JOURNAL OF SCIENCE (UNIVERSITY OF TEHRAN) (JSUT)
Year:2008 | Volume:34 | Issue:1|Papers Count:18

The studied area is situated in Ardebil province and in NW of Meshkin-shahr. From the structural point of view the area is part of Azerbaijan zone, and potassic rock of the area are quite vary in types, which are also known in other parts of Azerbaijan, aging middle-Eocene (Miocene?). Leucite bearing potassic rocks of the area consist of: leucitite, Thephrite and Phonolitic tephrite. Leucite as the indicator mineral of the rocks is present as small and large sizes grains. The rocks are enriched of LILE and depleted of HFSE. The most remarkable process of the area is the strong alteration of the rocks, which is resulted in a wide range of variations of the area particularly on those which were ready to change. Alteration of the area consist of three types or zones; Argilic, Alunitic and Silisic.

This study has been carried out in order to evaluate the relations between reservoir parameters by using classification of carbonate reservoir rocks to hydraulic flow units. As generally there aren't simple relations between porosity, permeability and electrical resistivity, in this study we show that by experimental measurements on some plugs which were taken from carbonate reservoir and by grouping and sorting data into hydraulic flow units we are able to establish good relationship between porosity, permeability and formation resistivity factor. Hydraulic flow units were calculated from measured porosity and permeability. The correlation between porosity and permeability is significant within each hydraulic flow units and correlation coefficient between permeability and formation resistivity factor is considerable in each hydraulic flow units. (The correlation coefficient (R2) lies in the range of 0.61 to 0.79). This correlation is an extension of the match between porosity and permeability within hydraulic flow units such that relation between permeability and formation resistivity factor is improved more than relationship between porosity and formation resistivity factor. Also we show that for porosity less than 7.5%, there is a linear relation between cementation factor and porosity and the scattering of cementation factor is in an inverse manner with flow zone indicator.

Different types of dolomitic carbonate rocks of Upper Cretaceous which are located in northeast of Shahmirzad, Centeral Alborz, hosted many lead-zinc deposits and occurrences. In this study 5 profiles of carbonate rocks of abandoned lead-zinc mines from Reza-Abad, Heydar-Abad and Reza-Barak have been selected. petrogenesis and composition of dolomites have been studied employing equation N CaCO3 = md + b, using stained thin sections, XRD graphs, Wet chemical analysis and XRF. Dolomites of this region are categorized in to 3 groups due to amount of calcium carbonate in which ranges from 49.5-51.5%, 51.5-53.5% and 53.5-55.5%.respectively Considering a/m studies, six types of dolomite textures have been recognized, which according to growth sequence of dolomite crystals in time, are consist of: Xenotopic A, Idiotopic E, P, S, C and Saddle dolomite. The decreasing of Na2+ and Sr2+ that create along diagenesis and increase crystal size, has not observed because of the influence of hydrothermal fluids on Cretaceous sequences. The amount of Fe2+ and Mn2+ are higher in dolosparite in comparison with dolomicrosparite. Considering the changes the amount of Fe2+, Mn2+ and Sr2+ in the composition of dolomites along profiles, it may be that there had been a flowing fluid from north to the south in accordance to Anzab Fault. Taking in to consideration the data gathered in the studies, the several-stage dolomitization in the region should be related to the early and late stage diagenesis. This may be due to sea and meteoric waters, basin waters, saline waters and influence of hydrothermal fluids. This phenomena occure during Cenozoic that may be associated with Eocene volcanic activities, which was affected to the Upper Cretaceous sequences.

This paper discusses the results of the engineering geological investigation and geotechnical studies carried out at the proposed Khersan 3 dam site. The dam will be built on Khersan River, is located about 50 km of west of Lordegan city in west of Iran. The dam is mainly founded on sedimentary rocks of the Tercier age and on Quaternary deposits. Geotechnical information obtained from both at the field and the laboratory studies. Field studies include engineering geological mapping, surface discontinuity mapping, drilled borehole and sampling for laboratory testing. Samples obtained from drilling were tested in the laboratory, included of uniaxial, triaxial and tensile strength tests and deformation parameters, unit weight and porosity. Rock mass classifications of the dam site rock units have been performed according to RMR (Bieniawski 1989), Q(Barton et al., 1980) and GSI systems (Hoek and Brown 1997). A detailed geological and geotechnical study was carried out in the project area to determine the engineering geological characteristics of the rock masses. In the study, rock mass properties was classified using Geological Strength System (GSI), and the Hoek-Brown equation was used to obtain rock mass strength parameters and modulus of elasticity. Finally, regarding to instability analysis in tunnel axis and probably instability wedges, suitable software based on finite element method has been used.

