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Stromatolites are laminated biosedimentary structures usually attributed to the trapping and binding action of nonskeletal algae in shallow-water environments. They have a geologic record dating back from the Holocene to the Archean, with an acmic development during the Proterozoic. The structures are generated by successive stacking of laminae, whose particular shapes are more or less uniformly maintained during the accretion process that yields the final gross morphologies. The laminae and their synoptic morphologies represent not only the microbathymetries at past instants in time, but also the preserved record of successive surfaces of equilibrium between interacting physical, chemical, and biologic factors in the environment. Analysis of the geometric, material, dime sional, and positional attributes of these active interfaces, as well as the final morphology of the stromatolite, provides information useful in classification of stromatolites and in the interpretation of environmental conditions during their formation. Changes in their morphology and microstructure through geologic time reflect evolutionary changes in stromatolite-building biotas and their environments, and are the basis for the correlation of stromatolitic Precambrian sequences. Stromatolites also have been used to determine paleolatitudes, to gauge ancient tidal ranges, to shed light on past rates of rotation of the Earth, and to date the apparent capture or closest approach of the Moon, but conclusions reached in these respects are not yet sufficiently firmly based.
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