Stratigraphy and Palaeontology
Fatemeh Vaez-Javadi; Mahdi Abbaszadeh
Abstract
Middle Jurassic sediments of the Hojedk Formation have been well-exposed in the Central East of Iran. In this study, plant macrofossils, which are collected from a coal exploratory well in the Mazino area, southwest of the Tabas were studied, so that 29 species of well-preserved plant macrofossils belonging ...
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Middle Jurassic sediments of the Hojedk Formation have been well-exposed in the Central East of Iran. In this study, plant macrofossils, which are collected from a coal exploratory well in the Mazino area, southwest of the Tabas were studied, so that 29 species of well-preserved plant macrofossils belonging to 15 genera of various orders such as Equisetales, Filicales, Caytoniales, Bennettitales, Cycadales, and Pinales were identified. One local biozone- Ptilophyllum harrisianum-Klukia exilis interval zone was recognized. The lower and the upper boundaries of this biozone were identified by the first and the last occurrences of index species. Based on the occurrences of the Equisetites sp. cf. E. beanii, Klukia exilis, Ptilophyllum harrisianum, Nilssonia macrophylla, and Elatides thomasii, an early Middle Jurassic age (Aalenian-Bajocian) was suggested for this plant assemblage. The relative abundance of Filicales (ferns), Cycadales, Pinales, and Equisetales are 43.18, 31.82, 13.63, and 4.64 percent, respectively. Moreover, the results of similarity indices of plant macrofossils indicate relatively strong value of similarity between the plant macrofossil assemblage of the Mazino area and elsewhere in the Tabas Block. Besides, the floral gradient score of this assemblage is 54.89. Based on the paleontological and lithological evidence, a humid ‘warm temperate biome’ is considered for this locality. Moreover, it is confirmed that a uniform vegetation and palaeoclimate occurred in Tabas Block during the Middle Jurassic and that Iran was located within Vakhrameev’s Euro-Sinian region, as Transcaspian subprovince.
Sedimentology
Ehsan Zamaniyan; Mohammad Khanehbad; Reza Mossavi-Harami; Asadollah Mahboubi
Abstract
Qadir Member of Nayband Formation in the eastern part of central Iran have a wide outcrop. Investigating the lithofacies and sedimentary environment of Qadir Member of Nayband Formation (Upper Triassic) in east central Iran, Tabas Block, resulted in identifying the coastal plain, deltaic and open marine ...
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Qadir Member of Nayband Formation in the eastern part of central Iran have a wide outcrop. Investigating the lithofacies and sedimentary environment of Qadir Member of Nayband Formation (Upper Triassic) in east central Iran, Tabas Block, resulted in identifying the coastal plain, deltaic and open marine deposits. Based onfield evidences, the facies features and the geometry of beds, this member consists of two lithofacies include carbonate and siliciclastic facies. The siliciclastic facies were identified as having four sandstone facies (medium-grained), including Sr, Sh, Sp, St and three fine-grained lithofacies, including FI, Fm, Fl (Sr) / Sr (FI) and one coal facies (C). Also carbonate facies are calcirudite and calcarenite. Regarding the field, laboratory studies and identifying the lithofacies, the coastal plain, deltaic (including deltaic plain, proximal delta front, distal delta front, and prodelta) and open marine environments were identified for Qadir Member on which it is under the impact of tidal currents.
F. Vaez-Javadi
Abstract
Hojedk Formation spreads well through the Tabas Block. Diverse and moderately preserved palynofloras occur in the Middle Jurassic sediments of the formation in south Kouchekali, southwest of Tabas, central-east Iran. The present investigation of the Hojedk Formation has revealed a diverse assemblage ...
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Hojedk Formation spreads well through the Tabas Block. Diverse and moderately preserved palynofloras occur in the Middle Jurassic sediments of the formation in south Kouchekali, southwest of Tabas, central-east Iran. The present investigation of the Hojedk Formation has revealed a diverse assemblage of dinoflagellate cysts in which 12 species allocated to 5 genera. Two acritachs were also recognized, permitting establishment of Nannoceratopsis triceras-Pareodinia ceratophora Assemblage zone, and Nannoceratopsis gracilis Total Rane Subzone in the upper part, lower and upper boundaries have been identified by the first and last observed occurrence (LOO) of these index species. These biozones are comparable to the other palynozones in Iran and elsewhere especially in the northern hemisphere (Greenland, Norway, Scotland, England, and Poland). Occurrence of various species of Nannoceratopsis is concluded that this locality was located at the south palaeocoastal line of the Tabas Block during the Aalenian-Bajocian.
