Stratigraphy and Palaeontology
Hamta Ranjbar; Abbas Ghaderi; Hossein Gholamalian; Vachik Hairapetian
Abstract
Middle Devonian to Lower Carboniferous siliciclastic-carbonate successions in Eastern Alborz are characterized by Khoshyeilagh Formation. It is underlain by the Devonian red siliciclastic sequences and is overlain by the Carboniferous Mobarak Formation, can be divided into three different members; lower ...
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Middle Devonian to Lower Carboniferous siliciclastic-carbonate successions in Eastern Alborz are characterized by Khoshyeilagh Formation. It is underlain by the Devonian red siliciclastic sequences and is overlain by the Carboniferous Mobarak Formation, can be divided into three different members; lower carbonate, middle siliciclastic, and upper carbonate. The Khoshyeilagh Formation comprises various fossil groups of invertebrates, conodonts, palynomorphs and fish remains. In the present study, a collection of microscopic fish remains, obtained from the lower and upper carbonate members in Mighan, north of Shahrood, have been determined and described. This assemblage contains 14 different taxa of chondrichthyan fish including: Cladodoides cf. wildungensis, Ctenacanthiformis gen. et sp. indet, Dalmehodus turnerae, Deihim mansureae, Lissodus lusavorichi, Phoebodus aff. turnerae, Phoebodus fastigatus, Phoebodus gothicus gothicus, Phoebodus gothicus transistans, Roongodus phijani, Siberiodus mirabilis, Squatinactis glabrum, Stethacanthus resistens and Thrinacodus ferox. Some specimens of scales and teeth of actinopterygian and osteichthyan fishes are also present which all indicate a shallow environment of the continental shelf. The associated conodonts with this assemblage demonstrate the age of Frasnian (rhenana biozone) to early Tournaisian (duplicata biozone) for the whole succession.
Economic Geology
nader taghipour; Tahereh Rabani; Reza Zahiri
Abstract
Coal deposits in Gheshlagh region are embedded in the sediments of Shemshak formation with lithological units such as sandstone, conglomerate, siltstone, limestone and argillite. For investigation of mineralogy and structural characteristics of Gheshlagh coal seams sampled of eleven coal seams in four ...
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Coal deposits in Gheshlagh region are embedded in the sediments of Shemshak formation with lithological units such as sandstone, conglomerate, siltstone, limestone and argillite. For investigation of mineralogy and structural characteristics of Gheshlagh coal seams sampled of eleven coal seams in four active mines. Occurrence of minerals with distribution and nature of organic – mineral bonds in coals seams of this region is considered by using of petrographic and XRD and FT-IR analyses. Study of hand specimen and polished section are approved the presence of clay minerals, pyrite, chalcopyrite, siderite and quartz. Also The presence of minerals like kaolinite, quartz, siderite, dolomite, calcite, pyrite, montmorillonite and biotite was revealed by XRD. Mineral–organic bands such as: OH, CO2, CH3, Si-O, S-S, C-S, Al-OH, carbonate minerals, C=C, aromatic and aliphatic CH have been identified by the FT-IR in Gheshlagh coal seams. Raman spectroscopic confirms the presence of the graphitic band (G) (1581 cm−1- 1585 cm−1) and the defect band (D1) (1341 cm−1 – 1352 cm−1) in Gheshlagh coal seams. Graphitic bands contain high intensity and insignificant broadening.
H. Ghasemi; M. Rostami Hossuri; M. Sadeghian
Abstract
The Lower Jurassic basin of northern margin of central Iran structural zone and south of eastern Alborz in Semnan province, contains igneous rocks with basic composition, belonging to early stages of occurrence and development of an immature extensional back arc basin at this time. These basic igneous ...
