Index Fossils and Correlation:

Discovery of utility of fossils for correlation: William “Strata” Smith & Principle of Fossil Succession

Index fossils:

• Common
• Geographically widespread
• Easily preservable
• Diagnosable
• Found in multiple environments
• Short species duration

Primary data of biostratigraphy: presence or absence of fossil in a geologic horizon

Last Appearance Datum (LAD): either local or global
First Appearance Datum (FAD): either local or global

Zones:

Types of Biostratigraphic units (and thus rock units):

• Biozone (often just "zone"): body of rock characterized by one or more taxa that permit it to be distinguished from adjacent rocks. Several different subtypes:
  • Teilzone: Between local FAD & LAD of that taxon – The True Observations!
  • Taxon Range Zone: Between global FAD & LAD of that taxon
  • Concurrent Range Zone: Overlap between ranges of two or more taxa
  • Interval Zone: Between two successive FADs or two successive LADs
  • Assemblage Zone: Characterized by 3 or more taxa in natural assemblage (a bit vague)
    • Special Case: Oppel Zone: DEFINED by FAD or LAD of one taxon, but CHARACTERIZED by additional taxa
• Abundance Zone (also called Peak Zone, Acme Zone): Subset of teilzone where index species reaches some higher level of abundance: useful locally, but almost certainly environmental rather than time!!

Some factors effecting all of these: local migration & extirpation; changes in preservation; changes in local environment; changes in sampling.

Lazarus Taxa: Taxa that temporarily “disappear” and then reappear in fossil record

Elvis Taxa: Taxa that converge on extinct forms, giving false impression of Lazarus taxon

Zombie effect: Post-extinction reworking of specimen

Biochronology (subset of geochronology, using biostratigraphy to generate biochrons, time units). Many different versions, of varying degrees of quality:

One famous version: Land Vertebrate Ages. Originally just North American Land Mammal Ages (for Cenozoic), then extended into mid-Late Cretaceous, then became Land Vertebrate Ages. Now practiced for many different continents.

Graphic correlation: method for correlation using first and last appearances, but not biozone terminology.

Signor-Lipps Effect: observation that lack of statistically signficant number of samples (both of horizons and specimens per horizon) may falsely "smear out" an sudden extinction event to make it look gradual.

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