At first I thought perhaps it was a non-h20 liquid, since that would explain the frozen bits on the bottom.

Bit apparently it’s more banal, and sediment doesn’t need a river or a liquid at all. It’s any kind of deposit. So wind can deposit sedimen, volcanic ash is sediment glaciers deposit it etc.

I think the most likely case for sedimentary deposition over ice would be something like volcanic eruption or an impact event redepositing material onto pre-existing ice.