I'll take a shot at the photo.
What you say is a puddle (figure I) looks to me like lighter (weight- not color) dust blown through that little valley and pushing up against the slope against the dune at the far side.
A puddle of water would be level- not raised up against the slope. Unless Opportunity was at a precarious angle and that slope isn't as sloped as it looks.

The "ice" is sand. Regular, normal sanddunes.