Barika gold mineralization occurred in a Cretaceous metavolcano-sedimentary sequence at northwestern Sanandaj-Sirjan zone. Major units in this area include Cretaceous Submarine volcano-sedimentary rocks. Host rock of mineralization is rhyolite to rhyolitic tuff unit which is completely in Barika shear zone. Mineralization occurred as lenticular ore bodies that has developed parallel to Barika shear zone foliation. Mineralization from footwall to hanging wall consists of: 1- Silica-Sulfide zone, which includes two part, pyrite-rich part and quartz with sulfide veins that crossed with shear zone foliation. Gold grade in pyrite-rich part is between 0.02 to 5 ppm and in quartz sulfide-bearing veins is between 0.05 to 0.5 ppm. 2- Sulfide and sulfosalt-rich zone. This zone contains of two part, pyrite-sphalerite-sulfosalt and massive pyrite part. Gold grade in this zone is 0.02 to more than 100 ppm. 3- Massive barite ore zone. This zone included of some barite lenses that longer lens has 10 thickness and about 60 m length. This zone is contained two parts, a sulfide and sulfosalt-rich part and sulfide and sulfosalt-poor part. Gold grade in sulfide and sulfosalt-rich part is between 0.02 to 25 ppm. Major minerals in mineralization zones are pyrite, sphalerite, galena, tetrahedrite-tenantite, bournonite-boulangerite, twinnite-veenite, stibnite, electrom, chalcopyrite and covelite. Electron microprobe studies on different minerals showed that gold occurs as electrom, and in minerals compose such as pyrite, galena and sulfosalts. The most important characteristics of mineralization of the Barika gold mineralization such as tectonic setting, host rocks, mineralogy, metal contents and metal zonation, wall rock alterations, shows similarities with gold-rich volcanogenic massive sulfide (VMS) deposits, e.g. , Rosbery, Hellyer and Que River deposits in Tasmania and some Kuroko type deposits at Hokuroko Basin, Japan.

Elika Formation at the Tash section (300 m in Thickness) is one of the most complete sections in the eastern Alborz basin. Petrographic studies indicate that carbonate sediments of the Tash section could be divided into several groups of microfacies which has been formed in four sub-sedimentary environments, including: Tidal flat, Lagoon, Bar and Open marine. The absence of reef and resedimented facies indicates that the carbonate platform of the Elika Formation is similar to the recent Persian Gulf shelf (Ramp). Field and laboratory studies showed that the sediments were composed of four third-order depositional sequences.

The main reservoir facies of the Upper Dalan Member consists of grain-supported ooilithic facies. This facies has been studied in terms of reservoir characterization and a core interval of the Upper Dalan Member (about 272m thick) was studied in the subsurface section of the Persian Gulf. According to sedimentological study, the facies can be subdivided into three microfacies; fine-grained peloid / ooid grainstone, medium-grained ooid grainstone and coarse-grained intraclast / bioclast ooid grainstone. These facies belong to lower intertidal (beach ridge) and oolithic-bioclastic shoal sedimentary environment. Effective factors on the reservoir subdivided into two sets; textural and diagenetic factors. Some cross plots and petrographical studies showing the significant effects of each parameter on the reservoir. Textural factors consist of grain size, grain shape, sorting and fabric and diagenetic factors as negative and positive effects includes of compaction, cementation, dissolution, dolomitization, anhydritization and fracturing.

