JOURNAL OF SCIENCE (UNIVERSITY OF TEHRAN) (JSUT)
Year:2006 | Volume:32 | Issue:2 (SECTION GEOLOGY 1)|Papers Count:22

Taknar Polymetal massive sulfide deposit is located at 28 km NW of Bardaskan within the Taknar inlier zone bordered with Doruneh and Taknar (Rivash) faults. Mineralization is dominantly hosted in Ordovician schists and has been dissected and displaced. The purpose of this research is to investigate and propose an appropriate geophysical exploration method for detecting new covered massive sulfide in the Taknar formation. Total Magnetic Intensity (TMI) was measured on a total of 10 survey lines in 300 points on Tak I, II and IV. This ground magnetic data showed very characteristic magnetic anomalies over surface mineralization on Tak I and U. Magnetic anomalies similar to Tak-I and II were observed in areas of Tak IV where mineralization is not seen on the surface. Mineralogical studies of samples taken from surface and old underground tunnel in Tak I and II showed variable amounts (5% to 65%) of magnetite along with sulfide mineralization. Country rock associated with mineralization has no magnetite. Measured Magnetic susceptibilities over schist samples as host rock in comparison with mineralized samples showed that the former is 1000 times weaker than the latter. This contrast is 10000 times between the massive part of mineralization and the country rock. Consequently there is a direct relation between magnetic anomaly and mineralization. Therefore, the strong contrast between the amount of magnetite in the deposit and host rock makes Taknar mineralization an ideal target for magnetic method. Quantitative interpretation of measured magnetic anomalies on Tak I assuming zero remnant components, constraining the depth to the top of the causative body to the surface on the basis of field evidence and susceptibility is constrained to the average range of the measured samples showed that the depth of the source extends to 147 meter. Comparison of magnetic anomalies on Tak I obtained from this research with the previous work of reported IP showed that these two anomalies are spatially coincident, but the former is larger in extension and amplitude than the latter. It is concluded that magnetic method is more effective and less expensive than other geophysical methods for discovery of similar massive sulfide mineralization in the Taknar zone.

Dezful Embayment located in Southwest of Iran is one of the most potential areas for exploration and development of hydrocarbon reservoirs in the world. There are several source rock units with different geological ages. Burial and thermal history modeling was performed to determine timing of hydrocarbon generation in the Pabdeh source rock in Dezful Embayment. Geology and sequence stratigraphic analysis of borehole data including drill-cuttings provided fundamental constraints for burial history reconstruction. In addition, estimates of exhumation from log-derived compaction data provide key insight into depositional patterns. One-dimensional and two-dimensional models of thermal evolution were derived from the burial history and calibrated with vitrinite reflectance, thermal conductivity, surface and bottom-hole temperature measurements, as well as with paleoclimate data. The resulting thermal history models were combined with the measured geochemical parameters in order to determine the timing of hydrocarbon generation for the candidate source rock (Pabdeh Formation). Results were compiled in maps and cross-sections representing multiple stages of basin evolution. Most hydrocarbon generation in the Dezful Embayment generally took place in Kazhdumi Formation and partly in Pabdeh Formation. The Pabdeh Formation is the youngest source rock in Dezful Embayment with type II and a mixture of type II and III Kerogens and has reached oil generation at most parts of the Dezful Embayment. Higher amounts of hydrocarbon were generated at deep and central part related to higher maturity levels. Based on thermal maturity modeling, Pabdeh Formation is early mature to mid mature.

A total of 66 surface samples from the Mila, Lashkarak and Ghelli Formations of Kuh-e-Kharbash (near Deh-Molla) were paleontologically investigated, to determine the geological age of the rock units. This study was also undertaken to assess the palaeogeographic relationships of the study area to Southern and Northern Hemispheres during the Palaeozoic interval represented by these Formations. Fifty two palynomorphs (51 acritarchs and one algal body) were recorded, which permit the recognition of six acritarch-based biostratigraphic zones. Acritarch assemblage zone I is Late Cambrian in age and occurs in the upper part of the Mila Formation. Assemblages zones II through IV are present in the Lashkarak Formation and suggest Lower Ordovician (Tremadoc-Arenig). Assemblage zones V and VI are presentin the Ghelli Formation and indicate Upper Ordovician (Caradoc-Ashgill) for this Formation. Based on palaeontological data, two hiatuses are present within the studied stratigraphical column. The first hiatus occurs between the Lashkarak and Ghelli Formations and encompasses the Middle Ordovician strata. The second hiatus is present between the Ghelli and Geirud Formations and includes the whole Silurian and Lower-Middle Devonian deposits. The above- mentioned hiatuses possibly correspond to the Caledonian Orogeny. Diverse acritarch assemblages in the Late Cambrian (Mila Formation), Lower and Upper Ordovician (Lashkarak and Ghelli Formations) indicate that a marine environment through the entire succession. Comparison of the acritarch recorded taxa with those reported from other parts of the world, suggests that the Alborz Mountain Ranges have been part of peri-Gondwanan palaeoprovince during the Ordovician.

