Decameter-scale pedestal craters in the tropics of Mars: Evidence for the recent presence of very young regional ice deposits in Tharsis

Global climate models predict that ice will be deposited in tropical regions during obliquity excursions from the current mean obliquity of similar to 25 degrees to similar to 35 degrees, but no geological evidence for such deposits has been reported. We document the presence of very small (decameter scale) pedestal craters in the tropics of Mars (the Daedalia Planum-Tharsis region) that are superposed on an impact crater dated to similar to 12.5 Ma ago. The characteristics, abundance, and distribution of these small pedestal craters provide geological evidence that meters-thick ice accumulations existed in the tropical Tharsis region of Mars in the last few million years when mean obliquity was similar to 35 degrees (similar to 5-15 Ma) before it transitioned to a mean of similar to 25 degrees (similar to 0-3 Ma). A reconnaissance survey reveals similar small pedestal crater examples superposed on the older Amazonian Arsia Mons tropical mountain glacier deposit, suggesting that ice can accumulate in these tropical regions without initiating large-scale glacial conditions. These results support the predictions of general circulation models that ice can migrate to the equatorial regions during periods of moderate obliquity and then serve as a source for mid-latitude deposits. (C) 2011 Elsevier B.V. All rights reserved.