Biostratigraphy and Zonation

Biostratigraphy uses the ordered appearance of fossils to subdivide and correlate rock strata, supplying the relative time framework of geology.

Definition

Biostratigraphy is the branch of stratigraphy that uses fossils to define and correlate units of rock and to establish their relative ages, organized into biozones.

Scope

This topic covers the principles of biostratigraphy, including fossil succession, index fossils and biozones, types of zones such as range and assemblage zones, correlation of strata, and the integration of biostratigraphy with the geological time scale and other dating methods.

Core questions

• How does the principle of faunal succession enable correlation?
• What makes a good index fossil for zonation?
• What types of biozones are recognized and how do they differ?
• How is biostratigraphy integrated into the geological time scale?

Key concepts

• Faunal succession
• Index fossils
• Range and assemblage zones
• Correlation and the geological time scale

Key theories

Principle of faunal succession

Fossil organisms succeed one another in a definite and recognizable order, so strata can be identified and correlated by their contained fossils, a foundational principle since William Smith.

Biozonation and the time scale

Biozones based on index fossils underpin the relative geological time scale and are calibrated against radiometric and other dating to build the integrated time scale.

Clinical relevance

Biostratigraphy provides the practical framework for dating and correlating sedimentary rocks in geological mapping and petroleum and mineral exploration, and it anchors the relative divisions of the geological time scale.

History

William Smith established the principle of faunal succession and produced the first geological maps around 1800. Albert Oppel formalized the zone concept in the nineteenth century, and modern syntheses such as the Geologic Time Scale integrate biostratigraphy with numerical dating.

Debates

Diachrony of biostratigraphic datums

Because fossil first and last appearances can be time-transgressive across regions, the precision and global synchrony of biostratigraphic datums are continually assessed.

Key figures

• William Smith
• Albert Oppel
• Felix M. Gradstein

Seminal works

• foote2007
• gradstein2020

Frequently asked questions

What is biostratigraphy?

Biostratigraphy is the use of fossils to divide rock layers into units and to match and order strata of the same age in different places.

What is an index fossil?

An index fossil is a species that was widespread and abundant but existed for only a short span of geological time, making it useful for dating and correlating rocks.