فهرست مطالب

Earth Sciences - Volume:12 Issue: 1, 2020
  • Volume:12 Issue: 1, 2020
  • تاریخ انتشار: 1398/10/11
  • تعداد عناوین: 6
|
  • Hitesh Kumar, Manoj Pandit * Pages 1-9
    Indian peninsular region comprises several Archean cratonic blocks (Dharwar, Bastar, Singhbhum, Aravalli – Bundelkhand), bordered by Proterozoic mobile belts. Therefore, this region is considered as tectonically stable and designated as the least vulnerable region to earthquake hazard except the still active Central Indian Tectonic Zone (CITZ). The latter is a major suture between southern and northern Indian blocks. Seismicity in India is common along its northern and northeastern (Himalayan) region defining the Indian Plate margin, in collision with the Eurasian (Tibetan) Plate. Being tectonically active, this region has a documented record of frequent earthquakes including some high magnitude and devastating ones. The northwestern Indian block is amongst the relatively stable Precambrian regions of India and categorized under Zone – II by the Indian Meteorology Department, one of the seismically least vulnerable regions. However, the region has been a site of recurring low to moderate magnitude earthquakes. Compilation of the earthquake data from the Rajasthan State in NW India documents at least 45 earthquakes in this region during the last one and a half decades. Several of these have remained unnoticed because of their low magnitude. The NE –SW trending Aravalli Mountain Region (AMR), running across the eastern half of Rajasthan State represents the most significant tectonomorphic feature of NW India. The AMR is an ensemble of Proterozoic age Aravalli and Delhi Supergroup rocks (metasediments, volcanics and intrusives) that overlie an Archean basement (Banded Gneissic Complex – BGC). These Proterozoic mobile belts have evolved through several episodes of deformation that have shaped its present day geomorphology. The western part of the State, the Marwar Block, is relatively younger in age and was accreted to the AMR during the 1 Ga subduction event. The western margin of AMR, also called as the Western Margin Fault, represents a major suture between the two terranes. However, the entire region was cratonized by end Proterozoic and has remained tectonically stable during the Phanerozoic Eon. The Archean basement and overlying Proterozoic cover rocks are infested with several major and minor faults and shear zones. The most prominent ones are the NE-SW trending major lineaments corresponding with the regional tectonic grain and several minor ones across. The earthquake epicenter distribution pattern shows a close spatial association with these lineaments. In the absence of any significant tectonic activity in the region and rise in pore pressure either due to magmatism or excessive rainfall, we attribute recurrence of earthquakes in the region to reactivation of such old sutures/weaker zones as a response to stress build-up along the northern margin of the Indian Plate resulting from ongoing northward convergence of the Indian Plate. Some of the faults in western part are traceable into the Cambay Basin active faults in the south that may have triggered seismic activity in western Rajasthan.
    Keywords: Recurrent Seismicity, Lineaments, Reactivation, NW India, Rajasthan, Indian Plate Convergence
  • Mahboobeh Jamshidibadr *, Sahar Tarabi, Kazem Qolizadeh Pages 10-31
    The Eocene-Oligocene Sarbisheh volcanic complex is a part of the Lut-Sistan Zone that outcrops in eastern Iran. In the east of this complex, three groups of volcanic rocks (i.e., andesite, dacite, and rhyolite) exist. Plagioclase as the main mineral of these rocks is found with varying micro-textures. Based on a changing trend in the concentration of anorthite, the developed micro-textures (coarse/fine-sieve, fine-scale oscillatory zoning, and resorption surfaces) are not affected by the chemical composition of the magma. Rather, such changes can occur by temperature variations during magma crystallization or H2O fugacity changes in the magmatic system. The recharge of basic magma leads to a temperature rise, partial melting of the central part of the crystal, and formation of sieve texture, and resorption surfaces. Consequently, the chemical changes of magma in the chamber cause the formation of An-enrichment in the outer layer of the plagioclase crystal and formation of oscillatory zoning. In addition, the morphological micro-textures (i.e., glomerocryst, synneusis, swallow-tailed, microlite, and broken crystals) are developed by the influence of dynamic behavior of the crystallizing magma and magmatic differentiation. The thermobarometry evaluation using pyroxene and biotite chemistry showed that the temperature ranges between 700 and 1150°C and the pressure were less than 2 kbar.
    Keywords: Plagioclase, micro-textures, Magma, Sarbisheh Volcanic Complex, Lut-Sistan Zone
  • Siamak Baharvand *, Jafar Rahnamarad, Salman Soori Pages 32-41
    One of the methods for dealing with the problem of water shortage and the decline of groundwater levels in the arid areas is the construction of underground dams. It is difficult to make a decision about suitable locations for the construction of underground dams because of the necessity to consider numerous factors. Some of these criteria are hydrological, geological and geomorphologic characteristics of the area. By applying the GIS and AHP methods, this study attempted to introduce the suitable locations for construction of underground dams in Roomeshgan area in Lorestan Province, Iran. For this purpose, factors such as slope, lithology, land use, alluvium thickness, water quality, and distance from the well, fault and stream and rivers network were used. Using the Analytic Hierarchy Process (AHP) for the possibility of considering various qualitative and quantitative criteria, the process can be one way to select the appropriate location for constructing an underground dam. In this study, after the assessment of the used layers in the Expert Choice software, weight mapping of each layer was prepared. Then, the map of suitable areas for construction of the underground dam was prepared by overlapping the weight mappings of each layer in ArcGIS software. According to the results, 15.87 %, 11.96 %, 35.75 %, 33.23 % and 3.18 % of the region are located in very poor, poor, moderate, suitable and very suitable areas, respectively. After several field surveys of the area with three percent, six locations were selected for underground dam construction. The results show that the factors mentioned above have the most important role in locating the underground dam construction and the chosen method has high accuracy.
    Keywords: Lorestan province, Roomeshgan, Underground dam, GIS, AHP
  • Behnam Mousavi, Kouros Yazdjerdi *, Mohammad Abdideh, Hossein Tabatabaei Pages 42-53
    Hydraulic fracturing and matrix stimulation are two major methods of the reservoir stimulation. Hydraulic fracturing, which is the newest technique and technically more complex, is very useful in low permeability reservoirs. Although it has been used widely in hydrocarbon production wells, it is a new method in Iran. In this paper, the effect of sufficient barrier layers on hydraulic fracturing design efficiency was done for Bangestan reservoir (one of hydrocarbon reservoirs in south of Iran). To do this, at first, mechanical earth model (MEM) was developed. This model comprise of in situ stresses and physical properties of reservoir rock (like porosity and water saturation obtained from petrophysical well logs analysis) and determination of the rock fracture pressures and fracture propagation. Then, zone 5 and Sarvak zone of Bangestan reservoir were selected as candidate layers for hydraulic fracturing modelling. Finally, hydraulic fracture was designed for selected layers. In this design, the created fracture length in zone 5 is very shorter than the created fracture length in Sarvak zone. The results show that hydraulic fracturing can be done in Sarvak zone more successful than zone 5, which shows the importance of sufficient barrier layers in hydraulic fracture efficiency.
    Keywords: In situ stress, mechanical earth model, Bangestan Reservoir, fluid, proppant, hydraulic fracturing modelling
  • Taghi Farmani *, Ebrahim Ghasemi Nejad, Bijan Beiranvand, Saeed Maleki Porazmiani Pages 54-68

