Pleistocene evolution of the Red Sea coastal plain, Egypt: Evidence from uranium-series dating of emerged reef terraces

Abstract

Eight emerged reef terraces (I–VIII) belonging to three cycles of reef formation were recognized along the Red Sea coastal plain of Egypt. The oldest cycle is represented by terrace VIII at altitude varying between +9 and +35 m, the middle cycle is represented by terraces VII-V whose altitudes vary between +22 and +32 m, while the youngest one is represented by terraces IV-I at altitudes of +9, +6, +3 and +2 m, respectively. The three lowermost terraces (I–III) of the youngest cycle give 230Th 234U ages between 72.1 ± 2.5 and 131.2 ± 4.4 ka BP which are distributed in three ranges; 72.1 ± 2.5–87.6 ± 2.2, 112.1 ± 3.3–113.2 ± 4.1 and 123.6 ± 4.7–131.2 ± 4.4 ka BP. These age ranges coincide with the chronology of the last interglacial cycle but their correlation with the Oxygen Isotope Substages 5a, 5c and 5e, respectively, is not evident. This suggests that the three dated terraces, combined with terrace IV, were built during the maximum high sea level stand of the last interglacial cycle (Oxygen Isotope Substage 5e) while their surfaces are the product of short still stands during a continuously falling sea level. However, the comparison of the stratigraphic relations of the older terraces, made up of recrystallized corals, with both the oxygen isotope record and the curve for solar insolation received by the earth at latitude 65°N, allowed the estimation of their minimum ages. The terraces of the middle cycle were considered to have formed during Oxygen Isotope Stage 7 (170–230 ka BP) while that of the oldest cycle was formed during Stage 9 (300–330 ka BP). The present-day altitudes of these terraces are the product of eustatic sea level fluctuations and differential tectonic uplift.