"but just for the benefit of this layman,maybe cite a couple of flood plains of equal or greater extent than the broomestone quoted."

The full extent of the Brome Sandstone isn't actually known (another lie in the CMI article) plus it does contain mudstones (yet another lie from the CMI author). See here: http://dbforms.ga.gov.au/pls/www/geodx.strat_units.sch_full?wher=stratno=2645

As this renders the question of which delta's on earth are bigger than the Broome system redundant. Suffice to say, if you Google delta you'll find the information you're looking for. Do the research Pete, you may never know where it will lead.