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The Lower Jurassic basin of northern margin of central Iran structural zone and south of eastern Alborz in Semnan province, contains igneous rocks with basic composition, belonging to early stages of occurrence and development of an immature extensional back arc basin at this time. These basic igneous rocks cropped out in at the base of Shemshak Formation and its equivalent in central Iran Structural zone, in the form of extrusive (basaltic rocks) and intrusive (dike, sill and microgabbroic small stocks) rocks. Magma forming of these rocks have had calc – alkaline nature and was enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) and also was depleted in heavy rare earth elements (HREE). The mentioned magmas was, originated from 5 to 30% partial melting of the spinel peridotitic (below the central Iran) and garnet lherzolithic (below the Eastern Alborz) mantle plumes in an immature extensional back arc basin tectonic setting due to oblique subduction of Nneothetyan oceanic lithosphere beneath the central Iran structural zone at late Triassic to middle Jurassic time, and were ascending to upper levels of continental crust by fault and fracture systems and emplaced in shallow sedimentary basins of these zones in different ways. This basin was formed in the behind of the upper Triassic – Lower Jurassic magmatic arc of central Iran and due to initiation of extensional movements in the continental crust of central Iran and Alborz.
M Rostamiyan; M Khademi; S.S Eslami; H Shahbazi
Abstract
In the western part of Miami fault zone (MFZ) as a partial boundary of two main structural zones (Centeral Iran and Binaloud) in the Iranian plateau, since the fault is covered by alluviums or displaced rocks, poor and limited field data cannot solve the problems concerning deformation history and evolutionary ...
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In the western part of Miami fault zone (MFZ) as a partial boundary of two main structural zones (Centeral Iran and Binaloud) in the Iranian plateau, since the fault is covered by alluviums or displaced rocks, poor and limited field data cannot solve the problems concerning deformation history and evolutionary path of the MFZ. To facilitate unraveling the structural problem, we tried to conduct five experimental models using a combination of compressional, dextral and sinistral mechanisms with changes in the geometry of two main boundary faults. Based on the results, evidences from transpression with dominant dextral component are very similar to field observations along the western MFZ, including folds, Riedel shears, duplexes, fault geometry and bends. Based on the model, deformation in the western part of MFZ is accommodated by dextral non-coaxial shear with compressional component. The experimental model provided a proper insight about deformation history and style. It is proposed that the western part of the MFZ has been deformed by dextral non-coaxial shear with compressional component, and some resultant rotations have probably changed structural trends during time.
R Farokhnejad; B Esfandiari; A Motamed
Abstract
In this paper the Fajan Formation of Paleocene age with a thickness of 172.5 meters is studied in northwest Shahroud (Eastern Alborz). Main lithology of this formation, at the studied section, consists of conglomerate and sandstone. The formation disconforably overlain upper Cretaceous limestones ...
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In this paper the Fajan Formation of Paleocene age with a thickness of 172.5 meters is studied in northwest Shahroud (Eastern Alborz). Main lithology of this formation, at the studied section, consists of conglomerate and sandstone. The formation disconforably overlain upper Cretaceous limestones and its upper boundry with Ziarat limestone of Eocene age is of transitional type. Dominant lithology of mentioned formation, at the studied section, consists of polymodal and polymictic orthoconglomerate which contains rounded to subrounded grains. These clastic grains are generally oval to spherical in shape and originated from limestone, sandstone and chert materials. Paleocene Conglomerate is characterized by two distinc lithofacies: clast-supported massive gravel (Gcm) and clast-supported horizontally stratified gravel (Gh) which are formed in a braided river system. This subject is interpreted by evidances as condensed texture gravels, imbrication fabric that indicate on one hand paleocurrent, non-existence of fossil by reason of oxidation conditions of sedimentary environment, sandstone lenses that have through cross bedding (St) and existence of gravels that are mostly rounded to subrounded and denote distance from origin. Abundant bed load mostly rang in size from pebble to cobble and partially boulder, gravelly beds with long extended lateral spread and lack of flood plain muddy sediments, are reasons in distinguish between recognized sedimentary environment and meandering river. The studied Sandstone layers are described by ripple marked sand (Sr) and planar-cross-bedded sand (Sp) which contain sublitharenite and quartzarenite type are deposited in tide-dominated deltaic system.Interpretation criteria are propounded by means of interference ripple mark that prove direction change of current bearing clastic particles, rounded to subrounded sands that can present repeated reworking of grains after deposition in sedimentary environment, well sorting, high textural maturity, insignificant matrix as criterion in distinction specified delta from other deltaic environments and herringbone cross bedding which is the most important evidence of tidal currents.
T Rabani; N Taghipour; R Aharipour
Abstract
Gheshlagh district contains coal deposits in a large syncline in Shemshak group sediments in East Alborz. To determine the palaeoenvironmental setting of the coal deposits based on organic and mineral components, eleven samples from coal seams from four active mines are collected. Minerals such as quartz, ...
