Global Boundary Stratotype Section and Point
Encyclopedia
A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic
section which serves as the reference section for a particular boundary on the geologic time scale
. The effort to define GSSPs is conducted by the International Commission on Stratigraphy
, a part of the International Union of Geological Sciences
. Most, but not all, GSSPs are based on paleontological
changes. Hence GSSPs are usually described in terms of transitions between different faunal stage
s, though far more faunal stages have been described than GSSPs. The GSSP definition effort commenced in 1977. As of 2004, 45 of the 96 GSSPs required have been approved.
No GSSP is ideal.
-Cambrian
boundary GSSP at Fortune Head
, Newfoundland is a typical GSSP. It is accessible by paved road and is set aside as a nature preserve. A continuous section is available from beds that are clearly Precambrian into beds that are clearly Cambrian. The boundary is set at the first appearance of a complex trace fossil Treptichnus pedum
that is found worldwide. The Fortune Head GSSP is unlikely to be washed away or built over. Nonetheless, Treptichnus pedum is less than ideal as a marker fossil as it is not found in every Cambrian sequence, and it is not assured that it is found at the same level in every exposure. In fact, further eroding its value as a boundary marker, it has since been identified in strata 4m below the GSSP!
However, no other fossil is known that would be preferable. There is no radiometrically datable
bed at the boundary at Fortune Head, but there is one slightly above the boundary in similar beds nearby.
These factors have led some geologists to suggest that this GSSP is in need of re-assigning.
Once a GSSP boundary has been agreed upon, a "golden spike" is driven into the geologic section to mark the precise boundary for future geologists (though in practice the "spike" need neither be golden nor an actual spike). The first stratigraphic boundary was defined in 1977 by identifying the Silurian
-Devonian
boundary with a bronze plaque at a locality called Klonk
, northeast of the village of Suchomasty in the Czech Republic
. GSSPs are also sometimes referred to as Golden Spikes.
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
section which serves as the reference section for a particular boundary 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...
. The effort to define GSSPs is conducted 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...
, a part of the International Union of Geological Sciences
International Union of Geological Sciences
The International Union of Geological Sciences is an international non-governmental organization devoted to international cooperation in the field of geology.-About:...
. Most, but not all, GSSPs are based on paleontological
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
changes. Hence GSSPs are usually described in terms of transitions between different faunal stage
Faunal stage
In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.Rock...
s, though far more faunal stages have been described than GSSPs. The GSSP definition effort commenced in 1977. As of 2004, 45 of the 96 GSSPs required have been approved.
An ideal GSSP
An ideal GSSP would:- Be accessible to research
- Be easily related to other exposures worldwide
- Be extensive enough to ensure future access
- Contain a radiometrically datable bed at the boundary, and
- Include well defined markers at the stage boundary that can be applied worldwide.
No GSSP is ideal.
Agreed-upon GSSPs
The PrecambrianPrecambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
-Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
boundary GSSP at Fortune Head
Fortune Head
Fortune Head is a headland located about 1.6 km from the town of Fortune on the Burin Peninsula, southeastern Newfoundland.A 410 m thick section of rock along its cliffs is designated the Global Boundary Stratotype Section and Point representing the boundary between the Precambrian era and the...
, Newfoundland is a typical GSSP. It is accessible by paved road and is set aside as a nature preserve. A continuous section is available from beds that are clearly Precambrian into beds that are clearly Cambrian. The boundary is set at the first appearance of a complex trace fossil Treptichnus pedum
Treptichnus pedum
Treptichnus pedum is regarded as the earliest widespread complex trace fossil...
that is found worldwide. The Fortune Head GSSP is unlikely to be washed away or built over. Nonetheless, Treptichnus pedum is less than ideal as a marker fossil as it is not found in every Cambrian sequence, and it is not assured that it is found at the same level in every exposure. In fact, further eroding its value as a boundary marker, it has since been identified in strata 4m below the GSSP!
However, no other fossil is known that would be preferable. There is no radiometrically datable
Radiometric dating
Radiometric dating is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates...
bed at the boundary at Fortune Head, but there is one slightly above the boundary in similar beds nearby.
These factors have led some geologists to suggest that this GSSP is in need of re-assigning.
Once a GSSP boundary has been agreed upon, a "golden spike" is driven into the geologic section to mark the precise boundary for future geologists (though in practice the "spike" need neither be golden nor an actual spike). The first stratigraphic boundary was defined in 1977 by identifying the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
-Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
boundary with a bronze plaque at a locality called Klonk
Klonk
Klonk, southwest of Prague, Czech Republic, is the location of the Global Boundary Stratotype Section and Point which marks the boundary between the Devonian and Silurian periods on the geologic time scale...
, northeast of the village of Suchomasty in the Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
. GSSPs are also sometimes referred to as Golden Spikes.
GSSAs
Because defining a GSSP depends on finding well-preserved geologic sections and identifying key events, this task becomes more difficult as one goes farther back in time. Before 630 million years ago, boundaries on the geologic timescale are defined simply by reference to fixed dates, known as "Global Standard Stratigraphic Ages".Related other topics
- Body form
- European Mammal Neogene
- Fauna (animals)
- Geologic time scaleGeologic time scaleThe 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...
- New Zealand geologic time scaleNew Zealand geologic time scaleWhile also using the international Geologic time scale, many nations - especially those with isolated and therefore non-standard prehistories - use their own system of dividing geologic time into epochs and faunal stages....
- New Zealand geologic time scale
- List of GSSPs
- North American Land Mammal Age
- Type localityType locality (geology)Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
External links
- The Global Boundary Stratotype Section and Point (GSSP): overview
- Chart of The Global Boundary Stratotype Sections and Points (GSSP): chart
- Table of Global Boundary Stratotype Sections and Points (GSSPs) with links to summary pages for each one: chart
- Geotime chart displaying geologic time periods compared to the fossil record - Deals with chronology and classifications for laymen (not GSSPs)