, the mature faults demonstrate clustering pattern in their earthquake recurrence pattern. Also, the ground motions produced by earthquakes on immature faults are larger than those generated by earthquakes on mature faults. In this paper, we defined maturity of major faults in EasternIranseismotectonicProvince, considering their segmentation, rupture length, displacement vector on the rupture and the history of clustered earthquake sequence on the fault. Then, the response spectrum of ground motions caused by large earthquakes occurred on these faults were calculated. To reduce the effect of unknown wave paths, we used ground motions recorded in the near field. Earthquakes of different mechanisms were selected in magnitude range from Mw=5.7 to 7.1. We compared the obtained response spectrum with those resulted from the experimental model presented by Boore et al. (1997). Study of this parameter can help to recognized ground motion potenial of the faults, and considering it in extracting attenuation equations increases the accuracy of the results for seismic hazard assessment. Using our evaluation for structural maturity of the faults, we try to present a model for evolution of seismic activity in Eastern Iran.
A Mahdavian; M Hassani
Abstract
In destructive earthquakes lots of break down in structures such as vital lifelines and buried pipelines also destruction of massive buildings have always been observed. These destructions can sometimes cause more serious injuries. The absorbed force and destruction caused by the earthquake in surface ...
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In destructive earthquakes lots of break down in structures such as vital lifelines and buried pipelines also destruction of massive buildings have always been observed. These destructions can sometimes cause more serious injuries. The absorbed force and destruction caused by the earthquake in surface structures are proportional to their mass and inertia, so that with increasing acceleration, the amount of forces is higher. This is despite the fact that the behavior of buried structures actually influenced by the behavior of the surrounding soil and the mass of structure in comparison with their environmental soil is very small and negligible. Therefore, using the methods based on earthquake acceleration parameter can’t be sufficient in designing of such structures and existing of the speed spectrum designing along with the acceleration spectrum available in 2800 building code is also necessary, because the seismic design of such structures is based on the displacement response method. That is, first the displacement of the earth in location of buried structures using velocity response spectrum is calculated and the interaction between earth and underground structure is analyzed with quasi- static method. Velocity response spectrum for seismic designing of buried structures based on the maximum response of the earth surface layer due to the desired acceleration entering the bottom layer is obtained from a soil profile analytical model. In this study, we have tried to determine the curve of the velocity spectrum factor for soil type 1 and 2 according to the accelerograms data obtained from different earthquakes in Iran For this purpose, among the received accelerograms data from the Building and Housing Research Center, we selected 306 horizontal accelerograms of soil type I and 323 horizontal accelerogram of soil type 2.The normalized velocity spectrum of each accelerogram were calculated separately based on the maximum values of the velocity domain and acceleration. Accordingly, for each of these two types of soil we obtained two sets of normalized velocity response spectrum. Then, for each set, mid and 84% - design spectrum were determined. Finally, mathematical model of velocity spectrum factor curves was determined and presented in the formula for soil conditions of types 1 and 2 of Iran.
M Yamani; A. A. Shamsipour; M. Jafari Aghdam; S. Bagheri Seyed shokr
Abstract
The Cheleh basin is located in the south of Kermanshah province and the Zagros morphotectonic zone. According to the vast of limestone formation, and the presence of tectonic faults, developed karst land forms has evolved. The purpose of this study is to survey the development of karst and the effect ...
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The Cheleh basin is located in the south of Kermanshah province and the Zagros morphotectonic zone. According to the vast of limestone formation, and the presence of tectonic faults, developed karst land forms has evolved. The purpose of this study is to survey the development of karst and the effect of permeable factors on it. Main data of the research are formed by topographic and geologic maps and aerial photos along with hydrology stats of Department Energy. In this study are nine environmental factors as independent variables and Geomorphological karstic landforms as the dependent variable were examined. At first was identified quantitative and qualitative criteria and then doing field works, interviews and questionnaires, these criteria and factors are analyzed using Analytical Hierarchy Process and finally were gained in GIS, maps and unificating and Final correction with the help of fuzzy logic, respectively. In order to better conclusions, the region in terms of development in karst was divided into four sections. Combining data layers approve the effective role of lithology (Asmari Formation) in the process of development in karsting. Also has seen development in karst on the southern highlands of basin and flat lands at the head of the northern anticline and along the main fault of the region. karst areas Developed 107.95 square kilometers about 22.5 percent and regions with average development of karst covers 34 percent of the watershed basin.
