113 © 2017 Conscientia Beam. All Rights Reserved. MICROBIOSTRATIGRAPHY AND SEDIMENTARY ENVIRONMENT OF THE SARVAK AND KAZHDUMI FORMATIONS IN BAHREGANSAR OIL FIELD Somayeh Ahmadi 1 Seyed Hamid Vaziri 2+ Keyvan Khaksar 3 Davood Jahani 4 Mohsen Ale Ali 5 1,5 Department of Geology, Science and Research Branch, Islamic Azad University, Tehran, Iran 2,4 Department of Geology, North Tehran Branch, Islamic Azad University, Tehran, Iran 3 Faculty of Basic Sciences, Qom Branch, Islamic Azad University, Qom, Iran (+ Corresponding author) ABSTRACT Article History Received: 6 September 2016 Revised: 14 July 2017 Accepted: 31 July 2017 Published: 9 August 2017 Keywords Microbiostratigraphy Depositional environment Microfacies Sarvak Kazhdumi Albian Cenomanian. The aim of this paper is investigation of microbiostratigraphy and sedimentary environment of the Sarvak and Kazhdumi formations in Bahregansar oil field. To investigate these units, microbiostratigraphy and microfacies analyses were carried out on nearly 600 m of cuttings, including cutting plug samples and thin sections prepared from Bahregansar oil field in the Persian Gulf, SW Iran. 22 Species and genera of foraminifera were recognized and four biozones were identified. Also the microfacies analysis of the Sarvak and Kazhdumi formations in Bahregansar oil field is led to recognition fourteen microfacies of three facies belts (depositional environment) including open marine, bar and lagoon environments. Contribution/Originality: This study is one of very few studies which have investigated the Upper Cretaceous of oil fields. The results of this study will help to make Upper Cretaceous biozones, interpretation of microfacies and depositional environments. 1. INTRODUCTION Many geologists have focused on the carbonate petroleum reservoirs of the Persian Gulf because of the well- known oil productivity of this region (Afghah and Farhoudi, 2012). The Sarvak Formation is one of the most significant carbonate reservoirs known to be an oil producer in the Bahregansar oil field (Tabiyejou et al., 2014). Bahregansar field consists of several separate hydrocarbon accumulations within following formations and from top to bottom respectively includes Ghahr, Asmari, Sarvak, Kazhdumi and Fahliyan formations. Although the Bangestan carbonates are known as significant reservoirs in the Middle East, their detailed biostratigraphy is still ambiguous. The stratigraphic position of the Sarvak Formation is also another reason for the importance of the biostratigraphic study. According to James and Wynd (1965) Zagros is divided into four main zones: Khuzestan, Lurestan, Coastal Fars and Interior Fars (James and Wynd, 1965). They suggested that Cenomanian benthic foraminifers are well expanded in the Khuzastan, Coastal and Interior Fars areas whereas pelagic facies are well dominant in the Lurestan region in order to determine the lower and upper lithostratigraphic boundary of the Sarvak Formation (Wynd, 1965). International Journal of Geography and Geology 2017 Vol. 6, No. 5, pp. 113-122 ISSN(e): 2305-7041 ISSN(p): 2306-9872 DOI: 10.18488/journal.10.2017.65.113.122 © 2017 Conscientia Beam. All Rights Reserved.