WOW!
The geology here is dazzling.
What if..and I'm just throwing this out there...
The dunes that NASA didn't RAT sample at the bottom of Endurance are a kind of ice (myself and others have suggested this previously).
Not necessarily a water ice, perhaps primarily a sulfurous and/or halogenated ice/evaporite deposit (what is the estimated chemical composition of that stuff?).
At one time this material may have been more abundant in this and other craters but has sublimed and ablated and is now less abundant. millions of years ago it may have filled the crater but has sublimed to such a presently small visible volume. Millions of years ago the crater walls and the adjacent martian soils/rock layers may have been saturated with this icy material, like a perma-frost on Earth. The spherules may have formed within this permafrost by biological and/or chemical reaction where the ice and the martian sediment/rock interacted.
As the icy material sublimated and ablated it shrank in volume. Some spherules moved with the shrinking ice field and others were left behind. Some of the spherules that were left behind on or near the surface would have a tendancy to be effected by gravity after the material supporting them was removed by wind erosion. Gravity would have of course caused unsupported spherules to roll downhill to stopping points (with or without ice at that time), gullies, and other low lying areas. The mechanical action of the spherules rolling downhill would have been sufficient to produce many of the channels that we see in crater walls. Channels may have been carved by rolling spherules instead of running water and the spherules may form in conjunction with a type of evaporite-like permafrost.
Robert Page
Also,
The "stems" may represent a time in the history of the spherules where they were exposed to the martian atmosphere or permafrost free zone on one side but still connected to the permafrost on the other.
