re: Compared to what?
Come on, Mars is Mars, and it ain't Earth, and what goes on there isn't necessarily analogous to what we find here. In fact we don't a Meridiani analogue on Earth at all, so saying it's a playa or sabkha -- while interesting and possibly illumninating -- is farrrrr from definitive.
As Gary points out, this is a unique environment -- by terrestrial standards. Precipitates in a highly acidic aqueous solution, wet in the past, but not necessarily under water as in an ocean or sea.
OK.
What now? Get to it!
Cheers, BRFelix