The closest sort of phenomenon might be the terrestrial "sea of clouds"
(image source: _tiffany on flickr).
Note the ill-defined edges and billowing surface.
What does that mean? Like, the stuff dissolved in it? Presumably very vertically stratified, but other than that it could be all sorts of stuff. Too broad to answer here, really.
The smooth density transitions seemLong term exposure to precludesupercritical CO2 might be capable of causing surface erosion, as you'll still get equivalents of wind and waves in it. No massive destructive mechanical wave action (the density transitions are too smooth for that), so coasts would look very different indeedbut slow sedimentation under gravity and they would be subjectrippled landforms due to completely different erosive effects"wind"/"current" movement. You probably wouldn't get rain eitherCoastlines would seem likely to be smooth, so that probably rules out conventional drainage landscape patternswith only fresh volcanic landforms or astroblemes showing sharp, toocomplex shapes. I'm not sure whether "soap-bubble"that rain is necessarily what you'd seelikely to occur, or all you'dso you probably wouldn't see classic drainage-basin type landforms, but other than "not at all like earth" your guess is as good as mineso mountain ranges upthrust by tectonic activity could have a very different set of shapes to terrestrial landforms, assuming that "ice" couldn't form on their peaks.
You seem have segued from supercitical to liquid, there. If you meant "supercritical", I'll point you straight back to the wikipedia page you started from. It has stuff to say about its use as a solvent. I think the overall pH seems likely to be neutral. I'm not at all sure if a supercritical solvent could be saline... it seems possible. The upper transitional layers would presumably not have much in the way of dissolved chemicals in them, but the deeper you go the more you'd find.