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.
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.