Layered mantling deposits in northeast Arabia Terra, Mars: Noachian-Hesperian sedimentation, erosion, and terrain inversion

[1] Thick, layered mantling deposits of different ages occur in several nonpolar regions of Mars and are thought to represent volcanic ash and/or climate-related ice-dust deposition. One such deposit is a layered mantling unit that unconformably blanketed highlands terrain in northeast Arabia Terra during the Late Noachian and/or earliest Hesperian. Shortly thereafter, by the mid-Hesperian, this deposit was substantially eroded; on the basis of its superposed crater population, it appears to have subsequently retained its approximate morphology and distribution in the 3.5 Gyr since. When the erosion occurred, in the Early Hesperian, the mantling unit was more resistant in some areas than its surroundings, resulting in inversion of relief: craters were transformed into highstanding buttes, and valleys were transformed into isolated ridges. On the basis of the scale of the observed inversion of relief, the magnitude of erosion in northeast Arabia Terra was substantial, up to hundreds of meters. We have used newly available data to assess the nature of the mantling material and probable mechanisms for its deposition and removal. We find that (1) the mantle unit is layered at scales of meters to tens of meters; (2) the deposit has a median thickness of 60 m, and the thickness of the deposit was locally controlled by the topography at the time of its deposition; (3) the mantling unit thins toward the south; and (4) characteristics of the mantling unit, such as its induration, as well as observed pits and fractures, suggest that volatiles may have been incorporated into the mantling unit either during or following its emplacement. Taken together, our observations lead us to favor models for the deposition of the mantling unit involving airfall of dust or ash. Either climate-driven dust deposition or plinian volcanic eruptions from the nearby Syrtis Major volcanic province are plausible candidate models for the emplacement of the unit in time and space.