Gorizont (geology)
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In
geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
, a horizon is either a
bedding surface In geology, a bed is a layer of sediment, sedimentary rock, or volcanic rock "bounded above and below by more or less well-defined bedding surfaces".Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds., 2005. ''Glossary of Geology'' (5th ed ...
where there is marked change in the
lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...
within a sequence of
sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...
or
volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...
s, or a distinctive layer or thin
bed A bed is a piece of furniture that is used as a place to sleep, rest, and relax. Most modern beds consist of a soft, cushioned mattress on a bed frame. The mattress rests either on a solid base, often wood slats, or a sprung base. Many beds ...
with a characteristic lithology or
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
content within a sequence. Examples of the former can include things such as volcanic eruptions as well as things such as meteorite impacts and tsunamis. Examples of the latter include things such as ice ages and other large climate events, as well as large but temporary geological features and changes such as inland oceans. In the interpretation of
seismic reflection Reflection seismology (or seismic reflection) is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismi ...
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 A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large man ...
and
density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
. It can also represent changes in the density of the material and the composition of it and the pressure under which it was produced. Thus, not only do the properties change but so too do the conditions of formation and other differences in the rock. The horizons can sometimes be very prominent, such as visible changes in cliff sides, to extremely subtle chemical differences.


Marker horizon

Marker horizons are
stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...
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 Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...
(lithified
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
) as well as sand and organic materials from the ocean (from tsunamis) are often used for this purpose. This is helpful when measuring the time periods of deposits and the layers they are in, as well as determining the age of fossils. Marker horizons can also indicate the existence of ancient lakebeds and riverbeds, as well as things such as inland oceans. Marker horizons can be important for all fields in geology because they are important indications of all the various changes in the geological time records. 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.


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. It is related to the marker horizons in that event horizons can be used as a marker horizon, though they are not always the same. Marker horizons can emerge from more situation sources such as inland oceans, whereas event horizons are more often associated with specific events. Event horizons can also be used to indicate events in the geological record. 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. This is just one of many important examples of the use of marker horizons and event horizons to study and date events from the past. These event horizons depending on the size of the eruption can commonly be located all over the world and throughout many volcanically active regions. Volcanic eruption deposits can often hold up better than tsunami deposits because they are not always on or near shorelines and as such are less likely to be eroded. However, unlike tsunamis, not all volcanic eruptions produce materials such as tephra that indicate an eruption. Some produce other materials that are not as likely to survive erosion. Whilst Iceland is a good example of this, there are other examples around the world. One of the other common examples of event horizons, besides volcanic eruptions. One more rare example are tsunami deposits. The reason for the rarity lies largely with the fact that tsunami deposits are in areas that experience frequent erosions, such as shorelines, and as such the ability for the ground to retain deposits and clean signs of such event horizons is dismal. However, there are some examples of tsunamis, including more prominent examples of mega tsunamis. Most deposits come from during and after the quaternary period, especially due to the aforementioned accumulation and erosion issues. The tsunami deposits are most commonly found along coastal areas especially in regions along ocean fault lines. These areas include places like Indonesia as well as Japan and the northwestern United States. These deposits are usually in the form of sand and organic material (such as corals) and other material that is often found along shorelines and the ocean floor. They can be found many miles inland or just along the coast. They are especially common in cliffs a decent amount inland and high above sea level. These are more common than those along the shore due to the aforementioned erosion.


Gorizont

The fundamental unit of
Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
n stratigraphy, the gorizont, can be
anglicized Anglicisation or anglicization is a form of cultural assimilation whereby something non-English becomes assimilated into or influenced by the culture of England. It can be sociocultural, in which a non-English place adopts the English language ...
as "horizon". However, this concept is not equivalent to the term used in western geological systems. While the western term "horizon" pertains to a small lithological section within a geological formation, a gorizont is a broad
biostratigraphic Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...
unit. It may encompass several "svitas" (
lithological The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lith ...
units equivalent to a formation). Both gorizonts and svitas are also considered chronostratigraphic units (correlated with a distinct time interval), while western geologists have separate chronological and stratigraphic systems.


References

{{Reflist Stratigraphy