Multiple evolution modes of Aeolian Megaripples and implications for mars
Résumé
Martian aeolian sedimentary rocks can unveil past wind-regimes and climates. Curiosity is exploring the layered sulphate-bearing unit exposed in the lower foothills of Aeolis Mons, Gale crater. Sedimentary structures indicate these strata were predominantly deposited within aeolian dune and sandsheet environments. Here, we report enigmatic erosional surfaces embedded within the sulphate-bearing strata and discuss their processes of formation. The surfaces form a set of concave-up scour-and-fill structures (width ~60 m; amplitude ~6 m). Their cross-sectional profiles show a planar central section with limbs inclined < 20°. The scour fill consists of: (1) low-angle inclined bedsets at the base which conformably drape the scour surface, overlain by (2) light-toned, relatively-planar strata lacking distinct bounding surfaces. Nearfield observations indicate that the scour-enclosing facies are composed of fine, even-in-thickness, laterally-extensive, planar laminations which are resemble the upper scour-fill strata. We interpret these laminations as wind-ripple strata. The geometry of the scours with broad cross-sectional concave profiles, flat central portions, and similar facies outside of and within the scour-and-fill structures suggest that the scours likely formed by aeolian processes. The scour-fill do not show evidence of fluvial facies. One plausible interpretation of the scours is that they represent saucer-shaped aeolian ‘blowout’ structures. Such structures, observed in both modern and ancient aeolian settings on Earth, commonly form through wind deflation from intense winds. The absence of such scour-and-fill structures in the lower part of the aeolian sulphate-bearing succession suggests that the presence of scours may indicate transition to enhanced wind deflation.
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