I am inclined to agree 5,600 BC coincides, I believe, with the eruption of Mt. Mazama (Crater Lake) which left a 6 mile wide caldera. Lots of dust in the northern hemisphere to serve as nuclei for catastrophic rains and floods. Just look at what we have been having in our own middle west this year, not to mention the 500 year flood of the Mississippi after Pinitubo.