Modern Red Sea coral reefs: a review of their morphologies and zonation

Abstract

Modern reefs in the Red Sea exhibit different controls on their formation. The majority of the reefs belong to the fringing type. These reefs grow close to the mainland and are absent in wadi mouths. Their arrangement and orientation are strongly controlled by the siliciclastic input from the hinterland. In addition, discharge events due to ephemeral precipitation may cause local but serious damage of the reef-building assemblages. However, the general pattern of reef arrangement follows the morphology of the coastline, which itself portrays the tectonic framework of the Red Sea. Barrier reefs and even atolls also occur, predominantly in the central and southern part of this young ocean. Both reef types show a strong control by the tectonic framework of rift- related origin. The outlines of the reef crest and the orientation of the foreslopes follow the tectonic pattern. Spectacular drop-offs are widespread and represent predominantly fault planes of horsts and graben structures parallel to the rift. Furthermore rift-related salt diapirism occurs, which influences reef shapes, indicated by circular and semicircular outlines. Besides these controls, sea-level changes are a trigger as well. They are documented in onshore and offshore terraces and their present-day position can be attributed to the last glacial-interglacial cycle. These different controls along with the two major reef types and their typical zonation patterns are discussed briefly.