فهرست مطالب

Geopersia - Volume:9 Issue:2, 2019
  • Volume:9 Issue:2, 2019
  • تاریخ انتشار: 1398/08/10
  • تعداد عناوین: 12
|
  • Mostafa Hamad * Pages 203-220
    The Lower Miocene deposits in Gabal Gharra, Cairo – Suez District, unconformably overlies the Oligocene and Eocene deposits. They consist predominantly of regressive and transgressive mixed siliciclastic / carbonate sediments of shallow marine environments. The Lower Miocene deposits are represented lithostratigraphically by the Gharra Formation that comprises four members, from base to top: Agrud, Sadat, Hommath and Genefe members. Two measured sections were described and investigated: Gabal Gharra section and Gabal Agrud section. The coralline red algae are highly abundant in Sadat and Genefe members as fragments, crusts and rhodoliths. Larger foraminifera, corals, echinoids, bivalves, gastropods, bryozoans, benthic and planktonic foraminifers, dasyclades are also present. These two members consist of dolomitized bioclastic packstone, grainstone to floastones / rudstone with rhodoliths (up to 3cm in size). The systematic study led to the recognition of 14 coralline algal species. Lithophyllum sp. dominates the coralline associations at the generic level, followed by Mesophyllum spp, Lithothamnion spp and Spongites spp. The vertical distribution of the coralline red algae in the two concerned sections allowed to subdivide the Lower Miocene sequence into two local coralline algal zones, from base to top: Lithophyllum ghorabi Zone  (including the Sadat Member) and Mesophyllum iraqense Zone (covering the Genefe Member). The rhodoliths populations in the two sections were analyzed in terms of their size, shape, massiveness, symmetry, algal growth forms, algal species diversity, epibionts and borings. These parameters reflect environmental differences between the two studied sections. A comparison of the two the analyzed rhodoliths populations show common features, but also significant differences are recorded. The rhodoliths populations of Gabal Gharra were formed under low energy conditions characterized by porous rhodoliths with higher primary porosity, less frequent epibionts, more boring and thick coralline algal thalli as well as greater asymmetry. On the contrary, in Gabal Agrud the analyzed rhodoliths population was formed in high energy conditions of shallower water marine environments and characterized by more mobile, symmetrical rhodoliths, more frequent epibiont, thin coralline thalli.
    Keywords: Early Miocene, Gabal Gharra, coralline algae, Rhodoliths, Egypt
  • Fatemeh Sabahi, Peyman Afzal *, Mohammad Lotfi, Nima Nezafati Pages 221-232
    Gardaneshir Pb–Zn deposit is hosted by dolomitic carbonates which is located in the SW Ardestan, central Iran. Ore body is stratabound type in this deposit. Primary ores in this type are composed of sphalerite, galena, barite and quartz with massive, banded, veined and disseminated structures. Evaluation of ore-grade at the Gardaneshir Pb-Zn deposit, based on chemical analysis which indicates average of 4.35% Pb, 0.17% Zn, 20 ppm Ag in form of galena, sphalerite, minor cerussite and smithsonite occurred along brecciated and silicified fractures. Based on studies in gangue minerals, liquid-rich two phase (L+V) inclusions as predominant types were recognized. These types of inclusions are homogenized into liquid state with ranges of TH and related salinities as 78-183 NaCl wt% and 216-283 C, respectively. These microthermometric data reflect the nature of two populations of fluid inclusions originating from different source. Furthermore; the range δ34S from -0.6 ‰ to -20.4‰ that have been extracted by galena can be an evidence of bacterial sulfate reduction in a subsidence sedimentary basin. This study suggests that the Gardeneshir Pb–Zn deposit is an epigenetic, thrust fold-controlled and stratabound deposit with fluids and metals derived via the Triassic sedimentary strata.
