Midyan: Window into Saudi Arabia’s Red Sea Geology

By

Geraint W. Hughes¹, Robert S. Johnson², Rami A. Kamal¹

(1) Saudi Arabian Oil Company, Dhahran, Saudi Arabia (2) Saudi Arabian Oil Company

 Within the Midyan area of northwest Saudi Arabia is exposed the most comprehensive succession of lithostratigraphic units deposited in the present Red Sea region during the Late Cretaceous to Pleistocene. The varied lithologies include siliciclastics, carbonates and evaporites, each of which relates to a different depositional episode in the regions geological history that resulted from anti-clockwise rotation of the Arabian Plate away from Africa. The region experienced additional deformation related to the transition from an Oligo-Miocene Red Sea extensional regime into the Aqaba Fault Zone left-lateral transtensional regime during the latest Miocene. Upper Cretaceous shales of the Adaffa Formation unconformably overlie basement, and are unconformably overlain by the Neogene succession that displays significant lithological similarities to that described from the Gulf of Suez hydrocarbon province - the lithostratigraphic equivalents are given in parentheses. The Tayran Group (Nukhul Formation) includes marginal marine siliciclastics of the Al Wajh Formation (Shoab Ali Member) and represents the earliest rift-associated sediments deposited during the earliest Miocene. Lower Miocene shallow marine carbonates of the Musayr Formation (Gharamul member) unconformable overlie the AlWajh, and are locally developed. Lower Miocene submarine evaporites of the Yanbu Formation (Ghara Member) were regionally deposited under locally restricted conditions but are not exposed in the Midyan region. Rapid Early Miocene subsidence enabled a thick succession of deep marine, planktonic-foraminiferal mudstones and thick submarine fan sandstones of the Burqan Formation (Rudeis Formation). Carbonates, marine mudstones and submarine evaporites of the Maqna Group (Kareem and Belayim Formations) unconformably overlie the Burqan Formation, and were deposited during latest Early Miocene to earliest Middle Miocene. Within the region, thick anhydrites of the Mansiyah Formation (South Gharib Formation) were deposited extensively during the Middle Miocene, and are overlain by poorly exposed sands, shales and thin anhydrite beds of the Ghawwas Formation (Zeit Formation), deposited during the Middle to Late Miocene.