Reconstruction of limnology and microbialite formation conditions from carbonate clumped isotope thermometry
- Department of Earth, Planetary and Space Sciences University of California Los Angeles CA USA
- Bay Area Environmental Research Institute NASA‐Ames Research Center Moffett Field CA USA
- Department of Civil Engineering University of British Colombia Vancouver BC Canada
- School of Geography and Earth Sciences McMaster University Hamilton ON Canada
- Department of Earth, Planetary and Space Sciences University of California Los Angeles CA USA, Department of Atmospheric and Oceanic Sciences Institute for the Environment and Sustainability Institute of Geophysics and Planetary Physics Los Angeles CA USA
Quantitative tools for deciphering the environment of microbialite formation are relatively limited. For example, the oxygen isotope carbonate‐water geothermometer requires assumptions about the isotopic composition of the water of formation. We explored the utility of using ‘clumped’ isotope thermometry as a tool to study the temperatures of microbialite formation. We studied microbialites recovered from water depths of 10–55 m in Pavilion Lake, and 10–25 m in Kelly Lake, spanning the thermocline in both lakes. We determined the temperature of carbonate growth and the 18 O/ 16 O ratio of the waters that microbialites grew in. Results were then compared to current limnological data from the lakes to reconstruct the history of microbialite formation. Modern microbialites collected at shallow depths (11.7 m) in both lakes yield clumped isotope‐based temperatures of formation that are within error of summer water temperatures, suggesting that clumped isotope analyses may be used to reconstruct past climates and to probe the environments in which microbialites formed. The deepest microbialites (21.7–55 m) were recovered from below the present‐day thermoclines in both lakes and yield radioisotope ages indicating they primarily formed earlier in the Holocene. During this time, pollen data and our reconstructed water 18 O/ 16 O ratios indicate a period of aridity, with lower lake levels. At present, there is a close association between both photosynthetic and heterotrophic communities, and carbonate precipitation/microbialite formation, with biosignatures of photosynthetic influences on carbonate detected in microbialites from the photic zone and above the thermocline (i.e., depths of generally <20 m). Given the deeper microbialites are receiving <1% of photosynthetically active radiation ( PAR ), it is likely these microbialites primarily formed when lower lake levels resulted in microbialites being located higher in the photic zone, in warm surface waters.
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- SC0010288
- OSTI ID:
- 1401122
- Journal Information:
- Geobiology, Journal Name: Geobiology Journal Issue: 1 Vol. 13; ISSN 1472-4677
- Publisher:
- Wiley-BlackwellCopyright Statement
- Country of Publication:
- United Kingdom
- Language:
- English
Similar Records
Fe-bearing phases in modern lacustrine microbialites from Mexico
Factors controlling the oxygen isotopic composition of lacustrine authigenic carbonates in Western China: implications for paleoclimate reconstructions