Sedimentary rocks on Mars provide insight into past aqueous and atmospheric processes, climate regimes and potential habitability. The Mars Exploration Rover Opportunity has investigated several outcrops in Meridiani Planum, Mars, studying the exposed sedimentary rocks in an effort to better understand the role of surface processes in its geologic history. Opportunity has recently completed its observations of Victoria crater, which is 750 m in diameter and exposes cliffs up to ~15 m high. The crater has a well-developed geomorphic pattern of promontories and embayments that define the crater wall. Opportunity spent several months traversing the rim of the crater and documenting the stratigraphy of several promontories. Observations of outcrops at several promontories revealed thick bedsets (3-7 m) of eolian dune cross-bedding. Analysis of cross-bedding geometry suggests a dominant paleo-wind direction from north to south. A lithostratigraphic subdivision of bedrocks units was made possible by the presence of a light-toned band that lines much of the upper rim of the crater. In ascending order three stratigraphic units are named Lyell, Smith and Steno; Smith is the light-toned band.
Opportunity was able to drive into the crater at Duck Bay, located on the western margin of Victoria Crater. Detailed measurements of the three stratigraphic units were taken as Opportunity descended into the crater. Data from the Microscopic Imager and Panoramic Camera reveal details about the structures, textures, and depositional and diagenetic events that influenced the Victoria bedrock. In this reference section, Smith is interpreted as a diagenetic band that also is bounded by an erosional contact with Steno. Elsewhere in the crater the diagenetic band crosscuts the physical stratigraphy. Correlation with strata present at nearby promontory Cape Verde suggests that there is an erosional surface at the base of the cliff face that may correspond to the erosional contact below Steno. This suggests that the material above the erosional contact was built on significant depositional paleotopography. The eolian dune forms exposed in Duck Bay and Cape Verde, combined with the geometry of the erosional surface, suggests that these outcrops are part of a larger draa architecture. This insight is possible only due to the larger-scale exposures at Victoria crater, in contrast to earlier studied, and much more limited exposures at Erebus, Endurance, and Eagle craters.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009