Abstract: This talk presents new data on reef development in a basin affected by a combination of rift and salt tectonics which exhumed Early Miocene reefs onshore and sank Plio-Pleistocene reefs offshore. The coast of the Red Sea is rimmed by shallow carbonate platforms and steep-sided platform fragments which extend as far as 25 km offshore.  These platforms have curvilinear coast-parallel shapes that resemble a jigsaw puzzle, and those near the shoreline are capped by modern reefs and lagoons.  These platforms consist of Plio-Pleistocene reef buildups which grew along the coast, but have split apart into rafts which glided offshore above the Middle Miocene salt detachment.   The shallow grabens between these rafts are occupied by reactive salt diapirs and younger sediments in shallow marine troughs, and some have active salt flows on the seafloor.  In areas of gentle bathymetric slopes, reef growth within rafts kept up with subsidence caused by seaward translation and salt withdrawal underneath.  This resulted in ~ 1 km thick keep-up reefs which aggraded as they glided seawards above the salt detachment.  In areas of steeper bathymetric slopes, reef growth did not keep up with subsidence, and Pliocene reefs back-stepped towards the shoreline as they sank and were buried by sediments to depths of 2 kilometers, and are classified as give-up reefs.  In general, keep-up reefs formed near the shoreline, and they transition offshore into give-up reefs as they glide over the salt detachment into deeper waters.

Using reefs as paleo-bathymetric indicators, our data indicate that the shelf areas in the northern Red Sea have subsided by ~600 meters during the Late Pliocene and Pleistocene due to reactivation of rift faults.  This substantially deepened the northern Red Sea relative to the southern Red Sea, where the shelves are broad and shallow.

In contrast to the subsidence of Plio-Pleistocene reefs offshore, Early Miocene reefs which straddle the eroded footwalls of tilt block outcrop in a 450 km long belt along the northern coast of the Red Sea.  These jack-up reefs have been exhumed by ~ 70 meters of footwall uplift along the eastern margin.  Significantly greater uplift is recorded by the elevations of Miocene reefs along the eastern flank of the Gulf of Aqaba, where jacked-up Miocene reefs reach elevations of 700 m.        

Bio: Dr. Abdulkader (Aboud) Afifi is a new Professor of Geology at KAUST with expertise in mineral and hydrocarbon exploration and the regional geology of the Middle East.  He started work in 1980 with the US Geological Survey Mission in Saudi Arabia on geological mapping and mineral exploration in the Arabian Shield.  He joined Saudi Aramco in 1991 and held various technical and management positions in its Exploration organization until August 2018.  

Aboud has a PhD in geology from the University of Michigan, Ann Arbor, a Masters from the Colorado School of Mines, and a Bachelors (high honors) from KFUPM.  He also completed the General Management Program at Harvard Business School.  He is active in professional societies as an author, lecturer, conference organizer, and field trip leader.  He served for many years as an associate editor of the journal GeoArabia. He served the American Association of Petroleum Geologists as an International Distinguished Lecturer, Councilor, and President of the Middle East Region.  He also served on various committees including the Alumni Advisory Board of the University of Michigan’s Earth and Environmental Sciences Department and the Advisory Committee of the Geohazards Research Center at King Abdul Aziz University.