Recognition of Ice and Remnant Freezing within GPR profiles of Sedimentary Stratigraphy

The search for water on Mars would best be performed over areas of sedimentary stratigraphy, which are most likely to contain ice. On Earth, distinct ice layers in sediments can be created by burial, moisture migration to a freezing front, or infiltration of water. Ice layers can be recognized in ground-penetrating radar (GPR) profiles by their internal structure, their association with other strata, and by the phase structure of the reflected wavelets. Thermally induced freeze-thaw horizons usually cut across sedimentary strata, have a consistent phase structure, and appear to vary greatly in depth because of changing heat conductivity and dielectric permittivity within the overburden. Several sets of examples of ice layers and freezing fronts within GPR profiles are discussed. Most were recorded with an antenna unit, the radiated pulse of which was centered at 250 to 350 MHz. The first set shows active and remnant thaw bulbs within alluvial channel fill of the floodplain of the Saganavirktok River, Alaska. The profiles include separated ice layers; strata upturned by possible freeze expansion; and stratified aufeis. A second set from interior Alaska shows freeze fronts within lake bottom silts and moraine. A third set shows possible remnant and scalloped-shaped freeze-thaw interfaces from glacial outwash in lower Taylor Valley, Antarctica. A final set shows buried ice and the differential surface settlement caused by subsurface melting. The examples provide a baseline of ice profiles that could aid the interpretation of unusual stratigraphy that might be found with a GPR survey on Mars.