Geochemical biosignatures preserved in microbially altered basaltic glass

Microbes play an important role in the alteration of volcanic rocks emplaced on the seafloor as pillow basalts and hyaloclastites. Microbially altered basaltic glass hosts characteristic hollow etch structures, which are commonly filled and preserved by the precipitation of new mineral phases within the etch structures. Bioalteration textures occur in two distinct morphologies: micron-scale granular aggregates, and long tubules (up to hundreds of microns). SIMS analyses of basaltic glass samples with abundant tubular bioalteration from the Ontong Java Plateau reveal significant chemical variations in areas with tubular microbial etch structures including: alkalis, which show depletion in Na and enrichment in K; enrichments in the alkaline elements (Ca, Sr, Ba) and the high field strength elements (Ti, Y, Zr); the first row transition metals V, Cr and Mn are slightly enriched, while Fe, Co, Ni, Cu and Zn are depleted; W and the lanthanides are enriched in tubule-bearing regions; slight enrichments in U and P are also observed. SEM imaging following SIMS analysis revealed complex micron-scale spongy textures that may be related to microbial glass dissolution.