re: Layering
Notice the lack of eject related rocks around endurance. Elsewhere on Mars, rocks would be thrown all over the area like this from an impactor, but yet we see no rocks scattered around. The only rocks we see around this area is where bed rock is exposed and where other rocks have been thrown there from impacters outside of the region, like bounce.
The parent rock does not seem to last long while exposed to the Martian air. It dissolves quickly leaving the darker blueberries.