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]

See also

• Geology of Iran
• Zagros fold and thrust belt