Deflation/erosion rates for the Parva Member, Dorsa Argentea Formation and implications for the south polar region of Mars

The origins of the surficial materials in the geologic units surrounding the Martian southern polar region have been poorly constrained on the basis of pre‐Mars Global Surveyor (MGS) data and studies. MGS studies suggest that these units are the remnant of volatile loss from an originally massive volatile‐rich debris blanket or the result of fluidized slurries resulting from magma/volatile interactions or impact shaking. We use Mars Orbiter Laser Altimeter data to examine a region adjacent to the south polar layered terrain at 72°–79°S and 230°–275°E, generally equivalent to the mapped Parva member of the Dorsa Argentea Formation (DAF). The pedestal and “ghost” impact crater morphologies in this area suggest that extensive deposits of loosely consolidated materials have been removed from this region. The Parva member is thus likely to be the remaining debris blanket from the deflated remnant of an unprotected deposit that was originally similar to the buried DAF deposits in the adjacent Cavi member. Crater counts indicate that the Parva member is of Hesperian age and overlies an older Noachian surface, likely the highland cratered terrain (Npl1). If regional deflation began in the Hesperian and continues through today, the region has been exposed to erosion rates of 1.3–1.6 × 10−7 m/yr. However, if deflation started later than the assumed times or ceased in the Amazonian, when deposition of the polar layered deposits began, erosion rates as high as 2.–5.2 × 10−7 m/yr might have existed. These erosion rates are within the range of published Martian nonbedrock erosion rates of 10−8–10−5 m/yr.