JOURNAL OF SCIENCE (UNIVERSITY OF TEHRAN) (JSUT)
Year:2006 | Volume:32 | Issue:3 (SECTION GEOLOGY 2)|Papers Count:20

Meyghan area is located 34 km north of Shahrud. The measured and studied strati graphical column is mainly composed of limestone, argillaceous limestone and shale. The brachiopods of stratigraphical column of Meyghan area were studied and resulted in 50 species such as Ripidiorhynchus elburzensis, Spiatrypina chitralensis, Cyphotherorhynchus arapaensis, Pampoecilorhynchus arianus, Leptocaryorhynchus jamensis, Schiziphoria impressa, Aulacella interlineata, Cleiothyridina coloradensis, Paurogastroderhynchus bikniensis, Athyis tau, Araratella dichotomians assimulata, Megalopter.orhynchus chanakchiensis, Prospira struniana. Based upon their stratigraphical distributions, the encountered brachiopod species are divided into three biozones. The biozone I is marked by brachiopod genera such as Ripidiorhynchus and Spiatrypina and indicates the middle-late Frasnian. The biozone 2 is characterized by the brachiopod genera Pampoecilorhynchus and Leptocaryorhynchus, suggesting the early-middle Famennian. The biozone 3 is introduced by brachiopod genera, consisting of Paurogastroderhynchus, Megalopterorhynchus and Athyris, representing the Late Famennian. Based on the above-mentioned biozones, the uppermost part of Khoshyeilagh Formation is assigned to the late Famennian (Strunian) in the Meyghan section. Furthermore, there is a sedimentary horizon at the top of Khoshyeilagh Formation, which contains iron-stained brachiopod and other shelly fauna such as ammonoids. Such a phenomenon corresponds to the global Annullata event (Hembergian, IV-A zone) which has also been reported from other countries such as China and Morocco.

Fourteen seismic-reflection profiles of northeast Ramsar, SW Caspian Sea, were investigated to define seismic fades, depositional processes and potential stratigraphic traps below the Upper-Pliocene time-line reflector. Four seismic fades were defined: I) parallel layered fades, 2) chaotic fades, 3) mounded fades, and 4) protruding fades. The parallel-layered fades is the most dominant, its continuity increases basin ward. The chaotic facies mainly occur as shale diapires which were intruded into the overlying sediments. The deep-water deposits are the mounded and prograding fades which are related to deltaic processes and occur north of the study area. Various internal reflection patterns of the mounded fades indicate different processes were active during their formation. Potentia l stratigraphic trapsmay be found in sediment mounds, buried channels, prograding clinoforms and debris-flow lobes, among which sediment mounds are more significant. The largest mound is 18.8 km wide and 480 m high.

The present study shows the results of the integrated geophysical and geological work carried out in the Abadan Plain and the North Persian Gulf offshore region. This region is an important petroleum province in the southwest of the Zagros Fold-Thrust Belt (SW Iran). The area is characterized by gentle N-S to NE-SW trending Arabian-type highs and NW-SE trending Zagros type anticlines. The northeastern border of the Abadan Plain is defined by the NW trending structures, which are located in the southwestern margin of the Dezful Embayment. The study area can be considered as a wide transition zone between the Arabian Platform in SW and the Dezful Embayment in NE. Based on the present study it can be concluded that the basement faulting and subsequent movements of the Early Cambrian Hormuz Salt are main factors in generation of the N-S and NE-SW trending structures. The climax of these activities occurred ih Cretaceous and the Arabian-type structures are reactivated by onset of the Zagros orogeny in the late Tertiary. In addition the Arabian type structures acted as buttresses partially protecting the Zagros deformation.

