Imagine the Indian Ocean filling the Red Sea in a spectacular rush after it disappeared, leaving behind nothing but a hot salt desert. In a study that was released in Communications Earth & Environment, a group from King Abdullah University of Science and Technology (KAUST) reported just that!
Based on chemistry, microfossils, and high-resolution seismic data, they determined that the basin dried up entirely around 6.2 million years ago and was later inundated by Bab el-Mandeb, which is located between Africa and the Arabian Peninsula, close to the Hanish Islands.
The region was reshaped by the opening, closing, and reopening againg of ocean gateways caused by shifting plates, which is how this dramatic swing fits into the larger picture of plate tectonics. The S-reflector, an important seismic marker that separates salt-desert layers from newer, open-ocean deposits, was also identified in the paper.
From ocean to a salty desert
Isolation started first. Not only did the Red Sea but it completely dried out. The bottom was exposed to air, water evaporated, and the basin was carved out by strong erosion since there was no connection to neighboring seas. Ancient salts, such as anhydrite and halite, were fractured, dissolved, and ended in thick piles. During this stage, the basin was closed, extremely saline, and dead, like a massive “geological Death Valley.”
How did things end up that way? Tens of millions of years ago, the Red Sea basin was created when the Arabian Peninsula separated from Africa. Lakes were found in the interior, followed by a northern connection that finally closed in the late Miocene. Similar to what happened in the Mediterranean during the Messinian Sablinity Crisis, the Red Sea became a closed bowl in a hot climate without a route for fresh ocean water, creating ideal conditions for catastrophic drying.
The change is clearly preserved in the rocks. Raw mineral layers can be found beneath the seismic S-reflector, and marine sediments with microfossils characteristic of open-ocean conditions can also be found directly above it. That line reflects the “before/after” of the Red Sea’s significant change.
The unexpected refill from the south
The return was fast (geologically speaking). The Hanish Islands and Bab el-Mandeb created a natural wall separating the basin from the Indian Ocean to the south. That barrier was penetrated by a large marine flood approximately 6.2 million years ago. In less than 100,000 years, the rushing water filled the basin again and formed a 320-kilometer-long submerged canyon that is still visible on the seafloor today.
The renowned Zanclean flood, which occurred almost a million years after the Messinian Salinity Crisis and originated from the Atlantic through Gibraltar, was not the same as this flood. Punching through a volcanic barrier was part of the previous reset of the Red Sea, which came from the south. The Red Sea transformed from a salt desert to a live sea after being reconnected to the global ocean system, reviving marine circulation and habitats.
The Red Sea serves as a “natural lab” for researching the birth and reshaping of oceans since the area is still geologically active today: the bottom is perpetually expanding, the oceanic crust is still young, and the salt formations at the margins are still unstable.
Why this ancient drama matters
This story shows how quickly things may change on Earth. Scientists can retrace a sea’s disappearance and reappearance in a geological blink by interpreting the subsurface, which includes salt layers such as anhydrite and halite, the seismic S-reflector, and microscopic fossils.
This information helps in our understanding of closed basins in other locations and their potential responses to changes in plate tectonics, temperature, or sea level.