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


Thomas, Nancy Helen (2019) Remotely Sensing Aqueous Alteration on Mars: Innovative Statistical and Analytical Methods for Large Spectral Datasets. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8JFC-BY64.


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.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Mars, aqueous alteration, remote sensing, spectroscopy, MSL Curiosity
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Planetary Sciences
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ehlmann, Bethany L.
Group:Astronomy Department
Thesis Committee:
  • Knutson, Heather A. (chair)
  • Ehlmann, Bethany L.
  • Fischer, Woodward W.
  • Grotzinger, John P.
  • Rossman, George Robert
Defense Date:28 May 2019
Funding AgencyGrant Number
NSF Graduate Research FellowshipDGE-1144469
NASA MSL Participating Scientist ProgramUNSPECIFIED
Record Number:CaltechTHESIS:06072019-115333958
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 4
Thomas, Nancy Helen0000-0003-1989-4860
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11711
Deposited By: Nancy Thomas
Deposited On:07 Jun 2019 23:55
Last Modified:10 Mar 2020 23:48

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