ORIGINS: Early Australians and Papuans - split or blend?

Here's one theory:

Mapping dispersion of early humans using mitochondrial DNA
"Regions coloured according to the gene pool: Australian lineages in yellow, Melanesians in pink and Filipinos in green."

by Mauricio Lucioni Maristany, in Peru (21 January 2012)
https://commons.wikimedia.org/wiki/File:Dispersi%C3%B3n_del_haplogrupo_P_(ADNmt).PNG

At this time during the last ice age, Australia and Papua were one landmass. The migration coincided with the start of a wet period that saw central Australia much wetter and greener.

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But looking at P3 and P4, there is another:

 "Modern human migrations in insular Asia according to mitochondrial DNA and non-recombining Y chromosome"

by J. Trejaut, J.-C. Yen, J.-H. Loo, M. Lin

Article

first published online: 20 OCT 2011 at 

http://onlinelibrary.wiley.com/doi/10.1111/j.1751-2824.2011.01516.x/full

According to this article, Papua and Australia were reached by different routes some 51,000 years ago and much later there was some limited genetic exchange between NE Australia and eastern Papua.

When the seas rose again, the land masses separated and so did the subsequent migration histories.