Oppel zone A concurrent range zone as originally conceived by Albert Oppel. The lower boundary of the zone is usually determined by the first appearance of one diagnostic taxon and the upper boundary by the last appearance of another (either might extend above or below into a region of overlap with the other taxon at the upper or lower end of their range). Other characteristic taxa may be contained within the zone or extend to either side, although long-ranging and slowly evolving lineages are not usually included in the diagnostic assemblage. Not all the significant taxa are required to be present at all levels and in all places. The zone is named after one of the diagnostic species. Oppel zones are thus more flexible and subjective than concurrent range zones in the rigorously applied sense of that term, although the term ‘concurrent range zone’ is commonly used for what is, in fact, an Oppel zone.

Oppel zone A concurrent range zone, originally described by the German geologist and palaeontologist Albert Oppel (1831–65), in which the lower boundary is usually marked by the first appearance of one diagnostic taxon and the upper boundary by the last appearance of another (either may extend above or below into a region of overlap with the other taxon at the upper or lower end of its range). Other characteristic taxa may be contained within the zone or extend to either side, although long-ranging and slowly evolving lineages are not usually included in the diagnostic assemblage. Not all the significant taxa are required to be present at all levels and in all places. The zone is named after one of the diagnostic species. Oppel zones are more flexible and subjective than concurrent range zones in the rigorously applied sense of that term, although ‘concurrent range zone’ is commonly used for what is in fact an Oppel zone.