acritarch

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acritarch

[′ak·rə‚tark]
(paleontology)
A unicellular microfossil of unknown or uncertain biological origin that occurs abundantly in strata from the Precambrian and Paleozoic.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The Early Cambrian age for orthoquartzite in the Glen Falls Formation, in the lower part of the Saint John Group, is also fairly well-constrained by dated ash beds, macrofossils, and acritarch assemblages in overlying and underlying formations (e.g., Tanoli and Pickerill 1988; Landing et al.
The Doushantuo formation shales and phosphorites, dated to 570 Ma, elegantly preserve acritarchs, multicellular algae, and significantly, animal embryos of uncertain affinity.
"One or a few species of phytoplankton monopolizes nutrients at the expense of others," said Porter, explaining the die-off of diverse acritarchs.
Other acid-resistant microfossils encountered during this study include acritarchs, foraminiferans, melanoscleritoids, chitinous hydroids, and graptolite siculae, but these were not studied quantitatively.
Marine oil shales are composed of lipid-rich organic matter derived from marine algae, acritarchs (unicellular organisms of questionable origin), and marine dinoflagellates (one-celled organisms with a flagellum).
In addition, palynologic analysis reveals the presence of land spores, acritarchs, chitinozoans, and scolecodonts.
A good fossil record exists for the dinophytes, proof of the group's antiquity; the remains of dinophytes similar to contemporary species are known from the Silurian and similar forms, such as some acritarchs, are even older, dating from the Cambrian period or before (see volume 1, p.
Paleontologists call these acritarchs, a catch-all category of unicellular eukaryotic fossils.
Other biotic components are rare but include calcareous sponge spicules, bryozoans, acritarchs, conodonts, scolecodonts, chitinozoans and various problematica (approximately listed in order of abundance).
The high percentages of [C.sub.29] steranes detected from the Silurian and Cambrian are attributed to algae such as benthic brown algae or macro algae, acritarchs, cryptospores, and arthropods, rather than a terrestrial origin ([15] and references therein).