Where does all the salt come from in the Dead Sea?
The composition of the Dead Sea is quite unlike most other salt lakes, and is not at all like sea-water. Compare the concentrations, in grams per litre:


The potassium, bromine and magnesium are all hugely enriched relative to seawater, so clearly, it is not just a case of evaporation of residual seawater from the time of isolation of the Dead Sea. In fact, the vast majority of the water, and almost all of the magnesium, is derived from rivers draining from the north, from around the sea of Galilee, where magnesium-rich volcanic rocks weather rapidly. Much of the sodium and chlorine is derived from evaporation of rainfall originating from the Mediterranean - rainfall being just massively diluted sea water to start with. The high calcium and potassium comes from evaporite dissolution from the surrounding and adjacent rocks, especially from the Lissan Marl and saline springs emanating therefrom.

The real problem is: Where did all that bromine come from? The Dead Sea has the highest concentration of bromine in the world, and it is far from obvious how it got there. Clearly, there has been a massive concentration process. Maybe it was concentrated in the saline base of a much larger lake during the time of formation of the crustal formation of the Aqaba - Dead Sea - Gollan Heights rift? Any 'armchair theorists' out there with a better hypothesis?