HELLAS-PLANITIA, MARS - SITE OF NET DUST EROSION AND IMPLICATIONS FORTHE NATURE OF BASIN FLOOR DEPOSITS

Hellas Planitia, located within an enclosed basin which includes the l owest topography on Mars, appears to be undergoing net erosion. Dust i s removed from the basin. It probably contributes to global dust storm s and should leave behind a coarse lag. The particle size distribution s and probably the rock or boulder populations in this lag might be us eful for distinguishing between processes which formed the lithologic units that comprise Hellas Planitia. This report concludes that the ab undance of rock particles larger than coarse sand is very low. Althoug h this hypothesis awaits confirmation from forthcoming spacecraft data , the origins for Hellas floor deposits favored by this study are indu rated volcanic airfall or ancient loess, lacustrine deposits, and some types of volcanic mud flows. The conclusions of this study tend to di sfavor such geologic processes as blocky lava flows, glacial deposits (e.g., moraines), or boulder-laden catastrophic flood outwash.