Reconstruction of eolian bed forms and paleocurrents from cross‐bedded strata at Victoria Crater, Meridiani Planum, Mars

摘要

Outcrop exposures imaged by the Opportunity rover at Victoria Crater, a 750 m diameter crater in Meridiani Planum, are used to delineate sedimentary structures and further develop a dune‐interdune depositional model for the region. The stratigraphy at Victoria Crater, observed during Opportunity’s partial traverse of its rim, includes the best examples of meter‐scale eolian cross bedding observed on Mars to date. The Cape St. Mary promontory, located at the southern end of the rim traverse, is characterized by meter‐scale sets of trough cross bedding, suggesting northward migrating sinuous‐crested bed forms. Cape St. Vincent, which is located at the opposite end of the traverse, shows tabular‐planar stratification indicative of climbing bed forms with meter‐ to decameterscale dune heights migrating southward. Promontories located between Cape St. Mary and Cape St. Vincent contain superposed stratigraphic units with northward and southward dipping beds separated by outcrop‐scale bounding surfaces. These bounding surfaces are interpreted to be either reactivation and/or superposition surfaces in a complex erg sea. Any depositional model used to explain the bedding must conform to reversing northward and southward paleomigration directions and include multiple scales of bed forms. In addition to stratified outcrop, a bright diagenetic band is observed to overprint bedding and to lie on an equipotential parallel to the preimpact surface. Meter‐scale cross bedding at Victoria Crater is similar to terrestrial eolian deposits and is interpreted as a dry dune field, comparable to Jurassic age eolian deposits in the western United States.