System (geology)
Encyclopedia
A system in the natural sciences and stratigraphy
is an idealized composite unit of the geologic record
made up of a succession of rock layers
that were laid down together within a certain corresponding geological time span, and are used in turn to date things to a certain corresponding geologic period. The system is thus a unit of the geologic record
or rock column, pieced together using the Law of Superposition
and mapped to its corresponding period— the associated continuous
chronostratigraphical
time unit
, a relative metric
that science committees
have determined solid dating for as organized on the geologic time scale
. A system is therefore a unit of chronostratigraphy
, unrelated to lithostratigraphy
, which subdivides rock layers on their lithology
. Systems are subdivisions of erathem
s and are themselves divided into series, epochs
and stages.
System is a term defining a unit of rocklayers formed in a certain time interval; it is in theory equivalent to the term period defining the interval of time itself, but unlike the system of time units, a system in many locations may be interrupted and incomplete as geologic forces alternately uplift or depress a region, bend the landscape and so expose a terrain feature once accumulating rock to weathering and vice versa. The overall rock record has been piecewise constructed throughout each physical system, series, et al. using superposition, and is treated in practice as one large continuous rock column, the whole matching the corresponding period. For this reason, the two words are sometimes confused in informal literature.
eonothem
were defined during the 19th century, beginning with the Cretaceous
(by Belgian geologist Jean d'Omalius d'Halloy in the Paris Basin
) and the Carboniferous
(by British geologists William Conybeare and William Phillips
) in 1822. The Paleozoic
and Mesozoic
erathems were divided into the currently used systems before the second half of the 19th century, except for a minor revision when the Ordovician
system was added in 1879.
The Cenozoic
has recently seen some revisions by the International Commission on Stratigraphy
; it will most probably be divided into three systems (Paleogene
, Neogene
and Quaternary
) while older (and currently still better known) names are now series (Paleocene
, Eocene
, Oligocene
, Miocene
and Pliocene
) or abandoned (Tertiary
).
Another recent development is the official division of the Proterozoic
eonothem into systems, which was decided in 2004.
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
is an idealized composite unit of the geologic record
Geologic record
The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata — deposits laid down in volcanism or by sediment deposition of weathering detritus including all its fossil content and the information it yields about the history...
made up of a succession of rock layers
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
that were laid down together within a certain corresponding geological time span, and are used in turn to date things to a certain corresponding geologic period. The system is thus a unit of the geologic record
Geologic record
The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata — deposits laid down in volcanism or by sediment deposition of weathering detritus including all its fossil content and the information it yields about the history...
or rock column, pieced together using the Law of Superposition
Law of superposition
The law of superposition is a key axiom based on observations of natural history that is a foundational principle of sedimentary stratigraphy and so of other geology dependent natural sciences:...
and mapped to its corresponding period— the associated continuous
Continuous function
In mathematics, a continuous function is a function for which, intuitively, "small" changes in the input result in "small" changes in the output. Otherwise, a function is said to be "discontinuous". A continuous function with a continuous inverse function is called "bicontinuous".Continuity of...
chronostratigraphical
Chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time.The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of...
time unit
Units of measurement
A unit of measurement is a definite magnitude of a physical quantity, defined and adopted by convention and/or by law, that is used as a standard for measurement of the same physical quantity. Any other value of the physical quantity can be expressed as a simple multiple of the unit of...
, a relative metric
Metric (mathematics)
In mathematics, a metric or distance function is a function which defines a distance between elements of a set. A set with a metric is called a metric space. A metric induces a topology on a set but not all topologies can be generated by a metric...
that science committees
International Commission on Stratigraphy
The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...
have determined solid dating for as organized on the geologic time scale
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
. A system is therefore a unit of chronostratigraphy
Chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time.The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of...
, unrelated to lithostratigraphy
Lithostratigraphy
Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology...
, which subdivides rock layers on their lithology
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, such as colour, texture, grain size, or composition. It may be either a detailed description of these characteristics or be a summary of...
. Systems are subdivisions of erathem
Erathem
In stratigraphy, paleontology, geology, and geobiology an erathem is the total stratigraphic record deposited during a certain corresponding span of time, an era in the geologic timescale....
s and are themselves divided into series, epochs
Epoch (geology)
An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...
and stages.
System is a term defining a unit of rocklayers formed in a certain time interval; it is in theory equivalent to the term period defining the interval of time itself, but unlike the system of time units, a system in many locations may be interrupted and incomplete as geologic forces alternately uplift or depress a region, bend the landscape and so expose a terrain feature once accumulating rock to weathering and vice versa. The overall rock record has been piecewise constructed throughout each physical system, series, et al. using superposition, and is treated in practice as one large continuous rock column, the whole matching the corresponding period. For this reason, the two words are sometimes confused in informal literature.
Systems in the geological timescale
The systems of the PhanerozoicPhanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
eonothem
Eonothem
In stratigraphy and geology, an eonothem is the totality of rock strata laid down in the stratigraphic record deposited during a certain eon of the continuous geologic timescale...
were defined during the 19th century, beginning with the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
(by Belgian geologist Jean d'Omalius d'Halloy in the Paris Basin
Paris Basin
Paris Basin may refer to:*As a hydrological basin, it is largely the basin of the River Seine* Paris Basin , the geological basin...
) and the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
(by British geologists William Conybeare and William Phillips
William Phillips (geologist)
William Phillips FRS was an English mineralogist and geologist.Phillips was the son of James Phillips, printer and bookseller in London. He became interested in mineralogy and geology, and was one of the founders of the Geological Society of London...
) in 1822. The Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
and Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
erathems were divided into the currently used systems before the second half of the 19th century, except for a minor revision when the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
system was added in 1879.
The Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
has recently seen some revisions by the International Commission on Stratigraphy
International Commission on Stratigraphy
The International Commission on Stratigraphy , sometimes referred to by the unofficial "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global...
; it will most probably be divided into three systems (Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
, Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
and Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
) while older (and currently still better known) names are now series (Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
, Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
, Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
and Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
) or abandoned (Tertiary
Tertiary
The Tertiary is a deprecated term for a geologic period 65 million to 2.6 million years ago. The Tertiary covered the time span between the superseded Secondary period and the Quaternary...
).
Another recent development is the official division of the Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
eonothem into systems, which was decided in 2004.
External links
- The Global Boundary Stratotype Section and Point (GSSP): overview
- Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
- Geotime chart displaying geologic time periods compared to the fossil record - Deals with chronology and classifications for laymen (not GSSPs)