Topography, roughness, layering, and slope properties of the Medusae Fossae Formation from Mars Orbiter Laser Altimeter (MOLA) and Mars Orbiter Camera (MOC) data

The enigmatic Medusae Fossae Formation (MFF) is one of the youngest surfici al deposits on Mars. Previously proposed modes of origin include pyroclasti c volcanism, eolian mantling, polar sedimentation, carbonate platform, and paleoshorelines. In order to assess mapped member boundaries and constrain likely origin processes we analyze five topographic transects from the Mars Orbiter Laser Altimeter (MOLA) collected during the aerobraking hiatus orb it period of the Mars Global Surveyor (MGS) mission together with several s imultaneously acquired Mars Orbiter Camera (MOC) images to examine the regi onal and local variations in the relief, slopes, vertical roughness, and re lative elevations of mapped MFF members. We find that the members are not p articularly flat or level but have average thicknesses of many hundreds of meters and substantially more internal relief than previously thought. Loca lly, the MFF members are sometimes distinguishable by slope, elevation, and surface roughness characteristics, but no unique formation-wide characteri stics are apparent in this analysis of the limited initial data. The relati ve elevations of the mapped members are not consistent with undeformed plan ar horizontal layers but may be consistent with layers draped over preexist ing topography with subsequent partial removal. Analysis of the initial coi ncident MOC and MOLA hiatus data suggests the possible presence of local la yers, as well as the mislocation of at least a few MFF member and formation boundaries. We conclude that carbonate and shoreline deposit origins are n ot as well supported in the initial MGS data as they were in the Viking dat a and that the MFF formation and member boundaries should be reexamined in conjunction with the incoming new MGS data.