Depositional Facies and Aqueous–solid Geochemistry of Travertine-depositing Hot Springs (angel Terrace, Mammoth Hot Springs, Yellowstone National Park, U.s.a.)— Discussion

Terrestrial CaCO3 precipitates, including travertines, tufas, and speleothems, are currently of great interest because of their potential as archives of environmental, climatic, and biologic information (e.g., Andrews et al. 1997; Bar-Matthews et al. 1997; Walter and Des Marais 1993). Detailed studies of examples of these terrestrial carbonates therefore provide valuable information to aid interpretation of their records of surface processes, environments, and associated organic influences. The recent paper by Fouke et al. (2000) is a useful contribution in this area, however, some of their comparisons with earlier studies are not wholly accurate and require clarification. More generally, we wish to debate further the issue of whether travertines such as those at Mammoth Hot Springs could record isotopic evidence of microbial activity.