L. Fateh Bahari; M.H. Mahmoudi Gharaei; A. Mahboubi; R. Moussavi-Harami
Abstract
Ab-Deraz Formation (Turonian to Santonian) is a marly - Carbonates sequence consists of three marl-chalky limestones intervals. This formation widely crops out in Kopet-Dagh Basin in NE of Iran. Chalk and calcareous marl couplets show decimeter to meter scale cycles. Carbonate content of chalky beds ...
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Ab-Deraz Formation (Turonian to Santonian) is a marly - Carbonates sequence consists of three marl-chalky limestones intervals. This formation widely crops out in Kopet-Dagh Basin in NE of Iran. Chalk and calcareous marl couplets show decimeter to meter scale cycles. Carbonate content of chalky beds are 80-95% in rhythmic couplets, and about 65-80% in calcareous marly beds. The Ab-Deraz Formation is studied in tow Hamam-Ghale and Padeha outcrops, and also in well No.56 of Khangiran. Three dominate frequency of sediments are identified based on gamma ray log, which are related to three type of Milankovitch cycles including the long eccentricity (413 ka), eccentricity (100 ka) and precession (21-23 ka) cycles. Biostratigraphic age determination based on foraminifera is comparable with orbital chronology calculated by on eeccentricity cycles counting. These cycles are also correlated with carbonate contents in studied sections.
A. Shafiei Bafti; M. Shahpasandzadeh
Abstract
According to potential of the intra-continental strike-slip faults for occurrence of large earthquakes, which are also considered as the main elements of active continental deformation, determination of their geometry and kinematics along with recognition of the active segments and temporal structural ...
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According to potential of the intra-continental strike-slip faults for occurrence of large earthquakes, which are also considered as the main elements of active continental deformation, determination of their geometry and kinematics along with recognition of the active segments and temporal structural evolution is necessary. The oblique-slip fault of Ravar with about 137 km length is extending in vicinity of Ravar, north of Kerman. In the north of study area, the fault extends parallel to the Lakar-Kuh fault, but in the south converges toward to the Lakar-Kuh and the Kuh-Banan faults. Upthrusting of the eastern block of the Ravar fault and east-ward thrusting of the Lakar_Kuh fault system constructed a positive flower structure. The motion of the Ravar fault have caused the dextral displacement and an accumulative horizontal displacement of the drainages about 940-970 in the north since Pleistocene. Regarding a minimum horizontal slip-rate of about 0.54 mm/yr, the recurrence time of earthquakes with Mw~ 6.7 would be about 1400 year. In the middle part of the fault, the Reidel fractures of R, R, and P has been well developed and caused a dextral deflection of the Esmail-AbadRiver about 16m. With assumption of characteristic earthquake occurrence, the maximum slip per event could be about 0.75 m, which is consistent with the minimum displacement of the recent gorges. The amount of horizontal dextral displacement of the fault decreases toward to the south, whereas the vertical component of the fault motion increases, so that the Pleistocene deposits show about 10 m difference in elevation across the southern part of the fault. Concerning the trend of meizoseismal zone of 1911/04/18 Ravar earthquake (M~ 5.8, I0~ VIII) and parallelism of trend of the co-seismic surface rupture (N13W) with the southern part of the fault, the Ravar fault could be responsible of this earthquake. In addition, the active cross-faulting of the Dehu, the Dehzanan, the Chatrud, the Pasib, and the Darbid-Khun control the recurrence time and magnitude of the earthquakes in the study area.
A. Amini; M. Shahosseini; A. Mohammadi; M. Shahrabi
Abstract
The hypersaline UrmiaLake is the most important intra-continental environment in Iran, with distinctive geological, environmental, and biological, characteristics. The Shahid-Kalantari Highway (under construction) between Urmia and Tabriz cities passes through this lake. Some 14 km dyke is constructed ...
