As to the argument that the brown nuggets could not have possibly been cemented by dry ice: I have been roundly criticized here for not having direct experience with 0.01 bar atmospheres. Oh, but I have!
I have a nice, glass thermos bottle that's insulated by a near vacuum. It works great! So the idea that CO2
ice will last about as long as an ice cube in an oven warmed up to 140o
F is exactly the wrong picture to have, and is guaranteed to give wrong, if intuitive, answers. The reason is that the vast majority of heat transfer at a 1 bar pressure is the result of conduction with the atmosphere, as opposed to radiation, which is the only option in a near vacuum. That's why thermos bottles and convection ovens work so well. So a proper picture would be to fill a vacuum insulated thermos with water, freeze that to well below freezing temperature, then stick one ice cube on top of the frozen block within the thermos, and then
stick the thermos in the warm oven, and see how long the ice cube lasts. I'll bet anything it lasts more than four minutes. This is the situation in Trench 270.
The lower left is the deepest part of the east-west trending trench is perpetually in the shade, so it cannot be heated by direct sunlight. Since it lies on top of permafrost, there is much thermal inertia there. But since the overlying atmosphere is 0.01 bar, radiation is the only method of heat loss. So, conduction works to keep the nuggets cold, whereas radiation works to warm the dry ice cemented nuggets to make them sublimate. Radiation eventually won out, but it took a lot longer than naive assumptions and calculations would suggest