H. Hajialibeigi; S. A. Alavi; J. Eftekharnezhad; M. Mokhtari; M. H. Adabi
Abstract
The Chenareh Anticline is located between Lurestan Zone (in north) and Dezful Embayment (in south) in the Zagros Folded-Thrust Belt. This anticline is documented and interpreted to constrain the kinematic evolution of a fold. The development of fractures is confined to the Asmari Formation. In the study ...
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The Chenareh Anticline is located between Lurestan Zone (in north) and Dezful Embayment (in south) in the Zagros Folded-Thrust Belt. This anticline is documented and interpreted to constrain the kinematic evolution of a fold. The development of fractures is confined to the Asmari Formation. In the study area, the fracture pattern is interpreted to identify six main fracture sets (from A to F). The first fracture set (A) striking 68◦, oblique to the further fold trend, is interpreted as a regional fracture set that predates compression phase. The second set (B) striking 110◦, parallel to the fold trend, are found in both limbs and interpreted as extensional fractures. Two other fractures set, (D, E) striking 10◦-70◦ and 80◦-140◦ are conjugate fractures existing in both limbs. The youngest fracture set (E) had formed during the folding process especially at the late stage of fold growth. Later on the first fracture group (A) are reactivated and called as (F) fracture set. Due to geometric characteristics of the Chenareh Anticline, it is categorized as a fault -propagation fold which is affected by the blind Balarud fault zone. The Z-shaped hinge zone of present anticline is attributed to the linkage of the two early individual anticlines.
S. A. Moallemi; M. H. Adabi; A. Sadeghi
Abstract
In order to determine the depositional environment and age of the carbonaceous Jahrum Formation, benthic foraminiferal assemblage of upper Eocene in the Jahrum Formation carbonates, located in GisakanMountain, 10 km east of the Borazjan city and adjacent fields, were studied. Based on the foraminiferal ...
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In order to determine the depositional environment and age of the carbonaceous Jahrum Formation, benthic foraminiferal assemblage of upper Eocene in the Jahrum Formation carbonates, located in GisakanMountain, 10 km east of the Borazjan city and adjacent fields, were studied. Based on the foraminiferal distribution and abundance, the paleoenvironment were reconstructed. Due to the presence of Nummulites fabianni and based on strontium isotopic analyses, the age between 33.7-35Ma (Priabonian) was determined. The mean sedimentation rate of ~ 2 m/10000 yr. was calculated. This study indicated Asmari Formation deposited after a hiatus, more than four million years (Rupelian stage). Gradual decreases of the sea level and hence the distribution of large benthic foraminifera resulted in the deposition of six sedimentary facies along the inner-middle to outer carbonate ramp system. These facies, from deep to shallow parts of the basin, include argillaceous carbonates containing planktonic foraminifera that were deposited in a hemipelagic to pelagic environment (which is the transition zone from the Pabdeh to Jahrum Formation), carbonate facies of operculina wackestone to packstone related to the outer carbonate ramp, discocyclina /nummulites wackestone to packstone facies deposited in the middle to outer ramp, nummulites wackestone facies occurred in the middle ramp, nummulites orbitolites wackestone to packstone belong to the middle to inner ramp, and finally the orbitolites/bioclast packstone deposited in the inner ramp.
Z.K. Mossadegh; M.H. Adabi; A. Sadeghi
Abstract
We studied the geochemistry of the Asmari Formation in two outcrop sections: Tang-e-Sapou a 260 m section near Dehdasht City (Kohgiluyeh va Bouyer Ahmad Province) and Tang-e-Ban a 214 m section near Behbahan City (Khozestan Province). Sampling included the complete Asmari Formation and the top of the ...