    Planktonic foraminifera and major palynomorph groups (i.e. terrestrial, marine, and amorphous organic matter) of the Campanian-Selandian strata of the Gurpi Formation were studied to evaluate the changes in the Zagros paleobasin in southwestern Iran. Planktonic foraminifera were categorized into four morphotypes according to their paleodepth, extending from Morphotype 1, comprising surface generalists, to Morphotype 4, comprising deep-water aphotic heterotrophic species. The relative amount of species belonging to Morphotype 4 is noticeable in the Campanian-Maastrichtian. It shows that the depth of the basin was generally greater than 200 m in the Late Cretaceous. Two major sea-level regressional phases could be recognized during the formation deposition. The first one occurred near the middle of the Maastrichtian in the Contusotruncana contusa Biozone, during which the relative abundance of terrestrial palynomorphs increased prominently, and the species belonging to Morphotype 4 became notably rare. This regression correlates well with the eustatic curves, suggesting that it was controlled by global factors. Also, the species belonging to Morphotype 4 disappeared in the Danian, the relative abundance of terrestrial palynomorphs increased, and the relative abundance of planktonic foraminifera (P%) decreased prominently. However, this regression does not correlate with the eustatic curves and indicates that local tectonic events should be considered. The palynofacies study of the strata shows that during the Campanian-Maastrichtian, the strata were deposited in a deep suboxic-anoxic setting (Palynofacies IX), whereas the Danian strata were deposited in a shallow-shelf setting (Palynofacies VI). The studies show that during the Selandian, the depth of the basin increased again.

    Keywords: planktonic foraminifera, Palynomorph, Palynofacies, Tethys, Paleobasin
  • Mohammad Nikbin, Mohammad Khanehbad *, Reza Moussavi Harami, Asadollah Mahboubi, Mahdi Khoddami, Ehsan Ghofrani Pages 69-84

    The Kangan Formation (Early Triassic) is one of the most important gas reservoirs in the Zagros fold-thrust belt. The study area is located in the west of Hormozgan Province and on the Gavbandi highland. This field is one of the important gas production anticlines in the SW Iran. To investigate the reservoir quality of the Kangan Formation in these wells, 163 microscopic thin sections were prepared from 97.68 m core for petrographic investigations. Then, petrophysical study was out carried using wireline well logs such as spectral gamma ray (SGR), sonic (DT), density (RHOB), and effective porosity (PHIE). The petrographic studies led to the identification of facies features and diagenetic processes affecting the quality of reservoir in the studied wells. These diagenetic processes include chemical and physical compaction, various cementation (especially anhydrite cement), fracturing, dissolution as well as different types of porosity resulting from these processes. Also, for the purpose of accurate evaluation, petrography studies with wells, matching and reservoir characteristics of these wells were qualitatively and quantitatively interpreted and reservoir potential horizons were determined. In general, for the first well (well "A") four and for the second well (well "B") three reservoir horizons were investigated.

    Keywords: Reservoir quality, Petrography, diagenesis, Well logs, Tabnak Anticline