I don't think Meridiani is unique.

Personally I view all the finely layered "white" rocks as probable sulphate occurences. (Mars Express has confirmed sulphate signatures for some of the occurences.) Most of the outcrops are within large craters where a basin does exist but they are often not conformable to the shape of the basin and sometimes build an off-centre mound which in some cases is so tall it overtops the crater rim (e.g. Gale Crater).

I think these are huge hot-spring deposits that have built up like volcanoes from an original fluid source coming up cracks in the crater floor, off-centre from the central uplift region.

They don't behave much like lakes, but they do show ubiquitous layering and mound-building.

Where does the fluid come from - it's probably this battery-acid grade sulphate water, coming from volcanic lava and ash deposits interbedded in the basement rocks, as well as igneous intrusions. - all this in earlier times on Mars when it was more geothermally active.