If calcium carbonate were found, would this not indicate the possibility of life forms?
I think so. I am trying to remember chemistry from 30 years ago, so I could be wrong.
An interesting question would be, if there is carbonate, what would be the ratio of lime to the carbonate; and the ratio of sulfate to sulfite? This might help to establish how strong was the oxidatizing environment when the minerals were laid down. It doesn't seem they have the instruments to determine these ratios on the rovers.
Calcium sulfate (gypsum, hemihydrate, or anhydrate) on earth are formed by precipitation from liquid water. Which form predominates depends on temperature and saline/pH of the ionic soup.