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A Geochemical Study of Speleothems and Cave Waters in Basaltic Caves at Lava Beds National Monument, Northern California, USA

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A Geochemical Study of Speleothems and Cave Waters in Basaltic Caves at Lava Beds National Monument, Northern California, USA A geochemical study of speleothems and cave waters in basaltic caves at Lava Beds National Monument, Northern California, USA by Joshua A. Ford B.A., Hanover College, 2018 A THESIS submitted in partial fulfillment of the requirements for the degree MASTER OF SCIENCE Department of Geology College of Arts and Sciences KANSAS STATE UNIVERSITY Manhattan, Kansas 2020 Approved by: Approved by: Co-Major Professor Co-Major Professor Matthew Brueseke Saugata Datta Copyright © Joshua Ford 2020. Abstract Lava caves within Lava Beds National Monument (LBNM), CA, were selected as terrestrial analog sites for caves observed on other planetary bodies. The lava caves at LBNM were found to contain active microbial communities, including colorful biofilms. Additionally, the caves were discovered to host a variety of morphologically distinct secondary mineral deposits known as speleothems. Speleothems and co-located cave waters were collected to determine their compositions and assess geochemical biosignatures. Speleothems were analyzed for mineralogical, elemental, and internal stratigraphic contents. Cave waters were analyzed for major elements, major ions, DOC, and stable isotopes. Speleothems were found to be comprised primarily of opal-A and calcite, with elemental chemistries dominated by SiO2 and CaO, alongside lesser concentrations of MgO. Speleothem formation was ultimately interpreted to be driven by both inorganic and biological factors, including availability of water, extent of evaporation, and nucleation influenced by microbial bioaccumulation. Mineral precipitation likely occurs due to evaporation of water films supplied by condensation and capillary action, with opal favored in wet conditions and calcite in dry conditions, where increased evaporative concentration favors the precipitation of calcite and Mg carbonate. Microbes likely mediate precipitation through nucleation of porous opal by bound silanol in microbial extracellular products. This creates a microsystem wherein autotrophic bacteria may encourage carbonate mineral precipitation via CO2 consumption increasing pH, and may be reflected in the presence of both microstromatolite-like opal and calcite lamina and a predominance of DOC in cave waters. These findings contribute to the further understanding and characterization of lava cave speleothems as potential biosignature targets. Table of Contents List of Figures ..................................................................................................................................x List of Tables ............................................................................................................................... xiii Acknowledgements ...................................................................................................................... xiv CHAPTER 1 – Introduction and Background ............................................................................1 1.1 Introduction to Lava Caves, Extraterrestrial Lava Caves, and BRAILLE ..........................1 1.2 Lava Cave Secondary Mineral Deposits – Speleothems .....................................................6 1.3 Mineralogical Variations among Speleothems ....................................................................6 1.4 Occurrence and Role of Water in Lava Caves .....................................................................8 1.5 Speleothem Formation Processes ........................................................................................9 1.6 Microbial Processes Influencing Speleothem Formation ..................................................10 1.7 Hypotheses and Objectives ................................................................................................13 CHAPTER 2 – Study Area..........................................................................................................16 2.1 Recent Medicine Lake Volcanism .....................................................................................17 2.2 Ground Water Hydrology of Tule Lake Subbasin and LBNM ..........................................18 2.3 Lava Cave Organisms ........................................................................................................19 2.3.1 Prokaryotes and Archaea .......................................................................................19 2.3.2 Eukaryotes..............................................................................................................20 2.3.3 Plants ......................................................................................................................21 CHAPTER 3 – Methods ..............................................................................................................22 3.1 Sample Collection ..............................................................................................................22 iv 3.2 Sample Preparation and X-Ray Diffraction Analysis ........................................................27 3.3 Clay Fraction ......................................................................................................................27 3.4 X-Ray Fluorescence ...........................................................................................................28 3.5 Thin Sections and Petrography ..........................................................................................29 3.6 Electron Microprobe ..........................................................................................................29 3.7 Water Chemistry ................................................................................................................30 3.7.1 Ion Chromatography ..............................................................................................30 3.7.2 Alkalinity ...............................................................................................................30 3.7.3 ICP-MS ..................................................................................................................30 3.7.4 TOC, DOC, and TDN ............................................................................................30 3.7.5 δ18O and δ2H Stable Isotopes .................................................................................31 3.8 Geochemical Modeling ......................................................................................................31 3.9 Scanning Electron Microscopy ..........................................................................................31 CHAPTER 4 – Results.................................................................................................................32 4.1 Variations in Speleothem Morphology ..............................................................................32 4.1.1 Cave Basalt ............................................................................................................32 4.1.2 Crusts .....................................................................................................................33 4.1.3 Polyps .....................................................................................................................34 4.1.4 Cauliflower ............................................................................................................34 4.1.5 Coralloids ...............................................................................................................35 4.1.6 Gours ......................................................................................................................36 v 4.2 Speleothem and Basalt Mineralogy ...................................................................................37 4.2.1 Cave Basalt ............................................................................................................37 4.2.2 Speleothems ...........................................................................................................38 4.2.3 Museum-Grade Opal Standards .............................................................................39 4.2.4 Crusts .....................................................................................................................40 4.2.5 Polyps .....................................................................................................................41 4.2.6 Cauliflower ............................................................................................................41 4.2.7 Coralloids ...............................................................................................................42 4.2.8 Gours ......................................................................................................................43 4.3 Clay Mineralogy ................................................................................................................44 4.4 Petrographic Analysis of LBNM Speleothems and Cave Basalt .......................................44 4.4.1 Cave Basalt ............................................................................................................44 4.4.2 Crusts, Cauliflower, Polyps, Coralloids, and Gours ..............................................45 4.4.3 Volcanic Fragment Inclusions within Speleothems ...............................................51 4.5 Cave Bare Basalt and Speleothem Elemental Composition ..............................................52 4.5.1 Cave Basalt ............................................................................................................52 4.5.2 Crusts .....................................................................................................................55
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