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Gheshlagh district contains coal deposits in a large syncline in Shemshak group sediments in East Alborz. To determine the palaeoenvironmental setting of the coal deposits based on organic and mineral components, eleven samples from coal seams from four active mines are collected. Minerals such as quartz, kaolinite, pyrite, siderite, biotite, montmorillonite and dolomite are identified in Gheshlagh coal mines. The Ground Water Index (GWI) suggests ombrotrophic hydrological conditions for coal layers in Gheshlagh coal region. K13 and k11 layers have much higher GWI among others due to its higher mineral content than other layers. Vegetation index (VI) of the Gheshlagh coals is less than 3, which could indicative of the dominance of aquatic/herbaceous plants in the formation of coal seams. Petrographic data on organic and inorganic matter with facies diagram suggest evidences of anaerobic to low oxygen, alkaline conditions and variations in water level with relative proximity to the marine environment.
M Lotfi; M Hekmatian; A.A Shabani; M.A Mokhtari
Abstract
Oras-kuh lead-zinc deposit is located at about 79 km north-east of Semnan city. This deposit is considered as stratabound and occurs in the upper part of the Triassic dolomitic limestone of the Elika formation. Oras-kuh structure includes a northeast - southwest trending normal anticline and follows ...
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Oras-kuh lead-zinc deposit is located at about 79 km north-east of Semnan city. This deposit is considered as stratabound and occurs in the upper part of the Triassic dolomitic limestone of the Elika formation. Oras-kuh structure includes a northeast - southwest trending normal anticline and follows the general trend of the eastern Alborz. Folding in the area has generatedthree sets of jointsincludingjoints trending parallel to the direction of anticline axis, extensional joints perpendicular to anticline axis and the conjugate joint systems. The first two setsof the joints host vein form mineralization. In addition, breccia and karst filling mineralization can be detected. Major minerals are galena, sphalerite and pyrite that altered to secondary minerals such as cerussite, goethite, hydrohetarolite and rosasite under the supergene processes. Gangue minerals are dolomite, calcite, barite, quartz, and small amounts of fluorite. The majority of the temperature data are between 298 to 323°C based on the fluid inclusion geothermometry of calcite and barite minerals. The relatively high temperatures of fluid inclusions are attributed most likely to a concealed deep intrusion in the crust inferred byairborne geomagnetic survey. Fluid salinities show a wide range from 0.6 to 15wt% equivalent weight of NaCl formed through mixing of basinal brines with meteoritic water. In general based on the present evidences, Oras-kuh lead-zinc deposit can be comparable with MVT deposits that its primary mineralogy and elemental ratios have been changed through secondary supergene processes.
H Ghasemi; Z Kazemi; SH Salehian
Abstract
On the basis of stratigraphical studies, parental rocks of the Gorgan schists have same petrological features and fossil contents as the Ghelli formation in the eastern Alborz Zone and despite to the previous theories, these schists are not Precambrian in age. Also, the mafic igneous rocks of these two ...
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On the basis of stratigraphical studies, parental rocks of the Gorgan schists have same petrological features and fossil contents as the Ghelli formation in the eastern Alborz Zone and despite to the previous theories, these schists are not Precambrian in age. Also, the mafic igneous rocks of these two rock units have considerable petrological and geochemical similarities. These mafic igneous rocks include basalt, trachybasalt and basaltic trachyandesite in association with microgabroic sills, dykes and small intrusions. Investigations on, and comparison of their petrological and geochemical features, indicate similarities in age, petrology, magma sources, geochemistry and tectonic setting. It seems that the parental rock of the Gorgan schists and the rocks forming the Ghelli formation were sedimentary and igneous rocks, deposited during the initial stages of extensional movements and rifting of the Paleotethys ocean during Ordovician in the eastern Alborz. However the, parental rocks of the Gorgan schists were metamorphosed in the greenschist facies in middle-upper Triassic (early Cimmerian orogeny), due to vicinity to the oceanic trench of the Paleotethys subduction zone. Geochemical features of the igneous rocks in these two units indicate 12-16% partial melting of an enriched garnet lherzolite mantle source (such as the Oceanic Island Basalt source) for generation of the original magma in the garnet peridotite stability field at 100-110 Km depth..
