Foraminiferal Biostratigraphy of Oligocene to Lower Miocene Deposits (Pabdeh, Asmari, Gachsaran formations) in south-west of Qir, Fars
Subject Areas :نوشا نوروزی 1 , Daneshian 2 , Baghbani 3 , Aghanabati 4
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Keywords: Foraminifera biostratigraphy Lower Oligocene-Miocene Fars. ,
Abstract :
Lower Oligocene and Miocene deposits in Zagros include several formations with considerable lithological changes and faunal diversification. To study these formations more accurately and identifying the boundary among them, 414 samples of Halegan well #1 on the southwest of Qir were studied. Lower Oligocene and Miocene deposits of Halegan well #1 with 414 meter thickness; consist of argillaceous limestone, dolomite, and limestone with intercalation of marl and gypsum and formed the Pabdeh, Asmari and Gachsaran formations. The upper parts of Pabadeh Formation at its upper section include planktonic foraminifera with the age of lower Oligocene Foramtion has Rupelian age and covers conformably the lower part with late Eocene age. The upper boundary of the Pabadeh Formation is conformable with the Asmari Formation. Based on Thomas (1948) definition of the Asmari Formation, in the Halegan well, the Asmari Formation consists of the lower (Oligocene) and middle Asmari (Aquitanian). The upper boundary of the Asmari Formation is unconformable with the Gachsaran Formation. Based on paleontological studies of the lower Oligocene-Miocene deposits of Halegan well, 32 genera and 48 species of benthonic foraminifera and 13 genera and 21 species of planktonic foraminifera were identified and five biozones can be correlated with Wynd’s (1965) biozones 55,56,57,59,63. In ascending order they are: 1-small Globigerina spp. assemblage zone (No. 55) 2-Lepidocyclina-Operculina-Ditrupa assemblage zone (No. 56) 3-Nummulites intermedius-Nummulites vascus assemblage zone (No. 57) 4-Austrotrillina asmariensis-Peneroplis evolutus assemblage zone (No. 59) 5-Rotalia-Elphidium assemblage zone (No. 63)