Tuesday

Aeolian systems are widely documented across the solar system, however aeolian strata, the preserved expression of migrating dune fields, have only been documented on Earth and Mars.
During its traverse of Gale crater, the Mars Science Laboratory rover Curiosity encountered the Stimson formation, a cross-bedded mafic sandstone which unconformably overlays the lacustrine Murray formation mudstones. The unconformity is documented to undulate with an amplitude of 10 m locally over 230 m and regionally by 140 m over 1.8 km of lateral traverse south towards Mount Sharp. Where grains are observed, the Stimson formation is characterised by well-sorted medium-grained sandstones with occasional bi-modally sorted medium- and very-coarse grained sandstones. These sandstones exhibit large-scale cross-beds (sets up to 0.8 m thick) characterised by mm thick self-parallel laminations interpreted to be wind-rippled laminations. The cross-strata dip predominantly toward the north-east, suggesting transport oblique to the regional dip of the unconformity toward the north. Cross-sets are separated by interdune migration surfaces that subdivide the succession, however fine-grained interdune facies associated with these surfaces are not identified anywhere on the traverse.
We interpret the Stimson formation to be the preserved expression of a dry aeolian system which accumulated on a deflationary unconformity. This is attributed to: large preserved cross-sets; migration of bedforms oblique across the regional slope; and absence of fine-grained interdune deposits. The Stimson formation represents a later stage in the drying out of Gale crater, in which dune fields migrated across the exhumed and deflated lakebed deposits represented by the Murray formation.