Ah, I hardly know where to start, other than to suggest you urgently read one of those books and get a sense of proportion about Mars. Magically summoning and dismissing oceans and dense atmospheres is a real conjuring trick in the solar system and pushing it back to some mythical "Early" time is just more smoke and mirrors.

The simplest and most obvious interpretation of the layering in Valles Marineris is that it's layers of Lava. The canyon walls show the spectral signature of basalt, including some very thich olivine-rich layers. Olivine is not stable for more than a few thousand or tens of thousands of years in water, and especially not in the sort of acids we're seeing evidence of at Meridiani.

You can't have the plateau around VM as a fossil seabed because it is too high. If it was flooded, all of Mars was flooded. The craters we see would have been eroded and covered by sediment and thew ground would look flat. The Surface age of the plateau (as dated by crater counting) is also too young for the atmosphere to have sustained an ocean and still be gone today. In short, it doesn't work, however you try to arrange the evidence

The northern plains, on the other hand, are relatively flat. Logically, one "could" have an ocean there, although there are other and more complex arguments why even that is unlikely.

As for hidden deeper layers, Herb Frey has done some really good work in recent years['big pdf - Frey's paper is half way through] using MOLA DTM's to map buried impact basins and thus date the basement of the highlands and lowlands, with very interesting results. Basically, his results show that there isn't time to fit an ocean in anywhere in Mars' history - you can't sweep the evidence under the carpet because we can see the floor through the rug!

Another useful online reference is the LPSC conference abstracts. They are preserved onlineat the LPI website