On the basis of field observations, petrographic evidences and chemical data two types of sodiccalcic and potassic alterations have been identified in the center and margin of the Panj-kuh intrusive body, respectively. Development of albitization on the corner of plagioclase crystals, presence of albite with chess board twining, scapolitization of plagioclase, high sphene and apatite content comparing with fresh igneous protolith and a general absence of magnetite are the most important evidences of sodic-calcic alterations in monzonitic rocks. Potassic alteration is defined by the presence of the shreddy aggregates of hydrothermal biotite and replacement of plagioclase by K-feldspar. Some elements such as Na2O, CaO, MgO, TiO2, P2O5, Sr, V and Sc are increased in sodic - calcic alteration at the same time as K2O, FeQ, Ba, Zr and Rb show decrease, whereas, potassic alteration show reverse trends. These evidences indicate that some elements such as Fe, K, and so on, leached from sodic-calcic zone and transported to the potassic zone by hydrothermal fluids.

Two stratigraphic sections in the Chaman-Bid Formation east of Mashhad have been measured and their ammonite fauna studied. These comprise 11 taxa coming from Narband and Radar sections. Based on ammonites the stratigraphic range of the Chaman-Bid Formation at Narband section is Bathonian to Oxfordian and at Radar section late Bajocian to Callovian. The ammonite fauna corresponds more or less to those reported from Alborz and Central Iran, which indicates that the basins of Koppeh-Dagh, North and Central Iran were connected to each other. The studied ammonite fauna shows close relations to the same-aged ammonites of Europe, especially to the Sub-Mediterranean Province.

Identifying reservoir rock types and their most significant vertical and horizontal heterogeneities is an essential component of reservoir characterization process, which are among the key input parameters in to a three-dimensional geological and flow simulation models. A reservoir classification and rock typing study were carried out on the Asmari formation of a mixed siliciclastic and carbonate reservoir in Iran. Detailed core analysis data including capillary pressure, core porosity, core permeability and core description supplemented by well logs revealed a complete vertical sequence of seven distinct clastic and carbonate reservoir rock types. Identification of the reservoir intervals and pay zones was carried out by means of the above results. Core based reservoir rock types were examined for each cored wells and log based reservoir rock types were selected and assigned in the uncured wells. The above data were applied as input parameters in a method based on Fuzzy Logic inference. The Fuzzy Logic technique was calibrated in 4 cored wells and blind tested in the other cored wells to determine the reservoir rock types. After the secondary calibration of the Fuzzy Logic against the core data, this technique was applied on 28 wells without any core data. The results reveal a very good match between the core data analyses and the Fuzzy Logic determination of the reservoir rock types. This technique can be applied to reduce the uncertainty of determination of the rock typing or as a very good predictor in uncured wells.

The Nain ophiolitic massif, in the north of Nain town, consisted in lhezolitic-gabbroic (pegmatitic) bodies. Harzburgites, amphibolites, isotropic gabbros, pillow lavas, gabbroic sills and dikes, pyroxenitic dikes, wherlitic dikes and gabbroic impregnations are also found. The crustal sequence is thin and is composed of limited volumes of pillow lavas and isotropic gabbros that gradually terminate into pelagic limestones and charts in the upper levels. Amphibolites can be divided into garnet amphibolites with hornblende lineation, amphibolite mylonites with amphibole stretched lineation and non-foliated massive amphibolites. The other metamorphosed units are spillites that include spillitized pillow lavas, diabases, isotropic gabbros and tuffites-tuffitic sandstones. Meta-gabbros associated with meta-peridotites and serpentinites are the abundant metamorphosed units of this massif. Pegmatitic gabbros are uplifted as melt mush in which the high plastically deformed clinopyroxenes can corroborate this hypothesis. Wherlitic dikes show shear or stress localization in the shear zones. The higher values of Cr and MgO# in isotropic gabbros than in basaltic rocks represent the equilibrium of gabbros with upper mantle peridotites. The clutter and fragmentation of this massif, also the thin crustal sequence, the volumetric serpentinites with intermingled exotic blocks of limestone, the heterogeneous plastic behavior of deformed minerals in mantle sequence and other factors demonstrate the derivation of this massif from the paleo-transform fault. We consider that this paleo-trans form fault belongs to a slow spreading oceanic ridge.

