Biotic alteration of oceanic basalt glass Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n870zt427

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  • The subsurface microbial biosphere in the igneous oceanic crust has implications for global geochemical cycling, early life on Earth, and the search for life on Mars. Microscopic evidence of a subsurface microbial ecosystem includes biotic alteration textures associated with basaltic glass. The exact conditions in the basaltic layer that make this a viable ecosystem remain unknown. Geologic investigations rely on the principle that the present is the key to the past and therefore the conditions evident in rocks today can be used to elucidate conditions occurring over time. The application of this principle to basaltic rocks sampled from the modern ocean containing biotic alteration textures is the primary objective of this study. This study is a global investigation into the relationship between the morphology of biotic alteration and its abundance in the ocean crust and the environmental conditions associated with the host rocks. The Ocean Drilling Program and the Deep Sea Drilling program provided subseafloor basaltic glass samples used in this study. The unique morphologies of the biotic alteration textures present were identified using a classification system and the abundance of biotic alteration was estimated as a percent of the total alteration present in the samples. Nine distinctive textures were selected for correlation with five environmental parameters including sample age, sample depth in basalt, overlying sediment thickness, temperature, and secondary mineralogy. These parameters served as proxies for the environment associated with biotic alteration such as oxidizing conditions, fluid flow, pH, and temperature tolerances for microbial growth. Preliminary results indicated the abundance and the frequency of biotic alteration textures varied with the environmental conditions. Statistical analyses were conducted to assess the strength and direction of the variation between the biotic alteration and environmental parameters. I found that several biotic alteration textures and biotic alteration abundance had statistically significant correlations with sample age, sample depth into basalt, temperature, and some secondary minerals. The subseafloor biosphere is a complex environment influenced by many variables. This investigation into how the evidence of biotic alteration preserved in basaltic glass varies with the environmental conditions represents a step towards understanding the dynamics of the ecosystem in the ocean crust.
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