Fossils that are relatively near Y=0 but is still completely submerged in deepslate can still sometimes generate with coal instead of diamonds.

To reproduce:
1. Generate a single biome desert, swamp or mangrove swamp world with seed -5927161911243197999
2. Run /execute in minecraft:overworld run tp @s 278.36 -15.00 239.30 325.38 27.40