A. Zohdi; S. A. Moallemi; M. A. Salehi
Abstract
In the Zagros sedimentary basin, the maximum thickness of the Guri Member carbonates is belonging to the eastern parts of the Bandar-Abbas region. In this research, the Guri Member in five outcrops at the Bandar-Abbas region has been sedimentological and stratigraphic studied. The Guri Member mainly ...
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In the Zagros sedimentary basin, the maximum thickness of the Guri Member carbonates is belonging to the eastern parts of the Bandar-Abbas region. In this research, the Guri Member in five outcrops at the Bandar-Abbas region has been sedimentological and stratigraphic studied. The Guri Member mainly consists of limestone with interbedded marl with a variable thickness from 540 m at the Handun outcrop to 52 m at the Nakh outcrop. According to facies study and using the 87Sr/86 Sr isotopic ratio (amounts 0.708522 and 0.708790 values) of the basal carbonate layers of this member, the beginning sedimentation of these deposits occur during the Burdigalian and Langian times within the five carbonate facies. Fieldwork observations and facies distribution suggested a shelf carbonate platform for deposition of the Guri Member at the Bandar-Abbas region. Petrographic investigation in addition to trace elements (Sr, Mn and Fe) and isotopic (oxygen and carbon) geochemical analyses, also indicate the main influence of the marine to shallow-burial diagenetic process with the marine fluids after primary deposition of the Guri Member. The comparison of the oxygen and carbon isotope values of the Guri samples with the least-altered oxygen and carbon range for the early to middle Miocene marine calcite and also the more variations of the oxygen isotope values (between -1.19‰ to -5.39‰ PDB), and lees variations of carbon isotope values (between -1.05‰ to 2.2‰ PDB), indicate the effects of shallow-burial fluids (marine-phreatic) on the carbonate of the Guri Member.
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.
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.