Actually the sea is the source of one of the theories of the mass extinction of 65 million years ago. There is a lot of methane locked up in the ocean floors and the theory is that something caused a mass release.
Personally I don’t buy it but I also don’t buy the asteroid impact as a reason for the extinction either. (at least not by itself)
Actually, I think you may be referring to methane and an extinction 55 million years ago.
So far as the Permian Extinction, I am still inclined to think asteroid, but the huge Siberian volcanic trappe formations certainly must have been involved as well. Just as there is a concurrent Yucatan asteroid and the Deccan Trappes in India. Of course, the salt lakes may have had an influence, but not necessarily the biggest one. What was the relative size of the Salt Sea and the Siberian Trappes? Stay tuned for additional information. This is why I love science.