Those "rivers" are most likely runoff from the flood waters, and tidal backdraw during the receding of the flood between deposition of layers.
Not likely....when you have whole systems of "fossilized" rivers and can find sandbars, deltas, etc., in them, buried a half-mile beneath Bartlesville, Oklahoma - and with other sediments beneath them in turn, all containing oil....I don't think you can make that scenario fly.
Edited by Coragyps, : fix tag