Distribution of primary and secondary features in the Pahrump Hills outcrop (Gale crater, Mars) as seen in a Mars Descent Imager (MARDI) "sidewalk" mosaic

Abstract

The Mars Science Laboratory Curiosity rover conducted a reconnaissance traverse across the Pahrump Hills outcrop within Gale crater from Sols 780–797. During the traverse, the Mars Descent Imager (MARDI) acquired a continuous imaging record of primary and secondary sedimentary features throughout the outcrop. The characteristics of the features (laminae, resistant features, fractures, gray clasts) and their spatial distribution provide insight into the processes that contributed to the formation of Pahrump Hills. Thin, regular laminae (mm-scale) are ubiquitous in the bedrock, implying that depositional processes at that scale did not change appreciably during deposition of the mudstone succession at Pahrump Hills. Higher bedrock slopes correlate with undulatory bedrock surfaces, bedrock with elevated Mg contents, and fractures exhibiting wide, raised edges. These collective features are consistent with increased erosional resistance caused by greater quantities of erosionally-resistant, Mg-bearing cement within the bedrock permitted by coarser grain sizes. Resistant features exhibit a range of morphologies, elevated Mg contents, and do not deflect laminae within the bedrock. Their characteristics implicate the involvement of Mg-enriched fluids in a late diagenetic overprint affecting the bedrock. The variations of fracture fill and edge morphologies and chemistries further suggest repeated fracturing and fluid interaction events within the strata exposed at Pahrump Hills. Gray clasts strongly resemble fragments eroded from sandstone horizons interspersed throughout the Pahrump Hills outcrop.