3.3 Lithodemic units
3.3.1 General properties and rules
A lithodemic unit consists of one or more bodies of igneous rocks which may be plutonic, intrusive or extrusive rocks and/or strongly metamorphosed and deformed rocks (Figs. 1, 5).
The unit is defined entirely on the basis of lithological character. In contrast to lithostratigraphical units, the classification of lithodemic rocks does not follow the principle of younger rocks being formed above older ones. Lithodemic units are therefore erected in areas where rocks do not succeed one another in compliance with the "Law of Superposition", or where it is very difficult to prove such a relationship.
Lithodemic units serve as units when geological mapping is being carried out in areas where the bedrock lacks unequivocal stratification. They are used during field work, when writing descriptions, elucidating the geological history and assessing economically exploitable deposits. Contacts with other geological units may be sedimentary, intrusive, metamorphic or tectonic in origin.
Lithodemic units are, in decreasing order of rank, supersuite, suite and lithodeme. The lithodeme is the fundamental unit. Complex is not ranked, but will usually correspond in size to suite or supersuite.
It has not been customary in Norway to use formal lithodemic names on geological maps and in map descriptions. Petrographical designations have usually been used for lithodemic units. However, in regional and petrographical descriptions, informal geographical names have often been applied to plutonic rocks, intrusive breccias and similar bodies. A few such designations, such as the Drammen granite and the Grefsen syenite, have been used partly as lithodemic proper names, partly as petrographical collective names. Double usage of this sort should be avoided. If one wishes to use a lithodemic proper name as an ordinary petrographical designation it should be written with lower case initials as a collective name, both in English and Norwegian. The type meaning can be emphasized by adding the word "type", e.g. "drammen granite-type", "grefsen syenite-type".
Formal lithodemic units should only be defined and erected if they serve a practical purpose. Names of informal lithodemic units are not to be constructed using a geographical name (or an alternative name in the case of the continental shelf) and a formal hierarchical unit designation (cf. Section 2.3.2).