In the recent studies of the Lame parameters (lp and l/m) for reservoir characterization, the main mathematical tool for investigating complex relationships between variations in Lame parameters and changes in the lithology and rock properties of reservoirs is regression analysis. The heterogeneity of the reservoir under consideration and few available wellsin the area pushed the authors to use soft computing methods instead of conventional mathematical tools. The self-organizing map is an excellent tool in exploratory phase of data mining. It projects input space on prototypes of a low-dimensional regular grid that can be effectively utilized to visualize and explore properties of the data. An improved identification of reservoir properties such as pore fluids and lithology variations can be obtained by analyzing changes in rigiditym, incompressibilityl, and density p. The reliability of results depends on extraction of useful petrophysical parameters (e.g. density, porosity and Vp/Vs ratio) from seismic data and linking them with lithologyor rock properties. In this study self-organizing maps and artificial neural networks are used to categorize the data into lithologically and petro physically meaningful classes and to model the rock parameters and lithology variations by exploiting AVO inversion (LMR) method.

The Silurian strata in eastern Alborz Range are called Niur Formation. This formation is well-developed between the Esfarayien and Bojnourd road, approximately 35 km southeastern Bojnourd city (35 km southeastern Caspian Sea). The Niur Formation is 750 thick and in ascending stratigraphic order, it has been divided into Member I and Member n. The Member I is 500 m thick and consists mainly of black shale with subordinate thin-bedded limestone. The Member II is 250 m thick and comprises of white sandstones, changing into red shale towards upward. The lower and uppercontacts of Niur Formation are conformable with underlying Ghelli Formation and overlying Padeha Formation.A total of 76 surface samples were treated for chitinozoans from this formation, in order to establish a chitinozoan biozonation and to determine the palaeogeographic relationships of eastern Alborz Range (Kopet-Dagh Region) to Zagros Basin of southern Iran as well as other parts of the world. All samples of Member I, contain well-preserved and abundantpalynomorphs (acritarchs, chitinozoans, cryptospores and scolecodonts), but those of Member II are barren.Thirty-two chitinozoan species (6 genera) were recognized in this study, and arranged in four biozones Biozone of Ancyrochitinamerga appears in the upper part of Ghelli Formation, suggesting the Ashgillian age. The biozones of Ancyrochitina laevaensis, Ancyrochitina ramosaspina/Angochitina aff. longicollis and Plectochitina saharica occur through Member I of Niur Formation suggesting Early Silurian for this part of formation. Member II lacks of chitinozoans, but some samples contain cryptospores and a few acritarchs, indicating Wenlockian age. 15 chitinozoan speciesout of 32 are new, including Ancyrochitina angelinae, A. bojnourdensis, A. pelmisensis, A. silurica, A. heterospinosa, A. alborzensis, A. niurensis, A. longifilosa, A. fatema, Angochitina kalatensis, Angochitina minor, Angochitinacaspiensis and Angochitina multipodspina. Except for the new species, the remainder is similar to those of the same age in Zagros Basin southern Iran, Saudi Arabia, Algeria, Libya, Morocco and Spain, suggesting the eastern Alborz Range has been part of North Gondwana Domain.

The influence of fractures in the production rate in carbonate reservoir of southern Iran has been established. The Gachsaran oil field is located in the Dezful embayment in SW of Zagros basin of Iran.The outcrop in the area mainly consists of Miocene- Pliocene Gachsaran formation evaporate and Aghajari classics. The main reservoir in this field is Miocene Asmari formation. Only upper Asmari is developed in this area, lower and upper Asmari is replaced by Oligocene-Eocene Pabdeh marly formation. In this study so also itself is a methodology, a new combination method has been established. Therefore, based on all possible methods and available data, the state of fractures intensity, orientation, type, spacing and etc. have been considered. More important of these methods that were used include the following: 1. Core analysis2. Open hole log analysis(such as FMS)3. Well drilling data analysis4. Structural analysis: fracture prediction base on stress and strain analysis5. Curvature analysis for a better geostatistical study, the Gachsaran anticline was divided in to thirteen different domains or blocks. Also some prediction and reservoir engineering data such as PI, RFT, BUT, maximum rate of production and permeability (K) parameters were studied and mapped. Later these maps correlated with other fracture analysis results. The correlations showed satisfactory results. Both flexural-slip and neutral surface folding mechanisms were active for this area. Regarding the prevailing mechanism of flexural-slip resulting in actives hear fractures in the present stress system, and the existence of gas-cap, the best areas of drilling for higher production are the flanks with thrust fault traces. The curvature analysis method, both in axial and cross sectional dimensions, together with stress-strain analysis are the best economical and powerful methods for exploration and development of oil fields. Also, the best geographical direction for drilling in some domains, based on fracture properties has been estimated.

