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A structure in calcareous rocks consisting of concentrically laminated masses of calcium carbonate and calcium-magnesium carbonate which are believed to be of calcareous algal origin; these structures are irregular to columnar and hemispheroidal in shape, and range from 1 millimeter to many meters in thickness. Also known as callenia.



a dense, layered structure that forms in limestones and dolomites as a result of the presence of colonies of blue-green and other algae. Stromatolites reach several meters in length and 1–2 m in height. They have been traced back to the Proterozoic; Upper Proterozoic and Lower Paleozoic fossils are particularly common. The formation of stromatolites occurs in warm, shallow waters with elevated or decreased salinity. The various morphological types, which evolved during the course of geological time, are used for the biostratigraphic analysis of Upper Proterozoic deposits, in which remains of other organisms are extremely rare.

References in periodicals archive ?
Stromatolites form when carbonate grains, sediment and slimy mat layers stack on top of one another.
The stromatolite Archaeozoon acadiense from the Proterozoic Green Head Group of Saint John, New Brunswick.
About a billion years before the dinosaurs became extinct, stromatolites roamed the Earth until they mysteriously disappeared.
It's one thing to read a description of a stromatolite and it's another to see a beach edged with them.
Recently, McNamara and Awramik (1992 [16]) have concluded, from the study of stromatolite, that at about 700 m.
Geobiologist Karim Benzerara and his colleagues came across the new species, Candidatus Gloeomargarita lithophora, while investigating Lake Alchichica's stromatolites, knobby pillars of sediment and microbes that can form in shallow waters.
Along the shoreline of Laguna Bacalar, a freshwater bay in the Quintanaroo region of Mexico, a field of over 50 stromatolite heads occurs with a growth form that is anomalous to their current freshwater setting.
Small structures, considered to be stromatolites, similar to the laminar and small domal stromatolite Ozarkcollenia, occur in ferruginous Mesoproterozoic bedded tufts of the Cope Hollow Formation near Johnson's Shut-ins, Reynolds County, Mo.
The early Neoproterozoic or late Mesoproterozoic age proposed for the Green Head Group based on locally preserved stromatolite occurrences (Hofmann 1974) is supported by a minimum U-Pb age of 1230 Ma for detrital zircon grains in a quartzite sample (Barr et al.
The microbial mound consists of stromatolite and of thrombolite with three different microstructures: (1) diffuse clots (grumose structure), (2) well-defined clots, or (3) homogeneous microspar.