Ieriodus and Polygnathus faunas from the Late Devonian of the Tabas region of eastern Iran, and from the Middle- Late Devonian of the Alborz Mountains, northern Iran, are documented. Twenty three species and/or subspecies of Icriodus and 33 of Polygnathus are described and illustrated. Among them are five new species of Icriodus: IC. housei, IC.talenti, IC.bultyneki, IC. walliseri and IC. jafariani.

This paper presents the results of engineering geology and geotechnical studies in the Hamadan city. The methodology of this research work was English Abstracts of Farsi Papers getting data from geotechnical reports of the previous works and engineering geology studies, which have been done by authors. This is the first geotechnical report from the area, which has an overall view to the soils profile and foundation of the Hamadan city. In order to study quaternary non-cemented alluvials in this area, a South-North section with a length of 14 Km from Hamadan Plain was chosen. This section started from Dareh- Moradbeig to the end of Hamadan Airport. Based on the field and laboratory studies, conditions and texture of the alluvial and foundation of Hamadan city were considered. As a result, non-cemented alluvial in this area were studied in details and a geotechnical profile of the soils in this section was prepared. Results of this research work as a geotechnical profile of soil and foundation of Hamada city can be used for engineering constructions in the study area. It should be noted that, this profile is introduced from the study area forth first time.

The theoretical best-possible resolution can be predicted using Beylkin's formula. This formula gives answers to the effect on resolution of frequency, aperture, offset, and acquisition geometry. In this paper, for each 3-D single-fold data seta spatial wavelet is obtained from migration of an event that attributed to diffraction. Then the width of the spatial wavelet is compared to the resolution predicted by Beylkin's formula. The measured widths confirmed the theoretical predictions (i.e. zero-offset data produces the best possible resolution; 3-D shot records produces the worst resolution, and common-offset gathers and cross-spreads producing the intermediate resolution. It is shown that the effects of sampling and fold cannot be derived directly from Beylkin's formula; these 79 effects are analyzed by looking at the migration noise rather than width of the spatial wavelet. Our results indicated that random coarse sampling may produce somewhat less migration noise than regular coarse sampling, though it cannot be as good as regular dense sampling. Generally speaking, increasing fold does not improve the theoretically best possible resolution. However, as noise always has a detrimental effect on the resolvability of events, fold by reducing noise will improve resolution in practice. Required algorithms were written by authors in MATLAB environment.

Reservoir zonation is the most important job in oil industry which dominantly relies on the major properties of rocks. Fundamental properties of rocks are usually understood by their detailed description in the field (lithofacies analysis) and laboratory (petrofacies analysis). The facies (lithofacies and petrofacies) determination in most subsurface studies is impractical, due to lack of cores and cuttings. In such situations, where the wire line logs are the only data available, the logfacies or electrofacies are determined instead. Using multivariate cluster analysis, in this study practiced the logfacies determination on the Asmari Formation of Marun Field by programming new algorithm with MATLAB software the study is carried out on the logs of a well in which the Asmari Formation is fully cored. Determined logfacies are correlated with lithofacies defined on the cores and thin sections. Reliability of the procedure in logfacies determination is examined and an appropriate cut off level is defined for the cluster analysis. Result from this study is prepared to use in logfacies determination of the adjacent wells with no cores and cuttings.

