Horizon (geology)

In geology, a horizon refers to either a bedding surface where there is marked change in the lithology within a sequence of sedimentary or volcanic rocks, or a distinctive layer or thin bed with a characteristic lithology or fossil content within a sequence.[1] In the interpretation of seismic reflection data, horizons are the reflectors (or seismic events) picked on individual profiles. These reflectors represent a change in rock properties across a boundary between two layers of rock, particularly seismic velocity and density.[2]

Marker horizon

Marker horizons are stratigraphic units of distinctive lithology (different from the bulk of the sequence) with a wide geographical extent that are used in stratigraphic correlation. Layers of tuff (lithified volcanic ash) are often used for this purpose.

Event horizon

An event horizon is a bed that marks a geological event, such as an earthquake or a meteorite impact. It is the basic unit used in event stratigraphy.[3]


  1. Rey, J. (2008). "Stratigraphy: Foundations and Perspectives". In Rey J. & Galeotti S. (ed.). Stratigraphy: Terminology and Practice. Editions OPHRYS. p. 10. ISBN 9782710809104. Retrieved 28 January 2013.
  2. Schlumberger Limited (2013). "horizon". Oilfield Glossary. Retrieved 30 January 2013.
  3. Grippo, A. (9 May 2011). "Event stratigraphy". Archived from the original on 13 June 2015. Retrieved 28 January 2013.
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