Horizon (geology)

The horizons can sometimes be very prominent, such as visible changes in cliff sides, to extremely subtle chemical differences.

Layers of tuff (lithified volcanic ash) as well as sand and organic materials from the ocean (from tsunamis) are often used for this purpose.

Marker horizons can also indicate the existence of ancient lakebeds and riverbeds, as well as things such as inland oceans.

As such, they are important in the study of the formation of the Earth and of certain landforms as well as the climate at certain times and the events that may have occurred in certain regions or all over the world.

For example, in regions such as Iceland, it is common to find deposits of tephra, a material spewed out of volcanoes in eruptions.

Researchers in Iceland have been able to identify roughly 65–75% of all 200 recorded eruptions since 900 AD using the study and analysis of event horizons composed of tephra.

These event horizons depending on the size of the eruption can commonly be located all over the world and throughout many volcanically active regions.

While the western term "horizon" pertains to a small lithological section within a geological formation, a gorizont is a broad biostratigraphic unit.

Both gorizonts and svitas are also considered chronostratigraphic units (correlated with a distinct time interval), while western geologists have separate chronological and stratigraphic systems.