When you find fossils in the soul sand valley, you can notice that some of the fossils have chunk borders. In certain chunks, where ever they are placed, they only generate in a single chunk. If they connect to two chunks, the blocks in the non-spawned chunks are cut off. It's a little weird on how they are generated.

To Reproduce:
1) load a world
2) go in the nether
3) find a soul sand valley
4) find many fossils (you notice many of them are cut off from chunk boarders)

Related Bug: MC-167213 (ocean caves only generate in ocean biome chunks, but get cut off when in a land biome)