2024

Kohonen, Jarmo; Köykkä, Juha; Mikkola, Perttu

The characterization, definition and classification of geological units and their correlation with geological time comprise one of the oldest branches of geology: stratigraphy. Systematic and hierarchical classification schemes for the different geological units largely define the structure of the data model, the framework underlying any digital map database and regional geological map compilation. This article reflects on the experience gained by the Geological Survey of Finland (GTK) during a reconstruction of the national map data architecture. We describe how different geological units have been used in the arrangement of the Precambrian rock bodies and present alternative options for the further development of (1) litho-based unit classification, (2) other geological unit types and their spatial representation and (3) chronostratigraphic nomenclature in Finland. This is a complimentary contribution related to the 2nd and revised (2024) edition of the ‘Guidelines and procedures for naming bedrock units in Finland’. Lithodemic classification has been found functional in the naming of various nonstratiform rock bodies. However, problems have appeared in the systematic characterization of lithodemes. We discuss the combined use of lithostratigraphic and lithodemic classifications and present insights into the improved applicability of the lithodemic system. The benefits of independently defined, overlapping geological units, such as deformation units and alteration units, are described and their increased use is recommended. General nomenclature referring to geological age is essential in scientific communication. To improve the inconsistent and insufficiently defined chronostratigraphic nomenclature, we introduce new regional time-stratigraphic scales for the (Paleoproterozoic) Karelian formations and Svecofennian rocks in Finland. Regarding the Meso- and Neoproterozoic rocks, the use of system and Period names of the International Chronostratigraphic Chart (ICS) is suggested and definitive abandonment of the obsolete traditional names Jotnian, postJotnian and subJotnian is proposed.