MINERALOGY AND GEOMICROBIOLOGY IN ACTIVE VOLCANIC CAVE ENVIRONMENTS IN CENTRAL AMERICAAndres Ulloa Carmiol
, 2019, doctoral dissertation
Abstract: Recently, the study of mineralogical and geomicrobiological interactions in volcanic caves is gaining relevance, because there are many factors to consider them as Mars analogues for astrobiology and planetary sciences. In addition, sulfuric acid caves have also shown to be an important field of study for the understanding of chemolithoautotrophic metabolic pathways, especially in regard to the biogeochemical cycle of sulfur compounds. Hitherto, sulfur-rich volcanic caves found in Central America were almost unknown to the scientific community. This work presents the mineralogical and microbiological diversity and the potential geomicrobiological links found in active volcanic settings, such as Cueva los Minerales (CMI) and Cueva los Mucolitos (CMU) at Irazú volcano (Costa Rica), and Cueva Hoyo de Koppen (CHK) at El Hoyo volcano (Nicaragua). The volcanic caves at Irazú volcano (Costa Rica) are located in the northwest (NW) foothills of the main crater. These caves became accessible after the partial collapse of the NW sector of the Irazú volcano in 1994, offering the opportunity to investigate in situ active minerogenetic processes. Detailed mineralogical and geochemical analyses were performed to study the speleothems at CMI and CMU. Mineralogical analyses included X-ray diffraction (XRD) and Raman spectroscopy, while geochemical characterization was done using Energy Dispersive X-ray spectroscopy (EDX) coupled to Scanning Electron Microscopy (SEM). In noveladdition, measurements of cave environmental parameters, cave drip water, and a compilation of geochemical analyses of the Irazú volcanic lake (located ca. 150 m above the cave level) and fumarole analyses, were conducted between 1991 and 2014. Forty-eight different mineral phases were identified, mostly rare hydrated sulfates of the alunite, halotrichite, copiapite, kieserite and rozenite groups; thirteen of which are described here, as cave minerals, for the first time, i.e. aplowite, bieberite, boyleite, dietrichite, ferricopiapite, ferrinatrite, lausenite, lishizhenite, magnesiocopiapite, marinellite, pentahydrite, szomolnokite, and wupatkiite. The presence of other novel cave minerals, such as tolbachite, mercallite, rhomboclase, cyanochroite, and retgersite, is likely, but this was not possible to confirm by the various mineralogical techniques employed in this study. It was determined that uplifting of sulfurous gases, water percolation from the Irazú volcanic lake, and hydrothermal interactions with the volcanic host rock are responsible for such extreme mineralogical diversity.
Moreover, acidic (pH < 2) viscous biofilms, known as snottites, were observed hanging from both, walls and ceiling, of the caves at Irazú volcano, in close relation with the presence of sulfate minerals. Knowledge about snottites in volcanic caves is scarce, being biofilms present in carbonated rocks the most studied, e.g. at Frasassi and Acquasanta caves (Italy), and Cueva de Villa Luz and Luna Azufre (Mexico). 16S rRNA techniques (with primers for target Bacteria and Archaea), together with bioinformatics analyses, were used to investigate the snottites from CMU and CMI. The results indicated that both prokaryotic groups in the snottites offer a vast metabolic potential to execute various reactions, including redox reactions. The phylogenetic findings revealed that approximately 65% of the identified taxa corresponded to species related to sulfur-oxidizing metabolic pathways (e.g., Leptospirillum, Mycobacterium, Acidithiobacillus and Acidiphilium), while just 0.04% corresponded to sulfur-reducing species (Desulfosporosinus). Since sulfur-oxidizing microorganisms appeared to be dominant in the acidic snottites, induced-gypsum precipitation by changes in micro environmental conditions, is strongly suggested as the path for biomineralization at the studied caves. 34S isotope signature of sulfur minerals presented negative values (from -16.2 to -3.4 ‰), comparable with data obtained...
Keywords: Volcanic caves, Costa Rica, Irazú, Cueva los Mucolitos, Cueva los Minerales, Nicaragua, Hoyo, Cueva Hoyo de Koppen, mineralogy, sulfur isotopes, hydrated sulfates, active volcano, microbiology, snottites, geomicrobiology, astrobiology, Mars analogue.
Published in RUNG: 15.04.2019; Views: 3543; Downloads: 158
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