Stratigraphy and evolution of emerged Pleistocene reefs at the Red Sea coast of Sudan

• Pleistocene coral reefs at the Red Sea coast of Sudan are excellently exposed and preserved.
• The spatial relationship of different reef units and their related zones is reconstructed.
• δ18O values and field relationships define interglacial stages MIS 5.5, MIS 7 and MIS 9.
• Assigning zones to individual interglacial stage and regional correlation are discussed.

Emerged Pleistocene coral reefs constitute a prominent landform along the Red Sea coast of Sudan. They are well exposed with a thickness of up to 12 m and extend over a width of about 3 km parallel to the coastline. Four major reef units that represent different reef zones are distinguished. Unit 1 is located directly at the coastline and is assigned to the rock-reef rim, while unit 2 represents the reef-front zone. Unit 3 is attributed to the reef-flat zone and unit 4 to the back-reef zone. The stratigraphic position and age of the four units respectively the facies zones are based on field relationships and δ18O analysis. Results of δ18O analysis of coral, gastropod and bivalve samples were correlated to previous age dating of correlative reefs in Sudan and other parts of the Red Sea region. Estimation of reef ages was mainly based on δ18O values of the reef-front zone (unit 2) and the observed sedimentary succession of the reefs. δ18O values of two Porites coral samples from the reef-front zone strongly suggest equivalent ages of 120 and 122 ka that correspond to marine isotope stage MIS 5.5. Based on δ18O values and the field relationship to the reef-front zone, ages of reef-flat zone (unit 3) and back-reef zone (unit 4) could be assigned to MIS 9 and MIS 7 respectively. MIS 5.1 is suggested for the reef-rock rim (unit 1). The relationship of the reef zones to individual MIS might be explained by the predominance of a specific zone during a certain stage, while other facies were less well developed and/or later eroded by wave action. The reef unit most distal from the recent coastline formed during interglacial stage MIS 7, while former studies assign this unit to interglacial stage MIS 9. Unique flourishing, high diversity and excellent preservation of corals in the back-reef unit of MIS 7 reflect growth in troughs landward of the oldest reef-flat formed during previous interglacial stage MIS 9.