The good stuff will be found 300-500 feet down.
I had the same thought, and I'm amazed that someone else had it also. I shouldn't be, because FR has always been a meeting place for thinkers.
To back up your statement, the rate of silting and sand deposition over the last 5000 or so years is probably enormous, especially in areas of the ocean close to shore, as this one is.
That said, I wish this team luck, because I suspect that the theory is correct.