Stratigraphy and Palaeontology
Nasrollah Abbassi; Safoora Shakeri; Javad Rabbani
Abstract
Numerous Proboscidean footprints have been discovered in the outcrop (135 m) of lower rock unit of the Upper Red Formation (Middle-Late Miocene) in the north Avaj (Qazvin province), central Iran. These footprints are preserved as circular concave epi-relief in the upper bedding planes with smooth or ...
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Numerous Proboscidean footprints have been discovered in the outcrop (135 m) of lower rock unit of the Upper Red Formation (Middle-Late Miocene) in the north Avaj (Qazvin province), central Iran. These footprints are preserved as circular concave epi-relief in the upper bedding planes with smooth or levee rims or with sediment accumulation in the front of the footprints. Five digit imprints present in some of the footprints. The frequency of footprints is considerable the most of the upper surface of layers which was resulted by movement of proboscis herds. Ichnotaxonomically these footprints identified as Proboscipedaen igmatica. The footprints are classified as two sizes as small (15 cm) and large (25 cm) categories, and based on the geometric relationships, the height of shoulder was estimated as 140-170 cm for adult and 76-106 cm immature individuals. According to reports of Miocene Proboscidean body fossils from Iran, and based on the distributions of the Proboscidean in this time, it seems that the Choerolophodon (Gomphotheriidae) is candidate as track-maker of the Avaj footprints. Among the Proboscidean footprints, there are crocodile and fish swimming imprints which were left in the shallow pools.
Economic Geology
Negar Kaboudmehri; Hossein Kouhestani; Mir Ali asghar Mokhtari; Afshin Zohdi
Abstract
The Toryan occurrence is located in the Central Iran zone, 120 km northwest of Zanjan. Pb–Zn mineralization at Toryan occurred as laminated and lens-shaped parallel to lamination of grey sandstone units of the Upper Red Formation. Mineralization often formed around and within the fragments of the ...
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The Toryan occurrence is located in the Central Iran zone, 120 km northwest of Zanjan. Pb–Zn mineralization at Toryan occurred as laminated and lens-shaped parallel to lamination of grey sandstone units of the Upper Red Formation. Mineralization often formed around and within the fragments of the plant fossils, and shows disseminated, replacement, solution seems, intergranoular cement, framboidal, and vein-veinlet textures. At Toryan, ore horizon has 1 m thickness and approximately 350 m length and contains three zones include the red oxidized zone, the bleached zone and the mineralized reduced zone. Galena, sphalerite, pyrite and arsenopyrite are the main ore minerals at Toryan occurrence. Cerussite and goethite are formed during supergene and wethering processes. Comparison of trace elements and REE patterns of barren red and grey host sandstones and mineralized samples indicate that mineralized samples show lower concentrations of trace elements and REE. Based on tectonic setting, sedimentary environment, host rock, presence of plant fossils, geometry, ore texture and mineralogy and alteration, Toryan occurrence can be classified as sediment-hosted Cu deposits of Redbed type, and is comparable with another Redbed type of Cu and Pb–Zn deposits in the Avaj-Zanjan-Tabriz-Khoy belt.
Sedimentology
Navid Qavim; Najmeh Etemad-Saeed; Mahdi Najafi
Abstract
The Mahneshan Basin is one of the syntectonic Neogene sub-basins of the Central Iran. The basin is filled by about 4 km of the Miocene Upper Red Formation deposits, showing a combination of halokinetic and growth strata patterns. To assess the provenance evolution of sediments in north of the Mahneshan ...
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The Mahneshan Basin is one of the syntectonic Neogene sub-basins of the Central Iran. The basin is filled by about 4 km of the Miocene Upper Red Formation deposits, showing a combination of halokinetic and growth strata patterns. To assess the provenance evolution of sediments in north of the Mahneshan basin named the Hesar section, we conducted remote sensing mapping, field survey, as well as petrographical and modal analyses of sandstones. Our results reveal that the sandstones are fine to medium-grained sedarenites (Q46F10Rf44) and mainly derived from fine-grained siliciclastics, metamorphic, carbonate, chert and andesitic volcanic rocks, which were exposed in an orogenic tectonic setting (Qm34F10Lt56 and Qt49F10L41). The combination of provenance data and northeastward paleocurrent direction, reflect that the sediments mainly supplied from basement rocks of the Takab Complex and Qom Formation in southwest of Mahneshan Basin. The unchanged provenance of sediments along the studied succession, indicate that regional shortening and uplift of parent rocks has begun before deposition of the Upper Red Formation (Miocene) and continued during deposition of these sediments. This is in agreement with previous age assumption for exhumation of Takab Complex during Oligocene time.