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The hypersaline UrmiaLake is the most important intra-continental environment in Iran, with distinctive geological, environmental, and biological, characteristics. The Shahid-Kalantari Highway (under construction) between Urmia and Tabriz cities passes through this lake. Some 14 km dyke is constructed in the lake for this passage and about 1400 meter is left for a bridge construction. The role of the constructed dyke on sedimentation pattern seems significant, as understood from satellite images and field observations. This study deals with sedimentological characteristics and origin of deposits along the Shahid-Kalantary Highway of UrmiaLake. Availability of 4 cores from boreholes drilled for geotechnical studies provided a good opportunity for this study. This study is carried out on the cores of the 4 boreholes (340 m thick in total) and samples collected from the sea floor along the dyke. Mineralogical, textural and structural characteristics of the sediments were studied for determination of chemical, biological and physical processes responsible for their development. Some 396 plugs from the cores (0.7 to 1 m interval) and 15 samples from the sea floor (cores of 20-40 cm long) were selected for these purposes. To investigate the role of surrounding rivers in providing detritus material to the study site, samples from suspension load of the major feeding rivers are collected. Major characteristics of these samples are studied and compared with those from the study area. All available data on the discharge and sediment load of the major feeding rivers are collected and analyzed for this study. Size and shape are two major textural characteristics investigated in this study using petrographic methods (including SEM). Chemical composition of sediments is studied by petrographic (coarse material) and XRD (fine material and clay minerals) methods. Organic mater, carbonate content, and evaporate portion of the sediments are measured using standard techniques introduced in the literature. Results from this study shows that 25 to 40 % of the studied sediments are derived from the land, through feeding rivers and 60 to 75 % of them are formed within the basin by chemical and biological processes. Quartz, feldspar, volcanic lithics, heavy minerals including pyrite and pyroxene, and clay minerals are major detrital constituents of the sediments. Kaolinite, illite, and montmorillonite are common clay minerals in the sediments, which characteristics are similar to those determined in the suspension load of feeding rivers. Some carbonates, as carbonate lithics, and organic material are also found detrital in origin. Gypsum, halite, calcite, and aragonite are the chemical components of the sediments occur as evaporate and mud crusts, or coated grains. Fecal pellets and some coated grains (produced by algae) are the main biological components of the studied sediments. Pyritization of pellets, especially in lower parts of the cores, is commonly observed, so that, pyrite is presented in the sediments both in detrital and diagenetic forms. Distribution pattern of the major constituents along the studied cores reflect the significant role of sea level fluctuation in their development. Results from this study show that the chemical components of sediments developed during the stages of sea level fall, during which the sea was barely receiving sediments from the land (dry periods). The coated grains of this origin were developed in the basin margin, where the wind-induced waves produced a relatively high energy sub-environment in the margin. The biological constituents of the sediments were developed during sea level rise (lower salinity conditions), during which environmental conditions were not suitable for development of chemical sediments. The origin of detrital material is related to the feeding rivers. TalkeRud in the eastern part of the sea had a major role in providing coarse terrigenous particles to the basin. Major characteristics of the detrital quartz, feldspars, pyroxene and volcanic lithics are similar to those find in the volcanic outcrops of the IslamiIsland and TalkeRud alluvial fans. The Shahr Chay, Nazlu Chay, and Barandoz Chay in the west and ZarinehRud and SiminehRud in the south had significant role in providing fine terrigenous (clay minerals) to the studied area.
On the basis of distribution pattern of terrigenous sediments and their ratio to chemical and biological sediments, the feeding rivers around the lake (major suppliers of the terrigenous sediments) are classified into three groups (most, moderate and low effective). This is designed for further investigation on the controls of sediments accumulation along the highway. This study emphasizes on more significant role of chemical and biological processes on the sediments accumulation in the studied area, than that of physical processes. Due to significant role of sea level fluctuation in chemical and biological sediments development, a thorough control on sea level fluctuation (dam construction, artificial evaporation for salt acquisition, and etc.) is vital in this basin. In this regard any program for sedimentation control along the dyke must take greater consideration on chemical and biological deposition.
M.H Emami; S Houshmand
Abstract
Mylonitic granite-granodiorites of Nowghan shear zone extend in NW-SE trend in the metamorphic rocks of the southwest Golpayegan. Different outcrops of mylonitic bodies have been studied in order to investigate the origin of granitoid rocks in Nowghan shear zone and determined their tectonic setting ...
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Mylonitic granite-granodiorites of Nowghan shear zone extend in NW-SE trend in the metamorphic rocks of the southwest Golpayegan. Different outcrops of mylonitic bodies have been studied in order to investigate the origin of granitoid rocks in Nowghan shear zone and determined their tectonic setting in Sanandaj-Sirjan zone. Field evidence, mineralogy and geochemical data suggest that the mylonitic rocks have S-type and strongly peraluminous characteristics. From the tectonic setting point of view, the granitoid bodies are of the collisional type and they formed as syn-tectonic to post-tectonic intrusions.
M. Maghsoudi; F. Rafia; M. Ghorashi
Abstract
Classification of discontinuities and fractures in rock plays an important role in study and problem solving in geosciences fields, especially in Engineering Geology and Rock Mechanics. Nowadays, joints are classified on the basis of two geometrical parameters of dip and dip direction, presented on stereonets. ...
