re: No. If I get what Nick is say it was very acidic water brine (battery acid) that eroded major features.
So, at some point you have long term liquids on the surface running very slowly. And it doesn't seem to be CO2 in any form.
This would explain "newer" large features with such odd things as oxbows and meanders I would think.
BTW, they have only looked at a very small area on Mars so far for current signs of liquid water underground and things don't look that negative for liquid brine...so far.