Nature of the mantling deposit in the heavily cratered terrain of northeastern Arabia, Mars

A portion of northeastern Arabia (∼20 degree-35 degree N, ∼285 degree-315 degree W) appears to be overlain by an extensive, several-hundred-meter-thick deposit of horizontally layered material subsequently subjected to erosion. Preexisting topography is visible but subdued, suggesting that it has been mantled rather than enveloped (infilled). Where uneroded, the surface of the deposit is smooth at ∼50 m/pixel resolution. Large craters on this landscape become less distinct with decreasing size until most craters ∼10 km in diameter are shallow, rimless circular depressions. The relative age of the mantle, as indicated by the crater density, appears to be consistent with deposition during the period immediately following the decline of heavy bombardment. The mantling deposit was episodically emplaced over a period of time, sufficient to permit a succession of channel formation, infilling, erosion, and subsequent new channeling of the Auqakuh Vallis, and variations over time in the amount of mantling material on large craters within the study area. In places, the deposit has either been extensively eroded to produce remanent mesas or entirely removed. Erosion of this extend indicates that the material is easily disintegrated to loose and freely transportable particles, possibly dust-sized. The observation that the mantle mutes but does not mask preexisting large-scale topography yet buries small-scale features implies that its constituents were deposited from atmospheric suspension (or saltation). Speculative origins for the deposit include formation as a differentially welded pyroclastic tuff or a differentially compacted, zonally indurated aeolian dust deposit