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Classification of discontinuities and fractures in rock plays an important role in study and problem solving in geosciences fields, especially in Engineering Geology and Rock Mechanics. Nowadays, joints are classified on the basis of two geometrical parameters of dip and dip direction, presented on stereonets. It is clear that the behavior of discontinuities cannot be thoroughly presented by these parameters in solving such related problems, as stability of geotechnical structures like rock slopes and tunnels. The present paper deals with the results of a research within which a new method of joint classification by 3 parameters has developed. This is done in 3D environment software, utilizing Matlab and SPSS softwares as supporting programs. Two employed parameters are conventional dip and dip direction, while the third parameter can be one of other joint characteristics such as infilling, length, aperture and so on. In order to check the validity of the method, it was applied in one of the Neyriz Marble quarries, where rock mass contains well defined and clear joints. In this research, the type of infilling of joints has been taken into account as the third parameter, and the results were compared to the traditional 2-parameters classification. This revealed that one joint system defined on stereonets, in new 3-parameter classification, is distinguished as two separate joint systems regarding their type of infilling, namely, iron oxides and non-filling. Field investigation shows the joint system with no infilling is contributing in instability of rock walls and also occurrence of spalling phenomenon in toes of some benches. Utilizing SPSS software, a regression analysis has been performed for each set of joint data, and it is shown that a better correlation factor exists between the values in the new 3D classification. It also shows that the more non-filling joints extend northward, their dips tends to 90°, and this can be a key in slope stability studies, as well as in mining design and planning.
Kh. Motaghi; A. R. Ghods; H. R. Siahkoohi
Abstract
Study of ground motion attenuation in Tehran region is a very important aspect of determining a more precise hazard map of the city. For the last 10 years, three short period seismic networks have been operating in the study region by the Institute of Geophysics, University of Tehran (IGUT). We ...
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Study of ground motion attenuation in Tehran region is a very important aspect of determining a more precise hazard map of the city. For the last 10 years, three short period seismic networks have been operating in the study region by the Institute of Geophysics, University of Tehran (IGUT). We have selected 47 events recorded by IGUT stations during 1996-2004 to estimate attenuation parameters for the study area. The selected events have provided 480 records with good spatial resolution. Only records with signal-to-noise ratio of greater than 4 have been selected. To find the distances at which the nature of geometrical spreading attenuation (R-b) changes significantly, we use a local regression smoothing method called Robust Lowess. It is found that a tri-linear function having hinges at distances about 106±10 and 191±10 km describes the geometric spreading attenuation with distance. Using a tri-linear regression analysis, we found that b1=1.1±0.1, b2=-0.4±0.1, b3=0.5 minimize the average absolute value of the residuals at a frequency of 4 Hz. The remaining attenuation is assumed to be caused by anelasticity. Using anelastic attenuation at different frequencies, the quality factor in Tehran region is obtained as .
B Taghipour; M Nejadhadad; M.A Makizadeh; M Noghreian; P Rahimi
Abstract
Dunite and serpentinized harzburgite from northwest of the Neyriz ophiolites are host rocks of some podiform chromite deposits in Cheshmeh-Bid area. These chromite deposits occurred as aligned massive lenses in various sizes. The most important ore textures are massive, nodular, layered and disseminated ...
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Dunite and serpentinized harzburgite from northwest of the Neyriz ophiolites are host rocks of some podiform chromite deposits in Cheshmeh-Bid area. These chromite deposits occurred as aligned massive lenses in various sizes. The most important ore textures are massive, nodular, layered and disseminated grains. These textures are goodevidences of crystals settling crystals during the process of magma cooling in the chamber. The mineralogical studies revealed that the pyroxene melting tookplace in the peridotite host rock and olivine is recrystallized in dunite envelope. Mineral chemistry of chromite indicates high Cr number(72-77), high Mg number(69-62) and low TiO2 content(0.04-0.14 %) in chromite samples. These amounts are comparable with those chromitites, which areformed from the high partial melting rate of mantle. The medium amount of PGE determined about 212ppb, which is much lessthan the Tang-e-Hana chromite (1556ppb) deposits. The trace element content of chromitite samples and dunite envelope like Ga, V, Zn, Co, Ni and Mn are between 17-24, 466-842, 852-1048, 22-84, 115-171, and 852-1220 ppm respectively. The U shape of REY pattern indicates the interaction of high volatile and REE bearing melt(boninitic source of parent magma) with host rock. Therefore,the Cheshmeh-Bid chromitite resulted likely from the intrusion of boninitic magma ofprimary mantle with high partial melting in the peridotite host rock. The geotectonic setting is above supra-subduction zone of island arc.
M.A Alimi
Abstract
The sequence of seismicity including three earthquakes in the Mohammadabad region, eastern Iran, within a period of 30 years has made it one of the most outstanding seismically active regions in the country. The Mohammadabad fault system is described using earthquake and satellite imagery data to support ...
