Oncolite

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Oncolites from the upper Burgsvik beds (Silurian), with shell fragments as nuclei. Large flower is 2 cm in diameter.

Oncolites are sedimentary structures formed of oncoids, which are layered spherical growth structures formed by cyanobacterial growth. Oncolites are very similar to stromatolites, but instead of forming columns they form approximately spherical structures.[1] Often the oncoids form around a central nucleus, such as a shell particle,[2] and the calcium carbonate structure is precipitated 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.

Recent/Subrecent freshwater oncoids in Bavaria

In two river of Bavaria is the appearance of recent/subrecent freshwater onciods documented. River Alz, the effluent of Chiemsee and river Moosach near Freising. [4] [5] [6]

  • Recent oncoid, nucleus -limestone-

  • Recent oncoid, nucleus -Unio pictorum-

  • Recent oncoid, nucleus -limestone-

  • Recent oncoid, surface

Gallery Oncolite

  • Oncolites formed around the Middle Jurassic gastropod Bactroptyxis trachaea (Normandy, France).

  • Oncolites in the Alamo bolide impact breccia (Guilmette Formation, Late Devonian, Frasnian) near Hancock Summit, Pahranagat Range, Nevada.

  • Oncolites in the Crown Point Formation (Ordovician) at the Crown Point Historical Site, New York

References

  1. ↑ 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. Retrieved 2007-06-28. 
  2. ↑ 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. 
  3. ↑ Riding, Robert. 1991. Calcareous Algae and Stromatolites, pp. 32. Springer-Verlag Press.
  4. ↑ D. Hägele (2006) (in German), [Online-Version; pdf-Datei; 8,6 MB Morphogenese, Wachstum und Ökologie der modernen Süßwasser-Onkoide der Alz], Dissertation an der Fakultät für Geowissenschaften, Ludwig-Maximilians-Universität München, Online-Version; pdf-Datei; 8,6 MB
  5. ↑ E. Rott (1994), [Online-Version; pdf-Datei; 7,6 MB "Der Algenaufwuchs in der Oberen Alz (Oberbayern)"] (in German), Berichte des naturwissenschaftlich-medizinischen Vereins in Innsbruck (Innsbruck) 81: pp. 229–253, Online-Version; pdf-Datei; 7,6 MB
  6. ↑ N.N. (2008), [Online-Version; pdf-Datei; 8,4 MB "Stop 7: Tufa oncoids of the river Moosach, Molasse Basin"] (in German), Geobiology of Stromatholites - Internationales Kalkowsky-Symposium (Göttingen): pp. 193–197, Online-Version; pdf-Datei; 8,4 MB
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