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Evidence for a sedimentary origin of clay minerals in the Mawrth Vallis region, Mars

¹ Jet Propulsion Laboratory, M.S. 183-501, 4800 Oak Grove, Pasadena, California 91109, USA
² Malin Space Science Systems, P.O. Box 910148, San Diego, California 92121, USA

Clay minerals detected spectroscopically in the Mawrth Vallis region of Mars correspond to a complex, layered, thick (>600 m) stratigraphic section of ancient bedrock. Because the light-toned, clay-bearing rocks are lithologically diverse over a broad area (>80,000 km²), have significant internal layering and complexity, and contain buried impact craters within the section (demonstrating that they were deposited over a geologically significant duration of time), we interpret the host rocks as sedimentary or possibly pyroclastic. Crater counts date the clay-bearing rocks to early-middle Noachian time (estimated as 3.8–4.1 Ga). Geomorphic observations suggest that the rocks were lithified early and deeply eroded during the late Noachian–early Hesperian. The combination of a probable ancient sedimentary context of the clays and a moderate pH formation environment implied by the occurrence of smectites clearly places these rocks among the most important targets for future astrobiological exploration.

Key Words: Mars • clay minerals • alteration • weathering • sediments • astrobiology