The role of endolithic cyanobacteria in the formation of lithified laminae in Bahamian stromatolites |
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Authors: | Ian G Macintyre Leslie Prufert-Bebout & R Pamela Reid |
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Institution: | Department of Paleobiology, National Museum of Natural History, NHB-125, Smithsonian Institution, Washington, DC 20560, USA (E-mail:;) NASA Ames Research Center, MS 239-4, Moffett Field, CA 94035, USA; Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA |
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Abstract: | The microboring activity of endolithic cyanobacteria plays a major role in the formation of the dominant lithified laminae in modern marine stromatolites in the Exuma Cays, Bahamas. These stromatolites are composed primarily of fine-grained carbonate sand that is trapped and bound by the filamentous cyanobacteria Schizothrix sp.. Periodic introduction of coccoid endolithic cyanobacteria Solentia sp. during hiatuses in stromatolite growth associated with very low rates of sedimentation results in the formation of lithified horizons, 200–1000 μm thick. These layers consist of micritized grains that are welded together at point contacts. The micritization is caused by extensive microboring and carbonate precipitation within boreholes concurrent with endolithic activity. Grain welding occurs when boreholes cross from one grain to another at point contacts. Thus, microboring destroys original grain textures but, at the same time, plays a constructional role in stromatolite growth by forming lithified layers of welded grains. These lateral bands of fused carbonate grains help to stabilize and preserve the stromatolite deposits. |
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Keywords: | Endolithic cyanobacteria lithification micritization stromatolites |
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