Light-toned deposit in the northeastern Hellas basin formed by terrain-conforming airfall sedimentation

Extensive exposures of a light-toned deposit (LTD) occurs on the northeastern interior slope of the Hellas basin. This deposit is on the floors of all but the youngest craters greater than 30 km in diameter in the study region centered at 83°E and 30°S, as well as in exposures on crater interior and exterior walls, on intercrater plains, and the northern bordering slopes of Navua Valles. Stratigraphic relationships indicate that the LTD was emplaced as a terrain-conforming mantle several decameters thick. The more than 5 km range in elevation of the LTD is consistent with deposition as an airfall deposit, perhaps emplaced as loess derived from wind erosion of the Hellas basin floor. The LTD was emplaced during the time period of waning fluvial activity within the region, tentatively dated to the Early to Middle Amazonian transition, and thus serves as a stratigraphic marker bed.