Carr and Head argue that successive floods could have flowed over ice
http://www.psrd.hawaii.edu/July03/MartianSea.html
"Possible Fate of Northern Oceans
The researchers have made a case for the presence of a large body, or bodies, of standing water in the northern plains over an area roughly equal to that mapped as the Vastitas Borealis Formation. Carr and Head argue that successive floods could have flowed over ice from previous floods to progressively fill the basins over a long period of time. Once flooding ceased and the ice sublimated away, layers of sublimation residues were left covering the ridged plains. "
Not much mention or support of liquid CO2 flows in this article. Also, it appears that Carr and Head clearly favor flowing water and an ancient ocean on Mars.
BD