Topostratigraphy (Swedish: topostratigrafi) is a method of establishing stratigraphical units based on a mix of biostratigraphy and lithostratigraphy.
[1] It is used locally in the Baltic region to study the Ordovician-aged sedimentary rock.
In topostratigraphy the ages of units is defined with the aid of fossils and their extent is known from their rock type.
[1] Having been in use since the 1950s[2] the term was introduced into Swedish in 1960 by Swedish-Estonian geologist Valdar Jaanusson.
[1] As of 2011 topostratigraphy was being replaced as a method but had still some significance due to its historical usage.