Some thoughts:

My guess is that this is a very old rock. We don't know what the conditions of Mars were when it was formed, but that's what the rocks are gonna tell us. We don't know how big this "sea" was, or how often it was dry. Could it have been a "sea" that evaporated down to a brine, then had a period of drying and wetting before all the water was gone? Such as a playa: Salt Lake, Death Valley, The Dead Sea...Many examples exist in the geologic record of thick, regionally extensive evaporite deposits (the Permian basin in Texas, the Permian evaporites of Utah...). Or was it a Sabkha? (here's some recent reserch from GSA) The really thick deposits need a restricted basin next to a wider ocean. Normal ocean water flows in, it evaporates in the shallows, becomes dense and saturated, sinks to the bottom, precipitates... Or was it a geography that was purely Martian? Like the total evaporation of surface water resulting from the waning of the Martian magnetic field and the destruction of a primative martian atmosphere by the solar wind?

What I got from the press release and the conference was that they have cross-beds that are both formed by water and by wind in the same outcrop (their respective cross bed morphologies are distinctly different), suggesting the repeated change of environments, from a subaqueous to a areal, wind blown setting. This is a pretty exacting science, actually. I'm no sedimentologist, but I know some, and they can tell you all sorts of stuff from cross-bed sets.

Perhaps lake is a better term to use than sea which is better than ocean.

This environment may have lasted a very long time. Apparently, this unit is fairly think. Sea levels rise, sea levels fall. Over and over and over. Depositional environments (facies) move laterally and vertically through the geologic record. We need more stratigraphy to get more of this story.

Good observations Buck, dtb, Marcia, Success, Tom.

Oh, I've heard of spanish artifacts emerging from the White Sands in New Mexico, but I've neveeer seen a macro-fossil in an evaporite. Especially a sulfate evaporite. Can't think of a single example. And I've seen a fair number of evaporites, both ancient and modern. Bacterial fossils maybe. I'll have to do some looking round the web. But again, it be Mars.

What fun! From one stupid outcrop enough arm-waving to lift me off the ground. That's geology.