White Rock like formations are found in a number of craters -- Trouvelot and Becquerel are two well known examples, both extensively studied by Robert Shepherd.

I could be wrong, but I'm not aware of similar formations found outside craters, and that may be significant. Why would White Rock like formations only be found within craters?

One thought is that they are sediments left by retreating lakes, or possibly carbonates. Yet there are no certain signs that there ever were lakes in these craters.

In Trouvelot, the white material overlies a very distinctive dark unit, and it's not clear that the white material has affected the underlying dark material at all. The presence of many pits and "pedestal" craterson the underlying dark material is interesting.

There is no noticable erosion product from any of these White Rock formations. Yet all are heavily eroded. Generally, the argument is that whatever the composition of these formations, it is so easily taken up by the wind that it essentially "vanishes." I think that was one reason White Rock itself was once widely thought to be ice.

What kind of material erodes so thoroughly nothing is left of it? Or is it possible that the dark material that forms dunes in some of these craters is the erosion product from the white material?

The formation in Becquerelhas the most obviously "fluid" appearance. It's layers are very obvious. And in the Viking context image,there is even what looks like a tiny opening near the center where fluid might have flowed out.

Maybe it's nothing special, though. I don't know!

Cheers, BRFelix