H. Mosaddegh; A. Barari; H. Hamdi2
Abstract
During the Carboniferous time, Iran was a part of the northern margin of Gondwana. Carboniferous deposits of Iran are characterized by continental to shallow marine deposits. The studied section (Simeh- Kooh) is located in 5 Km Northwest of Damghan city in the east Alborz region. The lower Carboniferous ...
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During the Carboniferous time, Iran was a part of the northern margin of Gondwana. Carboniferous deposits of Iran are characterized by continental to shallow marine deposits. The studied section (Simeh- Kooh) is located in 5 Km Northwest of Damghan city in the east Alborz region. The lower Carboniferous Mobarak Formation consists of variable thickness of limestones interbeded with shale beds. The thickness of this section is about 115 m. The Mobarak Formation overlay the upper Devonian Jeirud Formation with a transitional contact and is unconformably underlain by lower Permian mixed siliciclastic-carbonate succession of Dorud Formation. This research is focused on the conodonts and facies. Conodont elements consist of 13 genus and 19 species. 5 Biozones is identified including, costatus zone (Latest Famennian), Sandbergi-L. crenulata zone, isostaticha-U. crenulata zone (Middle Tournaisian), typicus-anchoralis-latus zone (Late Tournaisian) and G. bilineatus zone (Middle-Late Visean) correspond to global zonation. The Tournaisian succession consist of alternation of organic matter rich shales and dark thin-bedded limestones is supposed to have deposited in a deep marine environment with a low oxygen condition. The paleontological and facies characteristics of Devonian-Carboniferous transition definitely show a rapid sea level rise and flooding event in this time in Eastern Alborz which corresponds with the Hangenberg Bioevent known in other parts of the world.
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.
