Types of Biostratigraphic Zones:

Two types of formal biostratigraphic zones are recognized viz.,

1.      The assemblage zone

2.      The range zone

An assemblage zone is body of strata characterized by a certain natural assemblage or association of fossils, with regard to their ranges, eg. Meeker as assemblage zone of Spiti. Thus, it is a body of strata whose content of fossils of a certain kind taken in its entirety constitutes a natural assemblage or association from adjacent strata. An assemblage zone should have a specifically designated and decimated type section or reference section, eg., the otoceras – Ophiceras assemblage zone, Lilang, and Spiti, characteristics fossils of an assemblage zone are called guide fossils.

A range zone is a body of strata representing the total horizontal and vertical range of occurrence of one particular species or genus, e.g., Miscellanes miscella range zone. The principal reference of a range zone is the type specimen or reference specimen.

An epibole (acme zone/peak zone) is the body of strata representing the maximum development of a species/genus. It is a special type of range zone. Eg., Glossopteris acme zone in the flora of Raniganj Formation.

The fossil names are to be italicized. The initial letter of formal zone terms, except the name of species should be capitalized.

Biostratigraphic boundaries may be directly or indirectly applicable to establishing both rock stratigraphic and time-stratigraphic units. They contribute to a better understanding of the correlation, depositional and faunal history of strata sequence.