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Characteristic features of tsunamiites
Shiki, T.; Tachibana, T.; Fujiwara, O.; Goto, K.; Nanayama, F.; Yamazaki, T. (2008). Characteristic features of tsunamiites, in: Shiki, T. et al. (Ed.) Tsunamiites: features and implications. pp. 319-340
In: Shiki, T. et al. (Ed.) (2008). Tsunamiites: features and implications. Elsevier: Amsterdam. ISBN 978-0-444-51552-0. xiii, 411 pp., more

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Keywords
    Sedimentary deposits; Sedimentary structures; Tsunamis; Marine
Author keywords
    Tsunami, Tsunamiite, Tsunami deposit, Sedimentary feature, Sedimentary structure

Authors  Top 
  • Shiki, T.
  • Tachibana, T.
  • Fujiwara, O.
  • Goto, K.
  • Nanayama, F.
  • Yamazaki, T.

Abstract
    Tsunamiite beds can provide excellent keys to stratigraphic correlations over great distances, as they can have a wide extent. On the other hand, they occur only sporadically because of the gigantic tsunami energy and due to a great variety in sedimentary settings. The cooperation of a few elements of water movement, that is (1) shuttle movement of water currents and (2) deceleration (of the run-up tsunami) and acceleration (of the backwash tsunami) caused by gravitation, fundamentally results in a variety of tsunamiite features that depend on the variable conditions of the surrounding sedimentary settings and environments. Successive layers showing opposite palaeocurrent directions and intercalated mud drapes are characteristics and common features of tsunamiites in some environments such as coastal lakes and shallow-sea basins. Single sand sheets also occur inland, depending on their distance from the sea. An erosion surface may be the only record of a tsunami over an extensive coastal area where step-form run-up tsunami waves go forward and break, and where backwash tsunami flows (currents) are markedly accelerated by gravitation. The eroded sediments, including organic material, are transported both offshore and landward, forming a surge with some density. Because of the nature of the tsunami-induced water movement, many kinds of current structures, including those that indicate high-energy regimes, are common structural components in tsunamiites. Hummocky and swaley structures occur in submarine tsunamiites of various environments. Rip-up mud clasts are also common in submarine tsunamiites, showing the special nature of tractive tsunami currents that lack internal shear stress except in the thin bottom boundary layer. Tsunamiites are lacking almost completely in modern deep-sea areas. The Mediterranean homogenites induced by the collapse of the Santorini caldera provide a rare example of tsunami-induced sediments in a deep-sea area. Deposits from extremely gigantic tsunami, such as some Cretaceous/Tertiary (K/T) boundary tsunamiites, can be found in deep-sea records of the geological history. There is not one single convenient key to distinguish tsunami-generated sediments from those generated by other events. Integrated studies including facies analysis of the background environmental sediments are indispensable for identifying and clarifying tsunamiites and their implications.

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