Rock suites of Endeavour crater, Mars: Comparing Perseverance Valley, Spirit of St. Louis, and Marathon Valley

Abstract

Perseverance Valley is an erosional feature with the appearance of an eroded gully, located in the western wall of the Noachian aged Endeavour crater in Meridiani Planum, Mars. It is the most lithologically diverse location investigated by the Opportunity rover other than Cape York, where the rover first characterized the pre-, post-, and syn-depositional lithologies of Endeavour crater. We use hierarchical clustering and a similarity index combined with examination of Panoramic camera and Microscopic Imager images to classify these rock suites in Perseverance Valley, and contextualize them with comparison to rocks examined previously along the rim of Endeavour crater. The Perseverance Valley lithologies are classified into four rock suites, a clast-poor impact breccia that forms the “walls” of the valley, a competent basaltic outcrop of rocks that appear “blue” in false color Panoramic camera imagery, an outcrop of pitted rocks that has among the highest silica concentrations investigated by Opportunity, and a loose regolith mixture of martian soil, impact breccia, and local “blue” rocks that makes up the valley floor. Macro and micro textures indicate that the valley is currently being eroded by wind exiting the crater basin from west to east. Units that are offset both within and across Perseverance Valley indicate that the valley location and structure is likely influenced by a system of radial impact faults. Lithologies such as the co-located “blue” (in false color) and silica-rich pitted rocks, and observations of aqueous alteration such as “red” (in false color) zones, show similarities between Perseverance Valley and both Marathon Valley and the Spirit of St. Louis feature. We explore multiple working hypotheses to explain the formation mechanisms of Perseverance Valley, but can now say: the valley is likely structurally controlled including an ∼80 m vertical offset by a graben; the valley hosted local aqueous alteration; the floor material of the valley consists of mass-wasted local materials; and the current topographic expression was overprinted by modern aeolian erosion.