In your model, there needs to be a lot of salt somewhere underneath to erupt and form the bedded crater deposits. I take this a bit farther. I was fascinated by Gale crater most of all, and Pollack white rock, etc, which show hundreds of even layers. What I think I see is uniform beds of a cyclic type (in other words most of the layers are about the same thickness), very many layers, and that these layers are nearly flat lying or gently domed. This seems incongrous with a volcanic type origin. If these sulfate deposits in craters were from volcanism/hydrothermal formation, then the layering should be inclined with the flanks of the mound all around. This would lead to few layers actually being visible, unless the volcano flanks were eroded or undercut. Wind erosion within a crater would seem unlikely to undercut and expose so many layers, IMO. Often these layers can be traced a long way around the mound. It would be unusual for a volcano to issue a flow on more than one flank. I believe that these are the exposures of the underlying bedrock, which in some cases has arched and invaded as a salt dome would, and that some are from crater resurgence. Could there be more bedded sulfates in the crater walls, just covered up by dust? The sulfates of Meridianna escaped detection till identified from the ground. Perhaps some regions have silicates such as flood basalts on top of vast salt layers. It was mainly these bedded deposits in craters that led me to the global ocean model I am favoring. And the report of sulfates deep in Valles Marineris, while it could be from seeps, it could also be part of the cyclically bedded rock seen there, thousands of feet of it.