Journal
AMERICAN JOURNAL OF SCIENCE
Volume 320, Issue 1, Pages 72-95Publisher
AMER JOURNAL SCIENCE
DOI: 10.2475/01.2020.05
Keywords
microbial carbonates; cyanobacteria; extrapolymeric substances; Raman spectroscopy; carboxyl; spherulites
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Funding
- National Sciences and Engineering Research Council of Canada
- Canada Foundation for Innovation
- Ontario Research (Leaders Opportunity Fund) [22404]
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Many have postulated that a specific microbial metabolism or the presence of microbes or/and their extracellular polymeric substances (EPS) can lead to the formation of dolomite. Although now there is the consensus that dolomite can be formed in the presence of microorganisms, the exact nature of the involvement of microbes in the dolomite nucleation remains a matter of debate. The focus is now in understanding how microbial mats determine the mineralogy of dolomite. Here we report the effect of the EPS extracted from phototrophic microbial mat isolated from a sabkha in Qatar dominated by cyanobacteria (Lyngbya aestuarii) in the formation of dolomite precursors at 25 degrees C and 40 degrees C. Both the temperature and the presence of EPS impact the size and morphology of minerals, promoting spherulitic and dumbbell growth in sulfate free solutions. The formation of proto-dolomite was enhanced by the abundance of carboxylated molecules in EPS which controlled the polymorphism of carbonates. Our study emphasizes the dual importance of organic matter and temperature in dolomite formation and their impact on mineral morphology and chemical composition in sabkhas.
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