Sedimentology
Seyedeh Zahra Pourheidar; Mohamad Hosein Adabi; Mir Reza Moussavi Tasooj; Abbas Sadeghi
Abstract
The Elika Formation forms the major part of the Triassic carbonate sediments in the Alborz basin. In this study, facies and sedimentary environments of this formation were studied in Shahmirzad section whith a thickness of 746 meters and in Zereshk-Darreh section whith a thickness of 756 meters in the ...
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The Elika Formation forms the major part of the Triassic carbonate sediments in the Alborz basin. In this study, facies and sedimentary environments of this formation were studied in Shahmirzad section whith a thickness of 746 meters and in Zereshk-Darreh section whith a thickness of 756 meters in the southern part of central Alborz. Based on facies studies, four carbonate facies associations (tidal tlat, shoal, lagoon and open marine) have been identified, including twelve carbonate microfacies and have been deposited in a carbonate ramp. Deposition of sediments in this sequence can be divided into three stages. In the first stage, most of vermiculate limestone deposits are composed of bioturbated mudstone and clotted peloidal mudstone. The high frequency of facies such as laminated stromatolite, intraclastic packstone-grainstone and laminated mudstone are characteristic features of the second stage of sedimentation (middle dolomite) and indicate a decrease in the depth of sedimentary environment. In the third stage, the environment was suitable for the expansion of barriers and formation of packstone-grainstone facies.
Petrology
Leili Bastami; Reza Moussavi; Mahboobeh Hosseini-Barzi; Bahaedin Hamdi Hamdi
Abstract
The sandstones of the Dorud Formation (Early Permian) have been subjected to petrographic and geochemical studies in order to investigate provenance, tectonic setting, source rock and paleoclimate conditions in Khur section, Central Alborz. The Dorud Formation with a thickness of 360 m is mainly composed ...
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The sandstones of the Dorud Formation (Early Permian) have been subjected to petrographic and geochemical studies in order to investigate provenance, tectonic setting, source rock and paleoclimate conditions in Khur section, Central Alborz. The Dorud Formation with a thickness of 360 m is mainly composed of fine to medium grained sandstones with lesser amounts of carbonate and mudstone. In order to achieve the above-mentioned goals, 125 thin sections were subjected to petrographic studies. Modal analysis was performed on 20 thin sections and 13 samples of sandstones were analysed for major and trace elements. Based on petrographic studies the sandstones of the Dorud Formation are classified as quartzarenite with high textural and mineralogical maturity. Plotting point counting data on (Qt99.6, F0.2, L0.2( and (Qm95.9, F0.2, Lt3.9) triangles implies craton interior provenance. Also, major and trace elements based geochemical diagrams indicate that these sandstones deposited in a passive continental margin tectonic setting. According to petrographic and geochemical evidence the sandstones of the Dorud Formation derived from erosion of middle- to high-grade metamorphic, felsic igneous and quartoze sedimentary rocks. High mineralogical maturity, high values of chemical index of weathering (CIW) and chemical index of alteration (CIA) as well as SiO2 (%) versus Al2O3 + K2O + Na2O (%) diagram imply moderate to intense weathering under warm and humid climatic conditions. Passive continental margin tectonic setting and warm and humid paleoclimatic conditions is consistent with paleogeographic position of Iran during the Early Permian.