Central New York Association of Professional Geologists

February Dinner Meeting: Laura Demott, Syracuse University (CNYAPG 2017-18 scholarship winner) - Assessing Microbial Influence on Deposition of Frondose Lacustrine Carbonate Tufas from Winnemucca Dry Lake, NV, USA

  • Wednesday, February 20, 2019
  • 5:00 PM - 8:30 PM
  • Spaghetti Warehouse

Registration

  • Dinner and talk
  • Dinner and Talk
  • Dinner and Talk
  • Dinner and Talk for any student who is not a Student-member of the organization
  • Pay at the door on the day of the event with no prior registration.
  • Pay at the door on the day of the event with no prior registration.
  • Pay at the door on the day of the event with no prior registration.

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Assessing Microbial Influence on Deposition of Frondose Lacustrine Carbonate Tufas from Winnemucca Dry Lake, NV, USA

Laura M. DeMott

Lacustrine carbonates (tufas) in the lake basins of Pleistocene pluvial Lake Lahontan are important analogues for South Atlantic margin carbonate reservoirs and have been used as paleoproxies for assessing hydroclimate variations over time. However, the specific depositional mechanisms responsible for tufa formation are still a matter of debate, particularly with respect to microbial influences. In Winnemucca Dry Lake, NV, tufas are widespread along the western margin of the dry lake bed, and a variety of morphologies and textures are observed. The most common and laterally extensive variety of tufa is a frondose form that exhibits draping and branching textures and is deposited on hard substrates. This form of tufa occurs both at spring-associated sites on the lake bottom and at high elevations along bedrock cliffs. The tufa meso- and microfabrics are similar to those observed in modern microbialites from Fayetteville Green Lake (NY). Samples of frondose tufa were collected from a spring-associated site and a high elevation bedrock outcrop site. Hand samples exhibit a porous, branching mesofabric, with some samples containing areas exhibiting stromatolitic laminations. Thin section petrography and scanning electron microscopy show that frondose tufas are dominated by mixed micrite and shrubby calcite fabrics, with varying degrees of secondary calcite; some samples contain preserved microbial filaments. Organic geochemistry, including Corg content, d13Corg, d15N, and DNA sequencing indicate that tufa deposition at both spring-associated and shoreline sites may be influenced by photosynthetic microbes (Cyanobacteria, Chloroflexi). Radiocarbon age dating of carbonate and organic carbon lends insight into the timing of these processes and the relationship to lake basin history. These results have implications for paleoenvironmental interpretations of Lahontan tufa deposits and may have broader implications for studies of microbialites throughout the rock record.

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