Abstract

The Asmari Formation is a thick carbonate sequence of the Oligocene-Miocene in the Zagros Basin, southwest of Iran. This formation is located in Bandar Abbas and Coastal Fars regions on the following two sections: Anguro anticline (west-northwest of Bandar Abbas) and Gavbast anticline (southwest of Lar County). The Asmari Formation has diameters of 68 and 26 m in the Anguro and Gavbast sections, respectively. This formation is composed of limestone, dolomitic limestone and an altered form of marl. Based on the results of petrographic analyses, 7 facies were identified in the Anguro and Gavbast sections in the study region. The facies were deposited on the following 3 belts: tidal flat (MF 1 - 3), lagoon (MF 4 - 5) and open marine (MF 6, 7). According to evidence such as the gradual change of microfacies, the lack of main reef barriers, and the lack of slumping and sliding features, the Asmari Formation was formed in a marine environment of carbonate homoclinal ramp type. This environment is composed of the following two subenvironments: the inner ramp and the middle ramp. The comparison of the facies identified in the Anguro and Gavbast sections indicates that Gavbast section is mainly composed of lagoon facies. Moreover, the Anguro section demonstrates more facies diversity than Gavbast section.

Highlights

  • The Asmari Formation is a thick carbonate sequence of the OligoceneMiocene in the Zagros Basin, southwest of Iran

  • The Asmari Formation contained within the Anguro section includes sequences of limestone, dolomitic limestone, and an alternation of marl and gray limestone

  • At the base of the Asmari Formation located on this section, gray limestones enriched with large benthic foraminifera accumulations were found next to other skeletal components (Figure 4)

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Summary

Introduction

The Asmari Formation (the most important reservoir of Iran) is a thick carbonate sequence of the OligoceneMiocene in the Zagros Basin, southwest of Iran. The Asmari Formation, at its type section, is deposited during the late Oligocene (Rupelian)-early Miocene (Burdigalian) (Figure 1). In spite of the extension of the deposits of the Asmari Formation in the Zagros Basin, these deposits have not been studied properly. Numerous sections were studied for the careful examination of the Asmari Formation in the Bandar Abbas region, on the east of the coastal Fars (southwest of Lar County). The main objectives of this research were focused on 1) a description of the facies and their distribution on the Oligocene-Miocene carbonate platform, and 2) describing and interpreting the depositional environments represented by the Asmari Formation

Geological Setting
Study Area and Methodology
Previous Works
Lithology
Biostratigraphy
58. Archaias operculiniformis totalrange zone Oligocene
Coskinolina-Rhapydionina Assemblage Zone
Facies Description and Depositional Environment
MF 3: Ooid Packstone to Grainstone
Lagoon Facies Association
MF 5: Benthic Foraminifera Pelloidal Packstone to Grainstone
Facies Association and Depositional Model
Findings
Conclusions

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