stromatolite

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stromatolite,

layered structures produced by the binding together of sediments by a thin layer of cyanobacteriacyanobacteria
or blue-green algae,
photosynthetic bacteria that contain chlorophyll. For many years they were classified in the plant kingdom along with algae, but discoveries made possible by the electron microscope and new biochemical techniques have shown them to be
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. The layers, which are deposited very slowly, gradually produce rounded or hummocklike formations. Stromatolite fossils are common in Precambrian rocks, and the cyanobacteria associated with them are believed to have been a major contribubutor to the increasing oxygen of the early earth. Stromatolites now are found primarily in environments where high salt levels discourage animals from eating the cyanobacteria.

Stromatolite

 

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.

stromatolite

[strə′mad·əl‚īt]
(geology)
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.
References in periodicals archive ?
Stromatolitic laminae, either planar or crinkle, show microscopic features such as micritic laminae, clotted to peloidal micrite and fenestrae which are similar to examples de<05_TB001> scribed from Proterozoic and Early Phanerozoic nearshore settings (e.
Peloids, frequent within the stromatolitic laminae, are irregularly spherical.
They exhibit stromatolitic, microphytic thrombolytic facies with sedimentary fills, oncoids, oncolites, pesoids, lithoclasts and intraclasts.
The infilling deposits are integrated by successive episodes of concentrations of clasts filling the cavities and ammonite mould fragments and other fossils showing grain-size selection and bounded by hard-ground discontinuities and/or stromatolitic crusts (Melendez and Ramajo, loc.
A few showings of this type occur near Guillaume-Delisle Lake in a horizon of stromatolitic dolomite belonging to the Nastapoka Group in the Richmond Gulf graben (Chandler 1998; Labbe and Lacoste 2004).
They did this by looking at paleomagnetic studies of the rocks to determine the direction of the past field, and by using the plane along which the stromatolitic sine waves grew to define the past north-south plane of the earth and its spin axis.
294-295) reports stromatolitic linings with desiccation cracks from this surface at Suances.
Where present, primary and stromatolitic carbonates are separated from underlying diamictite units by unconformities or many tens and sometimes hundreds of metres of marine strata, thereby questioning any supposed immediate 'cap' relationship (e.
There are various types of dolostone including 30 stromatolitic dalostone erratics; most arc grey (74%) and pink (20%).