The Messinian Unconformity in the Red Sea: Evidence for Widespread Dessication?
Abdulkader M. Afifi1, Paul Tapponnier2, and Nickolas S. Raterman1
The Red Sea main trough is underlain by thick sheets of Middle Miocene salt, which are deformed into a variety of diapirs due to lateral salt movement from the margins. The salt diapirs are separated by syn-kinematic mini-basins that are filled with interbedded clastic and evaporitic sediments. Offshore seismic surveys reveal an extensive shallow unconformity under the main trough, herein referred to as the Messinian Unconformity, which corresponds to the bright S-reflector identified by the Deep Sea Drilling Project at the Miocene-Pliocene boundary. This unconformity occurs at depths between 600-1600 meters below sea level, and is overlain by 100-600 meters of nearly flat Pliocene and Pleistocene sediments, locally deformed by recent salt movements.
The Messinian Unconformity is typically angular along the flanks of salt diapirs, where it truncates tilted post-salt sediments, but becomes conformable with overlying and underlying sediments within the mini-basins. The unconformity has also leveled the rising Middle Miocene salt diapirs, resulting in near-flat tops marked by very large seismic amplitudes. These amplitudes correspond to a sharp increase in seismic velocity suggesting the presence of a residue of less soluble anhydrite. The Messinian Unconformity exists throughout the main trough, but is absent within the axial trough and deeps, and along the uplifted margins. Its contiguous lateral extent suggests that it formed by sub-aerial exposure during a period of desiccation when the Red Sea was completely isolated from the Indian and Mediterranean basins, probably during the Messinian salinity crisis in the latter.
AAPG Search and Discovery Article #90188 ©GEO-2014, 11th Middle East Geosciences Conference and Exhibition, 10-12 March 2014, Manama, Bahrain