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AAPG Bulletin

Abstract

AAPG Bulletin, V. 97, No. 11 (November 2013), P. 21132125.

Copyright copy2013. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/05171312168

Ordered low-temperature dolomite mediated by carboxyl-group density of microbial cell walls

Paul A. Kenward,1 David A. Fowle,2 Robert H. Goldstein,3 Masato Ueshima,4 Luis A. Gonzalez,5 Jennifer A. Roberts6

1University of Kansas, Department of Geology, Multidisciplinary Research Building, 2030 Becker Drive, Lawrence, Kansas; [email protected]
2University of Kansas, Department of Geology, Multidisciplinary Research Building, 2030 Becker Drive, Lawrence, Kansas; [email protected]
3University of Kansas, Department of Geology, 1475 Jayhawk Boulevard, 120 Lindley Hall, Lawrence, Kansas; [email protected]
4University of Kansas, Department of Geology, Multidisciplinary Research Building, 2030 Becker Drive, Lawrence, Kansas; [email protected]
5University of Kansas, Department of Geology, Multidisciplinary Research Building, 2030 Becker Drive, Lawrence, Kansas; [email protected]
6University of Kansas, Department of Geology, Multidisciplinary Research Building, 2030 Becker Drive, Lawrence, Kansas; [email protected]

ABSTRACT

Abundant in the ancient rock record, early dolomite remains scarce in modern systems at low temperatures (lt50degC), even those systems supersaturated with respect to dolomite. This scarcity is attributed to kinetic inhibition including complexation of Mg2+ by water and sulfate, carbonate activity, and Mg:Ca ratio. Recent investigations point to a function for microbial metabolisms and surfaces, in which disordered phases are formed. Here, we report the precipitation of primary ordered dolomite at 30degC, facilitated solely by the cell walls of two nonmetabolizing archaea from saline solutions with an Mg:Ca ratio of 1:1, 5:1, and 10:1, and slightly saturated with respect to dolomite. Control experiments using bacteria and functionalized microspheres did not precipitate dolomite. Archaeal cell wall functional groups were approximately one order of magnitude higher than the bacteria and spheres used in this study. From these results, we propose a mechanistic model in which carboxyl groups associated with cell wall biomass and exopolymeric substances dehydrate Mg ions, further promoting carbonation and leading to dolomite nucleation. These data explain reports of low-temperature dolomite formation associated with numerous microbial metabolic guilds, including bacteria and archaea, and those reported in association with exopolymeric substances or cell wall surfaces, and identify a key and widespread mechanism in the formation of disordered dolomite and ordered primary phases of dolomite at low temperature. Importantly, the functionalized dead and nonmetabolizing biomass is the key in low-temperature dolomite precipitation, not active microbial metabolism. These observations may lead to new predictive models for the distribution of dolomite.

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