Posted by: paulgarner | June 11, 2012

Microbes and the dolomite problem

Among the geological challenges facing creationism is how to explain the deposition of thick and extensive carbonate sediments during the Flood. Some of us suspect that microorganismal blooms played a major role, and indeed much of the micritic lime mud in the Palaeozoic may have been generated by cyanobacteria (Pratt 2001).

Intriguingly, a forthcoming paper in Geology suggests that microbes may also have helped generate dolomite deposits. Dolomite formation has been an enduring mystery for sedimentologists. Copious amounts of primary dolomite occur in the geological record, even though it forms today in only a few restricted localities such as hypersaline pools and lagoons. Stefan Krause, lead author of the new study, says, “As these systems are very limited in space, there is an explanation gap for geologists for the widespread presence of fossil dolomite.”

In the new paper, Krause et al. (2012) propose that large amounts of primary dolomite can form when quantities of organic matter in the sea bed are degraded by sulphate-respiring bacteria. This suggests some interesting avenues for developing catastrophist models of dolomite formation.

References

Krause S. and five others. 2012. Microbial nucleation of Mg-rich dolomite in exopolymeric substances under anoxic modern seawater salinity: new insight into an old enigma. Geology doi:10.1130/G32923.1 (Advance online publication)

Pratt B.R. 2001. Calcification of cyanobacterial filaments: Girvanella and the origin of lower Paleozoic lime mud. Geology 29:763-766.

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