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We studied the geochemistry of the Asmari Formation in two outcrop sections: Tang-e-Sapou a 260 m section near Dehdasht City (Kohgiluyeh va Bouyer Ahmad Province) and Tang-e-Ban a 214 m section near Behbahan City (Khozestan Province). Sampling included the complete Asmari Formation and the top of the Pabdeh Formation. The Late Oligocene to Early Miocene Asmari Formation lies above the Pabdeh Formation and is overlain by the Gachsaran Formation. Elemental geochemistry (Fe, Mg, Na, Sr, Mn, Ca), and Oxygen and Carbon isotope analyses indicate that meteoric diagenesis affected carbonates of the Asmari Formation. The δ18O/δ13C data plots in an inverted J-trend suggesting that meteoric diagensis occurred in a closed to semi-closed system. The geochemistry also suggests that the original mineralogy was Aragonite. The boundary between the Pabdeh and Asmari Formations can be recognized by changes in the δ 18O and δ 13C. In the Pabdeh Formation the δ 18O and δ 13C values are mostly negative, but in the Asmari Formation values range from positive to negative. Strontium is much higher in the Pabdeh Formation than in the Asmari Formation. Changes in isotope and elemental geochemistry clearly show the Chattian-Aquitanian and Aquitanian-Burgidalian boundaries.
M. A. Salehi; M. H. Adabi; H. Ghalavand; M. Khatibi-Mehr
Abstract
The Fahliyan Formation with the age of Lower Cretaceous (Berriasian-Hauterivian) were studied for microfacies analysis, diagenesis and original carbonate mineralogy in the type section at Fahliyan Anticline and subsurface section in well number 55 of Gachsaran Oil Field. Petrographic studies led to the ...
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The Fahliyan Formation with the age of Lower Cretaceous (Berriasian-Hauterivian) were studied for microfacies analysis, diagenesis and original carbonate mineralogy in the type section at Fahliyan Anticline and subsurface section in well number 55 of Gachsaran Oil Field. Petrographic studies led to the recognition of 10 microfacies that were deposited in four facies belts: tidal flat, lagoon, shoal and open marine. The observed facies patterns indicated a carbonate rimmed-shelf depositional environment. Recognition of different type of cements shows that the Fahliyan Formation has mostly undergone meteroric diagenesis. Major and minor elements and carbon and oxygen isotope values indicate that aragonite was the original carbonate mineralogy in the Fahliyan Formation, and suggests that alteration occurred in a closed diagenetic system, with low water/rock interaction.
N. Khodaei; M. H. Adabi; S. A. Moallemi; M. Moradpour
Abstract
The Kangan Formation is a carbonate-evaporate sequence that is considered as a part of the largest carbonate reservoir in the South Pars Field at Persian Gulf. Petrography analysis led to the recognition of 5 different dolomite types: such as dolomicrite, dolomicrospar, dolospar, dolomite cement and ...
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The Kangan Formation is a carbonate-evaporate sequence that is considered as a part of the largest carbonate reservoir in the South Pars Field at Persian Gulf. Petrography analysis led to the recognition of 5 different dolomite types: such as dolomicrite, dolomicrospar, dolospar, dolomite cement and saddle dolomite. Elemental studies on dolomicrite and dolomicrospar samples show a relative increase of Sr and Na and relative decrease of Fe and Mn in comparison with the dolomicrosparite samples. It is notable that the oxygen-carbon isotope trend in dolomite samples are due to slight influence of meteoric diagenesis (about dolomites type I, II and III) and burial diagenesis (about dolomites type IV and V). The dolomicrites have been undergone slight meteoric diagenesis, although they have formed in sabkha environment. The source of Mg for dolomicrites is the magnesium of seawater and interstitial waters equilibrium with seawater and on the other hand probably for the coarser grain dolomites in the Kangan Formation is connate waters and basinal brines. Based on the heaviest oxygen isotope in dolomicrite samples, paleotemperature of depositional environment of the Kangan Formation was around 44.5°C.
A. Zohdi; M. H. Adabi
Abstract
Carbonate sequences of the Taleh-Zang Formation mainly consist of large benthic foraminifera (e.g., Nummulites and Alveolina) along with other skeletal and non-skeletal components. In this formation, the water depth during deposition was determined based on the variation and different types of benthic ...