    Keywords: Fluid inclusions, Sulfur isotope, Stratabound deposit, GardaneShir, Ardestan
  • Salameh Afshar *, Mohammad Ghafoori, Naser Hafezi Moghadas, Gholamreza Lashkaripour Pages 233-249
    The present work was conducted to investigate the geotechnical properties of two meta-peridotites and meta-pyroxenites of an ultramafic complex mainly consisting of ultramafic rocks. For this purpose, microscopic studies were performed to determine the percentage of serpentinization in these rocks. In addition, a number of mechanical and physical tests were performed on collected samples with different serpentinization grades to determine their geotechnical properties. Finally, the serpentinization degree and geotechnical results were compared for meta-peridotites and meta-pyroxenites. The results revealed a closed relationship among the serpentinization degree, Brazilian tensile strength (BTS), uniaxial compressive strength (UCS), and density. Due to the high costs of the UCS test, this study attempts to establish a relationship between these parameters. To demonstrate the relationship between these parameters, the obtained results are presented as a single graph. So, the UCS can be estimated based on the BTS, density, and the serpentinization degree. The results showed that the field behavior of rock masses also could be used to predict the UCS) range and degree of serpentinization. Overall, these results can be useful for determining the geotechnical properties of these rocks.
    Keywords: ultramafic rocks, serpentinization degree, geotechnical properties
  • Saeedeh Senemari *, Fariba Foroghi Pages 251-264

    This study presents calcareous nannofossils biostratigraphy of the Campanian‒Danian interval at the Gurpi Formation in the southwest of Ilam Province, in the Zagros Basin. The studied sequence of the Gurpi Formation mainly consists of marly shale and limestones. The thickness of Gurpi Formation was measured as approximately 230 m. Forty-five species belonging to twenty-eight genera were recorded in these strata. The biostratigraphy based on calcareous nannofossil assemblages allows the identification of nannofossil standard zones such as CC18b, CC19, CC20, CC21, CC22, CC25b,‌c and CC26b, that equivalent to UC14cTP - UC20dTP for Cretaceous, and NP2 - NP3 (equivalent with CNP2, CNP3 and lower part of CNP4) for the Paleogene strata in the Gurpi Formation. The studied section spans the early Campanian to early late Campanian with good continuity. A biostratigraphic gap is identified in the late late Campanian to early Maastrichtian (CC23, CC24, and CC25a), across the late Maastrichtian (CC26a) and at the early Danian (NP1).

    Keywords: Biostratigraphy, Calcareous nannofossils, Cretaceous, Paleogene, Zagros
  • Parya Behzadtabar *, Mohammadhossein Ghobadi, Davood Fereidooni, Ali Asghar Sepahi Pages 265-277
    Salt crystallization can severely damage anisotropic foliated rocks, therefore it is necessary to have an understanding of crystallization process. The present study was conducted to investigate the effect of salt crystallization on Arakʾs calcareous slates, as anisotropic rocks of Mesozoic. To compare salt crystallization weathering (EN 12370 norm was used up to 30 cycles) with natural weathering conditions, some samples were exposed to natural weathering conditions for 12 months. The samples exposed natural condition were tested every 3 months. The measurements show a decrease in physical and strength properties with an increase salt crystallization cycles. At the end of cycle 30, the average weight, ultrasound wave velocity, uniaxial compressive strength (σc), Brazilian tensile strength (σt), and point load index value (Is) of the samples were reduced by 0.32%, 11.52%, 23.72%, 32.15%, and 16.09%, respectively. In comparison, after about 12 months of exposure to natural climatic conditions, these values were 0.18%, 8.84%, 12.64%, 22.23%, and 15.04%, respectively. To establish a relationship between salt crystallization and natural weathering conditions, weathering ratio (WR) was presented. The results of this study can be used to predict the behavior of the anisotropic slates of Arak, upon which the city is planned to be developed.
    Keywords: Salt crystallization, Natural weathering, Anisotropy, Calcareous slate, Arak
  • Mehdi Yousefi *, Seyed Morteza Moussavi, Mohammad Mehdi Khatib Pages 279-292
    Image logs of 13 wells in the Rag Sefid Anticline show two systems of fractures developed under two deformation phase in the Dezful Embayment. This deformation phases are folding resulted from Zagros NE contraction and reactivation of the basement fault rotated the fold axial trace within the Hendijan-Izeh fault zone. Folding phase comprises four sets of fractures, which include axial and cross axial sets that trend parallel and perpendicular to the fold axial trace, respectively and two oblique sets that trend at moderate angles to the axial trace in the eastern part of the fold. Reactivation of the Hendijan-Izeh Fault has caused the restraining bend and dextral shear zone in the western part of the Rag Sefid Anticline. This dextral shear has produced three fracture sets which include two sets of Riedel shear fractures and an extensional set. The mean shortening directions measured from the fold and fault related fracture systems in the eastern and western parts of Rag Sefid Anticline are N022±2° and N064±1°, respectively. The measured NNE and ENE shortening orientations in the well sites is consistent with maximum horizontal stress orientations derived from earthquake focal mechanism solutions.
