Biostratigraphy and depositional environment evolution of the Asmari Formation at the Shajabil anticline, Iran
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ORIGINAL PAPER
Biostratigraphy and depositional environment evolution of the Asmari Formation at the Shajabil anticline, Iran Zahra Saleh
Received: 3 February 2013 / Accepted: 10 June 2013 # Saudi Society for Geosciences 2013
Abstract In the present research, biostratigraphy and paleoecology of the Asmari Formation at the Shajabil anticline, northwest Yasuj in the Izeh zone are discussed. The Asmari Formation at the studied area is Rupelian–Chattian to Burdigalian in age. In the study, 18 genera and 29 species of benthic foraminifera have been identified. Besides, the following biozones which reflect Rupelian–Chattian to Burdigalian age are identified for the Asmari Formation: (1) Lepidocyclina– Operculina–Ditrupa; (2) Archaias asmaricus–Archaias hensoni–Miogypsinoides complanatus; (3) Peneroplis farsenensis_Elphidium sp.14–Miogypsina sp.; (4) Borelis melo–Borelis melo curdica. Relying on fossils, Coral and Corallinacea have been detected depositional environment. The paleo-ecological factors are identified for the Asmari Formation at the study area: water salinity, 34 to more than 50 psu; water depth of 90 to 0 m; water temperature of 14 °C to more than 27 °C in a subtropical to tropical environment, oligotrophoic to mesotrophic conditions. Keywords Oligomiocene . Asmari Formation . Biostratigraphy . Temperature . Salinity
color massive Limestone. Some sandstone and anhydrite layers (Ahwaz and Kalhur Members) inter-finger the carbonates of the Asmari Formation. In most places, The Asmari Formation overlies the shale and marls of the Pabdeh Formation and underlies with evaporates and marls of the Gachsaran Formation (Motiei 1993) (Fig. 1). Recent works concerning on the facies and depositional environments, paleo-ecology and sequence stratigraphy of the Asmari Formation are: Seyrafian (2000); Seyrafian and Hamedani (2003); Mossadegh et al. (2009); Allahkarampour Dill et al. (2010); Sooltanian et al. (2011); Seyrafian et al. (2011); Allahkarampour Dill et al. (2012). Study area The studied section is located at 40 km Northwest Yasuj close to the village of Miantongan in the Shajabil anticline with geographical coordinates of N 30˚54′36″, E 51˚02′16″ (Fig. 1). In this study, thickness of the Asmari Formation is 375 m.
Methods Introduction The Asmari Formation (Oligocene–Early Miocene) is considered the most important oil reservoir in the Zagros Basin, Iran. At first, the Asmari Formation was introduced in the Tang–e–Goletorsh and was called series of the Asmari limestone (Richardson 1924). In this section, thickness of the Asmari Formation is 314 m and includes cream to brown Z. Saleh (*) Department of Geology, Faculty of Science, University of Isfahan, Isfahan, Iran e-mail: [email protected]
The beginning research is assigned to biostratigraphy of the Asmari Formation based on benthic foraminifera using of Laursen et al. (2009) studies (Table 1). Carbonate microfacies classification of the Asmari Formation has been made according to the tissue content, the existence of microfossil and macrofossil based
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