Results from the first geologic traverse on the topographic rim of a complex impact crater, Endeavour Crater, Mars

A geologic traverse along the rim of the 22-km-diameter Endeavour Crater by the Opportunity Mars rover has provided the first field geologic observations of outcrop-scale structure and stratigraphy at a complex impact crater, characteristics that were previously undocumented due to erosion of similar-size craters on Earth. Two findings of note are (1) the attitude of sheets, foliations, and contacts between rim impact breccias and pre-impact substrate is antiformal, the limbs dipping inward toward the center of the crater inside the crater rim and outward exterior to the crater rim; and (2) coherent blocks of crust segment the rim topographically and structurally into a series of right- and left-stepping elongate rises of variable size and orientation. These segments experienced differing magnitudes of uplift during crater formation along identified vertical scissors faults. Brecciation along the faults bounding rim segments created zones of enhanced subsurface fluid transport through the crater rim, potentially responsible for localized areas of aqueous alteration identified in outcrops near segment boundaries.