Joint South-Central and North-Central Sections, both conducting their 41st Annual Meeting (11–13 April 2007)
Paper No. 41-4
Presentation Time: 2:30 PM-2:50 PM

NUCLEATION AND PRECIPITATION OF LOW-TEMPERATURE DOLOMITE BY METHANOGENS

KENWARD, Paul A.1, FOWLE, David A.2, GOLDSTEIN, Robert H.1, GONZÁLEZ, Luis3, and ROBERTS, Jennifer A.2, (1) Geology, The University of Kansas, 1475 Jayhawk Blvd. Room 120, Lawrence, KS 66045-7613, pK1@ku.edu, (2) Geology, The University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr, Lawrence, KS 66047, jenrob@ku.edu, (3) Geology, Univ of Kansas, Lawrence, KS 66045

Despite being abundant in the geological record the nucleation and precipitation of dolomite at low temperature (< 50 0C) under laboratory conditions has been a notoriously difficult endeavor. Recent studies have shown that several physiologic types of microorganisms are capable of overcoming kinetic barriers and driving the formation of low temperature dolomite. This study investigates the mechanisms employed by methanogenic microbes in mediating the nucleation of dolomite, using batch reactors containing a native methanogenic consortium and Archaeal cell wall sorption experiments with Ca2+/Mg2+ and two pure cultures. Microbial biomass increases from 1 x 105 to 7x 107 cells ml-1 and the methanogenic population within experimental vessels yields approximately 46 fmoles of CH4 per cell per day. Indicators of microbial metabolic activity demonstrate a shift from iron-reducing conditions to methane production within 90 days, indicative of population succession. Coinciding with the observed shift in metabolic activity, we precipitate ferroan dolomite from solution after 90 days of incubation. Once Fe(II) is removed from solution (after 166 days) ordered stoichiometric dolomite is precipitated as methanogenesis continues. Characterizations of mineral surfaces using scanning electron microscopy show small rhombohedra in close association with microbial cells and exopolysaccaride. Sorption experiments have demonstrated preferential adsorption of Mg2+ over Ca2+ to the cell wall of Methanobacterium formicicum, an autotrophic methanogen; such that Mg2+/Ca2+ ratios associated with the cell wall differ significantly with those originally in solution. These data support the microbial model for low temperature dolomite nucleation and formation and highlight the role of physiologic type in determining dolomite composition and stoichiometry. More complete understanding of dolomite formation in methanogenic systems should serve as models for predicting dolomite distribution in the subsurface.

Joint South-Central and North-Central Sections, both conducting their 41st Annual Meeting (11–13 April 2007)
General Information for this Meeting
Session No. 41
Traces of Life: Micro- to Macroscopic Evidence of Past and Present Biogenic Activity and Their Implications for Marine and Continental Settings
Kansas Union, University of Kansas: Big 12
1:20 PM-5:00 PM, Friday, 13 April 2007

Geological Society of America Abstracts with Programs, Vol. 39, No. 3, p. 74

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