Classes of geological time zones identified on the basis of the fossils they contain. All the strata that actually contain a given fossil species are within that particular zone. In a local section, the observed range of fossil is its teilzone (Prothero & Schwab 2004).

References
Donald R. Prothero, Fred Schwab,2004, Sedimentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy (2nd edition) W H Freeman & Co pp. 557