Tefra

Tefra je obecné označení pro pyroklastické sedimenty všech typů a velikostí.^[1] Někdy se uvádí, že jde o nezpevněná pyroklastika, která nebyla přesunuta z původního místa, kde se usadila.^[2]^[3] Termín nezohledňuje petrografické složení horniny, velikost pyroklastů, ani způsob jejich uložení.

Termín, podle řeckého označení prachu, v roce 1944 poprvé použil Sigurdur Thórarinsson.^[3]

Tefra vzniká při explozivních sopečných erupcích. Vrstvy tefry se při těchto erupcích mohou usadit v širokém okolí sopky na tisících kilometrů čtverečních. V sedimentárním záznamu tak mohou vytvářet novou dobře sledovatelnou vrstvu. Korelace sedimentů pomocí vrstev tefry se označuje tefrochronologie. V případě velkého množství akumulované tefry dochází v pozdějších stádiích k jejímu přepracování za vzniku úlomkových proudů nebo vulkanických brekcií na úpatích sopek a ve výplavových vějířích.

Je tvořena vulkanickým sklem, vznikajícím při chladnutí drobných kapiček lávy ve vzduchu, jakož i minerálními zrny. Silné erupce mohou mít za následek i výraznou příměs litoklastů starších hornin.

Odkazy

Reference

V tomto článku byl použit překlad textu z článku Tefra na slovenské Wikipedii.

↑ Nichols, G., 2009, Sedimentology and stratigraphy. Wiley-Blackwell, Chichester, 419 s.
↑ Vozárová, A., 2009, Petrografia sedimentárnych hornín. Univerzita Komenského, Bratislava, 173 s.
↑ ^a ^b Dugmore, A.J., Newton, A., 2009, Tephrochronology in Gornitz, V. (Editor), Encyclopedia of Paleoclimatology and Ancient Environments. Springer, Dordrecht, s. 937-938

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