Economic Geology
Ali Rajabzadeh; Hossein Kouhestani; Mir Ali Asghar Mokhtari; Afshin Zohdi
Abstract
In this study, petrography and major and minor elements geochemical data are presented for sandstone layers of the Upper Red Formation (URF) in the Chehrabad Pb-Zn deposit (NW Zanjan) to investigate sandstone composition, tectonic setting and their source rock. In this area, URF has 980 m thickness and ...
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In this study, petrography and major and minor elements geochemical data are presented for sandstone layers of the Upper Red Formation (URF) in the Chehrabad Pb-Zn deposit (NW Zanjan) to investigate sandstone composition, tectonic setting and their source rock. In this area, URF has 980 m thickness and is conformably overlies the Qom Formation limestones. Based on the microscopic studies, these sandstones mainly composed of fine- to coarse-grained clastic fragments including sedimentary and metamorphic rock fragments (45 %), quartz (38 %) and feldspar (17 %). Based on petrographic studies, these sandstones are feldspathic litharenite and litharenite (mainly chertarenite). Based on the main components and major and minor elements geochemical data, the tectonic setting of these sandstones is an active continental margins and foreland basins. These data represent an intermediate to felsic source rock for these sandstones which was affected by the semi-humid to semi-arid climate and a low chemical weathering.
Z Bikdeli; M Ebrahimi; Gh Nabatian; M.A.A Nabatian
Abstract
Chehrabad Cu deposit is located in the Zanjan province and in the northwest corner of Central Iran. Rock units exposed in this area belong to the Cenozoic era (especially Miocene period) and include the Lower Red Formation, Qom Formation, Upper Red Formation and Quaternary deposits. In the study area, ...
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Chehrabad Cu deposit is located in the Zanjan province and in the northwest corner of Central Iran. Rock units exposed in this area belong to the Cenozoic era (especially Miocene period) and include the Lower Red Formation, Qom Formation, Upper Red Formation and Quaternary deposits. In the study area, the Upper Red Formation which hosts the mineralization consists of alternating beds of marl, siltstone, oxidized red sandstone and light gray sandstone. Mineralization has occurred within the gray sandstones of bleached zone containing organic materials. In Chehrabad, copper deposit mineralization has been recognized in five horizons. Each horizon is composed of three zones including reduced zone with mineralization, bleached zone and oxidized red zone. The dominant texture in the Chehrabad Cu deposit is replacement texture which is accompanied with other textures such as disseminated, solution seams, lens like and interparticle cement texture. Lithology (sandstone host rock), sulfide mineralogy (e.g. pyrite, chalcocite, bornite and chalcopyrite), structure and texture, stratigraphy as well as factors controlling the mineralization (presence of plant remains performing as environment reductant and also the permeability in the host rock) suggest that this deposit is similar to the red-bed type sedimentary Cu deposits which is formed during the early to late diagenesis.
Chehrabad Cu deposit is located in the Zanjan province and in the northwest corner of Central Iran. Rock units exposed in this area belong to the Cenozoic era (especially Miocene period) and include the Lower Red Formation, Qom Formation, Upper Red Formation and Quaternary deposits. In the study area, the Upper Red Formation which hosts the mineralization consists of alternating beds of marl, siltstone, oxidized red sandstone and light gray sandstone. Mineralization has occurred within the gray sandstones of bleached zone containing organic materials. In Chehrabad, copper deposit mineralization has been recognized in five horizons. Each horizon is composed of three zones including reduced zone with mineralization, bleached zone and oxidized red zone. The dominant texture in the Chehrabad Cu deposit is replacement texture which is accompanied with other textures such as disseminated, solution seams, lens like and interparticle cement texture. Lithology (sandstone host rock), sulfide mineralogy (e.g. pyrite, chalcocite, bornite and chalcopyrite), structure and texture, stratigraphy as well as factors controlling the mineralization (presence of plant remains performing as environment reductant and also the permeability in the host rock) suggest that this deposit is similar to the red-bed type sedimentary Cu deposits which is formed during the early to late diagenesis.
