SPECTRAL EVIDENCE FOR ISOLATED OUTLIERS OF MERIDIANI “ETCHED TERRAIN” IN SOUTHERN SINUS MERIDIANI

The Sinus Meridiani region (including Meridiani Planum, the landing site of the Opportunity rover) contains expansive, laterally continuous layered units that have been previously mapped and investigated using orbital data. These light-toned, higher thermal inertia units known as the “etched terrain” units overlie Noachian cratered terrains. Early works referred to the “etched terrain” units as “sulfate-bearing units”; however, it was later shown that sulfate minerals are not consistently detected across the etched terrain units, even where well-exposed. From previous studies, it has been shown that the etched terrain units exhibit variable levels of hydration in Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and Mars Express Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) data sets, with isolated Fe/Mg-phyllosilicate, sulfate, and Al-phyllosilicate/hydrated silica detections. Previous studies also showed that the etched terrain units are regionally extensive over hundreds of km and generally follow the regional tilt of the pre-existing surface, with an average thickness of ~360 m. The lateral extent and dip of the etched terrain units strongly favor an aeolian or airfall origin for the clastic material that makes up the bulk of the etched terrain. However, it is unclear whether the sulfate-bearing materials found within these units formed from groundwater vs other (atmospheric, ice weathering) origin. Strong evidence for a groundwater origin comes from hydrological models that predict the currently known distributions of etched terrains, thus constraints on the distribution of etched terrains is important for interpreting their origin. In this work, I used Mars Odyssey Thermal Emission Imaging System (THEMIS) data and CRISM multispectral survey product (MSP) data to analyze two isolated, small exposures of light-toned bedrock in southern Sinus Meridiani (Noachis Terra) that exhibit spectral and morphological similarity to previously-mapped laterally extensive etched terrain units in Meridiani Planum and northward. One exposure has weak features consistent with sulfate, whereas the other has features consistent with phyllosilicate minerals. The potential additions to etched terrain inventory may have implications for their origin.