re: Yea!...And that creates a puzzle.
precisely,
Let's not jump to any conclusions and think laterally. One issue is that there could be quite a lot of pulverised meteorite debris in the upper layers of the soil - there is a high Ni content, and some of the olivine couild come from this source, or from the volcanics that appear widespread across the basin.
There appears to be a minimum of a couple of hundred metres of volcanic material burying the former "lake" surface. The volcanics could be lava flow, ash, or welded ashfalls that have reconstituted to solid basaltic rock.
And as for the salts, let's see if we can find what form the elements are in - are there any feldspars? And, did you know that S and Cl at least are quite soluble in liquid CO2?