Depending on the author, various definitions and names for the members of the Khuff Formation have been proposed, which may lead to confusion. Vaslet et. al. (2005) defines the members as such (from oldest to youngest):[2]
The Al Siqqah Member is the oldest of the members, tentatively dated to the middle Permian (Capitanian). It is 35 meters thick at the type section, becoming thinner to the southeast. It has previously been referred to as the Unayzah Formation or Unayzah Member.
The Huqayl Member has been dated to the late Permian (?Wuchiapingian) based on foraminifer assemblage. It ranges from 30 to 40 meters in thickness.
The Duhaysan Member is 13.4 meters thick at Jabal Duhaysan, and is believed to be late Permian (Wuchiapingian-Changhsingian) in age.
The Midhnab Member (or Midhnab Shale) is believed to date to the Changhsingian and is about 60 meters thick in the Ad Dawadimi quadrangle.
The Khartam Member (formerly the Khartam Limestone) is the youngest member, with the lower part dating to the latest Permian and the upper part to the early Triassic.
Depositional environment
The Khuff Formation was deposited on the outer shelf of the Arabian Platform and represents a shallow carbonate platform, with a coastline oriented northeast-southwest and facing the spreading Neotethys Ocean. The various units have been interpreted as lagoonal tidal sand flats or barrier beaches, outer-shelf conditions below storm wave base and deposition around storm wave base. The known fossil content supports the interpretation of the Khuff Formation as a marine environment. The presence of Tethyan brachiopods suggest a subtropical and warm climate, while cosmopolitan, endemic and Gondwanan brachiopod taxa indicate the area was open to outside influence, and the conodont fauna confirms a shallow marine habitat.[3][4]