Z Solaymani; N Taghipour
Abstract
The Olang area is located in 70 km of northeast Shahroud. This area is situated in Gheshlagh Olang syncline, which is a member of the EasternAlborzCoalBasin. The optical microscopes and X-ray diffraction (XRD) analysis on coal and coal ash samples and also SEM-EDX results revealed kaolinite, quartz, ...
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The Olang area is located in 70 km of northeast Shahroud. This area is situated in Gheshlagh Olang syncline, which is a member of the EasternAlborzCoalBasin. The optical microscopes and X-ray diffraction (XRD) analysis on coal and coal ash samples and also SEM-EDX results revealed kaolinite, quartz, siderite, pyrite, biotite, chlorite and illite minerals in coal seams at the Olang coal mines. Pyrite is observed as syngenetic (framboidal) and epigenetic (filling of the cell cavity, vein, and veinlet).The abundance of syngenetic siderite and absent sulphate minerals is usually thought to indicate deposition of the coal mainly under nonmarine conditions, or at least under the influence of swamp or formation waters with low sulphate content. The study of 15 potentially hazardous trace elements (PHTEs) includes: (Ba ®1054.7 ppm), (Co ®51.32 ppm), (Cr ®161.1 ppm), (Cu ®129.3 ppm), (Mn ®1600 ppm), (Mo ®19.56 ppm), (Sn ® 4.78 ppm), (Ni ®139.7 ppm), (Pb ® 48 ppm), (Tl ®1.36 ppm), (Th ®27.6 ppm), (U ® 9.45 ppm), (V ® 232.9 ppm), (Zn ®101/78 ppm(, (P® 6500 ppm) in coal ash deposits of the Olang region compared with the average of the world coal ash, shales, soils and also crustal Clarke. The results show that these coals are enriched in Mn, Mo, U, Pb, Zn and P and are dangerous elements.
Z Kiadaliri; M.R Majidifard
Abstract
The Lower- Middle Jurassic strata are well developed in northeast of Jajarm (E Alborz). At the study section, the Shemshak Group has a maximum thickness of 585 m, consisting of grey silty sandstones and light- green siltstones with brown sandstones, subdivided into 3 formations ofAlasht, Shirindasht ...
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The Lower- Middle Jurassic strata are well developed in northeast of Jajarm (E Alborz). At the study section, the Shemshak Group has a maximum thickness of 585 m, consisting of grey silty sandstones and light- green siltstones with brown sandstones, subdivided into 3 formations ofAlasht, Shirindasht and Fillzamin.The lower boundary of the Shemshak Group at Golbini sectionwith the red bauxite horizon of the underlying Elikah Formation is disconformity due to the EarlyCimmerian tectonic event.Its upper boundary with marly limestone and marl of the Dalichai Formation is disconformity, too. In the Shemshak Group at the study section, summing up 186 fossil specimens were collected, among which the ammonoids with 67 specimens clearly predominate and belonging to 6 biozones (ThouarsenseZone, Pseudoradiosa Zone,Aalensis zone, Opalinum Zone, Murchisonaezone, ConcavumZone) have been recognized. Based on the ammonite fauna, the age of the Shemshak Group in the investigated area ranges from the Upper Toarcian to Upper Aalenian. Paleobiogeographically, the fauna shows close relationship to Northwestern Europe and Sub-Mediterranean regions. This indicates a paleogeographical position of the area at the northern Tethys during the Lower-Middle Jurassic.
M. Nemati; D. Hatzfeld; M. R. Gheitanchi; M. Talebian; N. Mirzaei; A. Sadidkhouy
Abstract
The Shahroud fault system plays important role in seismotectonic of the eastern Alborz. In this paper we have surveyed the seismicity of the middle-eastern Alborz and its southern area. At this investigation, the data of the Geological Survey of Iran local seismological networks, the seismological networks ...
