Upon loading some old chunks from 1.6.4, the floor of the ocean does not blend like it should. The block palate has a harsh change from the legacy sand/dirt/clay to solid gravel or mostly solid dirt in the case of the swamps. It is very noticeable and will impact any chunk that uses the legacy block palate which I believe includes versions up to the update aquatic (1.13).  Screenshots of the results are included.