I've only read the press releases, but I hope to find copies and read them when I can.

The volcanic/hydrothermal idea has support, but a few problems.

The alteration is fairly uniform (at least along bedding). If there were hydrothermal cells, I'd expect some sort of zoning to the mineral assemblages. (Granted, we've got one traverse to go with.) With this limited exposure, we may not be seeing the major plumbing system, which should have some alteration halos in the vertical direction. But is this model more like steaming the whole volcanic pile? I'm used to hydrothermal systems with unlimited water supply. With limited amounts of water, the whole thing might get steamed like a pile o' rice in a bamboo steamer. And most of that water would be magmatic. Interesting.

The cross-beds bother me a bit in application to this model, and again, I've not read the paper. And it should be known that I can (or believe I can) see volcanoclastic textures in amphibolite grade terraines. These seem more more sedimentary, IMO. The big dunes below the alteration (lower burns cliff) and then the small ones within the sulfate unit seem to fit a sedimentary diagenetic model.

I agree that the chemistry is weird. (My geochem is not the sharpest tool in the box.) The seds do have lots of Mg, not so much the Ca, but that's so mobile it doesn't bother me much. I've not had the opportunity (no pun) to compare common immobile elements from protolith to altered rock. Can't really play REE ratio games here, can we?

The impact model carries less weight. I can't imagine ejecta blankets with this range of textures. Never studied them, though. Has anyone modeled the thermograds of an ejecta blanket over time? How thick do ejecta blankets get? How long do they hold heat?

Just some quick thoughts.

jms

ps (just saw ET's post, my question: do they show a range of cross-bedding? )