Topostratigraphy ( sv, topostratigrafi) is a method of establishing stratigraphical units based on a mix of

biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...

and

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. In general, strata are primarily igneo ...

. It is used locally in the

Baltic region The terms Baltic Sea Region, Baltic Rim countries (or simply the Baltic Rim), and the Baltic Sea countries/states refer to slightly different combinations of countries in the general area surrounding the Baltic Sea, mainly in Northern Europe. ...

to study the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

-aged

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

. In topostratgraphy the ages of units is defined with the aid of fossils and its extent is known from its rock type. The concept works better in Ordovician rocks in

Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...

than in Sweden. This is because in Ordovician rock

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial ...

s of Estonia changes in biostratigraphy are usually matched by changes in lithostratigraphy. In Sweden topostratigraphical units are mostly based on biostratigraphy as lithological variations are few, making topostratigraphy problematic as units are named after lithology. Having been in use since the 1950s the term was introduced into Swedish in 1960 by Swedish-Estonian geologist

Valdar Jaanusson Valdar Jaanusson (1923–1999) was an Estonian-Swedish geologist. In 1960 he introduced the concept of topostratigraphy into Swedish stratigraphy. A recognized expert on the geology of the Ordovician period, he was member of the Estonian Academy ...

. As of 2011 topostratigraphy was being replaced as method but had still some significance due to its historical usage. The Committee for Swedish Stratigraphic Nomenclature of the

Royal Swedish Academy of Sciences The Royal Swedish Academy of Sciences ( sv, Kungliga Vetenskapsakademien) is one of the Swedish Royal Academies, royal academies of Sweden. Founded on 2 June 1739, it is an independent, non-governmental scientific organization that takes special ...

argues against its use.

References

Stratigraphy Geology of Estonia Geology of Sweden Ordovician {{geology-stub