Seems to me that to turn sand dunes into a flat rock, and it IS flat and straight to the naked eye, couldn't happen by new sediments covering them over -- they would simply fall over the dunes into the valleys.
If you cut away a real life, modern sand dune, this is what you see.
Faith's hypothesis is that it would remain intact as the sea transgresses over them,
You mean Faith actually thinks that water will leave loose sand at such steep angles of repose? Seriously?
How about visiting any beach in the world. Look at where the sea meets the sandy beach. Notice the absolute absence of any sand dunes with 30 degrees of slope where the water is bashing up against the sand.
If Faith can't even get this simple observation right . . .