4.7.4 Span (Trinn)
4.7.4.1 Span is the diachronous unit that has formal rank next below phase and next above cline. A span will generally be the lowest diachronous unit that it is practical to distinguish in a reference succession. A span may, for example, be the time during which a single lava flow, ice-contact ridge (e.g. Ra Span) or conglomerate fan formed. A span may be defined without it needing to form part of a formal phase. When used informally, the word "span" should retain a corresponding meaning of relative time.
The Norwegian word "trinn" has previously also been used as a geomorphological term for marine terrace surfaces and for ice-marginal deposits. This usage for "trinn" is not recommended in Norwegian (see Section 3.10.2.8).