Microbial
Mediation in Dolomite Formation During Carbonate Diagenesis
McKenzie, Judith A.1, Crisogono Vasconcelos1, Mónica
Sánchez-Román1, Tomaso Bontognali1,
Rolf Warthmann1 (1) ETH
Understanding processes involved in
dolomite formation under Earth's surface conditions has been a long-standing
challenge for carbonate sedimentologists. Because
dolomite bodies are often significant hydrocarbon reservoirs, much emphasis has
been placed on the development of dolomite models to define the physico-chemical and hydrologic parameters involved in dolomitization. Nevertheless, these models have not been
adequately calibrated for real-world circumstances because it was not possible
to synthesis dolomite in the laboratory at Earth's surface temperatures. Now,
with the recent recognition that specific microbes can mediate dolomite
precipitation, it is possible to conduct culture experiments under controlled
conditions to better define boundary parameters. The results of these
experiments provide new information to interpret the conditions required for
dolomite formation during carbonate diagenesis and
necessitate a reinterpretation of currently applied models. For example,
dolomite apparently does not nucleate in the fluids contained in open pore
spaces, but precipitation occurs readily within an organic matrix (biofilm or EPS) produced by identifiable microbes. Factors,
such as the optimum growth temperature for particular microbes under defined
chemical conditions, are essential considerations for dolomite nucleation. In
addition, geochemical proxies that have been used to interpret the paleoenvironment of dolomite formation, such as the Sr partition factor, are being redefined with these
experimental studies. Further, using a geomicrobiologic
approach to investigate natural dolomite-forming environments demonstrates that
a diverse microbial community with various metabolic processes promotes dolomitization. Ultimately, microbes appear to be a
powerful driving force behind carbonate diagenesis
and must be included in any new model paradigm for dolomitization.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California