"Wouldn't that also indicate the existence of advanced civilizations prior to Mesopotamia and Indus River?"
If you are not already aware of the writings of Graham Hancock, you should make his acquaintance. He also has an on line forum. Long before I ever heard of him I thought fairly well developed settlements must have been flooded when the great meltings of the last ice age and the Younger Dryas took place. Before then the Mediterranean was two very large inland seas. Then the water rose and flooded through Gibralter. Was that Noah's flood?
Scouring marks on the bottom at Gibralter attest to this event. Similar marks are on the bottom of the Black Sea at the Bosporus. The Mediterranean has completely dried out at least 40 times however, the last time was 5 million years ago.
FYI. It is my opinion that Noah's Ark was built up on the mountain as rumors of flooding and refugees reached Noah from the Mediterranean 'refill'.
It's my theory that something similar may have happened in the Gulf Of Mexico.
It would seem that some kind of event took place that caused flooding throughout the world. As far as I know, every civilaztion on earth has a flood story. The trick would be to tie these stories together in a timeframe to discover when the event happened. I'm sure someone has come to that conclusion already. Anyway, there is much evidence to suggest lost cities throughout the world that are now underwater or overgrown in jungles, etc.