Assessing the Biogenicity of Tufas and Their Potential as Biosignature Repositories
Abstract
Modern columnar tufas (towers of porous, non-marine carbonate rock) from Big Soda Lake, a hypersaline alkaline maar lake near Fallon, Nevada, host diverse biological communities. Lake level records indicate that the rate of tufa precipitation has been faster than approximately 30 millimeters per year over the last 100 years, resulting in structures up to 4 meters tall. Recent declines in lake level have exposed the upper meter or so of the tufa towers. It is clear that organisms live on and in the tufa towers, but the role the organisms may play in tufa precipitation is unclear. Here, we address whether life plays a major role in tufa formation and whether rapid tufa precipitation preserves evidence of life. The pH, alkalinity, and carbon and oxygen isotopic data suggest that tufa form from the mixing of calcium-rich groundwater with carbonate-rich lake water (consistent with previous studies). In lake shoreline areas of active groundwater input, mixed waters are supersaturated with respect to calcite, likely facilitating rapid precipitation. Tufa surfaces and interiors host diverse biological communities as indicated by microscopic observations, small subunit rRNA gene surveys, and metagenomic analyses. Highly diverse biological communities are found on the tufa surface and in the interior compared to the lower diversity found in surrounding lake water. Tufa petrographic examinations show carbonate features suggestive of microbial activity, which is consistent with metabolisms found in the metagenome that may affect carbonate precipitation and dissolution dynamics. We propose that although tufas form primarily as a result of abiological mixing of groundwater and lake water, rapid mineralization may promote preservation of the associated diverse biological communities. Ultimately, the potential to preserve evidence of diverse life makes tufas optimal biosignature targets.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.B21E0471M
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0419 Biomineralization;
- BIOGEOSCIENCESDE: 0424 Biosignatures and proxies;
- BIOGEOSCIENCESDE: 0444 Evolutionary geobiology;
- BIOGEOSCIENCES