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]

• glacial origin
  • meltwater flow deposition
  • unsorted moraine glacial till
  • basal melt-out
  • ice rafted sediments deposited by melting icebergs or disintegrating ice sheets (dropstones)
• volcanic origin
  • lahars
  • lahar mass flows entering the ocean
• marine origin
  • debris flow
  • turbiditic olistostromes
  • mixing of sediments by submarine landslides
• tectonic origin
  • fault gouge
• erosional origin
  • regolith, in the form of a debris flow
  • other mass wasting events
• extraterrestrial origin
  • impact breccia

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

• Illustration of a Canadian diamictite

This article related to petrology is a stub. You can help Wikipedia by expanding it.v · Categories: Sedimentary rocks Petrology stubs Wikimedia Foundation. 2010. Игры ⚽ Поможем написать реферат Unterseeboot 551 Highpoint Look at other dictionaries: diamictite — noun A sedimentary, calcareous conglomerate containing a mixture of particles; mixtite …   Wiktionary diamictite —    A general term for any nonsorted or poorly sorted, noncalcareous, terrigenous sedimentary rock (e.g., pebbly mudstone) containing a wide range of particle sizes.    Compare: diamicton.    GG …   Glossary of landform and geologic terms Geology of Tasmania — Tasmania has a varied geological history, with the world s biggest exposure of diabase, or dolerite. Rocks from the Neoproterozoic, Paleozoic and Mesozoic time periods appear. It is one of the few southern hemisphere areas glaciated during the… …   Wikipedia Marinoan glaciation — Neoproterozoic Snowball Periods 1000  – …   Wikipedia Snowball Earth — The Snowball Earth hypothesis as it was originally proposedcite book author = Kirschvink, J.L. year = 1992 chapter = Late Proterozoic low latitude global glaciation: The snowball Earth title = The Proterozoic Biosphere: A Multidisciplinary Study… …   Wikipedia Till — is unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. It may vary… …   Wikipedia List of rock types — This page is intended as a list of all rock types. NOTOC A : Amphibolite: Andesite: Anorthosite : Anthracite: Aplite: Argillite: Arkose B : Banded iron formation: Basalt: Basanite: Blueschist: Boninite: Breccia C : Carbonatite: Cataclasite: Chalk …   Wikipedia Congo craton — Approximate location of Mesoproterozoic (older than 1.3 Ga) cratons in South America and Africa. The Congo craton, covered by the Palaeozoic to recent Congo basin, is an ancient Precambrian craton that with four others (the Kaapvaal,… …   Wikipedia Diamicton — In geology, diamicton (also diamict) is a very poorly sorted sediment. Large sedimentary grains gravel size and larger (>= 2 mm) are set in a matrix of fine grains. The term diamicton is a nongenetic term, although a common origin for… …   Wikipedia Superior craton — in the west. The western margin extends from northern Minnesota through eastern Manitoba to northwestern Ontario.The formation of the Superior craton is best explained within the context of 2.72 2.68 Ga accretion of small continental plates and… …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”