“A Stratotype or type Section is a geological term that names the physical location or outcrop of a particular reference exposure of a stratigraphic sequence or stratigraphic boundary.”
Classification of Stratotypes :
- Holostratotype: The original stratotype designated by the original author at the time of proposing a stratigraphic unit or boundary.
- Parastratotype : A supplementary stratotype used in the original definition by the original author to illustrate the diversity or heterogeneity of the defined stratigraphic unit or some critical feature not evident or exposed in the holostratotype.
- Lectostratotype : A stratotype for a previously described stratigraphic unit selected in the absence of an adquately designated original stratotype (holostratotype).
- Neostratotype : A new stratotype selected to replace an older one which has been destroyed, covered or become inaccessible.
- Hypostratotype : A stratotype proposed after the original designation of the holostratotype (and parastratotype) in order to extend knowledge of the unit or boundary to other geographic areas. It is always subordinate to the holostratotype.
GSSP (Global Boundary Stratotype Sections and Point)
A GSSP is an internationally agreed upon stratigraphic section which serves as the reference section of a particular boundary on the geological time scale. It is defined by International Commission on Stratigraphy. Most but not all of them are based on paleontological changes.
Ex :- The ‘golden spike’ (bronze disk in the lower section of the image) or ‘type section’ of the Global Boundary Stratotype Section and Point (GSSP) for the base of Ediacaran period (Ediacara, South Australia)
Conditions to classify a section as GSSP :
- It must be accessible to research
- It must be extensive enough to ensure future research
- It should be easily related to other exposure worldwide
- It should contain a radiometrically datable bed at the boundary
- It should included well defined markers at the stages boundary that can be applied worldwide.
REFERENCES :
- https://timescalefoundation.org/gssp/index.php?parentid=all
- https://en.wikipedia.org/wiki/Global_Boundary_Stratotype_Section_and_Point
- https://stratigraphy.org/guide/strats
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