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The sequence of seismicity including three earthquakes in the Mohammadabad region, eastern Iran, within a period of 30 years has made it one of the most outstanding seismically active regions in the country. The Mohammadabad fault system is described using earthquake and satellite imagery data to support a simple tectonic model. The interaction between the Mohammadabad strike-slip fault system and basement structures and also the en-echelon array of fault segments have resulted in formation of the Mohammadabad pull-apart basin and Tajkuh contractional zone. The Daqq-e-Mohammadabad basin is a topographic depression formed in a right-step releasing step-over related to the Mohammadabad-Taleb dextral strike-slip fault system. Geomorphologic evaluation of the Mohammadabad deformation zone at surface indicates both normal and reverse faulting. Normal faulting is obvious in the margin of the basin and reverse faulting is seen in the zone of contraction at the Taleb-Tajkuh left-step restraining step-over. The model presented for the formation of adjacent extensional and contractional structures based on traces of the Mohammadabad strike-slip fault system, basin, and uplifts to the south of the area is a double step-over (releasing and restraining) model. Fault segments associated with this step-over may be capable of earthquake ruptures. The linkage of main strike-slip zones (Mohammadabad-Taleb and Taleb-Tajkuh) by transverse faults could increase potential generation of large earthquakes and activity of sympathetic faults.
M. Hosseini-Barzi; N. Etemad Saeed
Abstract
The Early Cambrian Lalun Formation in Poshte- Badam block has been studied in Bahmoo section with 550 m thickness, to illuminate its sedimentary environment and sea level changes. The field investigations, collection of 110 paleocurrent data, petrography, study of SEM images and XRD analysis of shale ...
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The Early Cambrian Lalun Formation in Poshte- Badam block has been studied in Bahmoo section with 550 m thickness, to illuminate its sedimentary environment and sea level changes. The field investigations, collection of 110 paleocurrent data, petrography, study of SEM images and XRD analysis of shale samples have been used for facies analysis, paleocurrent recognition and sedimentary environment reconstruction. The facies analyses imply 5 silisiclastic coarse grained (Gm), medium grained (Sp, St, Sh) and fine grained (Fl) lithofacies and 1 carbonate (dolomite) microfacies. The lithofacies, bipolar bimodal paleocurrent pattern and petrographic evidences such as the existence of glauconitic sandstones with high textural and compositional maturity imply deposition of these sediments in a Tidal Flat environment. Studying the relative sea level changes of Lalun deposits in this area imply two sequences which have been bounded between SB1 unconformities.
A. Moradzadeh; F. Doulati Ardejani; B. Tayebi
Abstract
There are a few iron deposits in the north and northeastern part of Semnan city that none of them has a systematic exploration background. Ojat_Abad deposit is one of them located in 63 km of north-east of Semnan at the southern side of Semnan - Damghan main road. A magnetic survey including 1200 ...
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There are a few iron deposits in the north and northeastern part of Semnan city that none of them has a systematic exploration background. Ojat_Abad deposit is one of them located in 63 km of north-east of Semnan at the southern side of Semnan - Damghan main road. A magnetic survey including 1200 measuring points has been recently performed to explore the deposit within an area of 89 acres. The prepared total and residual magnetic field maps clearly demonstrate the existence of iron anomaly at seven locations in a zone with northeast - southwest trend. In this paper, attempt has been made to obtain more qualitative and quantitative information for the recognized anomalies by performing two and three dimensional (2D, 3D) numerical modeling. To achieve the goal, the residual anomaly map, obtained by professional software called Modelvison Pro is used. It was found that the results of 2D and 3D modeling confirm each other in the most cases and in addition are in quite good agreement with the results of existing mining excavations. The obtained results also demonstrate the explored anomalies locate separately, and except one of them, all are located at a depth less than 35 meters.
M Behyari; M Mohajjel; M Rezaeian; M Moayyed
Abstract
Misho Complex in NW Iran has a remarkable unique high topography surrounded by well known faults, where Precambrian basement rocks were uplifted and exposed. Structural data indicate that the exhumation of the Misho Complex was result of displacements along the North Misho, South Misho and Tasouj faults. ...
