and that may favor a fluid deposition a la sinter.

Speaking of which, I went back through the files.

Time was, Malin and Edgett argued that the "white" deposits on Mars, including those in Meridiani, were all pretty much the same -- in composition and deposition. IIRC, their argument was essentially that all these deposits were finely layered indicating deposition in fluid (water?) or of a fluid.

Their argument seemed to propose that all these deposits occurred underground and are only revealed today by erosion.

On the other hand, the deposits may have occurred on top of the surface.

It's been noted that all the "white" deposits are associated with dark debris and in some cases dark dune fields. We see the same thing in Meridiani. Some of the layered "white rock" deposits appear to be layered light and dark materials. At the Opportunity site, we see that at least some of the dark material consists of enigmatic spheres -- which were formerly embedded in the light colored matrix rock.

Some time ago, I spent some time thinking about Becquerel's "white rock" deposit, and its layers of dark and light material. Its resemblance to giant sinter deposits is startling. Could that be what's going on at the Opportunity site?

(Sorry that the link to the Malin/Edgett paper inititally referenced is now dead. I believe this is what is referenced: Malin, M. C., and K. S. Edgett, Sedimentary rocks of early Mars, Science, 290, 1927– 1937, 2000.)

http://mars4all.tripod.com/becquerelwhiterock/id1.html

There's so much more to learn about Mars. Clearly we've only begun!

Cheers, BRFelix