A. It is evident from land subduction earthquakes that massive amounts of water traveling at hundreds of miles per hour will scour land down to bedrock; further, all material would be swept into the oceans - now burred beneath who knows how many feet of deposits. So yes nothing would remain. See here (1720 foot high tsunami): http://geology.com/records/biggest-tsunami.shtml. Do you imagine that melting glacial lakes and busted ice-dams on glaciers up to 2 kilometers high produced nothing similar?
If anything did remain and was sufficiently different, would it be recognized as an artifact or just laid aside because it is assumed to be something else, something natural or even ignored?
B. I said “circumstantial” which implies what you said. Science is never boring nor settled. Anything is always possible until proven to the contrary (even then that might be wrong).
C. Who said intelligent creatures have to breath oxygen?
All evidence for the earliest pre-human apes comes from warmer climates not subject to glaciation.
And that evidence is all consistent with basic evolution theory -- gradually increasing complexity of life on Earth, no evidence confirmed for "advanced civilizations" grossly different from their expected time & place.
Of course, anybody can hypothesize anything, and have a very enjoyable time fantasizing about aliens, or pagan gods, or whatever.
But it's not science.
PIF: "Who said intelligent creatures have to breath oxygen?"
Riiiiiiiiiiiiight!