What do acritarchs represent?
The acritarchs form a polyphyletic artificial group that may represent many different types of organisms, from bacteria to unicellular (protists) or multicellular eukaryotes (e.g., fungi, algae, animal eggs). Their size ranges from a few microns to a few millimeters, although most are microscopic.
Where are acritarchs found?
Acritarchs are found in rock deposits that were once marine and terrestrial aquatic environments, and have been described from localities on all continents, as well as from all time periods from the Proterozoic eon (starting 2.5 billion years ago) to the present.
What are acritarchs made of?
Most commonly they are composed of thermally altered acid insoluble carbon compounds (kerogen). Acritarchs may include the remains of a wide range of quite different kinds of organisms—ranging from the egg cases of small metazoans to resting cysts of many kinds of chlorophyta (green algae).
What is an Arcitarch?
Introduction. Acritarchs, the name coined by Evitt in 1963 which means “of uncertain origin”, are an artificial group. The group includes any small (most are between 20-150 microns across), organic-walled microfossil which cannot be assigned to a natural group.
How Stromatolites are formed?
Stromatolite deposits are formed by sediment trapping and binding, and/or by precipitation activities of the microbial communities (Awramik 1976).
Are Acritarchs algae?
Acritarchs are a catchall group of various small microfossils that may represent the pelagically dispersed spore cases of benthic algae. Four major turnovers in Silurian acritarch species are recognized. Among those coinciding with highstands in sea level, the turnovers of the mid-Aeronian Age (Llandovery Epoch)…
What was before the Neoproterozoic Era?
Preceding the Neoproterozoic is the Mesoproterozoic era of the Proterozoic, and preceding this was the Paleoproterozoic, the oldest era of the Proterozoic. The Neoproterozic extended from 1,000 to 542 +/- 0.3 million years ago (Gradstein et al. 2005).
What does Paleozoic mean in science?
Paleozoic Era, also spelled Palaeozoic, major interval of geologic time that began 541 million years ago with the Cambrian explosion, an extraordinary diversification of marine animals, and ended about 252 million years ago with the end-Permian extinction, the greatest extinction event in Earth history.
What does Proterozoic mean in science?
Proterozoic. [ prŏt′ər-ə-zō′ĭk ] The later of the two divisions of the Precambrian Eon, from about 2.5 billion to 540 million years ago. The Proterozoic was characterized by the formation of stable continents, the appearance of abundant bacteria and archaea, and the buildup of oxygen in the atmosphere.
Why are graptolites only found in deep water?
Graptolites were common where food was abundant, especially in upwelling currents, where deep water, with its load of nutrients, is forced upwards and into shallower waters in areas such as the tropics and at the edge of the continental shelf.
What is the meaning of acritarch?
Definition of acritarch. : any of a group of fossil one-celled marine planktonic organisms of uncertain and possibly various taxonomic affinities held to represent the earliest known eukaryotes.
Acritarchs were originally defined as non- acid soluble (i.e. non- carbonate, non- siliceous) organic-walled microfossils consisting of a central cavity, and whose biological affinities cannot be determined with certainty. Most commonly they are composed of thermally altered acid insoluble carbon compounds ( kerogen ).
What is the taxon of an acritarch?
The nature of the organisms associated with older acritarchs is generally not well understood, though many are probably related to unicellular marine algae. In theory, when the biological source (taxon) of an acritarch does become known, that particular microfossil is removed from the acritarchs and classified with its proper group.
Are acritarchs microfossils?
Simple acritarchs have been found since the Archaean [5] and more complex forms since the early Paleozoic (~540 Ma). They are a key organic microfossil group for biostratigraphy and paleoenvironmental studies during the Paleozoic [6-8], as they predate many other organic microfossils.