Interesting... do you have any more information on this? My impression from studying this was that that dissolutional karst would probably not last the hundreds of millions or few billions of years kind of timeframe that separates us from when liquid water was prevalent on Mars. However, I'm not sure if that impression is based on good assumptions -- the oldest caves on earth are thought to be about 340 million years old but the processes that act to remove caves on earth are probably far more active than what goes on on Mars, so maybe there are caves on Mars from a wet period that still exist. However, my impression from working with people on mars and moon cave projects is that the community generally thinks that the entrances that have been found are lava tube collapse features, or related to impacts or small-scale tectonism.