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Misho Complex in NW Iran has a remarkable unique high topography surrounded by well known faults, where Precambrian basement rocks were uplifted and exposed. Structural data indicate that the exhumation of the Misho Complex was result of displacements along the North Misho, South Misho and Tasouj faults. Study of structural and thermochronometery and combination of their results show that uplift initiation time was not unique in this Complex. Analysis of 10 AFT samples clear that the western Misho Complex has the high amount of uplifting during early Palaeocene (72.7 10.6) mid Miocene (50.3-3.4) time. But uplifting in central and eastern parts of the Misho Complex was starting later in mid-Miocene (22.5 3.4). Difference in uplifting time in various parts of Misho Complex resulted in variety of basement uplifting and exhumation in different parts of the Misho Mountains. Interpretation of minimum and maximum topography homogenised samples shows that the rate of uplifting was more than that in the western part of the Misho Complex. It is concluded that, displacements variations along the surrounded faults and rotation of existing blocks resulted in variation of the uplifting and exhumation amount in the area.
B Ghasemshirazi; M.R Majidifard; A Kheradmand; T Mohtat
Abstract
In this research, the Campanian -Maastrichtian deposits in Jupar section, Central Iran have been studied to determine biozonation and Paleobathymetry of the deposits. The planktonic and benthic foraminifera were studied in order to assign palaeobathymetry of the Campanian- Maastrichtian deposits. A depth ...
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In this research, the Campanian -Maastrichtian deposits in Jupar section, Central Iran have been studied to determine biozonation and Paleobathymetry of the deposits. The planktonic and benthic foraminifera were studied in order to assign palaeobathymetry of the Campanian- Maastrichtian deposits. A depth of 490- 650 m was assigned for most parts of the sediments according to planktonic/epibenthic ratio and the regression equation D = e (3.58718+ (0.03534 × %P*)). In the present investigation, 58 planktonic species of 27 genera have been identified. The Campanian -Maastrichtian deposits is divided into 7 biozones on the basis of planktonic foraminifera, which are cosmopolitan and consist of biozone1-Globotruncanita elevata Partial Range Zone, Biozone2- Globotruncana ventricosa Interval Zone, Biozone3- Globotruncanita calcarata Interval Zone, Biozone4- Globotruncanella havanensis Partial range zone , Biozone5- Globotruncana aegyptiaca Interval zone, Biozone6- Gansserina gansseri Interval zone, and Biozone7- Contusotruncana contusa Interval Zone.
S.A Aleali; H. Rahimpour-Bonab; S. R. Moussavi -Harami; D. Jahani; A. Asadi-Eskandar
Abstract
The Early Triassic carbonates of Kangan Formation are major gas reservoirs in the Southwest of Iran and the northern Persian Gulf. Facies analyses of Kangan Formation led to recognition of 13 microfacies which are related to tidal flat, lagoon, shoal and open marine environments. Examination of vertical ...
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The Early Triassic carbonates of Kangan Formation are major gas reservoirs in the Southwest of Iran and the northern Persian Gulf. Facies analyses of Kangan Formation led to recognition of 13 microfacies which are related to tidal flat, lagoon, shoal and open marine environments. Examination of vertical and lateral facies changes and thire comparison with their modern and ancient counterparts, all indicate that Kangan Formation were deposited in a shallow carbonate ramp platform similar to the present day Persian Gulf. The sequence stratigraphic studies showed that the Kangan Formation consists of two third order depositional sequences (in the A and B wells), each consisting of transgressive and highstand systems tracts. The lower boundary of the first sequence is a type 1 unconformity, but other boundaries are type 2 unconformity. Typical reservoir zone in the Kangan Formation is dominated in early highstand systems tract deposits and concentrated in shoal grainstone facies. However, in this paper, typical intervals such as sequence boundaries, maximum flooding surfaces, stacking patterns and system tracts were studied.
F. Khoshbakht; H. Memarian; M. Mohammadnia
Abstract
Natural fractures are the main factor which control hydraulic behavior of oil and gas reservoir in naturaly fractured reservoirs. Thus it is important to fully characterize these features in fractured reservoirs. Image logs are one of powerful tools in fracture study in wells. Image log is high ...
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Natural fractures are the main factor which control hydraulic behavior of oil and gas reservoir in naturaly fractured reservoirs. Thus it is important to fully characterize these features in fractured reservoirs. Image logs are one of powerful tools in fracture study in wells. Image log is high resolution “pseudo picture” of borehole wall which records properties of fractures. In present study, FMI (Formation Micro Scanner) of two wells located in the same structural setting of a naturally fractured carbonate are considered. Well A and B drilled through three formations (Asmari, Pabdeh and Gurpi) and fracture data of these formations were acquired from these wells. Both wells located in the same structural setting near each other. We compared fractures of each formation in well A with well B to find out similarity and dissimilarity of fractures occurd in the same formation in different wells. This study shows that density and orientation of bedding planes of well A is completely similar to well B. Density of open fractures of well A is totally different from well B but orientations of open fractures are same in two wells. Density and orientation of filled fractures of well A are similar to well B. Pattern of fractures of Asmari and Pabdeh formations are similar but in Gurpi fractures are different. Comparison of density of bedding planes and fractures show that high fracture frequency occurred in the thin beds, for example FMI show that laminar intervals of Pabdeh coincide with highly fractured intervals.