M.A Rajabzadeh; Z Ghorbani; M Jalalifard; M Mohammadzadeh
Abstract
Parvadeh coalfield with an area of 1200 km2 is one of the largest coalfields in East-Central Iran. The coal-bearing clastic rocks of the coalfield belong to Ghadir Member of the Upper Triassic Naiband Formation and could be classified as bituminous coal, containing low volatile, high ash and medium to ...
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Parvadeh coalfield with an area of 1200 km2 is one of the largest coalfields in East-Central Iran. The coal-bearing clastic rocks of the coalfield belong to Ghadir Member of the Upper Triassic Naiband Formation and could be classified as bituminous coal, containing low volatile, high ash and medium to high sulfur. Pyritic sulfur is the main form of sulfur in the Parvadeh coals. Quartz, illite, kaolinite, pyrite, and calcite/dolomite are the principal mineral phases. Enrichment in major elements and depletion in minor elements were observed in studied samples when compared with those of the earth crust. The element contents of coal-bearing layers are similar to those of the US and world coals except for Cd, Li, As and Zn. Based on the calculated enrichment factor, the elements As, Co and Cd are the most pollutants in Parvadeh area. Strong correlations among ash contents and Si, K and Al values indicate that the coal ash is mainly composed of aluminosilicates. Meanwhile, Cd, Co, As, Fe, and S show that Cd, Co, As participated in pyrite lattice. These results were confirmed by factor and cluster analyses. The calculated recovery index shows that Li, Mo, Pb and Cu are bounded to maceral and organic matter thus are enriched in the cleaned coals. The other minor metals, however, are present in mineral part of the coal and enriched in ash.
M Nazemi; M Qurashi; M.R Ghassemi; M Arian
Abstract
Geomorphic characteristics of alluvial fans on the sides of the ShotoriMountains in east of Tabas represent two different groups . The first group is older and is more dominant with their heads near the ShotoriMountains' hillside and their toe spreading to the central parts of the plain. These alluvial ...
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Geomorphic characteristics of alluvial fans on the sides of the ShotoriMountains in east of Tabas represent two different groups . The first group is older and is more dominant with their heads near the ShotoriMountains' hillside and their toe spreading to the central parts of the plain. These alluvial fans on which no main recent channel sedimentation is occurring, are often consisted of old alluvial sediments with a thin cover of newer ones. The second group includes younger and active alluvial fans consisted of more recent sediments of stream bed, which are located at the termination of the first group or at the southern foothills of the ShotoriMountains. It can be said that in the first group, recent active sedimentation process by the main channel has been transferred to the lower parts and toe of the alluvial fan, but in the latter group sedimentation has been done on top of the alluvial fan and on older sediments. In other words, the first group consists of two obvious old and active (recent) parts, while the second group only includes recent and active alluvial fans. Our investigations indictaes that geomorphic pattern of these two alluvial fan groups has a clear relation with location and mechanism of active faults and geomorphic surfaces in the plain of Tabas and eastern slopes of the Shotori Mountains; in other words, it is related to the mechanism of structural evolution of this mountain. According to this pattern, wherever there is the active fault of the catastrophic 1978 earthquake at the front of mountain along which the ShotoriMountains are being uplifted, the second type of alluvial fans is formed. Where the fault is located in central parts of the plain as a result of deformational front propagation, and the old part of the alluvial fan and mountain are being uplifted along it, the first type of alluvial fans (with two separate parts) is formed. This uplift is accommodated by active faulting and folding associated with bedding plane faulting. Migration of deformational front during geologic evolution of the ShotoriMountains has caused four different geomorphic levels along with three generations of alluvial fans. It is concluded that investigating on geomorphic pattern of alluvial fans will provide valuable data about the location of active Quaternary faults in alluvial plains. This pattern shows an active fault near Boshruyeh (east of the ShotoriMountains). Although no major earthquake has been reported from the fault, all morphotectonic evidences show its activity and thus the occurrence of large earthquakes in the future is expected.
A. Ghaderi; A. Aghanabati; B. Hamdi; A. Saeedi
Abstract
To study the Shirgesht Formation biostratigraphy in Kalmard Horst in relation to its conodont content, the Miyugodar (Miangodar) stratigraphic section was selected which is located in southwest of Tabas city. The Shirgesht Formation in the mentioned section is mainly composed of siliciclastic rock units ...
