STABILITY OF SELIMA PLANUM, EARTH AND IMPLICATIONS FOR MERIDIANI PLANUM, MARS

The planar surface of the Selima Sand Sheet (Selima Planum) in southern Egypt and adjacent Sudan provides an analog surface to that of Meridani Planum, Mars, in that it consists of a no-relief, granule and pebble armoured surface with little apparent surface modification, despite several periods of climate change over the past million years. Surveys of decadal changes in topography indicate only throughgoing chevron-shaped low relief ripples that have done little to modify the current flat surface, whereas the underlying near-surface stratigraphic horizons indicate an undulating surface modified primarily during past pluvials. Only inferential arguments suggest a formation involving an ancient lake bed, as there are no terraces, or other positive relief landforms that are diagnostic of such an origin. However, near-surface stratigraphy, 14C dating, and measurements of current activity all indicate that the present surface was at least maintained, if not formed, as a result of the fluctuating climate of the Quaternary. Without the Space Shuttle Imaging Radar data, we would have little evidence of the prior fluvial environment that created initial low-relief channels beneath the sand sheet. Only those smaller, 10's of meters wide channels are visible at the margin of the sand sheet in areas of shallow bedrock, whereas channels elsewhere in the sand sheet are either incised into calcrete armored surficial deposits, or composed of subsurface lag gravels that outcrop in low relief hummocks. The latter channels are invisible at the surface, but readily apparent using orbital or ground penetrating radar. These channels were infilled and obscured during waning periods of rainfall, as the surface was covered by generations of sand sheet. A future Mars Imaging Radar system would provide key data as to the origin of Meridiani Planum by this, or alternative mechanisms.