EXPLORING THE ROLE OF MICROBIAL PROCESSES ON SPELEOTHEM FORMATION: A LOOK INTO CALCIUM CARBONATE SPELEOGENESIS

Morphological differences between calcium carbonate crystals produced by microbial activity and those growing on active speleothem surfaces might serve to identify the presence of microbial processes in the rock record. Published data has demonstrated that microorganisms isolated from caves are capable of producing calcium carbonate both as a direct and indirect result of their metabolic processes. The resulting crystal morphologies, however, do not resemble those of crystals growing in most active speleothem surfaces, leading to speculation about their possible role on speleothem growth. In contrast, recent experimental work that simulates speleothem growth under sterile conditions has produced crystal morphologies similar to those preserved in calcium carbonate cave speleothems. The results from this work indicate that most calcium carbonate speleothem growth may occur as a result of abiotic precipitation processes. Microbes, however, do live in these environments and might contribute to speleothem formation only when their metabolic activity surpasses the effects of abiotic supersaturation and precipitation. Additional experimental and empirical research is needed to determine the specific roles and impact of microorganisms in speleothem growth as this can serve to elucidate their preservation or recognition potential in the rock record.