Vol.:(0123456789) 1 3 Carbonates and Evaporites (2020) 35:103 https://doi.org/10.1007/s13146-020-00635-z ORIGINAL ARTICLE Biostratigraphy of the Kazhdumi Formation (Albian), northeast of Shiraz, Zagros Basin (SW of Iran) Massih Afghah 1  · Mahnaz Parvaneh Nejad Shirazi 2  · Mojtaba Keshavarzi 2 Accepted: 7 September 2020 © The Author(s) 2020 Abstract The Kazhdumi Formation is one of the most signifcant rock units in the Bangestan Group in Zagros Basin. In this study, one section of the Kazhdumi Formation (Kuh-e-Rahmat) was selected for research. The section is extended approximately 89 m thick. The lower lithostratigraphic limit of the Kazhdumi Formation is marked by an oxidized zone, while the upper boundary is described as gradational type. The stratigraphic distribution of foraminifer taxa confrms two biozones in the studied section: Hemicyclammina sigali and Mesorbitolina subconcava in the Assemblage Zone and Mesorbitolina aperta in the range zone. Based on the investigated calcareous algae, Trinocladus tripolitanus, Range Zone is described. The identifed calcareous algae are well distributed along Kazhdumi Formation. According to the received data of the established biozones, the age of the Kazhdumi Formation is Albian. Keywords Albian · Foraminifer · Calcareous algae · Zagros · Iran Introduction The Zagros area is one of the most well-known oil pro- ducing regions in the world. Many geologists have studied the stratigraphy of the mentioned area (e.g., James and Wynd 1965; Kalantari 1976). Previous oil exploration was conducted by the Anglo-Persian Oil Company in 1909 (Afghah and Farhoudi 2012). Because of the oil- field development in southwestern Iran, studies of the Zagros rock units are required by the National Iranian Oil Company (Motiei 1992). Among rock units studied in the Zagros basin, the Kazhdumi Formation (Albian) is significant for Iranian geologists because of its char- acteristics as a petroleum source rock. Thus, the strati- graphic position and the biostratigraphic characteristics of Kazhdumi Formation are valuable for National Iranian Oil Company geologists. James and Wynd (1965) studied the Kazhdumi Formation for the first time, which is a part of the Bangestan Group. This group consists of the Kazhdumi, Sarvak, Surgah, and Ilam formations. In gen- eral, the lithological aspect of the Kazhdumi Formation is comprised of dark bituminous shale (Soleimani 2009). The surrounding strata, Dariyan (Aptian) is the underly- ing formation, while Sarvak is known as the overlying formation (Cenomanian). These strata are well exposed in many parts of the Zagros mountain ranges. Both rock units are composed of carbonates that extend along the Zagros Basin. James and Wynd (1965) divided the Zagros Basin into four zones: Khouzestan, Lurestan, Coastal, and Interior Fars (Fig. 1). The Kazhdumi Formation changes laterally to carbonate facies from the type section (Khuz- estan area) to the Interior Fars region, which consists of brown orbitolinid marls (Afghah et al. 2007). The lithostratigraphic contact between the Dariyan and Kazh- dumi formations is marked by an oxidized iron nodule zone (Afghah and Shaabanpour Haghighi, 2014; Soleim- ani et al. 2014; Motiei 1992; James and Wynd 1965). The Sarvak formation (gray well-bedded limestone) covers the marl of Kazhdumi Formation. It should be emphasized that the biostratigraphy of the Sarvak Formation reveals various lower biostratigraphic limits covering the con- tinuous sedimentation of the Kazhdumiand Sarvak for- mations during the Albian-Cenomanian time. However, the biostratigraphic characteristic of the Kazhdumi For- mation is not clear, particularly in the Interior Fars area * Massih Afghah massihafg2002@yahoo.com 1 Department of Geology, Shiraz Branch, Islamic Azad University, Shiraz, Iran 2 Geology Department, Payame Noor University, PO Box: 19395-3697, Tehran, Iran