The Mediterranean was once the world’s largest dry salt lake

From time to time salt culminates at one particular part of the Earth’s oceans. This is called a ‘salt crisis’. 5 million years ago salt accumulated around what is now the Gibraltar Straits and flowed into the sea drying it up completely and leaving a mile-high wall of salt.

The Med became the largest salt-basin in the world and the rest of the Earth’s oceans rose by 10 metres. Eventually the Atlantic broke through the rock barrier at the Straits of Gibraltar. This was called the ‘Zanclean flood’ and refilled the whole ocean in two years at about 10 metres a day.

https://www.livescience.com/42115-giant-salt-crisis-explained.html