Vol.:(0123456789) 1 3 Carbonates and Evaporites (2021) 36:26 https://doi.org/10.1007/s13146-021-00696-8 ORIGINAL ARTICLE Biostratigraphy of early cretaceous sediments (Fahliyan Formation, Berriasian–Barremian) in Aghar19 (Zagros Basin, SW Iran) Masoud Abedpour 1,2  · Massih Afghah 2  · Mohammadsadegh Dehghanian 3 Accepted: 17 April 2021 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract The Fahliyan Formation, which is part of the Khami Group is one of the important oil resources in the lower cretaceous strata in the Zagros area. Index Foraminifera, continuity, and discontinuities have been used to identify the boundaries of this formation. To study biostratigraphy on Fahliyan Formation, the subsurface stratigraphic section of Aghar19 was selected in the southwest province of Iran. The thickness of this formation in this section is measured 215 m, including thin-to-medium-bedded limestone and dolomitic limestone. Fahliyan Formation continuously overlies Surmeh and Hith Formation and underlies Gadvan Formation. Vertical study of this formation has led to the identifcation of calcareous algae and foraminifera, which include 48 genera, 32 species, and three biozones in the sediments of the Fahliyan Formation. These biozones include: (1) Dukhania zone; (2) Pseudocyclammina lituus, Trocholina zone; and (3) Orbitolina, Choffatella, Salpingoporella Assemblage zone. Based on the established biozones, the age of the Fahliyan Formation in the Aghar19 section was determined from Berriasian to Early Barremian. Keywords Biostratigraphy · Fahliyan Formation · Berriasian · Barremian · Zagros · Iran Introduction Fahliyan, Gadvan, and Garau Formations were introduced by Berriasian–Barremian sediments in the Zagros and Per- sian Gulf areas. In the Zagros area, these Formations were laterally changed in terms of biofacies and lithofacies, due to the tectonic and paleogeographical settings in Berria- sian–Barremian. The sediments with neritic shale, carbon- ate, hemipelagic and pelagic facies formed. The Fahliyan and Gadvan Formations in Fars, south of Dezful, and south- east of Persian Gulf, as well as Garau, Fahliyan, and Gadvan Formations in the north of Dezful embayment, Lurestan, and northwest of Persian Gulf. Zagros has been frst divided into four zones, including Khuzestan, Lurestan, Coastal, and the Interior Fars (James and Wynd 1965). The boundary between Jurassic and Cretaceous of Zagros area was a topic of interest for Iranian geologists. There is no evidence on the break-in sedimentation between Jurassic and Cretaceous sequence, particularly in feld observation. Thus, studying the biostratigraphy of the Jurassic–Cretaceous sequence reveals regression between the mentioned strata in diferent parts of the Zagros area, as well as a better comparison efect of the Cimmerian orogeny phase on other regions in the Arabian Plate (Aghanabati 1998). Biostratigraphic data were previously collected from the upper Jurassic and the lower Cretaceous of Interior Fars by Afghah (2006) and Kalantari (1976). Some records confrmed that the upper lithostrati- graphic limit of the Fahliyan Formation was not synchronous with biostratigraphy (Afghah et al. 2016). Based on the tectonic setting, the rate of sediment supply, relationship between the formation sequences, the sea-level fuctuation, and the age determination is provided by the biofacies and lithofacies study which creates a sedimentary model and creates a relationship between the depositional system with other regions of the Zagros and the Arabian Plateau and enables the analysis of Jurassic–Cretaceous suc- cession facies. Few studies have been performed on the Fahliyan oil-rich Formation. (e.g. Afghah 2006; Abedpour 2016; * Masoud Abedpour Ma_493@yahoo.com 1 Department of Geology, College Fars Science and Research Branch, Islamic Azad University, Fars, Iran 2 Department of Geology, Shiraz Branch, Islamic Azad University, Shiraz, Iran 3 Department of Geology, Bandar Abbas Branch, Islamic Azad University, Bandar Abbas, Iran