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Geobiological investigation of the hypersaline sediments of Pilot Valley, Utah: a terrestrial analog to ancient lake basins on Mars, A
Lynch, Kennda Lian
Lynch, Kennda Lian
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2015
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2017-01-04
Abstract
Martian paleolake basins are prime habitability targets for future Mars rover missions as they are thought to be reasonable proxies for a Hadean-like origin-of-life environment. This is especially the case for the upcoming Mars 2020 mission as over half of the top landing sites being considered show evidence of lacustrine sediments. Many terrestrial paleolakes transitioned to modern day evaporite basins due to climate change and exhibit clay, sulfate, and chloride compositions similar to the aqueous minerals identified across the martian surface. These terrestrial systems are considered excellent analogs for habitability studies that will be useful for identifying and exploring lacustrine systems on Mars. This dissertation focuses on evaluating several aspects of martian paleolake basin habitability in a relevant analog environment, the Pilot Valley basin in northwestern Utah, in preparation for Mars 2020 and other future surface missions to the red planet. Lacustrine sediments from the Pilot Valley basin were characterized using X-ray diffraction (XRD) and automated scanning electron microscopy (QEMSCAN) to gain contextual insight into the mineral assemblages deposited in terrestrial paleolakes and to use as ground truth for evaluating the efficacy of visible-near-infrared spectroscopy (VNIR) as a tool for the identification and characterization of martian paleolake surfaces. Results of this effort show that lacustrine sediments can be very complex and that current spectral reference libraries are not sufficient to interpret the spectral influence from complex mixed mineral matrices. Second, the microbial ecology was investigated in order to characterize the biological diversity within this understudied environment, assess the relationship, if any, between the microbial diversity and the mineralogical and geochemical variation present in the basin, and assess the influence of this relationship on biosignature preservation as a model for paleolake systems on the red planet. General results from this effort show that a novel ecosystem is present in Pilot Valley and community assembly is influenced by sediment grain size. Finally, the presence and distribution of naturally-occurring perchlorate was investigated along with the potential for perchlorate reducing organisms co-existing with naturally-occurring perchlorate as a model for potential metabolisms that could support a microbial ecosystem in ancient martian lacustrine sediments. Results show that naturally-occurring perchlorate exists in the near surface sediments as does a small population of known perchlorate reducing organisms.
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