Bacterially induced precipitation of CaCO 3 : An example from studies of cyanobacterial mats. Final report

• Main Author: Chafetz, Henry S.
• Language: unknown
• Published: 2017
• Subjects: 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; CARBON CYCLE; CYANOBACTERIA; WATER CHEMISTRY; LIMESTONE; ELECTRON MICROSCOPY; CLIMATIC CHANGE; CALCIUM CARBONATES; TEXAS; BAHAMA ISLANDS; PROGRESS REPORT; Baffin Bay
• Online Access: http://www.osti.gov/servlets/purl/10171562; https://www.osti.gov/biblio/10171562; https://doi.org/10.2172/10171562

Bacteria induce the precipitation of calcium carbonate in the laboratory and in nature by altering their chemical environment. Geologists are recognizing the possibility that bacterially induced precipitates may form significant mineral deposits, unfortunately, there are currently no sound criteria by which they can be recognized in recent sediments, or in the rock record. Cultures of aerobic and facultative bacteria from cyanobacterial mats on Andros Island, Bahamas, and Baffin Bay, Texas, induced the precipitation of calcium carbonate under controlled conditions. Crusts, the largest features formed, are composed of 5--200μm diameter bundles which are, in turn, composed of numerous individual crystals. The smallest observed features are 0.1--0.4μm spheres and rods which comprise some individual crystals and crystal bundles. Crystal bundles resembling rhombohedra, tetragonal disphenoids, tetragonal dipyramids, and calcite dumbbells appear to be uniquely bacterial in origin, and they have all been observed in recent sediments. Swollen rods, discs, curved dumbbells, and 50--200μm optically continuous crystals resembling brushes may be uniquely bacterial in origin, however, they have not been reported by other laboratories nor observed in natural settings. Presence of any of these forms in recent sediments should be taken as strong evidence for bacterial influence. Spheres and aragonite dumbbells have also been observed in natural environments, however, they are not always bacterial in origin. Precipitation of calcium carbonate occurs preferentially on dead cyanobacteria in the presence of bacteria. Lithification of algal mats to form stromatolites may take place in the zone of decaying organic matter due to bacterial activity.