3.4.2 Polarity zone (Polaritetssone)
3.4.2.1 A polarity zone is a body of rock or superficial deposits that is characterized by its distinctive remanent-magnetic polarity, which differs from that of an adjacent magnetopolarity unit. If there is a risk of confusion with other types of polarity, the term magnetopolarity zone should be used instead of polarity zone.
3.4.2.2 Polarity zone is the fundamental formal unit for magnetopolar-stratigraphical classification.
3.4.2.3 In principle, no limitation is placed on the thickness and extent of the body of rock or superficial deposits that defines a polarity zone, nor on the time period represented by the zone.
3.4.2.4 A polarity zone is identified and mapped on the basis of its distinctive remanent-magnetic polarity, using palaeomagnetic analytical methods.
3.4.2.5 A polarity zone is defined by a lower and an upper boundary, each of which marks a change in the polarity of the remanent magnetization. These boundaries may represent a break in deposition or a change in the magnetic field. Such boundaries may be of two main types: (a) polarity-reversal horizon (polaritetsrevers horisont), which is either a clearly definable surface or a transitional interval of 1 m or less, (b) polarity transition zone (polaritetsovergangssone), which is a boundary where the change in polarity takes place over a stratigraphical interval of more than 1 m.
A polarity zone should possess a certain degree of inner homogeneity. It may contain rocks and superficial deposits that are characterized by a single polarity or a mixed polarity.
3.4.2.6 A polarity zone is given a formal name in accordance with the "general rules for naming and defining geological units" (Chap. 2). The name consists of a geographical name from a type section or type locality and the term "the ... Polarity Zone" (polaritetssonen). A descriptive designation for the polarity (normal, reverse, mixed) can be inserted between the proper name and the unit designation.
3.4.2.7 A polarity zone can be divided into Polarity Subzones (polaritetsundersoner). Two or more polarity zones can be grouped in the higher-ranking Polarity Superzone (polaritetsoversone) (Table 1).
3.4.2.8 Examples: No polarity zones have been defined on Norwegian territory.
3.4.2.9 Key reference: NACSN (1983).
