MISSING MARS: CLUES FROM RELICT CRATERS (Invited Presentation)
New estimates based on relict craters and terrains indicate the disappearance of more than ~15 million km3, which greatly exceeds the inventory of both north and south layered terrains (~3 million km3). The re-distribution and/or loss of such large volumes of unconformable deposits is problematic unless once-frozen volatiles once comprised a significant fraction.
Impacts into a layer 3 km thick significantly reduce shock effects in the substrate [Stickle & Schultz, 2013] and once gone, can erase craters as large as 30 km [Schultz, 2007]. Relict features include inverted crater floors and ghost craters, but muted terrains (buried craters) also implicate significant residual deposits. Removal of such deposits constrains exhumation (rather than formation) ages based on crater statistics [e.g., Schultz & Lutz, 1988; Grant and Schultz, 2010]. Because a low-impedance layer is as an ideal capture medium, its disappearance should leave behind relict antecedent drainage systems and lag deposits (composed of accumulated debris including ejecta fragments, impact glass, meteorites, and diagenetic nodules). If such lag surfaces are not evident in exhumed terrains, then they must be masked by ongoing reworking or later burial.