GRADATION OF THE ROTER-KAMM IMPACT CRATER, NAMIBIA

Interpretation of ground penetrating radar data from the 3.7 Ma old Ro ter Kamm impact crater, together with results of petrographic and sedi mentologic analysis of sediment samples, indicates that similar to 40 m or more of slope sensitive degradation of the rim was accompanied by reduction of wall slopes well below the angle of repose and nearly co mplete erosion of ejecta from around the crater. Only one patch of in situ ejecta deposit was identified. Degradation of both the interior a nd exterior of the crater was dominated by fluvial/alluvial activity, likely during the first 1.0-2.7 Ma history of the crater. Eolian modif ication has dominated gradation since the last half of the Pleistocene . Results from Roter Kamm can help in evaluating evolution of degraded Martian craters that may have experienced fluvial/alluvial gradation followed by eolian modification. On Mars, extended fluvial/alluvial ac tivity should produce a low sloped, incised rim, thereby eroding most of the continuous ejecta well before removal of easily recognizable ri m relief. Subsequent eolian deposition can bury all but the raised rim of craters, thereby creating a focal point for efforts geared towards constraint of gradational history.