Geologic time scales

a system of chronological dating that classifies geological strata (stratigraphy) in time

subdivision of geological time; short than a supereon and longer than an era

unit in chronostratigraphy

sequence of rock depositions defining a chronostratigraphic unit corresponding to a specific epoch on the geologic time scale

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). According to the International Commission on Stratigraphy, the term "chronozone" refers to the rocks formed during a particular time period, while "chron" refers to that time period.

In stratigraphy, paleontology, geology, and geobiology, an erathem is the total stratigraphic unit deposited during a certain corresponding span of time during an era in the geologic timescale.

idealized composite unit of the geologic record representing the totality of rock strata laid down during a certain period of the geologic time scale

thumb|200px|right|Horseshoe Canyon Formations exposed in Horseshoe Canyon (Alberta)|Horseshoe Canyon near [[Drumheller, Alberta.]] thumb|200px|right|Oxfordian (Upper Jurassic) cyclic sediments at Péry-Reuchenette, near Tavannes, kanton Bern, Switzerland. Alternating layers are limestone (light, more competent) and [[marl/clay; dominant cycle is the 200000 year-cycle.]]