The rear many factors which control the quality of a hydrocarbon reservoir Pore geometry is one of those that have a profound effect on reservoir quality. In this study, image and core data of a carbonate oil reservoir, southwest of Iran were combined to assess controls of pore geometry on reservoir quality. The results indicate that in spite of complex pore system in carbonate rocks, there are meaningful relationships between pore elements, such as pore area, pore perimeter, pore diameter and core permeability. The relationships improve dramatically when they are mathematically combined, specially pore perimeter/pore diameter ratio. Also there is an acceptable relationship between image porosity and permeability. The obtained relations between pore elements and permeability enable us to estimate permeability without costing core analysis expenses. In addition, pore elements cross-plots help us to separate pore types to some extent.

The Kashafrud Formation, at the Senjedac Section, in southeast of Mashhad, lies unconformably on ophiolitic rocks (Late Permian- Triassic) and faulted against the Shurijeh Formation (Late Jurassic-Early Cretaceous). Fourty seven species of spores (distributed among 30 genera), and 15 species of pollen (distributed among 8 genera) are particularly abundant. Dinotlagellates, fungal spores, acritarchs and foraminiferal test lining are also present. The association of marine palynomorphs (proximate dinotlagellates, Micrhystridium and foraminiferal test lining) with spores and pollen collectively indicate an open marine, nearshore depositional setting for the Kashafrud Formation in Senjedac Section. Inferred natural relationship of the spores and pollen grains imply derivation from a diverse parental tlora of Pterophyta and gymnosperms such as Coniferophyta, Ginkgophyta and Cycadophyta growing under a humid, warm temperature condition during the Middle Jurassic (Bajocian- Bathonian).

The Tanurjeh area is located in the Khaf-Darouneh volcano-plutonic belt, North of Darouneh Great fault. Eocene "Volcanicrocks such as rhyolite, dacite, rhyodacite and minor andesite are present. They are found mainly as tuff, lapilli tuff and flow. 19 sub volcanic (Oligo-Miocene) bodies with composition of monzonite, quartz monzonite, diorite and quartz diorite porphyry are mapped. Different types of alteration such as propylitic, solidification with vugs, sericitic are well developed in the area. Silicified zone cover a large area. Alteration zones are not linear and it is inferred that they are formed due to sub-volcanic intrusive. Pyrite and minor chalcopyrite are the main primary sulfides. They occur both as dissemination and fracture filling. In most of the areas, sulfides are oxidized. Secondary oxides are between 0.3 8 percent. Au, Cu, Zn, Pb, As, and Mo show anomaly in the area The Au content of rock samples are between 0.1 11.2 ppm. Tanurjeh has several features analogous to gold-rich porphyry deposits: cluster of sub-volcanic intermediate calcalkaline rocks, hydrothermal alteration closely associated with the intrusive bodies, present of gold anomaly in most of the area, extensive solidification. (vuggy quartz) is dominate, and presence of pyrite, mostly oxidized, both disseminated and veinlets.

The study area is located about 35 km southeast of Masjed Soleyman in Khuzestan province (in Zagros basin). Carbonate rocks of Asmari Formation at Tang-e-Gel Torsh consist of 320 meters of thin bedded limestone with intercalation of marls and I thick to massive bedded grey limestones. Petrographic and facies analysis led to recognition of II microfacies deposited in an open marine, barrier, lagoon and tidal flat environments. Major and minor elements and stable isotopes (oxygen and carbon) suggest original aragonite mineralogy for Asmari.Formation Stable oxygen and carbon as well as major and minor elements such as Sr/Cavs Mnalso show that Asmari carbonates were affected by meteoric digenesis in a semi-close to close system.Pale temperature calculation indicates an average ambient sea water temperature of 24S0 C.