    Keywords: Asmari Formation, Rag Sefid Anticline, Fracture Systems, Hendijan-Izeh Fault, Image logs
  • Mehdi Boroumandi, Mashalah Khamechiyan *, Mohammad Reza Nikoudel, Mohsen Mohammadzadeh Pages 293-304
    The increase of heavy metals concentration in soils is potentially threatening the environment and human health. In this paper, multivariate analysis methods such as Positive Matrix Factorization (PMF), Principal Component Analysis (PCA) and Cluster Analysis (CA) combined with geostatistical method were employed to identify the potential sources of soil pollution. A collection of 103 samples were obtained from surface soils of different types of lithology and landuse in Zanjan Basin, Iran. The concentration of As, Bi, Cd, Co, Cr, Cu, Pb, Fe, Mo, Ni, Zn, Se and Hg beside of physical and chemical properties were measured. The results showed a strong effect of anthropogenic sources on the enrichment of heavy metals especially, Zn, Pb, Cd, As and Cu in soils. From the results of PMF and PCA, the four-factor model showed the optimized solution for this study. One of the factors is related to the background concentration, another one is associated with agricultural activities and the other two are associated with industrial activities and industrial waste. The PMF method in comparison with the other common methods in multivariate analysis presents physically acceptable and more reasonable results because of non-negative condition for factors and weighting of the variables.
    Keywords: soil pollution, Heavy metals, Multivariate analysis, positive matrix factorization, GIS
  • Hossein Kamyabi Shadan *, Hooshang Dashtban, Bagher Roshandel Arbatani, Fariba Foroghi Pages 305-350
    In the present study, Kabir kuh Section, related to the Seymareh or Lopha Limestone member (Gurpi Formation) have been Selected. The member has yielded a rich echinoid fauna and 21 species of Echinoid belonging to 14 genera are recognized and described. The Kabir Kuh section yielded two regular echinoid taxa: Salenia nutrix and Goniopygus superbus, one holectypoid taxa: Coptodiscus noemiae, two conulid taxa: Conulus douvillei and Globator bleicheri, six cassiduloid taxa: Parapygus cotteauanus, Parapygus declivis, Parapygus inflatus, Parapygus vassilini, Vologesia tataosi and Pygurostoma morgani, one holasteroid species: Hemipneustes persicus and nine spatangoid taxa: Iraniaster douvillei, I. morgani, I. nodulosus, Hemiaster noemiae, Hemiaster opimus, Mecaster kanepanensis, Mecaster longus, Proraster morgani and Epiaster lamberti, that indicating Campanian age. Some of this taxa are known from the similar age Campanian of Saudi Arabia such as: Coptodiscus noemiae, and Globator bleicheri and Salenia nutrix comes from Maastrichtian deposits of UAE and Oman and also some specimen are reported from Campanian deposits of Afghanistan such as: Hemiaster noemiae, H. opimus and Parapygus vassilini.
    Keywords: Echinoid, Campanian, Seymareh member, Southwest Iran
  • Mohsen Ranjbaran *, Somayeh Rahmani Javanmard Pages 351-365
    The travertine deposit springs are located on the southeast of the Damavand Volcano, 85 km northeast of Tehran Province. The deposits of these springs mainly outcropped with cascade, hill, conical, layered, calcareous Tufa and Fissure-Ridges morphologies. Travertine studies have usually been conducted based on field observations, geochemistry and hydrology. The tectonic activity of the region, faults and fractures have provided some channels for the rise of CO2-rich hydrothermal fluids. The present study was carried out based on field, geochemical and hydrological surveys. The results of thin section and SEM analyses show that photosynthetic microorganisms such as blue-green algae and diatoms play a key role in the formation of these travertines. Field studies alongside with petrographic characteristics revealed presence of crystalline crust, rafts, foam, laminated and tufa lithofacies. The mineralogy of these lithofacies is calcite. There is a significant enrichment in δ13C values of all travertine types due to decarbonation of limestone. Based on the isotope, performed on travertines of the region, the linear trend observed between δ13C and δ18O values is attributed to the mixture of two or more different fluids. This enrichment is attributed to the de-carbonation of limestone, algae activities and rapid de-gasification of hot springs.