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The Shahroud fault system plays important role in seismotectonic of the eastern Alborz. In this paper we have surveyed the seismicity of the middle-eastern Alborz and its southern area. At this investigation, the data of the Geological Survey of Iran local seismological networks, the seismological networks of the Institute of Geophysics of the University of Tehran and the International Institute of Earthquake Engineering and Seismology of Iran were used for processing the focal mechanism of micro-earthquakes and the south of Damghan earthquake and its greatest aftershock. Distribution of the micro-earthquakes and the south of Damghan events epicenters indicate intense activity of the Shahroud fault system and the Toroud fault. Focal mechanisms of them shows near vertical dipping of the faults and left lateral mechanism of the western segments of the fault system and the Toroud fault. The focal mechanisms suggest the Astaneh, Chashm and Firouzkuh faults from the system fault behave in a same manner with no deference between them at depth and have seismic potential proportion to their total length. Also due to left lateral mechanism of the south of Damghan earthquakes, Toroud fault treats like of the eastern Alborz seismotectonically and this area could cover Toroud fault.
K. Seyed Emami; N. Behfar; M. R. Majidifard; A. Behfar
Abstract
Middle Jurassic strata are well developed northeast of Damghan (E Alborz). At the study section the Dalichai Formation has a maximum thickness of 156 m, consisting of an alternation of bluish-grey limestones and marls, being subdivided into 4 members. The lower boundary with the siliciclastics of the ...
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Middle Jurassic strata are well developed northeast of Damghan (E Alborz). At the study section the Dalichai Formation has a maximum thickness of 156 m, consisting of an alternation of bluish-grey limestones and marls, being subdivided into 4 members. The lower boundary with the siliciclastics of the underlying Shemshak Formation is unconformity, due to the Mid-Cimmerian tectonic event, whereas the upper boundary with the light and cliff-forming carbonates of the Lar Formation is gradational. The Dalichai Formation at the study section is very fossiliferous. Summing up 1750 fossil specimens were collected, among which the ammonoids with 1491 specimens clearly predominate. Altogether 27 genera, 33 species of ammonites, belonging to 6 biozones (Parkinsoni Zone, Zigzag-Aurigerus zones, Subcontractus Zone, Bullatus-Gracilis zones, Anceps-Coronatum zones, Athleta Zone) has been recognized. In addition 17 genera and 8 species of planktonic and benthic foraminifers are described.These can be divided into 2 biozones. The fossil-content is mainly concentrated within few meters of red and nodular limestone in the upper part of the section. Based on the ammonite fauna the age of the Dalichai Formation in the investigated area ranges from Upper Bajocian to Oxfordian. Paleobigeographically the fauna shows close relationship to western Europe and Sub-Mediterranean region. This indicates a paleogeographic position of the area at the northern Tethys during the Middle-Upper Jurassic.
M. R. Kebria-ee
Abstract
Geirud Formation has a wide distribution in the Damghan region. The Formation Lithology is mostly composed of limestone, marly limestone, shale and quartizic sandstone and its thickness ranges from 10 - 200 meters. Brachiopoda of Geirud Formation in the southwest, north and northeast of Damghan region ...
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Geirud Formation has a wide distribution in the Damghan region. The Formation Lithology is mostly composed of limestone, marly limestone, shale and quartizic sandstone and its thickness ranges from 10 - 200 meters. Brachiopoda of Geirud Formation in the southwest, north and northeast of Damghan region (Darvar, Simeh- Kuh and Deh- Molla sections) were studied and resulted in recognizing some species that are as follows: Schellwienella sp., Mesoplica sp., Sentosia sp., Schizophoria impressa, Leptagonia sp., Aulacella interlineata, Zaigunrostrum iranicum, Leptocaryorhynchus jamensis, Araratella dichotomians assimulata, Araratella sp., Centrorhynchus charakensis, Megalopterorhynchus chanakchiensis, Paurogastroderhynchus nalivkini, Paurogastroderhynchus bikniensis, Cleiothyridina coloradensis, Cleiothyridina sp., Athyris tau, Composita cf. globosa,Lamellosathyris sp., Cyrtospirifer sergunkovae, Cyrtospirifer sp.,Cyrtiopsis graciosa chakhaensis, Cyrtiopsis lapparenti, Prospira struniana, Prospira lapparenti, Rigauxia cyrtinaeformis, Rigauxia crassiplicatus, Dichospirifer thylakistoides, Eobrachythyris sp.,Toryniferella echinulata, Cryptonella sp. Based on the above mentioned Brachiopoda an age of Early Famennian- Late Famennian can be considered for carbonate part of Geirud Formation in the these sections. Also, Geirud Formation in the sections is equivalent with middle and upper parts (with the exception of Rossirhynchusbiozone) of Geirud Formation in the type section (Central Alborz).