LATE AMAZONIAN WIND REGIMES AND LANDSCAPE EVOLUTION IN NORTHERN MERIDIANI PLANUM, MARS

The etched deposits of Meridiani Planum, consisting of layered bedrock discontinuously exposed across a ~400,000 km² area near the Martian equator, have long been observed to have been eroded by the wind. However, little work has been done to characterize the aeolian features of this unit compared to the ripples and dunes of the nearby Opportunity rover landing site. In this study, the locations and orientations of aeolian bedforms, yardangs, and wind streaks within a ~120 km long valley of the etched unit northeast of the Opportunity landing site are mapped with CTX and HiRISE imagery, and THEMIS thermal inertia data. Observations of cliffs, sand cover, and the characteristics of geologic units were also used to interpret the evolution of the landscape. Ripple orientations suggest formation from westerly to west-northwesterly winds, while wind streak orientations suggest formation from northeasterly winds. Northerly to easterly formative winds are interpreted for sawtooth-shaped yardangs. Smaller yardangs in high-albedo bedrock are oriented parallel to ripples, and suggest formation from easterly to east-southeasterly winds. The high-albedo bedrock is exposed at the base of valley-bounding cliffs, where it is overlain by darker caprock. The most significant sand accumulations are found near these cliffs, where they are sometimes overlain by boulders of the caprock. Low crater densities on the valley floor indicate a recent Amazonian age for the surface. The disparate formative winds interpreted from the aeolian features may represent a changing wind regime over diurnal, seasonal, or geologic timescales. The small yardangs and ripples may have formed synchronously in a diurnally-reversing wind regime, while wind streaks might represent winds during global dust storms. The valley likely formed by cliff retreat driven by aeolian erosion of the bright, yardang-forming unit, the following collapse of the caprock supplying the sand seen near the cliffs. This data helps constrain wind regimes in the equatorial regions of Mars, for which there is little direct measurement of near-surface wind, and reveals how the Martian landscape continues to be shaped in the very recent geologic past.