Biostratigraphy, paleoecology, and paleoenvironmental reconstruction of the Asmari formation in Zagros basin, southwest
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ORIGINAL PAPER
Biostratigraphy, paleoecology, and paleoenvironmental reconstruction of the Asmari formation in Zagros basin, southwest Iran Umid Kakemem 1 & Mohammad Hossein Adabi 2 & Abbas Sadeghi 2 & Mohammad Hasan Kazemzadeh 3
Received: 7 February 2015 / Accepted: 18 September 2015 # Saudi Society for Geosciences 2016
Abstract The present work is focused on the biostratigraphic analysis, paleoecological interpretations, and paleoenvironmental reconstruction of sediments of the Asmari Formation. The Asmari Formation, which is mainly composed of carbonates, has been studied in the Rig anticline in the Izeh zone, Zagros Basin, Iran. The Asmari Formation at the study area is Rupelian to Burdigalian in age, based on the occurrence of 21 foraminiferal species belonging to 21 genera which led to identification of five assemblage zones including (1) Nummulites vascusNummulites fichteli, (2) Lepidocyclina-OperculinaDitrupa, (3) Archaias asmaricus-Archaias hensoniMiogypsinoides complanatus, (4) Miogypsina sp.Elphidium sp. 14-Peneroplis farsenensis, and (5) Borelis melo group-Meandropsina iranica. Detailed petrographic analysis led to the recognition of 13 facies that are belonging to four depositional environments including tidal
flat, lagoon, shoal, and open marine environments. These carbonate facies were deposited in shallow marine carbonate platform as a homoclinal ramp type. The lower part of the Asmari Formation deposited in an open marine environment with normal water salinity, while the middle and upper parts of the Asmari Formation were deposited in a shallower water with alternating intermittent normal and higher water salinity. Occurrence of larger benthic foraminifera such as Nummulites, Operculina, Heterostegina, Amphistegina, Archaias, Peneroplis and Borelis, coral and red algae reflect mesophotic to oligophotic conditions in subtropical to tropical environments with a high nutrient stability in a mesotrophic to oligotrophic conditions existed during deposition of the Asmari Formation. Keywords Asmari Formation . Biostratigraphy . Paleoecology . Paleoenvironment . Oligocene-early Miocene
Introduction * Mohammad Hasan Kazemzadeh [email protected] Umid Kakemem [email protected] Mohammad Hossein Adabi [email protected] Abbas Sadeghi [email protected] 1
Special Drilling Services Devision, National Iranian Drilling Compay, Ahwaz, Iran
2
Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
3
Tehran Energy Consultants Company, Tehran, Iran
The Asmari Formation is a thick carbonate sequence in Zagros Basin and is the largest oil reservoirs in Iran (Alavi 2004). At its type section in Tang-e Gel Tursh on the southwestern flank of the Kuh-e Asmari anticline, this formation consists of a 314 m of medium to thick bedded carbonate succession (Thomas 1950). In other regions, the thickness of the Asmari Formation varies from 90 to 594 m with some sandstone and anhydrite layers. The Asmari Formation varies in age so that the age of this formation is Rupelian to B
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