The Permian-Triassic Khuff Formation of central Saudi Arabia
Résumé
The Permian-Triassic Khuff Formation crops out in central Saudi Arabia along a N-S belt, some 1,200 km in length. It is 171.4 m (562.2 ft) thick in the type section and divided into five members; from oldest to youngest: Ash Shiqqah (formerly Unayzah member of the Khuff Formation), Huqayl, Duhaysan, Midhnab and Khartam. The base of the Khuff Formation is recognised as a regional unconformity (Pre-Khuff Unconformity), and the top of the formation is defined by the conformable contact with the overlying Sudair Shale. The Ash Shiqqah Member is tentatively dated as ?Middle Permian ?Capitanian (?Midian) based on the presence of the fusulinids Monodiexodina kattaensis and Reichelina sp. The Huqayl Member is tentatively dated as ?Late Permian ?Wuchiapingian (?Dzhulfian) based on an assemblage of smaller foraminifers dominated by Pseudomidiella cf. labensis, Earlandia? spp. and Neodiscus aff. qinglongensis. The Duhaysan Member is dated as Late Permian (Wuchiapingian-Changhsingian) based on Hemigordius baoqingensis, Graecodiscus cf. kotlyarae, "Dentalina" hoi, and Colaniella cf. minuta. The Midhnab Member is dated as Changhsingian (Dorashamian) based on Paradagmarita sp. and "Glomospirella spirillinoides" and the disappearance of the genera Nankinella and Globivalvulina. Within the continental facies in the upper part of the Midhnab Member, incised channels facies yielded the Late Permian Midhnab Flora. The Lower Khartam Member is also dated as latest Permian (Dorashamian) based on the presence of several species of Paradagmarita and "Nodosaria" dzuhulfensis in the lowest beds of the member, and the ostracods Paraparchites spp., Knoxiella spp. and Kloedenellitina sp. throughout the Lower Khartam Member. The Upper Khartam Member is assigned to an Early Triassic ("Scythian") age based on the occurrence of the characteristic annelid Spirorbis phlyctaena.