Undecayed Lake-Bed Vegetation Remains

"Undecayed" is an overstatement, I'm sure, but I once made this interesting observation in my childhood:I remember swimming in some lake, and dredging up some leaves with my feet. They were black, but otherwise they looked as if they had just fallen from their trees.Has anyone observed anything similar?I think that this is relevant to the question of polystrate trees. They could have been drowned and then gradually buried by different sediments, lasting the whole time because they decay too slowly.And why the slow decay? Decay is easier with oxygen; aerobic metabolism can release over 10 times as much energy as anaerobic metabolism. And lake-bottom decay microbes can easily consume most of the oxygen in their habitat, limiting how much decay they can perform.

Thanx, Bill Birkeland.It would seem that almost-undecayed leaves and branches are common in lake bottoms.BTW, that leaf-carpeted lake I had visited was a lake in the mountains near central Pennsylvania.