biostratigraphy
Biostratigraphy is employed to correlate the age of rocks within strata according to their fossil assemblages.
Despite differences in sedimentary environment, and hence appearance, rock formations with similar fossil species can be assumed to be roughly contemporaneous. The more rapidly a species evolved, the narrower the geological time frame in which it was fossilized and the more useful it will be for age correlation. Some index fossils are particularly useful in biostratigraphy by virtue of rapid evolution, abundant and widespread occurrence relatively unaffected by environment, and easy identifiability.
Stages are defined by the group of strata containing the same major fossil assemblages, while zones or biozones are strata displaying an overlapping range of fossils.
Despite differences in sedimentary environment, and hence appearance, rock formations with similar fossil species can be assumed to be roughly contemporaneous. The more rapidly a species evolved, the narrower the geological time frame in which it was fossilized and the more useful it will be for age correlation. Some index fossils are particularly useful in biostratigraphy by virtue of rapid evolution, abundant and widespread occurrence relatively unaffected by environment, and easy identifiability.
Stages are defined by the group of strata containing the same major fossil assemblages, while zones or biozones are strata displaying an overlapping range of fossils.