The Zargoli intrusive body, which is located in the northern part of the Zahedan-Saravan plutonic belt, is mostly composed of granodiorite, monzogranite and biotite granite. The granitoid rocks had deformed during dynamic metamorphism within numerous shear zones. Deformation intensity could be classified to low, medium and high grade based on the increasing stress from south towards the north. This deformation, which occurred under ductile to semi-ductile conditions, had formed the S-C mylonite in the granitic rocks. Occurrence of the cataclastic granitoid in the western margin of the pluton could be related to the final stage of deformation under brittle conditions. Brittle to ductile deformations of feldspars, along with oc-currence of the ribbon quartz, demonstrate that dynamic deformation occurred as medium to high grade greenshist facies between 300 to 450°C.Macroscopic and microscopic evidences show asyntectonic emplacement for the Zargoli intrusion.Seemingly, these intrusive rocks suffered dextral shear deformation in the early stage of crystallization or after solidification.

In this study twenty seven shale and marl cutting samples, which where source rock candidates in the Binakoil field were pyrolyzed using Rock-Eval-6 instrument. Results indicate lower hydrocarbon potential for Pabdeh and Gurpi formations while, Kazhdumi and Laffan show much better potential and act as main source rocks. Kerogen type 11 and mixed type II/III which are oil and oil/gas precursor, are prominent. Organic matter depositional environment was determined by hydrogen index vs.oxygenindex, and reducing with minor oxidation environments exhibited. Thermal maturity index (Tmax) of organic matter shows that all the samples entered oil window while none crossed it to metageneticst age. Hydrocarbon potential (S2) to total organic carbon (TOC) indicate negligible role of mineral matrix to the pyrolysis process. Trend of Toe increase is from north to north east of the oil field to south and south west and this exhibits the higher hydrocarbon potential in the same trend. It is therefore suggested to .consider this trend in future exploration drilling so as to reduce the 4rilling risks and increase forecasting efficiency significantly.

Akapol Granitoid is located in the south-west of Kelardasht and is counted of plutonic massive in central Alborz zone. This plutonic massive with the age of about 54±4 to 56±3 Ma intruded in to the Formations of Mobarak and Shemshak and due to petrology, is containing syenodiorite, monzonite quartzmonzonite, granodiorite and monzogranite. The under-study samples have meta-aluminus and high K-Calk alkaline characteristics. Multi-element spider diagram of these samples shows lacking of Ti, Tb, Y, Tm, Yb and richness of K, Rb, Ba, Tb.These features show subduction related magmatism. Petrographic evidences which are presented in the monzogranite unit of Akapol, contain the partial absorbtion of plagioclases phenochryst, formation sieve texture in the plagioclases, presence of poikilitic texture, rapakivi and antirapakivi texture, as well as presence of microgranular enclaves and reactive margin between enclaves along with rounding stone and also presence of needle apatites, showing that magma mixing is an essential factor in the petrology of Akapol granitoid.

The Gurpi type section in northeast of Lali, Masjed Solyman, was studied in detail for environmental changes and water-level fluctuations via using Planktonic Foraminifera and organic matter contents of the rock samples. The lower contact of the formation is marked by the first appearance of Globotruncana calcarata with an age of Late Campanian. The formation overlies with a disconformity on the Ilam Formation. The upper limit of the formation is marked by the last appearance of Morozovella. velacoensis with an age of late Paleocene where it turns to purple shales of the base of the Pabdeh Formation. Study of foraminifera recorded in the thin sections indicates an increase in benthonic and shallow water forms, while their variations show a concordant decreasing trend upwards. Palynomacerals also indicate an increase towards the KIT boundary at the upper part of the section. The change from Calcareous shales and marls at the lower part of the section to black shales of the upper part is also in accord with an increase in "selective preservation of organic matter" (increase in lability, abundance and variation of dinoflagel-lates) and with gradual extinction of ecological specialist foraminifera. These indicate a decrease in water temperature. The decrease in water temperature may cause a rise in Pycnocline level and retardness of subsurface currents at the end of Cretaceous. These factors may stop bacterial activities and increase in organic matter preservation in one hand and induce extinction of ecological specialist foraminifera preceded by a sharp increase in ecological generalist of the early Paleocene. The rising Pycnocline may ease upward movements of cold water (upwelling currents) during the early Paleocene transgression. These currents in turn increase roundness and sorting of palynomacerals and abundance of marine palynomorphs and generalist foraminifera. Presence of such minerals as phosphate and glauconite in samples of KIT boundary confirm increase in these currents.

