Mars Global Surveyor observations of Martian fretted terrain

The Martian fretted terrain between latitudes 30 degrees and 50 degreesN an d between 315 degrees and 360 degreesW has been reexamined in light of new Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) data from Mars Global Surveyor. Much of the terrain in the 30 degrees -50 degrees la titude belt in both hemispheres has a characteristic stippled or pitted tex ture at MOC (1.5 m) scale. The texture appears to result from partial remov al of a formerly smooth, thin deposit as a result of sublimation and deflat ion. A. complex history of deposition and exhumation is indicated by remnan ts of a former, thicker cover of layered deposits. In some hollows and on s ome slopes, particularly those facing the pole, are smooth textured deposit s outlined by an outward facing escarpment. Throughout the study area are n umerous escarpments with debris flows at their base. The escarpments typica lly have slopes in the 20 degrees -30 degrees range. At the base of the esc arpment is commonly a deposit with striae oriented at right angles to the e scarpment. Outside this deposit is the main debris apron with a surface tha t typically slopes 2 degrees -3 degrees and complex surface textures sugges tive of compression, sublimation, and deflation. The presence of undeformed impact craters indicates that the debris flows are no longer forming. Fret ted valleys contain lineated fill and are poorly graded. They likely form f rom fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass-wasting processes that formed the debris aprons. Slope reversals indicate that downvalley fl ow of the lineated fill is minor. The ubiquitous presence of breaks in slop e formed by mass wasting and the complex surface textures that result from mass wasting, deflation, and sublimation decreases the recognizability of t he shorelines formerly proposed for this area.