1. The subduction of the lithosphere at convergent boundaries was strong enough to temporarily “pull” the entire continent lower into the mantle making it easier to flood. Continents not being fishing bobbers aside, do the physics of matter sorting itself out due to density differences actually support this as plausible (remember other absurdities aside).
I've actually heard this theory in mainstream circles. I read a paper several years back that discussed the possibility that shallow or flat-slab subduction under both North America and Australia may be responsible for 'sucking' down the interior portion of both continents (right above where the plate finally starts diving down) enough so that they were low enough to be flooded by shallow epeiric seas. In North America, they suggested it could have resulted in the Cretaceous Sea. (I don't remember the name of the sea in Australia.)
The image below and the
site where I took it from discusses flat-slab subduction, only they place it sometime after the Cretaceous Seaway formed. I haven't heard much more about this theory since then, so it doesn't seem to be very popular.
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