Well of course there are no references in the original argument so it's impossible to check the numbers. But it assumes that subduction is the only process that removes sediment from the ocean basins. But subduction of sediments is actually fairly insignificant. The numbers sound right; about a 20th of all sediment being subducted. And once it's subducted you never see it again, except in it's geochemical signature in arc magmas. But California's Great Valley has over 50,000 feet of sediment that was never subducted. The stratigraphic thickness of sediments exposed in the mountains of the western U.S is substantially more than this. The total stratigraphic thickness of sediments deposited and then metamorphosed to form the Appalachians is staggering to even imagine. Accretion (that is closing of ocean basins, scraping off sediment, adding it to the continent) is the primary plate tectonic process that removes sediment from the ocean basins.
Edited by bdfoster, : No reason given.