Abstract

The stratigraphy of sedimentary rocks within the Red Sea basin is the key to understanding its geological evolution over the past 30 million years. This dissertation addresses three poorly known aspects of the Red Sea basin stratigraphy: (1) the age of evaporitic units, (2) the age and origin of the shallow seismic S-reflector, and (3) the type and origin of carbonate platforms along its margins.

Due to a lack of fossils, the ages of the main salt layer (Mansiyah Formation) and layered evaporites (Ghawwas Formation) were previously uncertain, ranging between 14 and 5 Ma. This study determined their ages using Sr isotope stratigraphy. Results show that the Mansiyah thick salt layer precipitated rapidly between 14 and 13.2 Ma, while the overlying layered Ghawwas anhydrites between 13.2 and 6 Ma. Furthermore, the timing of salt deposition aligns with the onset of ultra-slow seafloor spreading, suggesting that salt saturation may have been triggered by the hydration of the newly exhumed mantle alongside evaporitic conditions.

Reflection seismic data, calibrated by deepwater well core data, were interpreted based on modern salt tectonics knowledge. S-reflector is identified as a widespread angular unconformity that flattened salt diapirs and truncated tilted layers throughout the basin. Sr isotopes from a deepwater well core date the unconformity at 6 Ma. The unconformity is attributed to subaerial erosion resulting from the desiccation of the Red Sea basin during the Messinian salinity crisis. This desiccation ended with seawater breakthrough from the Gulf of Aden, forming a deep canyon through the Bab el Mandab strait.

This study covers litho- and biofacies examinations of the Miocene carbonate outcrops along the eastern margin of the Red Sea. Three types of carbonate platforms associated with major rift faults were identified: (1) low-relief ramps during the Aquitanian, (2) delta-top platforms, and (3) fringing reef during the Burdigalian. Well and seismic data reveal that after the Messinian desiccation, thick aggradational reef platforms developed along the eastern margin and were rafted seaward by gliding over the salt layer.