The secret of Ouze is now clear. The Bosmer, it appears, did not all accede to the Green Pact. Something happened ... civil war? A disagreement between their gods? It does not matter. One contingent of the Wood Elves lost to the other.
As punishment for their refusal to give up their powerful shapeshifting abilities, these Bosmer, called "Oathbreakers" by the rest, were subdued and buried in Ouze. We can only hope they were buried alive; the corpses are more likely to be fresh and intact that way. Digging in the tar-pits should render us one of the greatest finds in recent history, putting us ahead of even the great discovery of Stillrise Village in Shadowfen.