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Carbonate sequences of the Taleh-Zang Formation mainly consist of large benthic foraminifera (e.g., Nummulites and Alveolina) along with other skeletal and non-skeletal components. In this formation, the water depth during deposition was determined based on the variation and different types of benthic foraminifera and other components in different facies. Microfacies analysis led to the recognition of 10 microfacies that are related to 4 facies belts such as: tidal flat, lagoon, shoal and open marine.The absence of turbidite deposits, reefal facies, gradual facies changes and widespread tidal flat deposits indicate that the Taleh-Zang Formation was deposited in a carbonate ramp environment. Due to the great diversity and abundance of larger benthic foraminifera, this carbonate ramp is referred to as "foram-dominated carbonate ramp system". Comparison between elemental and isotopic compositions of biotic (benthic foraminifera) and abiotic (micrite) components in Taleh-Zang Formation shows an equilibrium condition due to minor biological fractionation and kinetic effects such as growth rate or other unknown factors. Thus, palaeotemperature calculation of seawater based on heaviest oxygen isotope values of biotic and abiotic carbonates are similar. Petrographic and geochemical studies illustrate that these carbonates were affected by weak meteoric digenesis in a closed diagenetic system with a low water/rock interaction.
M. H. Adabi; M. Khatibi Mehr; A. Moallemi; A. Sadeghi; M. A. Salehi
Abstract
The Ziyarat Formation is an Upper Paleocene to Middle Eocene carbonate sequences, located in North of Tochal Village (south-east of Tehran), near Emam Zadeh Abdollah. The Ziyarat Formation with the total thickness of 212.5 m conformably overlies the Fajan conglomerate and is overlain by greenish tufaceous ...
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The Ziyarat Formation is an Upper Paleocene to Middle Eocene carbonate sequences, located in North of Tochal Village (south-east of Tehran), near Emam Zadeh Abdollah. The Ziyarat Formation with the total thickness of 212.5 m conformably overlies the Fajan conglomerate and is overlain by greenish tufaceous siltstone of the Karj Formation. Petrographic studies led to the recognition of 11 microfacies. Different facies and evidences such as the absence of reefal facies, calciturbidite deposits, and widespread tidal flat deposits indicate that the Ziyarat Formation was deposited in a homoclinal carbonate ramp environment. Micritization, cementation, compaction, neomorphism, dissolution, dolomitization, fracturing and silicification are the major diagenetic processes in the Ziyarat Formation, occurring in meteoric and burial diagenetic environments. Major and minor elements and oxygen and carbon isotope values indicate that Ziyarat carbonates were deposited in a shallow warm water tropical environment and original carbonate mineralogy was aragonite. Bivariate plots of Mn versus Sr/Ca and δ18O illustrate that Ziyarat limestones were affected by open system diagenesis with high water/rock interaction. Early burial diagenetic temperature calculation based on heaviest oxygen isotope values of micrite and δw of Eocene seawater of 0.85 SMOW, shows that temperature was around 39˚C. Cathodluminescence studies of carbonate cements illustrated dull luminescence, because these carbonates afftected by both meteoric and burial diagenesis, and thus typical yellow to orange luminescence and zonations, evidence of meteoric diagenesis, are absent. This statement is confirmed by isotropic evidences.
F. Karimzadeh; M. H. Adabi
Abstract
Carbonate and siliciclastic sedimentary sequences of Sorkh Shale and Shotori Formations ( Lower and Middle Triassic) with a total thickness of 870 m , have a gradational and conformable contacts, at Behabad region of Bafgh in Central Iran. At the beginning of this sequence, shale, ...
