The Geology and Geochemistry of Strata at the Base of Aeolis Mons as Characterized by the Curiosity Rover, Gale Crater, Mars

Abstract:

The Mars Science Laboratory team is using the Curiosity rover to investigate fluvial, lacustrine, and eolian strata that form the base of Aeolis Mons (Mt. Sharp). Basal outcrops that form the lowest stratigraphic unit of Aeolis Mons, the Murray formation, are dominated by lacustrine mudstones with interbedded fluvial sandstones and conglomerates. They are unconformably overlain by younger, likely eolian sandstones, which onlap the slopes of Aeolis Mons. Interpretation of the stratal relationships requires combined regional-scale orbital mapping and in situ observations of bedding geometry and sedimentary structures due to the laterally discontinuous nature of fluvial interbeds in the Murray formation and the similarity in appearance of the fluvial and eolian sandstones in orbital data. Team efforts demonstrate at least 10’s of meters of relief on the unconformity separating the Murray formation from younger sandstones.

The mudstone facies of the Murray formation show substantial variations in elemental composition. SiO2 ranges from <50 to >80 wt %, and Fe (calculated as FeO) varies from <3 to >15 wt %. Magnetite, hematite, ilmenite, and jarosite are present in significantly varying ratios. Cristobalite is also present in some, but not all of the mudstone. Textures in the mudstones include sub millimeter-scale lamination as well as diagenetic textures such as small crystal laths, 3d dendritic concretions, subspherical concretions, and at least two generations of mineral precipitation in fractures.

Overall, the stratigraphic relationships, textural characteristics, elemental composition and mineralogy indicate deposition in a lake followed by multiple diagenetic events related to lithification, burial, subsurface fluid flow, and weathering. Cross cutting relationships constrain the relative timing of some of these events, but the complexity of the geological history of the basal strata of Aeolis Mons suggests a rich geological history for the basal strata of Aeolis Mons.