Global Stratotype Section and Point

The Global Stratotype Section and Point (GSSP) is a boundary of stratigraphic (geochronologic) subdivision of International chronostratigraphic chart accepted by the International Union of Geological Sciences (IUGS) on the base of biologic and other characteristics in type section. Sometimes it is marked by driving a golden spike into the rock mass, which is why GSSPs are also called the golden spikes. Contrary to its name, a "spike" is not necessarily a spike and is not always gold. In addition, the GSSP may not be a point, but an extended line parallel to the Earth’s surface or inclined to it. Despite the desirable presence of sediments of overlying units in a type section, only the lower boundary, which is, at the same time, the upper boundary of the underlying (older) unit, is usually determined. For example, the GSSP of the Homerian also defines the upper boundary of the Sheinwoodian stage of the Silurian. Such practice prevents nonconformities in subdivision volumes.

Since the main stratigraphic unit is a stage (its geochronologic equivalent is an age), the largest number of accepted GSSPs occur at the lower boundaries (bases) of the stages. If the stage is a lower subdivision of a bigger unit (series, system, erathem, eonothem), then GSSP also related to this unit. For example, the GSSP of the Induan stage is also the GSSP of the Lower Triassic series, Triassic system and Mesozoic erathem. The GSSP of the Fortunian stage is even more significant since it also related to the base of the Terreneuvian series, Cambrian system, Paleozoic erathem and Phanerozoic eonothem. It is important to say that GSSPs can be established in places very far from the type localities of their units. As example, Tremadocian stage of the Ordovician system was distinguished on the British Isles, although the GSSP was defined on the island of Newfoundland near the continental Canada in 2000. The reason lies in the necessary requirements for all GSSPs.

Requirements

GSSPs are the benchmarks for geologists around the world, so the establishment of each GSSP is preceded by careful checks for compliance with the requirements. When selecting sections for a single GSSP, the preference is given to those with the largest set of markers or the most remarkable features of the boundary between units. While establishing a GSSP, the authors indicate the coordinates of the section, the most convenient paths to this place and accompanying landmarks such as nearest reservoirs and settlements.

Necessary conditions include:

• Accessibility of the section for scientists from all countries of the world;
• Absence of necessity in organizing an expensive expedition to the section;
• Travel safety;
• Safety of the territory with GSSP from both human activity and natural disasters.

The ideal option is to establish a GSSP in a protected reserve.

Number and prevalence

Over 70 GSSPs have already been defined, but, as of 2024, only one of them was established for the Precambrian unit, the Ediacaran period of the Neoproterozoic. The bronze disk is placed in the thickness of the rocks in Flinders Ranges, South Australia, in 1990. It is expected that GSSPs will also be installed for some of the older units. In the same time, several younger units still need GSSPs.

Trivia

• In the September 2023 version of International Chronostratigraphic Chart a golden spike near the Barremian can be seen. However, as of 2024, the GSSP of this stage is not ratified yet.
• As of 2024, Ordovician, Silurian and Devonian are the only three systems, each stage of which has its GSSP.
• Cretaceous is the last Phanerozoic system not to have a GSSP definding its base. As it said by Alekseev A. S. (Lomonosov Moscow State University) in 2013, "the search process and confirmation of the Jurassic-Cretaceous boundary has long become a joke".