Award Date
August 2023
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Geoscience
First Committee Member
Elisabeth M. Hausrath
Second Committee Member
Oliver Tschauner
Third Committee Member
Elizabeth B. Rampe
Fourth Committee Member
Pamela Burnley
Fifth Committee Member
Aude Picard
Number of Pages
391
Abstract
An ongoing debate exists around the nature of the climatic conditions present during the Noachian and early Hesperian periods (~4.1 to 3 Gyr ago) of Mars’ ancient history. The various theories put forward can reasonably be grouped into “warm and wet” vs “cold and icy” camps. Warm and wet approximates an Earth-like system with a relatively clement climate with significant liquid water present including potentially long-lived oceans. Cold and icy theories generally postulate thick ice sheets at high elevations with periodic warming events driving precipitation and the formation of river channels and leading to the formation of chemical alteration products. The presence of abundant olivine on Mars, a mafic silicate relatively unstable at surface pressure and temperature conditions in the presence of water, and juvenile aqueous alteration products is sometimes cited as evidence for cold and icy climatic conditions.
One way of investigating the past environmental and climatic conditions on Mars is to land instruments on the surface of the planet to directly measure the mineral and chemical makeup of Martian sediments and rocks. To that end, the Curiosity rover landed in Gale crater, the site of paleolakes and rivers, in 2011 to investigate past climatic and habitability conditions recorded in the sedimentary rocks deposited by liquid water. One finding of the Curiosity mission was the discovery in CheMin instrument XRD patterns of an abundant (15-73 wt.%) X-ray amorphous component within Gale crater rocks and sediments. Chemical data from the Sample Analysis at Mars (SAM) and Alpha Particle X-ray Spectrometer (APXS) instruments suggest this X-ray amorphous material is Fe-rich, Si-rich, sometimes Mg-rich, and contains volatile compounds indicative of the presence of incipient aqueous alteration products. However, beyond its presence and bulk chemical makeup, little remains known about the nature of this material or the implications of its presence for past environmental conditions on Mars.
This dissertation investigates the potential implications of the presence of Fe-rich, Si-rich, and Mg-rich X-ray amorphous material in Gale crater for past climatic conditions on Mars, and how composition affects olivine’s potential utility as an indicator for past environmental conditions and duration of water-rock interaction. We accomplish this through an investigation of climatic effects on incipient aqueous alteration within terrestrial ultramafic soils chemically relevant to Gale crater X-ray amorphous material. As we cannot yet directly examine Martian X-ray amorphous material and olivine using terrestrial facilities, we must turn to investigations of terrestrial environments analogous to Martian environments or materials. Ultramafic soils are generally Fe-rich, Mg-rich, siliceous, and Al-poor, and produce particularly Fe-rich secondary alteration products including oxyhydroxides and clay minerals. These characteristics make them chemically relevant environments for studying the formation of Fe- and Si-rich incipient alteration products like the X-ray amorphous component within Gale crater sediments.
This project is divided into three interconnected but distinct chapters that examine different aspects of incipient aqueous alteration within terrestrial ultramafic soils chemically relevant to incipient alteration processes on Mars. To examine the influences of climate on incipient aqueous alteration, we examined alteration processes in ultramafic soils developing under the warm and wet mediterranean climate of the Klamath Mountains of northern California, the cold and wet subarctic climate of the Tablelands of Newfoundland, Canada, and the hot and dry climate of Pickhandle Gulch, Nevada. The first chapter examines climatic influences on the formation and persistence of Fe-rich X-ray amorphous at the bulk scale utilizing X-ray diffraction and bulk and selective chemical dissolution techniques. I show that warm and wet conditions promote the formation crystalline Fe-containing secondary material whereas cold and wet conditions promote the formation of amorphous Fe-containing secondary material. The second chapter details a nanoscale investigation of the heterogeneity within X-ray amorphous material in the Klamath Mountains and Tablelands soils utilizing synchrotron microprobe and high-resolution transmission electron microscopy techniques. I show that warm and wet conditions initially promote crystallinity within the X-ray amorphous fraction in the form of nanocrystalline Fe-oxides and that X-ray amorphous material is generally absent from older soils. Cold and wet conditions promote the formation of Fe-rich, Si-rich, and Mg-rich purely amorphous material and promote higher overall silica abundance within the X-ray amorphous component. Together, these results suggest that the widespread presence of Fe- and Si-rich and sometimes Mg-rich amorphous material in Gale crater are consistent with cold and wet conditions. The third chapter details a burial experiment, wherein pristine disks of olivine were buried in the same soils utilized for the first two chapters to examine how variations in olivine composition affect incipient alteration and the kinds of climatic signals that might be gleaned from studies of Martian olivine alteration both in-situ and from future returned samples. We examine alteration of polished surfaces of pure forsterite and fayalite disks using scanning electron and atomic force microscopy, visible and near infrared spectroscopy, and X-ray photoelectron spectroscopy. Our results show that forsterite alteration correlates well with precipitation, temperature, and soil pH conditions. However, fayalite disks appeared relatively unaltered, suggesting that the oxidizing soil conditions might be limiting alteration of the Fe-rich fayalite surfaces. These results could help evaluate future returned samples from Jezero crater collected by the Perseverance rover mission.
Keywords
Amorphous; Climate; Mars; Olivine; Ultramafic; Weathering
Disciplines
Astrophysics and Astronomy | Geochemistry | Soil Science
File Format
File Size
53370 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Feldman, Anthony, "Climatic Influences on Incipient Alteration in Mars-Relevant Ultramafic Soils" (2023). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4826.
http://dx.doi.org/10.34917/36948176
Rights
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