EVIDENCE FOR ICE-RELATED PROCESSES IN SOUTHEASTERN ARGYRE PLANITIA, MARS

Evaluation of high-resolution datasets of the Martian surface allows for critical testing of hypotheses regarding surface processes that have operated on the planet, which in turn may provide insight into the planet's geologic and climatic history. In light of this potential insight, a series of landforms that warrant further examination are sinuous ridges in southeastern Argyre Planitia in Mars' southern hemisphere. Ridges in this region occur as braided and discontinuous traces up to 100s of kilometers long, several kilometers wide, and 100s of meters tall. The origin of these ridges remains unresolved with workers proposing ridge formation through tectonic, volcanic, aeolian, fluvial, glacial, or lacustrine processes. Here, we use Mars Odyssey THermal EMission Imaging System (THEMIS) data together with data from Mars Global Surveyor's Mars Orbital Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) to re-evaluate hypotheses of sinuous ridge formation in southeastern Argyre Planitia. MOC imagery reveals that the ridges consist of horizontal to sub-horizontal meter-scale bedding that contains boulder-sized material. MOC imagery also reveals the presence of numerous pits located on top and along the sides of the ridges. The pits are ~10 m in diameter and lack a raised rim and obvious ejecta blanket. The absence of a rim and ejecta blanket suggests that these pits may not represent impact craters. In addition, MOLA profiles taken perpendicular to the ridge crests indicate that the ridges do not follow a topographic gradient, but instead cut across primary topography. We argue that, when taken together, all of the observations are consistent with these sinuous ridges having formed from melt water flowing in a sub-ice environment (either sub-glacial or under a frozen lake). This is a process analogous to terrestrial esker formation where the rimless pits may represent kettles that formed by blocks of ice broken from a dissipating ice layer, and is an interpretation consistent with a growing body of evidence that ice-related processes have operated on Mars. Acquisition of High Resolution Imaging Science Experiment (HiRISE) imagery of the ridges from the Mars Reconnaissance Orbiter may provide an additional means of testing and refining hypotheses of sinuous ridge formation within Argyre.