Personally, I believe the flood myth arose from an actual flood. Problem is, there's lots of floods in the past. Big ones.

I don't see why similar tales wouldn't have arisen from completely different floods.

Once a culture has some sort of flood myth, it's easy to see how such myths from different cultures could be confabulated at a later date through cultural contacts. I mean, hunter gatherers sitting around the fire at a regional gathering place - such as Gobekli Tepe may well have been.

Harte