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To study the Shirgesht Formation biostratigraphy in Kalmard Horst in relation to its conodont content, the Miyugodar (Miangodar) stratigraphic section was selected which is located in southwest of Tabas city. The Shirgesht Formation in the mentioned section is mainly composed of siliciclastic rock units and overlay unconformably on Kalmard Formation (attributed to Pre-Cambrian) and is overlain by Gachal Formation (Carboniferous). Thirty five rock samples were selected from appropriate rock units (Shirgesht and Gachal Formation). Samples were studied in laboratory for more details. According to the extracted conodont from Shirgesht Formation in Miyugodar section, the age of this formation can be regarded as Early Ordovician (Tremadocian – Arenigian). Three conodont assemblage zones were recognized in Early Ordovician units. They are: Cordylodus spp., Deltifer and Proteus Global Standard Conodont biozones. The recognized biozones are as followed:
1- Oneotodus - Drepanodus Assemblage Zone
2- Acodus deltatus - Protopanderodus Assemblage Zone
3- Acodus - Oistodus Assemblage Zone
S. M. Hashemi; M. Emami; M. Vossoughi Abedini; M. Pourmoafi; M. Ghorbani
Abstract
In southeastern Tabas there is a 400 square kilometer area of Quaternary basalts, which is geologically located in Lut zone. According to petrographic studies and EMPA analysis, the textures of these rocks are generally porphyric and some times aphyric. The phenocrysts of these basalts are generally ...
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In southeastern Tabas there is a 400 square kilometer area of Quaternary basalts, which is geologically located in Lut zone. According to petrographic studies and EMPA analysis, the textures of these rocks are generally porphyric and some times aphyric. The phenocrysts of these basalts are generally chrisolite, augite, and plagioclase (andesine to labradorite), which are embedded in a texture of plagioclase microlites and small blades of pyroxene. According to the diagrams of accumulative amount of alkaline against the amount of SiO2, the nature of the magma is alkaline to sub-alkaline. The reason for the sub-alkaline character of some of these rocks is that the alkaline magma has been contaminated with crust materials. One of the most important reasons for this is the reduction of niobium in rocks enriched with SiO2. The alkaline samples have normative nepheline and the sub-alkaline samples normative quartz. The studies of Nd and Sr isotopes have confirmed the crust contamination and also the source for early magma of basalts is the upper parts of mantle. Based on the field studies and tectono- magmatic diagrams, these basalts are of intercontinental type because of the activities of great fault of Nayband in Quaternary and separation in their cross point reaching the earth's surface.
A. Ghaderi; A. Aghanabati; B. Hamdi; J. F. Miller
Abstract
The Shirgesht Formation is one of the fossiliferous units of Central Iran which in the type section is defined (informally) in the terms of 3 members. This formation is mainly composed of limestone, marl, siltstone, shale and dolomite, conformably overlay on the upper part of the Derenjal Formation with ...
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The Shirgesht Formation is one of the fossiliferous units of Central Iran which in the type section is defined (informally) in the terms of 3 members. This formation is mainly composed of limestone, marl, siltstone, shale and dolomite, conformably overlay on the upper part of the Derenjal Formation with a gradual contact, composed of brachiopods limestone bearing (Billingsella limestone). The Shirgesht Formation is overlain by sandy limestone and volcanic rocks of the Niur Formation.
To do biostratigraphy studies on the first and second members of Shirgesht Formation in the type section, totally 99 rock samples were selected. The conodont fauna of lower part of its first member contain some species of Westergaardodina, Furnishina and prooneotodus which show an age of late Cambrian. Several species of Cordylodus, Oistodus, Drepanodus, Proconodontus and Paroistodus in distance of middle part of the lower member to the end of the second member represent an age of Tremadocian – Arenigian. According to conodont content of the first and second members of Shirgesht Formation, 7 conodont assemblage zones were determined in the type section which show an age of Late Cambrian – Early Ordovician. The recognized biozones are as follow:
1. Furnishina - Westergaardodina Assemblage Zone.
2. Proconodontus - Oneotodus Assemblage Zone.
3. Cordylodus proavus - Cordylodus oklahomensis Assemblage Zone.
4. Cordylodus lindstromi Assemblage Zone.
5. Cordylodus angulatus Assemblage Zone.
6. Drepanodus - Paltodus deltifer Assemblage Zone.
7.Paroistodus proteus Assemblage Zone.
The mentioned conodont assemblage zones are equivalent to Cordylodus spp., Deltiferand Proteus global standard conodont biozone. In contrast with the previous reports, the Cambrian – Ordovician boundary is located in the first member of the Shirgesht Formation. Thus, the Shirgesht Formation in type section is diachronous formation.
