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stromatolite |
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stromatoliteLayered deposit, mainly of limestone, formed by the growth of blue-green algae (see cyanobacteria). These structures are usually characterized by thin, alternating light and dark layers that may be flat, hummocky, or dome-shaped. Stromatolites were common in Precambrian time (more than 543 million years ago). Some of the first forms of life on Earth are recorded in stromatolites in rocks 3.5 billion years old. Stromatolites continue to form in certain areas today, most abundantly in Shark Bay in western Australia. 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. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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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). This portrayal of the environment in which stromatolitic communities flourished billions of years ago is a classic one. 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. |
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