Kashafrud Formation in the Ghale Sangi Section (east of Mashhad), has been selected and measured for palaeoecological studies. Moderately diverse and reasonably well-preserved palynoflora occurred in the middle to upper parts of the Ghale-Sangi Section (with a thickness of about 1090 meters). In this section, the Kashafrud Formation overlies with a strong angular unconformity Sina Formation and it is disconformably overlain by the limestone of Mozduran Formation. In this study 60 species of spore (distributed among 36 genera), 22 species of pollen (distributed among 12 genera), 19 species of dinoflagellates (distributed among 14 genera), 2 species of algal spores (distributed among 2 genera), 3 species of fungal spore (distributed among 3 genera) and 1 species of acritarch have been identified. Of these, the miospores are mainly radiosymmetrical and triletes, wheras the pollen are represented by monosulcate, monosaccate, bisaccate and three saccate taxa. Inferred natural relationship spores and pollen grains imply derivation from a diverse parental flora (e. g. Pterophyta, Bryophyta, Cycadophyta, Ginkgophyta, Coniferophyta, and Lycopodophyta). Furtheremore the abundance of Dictyophyllidites, Klukisporites and Cyathidites which are related to Pterophyta indicate the domination of Pterophyta suggestive a moist warm climate during Bajocian – Bathonian. The presence of some proximate dinoflagellates such as Sentusidinium villersense, Chytroeisphaeridia chytroeides, Lithodinia sp. cf. L. jurassica, Rhynchodiniopsis cladophora, Gonyaulacysta centriconnata, Pareodinia antenata, Pareodinia ceratophora, Cribroperidinium sp., Dichadogoyaulax culumula, Egmonthodinium sp. cf. E. polyplacophrum accompanied by fungal spores testified warm temperate conditions during Bajocian-Bathonian. The association of marine palaeontological evidence (amonites contents) and marine palynomorphs (proximate dinoflagellates, acritarch and foraminiferal test lining) with terrestrial palynomorphs (spores and pollen) collectively indicate an open marine, nearshore depositional setting for the Kashafrud Formation at Ghale-sangi Section. A detailed comparision of the Ghale-sangi palynoflora (east of Mashhad) with the Senjedac suite (southeast of Mashhad) indicates that, except for the presence of some different species, the two assemblages feature significant similarities and suggest a similar depositional and climate conditions in the east and southeast of Mashhad during the Bajocian-Bathonian.

Pabdeh Formation in Ivan- Gharb area comprises alternation of thin to thick limestones (mudstone, wackestone and packstone) and dark to light gray planktonic foraminifera bearing shale beds. Five ichnogenera, which classified in two ichnoassemblages, were recognized. The first ichnoassemblage with relatively high ichnodiversity (Arenicolites, Chonderites, Planolites and Neonerites) occurs in wackestone, mudstone and packstone facies. This assemblage of ichnofauna represents the Cruziana ichnofacies, formed in a relatively high energy condition. The second ichnoassemblage with lower ichnodiversity (Zoophycos and Chondrites) is found in shale, wackestone, mudstone and packstone facies and represents the Zoophycos ichnofacies which were formed in a low energy and deeper condition. Presence of horizons rich in organic matter (TOC>2%) in the middle and lower units of Pabdeh Formation containing Zoophycos ichnofacies, indicate an environment with low oxygen level.

At the southwest of Sanandaj (Sahneh-Marivan area), in the Zagros thrust zone, with NW-SE direction, some major intrusive bodies with basic to intermediate composition and minor acidic veins are intruded in the Cretaceous-Paleocene formations, causing contact metamorphism up to albite- epidote or pyroxene hornfels facieses. In addition to intrusive bodies there are minor outcrop of basic volcanic rocks. In southwestern margin of intrusive bodies some dismembered ophiolitic complex are outcropped along the Zagros thrust faults. The intrusive bodies and associated volcanic rocks are of Oligocene age. Chemical composition, especially the behavior of major, trace and rare elements indicate that these intrusions and related volcanic rocks are calc-alkaline to tholeiitic and generated from a heterogeneous mantle in an active margin. Age, chemical composition and tectonic setting of these rocks may indicate that after the breakdown of Neotethyan oceanic crust in the Late Cretaceous, the southwestern part of the oceanic crust was subducted beneath the northeast part of it, and Oligocene magmatism is outcome of such an event. If these inferences are rational, the final collision of Arabian and Iranian plates must be occurring in the end of Oligocene and the beginning of Miocene.

Fusulinacea are diverse and abundant in the Upper Carboniferous-Permian rocks of Tabas Block. The comparison between this region’s fusulinacea and Cimmerian Continent shows that during Upper Palaeozoic, Tabas Block was part of the west Cimmerian Continent. In the Cimmerian Continent, which the Tabas block is part of its west, the generic diversity of Permian fusulinacean fauna in space and time gradually increases from the Early to Late Middle Permian as well as from the eastern Cimmerian to the western areas. In contrast, the low generic diversity of Permian fusulinacean faunas in eastern Cimmerian against western ones is possibly due to an oblique placement of the continent to paleolatitude. Thus, the western Cimmerian Continent, compared to its eastern part, was closer to the tropical Tethyan. Based on the distribution of this fauna, the sedimentary succession of the studied area is subdivided into several sedimentary sequences including Late Ghezelian-Asselian, Bulurian, Kubergandian-Murgabian and Midian-Dourashamian in age.

