Formation and Alteration of Basaltic Soils on Mars

The current surface of Mars is an arid inhospitable environment, dominated by aeolian processes, composed of largely volcanic rocks that have little apparent indication of pervasive aqueous chemical weathering, and blanketed by dust. Rocks are composed of basalts and the “soil” sediments appear to be largely basaltic-derived, and are chemically similar on a global scale. If the climate was once warmer and wetter during the Noachian period, with environmental conditions favorable to the development of life, physically weathered remnants, such as large quantities of phyllosilicate minerals, should remain. Basaltic soils provide a crucial constraint on chemical and physical weathering processes, and are critical for determining the environmental and climatic history of Mars. To understand the origin of sediments, this dissertation investigated the (1) textures of sedimentary grains at Gusev Crater, (2) the chemical and mineral compositions of sediments at the Mars Exploration Rover landing sites in Meridiani Planum and Gusev Crater, and evaluated the potential chemical alteration from weathering, and (3) applied mineral fractionation experiments of analog basalt sediment with implications for interpreting the sorting of sediments on Mars. Textural results indicate that soils are continuously transported and modified by aeolian conditions, and originate primarily from comminuted impacted bedrock. Soil chemical compositions resemble unaltered basalt but mixing of sulfates and phyllosilicates is permissible. Comminuted and grain size sorted basalt analog sediments demonstrate the potential for significant compositional variations imposed by hydrodynamic sorting, an important determinant of soil compositions on Mars. Combined, these results show that soils on Mars are heterogeneous mixtures of comminuted locally derived rocks that have been minimally altered by chemical weathering from olivine dissolution, and are mixed with dust containing older phyllosilicates and sulfates.