The Salafchegan quartz diorite intrusion (Aleh Mountain) has intruded the sandy-limestone and sandstone of the Upper Red Formation as a concordant pluton and has metamorphed its country rocks slightly. The gentle dip of the sedimentary layering of country rocks suddenly increases near the pluton contact to a vertical position. This body has a circular shape, composed of quartz diorite and structurally could be divided into outer and central parts. While the outer part, with 500 meter thickness, shows alternation of leucocratic and melanocratic layers, the central part has a massive outcrop. Both outer and central parts of this pluton show porphyritic texture typical of subvolcanic rocks. Moreover, the absence of ductile deformation within contact metamorphic aureoles, the presence of reverse faults surrounding the intrusion, the occurrence of concentric layering in the eouter parts of the pluton, and the existence of magmatic foliation parallel to the contact zone in the outer dioritic layers could demonstrate ballooning mechanism in the Salafchegan intrusion. Accordingly, this pluton emplaced by ballooning mechanism due to repeated 80 forceful injections of magma into an expanding shallow magma chamber, in the upper crust.

A 2.5x10 km body of NE-trending mylonitic granite is exposed north of Aliabad-e-Damag, 35 km south of Hamadan. Mylonite and the surrounding schists have concordant fabrics parallel to the dominant foliation in the region. Structural and fabric analysis suggests deformation in a dextral strike-slip shear zone. The strong deformation and associated low grade metamorphism were coeval with plastic intrusion and continued to the end of crystallization. The granite has a retrograde thermal effect on the surrounding metamorphic rocks. Sigmoidal geometry of the large Hamadan pluton and the position of the dextral shear zone at the southeastern part of this system indicate the significance of dextral transpression tectonic in this region of the Sanandaj- Sirjan zone and rotation of the shear fractures in emplacement of the Aliabade-e-Damag pluton and subsequent intrusion of the Hamadan batholith.

The Mid-Cretaceous succession in west of Kerman city is represented by distinctive, correlatable green marls rich in macro and microfossils. The marls can be assigned an Upper Albian to Lower Cenomanin age based on the associated macrofossils assemblage, which is dominated, by molluscs and echinoids. Six species of echinoids are described all of which are new records for the region Pliotoxaster sp. together with Exogyra spp. Dominates macro fauna assemblage. Many of the taxa have previously been reported from Oman, Egypt and Jordan. The fossil assemblage indicates favorable condition during deposition of the green marls.

The area of study is located in NW of Zagros fold-thrust Belt, between Kazerun and Balarud faults (Dezful zone). This part of the belt shows a complex structure, is affected by subsurface lineaments possibly during late Alpine orogeny. Detail assessment of landsat images together with geomagnetic and earthquake data resulted in identification on subsurface shear-transverse faults. Two sets of such transverse faults were identified using curved geometry of foreland folds and geometry of newly developed folds. First set, oriented NNW-SSE shows right-lateral strike-slip movement and developed more than that of the second set, oriented NE-SW and demonstrates left-lateral strike-slip movement. There are similarities between the orientation of these lineaments with the geomagnetic fault lineaments which identify basement faults in the Zagros and northern margin of the Arabian platform. This, together with depth of the earthquakes, related to reactivation of these fault English Abstracts of Farsi Papers lineaments, implicitly reveals that these fault lineaments are likely deep seated basement faults. Most of these lineaments were not identified and cannot be seen on the same scale geological maps. This demonstrates the significance of implication of landsat images and aeromagnetic data on verifications of such deep seated fault lineaments. It is proposed that newly generated folds by these basement fault sets, can be a prospective goal in hydrocarbon exploration in Zagros foreland fold-thrust Belt.

The foraminiferal content of the Gurpi Formation at the type section in Anbar Sefid Valley NE of Lali city in Masjed Soliman was studied. The recorded foraminifera indicate an age of Late Paleocene for the upper boundary of the formation that turns to purple sandy and silty shales at the base of the Pabdeh Formation. The K/T boundary lies 57m below the purple key layers. The Study of the foraminifera at the K/T boundary demonstrates that the specialist polytaxic species with large size and complex morphology (such as pseudotextularids, rugoglobigerinids and globotruncanids) which were sensitive to changes in environmental condition disappeared, while generalist oligotaxic species with small size, simple morphology and fine shells (such as hedbergellids and heterohelicids) became dominant. As the changes in fauna's composition are usuallyraised from ecological factors, thus the changes in the most important ecological factors such as salinity, temperature, Oxygen, PH, subsurface currents and nutrient supply have been evaluated to interpret the changes in faunal composition. Definite decreases in temperature, salinity, xygen amount and pH and increase in sea current and nutrient amount have been concluded as the most important factors effecting faunal changes across the K/T boundary. These changes in ecological factors might have been results of an increase in upwelling currents generated in Early Paleocene preceded by a regression at the end of Cretaceous.