image: This image shows actively growing, subtidal stromatolites north of Carbla Point, Shark Bay, Western Australia. The individual build-ups are separated by areas of rippled, bare sand. The sand is not overgrown by microbial mat because the grains are in constant motion by waves and tidal currents. Photo by Stan Awramik. view more
Credit: Stanley Awramik for <i>GSA Today</i>.
Boulder, Colorado, USA – In the September issue of GSA Today, Nora Noffke of Old Dominion University and Stan Awramik of the University of California, Santa Barbara, describe the interaction of carpet-like communities of benthic microorganisms (biofilms) with sediment dynamics at the sediment-water interface to form distinctive sedimentary structures called microbialites.
The best known microbialite structures are stromatolites -- multilayered microbialites up to meters in thickness, built up by repetitive binding, biostabilization, baffling, and trapping of sediment particles by microorganisms, coupled with carbonate precipitation. In the absence of such precipitation, however, these processes result in the formation of very characteristic microbially induced sedimentary structures, or "MISS," best seen on sediment surfaces.
Both stromatolites and MISS are first found in the early Archean, more than three billion years ago, recording highly evolved microbial activity quite early in Earth's history. Whereas the stromatolites show enormous morphologic and taxonomic variation, MISS have remained essentially unchanged with time. MISS may be the older relative, but due to the paucity of well-preserved sedimentary rocks older than three billion years, the origin of both stromatolites and MISS remains uncertain.
ARTICLE
Stromatolites and MISS—Differences between relatives
N. Noffke, Old Dominion University, Dept. of Ocean, Earth & Atmospheric Sciences, Norfolk, Virginia, 23529, USA, nnoffke@odu.edu; and S.M. Awramik, University of California, Dept. of Earth Science, Santa Barbara, California 93106, USA, awramik@geol.ucsb.edu. v. 23, no. 9, p. 4–9, doi: 10.1130/GSATG187A.1.
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Journal
GSA Today