Wasn't it that giant water canopy from Edenic times....when the atmosphere was warm and humid and bright sun didn't shine through as we know today....and then the canopy plopped and submerged earth in massive tons of water and reshaped the geography and altered the geology???
I personally believe there was a flood in ancient days.....localized however....and speculations as to the topography and changes wrought are just that....speculations.