Everything about Global Boundary Stratotype Section And Point totally explained
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 stages, 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 would
- be accessible by public transit from a major airport
- be accessible to research
- be extensive enough to ensure future access
- be easily related to other exposures worldwide
- 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
Precambrian-
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
Trichophycus pedum that's found worldwide. The Fortune Head GSSP is unlikely to be washed away or built over.
Trichophycus pedum is less than ideal as a marker fossil as it isn't found in every Cambrian sequence, and it isn't assured that it's found at the same level in every exposure. Further, it has since been identified in strata 4m
below the GSSP!
[1]
However, no other fossil is known that would be preferable. There is no
radiometrically datable bed at the boundary at Fortune Head, but there's one slightly above the boundary in similar beds nearby.
These factors have lead 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 Suchomastyin in the
Czech Republic. 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.
See also:
Type locality
List of GSSPsFurther Information
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