I don't know, this Richat hypotesis doesn't really convince me...

But I will read the Apocalypse of Yajnavalkya as you advice.

On the subject of Eden, there is a very interesting book called "Eden" by Anton Parks where the writer reports the translation of some sumerian tablets that tell an alternative story of the biblical Eden. In this story, the god Enki (who is sometimes represented as a snake or half snake) teaches men secret knowledge and especially metallurgy and how to make weapons. With this new knowledge, men try to attack the other gods and take the Eden, but are defeated and banished.

The same author wrote also another book called "The last march of the gods", that recount parts of the texts taken from the temple of Horus at Edfu. Among other things, these texts talk about a group of mythical islands which were placed in the west, and where ancient gods once lived, and were hit by a flood.