Stratigraphy of Phyllosilicates and Sulfates in Northern Meridiani Planum, Mars

The Meridiani Planum region on Mars is currently being explored by the Mars Exploration Rover Opportunity, and multiple landing sites for the upcoming Mars Science Laboratory (MSL) have been proposed in the region. Northern Meridiani is characterized in part by expanses of exposed light-toned layered rock (formerly known as "etched terrain"). We have generated new regional mosaics of Meridiani Planum data from the OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) near-IR imaging spectrometer on the Mars Express orbiter and have used them to map spectral parameters that are indicative of hydrated minerals, sulfates, and phyllosilicates. Our maps are consistent with though not identical to previous OMEGA maps of this region. They reveal widespread (thousands of km2) evidence for hydration in the Meridiani light-toned layered rock (indicated by an absorption band at 1.9 microns). Sulfates, indicated by a decrease in reflectivity at 2.4 microns, are also apparent in our OMEGA mosaics, and are most clearly detected in a specific ~130 km × 30 km valley in the light-toned layered rock, near 2°N, 0.4°W. We also detect phyllosilicates in small (several km2) isolated patches of the light-toned layered rock. Of particular interest is a phyllosilicate detection in the light-toned layered rock roughly 60 km southwest of the sulfate-bearing valley. This phyllosilicate detection has not been reported in previous OMEGA maps of the region. The phyllosilicates occur ~300 m higher in elevation than the floor of the sulfate-bearing valley. If both the phyllosilicates and sulfate detections are representative of bulk bedrock, this may indicate that the phyllosilicates are stratigraphically younger than the sulfates. Alternatively, it is possible that the sulfates and/or the phyllosilicates were not deposited with the bedrock but are the result of subsequent alteration, or have been transported to their current location by aeolian or fluvial processes. Finally, it is possible that in the Meridiani region, phyllosilicates and sulfates were forming concurrently at some points in the past. To test the hypothesis that the phyllosilicates are stratigraphically younger than the sulfates in this region, we are examining high resolution images from the Mars Orbital Camera (MOC), the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) and determining the tilt and stratigraphy of the sulfate- bearing valley, the phyllosilicate-bearing regions, and the surrounding terrain. This investigation will be supplemented by Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observations of the same region. Wherever possible, we will correlate composition with morphology to develop a more complete understanding of the stratigraphy in Northern Meridiani Planum.