ABSTRACT
Beachrock is common and widely distributed along the Saudi Red Sea coast. It onlaps the 3–6 m high OIS5e coastal coral reef platform along many parts of the Saudi Arabian Red Sea coast between Duba and Al-Qattan. The dominant cements in the beachrock are aragonite and 19.7%–30.8% MgCO3, suggestive of marine phreatic diagenesis, leaving a low primary intergranular porosity. At Rabigh, the age of the beachrock ranges from 4,200 to 2,400 ± 30 yr BP with the laterally extensive beachrock layers deposited during the falling stage of the Holocene sea-level highstand. A prominent notch cut into the OIS5e coral reef platform, between 1 and 1.5 m above mean sea level, probably represents a wave cut feature formed during the Holocene sea-level highstand. This is confirmed near Rabigh where minor beachrock is present within the notch and articulated Holocene Tridacna in growth position are incorporated into beachrock at the base of the coral reef platform. In the coastal region, the lower porous part of the coral reef platform was extensively cemented with aragonite during the Holocene sea-level highstand, thus making this part of the reef platform more resistant to current marine erosion.
