It seems to me that dry soils would preserve certain things better than wet soils would.
Peat is mostly anoxic, so organic material tends to be preserved. That’s why peat is peat - it’s almost entirely vegetable fibres which have never completely decomposed.
It’s a different matter with peat bogs. It’s the ph of the bog, along with the lack of oxygen, that keeps the bacteria out that would normally accomplish the majority of the decomposition. They simply can’t live in that environment so biological matter can persist a very long time.
Dry it out and the bacteria would instantly come back and gobble everything up.