Hmm, the base surge idea is interesting, especially if it explains the cross bedding.

Three issues. First, the idea does propose Meridiani forming w/o standing water or even saturated ground a la the sabkha analog. But, it still requires impactors hitting in terrain composed of a very high fraction of frozen brine somewhere else. The chemistry argument they make is beyond my meager chem, but given that youve got so much concentrated sulfate salt, it seems like if not evaporite in place, you'd just about have to have had it form as evaporate somwhere.

Also, the impact surge story would apply anywhere on Mars. It raises the question of why Meridiani (and a few other locales) are so rich in sulfate deposits. Different target rocks -- if so, why so much frozen brine? Different post-impact processes?

Third, I guess they are proposing that the "blueberries" are impact surge lapilli. If so: 1) why no concentric layers?, and 2) why are they so chemically distinct from the rest of the deposit? If you have a cloud of turbulent rock vapor, would you get the hematite separating into nice little balls? And where did all the hematite come from originally?

My utterly unqualified sense -- I'm only a social science PhD after all -- is that I like the hydrothermally modified ash/tuff bed idea better. Seems like a *lot* of salt for that but I really don't know the terrestrial analogs they mention so I'll defer on that. Whether their model beats the sabkha or lake model, well, I look foward to the debate!