MAHLI ON THE ROAD TO MT. SHARP: SEDIMENTARY ROCK GRAIN-SCALE STRUCTURES AND TEXTURES WITHIN GALE CRATER, MARS

The Mars Hand Lens Imager (MAHLI) is located at the end of the robotic arm of the Mars Science Laboratory rover Curiosity. MAHLI observations serve as a bridge between outcrop-scale observations made by Mastcam and the geochemistry, mineralogy and volatile budgets of materials measured by APXS, ChemCam, SAM and CheMin. Since Curiosity’s arrival at Yellowknife Bay (YKB) on Sol 122, MAHLI has revealed grain/clast size and characteristics, sorting, porosity and secondary materials (e.g., veins, nodules) within sedimentary rocks encountered in Gale crater, and provided insights into their depositional environments.

Within the YKB formation, MAHLI observations at 16–17 µm/pixel constrained that its lowermost member, Sheepbed, was a mudstone, and that the Gillespie Lake member overlying the Sheepbed member was a coarse sandstone. The relatively featureless matrix, vugs and fine-grained vug fill of the Point Lake outcrop, above the Gillespie Lake member, were difficult to interpret even with MAHLI images of ~30 µm/pixel. The Shaler outcrop, above Point Lake, consists of interbedded finer- and coarser-grained sand beds that exhibit a variety of cross bedding styles. MAHLI images helped define subfacies within Shaler and characterize structures indicative of fluvial deposition.

Since departing YKB, major contact science campaigns have been limited to “waypoints” selected to complement observations at YKB and provide pretext for the layered strata of Aeolis Mons (a.k.a., Mt. Sharp). At the Darwin waypoint, MAHLI characterized multiple pebbly sandstones distinguished by variations in matrix and clast sizes/lithologies. These observations complemented conglomerate observations made prior to robotic arm commissioning. At the Cooperstown waypoint, MAHLI identified sandstones of different erosional resistances. The well-sorted and cemented matrix of the more resistant sandstone was indistinguishable from that of Point Lake, thus establishing the sedimentary nature of Point Lake and linking similar lithologies separated by 2 km.