Stilbites, along with other zeolite group minerals such as analcime, tetranatrolite, mesolite and heulandites occur as filling minerals in the veins and cavities of the intermediate to basic volcanic rocks in south Kahrizak, south Tehran. Calcite, opal, quartz and pyrolusite are associated with zeolite.Stilbites appear mainly in sheaf-like aggregates in macroscopic specimen and pseudo-orthorhombic prisms in electronic microscope images. Whereas, powder X-ray diffraction study has revealed a monoclinic symmetry (C2/m) with the unit-cell parameters of a =13/49A b = 18/04A, c = 11/20A ' b= 127/42°Mineral paragenesis and chemical investigations has indicated that a late-stage hydrothermal process has been responsible for the formation of these stilbites.

Determining near-surface velocity structure is a crucial step in seismic data processing and imaging, especially in engineering seismology. First arrival seismic tomography can determine the velocity structure in area with strong lateral and vertical, velocity variations. Seismic tomography has two major parts, forward modeling and inversion.Forward modeling generates ray paths and first arrival times in a prior velocity model and inversion updates the prior model to minimize data misfit. In this study a forward modeling' was carried out using a method based on finite difference and. LSQR algorithm to perform inversion. Velocity structure of the subsurface is represented by a grid model. A velocity value was assigned to each node within the grid, and velocity of a grid cell was determined by averaging of the velocities of the surrounding nodes.We applied the method for an engineering seismic project to explore velocity structure in near surface strata. The method was highly efficient and capable of recovering velocity structures in geologically complex areas. We also compared our results from tomography with that of the GRM method. It has been demonstrated that seismic tomography has more realistic results.

Genetic potential of four probable source rocks in Marun oilfield; Pabdeh, Gurpi, Kazhdumi and Garau were investigated. It shows that only pabdeh and particularly Kazhdumi Formations have potent ial to generate hydrocarbons. The Hydrogen Index (HI) vs. Total Organic Carbon (TOC) in four formations indicates direct relation between the two parameters. Kazhdumi Formation with high Hydrogen Index comprises higher amount of total organic carbon. This could be due to reducing environment of organic matter depositional conditions. Maximum Temperature (Tmax) and depth variations shown by diagram in well No. 123 and 222 of Bangestan reservoir in Marun Oilfield indicate that inbothwells Sarvak shales are just at the beginning of oil window, but in well No. 222 Tmax variation versus depth is more severe and Tmax is higher in Kazhdumi Formations. Plot of S2 vs. TOC for inert carbon determination indicates 0.5% in Pabdeh and Gurpi, whereas inert carbons in Kazhdumi are not more than 0.25%. Organic facies curves for Kazhdumi and Garau places them in B to BC zones showing marine reducing with minor oxidizing environment. In Pabdeh and Gurpi, organic facies is variable and consist of a mixture of marine and terrestrial organic matter, indicating transgression and regression of the sea. The van Krevelen diagram indicates kerogen type II/III for all formations, but only Kazhdumi Formation is in the cat agenesis and oil window territory. Finally, among the four studied formations, Kazhdumi with highest organic carbon and optimum thermal maturation is introduced as the best source rock for Marun Oilfield.

An elephant tusk fossil found during a road construction at southwest of Idughmoush dam located at southwest of Mianeh, was studied. It was in the route of migration of the elephants of Pleistocene from Africa towards Europe. The fossil's weight is 12.95 kg with total length 110, length at lipline 60.5, circumference at lipline 40, circumference at base 45 and pulp length 61 cm. The fossil is free of carbonates and organic impurities. The chemical composition of the fossil is calcium (fluoro, hydroxyl) phosphate or fluor-, hydroxyapatite, Ca5(PO4)3(FOH). The fossil char acteristics show that the elephant was male and it has been estimated to be 25 years old. Based on the height of Pleistocene deposits covered on the fossil, compared to the total thickness of the deposit, the age of fossil is estimated to be more than 150000 years.