Willa channelFrom Tacoma
This procedure avoids gaps and overlaps in the Standard Global Chronostratigraphic Scale. Many other lines of evidence may in some circumstances be helpful as guides to time-correlation and as indicators of chronostratigraphic position. The purpose of chronostratigraphic classification is to organize systematically the rocks forming the Earth's crust into named units chronostratigraphic units corresponding to intervals of geologic time geochronologic units to serve as a basis for time-correlation and a reference system for recording events of geologic history. Chronostratigraphic Units A.
Rock units can also be divided on the basis of fossils into zones that are named after key index fossils. In many cases, features are more difficult to distinguish because they occur within or between fairly homogenous depositional layers. Biostratigraphic units exist only where the particular diagnostic feature or attribute on which they are based has been identified.