CURIOSITY'S MARS HAND LENS IMAGER (MAHLI) INITIAL INVESTIGATIONS OF LOWER AEOLIS MONS STRATA, GALE CRATER, MARS

Aeolis Mons is a 5 km high mountain of stratified, sedimentary rock in the 155 km diameter Martian crater, Gale. The lowermost stratal package exposed on its north slope is informally named the Murray formation. The Mars Science Laboratory (MSL) rover, Curiosity, reached its first Murray formation outcrop at a site named Pahrump Hills in September 2014. The MSL Science Team is using Curiosity’s instrument suite to address the hypothesis that the Murray consists of lacustrine mudstones with occasional, interfingered fluvial sandstones and conglomerates. Critical to the investigation is MAHLI, a color camera with a macro lens, on the rover’s robotic arm, that can focus on targets at working distances of 2.04 cm to infinity. At close range, the images permit distinction of very fine sand from coarse silt. When the fines sharply contrast with their surroundings, the highest resolution images distinguish grains as small as 28–34 microns. The most prevalent facies observed is a light-gray, recessively-weathered, finely-laminated (mm to cm) rock. Lamination is expressed as alternating bands of greater and lesser resistance to eolian abrasion over stratigraphic intervals of thicknesses ~20 cm to > 1 m. On surfaces brushed by the rover’s dust removal tool, we observe a “salt and pepper” matrix with minor single pixel variability and scattered objects typically < 60 microns across. As such, the matrix clasts are mostly finer than 60 microns, with a substantial portion considerably finer. Because the matrix is, by volume, dominant, the laminated facies is therefore a mudstone. It has three basic components: the fine-grained matrix, a cementing agent that hardens individual laminae and probably fills interstitial spaces within the fine grained matrix, and larger (~0.2–1 mm) crystals or crystal pseudomorphs that are enclosed in the fine grained matrix. Decimeter-scale lenses of cross-stratified, very fine to fine-grained sandstone locally form caprocks and are interbedded within the mudstones. A variety of diagenetic textures are observed, including concretions of various aggregate, spherical, and dendritic morphologies; and white to dark gray mineral-filled fractures of varied tone and texture. The vein fills are typically more resistant to erosion than the mudstones and form cm-scale, protruding fins and boxworks.