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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.

We assessed dust coverage on the Mars Science Laboratory Mars Hand Lens Imager (MAHLI) and Alpha Particle X-Ray Spectrometer (APXS) calibration targets from 14 MAHLI images acquired at

Craters within Arabia Terra, Mars, contain hundreds of meters of layered strata showing systematic alternation between slope- and cliff-forming units, suggesting either rhythmic deposition of distinct lithologies or similar lithologies that experienced differential cementation. On Earth, rhythmically deposited strata can be examined in terms of stratal packaging, wherein the interplay of tectonics, sediment deposition, and base level (i.e., the position above which sediment accumulation is expected to be temporary) result in changes in the amount of space available for sediment accumulation. These predictable patterns of sediment deposition can be used to infer changes in basin accommodation regardless of the mechanism of deposition (e.g. fluvial, lacustrine, or aeolian). Here, we analyze sedimentary deposits from three craters (Becquerel Crater, Danielson Crater, Crater A) in Arabia Terra. Each crater contains layered deposits that are clearly observed in orbital images. Although orbital images are insufficient to specifically determine the origin of sedimentary deposits, depositional couplets can be interpreted in terms of potential accommodation space available for deposition, and changes in the distribution of couplet thickness through stratigraphy can be interpreted in terms of changing base level and the production of new accommodation space. Differences in stratal packaging in these three craters suggest varying relationships between sedimentary influx, sedimentary base level, and concomitant changes in accommodation space. Previous groundwater upwelling models hypothesize that layered sedimentary deposits were deposited under warm climate conditions of early Mars. Here, we use observed stacking patterns to propose a model for deposition under cold climate conditions, wherein episodic melting of ground ice could raise local base level, stabilize sediment deposition, and result in differential cementation of accumulated strata. Such analysis demonstrates that a first-order understanding of sedimentary deposition and accumulation—despite a lack of textural information that inhibits interpretation of depositional mechanism—can provide insight into potentially changeable depositional conditions of early Mars.

We combine the results of orbitally-derived morphologic and thermal inertia data with in situ observations of abundance, size, morphologic characteristics, and distribution of pebble- to cobble-sized clasts along the Curiosity rover traverse. Our goals are to characterize rock sources and transport history, and improve our ability to predict upcoming terrain. There are ten clast types, with nine types interpreted as sedimentary rocks. Only Type 3 clasts had morphologies indicative of significant wear through transport; thus, most clast types are indicative of nearby outcrops or prior presence of laterally extensive sedimentary rock layers, consistent with the erosional landscape. A minor component may reflect impact delivery of more distant material. Types 1 and 4 are heavily-cemented sandstones, likely associated with a “caprock” layer. Types 5 and 6 (and possibly 7) are pebble-rich sandstones, with varying amounts of cement leading to varying susceptibility to erosion/wear. Type 3 clasts are rounded pebbles likely transported and deposited alluvially, then worn out of pebbly sandstone/conglomerate. Types 9 and 10 are poorly-sorted sandstones, with Type 9 representing fragments of Square Top-type layers, and Type 10 deriving from basal or other Mt. Sharp layers. Types 2, 8 and 9 are considered exotics. There are few clear links between clast type and terrain surface roughness (particularly in identifying terrain that is challenging for the rover to navigate). Orbital data may provide a reasonable prediction of certain end-member terrains but the complex interplay between variables that contribute to surface characteristics makes discriminating between terrain types from orbital data problematic. Prediction would likely be improved through higher-resolution thermal inertia data., This research was supported by the Mars Science Laboratory Program through Malin Space Science Systems contract 08-0315 to R.A.Y. Work in Denmark was funded by the Danish Council for Independent Research/Natural Sciences (FNU grants 12-127126 and 11-107019) and the TICRA Foundation. Work in Germany was funded by the Deutsche Forschungsgemeinschaft (DFG grant GO 2288/1-1). V.E.H. was supported by the Mars Science Laboratory Participating Scientist Program (JPL subcontract 1449892).