Whether carved by catastrophic flooding, fed by groundwater seeping from ancient highlands, or shaped by some combination of both, the question of how Mawrth Vallis formed has never been fully resolved. Along its flanks lie some of the thickest and most extensive clay mineral (phyllosilicate) deposits on Mars, formed during the Noachian period when liquid water was stable on the Martian surface.

These deposits preserve a detailed stratigraphic record of how aqueous conditions evolved through time. Unpicking that stratigraphy is central to understanding not just Mawrth Vallis itself, but the broader story of water on early Mars and what it means for the planet's long-term habitability.

The hemispheric crustal dichotomy — the stark divide between Mars' ancient southern highlands and its younger northern lowlands — has been eroding and retreating since the Noachian. Scattered across this boundary at Mawrth Vallis are isolated remnants of the old highland surface, and it is in these outcrops that a remarkable mineralogical record is preserved, distinct to that of the highlands.

This project combined spectral and morphological analysis of thousands of isolated mounds scattered across the lowlands north and west of Mawrth Vallis, showing that these features are erosional remnants of the highland plateau — meaning the dichotomy boundary once extended hundreds of kilometres further north.

The mounds preserve a layered stratigraphic record spanning the full arc of Noachian aqueous activity: from unaltered material at their base, through hundreds of metres of clay-mineral-bearing strata deposited during multiple phases of water–rock interaction, to a thin capping unit marking the end of large-scale regional alteration. It is one of the most complete records of the onset, evolution, and cessation of habitable conditions anywhere on Mars.

This project has been covered by CNN, Ars Technica, and Space.com amongst others.