Nice model Nick, and thanks also to JMS and others have added their own geological insights.

I like the from-below notion for creating those interior layered deposits in craters. Makes sense as a way to deposit minerals inside a crater without any good evidence of there having been a lake or liquid flow in/out of the crater.

In fact, if the light-colored layered deposits are things like sulfates globally, don't all these piles them sitting exposed in the highlands argue against large scale surface flow? Those minerals are very easily eroded by water, and if there was large-scale sustained flow from south to north, shouldn't we see a lot fewer salt-and-sulfate piles sitting exposed in the highlands, and more of it in the lowlands? Seeps of underground brine into low-lying areas seems plausible.

Of course, we don't know for certain what's underneath the northern plains, so perhaps there is a huge layer of salty sediments underneath recent lava flows.

Where does the hematite fit into this model? With all that chemical preciptiation going on I can see the hematite being involved, though the outcrop is actually low in hematite. Maybe a hematite rich layer that has largely been eroded above the sulfurous outcrop, with the hematite sand/gravel left as a lag deposit.

Or maybe it is a modern thin coating as argued in that LPI paper Nick cited earlier. If that's the case, it would be especially ironic if we do end up finding evidence of aqueous alteration and deposition at Meridiani, but that the hematite has nothing to do with it.

Either way, there is still the question of why hematite at Meridiani, and not elsewhere?

If we do decide this outcrop is aqueous in origin, I sure hope we can figure out some sort of signature it has that can be picked up by TES or THEMIS in orbit. It would be really nice to know if the conclusions we reach can be generalized to those light-toned layers seen elsewhere on the planet.