A long time ago, you or someone in one of your threads, posted a site that had a study with survey pics that looked to indicate a massive gianormous impact that pretty much covered the entire southern ocean basin iirc. Scar marks radiating outwards stretched all the way to the landmasses from the impact just north of the antartic landmass or thereabouts.
It was supposed, or theorized, that the world was much drier prior and that the impact was an ice comet and that’s where much of the ocean waters came from. This was also the same site that showed the river runs from the continental shelves down to the seabeds.
You still have that link? Or was that someone else?
The Eltanin Impact may be what you're sort of remembering, conflated with the Louis Frank small comets. The latter have delivered enough water to Earth over the 4.5 billion years to account for every drop in the oceans; the former was about 2 million years ago and IMHO glaciated Antarctica, which (contrary to what is often claimed) had a temperate climate in at least part of the continent only 2.5 million years ago.