    Keywords: Ab Ask, Travertine, Lithofacies, Geochemistry, Tufa
  • Zahra Orak, Majid Mirzaie Ataabadi *, Ali Solgi, Mahmoud Reza Majidifard, Dimitris Kostopoulos Pages 367-379
    A new and the first mammal fossil locality from the Zagros Basin of Iran is reported here. The fossil locality, known as Dimeh, is located in the Lorestan province, west of Iran. The fauna includes abundant bovid cranial remains, mostly representing boselaphines and palaeoryxoids, as well as gazelles and spiral horned antelopes. Hipparionine horses similar to Hippotherium group are also represented by many individuals and specimens. In addition, large giraffids are among the common elements. Rhinocerotidae, Proboscidea and hyaenids are also present. Based on the current assessment of this fauna, it is most similar to the Middle Maragheh biostratigraphic levels in northwest Iran. Hence, an age of 8-7 Ma (MN 11-12 equivalent) can be assigned for this assemblage. This new fauna is comparable to the Pikermian-type mammal palaeocommunities of the late Miocene and may indicate an extension of these faunas toward Zagros high lands in pursuit of seasonal precipitation and vegetation.
    Keywords: Neogene, Lahbari member, Bovidae, Lorestan, Dimeh
  • Khalid Ubeid * Pages 381-393
    The Gaza Strip constitutes the south-western part of Palestine. The loess deposits were observed in the Middle and Gaza Governorates in Gaza Strip. This study carried out in the Wadi Gaza where Quaternary loess well crops out. Twenty three samples were collected from nine observation sites in the study area, and performed a textural, calcium carbonate and organic matter content studies. The loess sequence which is in some locations intercalated by conglomerates overlies sand dunes. The exposed loess shows stable steep walls, easily eroded by water. It consists of sandy loam to loam, with light brown to dark reddish brown color. It composed of clay (1-20%), silt (28-49%), and very fine- to fine-grained sand (43-71%). The carbonate contents range from 6 to 20%, and organic matter contents range from 1 to 2%. The dominant coarse silt- to very fine-grained sands, and quartz-rich composition suggest that the sand dunes of the northern Sinai and western the Negev sands are the most prominent reservoir of loess sediments in the study area. The silt- to very fine-grain sand could be direct contribution from exposed Mediterranean shelf during period of eustatically low sea levels in early MIS 4 (73-60 ka) or even earlier.
    Keywords: Gaza Strip, Wadi Gaza, loess, sand dunes, Climate
  • Ali Kadkhodaie, Sirous Hosseinzadeh, Hossein Mosaddegh *, Rahim Kadkhodaie Pages 395-410
    Investigation of pore system properties of carbonate reservoirs has an important role in evaluating the reservoir quality and delineating high production intervals. The current study proposes a three-step approach for pore throat size characterization of these reservoirs, by integrating core data, well logs and 3D seismic volume. In this respect, first the pore throats size was calculated using Pittman and Winland models based upon routine core analysis data, and calibrating the results with the laboratory-derived capillary pressure curves. In the second step, the pore throat size as a continuous log was calculated using petrophysical data for each studied well. Finally, the calculated pore throat size log was tied to 3D seismic data at well locations. The results show that seismic attributes including acoustic impedance, amplitude envelope, filter 15/20-25/30 and derivative instantaneous amplitude are the best predictor set for converting the 3D seismic volume into a pore size cube by a probabilistic neural network mode. The methodology illustrated in this study, was employed on Ilam carbonate reservoir in one of the southwestern oilfields of Iran.The findings demonstrate that seismic data in combination with core and well log data could be considered as an effective tool for spatial modeling and characterization.
    Keywords: Pore throat size, Artificial Neural Network, seismic attributes, seismic inversion, carbonate reservoirs