Deep chemical weathering on ancient Mars landscapes driven by erosional and climatic patterns

Across Mars exist thick clay mineral-bearing stratigraphies (CSs), thought to have formed through top-down leaching early in Mars’s geological history (>3.7 billion years ago) under warmer, wetter conditions than at present. On Earth, such deposits require specific landscape and climatic conditions to develop; however, it is unclear how Mars’s local and global topographic variations and past climate activity influenced surface weathering and CS formation. Here we present observations that show that CSs tend to occur in areas where chemical weathering was favoured over physical erosion, farther from valley network activity and nearer standing bodies of water. We conclude that the development of thick CSs through enhanced chemical weathering on this tectonically inactive planet may have led to an imbalanced weathering–climate feedback compared with Earth. Our results support the hypothesis that long-term irreversible sequestration of water and cations within clay minerals may have inhibited hydrological activity, and potentially carbonate mineral formation, over time.