Stratigraphy and Palaeontology
mahdi badpa; Hamed Yarahmadzahi; Kaveh Khaksar
Abstract
The Anarak Group with Zaladu (Gzhelian-Asselian age) and Tigh-e-Madanu (Sakmarian age) formations in the Ozbak Kuh Mountains (Central Iran) is more than 180 m thick and includes thick units of conglomerate, shale, sandstone, calcareous sandstone, sandy limestone, fusulinid limistone, marl and dolomite ...
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The Anarak Group with Zaladu (Gzhelian-Asselian age) and Tigh-e-Madanu (Sakmarian age) formations in the Ozbak Kuh Mountains (Central Iran) is more than 180 m thick and includes thick units of conglomerate, shale, sandstone, calcareous sandstone, sandy limestone, fusulinid limistone, marl and dolomite layers. In the sequence of Zaladu formation, the accumulation of coral species of Pseudozaphrentoides winsnesi Flügel, 1995, was abundantly identified in two horizons in the upper part of the Ghezelin layers. Based on fuanal composition, diversity and abundance, spacing of corallits and microfacies, the mentioned accumulation is categorized as low-level (of Type A, ecological zone of A2). This zone represents a tough ecological condition where only a limited number of solitary corals could have survived the life-threatening factors. Based on microfacies studies, the coral community was identified to be restricted to the shoal and around it (lagoon toward shoal and open sea toward shoal) in a shallow platform.
T Akbari; L Bakhshandeh
Abstract
Based on stratigraphic value of calcareous nannoplanktons in determing the age of sedimentary layers, they have been used for biostratigraphic studies of Surgah Formation in sadd Ilam (Ilam damp) section ,Kabir –Kuh of Ilam. This formation is composed mainly ot dark gray shales. In Type section ...
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Based on stratigraphic value of calcareous nannoplanktons in determing the age of sedimentary layers, they have been used for biostratigraphic studies of Surgah Formation in sadd Ilam (Ilam damp) section ,Kabir –Kuh of Ilam. This formation is composed mainly ot dark gray shales. In Type section , the thickness of the Surgah Formation is 153.7 m. 109 samples were taken from shaly layers and for the first time their calcareous nannofossils were studied.The result of taxonomic studies lead to identification of 16 family , 44 genera and 80 species. Based of first occurrence of the index species and the assemblages zones is nannofossil Zones CC13-CC15 or Uc 8- Uc 12 of standard pattern. Based on biozone,the Upper Cretaceous sediments in the study area are of the Turonian through Early Santonian ages.
Economic Geology
Mitra Eftekhari; Mohammad reza Hosseinzadeh; Mohsen Moayyed
Abstract
The Studied area is located in vicinity of the Sherbit village, about 28 km to the northwest of Ahar (in Eastern Azerbaijan province. Quartz monzonite intrusion is the host rock of hydrothermal tourmaline in this area. On the basis of their textural features, the tourmalines can be divided into four ...
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The Studied area is located in vicinity of the Sherbit village, about 28 km to the northwest of Ahar (in Eastern Azerbaijan province. Quartz monzonite intrusion is the host rock of hydrothermal tourmaline in this area. On the basis of their textural features, the tourmalines can be divided into four groups: 1) tourmaline veins, 2) tourmaline-breccias, 3) massive tourmaline and 4) pore space filling tourmaline. Based on the petrography and electron microprobe analysis studies, tourmalines of Sherbit area are correspond to intermediate schorl-dravite with more tendencies toward dravite composition and have been formed in hydrothermal conditions. According to reasons such as more Mg values compared to Fe, low Al amounts, fine scale zoning, content of fluorine, tendency toward outer side of alkali- and proton-deficient vectors and lack of negative correlation between Fe and Mg. Separated tourmaline from the quartz– tourmaline vein shows a very similar pattern to the quartz monzonite samples, which are characterised by a pattern with depletion in HREEs relative to LREEs. It can be concluded that REE concentrations and patterns of tourmaline from the different studied tourmaline rocks are controlled by the host rock and not by the hydrothermal fluid causing boron metasomatism.
M. A. Dezfoolian
Abstract
Lithology Prediction is a fundamental stage in petroleum engineering and formation evaluation. This research is a type of artificial neural network modeling in order to use well bore logs in lithology prediction in a South Pars hydrocarbon reservoir. Here, two networks with three-layer back propagation ...
