Stromatolites: Characteristics and utility

Stromatolites are laminated biosedimentary structures usually attributed to the trapping and binding as well as chemical action of non-skeletal algae in shallow-water environments. They have a geologic record dating back from the Recent 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 beteen interacting physical, chemical, and biological factors in the environment. Analysis of the geometric, material, dimensional, and positional attributes of these active interfaces, as well as the final morphology of the stromatolite, provides information useful in classification 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 Precambrian stromatolite sequences. The structures have also been used to determine paleolatitudes, to gauge ancient tidal ranges, to shed light on past rates of rotation of the Earth, and to time the capture or closest approach of the Moon, but conclusions reached in these respects are not yet sufficiently firmly based.