Distinguished Speaker Steve Kaczmarek is "Poking Holes in Hypotheses" Friday
- Nov 10, 2017
EES is pleased to present Distinguished Guest Speaker Steve Kaczmarek form Western Michigan University. He'll be presenting "Poking Holes in Hypotheses: A Critical Reappraisal of Microbial Dolomitization."
Dolomitization - the process whereby dolomite [CaMg(CO3)2] replaces limestone [CaCO3] - has been enigmatic for over two hundred years. Many dolomitization models have been proposed, but no model sufficiently explains the varied occurrence of this common sedimentary mineral in the rock record. Claiming that microbial processes are responsible for dolomitization, the microbial dolomite model has recently gained considerable interest. In large part, this model rests on numerous reports that microbes have catalyzed nucleation and growth of dolomite at low temperatures in the laboratory. Critical reexamination of published X-ray diffraction (XRD) patterns, however, indicates that the precipitates are not dolomite, but a mixture of minerals, most notably very high-magnesium calcite (VHMC). Dolomite and VHMC can have the same elemental composition but are mineralogically distinct. Whereas dolomite is characterized by an ordered arrangement of magnesium and calcium cations in alternating layers, VHMC lacks cation ordering. Mineralogical arguments notwithstanding, petrological observations show that VHMC produced in the laboratory experiments is dissimilar to natural dolomites. Laboratory grown VHMC forms as a cement via precipitation from solution rather than by replacement of a CaCO3 precursor. Furthermore, VHMC precipitates exhibit fundamentally different crystal forms than those observed in natural dolomites.
Join us for this critical examination of microbial dolomitization on Friday, November 11, 2017 at 12:30 PM in Room 204, Natural Science building on the East Lansing campus.