Diamictite

Diamictite
Diamictite from Stolpe, eastern Germany
'Snowball Earth'-type diamictite from the Pocatello Formation, Idaho, USA
Boulder of diamictite of the Mineral Fork Formation, Antelope Island, Utah, USA

Diamictite (pronounced /ˈdaɪ.əmɪktaɪt/, from Greek δια (dia-): through and µεικτός (meiktós): mixed) is a poorly or non-sorted conglomerate or breccia with a wide range of clasts,[1] up to 25% of them gravel sized (greater than 2 cm). Diamictites are composed of coarse, angular to well rounded sedimentary clastic fragments, or other type of fragments (igneous and metamorphic rocks) supported by a typically argillaceous (clay sized) matrix.

The term was coined in 1960 by Flint and others as a purely descriptive term for poorly sorted and laminated rocks, avoiding any reference to a particular origin.[2]

Diamictites are often interpreted mistakenly as having a glacial or ice sheet origin only (see Snowball Earth), while in fact they can be produced by a wide range of different geological mechanisms. Possible origins include:[3][4]

The most common origin of diamictites is deposition by submarine mass flows like turbidites and olistostromes in tectonically active areas.[3]

References

  1. ^ Hallsworth, C.R., Knox, R.W.O'B.: Classification of sediments and sedimentary rocks. British Geological Survey, Research Report RR 99-03, p. 6. (pdf 470 Kb)
  2. ^ Flint, R.F., Sanders, J.E., Rodgers, J. : Diamictite, a substitute term for symmictite. Geol. Soc. Am. Bull. 71, 1809–1810, 1960.
  3. ^ a b Eyles, N.; Januszczak, N. (2004). "’Zipper-rift’: A tectonic model for Neoproterozoic glaciations during the breakup of Rodinia after 750 Ma". Earth-Science Reviews 65 (1-2): 1-73. (pdf 4 Mb)
  4. ^ Huber, H., Koeberl, C., McDonald, I., Reimold, W.U.: Geochemistry and petrology of Witwatersrand and Dwyka diamictites from South Africa: Search for an extraterrestrial component. Geochimica et Cosmochimica Acta, Vol. 65, No. 12, pp. 2007–2016, 2001. (pdf 470 Kb)

Further reading

  • Deynoux, M., et al. (Editors) (2004) Earth's Glacial Record, Cambridge University Press, pp. 34–39 ISBN 0-521-54803-9

External links