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Abstract
Journal of Sedimentary Research, Section
A: Sedimentary Petrology and Processes
Vol. 66 (1996)No.
5. (September), Pages 935-947
Texture of Microbial Sediments Revealed by Cryo-Scanning Electron Microscopy
Christian Defarge (1) (2) Jean Trichet (1), Anne-Marie
Jaunet (3), Michel Robert (3), Jane Tribble (4), Francis J. Sansone (4)
ABSTRACT
Textures of modern lacustrine stromatolites on Kiritimati (Line Islands,
Central Pacific Ocean), and of buried layers in the stromatolitic carbonate
sediments from French Polynesian atoll lakes (kopara), have been
studied using cryo-scanning electron microscopy (SEM equipped with a freeze-drying
sample preparation device). This study confirms that microscopic three-dimensional
organic networks built through reorganization of polysaccharide fibers
inherited from sheaths of dead cyanobacteria, and from other extracellular
polymer secretions, are common components of microbial sediments, of which
they may form the framework, In addition to this role in sediment cohesion
and formation of microstructure, the organic framework appears to be involved
in carbonate precipitation with n the stromatolites, through chemical (nucleating),
steric, and hydrodynamical controls. The role of the dead organic constituents
of the stromatolites is not only confirmed in micrometer-size crystal precipitation
but extended to the post mortem internal mineralization of cyanobacterial
filaments, and to the formation of peloids that evolve into spherulites.
Bacterial, including nannobacterial, carbonate bodies, and carbonate-impregnated
cyanobacterial sheaths are also shown to form in the stromatolites studied.
All these carbonate precipitation processes may cooperate in lithification
of a given sediment.
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