Fine-scale textural observations at vera rubin ridge, gale crater, from the mars hand lens imager (mahli)

Introduction: The Mars Science Laboratory (MSL) rover (Curiosity) is operating in Gale, a ~155 km diameter impact crater that hosts a stratified central mound. Curiosity is traversing across a topographically high, hematite enriched landform named Vera Rubin Ridge (VRR) [1,2] located along the northern slope of the mound. Understanding how the sedimentary rocks exposed on this ridge were deposited and altered may yield constraints on ancient martian environments recorded in Gale crater. Orbital datasets show that VRR exhibits varied textures and colors at decameter scales. Figure 1 shows that the north-facing slope of VRR exhibits stratified, light-toned bedrock and blue sand, while the top of the ridge has some surfaces that are lighter, that exhibit fractures, that retain craters, that are dark-toned and mottled, and that are light blue in HiRISE enhanced-color images (black dashed lines show the boundaries of these surfaces as identified from orbit). These color, tone, and morphology differences lead to the hypothesis that there might be several distinct geologic units within the ridge. Our on-going investigation considers whether these differences correspond to distinct sedimentary facies within VRR, or whether the morphologies identified from orbit are a result of different erosional expressions [3]. Here we investigate the lithology and diagenetic features of VRR rocks at a sub-mm-to-cm scale to identify variations that occur within the ridge and to address the hypothesis that there are distinct facies within VRR. Data: MAHLI (located on the rover’s arm) is capable of acquiring color images from a standoff distance of ~3 cm away from a surface, which yields a resolution of ~17 μm/pixel [4]. Here, we use MAHLI data from Sols 1795 to 1904, which correspond to observations of strata from elevations between -4222 m and -4154 m, from the northern slope of VRR to the “top” of the ridge. Observations: In all the rock targets imaged by MAHLI at VRR in which the dust was removed from the surface, the grain size is generally finer than MAHLI can resolve at 3-4 cm standoff distance, suggesting that the rock targets are composed of grain sizes finer than sand. Most rock targets observed by MAHLI reveal abundant planar lamination (i.e. Figure 2). MAHLI observations of rocks that were in contact with the Dust Removal Tool (DRT) [5] suggest that the rocks at the top of VRR are harder than those previously investigated. The DRT [5] was used at 14 of the targets imaged by MAHLI at the top of VRR. In soft rock, the Figure 1: HiRISE enhanced-color image of VRR. Red line shows the MSL traverse up to Sol 1910. Orange circles show the location of Figures 2-6. Dashed lines show morphologic boundaries identified from orbit. (ESP_042682_1755)