M Baghernejhad; M.R Ghassemi; B Oveisi
Abstract
There is a close relationship between resistance to slip along decollement surfaces and presence of deep and shallow decollement levels in thin-skinned fold and thrust wedges. Decollement units in lower (Upper Red Formation) stratigraphic levels in Mianeh-Mahneshan fold belt have an effective role onthe ...
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There is a close relationship between resistance to slip along decollement surfaces and presence of deep and shallow decollement levels in thin-skinned fold and thrust wedges. Decollement units in lower (Upper Red Formation) stratigraphic levels in Mianeh-Mahneshan fold belt have an effective role onthe geometry and kinematics of deformation of the area. In order to understand the fold geometry and folding mechanisms, and to exploredepth-to-the-decollement surface, we carried out data collection and field study in an area between Mianeh and Mahneshan cities. Folded structures in the study area are different from other structures within the area, as well as from the structures in the neighboring Alborz Mountains.The rise of salt domes along with the plasticity of marls in the Upper Red Formation have resulted in extreme complexities in folding pattern. In order to analyze syn-sedimentary structural features and interpret the geological evolution of the area, we used detailed structural measurements, sedimentological and sedimentary environment features, sedimentary rock studies, and paleogeography.One of the results of this study was the interpretation of syn-sedimentary growth structures in the Mianeh-Mahneshan area, which helped us to construct six structural cross-sections (AA’, BB’, CC’, DD’, EE’ and FF’)across the folded structures. Measured shortening along two Sections AA’ and DD’is 46.65% and 38.05%, respectively, with an average of 42.3%. These values are different from those estimated forthe neighboring Alborz and Zagros Orogens, where shortening ranges between 16-30%. We attribute this difference to local intense shortening in the study area caused by several factors such as basin slope, deep faults and weak beds along decollement surfaces. This study indicates that dominant folding mechanisms in the study area are detachment folding, and fault-propagation or fault-bend folding. The presence of evaporitic material (gypsum and salt) within the succession has played a major role in the kinematics of folding.
N. Abbassi; A. H. Amini
Abstract
The Upper Miocene Upper Red Formation in the Evan-e-Key Section is composed of conglomerates, sandstones, mudstones, and thin lenses of evaporates (gypsum). The formation is dominated by gypsiferous mudstones and characterized by fining-up cycles in this area. The whole ...
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The Upper Miocene Upper Red Formation in the Evan-e-Key Section is composed of conglomerates, sandstones, mudstones, and thin lenses of evaporates (gypsum). The formation is dominated by gypsiferous mudstones and characterized by fining-up cycles in this area. The whole formation occurs as a fining upward megasequence, in which the sandy facies dominate the lower half and muddy facies the upper half. Gypsum layers, up to 10 meters thick, are locally observed in the basal part. The formation has suffered an extensive weathering in the region, as a result of which primary features (e.g. sedimentary structures, trace fossils) are partially obscured. In the sandy units of the middle part of the formation some vertebrate footprints are observed, which are locally deformed due to intensive weathering of the rocks. Two types of Carnivoripedida footprints however, are distinguished and described here, so that well preserved Chelipus isp. is related to Felidae. Depositional environments including alluvial fans with abundant debris flows, gravelly bed load braided systems with wide flood plains and local swamps provided a good opportunity for development of the track makers. The transverse and longitudinal bars within the channels, levees, and over-bank sub-environments were found more suitable for development and preservation of the footprints. Comparing with other sections of the formation (e.g. Qum area), desirable climate was found a major control on development of the vertebrate track maker in the Evan-e-key area.
