One example is the story of the Flood.
They find in it two distinct narratives with their own separate linguistic and stylistic characteristics and with contradictory details.
As an example, there seems to be a source where Noah brings one pair of animals into the ark and in another, one pair of unclean animals but seven pairs of clean animals.
But when you look at the text you find little warrant for this view. The crucial words are sh’nayim mi-kol (Gen. 6:19). They are only problematical if translated “two of every kind”, but not if they are rendered “pairs of every kind”, i.e. male and female, as the end of the verse makes clear.
A second argument is that the length of the Flood is described in two different ways – in one source, over a year (the waters prevail for 150 days and then decrease) and in another, 61 days (40 days and 40 nights and then three weeks).
The question revolves around the sending of the dove.
The 61-day theory presumes that Noah sent out the raven the moment the rains stopped; on that same day the raven failed to return; and seven days later the dove was sent out.
Logic, and the text of Gen. 8:6, would dictate that after the water began to subside, Noah waited forty days until he sent out the raven, which came and went several times (verse 7) at seven-day intervals before it finally failed to return, having found dry land.
The whole episode thus took much longer than a mere 40 or 61 days.