Remotely Sensing Aqueous Alteration on Mars: Innovative Statistical and Analytical Methods for Large Spectral Datasets

Abstract

Liquid water once flowed on Mars and altered the crust. Aqueous minerals and salts record a rich history of aqueous processes and environmental changes. In this dissertation, I developed and applied innovative analytical and statistical methods to large spectral datasets to better characterize aqueous alteration on Mars. The Mars Science Laboratory (MSL) Curiosity rover is investigating the sedimentary sequence at Gale crater recording a potentially global transition from clay-enriched to sulfate-enriched rocks. Volatile elements like H and Cl are important for investigating aqueous processes but are difficult to quantify in the large ChemCam laser-induced breakdown spectroscopy (LIBS) dataset. In the first part of this dissertation, I measured aqueously altered samples with LIBS in the laboratory under Mars-relevant conditions to develop analytical methods for application to ChemCam. The Murray formation, the lowest exposed strata of the sedimentary sequence, contains 2.6 ± 2.1 wt. % H2O. Carriers of H enrichment including clays, opal, Mg-sulfates, Ca-sulfates, hydrous Mn-oxides, akageneite, and jarosite are identified. Variability in the H content of the Murray formation records multiple aqueous alteration events as well as potential increases in salinity in the Gale crater lake. In the fourth chapter, I measured chlorine in Gale crater using multiple MSL instruments. Cl-enrichments correlated with increased Na2O are detected in the bedrock, in nodular textures, and at vein margins, indicating halite. The scattered, isolated occurrences of chlorides are consistent with late groundwater reworking and remobilization. Halite is concentrated in particular members of the Murray formation; the chlorides may have been emplaced as primary deposits in these members, consistent with varying salinity in the past lakewaters. In the second part of this dissertation, I adapted and applied semi-automated statistical methods called factor analysis and target transformation to the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) dataset to systematically search for hematite in stratified, candidate sedimentary outcrops. Few outcrops containing hematite are found and no obvious analogs to terrestrial iron formations are identified. Future studies will search for hematite in other geologic settings as well as other Fe-bearing phases such as Fe-phyllosilicates and Fe-sulfates to better characterize aqueous processes on Mars.