Asmari Formation

The Asmari Formation is a geological formation in western Iran. Located in the western Zagros Mountains, it is a carbonate formation that largely consists of limestone, dolomitic limestone, dolomite, and marly limestone.[1] There are also smaller amounts of anhydrite, lithic sandstone, and limey sandstone.[1] The formation dates to the Oligocene and Miocene periods and is a major hydrocarbon reserve.[2][3] It has been producing oil since the 1930s.[4] It also forms a major aquifer, which discharges at various springs in the Zagros region.[5]

The Asmari Formation's basic biostratigraphy was established in the 1950s and it was formally described in 1965.[4] It consists of carbonate platforms that were formed in 6 distinct stages.[3] The formation is named after the Asmari Mountains southeast of Masjed Soleyman, and its type sample was taken from the Tang-e Gel Torsh in these mountains.[6]

The Asmari Formation was deposited at a time when the Tethys Ocean was finally closing and the Zagros Mountains were first rising.[6] During this period, the region was a shallow ocean gradually getting less deep.[6] By the time of the succeeding Gachsaran Formation, this process had culminated in the sea shrinking to lagoons.[6]

In the southwestern Zagros, the Asmari Formation sits on top of the Pabdeh Formation.[1] In the Fars and Luristan regions, the Asmari Formation sits on top of the Jahrum and Shahbazan Formations.[1] The Asmari Formation is thickest in the northeastern part of the Dezful Embayment.[1]

The formation has various microfossils including planktonic foraminifera, echinoids, red algae, ostracoda, and oncoids.[3] Individual species include Globigerina, Turborotalia cerroazulensis, Hantkenina, Nummulites, Lepidocyclina, Miogypsina, Elphidium, Peneroplis farsenensis, and Borelis melo curdica and Borelis melo melo.[4]