A chronozone or chron is a unit in chronostratigraphy, defined by events such as geomagnetic reversals (magnetozones), or based on the presence of specific fossils (biozone or biochronozone).
[1] Although non-hierarchical, chronozones have been recognized as useful markers or benchmarks of time in the rock record.
Although a former, early constraint required that a chronozone be defined as smaller than a geological stage.
Another early use was hierarchical in that Harland et al. (1989) used "chronozone" for the slice of time smaller than a faunal stage defined in biostratigraphy.
[3] The key factor in designating an internationally acceptable chronozone is whether the overall fossil column is clear, unambiguous, and widespread.