Sulfur Speciation and Curation Considerations for the Carbonaceous Chondrite Tagish Lake and Other Meteorites
Creators: Holt, Miranda C
Publisher: name: University of Alberta Library
Year: 2023

<p>Carbonaceous chondrites contain significant abundances of sulfur components such as sulfide, sulfate, elemental sulfur (S0), and organosulfur compounds. These are significant because questions remain regarding the role of S in the origin of life. Chondrites and all other meteorites are out of equilibrium at Earth’s surface, and if stored improperly will undergo modification relatively rapidly. Additionally, analysis that modifies the form of the sample has the potential to alter its intrinsic properties. This is an important consideration when determining whether a sample can be used for multiple analyses, a necessity for future sample return missions where a limited amount of material may be available.<br>
This thesis will: 1) Examine the Fe-Ni sulfides present in several carbonaceous chondrites to constrain their formation mechanisms and temperatures as well as the extent of aqueous alteration experienced by their parent bodies; 2) Perform chemical extractions to determine the nature of any organosulfur species which may be present within Tagish Lake; 2) Assess the extent to which the organosulfur content of Tagish Lake may have been modified following collection, storage, and processing during analysis; 3) Assess the degree to which sample heterogeneity and experimental method may influence analytical results; 4) Develop recommendations for proper curation methods for extraterrestrial materials. <br>
As a part of this study, analysis of Fe-Ni sulfide grains within three carbonaceous chondrites, C2 Tagish Lake (TL), CM2 Aguas Zarcas (AZ), and C2 Tarda by scanning electron microscope and electron probe microanalyzer has revealed multiple morphologies, textures, and mineral phases, including some which may have formed at high temperatures of ~500-600°C within the solar nebula and some which formed at lower temperatures of ~25-135°C during parent body aqueous alteration. These temperatures of formation are based on mineral compositions plotted on Fe-Ni-S ternary diagrams, yielding the temperature of the altering fluid.<br>
Organosulfur species provide an important record of pre- and early solar chemical reactions and parent body aqueous alteration processes. Chemical extractions designed to establish whether organosulfur species may be present within a pristine sample of Tagish Lake (specimen TL1) which has remained frozen since collection have determined that the most likely compound to be present, methane sulfonic acid, is not present within this sample in an easily accessible form. As this compound has previously been found within Tagish Lake, potential explanations for its absence in the samples studied herein, including previous extractions of samples of TL 5b and TL 11h as well as a new extraction of sample TL1, are investigated. Possible explanations include lithologic differences between samples, changes to the organosulfur or other S-species and the growth of a new mineral, gypsum, as a result of previous chemical extractions or long-term storage of samples, potential contamination, and loss of compounds during extraction and analysis as a result of the failure of existing experimental methods. <br>
    Following investigations on the effects of storage conditions into the preservation of both organic-containing stony meteorites as well as iron-based meteorites, recommendations for the storage conditions of these types of materials are made to ensure their continued preservation. In particular, storage of extraterrestrial materials in anoxic or inert atmospheres is found to be beneficial to the preservation of both carbonaceous chondrites as well as iron meteorites.</p>