Mantled and exhumed terrains in Terra Meridiani, Mars

Hematite‐bearing deposits in the Terra Meridiani region of Mars constitute the top stratum of a partially eroded layered complex that covers dissected Noachian‐aged cratered terrain. The hematite unit consists of dark plains and dunes covering a bright substrate. This substrate is fully exposed beyond the borders of the hematite‐bearing deposit and consists of polygonal ground separated by ridges or valleys, together with layered deposits that have been eroded into a variety of landforms. The complex is partially covered by a regional‐scale aeolian mantle that thickens toward the north. The hematite‐bearing stratum exhibits low albedoes, pulse widths, and intermediate thermal inertias, whereas the underlying unit exhibits high values of these parameters. Both units have spectral emissivity signatures similar to those for the low albedo cratered terrain to the south, with the addition of hematite for the top stratum. The complex is interpreted to consist of extensive plains‐forming lava flows and tephra deposits emplaced during an extensional regime and at least partially buried by an aeolian mantle. Aeolian stripping of the mantle exposed much of the complex and differentially eroded the deposits to produce the landforms existent today. Exploration of the hematite‐bearing deposits by the 2003 Mars Exploration Rover, “Opportunity,” will allow testing of the hypotheses presented since this stratum has been locally reworked into dunes that only partially cover the underlying brighter portion of the complex. In particular, the rover‐based measurements will allow us to test the extent to which the unusual remote‐sensing properties of the units indicate aqueous alteration.