Counterproofs changes in strontium isotopic ratios (87Sr/86Sr) in oceanic waters are not detectable because they occur very slowly. Strontium is incorporated into the calcareous structure of living organisms that eventually precipitate with other sediments. The 87Sr/86Sr of oceanic waters at different geologic times can be estimated by measuring this ratio in the calcareous shells of living organisms incorporated with sedimentary rocks. By studying changes in isotopic ratios of 87Sr/86Sr, comparable age correlation, similar to that from other conventional techniques can be established. By applying this study method, geologists, paleontologists and oceanographists have been able to find answers for many ambiguities. In this study, the strontium isotopic ratios for 201 cutting samples from Well Sulabdar#3 located in the southern part of North Dezful (from an interval with the age of Paleogene to lower Jurassic) were measured and a 87Sr/86Sr profile was established and compared with the world’s profile. Results show that there is a good correlation between the87Sr/86Sr data obtained for Paleogene-Jurassic sediments with the corresponding data reported for the evolutionary curve of the Phanerozoic seas.

The mentioned model is one of the statistical analysis methods for landslide hazard predication based on quantitatively defined weight values. The method used is called landslide index method. A weight – value for a parameter class, such as a certain lithological unit or a certain slope class, is defined as the natural logarithm of the landslide density in the class divided by the landslide density in the entire map. The method is based on map crossing of a landslide map with a certain parameter map, in geographical information system. The mentioned model is run in Amiry and Haftan subbasines. The output results has assessed base on Density ratio (Dr) index. Comparisons of the results with those of other researchers confirm the modeling efficiency.

In this study, 25 oil samples from different reservoir horizons in the Iranian oil fields located in the Persian Gulf were subjected to experimental analyses in order to determine carbon isotope signatures, API gravity, sulfur content and Ni/V ratio. Gas Chromatography and gas chromatography- Mass spectrometry techniques were used to identify and investigate characteristic biomarkers or fingerprints representative of origin, depositional environment, maturity and geological age. Based on distinct physical properties and representative biomarkers, the oil samples were divided into three major families including A, B and C in four different areas. The family A is characterized by carbonate source rocks. The families B and C are assigned to shaly-carbonate and clastic source rocks respectively. The family A is divided into two sub-families including a1 and a2. The sub-family a1 is related to the late Paleozoic to Mesozoic (Lower Jurassic) time interval, and the sub-family a2 is assigned to the source rocks formed during Paleozoic. The family B is divided into three sub-families namely b1 (Late Jurassic- Miocene), b2 (Late Paleozoic- Mesozoic (Lower Jurassic), and b3 (younger than Cretaceous). Moreover, the family C is divided into c1 (Late Paleozoic- Mesozoic: Lower Jurassic), and c2 (younger than Cretaceous) sub-families. This study indicates that petroleum systems in the study area show close similarities with that of the dominant petroleum systems in the neighboring countries; thus, it can be inferred that petroleum systems in this study share many common features by the petroleum systems active the in the Persian Gulf region.

Planktonic and benthic foraminifera were studied in a section, south of Ilam in order to assign palaeobathymetry and the changes through sedimentation course of the Gurpi Formation. The formation consists of 213m marl with intercalation of limy marl with two formal members of Seymareh (Lopha) and Emam-Hasan. The Seymareh Member is made up of Limestone and Emam-Hasan Member is argillaceous limestone. The formation was deposited from middle Campanian through late Paleocene according to the planktonic foraminifera recorded. For the benthic foraminifera, percentage of hyaline, agglutinated calcitic and noncalcitic also epifaunal and infaunal were calculated. A depth of over 800m was assigned for most parts of the formation according to planktonic/epibenthic ratio and the regression equation (D=e(3.58718+(0.03534x%P))). Study of depth indices benthic foraminifera also confirm the depth gained by the regression equation. The relative sea-level curve resulted in from this study is well in accord with the existing eustasy curves indicating the great effect of eustasy on relative sea-level changes against the other factors.