Biostratigraphy microfacies of Oligo-Miocene deposits, Asmari Formation, in the Northeastern of Ilam, Lorestan zone

Authors

1 Master's degree in stratigraphy & Paleontology, Department of Geology, Faculty of Science, Lorestan University, Khorram Abad, Iran

2 Geology Department/ science Faculty/Lorestan University

3 National Iranian South Oilfield Company

Abstract

In order to interpret thebiostratigraphy, facies and depositional environment of the Asmari Formation in the northeast of Ilam, located in the Lorestan zone, a stratigraphic section with a thickness of 215 meters including thin, medium to thick layered limestones was selected. The Asmari Formation conformably overlies the Pabdeh Formation and is overlain the Gachsaran Formation n. The study of communities of large benthic foraminifera in this research led to the identification of 4 biozones of Ruplin- Chattian age:
Nummulites vascus, Nأummulites intermedius assemblage zone
Lepidocyclina- Operculina- Ditrupa assemblage zone
Archaias asmaricus, Archaias hensoni, Miogypsinoides complantus assemblage zone
Elphidium sp.14, Miogypsina sp. Peneroplis farsensis assemblage zone
Also based on the field observations, petrographic studies and textural characteristics as well as the abundance and distribution of foraminiferal fauna and other components, 10 carbonate microfacies have been identified. These carbonate microfacies were deposited in the inner, middle and outer ramp environments. The co-existence of coral and large benthic foraminifera such as Amphistegina, Archaias and Borelis , is indicative of tropical to subtropical waters under oligotrophic to slightly mesotrophic nutritional conditions.

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