Experimental production and geochemical modeling of abiogenic and biogenic carbonates in Great Salt Lake, Utah, USA
Abstract
Great Salt Lake, Utah (GSL), a remnant of Pleistocene Lake Bonneville, is a hypersaline, closed-basin "carbonate factory". Controls on carbonate precipitation include pH, temperature, salinity, cation availability, degassing, and biological activity. The availability of different ions in solution, in addition to biotic factors, affect the kinetics, amount, and mineralogy of precipitated carbonates. However, the particulars of carbonate mineral production in the unique chemical conditions of GSL are not well-characterized. In order to better understand abiotic and biotic controls on carbonate mineral production in GSL, we used a two-pronged approach of geochemical modeling and laboratory precipitation experiments. In one experiment, we established the abiotic conditions required to force carbonate precipitation in simulated "best case" modern GSL waters (salinity = 5%, pH = 8.5, TIC = 2.8E-05 M, [Mg 2+ ] = 0.07 M, [Ca 2+ ] = 0.02 M) by separately varying pH, total inorganic carbon (TIC), and calcium ion concentration [Ca 2+ ]. Abiogenic carbonate precipitation occurred when pH was increased to 9.25, TIC to 1.1E-02 M, or [Ca 2+ ] to 3.4 M. The mineralogy of precipitates was assessed using SEM-EDX and was different for each forcing scenario: high pH produced rhombohedral prismatic crystals with high amounts of magnesium (likely dolomite), high TIC produced amorphous spheres of calcium carbonate, and high [Ca 2+ ] produced gypsum. Our experimental results were largely consistent with geochemical modeling using PHREEQC. High-magnesium carbonates and spheroidal carbonates have been observed in GSL shoreline microbialites. Because conditions required to force carbonate precipitation in our experiments were largely outside the range of modern lake chemistry, our results support an interpretation of a microbial influence on microbialite carbonate precipitation in GSL by metabolisms that increase the availability of bicarbonate anion. We are now conducting a series of experiments with GSL native species of algae and bacteria with different metabolisms in an attempt to quantify microbial influences on carbonate-producing conditions and will present our preliminary results.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP0080003W
- Keywords:
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- 0448 Geomicrobiology;
- BIOGEOSCIENCES;
- 1039 Alteration and weathering processes;
- GEOCHEMISTRY;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL