Microbial fossilization in carbonate sediments a result of the bacterial surface involvement in dol【荐】.pdfVIP

Sedimentology (2003) 50, 237–245 Microbial fossilization in carbonate sediments: a result of the bacterial surface involvement in dolomite precipitation YVONNE VAN LITH 1 , ROLF WARTHMANN, CRISOGONO VASCONCELOS and JUDITH A. MCKENZIE Laboratory of Geomicrobiology, Geological Institute, Swiss Federal Institute of Technology (ETH), Sonneggstrasse 5, CH-8092 Zu¨rich, Switzerland ABSTRACT Recent dolomitic sediment samples from Lagoa Vermelha, Brazil, were examined microscopically to study the process of bacterial fossilization in carbonate sediments. Bacteria-like bodies were intimately associated with carbonate mineral surfaces, and coatings on the former demonstrate the calcification of single bacterial cells. The bacterial fossilization process in Lagoa Vermelha sediments was simulated in the laboratory by cultivation of mixed and pure cultures of sulphate-reducing bacteria, which were isolated from the Lagoa Vermelha sediments. These cultures produced carbonate minerals that were studied to provide insight into the initiation of the fossilization process. In mixed culture experiments, bacterial colonies became calcified, whereas in pure culture experiments, single bacterial cells were associated with dolomite surfaces. Dolomite nucleated exclusively in bacterial colonies, intimately associated with extracellular organic matter and bacterial cells. Electrophoretic mobility measurements of the bacterial cells in electrolyte solutions demonstrated the specific adsorption of Ca2+ and Mg2+ onto the cell surfaces, indicating the role of the bacterial su