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Carbonate and siliciclastic sedimentary sequences of Sorkh Shale and Shotori Formations ( Lower and Middle Triassic) with a total thickness of 870 m , have a gradational and conformable contacts, at Behabad region of Bafgh in Central Iran. At the beginning of this sequence, shale, siltstone and sandstone gradually change into dolomitic carbonates of tidal flat sub-environment. Thick layered or massive sequence of mainly dolomitic rocks of Shotori Formation, are transitionally overlain by a limestone member namely Espahak limestone. Based on petrographic studies, four different types of dolomites (based on shape, crystal size and crystal boundaries), have been recognized. Dolomite type 1 (dolomicrite) formed during the first stage of sedimentation and under surface temperature, this is very early diagenetic dolomite. The other types, having coarse crystal size, formed during shallow to deep burial environments. Change of composition and temperature of dolomitizing fluids at several stages of diagenesis (early to late ) led to formation of different types of Shotori dolomites. On the basis of geochemical studies (elemental analysis such as Ca, Mg, Sr, Na and stable isotopes such as ,), formation of these dolomites occurred in a reducing environment and increasing temperature. The source of Mg is sea water for dolomite type 1, but for the other types of dolomites, Mg provided was by clay minerals diagenesis and basinal brine. The results of XRD and XRF on chlorite and montmorillonite clay minerals of Sorhk Shale Formation show a decrease in MgO content from 36% and 84% respectively compared to standard clay minerals. This reduction is due to diagenesis of clay minerals that exist in shales and Mg was originated from overlain layers. Measurement of organic carbon contents of dolomites and limestones showed that dolomites have several times more organic carbon than limestones. This information confirm that limestones rich in organic matter, are more susceptible to dolomitization. Microbial structures such as stromatolites, in the Shotori Formation have major role in trapping of organic matters. The calculated paleotemperature for the formation of early dolomites is about and for late diagenetic dolomite is .
M. Vahidinia; A. Sadeghi; A. Shemirani; A-A. Aryai; M-A. Adabi
Abstract
The Kopet Dagh basin was formed during and after the collision of Turan plate with Iran plate before late Carnian (about 225 m.y. ago). It is located in the northeast of Iran and has a WNW to ESE trend. Neyzar Formation is composed of siliciclastic sediments and sandy shale and sandy limestone. This ...
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The Kopet Dagh basin was formed during and after the collision of Turan plate with Iran plate before late Carnian (about 225 m.y. ago). It is located in the northeast of Iran and has a WNW to ESE trend. Neyzar Formation is composed of siliciclastic sediments and sandy shale and sandy limestone. This unit is widespread in the east and northeast parts of the basin. To determine the stratigraphy, microfossils, microfacies and depositional environment of Neyzar Formation, three stratigraphic sections were selected and measurement and detailed sampling carried out on each of them. These sections from east to west are as fallows :
1) Tang-e Neyzar (Neyzar gorge) section
2) Tang-e Chahchaheh section
3) Jalil abad section
In the previous studies, the base and top boundaries of Neyzar Formation with Abtalkh and Kalat Formations were reported conformable and transitional (Afshar Harb, 1373). However, according to present investigations in eastern regions, lower boundary of Neyzar Formation with Abtalkh Formation in sections 1 and 2 are disconformable (as a Paleosol). This boundary in the section 3 is conformable and transitional. The upper boundary of Neyzar Formation with Kalat Formation in 1, 2 and 3 sections are disconformable (as a paleosoil).
Two types of facies were identified based on micropaleontologic and petrographic studies: 1) Siliciclastic facies, 2) Carbonate facies. Based on microfacies studies it seems that the siliciclastic parts of Neyzar Formation was deposited in a lagoonal-barrier island environments and the carbonaceous parts in a shallow carbonate platform (ramp type).
In most of the published reports and articles Neyzar Formation was introduced as low fossil bearing unit with no index–fossil. The age of this formation was determined only by the basis of its stratigraphical situation, but in the present investigation, in addition, 41 genera and 30 species of microfossils have been identified for the first time from index fossils such as:
Orbitoides apiculata, Orbitoides tissoti, Lepidorbitoides sp., Siderolites calcitrapoides, Pseudosiderolites vidali, Abathomphalus mayaroensis.
These fossil assemblages suggest the Maastrichtian, especially Late Maastrichtian age for Neyzar Formation.
