GEOMORPHIC MAPPING OF CRATER FLOOR DEPOSITS IN SOUTHERN MARGARITIFER TERRA, MARS

The Margaritifer Terra region on Mars has experienced large amounts of fluvial activity in the past, and the cratered and dissected surface can be studied in detail using orbital images. To complement other research and ongoing mapping in adjacent areas of Margaritifer Terra, this study looks at a region approximately 500 km southeast of Jones crater (-25.1 to -23.6, 343.8 to 345.6) that contains five larger impact craters of various ages. A geomorphic map was compiled in order to consider the nature and timing of surface processes within the five large craters. The crater in the southwest corner of the area (Dison) is 20.7 km in diameter and has an alluvial fan emanating onto its floor from the southeast. The crater to the east is larger and older, as it contains some of the ejecta from Dison. It also has a smooth deposit coating the northwestern part of its interior. This smooth material is interpreted to be an aeolian deposit blown in from the northwest, and it is also seen in a larger crater to the north and another crater to the east. That crater to the east is approximately 38.8 km in diameter and has four distinct alluvial fans of different ages spreading onto its floor as well as several fans that coalesce into a bajada along the crater’s eastern edge. The older fans have steep fronts, which suggests that a lake existed in the crater when they formed, but the younger fans do not exhibit steep fronts. One of the youngest features in this crater is a landslide on its eastern wall. This crater lies within an older, slightly larger crater, and all five of the large craters in the study area have at least some fluvial erosion of their walls. Although some of these fluvial features likely formed from overland flow over a distance, some could be the result of more localized rainfall or snowmelt. Areas outside of the craters are mostly covered by an old plains unit, several areas of older cratered plateau material, and several younger impact craters and their ejecta. Overall, this area possesses a mix of features that reveal an interesting history of impact cratering, mass wasting, and fluvial erosion and deposition.