Investigating paleoenvironments and reservoir potential of rudist facies of the Tarbur Formation in the Zagros sedimentary Basin, SW Iran

This study investigates paleoenvironments and reservoir potential of rudist facies of the Upper Cretaceous Tarbur Formation in the Zagros sedimentary Basin. Deposition of the Tarbur Formation mainly took place on a carbonate homoclinal ramp. The rudist facies associated with a shoal, barrier or buildup environment include: 1–rudist grainstone and 2– bioclast-rudist packstone/grainstone together with the autochthonous rudist boundstone facies.‌The middle ramp or reef front environment is represented by:‌1–rudist wackestone/ packstone, 2–‌rudist-orbitoid wackestone/‌packstone, 3– bioclast-rudist-orbitoid wackestone/ packstone, 4–orbitoid-‌rudist grainstone, ‌‌‌5–rudist- foraminifera-intraclast grainstone and 6– bioclast- rudist packstone/floatstone/rudstone. The rudist facies deposited in a lagoon or back reef environment are as follows: 1–miliolid-Loftusia-orbitoid- rudist wackestone/ packstone. 2–Dicyclina-miliolid-bioclast (rudist) wackestone/ packstone. 3–bioclast- miliolid-‌rudist wackestone/ packstone. 4–foraminifera-bioclast-rudist wackestone/ packstone.‌5–rudist-intraclast-miliolid packstone.‌ ‌6–foraminifera-rudist packstone/ grainstone. Rudist boundstone facies was occasionally deposited in lagoon rudist patch reefs. The rudist facies of the carbonate ramp of the Tarbur Formation were deposited in shallow warm waters with temperature of more than 25 ºC. Bioclastic fragments of rudists could have been removed from in situ rudist colonies in a shoal, barrier or buildup environment, and possibly also from a restricted lagoon patch reef and transported by waves and high water energy. Autochthonous rudist boundstone facies as well as rudist packstone/ grainstone and rudist rudstone/floatstone facies tend to have high reservoir potential in the Tarbur Formation.