Biozone

In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa, as opposed to a lithostratigraphic unit which is defined by the lithological properties of the surrounding rock.

The same strata may be zoned differently depending on the diagnostic criteria or fossil group chosen, so there may be several, sometimes overlapping, biostratigraphic units in the same interval.

Oppel's biozonation was mainly based on Jurassic ammonites he found throughout Europe, which he used to classify the period into 33 zones (now 60).

Alcide d'Orbigny would further reinforce the concept in his Prodrome de Paléontologie Stratigraphique, in which he established comparisons between geological stages and their biostratigraphy.

This makes them similar to chronostratigraphical units - however, lineage zones, being a biozone, are restricted by the actual spatial range of fossils.

[4] Microfossils, such as dinoflagellates, foraminiferans, or plant pollen are also good candidates because they tend to be present even in very small samples and evolve relatively rapidly.

[4] As only a small portion of fossils are preserved, a biozone does not represent the true range of that species in time.

Moreover, ranges can be influenced by the Signor-Lipps effect, meaning that the last "disappearance" of a species tends to be observed further back in time than was actually the case.