Pleistocene coral reef terraces on the Saudi Arabian Side of the gulf of aqaba, red sea

Abstract

A major geomorphic feature of the coastal Red Sea region is represented by Pleistocene raised marine terraces that occur on both sides of the Gulf of Aqaba. Those bordering the Saudi Arabian sector have received little attention thus far, and are comparatively less known than their counterparts in the Sinai sector of the Gulf and in the Red Sea. As is the rule in the Red Sea region, the best developed marine terrace system is reefal and pertains to the last interglacial (Marine Isotope Stage 5e = MIS5e, *125 ka BP), although older Pleistocene terraces also occur. All such deposits are very fossiliferous and most carbonates are relatively unaltered, providing suitable material for geochronological purposes. Syndepositional marine botryoidal aragonite cements have been identified infilling vugs in the host bedrock at some sites. In some respect, the MIS5e deposits are unique, reflecting the structurally-controlled bedrock geology and the Gulf’s topography. The Gulf of Aqaba is rather narrow and characterized by steep and precipitous topography along its flanks. Coastal marine deposits commonly plaster the crystalline Arabian basement which faces the present seashore, extending from the Jordan border to almost two thirds of the coastal strip. Terraces sitting on this basement have been tectonically uplifted to considerable altitudes (up to 26 m) over the present mean sea level (m. s.l.). The bulk of the marine deposits represent upper fore-reef to beach settings, with better developed back-reef to lagoonal facies only preserved in those favourable conditions (wadi valleys) where sufficient accommodation space was available during the MIS5e to allow inland marine expansion. This is observed in the north at Al Wasel, and *14 km south of Ra’s Suwayhil as Saghir. The terraces further to the south lie instead over a more recent bedrock, including Miocene sedimentary strata. Here MIS5e deposits are found close to standard altitudes between *4-8 m above present m.s.l., and preserve shallow reefal habitats, as seen at Ash Shaykh Humayd. A rare example of a putative MIS5e salinamangal complex has been identified in the area of Ra’s Suwayhil as Saghir at *23 m above m.s.l.