Do Microbial Processes Control CaCO₃ Crystal Morphology?

DeChoudens, Vionette¹, Jennifer Roberts¹, Luis A. Gonzalez¹ (1) University of Kansas, Lawrence, KS

Alleged morphological differences between calcium carbonate crystals produced by microbial activity and those grown abiotically have been used by several researchers to identify the presence of microbial processes in the rock record. Although published data have demonstrated that microorganisms isolated from caves and other environments can influence the production of calcium carbonate through their metabolic activity; the resulting crystal morphologies are not exclusive to microbially influenced precipitation and should not be used as the sole indicator of microbial presence. Recent experimental work that simulates speleothem growth under sterile conditions has produced crystal morphologies similar to those attributed to microbial activity and those commonly found in cave speleothems. The results from this work indicate that most calcium carbonate speleothem growth may occur as a result of abiotic precipitation processes because CaCO₃ crystals lack definite diagnostic indicators for microbially influenced precipitation. Microbes, however, do live in these environments and might contribute to speleothem formation when their metabolic activity surpasses the effects of abiotic supersaturation and precipitation. Additional experimental and empirical research is needed to determine the specific impact of microorganisms on speleothem growth as this can serve to elucidate their preservation or recognition in the rock record.