The Sedimentary Cycle on Early Mars

Two decades of intensive research have demonstrated that early Mars (greater than or similar to 2 Gyr) had an active sedimentary cycle, including well-preserved stratigraphic records, understandable within a source-to-sink framework with remarkable fidelity. This early cycle exhibits first-order similarities to (e.g., facies relationships, groundwater diagenesis, recycling) and first-order differences from (e.g., greater aeolian versus subaqueous processes, basaltic versus granitic provenance, absence of plate tectonics) Earth's record. Mars' sedimentary record preserves evidence for progressive desiccation and oxidation of the surface over time, but simple models for the nature and evolution of paleoenvironments (e.g., acid Mars, early warm and wet versus late cold and dry) have given way to the view that, similar to Earth, different climate regimes on Mars coexisted on regional scales and evolved on variable timescales, and redox chemistry played a pivotal role. A major accomplishment of Mars exploration has been to demonstrate that surface and subsurface sedimentary environments were both habitable and capable of preserving any biological record. Mars has an ancient sedimentary rock record with many similarities to but also many differences from Earth's sedimentary rock record. Mars' ancient sedimentary cycle shows a general evolution toward more desiccated and oxidized surficial conditions. Climatic regimes of early Mars were relatively clement but with regional variations leading to different sedimentary mineral assemblages. Surface and subsurface sedimentary environments on early Mars were habitable and capable of preserving any biological record that may have existed.