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Lithology Prediction is a fundamental stage in petroleum engineering and formation evaluation. This research is a type of artificial neural network modeling in order to use well bore logs in lithology prediction in a South Pars hydrocarbon reservoir. Here, two networks with three-layer back propagation (BP) method and Levenberg-Marquwardt algorithm have been used for lithology estimation. The network in the first stage, utilized gamma-ray, neutron, density and photoelectric effect (PEF) logs as inputs. On the other hand, the data of sonic log has been also added to the inputs and the results of the two stages have been compared in the second network. Considering the excessive coring expenses, this method can be used as a milestone in decreasing the coring expenses. In this paper, the following procedure is considered first, data from four wells in South Pars field has been used. Second, the network has been trained in one of the reservoir wells (well C) in which core analysis data was available. Third, in another well (well D) which its data does not affect the training process, it has been tested. Forth, after approching to the desired level of confidence in network efficiency, it has been utilized to estimate the lithology in the two other wells (wells A and B). lithologies investigated interval consist of: Dolostone, Limestone, Dolomitic Limestone, Limy Dolostone, Anhydrite, Shale, Shaly Limestone and Shaly Dolostone. In the first case, the mean square error (MSE) for well A was 0.081 and for well B was 0.094. In the second case, the sonic log was added to other input, MSE has become 0.051 in well A and 0.063 in well B. Comparing two cases, it was revealed that the model accuracy has been improved significantly in the second case and sonic log data caused the estimated lithology become closer to the real case.
Seyed Javad Moghaddasi; Y. Negahban
Abstract
Robat Karim manganese deposit is located in 7 km northwest of Robat Karim (southwest of Teharan), within northeastern margin of Orumiyeh-dokhtar volcanic belt. Based on regional geology, the studied area is situated in the northern Saveh Eocene volcanic assemblage, composed of rhyolite, trachyte, andesite ...
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Robat Karim manganese deposit is located in 7 km northwest of Robat Karim (southwest of Teharan), within northeastern margin of Orumiyeh-dokhtar volcanic belt. Based on regional geology, the studied area is situated in the northern Saveh Eocene volcanic assemblage, composed of rhyolite, trachyte, andesite and basalt. Manganese mineralization is occurred as veins, in faults, joints and fractures that crosscut the volcanic rocks. According to mineralogical studies, the manganese ore of the studied area is composed of pyrolusite, psilomelane, ramsdelite and hollandite, as well as calcite and quartz. Intergrowths of manganese oxides and quartz (or calcite) associated with various open space filling textures support the epithermal origin of the ore forming fluids in this area. Geochemistry of major and trace elements in Robat Karim manganese ores, similarity of their chondrite normalized REE pattern with volcanic host rocks and other hydrothermal manganese deposits of the world, as well as negative Ce anomaly indicate a probable epithermal origin of the deposit. Ore forming fluids could be originated from meteoric and/or magmatic waters circulating through Eocene volcanic rocks, dissolve manganese and other metals and deposit them in fault planes and major fractures. High pressure of the ore forming fluid has caused the formation of brecciated trachyte.
F. Motaki; H. Motamedi; N. Dehbashi
Abstract
Goshtasb anticline is situated in southeast of Shiraz. The dimension of this anticline is about 54 km length and maximum width of 7 km in the level of the Asemari–Jahrum carbonates exposure. The general trend of the structure is NW-SE which swings to an E-W trend in its eastern plunge possibly ...
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Goshtasb anticline is situated in southeast of Shiraz. The dimension of this anticline is about 54 km length and maximum width of 7 km in the level of the Asemari–Jahrum carbonates exposure. The general trend of the structure is NW-SE which swings to an E-W trend in its eastern plunge possibly offsetted by branches of the Sarvestan fault. The northern flank of the anticline is steeply dipping to overturned whereas the southern flanks dips about 25-35, and therefore the anticline shows a distinct asymmetry to northeast in surface. In this research we show that this geometry is a result of activation of intermediate detachment levels in the stratigraphy succession specially Triassic evaporates of the Dashtak Formation, and the surface culminations of this anticline are merged together at depth to form a single structure (the Mozaffari anticline) in the Dehram level below the Dashtak Formation. In this research, an integration of field survey and available subsurface combined with modern structural ideas have been used to study of the geometry of the Dehram horizon. For this purpose, 6 geological cross sections with the total length of 147 km and one 51-km-long longitudinal section have been constructed. Also an underground contour map of the Dehram horizon is produced using structural cross sections. According to this map, the areal and vertical closure of the Goshtasb anticline is 11.5X47 km² and 2000 m, respectively.
