Microfacies, biostratigraphy and sedimentary environments of the Eocene sedimentary successions in the Zagros and Sanandaj-Sirjan Zone (Iran)

Language
en
Document Type
Doctoral Thesis
Issue Date
2017-08-08
Issue Year
2017
Authors
Almasinia, Banafsheh
Editor
Abstract

Two Eocene sections in the Zagros Mountains and two in Sanandaj-Sirjan Zone of west and cental Iran have been investigated with the purpose to determine the age of the sections based on planktonic and benthic foraminifera, to analyze the sedimentary micofacies, sedimentary environments, sequence stratigraphic pattern, diagenetic processes, stable isotopes (δ18O, δ13C), and to determine the absolute age span using strontium isotopes. Based on foraminifera, the Shalamzar section (446.2m) belongs to the Middle Eocene (Lutetian), the Hamzeh-Ali section (172m) belongs to Upper Cuisian-Lutetian, and the Zefreh section (43m) to the Bartonian and Priabonian. Finally, the Soh section (171m) is Priabonian in age. The former two sections are from the Zagros Mountains, the latter two from the Sanandaj-Sirjan Zone. The carbonate microfacies consist mainly of mudstone, wackestone, packstone, and occasionally grainstone with a variety of planktonic and benthic foraminifera. Altogether 17 microfacies could be recognized. According to Wynd (1965) six subzones could be determined in the sections, one belonging to the Late Early Eocene (No.46), the other five to the Middle and Late Eocene (49-53). In the Sanandaj-Sirjan Zone also siliciclastic facies occur (mainly siltstone, sandstone, and conglomerate). For the Shalamzar section a homoclinal ramp is postulated, whereas the Hamzeh-Ali section conforms to a distally steepened ramp. In the Hamzeh-Ali section five depositional sequences corresponding to third-order sea-level fluctuations could be recognized, in the Shalamzar section three, in the Zefreh section two, and in the Soh section three depositional sequences. Post-depositional and diagenetic processes include bioturbation, cementation, dolomitization, silicification and formation of porosities. Based on oxygen stable isotopes paleotemperature values for the Hamzeh-Ali section averaged 28°C and for the Shalamzar section 22°C. Three diagenetic trends have been determined using organic matter: In the Hamzeh-Ali section, most samples were affected by marine diagenesis and a few samples by shallow burial diagenesis; samples of the Shalamzar section were affected by marine to burial diagenesis; in the Soh section most samples indicate shallow burial diagenesis and a few samples meteoric diagenesis. In the Zefreh section, all samples were affected by shallow burial diagenesis. Based on strontium isotope analyses the Hamzeh-Ali section could be chronostratigraphically placed in the Cuisian and Lutetian, whereas the Shalamzar section belongs to the Lutetian. The Zefreh section belongs to Rupelian and the Soh section to the Priabonian—Rupelian.

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