Epochs and "fluids"
Count the number of major sedimentary bands exposed...
Mars is hit with large impactors roughly at the same rate the Earth is, chaotically aroung 26 million years, when our solar system passes through the plane of the Milky Way... so count the bands exposed and multiply...
I pretty much agree with Hoffman that the "fluid" is largely CO2 with a little water thrown in...
The interesting thing about the erosion is that the material deposited had to come from somewhere...
EP