Nick,

Thanks for the reply -- and for acknowledging what you don't know yet!

>>>>Some guesses we can make - when a CO2 flow runs out of energy, it would do so suddenly, and dump a patch of rocks... CO2 flows won't pond in the way that water does and settle out gently. The flow would be trapped, but its energy and volatiles would boil away upwards, and a fairly chaotic layer of sediment accumulate below.

Hmm, again I have this vision of pyroclastic flows as something of an analogue. Especially from glaciated volcanoes where you get some ice chunks trapped in the mix and ave lots of venting/explosions/etc from the deposits, leaving you with a real messy landscape (e.g., Katmai and the "Valley of 10,000 smokes"). Having grown up with Mt. St. Helens visible from my bedroom window (though somewhat less visible after 1980...), I'm probably biased in that direction. On the other hand, you wouldn't have welding going on so that would be a big difference.

In terms of minerals, well, I was never that excited about chemistry so I don't have much to say. Bottom line I guess is, is there something detectable by Spirit/Opportunity that would be an indicator of anhydrous interaction with CO2?

>>>>If I was really playing the role of nutty proffessor, this would be the term paper and *you* would have to give *me* the answers!

Heh, been there, done that with my own advisor. I'm looking forward to inflicting such problems on grad students of my own, though I'm not sure that aspiring political scientists will be able to help much with the morphology of CO2-driven debris flow deposits!