Interaction bounding surfaces exposed in migrating transverse aeolian ridges on Mars

Wind-blown sand self-organizes into bedforms that have now been identified on six different planetary bodies. These bedforms, including ripples and dunes, exhibit patterns that are diagnostic of surface-atmosphere interactions and can be used to interpret winds and sediment supply from satellite images of planetary surfaces. Patterns in dune and ripple fields change when one or more bedforms interact, for example, by linking, colliding, or merging with one another. When two bedforms interact, the cross-strata developed by the bedforms include a bounding surface where the two bedforms combined. These “interaction bounding surfaces” have been interpreted from ancient and modern strata in recent literature, but they have not yet been identified beyond Earth. On Mars, aeolian dunes and ripples form much as they do on Earth, but additional enigmatic bedform types are also present. Transverse aeolian ridges are straight-crested bedforms found abundantly on Mars, but with few analogs on Earth. Formation mechanisms for these enigmatic bedforms range from dune-like migration and construction to growth in place via wedge stacking or kinetic sieving. In this work, I studied exposed stoss-slope stratification on these enigmatic Martian bedforms to (1) identify the first in situ examples of interaction bounding surfaces captured visually, and (2) demonstrate that the transverse aeolian ridges must have been forward migrating.