Oncolites from the upper Burgsvik beds (Silurian), with shell fragments as nuclei. The large flower is 2 cm in diameter.Oncolites formed around the Middle Jurassic gastropod Bactroptyxis trachaea (Normandy, France).
Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but, instead of forming columns, they form approximately spherical structures.[1] The oncoids often form around a central nucleus, such as a shell fragment,[2] and a calcium carbonate structure is deposited by encrusting microbes. Oncolites are indicators of warm waters in the photic zone, but are also known in contemporary freshwater environments.[3] These structures rarely exceed 10 cm in diameter.
Oncolites may have either a porostromate or spongiostromate texture. Most oncolites are spongiostromate, having no recognisable cellular texture or microstructure. Porostromate oncolites are mostly unknown during the Precambrian; since the Eocene they have mostly been confined to freshwater environments.[4]
^Corsetti, F.A.; Awramik, S.M.; Pierce, D. (2003-04-15). "A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA". Proceedings of the National Academy of Sciences. 100 (8): 4399–4404. Bibcode:2003PNAS..100.4399C. doi:10.1073/pnas.0730560100. PMC 153566. PMID 12682298.
^Gutschick, R.C.; Perry, T.G. (1959-11-01). "Sappington (Kinderhookian) sponges and their environment [Montana]". Journal of Paleontology. 33 (6): 977–985. Retrieved 2007-06-28.
^Riding, Robert. 1991. Calcareous Algae and Stromatolites, pp. 32. Springer-Verlag Press.
^Monty, C. L. (1981). "Spongiostromate vs. Porostromate Stromatolites and Oncolites". In Monty, Claude (ed.). Phanerozoic Stromatolites. Berlin, Heidelberg: Springer. pp. 1–4. doi:10.1007/978-3-642-67913-1_1. ISBN 978-3-642-67913-1.
Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are very similar to...
channel – Deposits form within a fluvial channel, dominated by oncoids (see oncolite) Cascade – Deposits form at waterfalls, deposition is focused here due...
the time. Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are similar...
organisms for photosynthesis. Layered spherical growth structures termed oncolites are similar to stromatolites and are also known from the fossil record...
life extinct entirely. However, microfossils such as stromatolites and oncolites prove that, in shallow marine environments at least, life did not suffer...
siliceous sponges and calcifying bacteria, producing structures such as oncolites and stromatolites, although there is evidence this shift in reef composition...
organisms for photosynthesis. Layered spherical growth structures termed oncolites are similar to stromatolites and are also known from the fossil record...
may be considered an allochem. Examples would include ooids, peloids, oncolites, pellets, fossil or pre-existing carbonate fragments. Fragments are still...
Formation Stratigraphic range: Devonian Guilmette Formation, Alamo breccia with oncolites Type Formation Location Region Nevada Country United States...
used as a descriptor of textures and microstructure of stromatolites and oncolites which contain tubules or other cellular structures. The group was defined...
diatoms and ostracods. Microbes form rocky structures including mounds and oncolites. There is evidence of a progressive increase in water levels, followed...
the brook's bedrock dissolved in its waters forms rare lime carbonate oncolites, known locally as "water biscuits", on its shores. Rises in the lake level...
assemblage includes trilobites, hyoliths, and microbialites (stromatolites/ oncolites). Hiscott, R. N. (1982). "Tidal deposits of the Lower Cambrian Random...
indeterminate Indeterminate "Spherical bodies 3-5 microns in diameter". Oncolite "Some post-depositional crushing of the sample has occurred". Renalcis...
cyanobacteria. "Spongiostromate" is also used to describe stromatolites and oncolites that do not preserve clear tubules or other cellular microstructure. Pia...
brownish grey muds; sandier layers orange. Upper layers include oolites and oncolites. Trace fossils include burrows and 'worm trails'. In some places unit...
In at least three localities, nearly spherical algal stromatolites (oncolites) occur near the top of the unit. The contact between the Surprise Canyon...
lower sedimentation areas,with carbonate ramps and dolomitized oolite/oncolite banks deposited under fluctuating sea level conditions, and the Taquari...
Monty, C. L. (1981). "Spongiostromate vs. Porostromate Stromatolites and Oncolites". In Monty, Claude (ed.). Phanerozoic Stromatolites. Berlin, Heidelberg:...
micrites (microbialites) (b) Clay sediments with stratified oolites, oncolites, tuffites, turbidites and calcarenites with abundant gastropod and bivalve...
coastal environment at a transgressional phase with smaller channels where oncolites were laid down. The river systems on both sides of the Montsec were sourced...
covered by material with a composition resembling brine, clay and silt. Oncolites have also been reported from Laguna Socompa and there are diatomite deposits...
consist of invertebrate burrows and trails and Girvanella-like structures (oncolites). Pervasive bioturbation of the calcareous sediment is responsible for...
There have been records of freshwater lue green algal stromatolites and oncolites, suggested to be deposited on low energy and low bathymetry lacustrine...
consist of invertebrate burrows and trails and Girvanella-like structures (oncolites). The Frenchman Mountain Dolostone consists of white to dark gray, thin-...
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